Image 1: Photo of Monument Geyser. Yellowstone: the Premier Park. Yellowstone, the world’s first national park, may be the most famous and the best--it is an incredible wonderland of geology and biology. The pictures in this show are all by R. Alley. This one shows Monument Geyser, in the Upper Geyser Basin, not far from Old Faithful.

Image 2: Photo of Lower Falls of the Yellowstone River. Yellowstone was the world’s first national park. The Washburn Expedition of 1870, which included government officials and important citizens of the Montana Territory, envisioned holding land for the common good. The 1871 Hayden Expedition, led by the director of the United States Geological Survey and including the incomparable artist Thomas Moran and the great photographer W.H. Jackson, provided information that convinced Congress to establish the park in 1872. The Lower Falls of the Yellowstone River, shown here, is one of the icons of the national parks.

Image 3: Photo of Old Faithful. Yellowstone has more than half of the world’s geysers, including Old Faithful, shown above. In proper rocks, with volcanic heat and lots of water, deep water is heated but held down by the cold water above. Finally, a little deep boiling pushes the cold water aside, the pressure on the deep water is reduced, and it flashes to steam, causing an eruption.

Image 4: Photo of Mats of Microbes in the hot runoff from a spring near Old Faithful. Many interesting and important things can be found in Yellowstone. These are mats of microbes living in the hot runoff from a spring near Old Faithful. Hot-water creatures have special enzymes, cell-wall chemicals, etc. to allow life in water that would burn you, and humans are learning how the bugs do it so we can copy them. Biological industries worth billions of dollars per year are based on the polymerase chain reaction (PCR), which is based on a Yellowstone microbe.

Image 5: Photo of Terraces in Midway Geyser Basin. Runoff from hot springs often forms terraces. Where water flows a little faster over a steeper spot, cooling and loss of dissolved gases cause precipitation of minerals dissolved in the hot, sulfurous (stinky) water, making a little ledge. Hot-water-loving microbes colonize the surfaces, with bugs of different colors preferring water of different temperatures. These terraces in Midway Geyser Basin, below the Grand Prismatic Spring, are classic.

Image 6: Photo of Grand Prismatic Spring. Here is the Grand Prismatic Spring. Rainwater and snowmelt moving down through cracks in the rocks are warmed by the volcanic heat of the Yellowstone Hot Spot, and then rise to the surface in springs as well as geysers. The next three pictures show animal tracks in the microbial mats on the terraces in the lower part of this picture.

Image 7: Photo of mountain lion tracks. Yellowstone is known for its wildlife. Animals have died when they broke through thin crusts over hot pools, but such events are rare. Elk often use the vegetation-free upper surface of Mammoth Hot Springs as a retreat from mosquitoes and other bugs, and many creatures enjoy the warm waters of the park during the winter. Here, the tracks of a mountain lion show white where the animal broke the bacterial mat. Lions are four-toed, but often put their hind feet where their front feet were, complicating the appearance of the tracks, as seen here.

Image 8: Photo of Coyote Tracks in spring deposit. Yellowstone now has a healthy population of wolves, and many coyotes, including the one that made the track shown here. The national parks were usually established for geological reasons, when the park boundaries separated wilderness containing amazing geological features from wilderness containing slightly-less-amazing geological features. Now that humans are using so much of the country and the world, the parks are becoming islands of nature in a human-dominated world, and so the parks are critical for maintaining biodiversity.

Image 9: Photo of Bison tracks in spring deposit. Bison (or, informally, buffalo) once thundered across the Great Plains of the U.S. in uncounted numbers. Uncontrolled shooting nearly exterminated the bison, but those protected in Yellowstone persisted and helped preserve the species. Here are bison tracks, in the same spring deposit.

Image 10: Photo of grazing bison. And, here are the bison, just down the road along the Firehole River. Hot springs in the river bed may have been behind the tall tale attributed to Jim Bridger, that the Firehole River ran so fast that friction made it hot on the bottom.

Image 11: Photo of Bison on the road creating a traffic jam. And here is a bison jam. The national parks must conserve for future generations, but also provide enjoyment for the current generation of people. Sometimes, doing both isn’t easy. This picture was taken in September, after the crowds had returned home; in midsummer, this really would have been a traffic jam.

Image 1, Picture of musk ox on the tundra in North East Greenland National Park. Preserving the best of the landscape in national parks is a U.S. invention that much of the world has adopted. The largest national park, Northeast Greenland National Park, is in NE Greenland and was founded in 1974. Both Dr. Anandakrishnan and Dr. Alley have conducted research in it. The pictures here were taken by Richard Alley in or just outside of the national park, during a research expedition to Scoresby Sund in the autumn of 2005. Enjoy!

Image 2, Picture of a glacier. Most of the park is on the Inland Ice, the great, two-mile-thick ice sheet that covers most of the island of Greenland, and one that could raise global sea levels about 23 feet (7 m) if melted. However, some of the park includes spectacular coastal mountains and the rich adjacent seas. This glacier has melted back over the last century from the light-colored regions around it. The mountain peaks from which the glacier flows are barely visible above the clouds.

Image 3, Picture of Corridoren Glacier. Corridoren Glacier. The great Inland Ice of Greenland is thick and extensive, but many smaller glaciers exist in the coastal mountains. The black stripes on Corridoren are medial moraines—each is a band of rocks that were picked up by the ice, or that fell on the ice, from a ridge that separated two tributary glaciers. The picture was taken from a helicopter flying just below a low cloud deck, looking west into the interior of Milne Land.

Image 4, Picture of cotton grass on the tundra. Cotton Grass. The tundra is one of the most beautiful, and least appreciated, landscapes on earth. Cotton grass, shown here, grows in wet places, and produces seeds that are carried on the wind. The picture was taken in Kjove Land, just north of Scoresby Sund.

Image 5, Picture of a mushroom nestled in bearberry. Bearberry provides the most spectacular fall colors on the tundra. Here, a mushroom nestles amid the fruit and leaves of the tundra plant. The fruit is edible, but not especially tasty.

Image 6, Picture of a Fulmar (a bird similar to the albatross) flying over the sea ice. Fulmar and Sea Ice. Fulmars are akin to small albatross, true sea birds with the special glands along their noses that allow them to excrete the salt from salt water, so that there is no need for the birds to go find fresh water. Fulmars often “surf” the wind around boats, or skim low over the water. Behind this fulmar is sea ice, frozen ocean water. Freezing the ocean is not as easy as freezing freshwater, both because salty water freezes at a lower temperature, and because seawater becomes denser as it cools all the way to the freezing point, and may sink to great depths in the ocean, allowing warmer water to flow in and replace it.

Image 7, Picture of icebergs in Scoresby Sund. Icebergs, Scoresby Sund. A lot of snow falls on Greenland—enough each year to make a layer about 1/25 inch (1 mm) over the whole ocean. About half of Greenland’s snow melts and runs into the ocean. The other half flows to the coast and breaks off as icebergs, as seen here. Recent warming has increased Greenland’s loss of meltwater and icebergs; the ice sheet and surrounding mountain glaciers are shrinking and helping raise sea level. This is freshening the North Atlantic, favoring winter freezing; the future may see warmer summers but colder winters from this strange situation.

Image 8, Picture of Scoresby Sund. Kap Brewster. The south side of the great fjord of Scoresby Sund is guarded by the bird cliffs of Kap Brewster. Huge flocks of sea birds nest high on the rocks and feed in the rich ocean nearby. The steep slopes were carved by the glaciers that once filled Scoresby Sund.

Image 9, Picture of a musk ox next to a tent. Musk Ox, Schuchert Dal (Valley). The dramatic Schuchert Valley spreads north from Scoresby Sund, and is well-populated by musk oxen. With about the same size, shape and speed as minivans (not really, but not that far off!), musk oxen are beautiful denizens of the tundra. More closely related to mountain goats than to bison, the musk oxen form defensive circles around their young if threatened, as shown in the first slide of this show. Here, a bull has wandered into our research camp. The best way to handle musk oxen is to leave them alone; although typically peaceful, they have sharp and potentially lethal horns, and they are a lot faster and bigger than you are.

Image 10, Picture of Alpefjord. Alpefjord, a major tributary to Kong Oscar Fjord, north of Scoresby Sund. The glaciers flow from the high ground at the top of the picture toward the sea at the bottom. The glaciers now end about where the white ends, but extended much farther in the recent past, as shown by the piles of rock and rubble, called moraines, that surround the ice. Almost every mountain glacier on Earth for which we have data has shrunk over the last century or so. Mountain glaciers have enough frozen water to raise sea level globally by about 1 foot (just under 1/3 m) if all melted.

Image 11, Picture of an arete. An arete (a knife-edge ridge left when two glaciers erode into a highland, one from each side) sits above glaciers in the Stauning Alps of the Northeast Greenland National Park. Many knowledgeable people consider the Stauning Alps to be the most spectacular alpine scenery on the planet. There is no objective way to pick a “winner”, but the Stauning Alps are truly stunning.

Image 12, Picture of an Rainbow and an icerberg. Rainbow and iceberg, Scoresby Sund. The warmest summertime weather is well below freezing at the top of the ice cap, but temperatures in the 50s Fahrenheit are common along the coast, where the limited summertime precipitation often comes as rain.

Hello, and welcome to Geosciences 10, the Geology of the National Parks. I'm Richard Alley, and with Sridhar Anandakrishnan, my very good colleague, we will be taking you on a tour of some of the most interesting ideas about how the world works and how it affects you, and some of the most interesting and beautiful places on the planet. I think we'll have a lot of fun. I think we'll learn some very interesting things before we get done. And I am looking forward to the tour.

I'd like to start with a little bit of look at our national parks. Just so you know, national parks are an invention of the United States. The first national park was Yellowstone. You see the glorious lower falls of the Yellowstone River here, the coloration of the rocks giving rise to the name of the place.
Of course, Yellowstone is famous for the geysers. There's a giant pot of hot rock down underneath there of melted rock that erupts occasionally and causes big trouble. And between, it heats things and makes it wonderfully beautiful.

This is a geology class, but don't worry too much. We take a fairly broad view of what constitutes geology. We will look at biodiversity. We will look at climate, at living on the planet.

Here you actually see the tracks of a mountain lion walking across the deposits of a hot spring in Yellowstone. Mountain lions often put one foot on top of the other and give interesting looking tracks, and so you can see them there. And here you see the tracks of the bison that are famous in Yellowstone and other places.

Bison came very close to not making it. Yellowstone was important in their survival. Yellowstone was a little island in which no one could shoot them. No one could disrupt their habitat. And so, the existence of these owe something to the foresight of the people who said, let us save this piece of the world for the public.

These things are valuable. This is a picture of a hot spring mat that is sitting right below Old Faithful Geyser.

People are prospecting in these, looking for interesting chemicals that will help us. There are biotechnology industries that are founded on things that were discovered in Yellowstone. A bug that has learned to live and do things in really, really hot water has ways of doing things that are useful to us. And so, we save this as a beautiful place to go see canyons and geysers, but it's turning out to be a place to save lives and make money as well.

The Park Service has a very interesting difficulty. They have to preserve and protect, they also have to allow us to enjoy things. And sometimes these meet in interesting ways. And so, here you see a bison jam. If you go to Yellowstone, you will also see bear jams, and elk jams, and moose jams, and coyote jams. It's the way the world works.

But the bison are beautiful. The Fire Hole River here, behind the bison, was described by the mountain men as flowing so fast it gets hot on the bottom. Well, no, there's hot springs under there. But it's a beautiful place.

Now, I am a geoscientist, a geologist, a glaciologist. I'm one of the luckier people in the world. I get to go to incredibly beautiful places, and people pay me to do things that matter.

I'm a happily married person. I have two wonderful daughters. And you see us here in front of a glacier in Alaska on a trip we took with Penn State at one point.

And I am trained in rocks first, and then in climate and ice and other sorts of things. I studied at Ohio State, and then I finished my studies at Wisconsin, and then I moved to Penn Stat, and been at Penn State since 1988. So, I've been around a little bit now at this point.

I have the usual sort of accoutrements of someone who hangs around a place like Penn State for a while. I've got a good bicycle. I play a little soccer reasonably badly. I have, as I said, a wonderful family, a nice gardens, an interesting collection of critters. Prancer there is about 22 pounds. He's quite a beast.

But I do. I get to go to great places. These next few pictures are going to be from the world's largest national park. This is Northeastern Greenland.

I study ice sheets, the history of climate that's contained in ice sheets, and whether the ice sheets will fall in the ocean and flood the coasts. And so we get to go to neat places to do this. And so, here you can see Korridoren Glacier in East Greenland flowing out from Milne Land towards you, the stripes or rocks that it carries along and dumps into the ocean. And I hope you get the vague idea that this thing might actually be moving.

If you were to go out on that glacier and put markers out, you'd fall in a crevasse, so don't do that. But if you did and came back and surveyed them later, you actually would see that they are moving. If you do you ever get to go to the world's largest national park, the tundra is beautiful in the fall. It's an amazing place to go to.

There are glaciers. There's a huge ice sheet in the middle of Greenland and then little glaciers on the side. Those glaciers are actually shrinking now, as is the big ice sheet.

And if you see these little red lines, the big outer loop there is where the glacier was 100 years ago, and now you can see the glacier has backed up. It is slowly melting away. Why? We'll get there before we're done.

OK, this is the tundra in the fall, a little mushroom and some bearberries there looking at you. The colors do turn. They're very pretty.

This is a fulmar. It's sort of a little albatross. It can stay at sea. It doesn't need to come in for fresh water because it can drink seawater because it has a fancy gland in its nose to exclude the salt. And its flying over the ocean, and the ocean in cold places gets interesting.

The marker there on the white, that's frozen ocean water. That's sea ice, and the ocean really can freeze. And between that and the open water, where that circle is, you can see into the ocean through the sea ice.

It gets warmer. The sea ice tends to melt. The ocean soaks up more heat, and that makes it warmer still. So, there's some interesting things we will get to chat about in a little bit.

These are icebergs coming off of Greenland. A glorious fall day, a little fog hanging around up above there, and the sun breaking through. It's just such a great place. It's such a great— and this is a musk ox.

Musk ox is the same size and shape as a bison, or a minivan. Either is fairly similar. It probably has a better acceleration and cornering than a minivan does. They're actually more related to mountain goats than they are to bison. But this is the Northeast Greenland National Park equivalent of our buffalo or bison here.

OK, in a marker of goodwill, we will see some beautiful things. We will have some fun before we get out of here. My colleague Sridhar and I have had some wonderful opportunities in the way of putting together this course, and you will see some very interesting things that we did, along with Eric Spielvogel from Penn State's e-Education Institute and others.

We had the opportunity to get a really wonderful group of advanced students and then go out and tour some of the national parks with the students carrying cameras. And so, you will get to see pictures they took. You will get to see experiences they had as part of our cause, adventure in the great west.

Here's Sridhar in Arches National Park, and these are some of the things that we got to do with the Arches people. We did, indeed, walk through arches. Why are there arches? It will come.

We went to Canyon de Chelly. What happened to the ancestral Puebloans who lived there? We will get to see that before we're done. This is Eric Spielvogel, who put a lot of this together, getting a really good picture for you. And so, we got a lot of nice things that came out of this.

We took our crew to the bottom of the Grand Canyon. We hiked down. We had this glorious moonlit night. If you ever get the chance, you got your headlights, so you're not going to fall over the cliff and the fall into the river. And the moon is out. And oh, what an opportunity to go with Stephanie, and Dave, and the rest of the crew, and wander through the depths of the canyon and the glorious moonlight that we saw there.

When you get up in the morning and you're at the bottom of this mile deep hole, and the flowers are blooming, and the hummingbirds are humming by, and it's-- and there's a lot of geology. If you look into this picture, you'll see flat layers, and then you'll see them bend. Why do they bend? This will come. We'll get to that.

Again, we do sneak up on biodiversity whenever we get the chance. And so, it's not just the— most parks were built for geology, but they're increasingly islands of biodiversity in a human- controlled world. And we really do rely on the parks to keep things alive for us.

So, more of our happy campers on the way up out of the canyon. It is, indeed, somewhat slower coming out of the canyon than it is going in, a little hotter. We zipped by Glen Canyon. We looked at the lake.

Behind Samir, here, you can see this huge white wall, and then it turns orange at the top. That white was fairly recently flooded. The lake is really low. Why is the lake low? The climate has changed a little bit, and humans are using more of the water.

What does this mean for downstream? What does this mean for the things in the canyon? What does it mean for the Colorado? We will get there before we're finished.

OK, and here's our crew. We're rafting the Colorado below the dam. That dam changed everything on the river. What did it change? We will get to wander through that a little bit and see what it means.

Again, you will see film clips, items, pictures, excitement that our crew generated for you. You'll get to meet them. You'll get to learn from them from Amish and others, here, as we wander through. Here Amish is at Canyonlands, filming something about the river before it gets to the dam.

Here's a crew, really excited. We were down on the slick rock in Canyonlands in the early morning here, waiting for the sunrise to get off and see pretty things. And here's our crew up in Hidden Canyon in Zion. You walk up this cliff, and you hang on to the chain to get around the corners. And that chain is wearing grooves in the rock, and so you will see a little film clip that they made for you when we get that far, and some fun things coming there.

Here are ancestral Puebloan sites, Wupatki, up there with Dave Witmer and Laney and Irene down in Mesa Verde, and then Kim over there filming just outside of Bryce, actually. Stephanie has gone off to work in parks doing some very interesting things now, here with Ranger Jan Stock at Bryce. Here we are looking at a geologic feature. And fairly soon we will get to these.

You look at the picture there above Dave Janesco, and you see that one side is orange, and the other side is black. The orange are rocks from a lake. The black is rocks from a volcano. And that line where they meet is a giant earthquake fault.

What's a giant earthquake fault doing there? Well, Dave is explaining it to you. And you will get to see this before we get finished.

A couple more interesting people in glorious places, very, very glorious places. These are the wild flowers outside of Canyonlands on the drive in. We can show pictures for the whole semester because it's cool. And it's so fun. But we're not allowed to do that.

The university actually believes that you're taking a science course, and the university is typically much more interested that you know something about science than that you focus on a particular science, such as my science, 'cause this is stuff that I really care about. And so, we do have to chat a little bit about science. We will actually throw up some facts before we get done. And we will do so.

So, I want you to hark back in your memory for a moment to, say, taking the SAT, or the ACT, or the PSATNMSQT, or the CAT, or the— what, ETC, or whatever you took. OK, hearken back. When I was a student, lo these many years ago, they used to give us questions that involved lists. And they'd— so you'd be down to about question 243, and they'd say, OK, I'm going to give you a list of things. What would come next in the list?

I think they have gotten rid of these questions, but you may have run into one that's something like this. Here's question 243. What would come next in this list? You got two. You got four.

well, what could come next there? You add 2 to get to 4, maybe you had 2 and you get to 6. That would be a perfectly possible answer.

But no, no, wait a minute. You multiply by 2 to go from 2 to 4, and if you multiply by 2, well, you'd get 8. That would be a perfectly fine answer.

But maybe you multiply 2 by itself to get to 4, and you'd multiply 4 by itself. And that would give you 16. And so you'd sit here and go, hey, this was a lousy question. This is a piece of dookey. OK, get rid of that one.

OK, now suppose that they gave you something that was actually a somewhat better question. So, you give you 2, 4, 6, 8. What comes next? Now, that one looks very easy. You say, oh, yes, you're gonna add 2 and you're gonna get 10.

When I was much younger, I played Little League. We were really serious about Little League. And you can't believe it. We'd have lawsuits over Little League. We had coaches yelling at each other. At any rate, I played Little League. It was very interesting undertaking.

And the coaches used to be really big on having us out there doing infield chatter. Now, we were not out there chattering uplifting and morally relevant statements. We weren't saying, batter, do your best for your team and country.

We were out there saying, hey, batter, your shoes untied. Hey, batter, you're ugly. Hey batter, hey batter, hey batter, swing! Two, four, six, eight, the batter's got a bellyache.

OK, so, it could have been 10. We would never out there go 2, 4, 6, 8, 10, 12 in the Little League. We were out there saying, 2, 4, 6, 8, the batter's got a bellyache.

Now, this actually might be relevant to something. If you were sitting there saying, two, four, six, what comes next— eight— you get it right. And you sit there and two, four, six, eight, what comes next? And you say 10, you get it right. You say, I know what's going on.

But if you're out there playing Little League and you're saying 2, 4, 6, 8, 10, you got it wrong. Your ability to see two, four, six and fill in eight doesn't prove that you know what's going on, because if you thought you were taking the SAT and you're really playing Little League, you got eight right, but you got the next one wrong. You're sitting there, 2, 4, 6, 8, 10, 12.

And the batter— that might have worked, actually. The batter looks at you, says what's wrong with you? And the pitch goes right by. But that is not the way one does it.

OK, this does feed back into science. This is relevant to science. And let's look at how this works. What is science?

It's humans. It's humans doing human activity. There is no crank that you turn that spits out knowledge.

Science is done by humans. They are humans who have foibles and failings. They are humans who have mistakes. They cheat, and lie, and steal. They have mating rituals. They're just like everybody else.

But science has a very loose set of rules that allows it to do better at some things than other human activities. It's very limited. It does certain things well, and it doesn't do other things at all. But the things that it does, it actually works on.

So, what is science? The first thing in science that you do is you find something interesting. You gotta care about it. It has to matter, people. You go out and look at things and you find something interesting. OK, this is cool. I could learn about this.

What you then do is ask, what do we know about this something? There are many people in the world. There have been many people in the world. Your ancestors were smart. Lots of people around the world in lots of places were smart. You will never in your life reinvent everything they did.

So, first of all, you go and find out what they did. You could call this research. You could call this going to library. You can go and talk to people. There's other ways to do it. But if you're interested in something, you're really stupid if you don't find out what other people knew. They may have your answer for you already.

OK, so you find out what's known. Then you say, OK, they were really bright people. They did really good things. But they were human.

They might not have put together everything. They might not have had the ideas that I have. I, as a new human standing on their shoulders looking out, may be able to improve things.

So you take what you know and you say, how can I move forward? How can I go beyond them? Where can I get a new idea?

This is the fun stuff. No one has any idea where new ideas come from. It may come from dreams. It may come from traditional knowledge. It may come from brainstorming.

I take hot baths. I get really good ideas while taking hot baths. I don't know why, but it works.

OK, so you look for a new idea. You get a new idea. And then, you can't stop. If you just stop, there's some other human activities. You got new idea. You write your novel and you're there.

But in science, you actually have to ask, is my new idea really a step forward? Have I gotten somewhere that those people before me did not get? And so you actually have to go test your new idea, and you have to test your new idea against nature, against the real world. You have to see if your new idea is better than what other people had done.

And the way this is done— and this is a very, very strict rule in science, and this is what sets science apart from other human activities— you have to find a situation in which you predict something, and the old ideas predict something else. If you always agree, then you have just found a new way to restate the old idea. You actually have to find a place where you say, tomorrow, the sky will be purple, and the other one says no, it will be blue, where you say, if I do this, that will happen, and the other idea says no, if you do this, the other thing will happen.

You find a way that they differ, that you make different predictions. And you have to predict it. You're not allowed to just explain it. You have to predict what's going to happen. Then you set up the situation. You see what happens.

you can call this making hypotheses and doing experiments. There's lots of terms that you probably learned in fifth grade. This is a list of terms of the scientific method. But this is really the scientific method.

Get interested. Learn. Get a new idea. Test it. But you have to test it by making predictions, and then you have to say see what happens.

If your idea repeatedly fails— one time, yeah, nature might be fooling you, there's lots of things can go wrong in an experiment— your new idea just keeps— pff, it fails. Pff. It fails. Pff. It fails. OK, throw it away. You were wrong.

Even if you loved it, even if you desperately thought it was a beautiful idea, if it fails, you gotta throw it away. You're wrong. If it succeeds— OK— if it succeeds, are you right?

And this is the point where we go back to playing Little League and two, four, six, eight. If your idea succeeds, you make the prediction correctly over, and over, and over again, it is possible that it is true. You have Truth with a capital T. You've nailed it. It's there. There's choir singing, and everybody's giving you— you might have it right.

You might have been close. Isaac Newton came up with rules of physics. Isaac Newton is really, really accurate for a lot of things. Scientists started to say, well, Newton is truth. We're done. All we have to do is estimate things better. Newton's got it nailed.

We still teach Newton in physics because it's still very useful. But Newton— if you go to really big things, you got to really small things, you go to really fast things, Newton is wrong, and you need Einstein, and you need quantum, and so on. Now, really big is a solar system or a galaxy, and really small is an atom, and really fast is 90% of the speed of light.

So, Newton's really good for the world we live in today. When people build buildings, they don't actually worry too much about quantum. They use Newton's laws. But Newton is not right. He's not true in any way, shape, or form. He was just close. He's useful.

The other option, of course, is that you got it right, but you were just lucky. And this is where you're sitting there and saying, two, four, six, what comes next, eight. And you say, 2, 4, 6, 8, what comes next, 10, and you're playing Little League. You got eight right because you were lucky, not because you knew what was going on.

And so, there's three options. If you make your predictions right, you may be true. You may be close. You may be lucky. No one ever actually tells you, you are now playing Little League. Nor do they tell you, you are now taking the SAT in the real world.

And so you never will know. So science is not really about Truth with a capital T. In fact, if there's one thing that we do know that comes very close to Truth with a capital T, it's that eventually, as a professor, the students always show us up. The students learn something we don't know. The students find some mistake that we made. And so the experience of every professor in history is to watch students go blazing by at full speed, which in turn says that the professors did not know everything, and there was not Truth with any capital T.

And so, science is not really Truth with a capital T. What science is is building. Our ideas will we be revised.

It's getting better. It's getting closer to being really good, to having it really right, and keeping on doing this. Get a new idea. Test it.

If it's better than the old one, keep it. Get a new idea. Test it. If it's better than the old one, keep it. Accumulate the knowledge. Accumulate the wisdom of the brightest people in the world over generation after generation, always testing it against nature to make sure that it works, and pull this together.

Now, we will all occasionally trip over some questions that are very interesting to people. There are people who say, look. The world is no older than Britain history. I have a sacred book, and the story in this goes back 6,000 years and that's it. And I know this. This is revealed truth.

And the scientists said, well, no, it doesn't look that way. I have counted more tree rings than that, and we know trees put down annual layers. So, we will come to interesting questions like this.

We will come to questions of evolution and other sorts of things. And when we do, we should chat about them a little more. These are things that matter to people.

They're things that matter in politics. They stir up a lot of fervor and fever on many sides, and it's not just both sides. There's all sorts of interesting ideas floating around out there.

When we get there, just remember what science is. It's subject to revision. It is not Truth with a capital T. What it is, though, and I think that everybody knows this— if we pretend that science is true, we are successful.

I did not die in second grade of a really virulent fever because somebody had antibiotics that were generated by science. I walked in this building and I did not worry that this huge open space, with these heavy things over my head, that it was going to come crashing down on me and kill me. I'm speaking to you through the wonders of a cup of sand, a cup of oil, a little bit of red rock, and an amazing amount of intelligence in science that turned them into computers, and fiber optics, and other sorts of things, so that we can actually chat this way.

If you were to get lots of different groups of people around— get the volleyball team, and the knitting circle, and the bridge club, and whatever else— get a whole bunch of different groups of people, and give each group a cup of the right red rocks, a cup of sand, a cup of oil, and say, turn this into a computer communication system. Science and engineering have done this. And I am reasonably confident that the volleyball team and the knitting circle will not succeed in doing so. Science works, and it works really, really, really well.

It works. It works. It works— there just isn't much doubt about this— if you [UNINTELLIGIBLE] it to engineers.

Once you have the idea, you gotta turn into reality. You've gotta make it work. And then you need business people to sell it, and what have you.

But science really, really does work. It's out there. It's one of the great things of humanity.

It's one of the things that allows us to get new ideas. It allows us to share information. It allows us to communicate.

Now, I would like, briefly, to just tiptoe around some other ideas that you would probably get in different classes to a greater extent. We're coming to you as a communication medium. We're coming to you over the Internet. We're chatting about way things are.

The Internet has changed a lot of things. We can sit at home and we can Google each other, and we can find out what's going on. And that's very fun.

It has changed information. If you go out and look on the web at certain things that we will talk about in class, evolution, climate change, age of the Earth, what have you, you will find an incredible spectrum of views out there, some of which are based on this vast pyramid of knowledge that's been put together by humans, in the scientific method, over thousands of years, and some of which are based on somebody sitting down in front of a computer and a blog and typing what they think. And you pull them up on the search engine, and they'll all pull up as being equal.

They just show up. There's no sorter in there. And so, why should you believe my communication, that's a scientific communication, and not the blogs that you will find that say, oh, he's an evil liar. He's trying to corrupt your poor minds.

And so, I presume the great majority of you actually have a pretty good understanding of this, but it's worth just a word or two to chat about that. There are so many different sources of information. You could go to an Internet. You can go to magazines. You can go to books. You can go to the scientific literature.

And you know where I'm going. The scientific literature is the one I want you to lodge in your brain for a little bit. There is a great difference in some of these communications between a blog, which may have nothing behind it but the informed or uninformed opinions of one person, and a scientific result that we're going to try to present here in class, which has, sitting behind it, this pyramid of knowledge, of testing against nature by thousands and thousands and thousands of people in all the countries of the world over all of recorded history, that's very carefully put together to see if it works.

You go, look, and say, OK on the Internet site, in the blogs, there's some great stuff out there. But there's a lot of garbage out there, too. There's just dookey knee deep or higher. And as you go from the Internet through these other things, what you find is you get to typically better quality information, not always, not everywhere, but typically better quality than Internet.

The Internet's so cheap, and so easy, you don't have to be in it for the long haul. There's a huge amount of it that is not carefully examined to see whether it's even vaguely true or not. Whereas, if you get on the other end out there in the scientific literature, we jump through incredible hoops to try to make sure that it is basically correct.

If I wanted to tell you that my new idea works, I have to, first of all, get the new idea. Then I have to test it. Then I have to do all this stuff and see if it works. And then, I have to write it up.

I have to say, this is what I did. And you have to be able to know exactly what I did. You have to be able to duplicate what I did.

Put it out there. Tell the truth, what I did, what other people did. And then I send it in and I say, please, please publish this over the world.

And they say, well, no, not yet. We're going to get a couple world experts, and they're going to look at this really carefully. And they're gonna make sure that you're not lying, or cheating, or stealing, that you have acknowledged the knowledge that you pulled in from other people, that you've told us what you did, that your results look good, that you have run careful tests, that your statistics are not cheating.

And they're gonna run a whole bunch of different things. And they'll get these world experts to look over it. And only after the world experts have said, yeah, that makes sense am I allowed to put it out there.

And this still doesn't make it true. Don't for a minute think that it does. But it means that a whole lot of the dookey is missing. And if it matters, the scientific literature is the place you go to look.

It may not be friendly. It hasn't been distilled down. In this course, we will try to distill the scientific literature into something that's useful, but no world experts are actually vetting the last word I just said to make sure it was the right word.

It is slow. It is careful. It's not the fastest way to get there. There are things that— you'd say, can't you get that out faster? This is such a cool idea. I really want it.

Now, we have to be careful. We have to follow the rules. When people read the scientific literature, they should know that it is standing on this pyramid of knowledge that comes up from the depths of antiquity and the care of all these people across the planet.

And so, that's just a little bit of where we're going, what we're doing. We will get much more down to specifics. We will talk about rocks, and we'll talk about rivers, and we'll talk about glaciers, and all sorts of fun things.

But in the end, keep in mind what it is. It is humans doing really important things to keep humans happy, healthy, and terrific, fed, and cured, and clothed, and housed, and healthy and wealthy enough that we can actually worry about big questions of what we're doing here and what we should be doing here. Science doesn't really tell us those. But it does give us the wherewithal to address those.

And we are going to address those, some subset of them. How do we humans stay happy, healthy, and terrific on the planet? How do we keep from being killed by giant waves, and volcanoes, and earthquakes, and what have you?

How do we find valuable things? How do we track down keeping things alive? And we're going to do that by going to some of the really beautiful places on the planet with some really good people who worked hard to show it to you and having a lot of fun. I personally look forward to the trip, and I hope you do too. Thank you.

4.6 billion years, as the story starts before our new crowd'll shuffle in; the ones who can learn from the scary parts, and enjoy that the ball's still in spin. Falling meteorites hit with energy bringing radioactivity. And the melt from that heat, gave us layers, discrete the core, mantle crust, air and sea. Then a Mars-sized one blasted the moon out to make tides, and to shine down on us from on high.

Sings us a song, you're the GeoMan. What was, and what is, and will be, On this blue-green ball spinning as fast as we can, with rocks, water, air, you and me.

No living thing softened that Hadean scene. No oxygen blew through the sky. 'Til photosynthetic bacteria, blue-green gave us something to breathe by and by. That oxygen changed the Earth's chemistry, and broke down so much greenhouse gas that the new O₂ breeze gave a Snowball deep-freeze 'til volcanic CO₂ made it pass. Now, while Venus melts lead, and Mars shivers, this ball that we love is fine-tuned in-between.

Sings us a song, you're the GeoMan. What was, and what is, and will be, On this blue-green ball spinning as fast as we can, with rocks, water, air, you and me.

Precambrian microbes, then trilobites in Paleozoic warm seas, led to sauropod - Tyrannosaurus fights across Mesozoic countries. 'Til one fateful day of the meteorite, just 65 million years past, in that fire-ice hell the great dinosaurs fell, while a few mammals weathered the blast. And the jobs that the dionos left open have slowly been filled by those mammals' offspring.

Sings us a song, you're the GeoMan. What was, and what is, and will be, On this blue-green ball spinning as fast as we can, with rocks, water, air, you and me.

There's a pretty good crowd here on Saturday. Procreation for mammals a thrill. Cenozoic's long scene becomes Anthropocene, and we wonder if we have the will. 4.6 billion years of just nature, Then 6 billion of us join the mix (2012 update -7 billion and counting). Some are thinking quite clear, but some smell like a beer, and there's lots of things here we should fix. But as long as the ball keeps on spinning, and as long as the music keeps playing, we're in.

Sings us a song, you're the GeoMan. What was, and what is, and will be, On this blue-green ball spinning as fast as we can, with rocks, water, air, you and me.

Image 1: Death Valley: Take a stroll through one of the lowest peices of land in the Western Hemisphere (282 feet below sea level), a place that, strangely enough, also happens to be adjacent to the highest point of land in the lower 48 states of the U.S., the 14, 494 ft. mountain peak of Mt. Whitney.

Image 2: Zabriskie Point, in midwinter. The soft sediments at Zabriskie Point were deposited in an old lake, and are being eroded into the beautiful features seen here. The snow-covered peaks in the background tower two miles above the valley floor. (Photo by Penn State graduate, now University of New Mexico professor, Peter Fawcett.)

Image 3: Badwater in midwinter. Peter Fawcett, noted Penn State alumnus and University of New Mexico professor, at 282 feet below sea level. The little bit of water from a midwinter storm will evaporate quickly.

Image 4: Salt flats in midwinter, Death Valley. Water, such as seen in the previous picture, carries dissolved minerals (ask a plumber who has tried to remove a faucet in a house with hard water if you don't believe this!). When the water evaporates, the salt is left. Photo by Peter Fawcett.

Image 5: 20-mule team. The salts deposited in Death Valley included valuable materials such as borax, containing boron dissolved from volcanic and other rocks around the valley. The salts were mined, and the borax hauled out by 20-mule teams. This is a picture from a reenactment of the mule teams, years after the mining ceased. Photo by Ed Derobertis of the National Park Service.

Image 6: Probably the most familiar of the many uses of borax is in laundry detergents. Before he was president of the United States, actor Ronald Reagan advertised a laundry detergent containing borax, as shown in this photo from the National Park Service archives.

Image 7: Another salt flat is shown here. Behind the salt flat, at the foot of the mountains, is an alluvial fan, a pile of gravel brought down into the valley from the mountains by streams that run for a short while after rainstorms. The vertical distance between the lowest point and highest point on the fan is greater than the vertical distance from Spring Creek to the top of Mt. Nittany near Penn Stateas University Park Campus--the fan is taller than most eastern mountains! The scale of things in Death Valley is immense, and very difficult to comprehend. Photo by Peter Fawcett.

Image 8: Again, putting Penn State’s Mt. Nittany, or many other eastern mountains, into this picture wouldn’t change it much - they would reach only part of the way from the salt flat at the bottom (shown by the orange arrow) up the fan (the top of the fan is shown by the yellow arrow), far shorter than the peaks in the picture. Photo by Peter Fawcett

Image 9: During the ice age, more rain fell in Death Valley because storm tracks had moved, and less water evaporated because temperatures were lower than today. A huge lake filled Death Valley then. In this rather fuzzy slide downloaded from the USGS-National Park Service web site, the horizontal lines (the ends of one are shown by the blue arrows) are old beaches from that lake. The photo of Shoreline Butte is by Marli Miller.

Image 10: Some of the gravels washed into the valley by streams are shown in this photo by Peter Fawcett.

Image 11: Deserts are not dominated by dunes in many places, but dunes do occur. The streams flowing into Death Valley carry salts, big rocks, but also sand. If the sand is piled by wind, beautiful forms may result, such as these. Photo by Paul Stone, United States Geologic Survey

Image 12: The enigmatic Devil's Racetrack. The stones rather clearly have moved across the surface of the salt flat. Strong winds during wet times are probably involved. Perhaps a thin water layer forms in a winter storm, freezes on top on a cold night, and then the wind drags the ice carrying the rocks. Photo by Marli Miller, from the Death Valley National Park web site.

Image 13: Death Valley was dropped along faults (or the mountains were raised, or both). The Hanaupah Fault (between the blue arrows) cuts the toe of an alluvial fan coming down from Telescope Peak, shown in this photo by Marli Miller from the Death Valley National Park web site.

Image 14: A closer view of The Hanaupah Fault (between the blue arrows) as seen in the previous picture, with labels showing which side of the fault was raised (“UP”) and lowered (“DOWN”). Photo by Marli Miller, from the Death Valley National Park web site.

Image 15: Hot rocks occur at shallow depth under Death Valley, and break through occasionally in volcanoes, usually coming up along faults; farther to the south, stronger volcanism has made the sea floor of the Gulf of California. In Death Valley, the eruptions are not especially strong, but they have made craters, such as those in the Ubehebe volcanic field, shown in these photos.

Image 16: Sometimes, volcanoes make small cinder cones, composed of little rocks and hardened blobs of lava thrown through the air. And, sometimes faults move rocks horizontally, as shown here (upper left without lines, and lower right with fault shown by dashed line and motion by arrows) for Split Cinder Cone in Death Valley. Most of the faulting in Death Valley is related to the dropping of the Valley and raising of the mountains, but horizontal motions such as this do occur occasionally.

Image 1: Earthquakes! Take a quick virtual tour with Dr. Alley through the U.S. Forest Service Madison River Canyon Earthquake Area. (last picture is in Yellowstone National Park)

Image 2: On the night of August 17, 1959, at 11:37 PM, a large (magnitude 7.5) earthquake struck just northwest of Yellowstone, near Hebgen Lake in the Madison River Canyon of Montana. Land on the west side of the Cabin Creek Fault moved down about 21 feet (almost 7 m) relative to land on the east in a sudden drop that shook the surroundings, forming the Cabin Creek Scarp, shown here. (A scarp or escarpment is a steep ramp connecting places that are more nearly horizontal; think of a wheelchair ramp between sidewalks down here and up there.)

Image 3: The shaking caused a massive landslide from the south side of the Madison River Canyon. An estimated 80 to 90 million tons of rock and debris thundered into the canyon, forming a layer estimated at 400 feet (120 m) thick in the bottom of the canyon and bouncing another 400 feet up the north wall. The scar left when the rocks fell is shown here. 26 people died in this vicinity, most in a campground that was buried under the landslide debris. (Two more were killed by a falling boulder elsewhere.)

Image 4: This closer view of the scar from the landslide shows large trees next to the slide and growing in the scar, emphasizing the immense size of the slide.

Image 5: Huge boulders were carried across the valley and up the other side. The rapidly moving mass of rock blasted air and river water in front of it; some survivors reported having their clothes ripped off by the force of the blast.

Image 6: Another shot of the immense boulders carried across the valley by the rapidly moving mass of rock.

Image 7: The landslide dammed the Madison River, and the trapped water rose to form Earthquake Lake, drowning many trees that still are visible, as seen here. Quick work by the US Army Corps of Engineers stabilized and lowered the new dam. Landslide-dammed lakes often overtop their dams, cut down through the loose debris, and release a devastating flood; this was avoided by the quick government response.

Image 8: Hebgen Lake was a reservoir a little upstream of the new Earthquake Lake. On the night of the earthquake, Hebgen Lake’s dam cracked and water washed over, but the dam did not fail. The land under the lake tilted, raising one side and lowering the other. One person ran safely from her house as the lake rose and the house and land slipped into the waters. Huge waves sloshed back and forth in the lake after the quake. Houses knocked down and flooded by the tilting and waves are still visible, as seen here.

Image 9: The quake caused many changes in Yellowstone, stopping some geysers, starting others, and changing the patterns of still others. Many tourists fled in panic, small landslides and rockfalls were triggered, dishes fell off walls in houses, etc., but no one was seriously injured in the park. Earthquakes such as this probably have occurred many times over the geologic history of Yellowstone, although this was the largest experienced in Yellowstone since modern instruments were installed to provide measurements. Monument Geyser, in the Upper Geyser Basin, is shown here; this one was not affected more than most, but it's pretty.

Image 1: More Earthquakes! Visit Alaska & San Francisco to get a glimpse into the effects of major earthquakes. Photos courtesy of the U.S. Geological Survey

Image 2: Alaska Earthquake, March 27, 1964. The geologist on the left stands in front of the Hanning Bay fault scarp on Montague Island. During the earthquake, the scarp formed when the rocks on the right dropped suddenly relative to the rocks on the left--the scarp is 12 feet high beside the geologist, and 14 feet high near the trees in the background.

Image 3: Alaska Earthquake, March 27, 1964. The Four Seasons Apartments in Anchorage was a six-story lift-slab reinforced concrete building, which cracked to the ground during the earthquake. The building was under construction, but structurally completed, at the time of the earthquake.

Image 4: Alaska Earthquake, March 27, 1964. The shaking caused some land to slide toward the ocean. Everything in the lower-left corner of the picture moved about 11 feet farther to the lower left in the direction shown by the magenta arrow, toward the ocean bluffs that are just out of the picture in that direction. The strip of land between the yellow arrows dropped by 7 to 10 feet, as indicated by those arrows. Notice that several houses were left hanging over the void, to be destroyed later. The collapsed apartment building from the previous slide is visible at the top of this picture (blue arrow).

Image 5: Alaska Earthquake, March 27, 1964. The shaking caused the banks on both sides of the river to landslide toward the water carrying the rails along, as shown by the blue arrows at the bottom. This in turn caused the rails to bend, and also buckled up the center of the bridge, as shown here. This is near the head of Turnagain Arm, not far from Anchorage.

Image 6: Alaska Earthquake, March 27, 1964. The Denali Theater was built on a block that dropped as the shaking of the earthquake moved land toward the sea, but Fourth Avenue was just beyond that moving block and did not drop. The marquee is now at eye-level.

Image 7: Alaska Earthquake, March 27, 1964. This was the Government Hill Elementary School in Anchorage. It was not designed as a split-level.

Image 8: Alaska Earthquake, March 27, 1964. Bridges and buildings are usually designed so that they don’t fall down. An earthquake moves the ground horizontally as well as vertically, so buildings and bridges often fail by falling sideways, as happened to the “Million Dollar” railroad bridge over the Copper River.

Image 9: Loma Prieta, California, Earthquake, October 17, 1989. The Bay Bridge between San Francisco and Oakland failed during the earthquake, with the upper deck falling onto the lower deck of the double-decker bridge, killing one person.

Image 10: Loma Prieta, California, Earthquake, October 17, 1989. The shaking of the earthquake caused landsliding and other land motion, destroying this driveway in the Santa Cruz Mountains.

Image 11: Loma Prieta, California, Earthquake, October 17, 1989. The shaking knocked this section of Highway 1 near Watsonville off its bridge supports, which poked through the road bed.

Image 12: Loma Prieta, California, Earthquake, October 17, 1989. The shaking of the earthquake caused collapse of the Cypress Viaduct of Interstate 880 in Oakland. 40 of the 67 fatalities caused directly by the earthquake happened here, primarily to drivers on the lower deck who were crushed by falling of the upper deck.

Sierra Nevada Mountains, a big, beautiful mountain range sitting way the heck up there. Got gimongous trees growing on top of it, and so you're going to tell that this is a slice that I am showing you through the mountain range, and then bang, down into Death Valley, way down, deep, hot, starkly, gloriously beautiful place. Place you desperately do not wish to be in the summer without your water bottle. But then there's another range, and another valley, and another range, all the way across Nevada, many more than shown here. And eventually, up in the Wasatch in Utah, end up where you'll find all these skiers standing around. That's Snowbird, so here's a skier so you can remember that this is Snowbird.

And so this is a picture of the west. If, however, you could see underground, what you would find is that there's a break along the front of the mountains. And that break continues on down. And all of these things have breaks sitting underneath them, running down underground. They're earthquake faults.

Furthermore, what you would find is that there has been motion, that the mountains have been raised and the valleys have been dropped, the mountains raised and the valleys dropped all the way across here. And for this to be happening, there has to be space made for the valleys to drop into. And so, in fact, the west is getting wider, and that creates the space into which the valleys drop and the mountains raise.

If you were able to find a particular layer of rock that you cared about, you might find it up here, and then you would find it way down below somewhere. And then you'd find it up, and then you'd find it down below, and so on across. And so it's a fascinating thing that the west is getting wider. You can measure this with GPS. It's actually there. It's shown in the geology, and there's a big story here.

In addition, one thing that one finds in the west is that there are volcanoes, as well. And those volcanoes tend to come-- that blue line-- it really should be a red line there-- the volcanoes come up, and they often leak up along the cracks, and spout up along the sides like this. And you get pretty little volcanoes growing. And that's part of the important story of how the west works, as well.

So we're going to slice our way through the earth. We're gonna drive off of Baja, California, down undersea, and across. And out in the middle, we find this big bridge. And then sitting out there is Death Valley. And then we're going to come on across and back up onto the coast of Mexico.

And just to make sure it's clear, this is all under water. So here's the waves of Baja. If you're really keen about SCUBA diving, this is a good place to go. And there's birds flying over the top, and there's little boats that are floating in the water, so you can see what the thing is.

Now, if you were to measure the motion of this stuff, we're going to find that it's doing what we've seen elsewhere, which is, there's a motion going away from this ridge. If we could look very carefully, we would find that there is a volcano underneath this, and so material is leaking up into the cracks and making little volcanoes. And as it comes up in the cracks here, it hardens.

Looking at what's undersea, you find that there are lots of rocks that hardened in the cracks. And so the whole seafloor is made of these rocks that hardened in the cracks, and the oldest ones are farthest away from the center. So they get older if you go out on either side.

If you were interested in fish poop and wind-blown dust, and things of that sort, you'd find there's almost none of them on the seafloor very close to the center. And then as you go away, they become more and more common. And that's because there's been more time for them to pile up, and very close to the center of the ridge, they just have not had very much time to pile up at all.

Now, you might imagine that this is related to other things. Then you remember that way down in the earth, one finds convection cells. And so you get the convection cells coming up and then spreading aside, and a little bit of leakage is coming up into the crack that it makes, making seafloor. And all of the world's sea floors are made in this way.

There's three major fault types that correspond to the three major plate boundary types. And we're going to look at these. They're push together, pull apart, and slide past. And so right now, we're looking at a block of rock. And this block of rock is being squeezed by great tectonic stresses that are pushing on it from the sides. And this block of rock happens to be the place that you decided to build your giant, multi-million dollar McMansion that's just sitting up there on a hill.

Underneath your beautiful McMansion, there is an interesting yellow layer of rock, which you can follow. Now, we hope that you were smart enough, when you built your McMansion, that you didn't fail to account for the earthquakes that happen in the place that you built it, because otherwise, you're going to be an unhappy camper. Because when the earthquake happens, you shove one side above the other in the push together environment, and then your house tends to fall down, and then you'd better know your insurance agent very well. And the layer of rock will be offset in the earthquake. So that is a push together plate boundary.

We also know that there are pull apart plate boundaries that are going to do a different motion pattern. There is a block of rock again. You have gotten the insurance settlement on your McMansion, and you have built a new one, which is sitting up here on the hill. But uh-oh, you didn't check with your geologist friends, or you didn't remember your GEOSC 10, and so now you have a fault underneath you.

But it's a slightly different fault in this case, in the sense that rather than being pushed together, now this one is being pulled apart. If you have a pull apart fault going on, then what you will find is that sometime later, you're in a Death Valley situation. The earthquake happens. It drops the valley relative to the mountain, and you get an offset that looks something like this.

Your yellow layer of rock is still there. It has still been offset. And again, if you haven't been careful in your construction, or you haven't worried too much about things, your house has fallen down and your insurance agent would be a good phone call.

Now, there's a third possibility. Suppose that you've now gone broke because you didn't have good insurance. You're flying over the San Andreas Fault, and as you look down at the San Andreas Fault, you see the highway that's crossing the fault, and you're very pleased to see your new gas station where you're working because you have to raise money somehow. And in the middle of your highway, there are these beautiful, really fat dashed yellow lines that you see.

Now unfortunately, if you're not careful, you may have problems yet again, because the San Andreas Fault has motion going on. And so you come back some time later and the road has been offset, and the offset of the road is not a good thing for you. It came about because of the tendency for the west side of California to move north and the east side of California to move south.

And when it did what it was doing, the cars come driving along. And if a car comes driving along this particular highway and isn't careful what the car is doing, why, the car will run over the rubble that is left of your gas station after the earthquake. And so these are the three possibilities, the push together, the pull apart, and the slide past earthquakes corresponding to those plate boundaries.

OK, so we're standing on the Sevier Fault right now. This side over here is basalt. You can see the dark, black color. Over here, again, is the Eocene pink member of the Claron Formation, and it's the red rocks. So right now I'm going to show you exactly what was going on here, what a normal fault means.

So all right, let me figure this out. Richard, how do you think I should do this?

What I would probably do is something like this. I'd do this one's deposited in a lake, later the lava flows came out and they were deposited on top and across in various places. And then after that, the fault broke and this one has dropped down so now that it's next to it rather than being on top of it.

Sounds good.

Something like that.

All right. Maybe I should just use that.

This rock right here is 40 million years old. This is from the Eocene Claron Formation, and it's a lake deposit. This is what we saw earlier. And this right here is a piece of the basalt, which is Miocene, which is 10 million years ago.

And what this would look like in cross-section, something like this. The Claron, some more rocks, and then the basalt was deposited on top of it. Now when the fault occurred, these rocks would drop down along it like that. And now they're sitting right next to the Claron Formation, which they really didn't have any association before.

Right now we're on this basalt here. I'm on the south side, and if you can look in the distance there, you can see how this line of this fault moves right along into the distance. So again, the red rocks on that side, and the basalt on that side.

Richard, you, why does the basalt have more trees than the red side?

The soil probably?

It erodes faster on the right.

It will erode faster, and it's probably more minerals and nutrients in it.

In basalt?

Yeah.

Yep, doing great. Just be careful out there.

Then just take a pan from this.

Hello, and welcome to another day of Geoscience 10. This one is maybe a little bit like an old-style fraternity initiation. We make you run through something really hard to get started.

And so we're going to go cranking through a lot of material in a fairly big hurry here. You will find this material is supplied to you in the textbook, in much slower and greater detail. You also will find there's a lot of v-trips, virtual field trip slide shows that are online. So you can see the pictures that I'll show you here, in much greater detail and at your leisure.

There's actually only a few big ideas that we're going to go through here. But they may be different for you. You may have seen them in some earlier class. But if you haven't, I hope you'll find this interesting.

We have started into the big picture of how do you make mountains. After we make mountains, then later we will tear down mountains. And then we will see about how people live on earth, how animals live on earth, what the history of the planet is. So that's sort of the broad outline of the course, building mountains, tearing mountains down, living on the planet.

And we're going to start with making mountains. We'll do some earthquakes, and we will look a little bit at what we call plate tectonics, which is the vast underlying processes that make the mountains. We're going to do this by starting at one of the more interesting places that you could go for a national park, which is to go to Death Valley. OK?

So we'll look at Death Valley. We will look at how it is spreading apart. How that spreading is being driven by the heat within the planet. And then we will briefly pop by Yellowstone, just long enough to see that it's shaking, and what we can learn about that, about the interior of the earth from earthquakes and so on.

You will be given, for each of the parks we visit, one or more v-trips, virtual field trips. We would love to take you and zip out to the parks and have a good time. We haven't quite figured out how to do that. And so we've done the next best thing. We've gone ourselves. Some of our friends have gone. We've collected pictures and put them together, so that you can see virtual field trips. And so you will find these online.

This is Death Valley. Death Valley is tremendous. You're looking at the lowest spot on the continent, right here. And in the background you're looking at a spot that is more than two miles higher. It is just phenomenal.

These pictures were actually taken by Peter Fawcett, shown here. Peter worked with me a number of years ago and is now a professor in New Mexico. And he was out there in the dead of winter. You can see the snow way up high on the peaks above Peter's head. You can see a little bit of water behind Peter.

It does snow, it does rain in Death Valley. The water does come down in the valley. And in the winter it may puddle for a little while. And then, poof, it evaporates. And it's gone very, very quickly. And when it evaporates it leaves salts behind. And so you can see the white salt behind Peter, there at the picture.

That was economically important in Death Valley. Some interesting things dissolve out of the rocks. They come down in the valley with the water. They're left when the water evaporates.

And you could go and mine these. And so early people actually did mine in here. The 20-mule teams hauled boron salts, borax out. And this was used in soaps and paints and glass making and all sorts of other things. And it contributed to economic development in this area.

And also, one of our former presidents, President Reagan, earlier in his career, before he was president, sold soap. And he sold Boratine, which had borax, which came with the 20-mule teams. And so he was something of a celebrity, in part, based on Death Valley soaps.

A point in this course, you will get the joy and privilege of taking quizzes occasionally. In each time we visit a park, we're going to give you introductory material such as this. And we do this, because we find it interesting. We think you will. We hope that some day you'll be off on a road trip, and you'll get to go see these things. And this will help in your visit.

We would never, on a quiz, ask you which president sold soap. Nor would we ever ask you, which soap did the president sell? This is strictly for your edification and enjoyment.

Once we get to the point of saying, OK, geology is tearing Death Valley apart, that could show up on a quiz. But this early stuff, what's pretty, what's neat, what's exciting that you want to go see this park, this is for you. So please do not attempt to memorize the soap that President Reagan sold before he was president. That doesn't— that's just for you.

But Death Valley is something. This picture, the scale here, if you ever been to Penn State's University Park campus— and we're very impressed around here with our mountain, Mount Nittany. If you put Mount Nittany in this picture, it would tower over that little white line on the far side of the picture, almost a third of the way up that first slope.

There's nothing in the Appalachians that you could put in this picture that would look even vaguely large. You'd drop the whole Appalachians in this picture, and they would not go halfway up. This is immense. It's just truly an awesome place to get to.

You find the right place in Death Valley, such as the one you see right here, and there's beaches. During the ice age, when it was colder, the rains that came in didn't evaporate as fast. There was a big lake in Death Valley, which has now evaporated.

You go and look various places in Death Valley, and you'll find that the floor of it is salt and it's gravels and things. The streams are tearing down the mountains. They're dumping stuff down in the valley to fill it up.

And yet the valley is there. The valley is there, even though they're trying to fill it up. There's a little bit of sand, a little bit of sand dunes. Not too much. Usually the desert is not sandy. But there are such beautiful things as this.

There are really amazing things. You can look at this picture. You see those big rocks out on the salt flat. And those rocks have moved. And people have come and surveyed them, and they do move.

And we're still not absolutely positive how. The best picture is when it rains, you get a little water here. And then in a really cold day in the winter, it might freeze. And then these rocks are locked in the ice.

And the wind blows, and it pushes along on the ice, and it actually sort of skates these things along. But no one's sure. Racetrack Playa, the rocks move somehow. Neat place, neat place to visit.

The valley is actually growing. It's widening and it's deepening. And if you look at this picture, you can see the great mountain range towering more than two miles above the valley.

And you'll see right along the bottom, it's just a straight line. Well, that straight line is actually an earthquake fault. And here's another view of it. The near side has dropped. The far side has been raised.

These things happen. They are ongoing. It is part of our world today. And that's really what's very interesting and why we're visiting Death Valley at this point, is why are things moving? What's going on on the planet?

When this motion occurs, occasionally volcanoes come leaking up along the cracks. And so you can see volcanic craters if you go and visit Death Valley. You can see some places. This is an old, little volcanic feature, which has been torn apart by motions.

This is a slightly different motion. Most of Death Valleys' motion is sort of an up and down thing. This one's a little bit of side to side as well. And the diagram will show you what's going on. Things are moving away there.

So there's some pictures of Death Valley, if you get the chance to go. If you want to impress your friends, go in midsummer. If you want to have fun, don't. It's really stinking hot. But it's a wonderful park, big park sitting on the California, Nevada border.

Now, what's going on? Death Valley is getting bigger. And it's doing so from heat down within the planet. And so that's what we have to look at a little bit now. And then we'll go see what that does at Yellowstone.

So let's do the Death Valley. OK, Eastern California, Nevada border, the lowest, the hottest, the driest spot in the country. The water does come down. It does evaporate. It does leave salts behind. This drove various economic activity. It's largely turned off now.

And now, let's see what we do. This is a cross-section of Death Valley. If you could go in and you could take a giant saw and hack your way down and then look at it sort of as a cliff, you have spaces up above in this picture. And the earth is down below, and it's shown to you as blue. And we're going to look at it. The little line across the top is just for your reference in there.

And so what's going on, Death Valley measured? If you go in and you put in GPS receivers across Death Valley and on across Nevada and over to Utah, and then you survey what's happening, what you will find is it's very slowly, about as rapidly as your fingernails grow, the west is getting wider. One side and the other side of the valley are very slowly pulling apart.

As they do so, the valley drops down. And it drops down on what we call pull-apart faults. Because you pull it apart, and then the fault allows the drop. The fault is a break where there's motion. OK.

So the block in between is going to drop down as we pull apart. And it is measured. This is not storytelling anymore. The early geologists look at this, and they said, this has to be happening. We understand that, but we can't measure it.

It's pretty hard to measure a state spreading at the rate your fingernails grow. But we can do that now. This is directly measurable by GPS. It does work.

And so this is the picture. You can actually put out your GPS and measure that the mountains on the east of the valley and the mountains on the west of the valley are moving apart. It's actively going on. This is real. It's happening today. And as they do, they allow earthquakes. And the earthquakes drop the valley down.

Erosion takes stuff off the top. It fills it in the bottom. But then the bottom drops, and the sides are raised as the whole thing is pulled apart. And so Death Valley is getting bigger. The west is getting bigger. And the fault, the break in the rock along which there's motion, there's one on each side of the valley. And basically every valley in Nevada and Utah has this same structure going on.

If you were to find a rock layer, an old friend that you happen to know— the pretty purple rock, the pretty red rock, whatever it is— you can see the pretty red rocks scribbled in on either side. If you wanted to find that in the valley, and you drilled in your oil well— you're not allowed to drill there now, but if you were, you'd drill down— you would find that same rock layer. It's down there. And you would find it down there.

Now, this is one of the things that geologists were quite confident that this motion was going on, before they had a GPS satellite to help them measure it, because of things such as this. You say, OK, what happened to the layer in the middle? There it is. It's way down below. The valley, the west is getting wider. The bottom is dropping down.

Now, here's a map version. If you want to get in your satellite and look from above, down onto these things, Death Valley you'll see labeled way up at the top of the map there, above Las Vegas. That's sort of along the California, Nevada border. And Death Valley and through Las Vegas and on down passed Scottsdale and headed to the south, all of that region is getting wider.

You'll also see looking farther down, past San Diego and Tijuana down there, that we get down to water. We get down to very pretty beaches, plus fun places that you could go diving. And what you find is that this pull-apart action of Death Valley is running all the way down to the ocean, down to the Gulf of California, down past Baja there. This whole area is being pulled apart. Baja, that piece out on the left, and Mexico as a whole are pulling apart. The same spreading that tends to open Death Valley is opening this whole area.

And so we've drawn in here, you can see a circle up by Death Valley and then a green line that runs down to the Gulf of California. And the Gulf of California actually is getting wider. It's unzipping. It's open.

Given enough time, it possibly will open all the way up to Death Valley. It is conceivable that you could, over time, actually have the ocean extend on up into the central part of the West there. We're not sure if it will get there or not, but that's what's going on. Is that whole thing is measured to be unzipping, with Baja moving out towards the Pacific, Mexico moving over towards the Atlantic, the space in between, the ocean basin getting larger.

Now, this is part of a much bigger phenomenon. As you might possibly imagine, if it's going— we started in a cool place, but you start moving things around on the continent. And if I move here, it's going to bump my neighbor and bump the other neighbor, you sort of get the idea that this must extend much farther along. And so what you find is this sort of spreading behavior. This pulling apart behavior happens not only at Death Valley, not only where Baja is moving away from the mainland of Mexico, across the Gulf of California, but it actually happens through the world's oceans.

The places that they pull apart from, it turns out, tend to be raised a little bit. We know that there's these big mountains next to the valley at Death Valley. And so there's high stuff associated with that.

If you go down under the Gulf of California, the center where it's pulling apart is a little bit higher than the rest of the sea floor. It's sort of arched up a little bit. And so we talk about spreading from ridges. And so that's spreading ridges. And so we find a lot of places in the oceans have these places that it's being pulled apart from, and they're a little bit high. OK?

If you played baseball, or if you play tennis— tennis would work too— but you'll find that the ball has a seam on it. And that seam sort of wraps around it. And we often say that you can follow these spreading ridges of the earth, and they wrap around the planet like the seam of a baseball. And they're raised a little bit like the seam of a baseball.

And so here is a map. And the black lines— you'll see one black line disappearing up there, pointing towards Death Valley. And then you'll see the black lines wrapped around the rest of the planet, primarily running through the oceans. If you look very carefully, way over on the far right of the picture, you can see where one black line sort of points down into Africa, towards the great African rifts.

And so there are other places that these black lines, these spreading ridges are trying to tear a continent apart, the same as is happening up in Death Valley. But for the most part, they're out in the oceans, wrapping around, and again, sort of like the seam of the baseball. If you're not a Mets fan, well, just imagine that that's whatever team you like to cheer for.

You will see that these black lines look a little bit like the edges of jigsaw puzzle pieces. And so you can sort of see between the black lines what you might think of as being jigsaw puzzle pieces. These are plates. And you'll see they're labeled in there, the Antarctic plate, the Pacific plate, the Cocos plate, and so on. These plates are going to be very important in our story of how the world works here, as we try to put this together.

You also see the Ring of Fire all the way around the Pacific. At the edge of the plates there's volcanoes. That's sort of fiery. And so that gives us a Ring of Fire. That is something we will revisit a little bit later. OK?

Where we started again was in Death Valley, where you can see one of these spreading ridges disappearing and trying to unzip the continent. And then you can follow that out and then on around. And these are some of the plate boundaries.

We will see, in a little bit, that while plates, these big chunks, the jigsaw puzzle pieces often have a spreading ridge at the edge. Sometimes they will have something else at the edge. And so some of the plate boundaries are shown by the red lines in here, but there are other sorts of plate boundaries that we will revisit.

And there's your baseball. And again, I can't say I grew up a Mets fan. I'm from Ohio, and so it's Cincinnati or Cleveland. But that's life.

All right, now, if you go to Death Valley, you find there's volcanoes. If you go to the center of the Gulf of California, you'll find it's hot along that spreading ridge. And in fact, there's a volcano there. There's melted rock, leaks up along that crack.

And as Baja moves away from Mexico, melted rock will sneak up along that crack and freeze. And then they move away. And more melted rock sneaks up and freezes, and it moves away. And more melted rock--

And so that should tell you one thing. It's hot down below, because there's heat coming up from there to drive the volcanoes. Certainly, if you see a volcano at Death Valley, there has to be a heat source. And so we're going to talk a little bit about heat. Because it turns out that all of this action on top is being driven by heat from below. So let's take a quick look at what is heat and how it moves around.

I'm sure, for some of you, this is really old hat. Some of you may have not encountered this before, and I hope you get something interesting out of it. The normal way we look at it, if you were able to look inside of me very, very careful, you could see all the little pieces of which I'm made are vibrating. There is heat in me. There's vibration going on in the atoms that make me up.

Atoms, as you know, smallest units of matter that are sort of recognizable as something. If you started to— please don't do this— if you started to break me up into pieces, using chemistry, using fire, using other tools that you have available to you, you could make smaller and smaller and smaller pieces down to some limit. Below that, if you wanted to break it up more, you're going to need an atom smasher or something like that.

And so the things that you can get to with a fire or your stomach or something like that are atoms. And they have, we talk about different types. I'm made mostly of carbon and oxygen and hydrogen and a little nitrogen and a tiny bit of iron and other things.

And each one of those carbons, you could pull it out, and you could weigh it. And say, oh that's carbon. And that's because of how many pieces are in it, the little protons and neutrons. And so there's a little blurb in your textbook. If chemistry is completely foreign to you, it might be worthwhile to go back and read through in the textbook. If this is old hat, great. Don't worry about it.

Now, we will come back to some of that terminology. It is true that a carbon inside of me, one of them may be a little heavier than its neighbor. And so if you've never run into an isotope in your life, you might have a quick look at that. This is going to show up for us in just a little bit.

But again, if you've never had chemistry or you completely forgot your chemistry— Oh my goodness, don't tell me about chemistry— there's about a half a page or three-quarters of a page in the text. It will get you completely up to speed. So you might have a look at that.

Now, suppose we started making it cold. The vibration slows down. It slows down. At absolute zero the vibration stops, or very nearly. There's a little quantum stuff, but don't worry about that. OK. So as you warm from absolute zero, the stuff in me vibrates and that's heat. And that's there. And it's very good, because if it wasn't going on I would freeze and that would be the end of us.

OK. So now, suppose we have some heat. There's someplace that the molecules in me are vibrating like crazy. Does the heat always stay in me, or does it go somewhere else? And the answer is, it goes somewhere else. There are other ways to get things going.

And so if something cold were next to me, if you put an ice cube on my head, it will melt. The atoms in it will start vibrating faster. The atoms in me will vibrate slower. And so I will transfer heat to it.

And so there are ways that heat is moved around in things. How does it work? One way that heat gets moved around is by what we call radiation. The lights are shining on me. I'm picking up just a little warmth from the lights that are shining on me.

It gets here by radiation through space. Radiation works great. If you wanted to get a suntan, you go out and lie in the sun, and you soak up the sun. And then you get skin cancer. And so that's maybe not a good idea.

But our cats are very clearly solar powered. Now the radiation brings energy all the way from the sun, all the way down to the cat. And the cat just sits there and soaks it up. And then the cat goes and runs around like crazy at 2:00 in the morning. And so radiation moves heat around very well through space. And as noted, don't soak too much of it up, or when you're old and feeble, you won't be happy about that.

How else do you move heat around? Conduction. If you turn on the stove burner, and you let it get hot, then you hold your hand out to one side, you feel a little bit of heat coming off the side. That's radiation actually. If you take your finger and you touch the burner, you will notice very quickly that you feel a whole lot of heat. You're feeling that heat by conduction.

The atoms in the stove burner are vibrating really fast. And when you put the atoms in your finger against the atoms in the stove burner, the collisions between the two make the atoms in your finger vibrate really, really, really fast. And then they jump out of the places where they're supposed to be, and they sizzle and combine with oxygen and disappear in the atmosphere, and your finger burns up. So don't do that either.

That is really all it is though, conduction moving heat around by collisions between a fast one running into a slow one. And then they sort of share their speed. That works really well over short distances. You touch your finger to that stove burner, and immediately you'll notice it.

It doesn't work very well over space. If I vibrate really fast, I can't make a molecule on the moon vibrate faster. It doesn't even work really well over miles and miles. If I vibrate really fast, if I had a neighbor that I could shake, and the neighbor would shake the neighbor, by the time you try to go a few miles away, it's really hard to get your neighbor to shake the neighbor to shake the neighbor to go few miles away. And so conduction works really well over short distances, not over long distances.

Convection is where we're headed. This is sort of the third big way of moving heat around. And essentially this is just taking something hot and moving it.

If you cook dinner, and the dinner's on the stove, and it's hot, and you want hot food on the table, you could go bring the hot food over. You could wait for radiation to bring the heat. You could wait for conduction to bring the heat. But I think you're going to go get the food and bring it over. OK, that's advection. But convection is just sort of that. It's the natural way for hot things to move to somewhere else, taking the heat with them.

You've probably seen convection work if you've ever cooked spaghetti on the stove. You make it hot at the bottom. It expands. It's lower in density, then it rises. It gets to the top and it cools, and then it's going to sink again. But it can't sink where it's rising, so it gets out of the way and goes around in a loop.

Wherever you have soft solids, really soft, or liquids or gases, and you heat them and they expand, you end up with convection cells running after a bit. And it works in spaghetti. It works in spaghetti sauce, even though that's a little thicker. As you can imagine, if we're talking about it here, it's going to work in the planet as well.

So convection, heated material moves to a new place, carrying the heat with it. Primarily because hot things are less dense. The vibration, as you heat it up, it shakes around more. It shoves its neighbors away.

Now you've got the same amount of stuff taking up more space. And so you get a little lower mass in a place, it's less dense. It tends to rise. In case you forget what density was, it's mass divided by volume.

So what happens if you have a low density thing down, it tends to rise. If you have a high density thing up, it tends to sink, and they get organized. And that's not a terribly tough thing.

You've probably seen it in the atmosphere. What happens and what's very interesting is that over the times of geology, slow times, even rocks will do this if they're very warm. And so you go down in the earth, and it gets hotter and hotter. It's mostly solid, except in a couple of places. But most of what's down there is solid, but it's soft. And you know if a blacksmith takes a horseshoe and heats it almost up to the melting point, it can be deformed. It can be worked.

Well, if you get a huge mass of stuff and you heat it up, almost to melting, it gets soft. If you heat it at the bottom, it can convect, even though it's essentially solid. And that's a cool thing.

But if I had a chocolate bar in my pocket, I'd eat it right now and I'd be happier. But if I had a chocolate bar in my pocket, it would be fairly soft. As you warm it almost to melting it gets soft. And I could deform it. I could make it do things.

And so the same is true in the Earth. It's warmed almost to the melting point. It's soft. And because it's soft, it can do things.

So that's a convection cell, here's a picture. OK? Now we're going to very briefly sort of divide the world up for you. What you see here is a diagram planet. There's a much nicer diagram in your text that you might want to look at.

The planet is layered, as described in the text. The center is sort of an iron ball. It's got an outer core, which is liquid, and an inner core that's solid, that's basically iron. Around that there's this vast shell that's got some iron, but it's got some silicon and oxygen and a few other things. And that is soft. It's not melted, but it's almost melted. And so that's soft.

And then on top there's sort of a layer that's too cold to flow very well. It prefers to break rather than flowing. And we call that the lithosphere. And at the very top of it, especially the crust, has a little bit more silicon and oxygen and a little less iron than the rest. And it's got a little water in it, little [? us, ?] and some other things. So it's fine.

But anyway, here's the picture, if you can see it. And so you've got stirring going on down below. You'll see the surface of the earth labelled there. You'll see that this is only part of the earth. Yes, the whole planet is spherical. And you'll see the center marked down below there. Just so you know what we're looking at and what's going on.

The spreading ridge is right in the middle, on top there, where it says ridge. You'll notice that the convection cell comes up and it spreads. And as it does that, a little bit of melt will leak up and freeze and then get pulled away and leak up and freeze.

And so you'll get the volcanoes in Death Valley. And you will get the spreading and making of new seafloor at those places that allow the motion of Baja away from the mainland of Mexico and so on. The process here, we've got this cold stuff on top, the jigsaw puzzle pieces, we call those plates. And the moving around of these on the convection cells we call plate tectonics. It's a big, fancy word. It's a fun word. And it's written out there for you, in case you can't spell from my speaking.

So again, pull apart. We started in Death Valley. It's pulling apart. A little bit of melt leaks up. And you go south from Death Valley into the Gulf of California. Baja is moving away from Mexico. There's pull-apart going on. A little bit of melt leaks up. Things are pulling apart, and they're doing so riding on the back of giant convection cells. The stuff on top is just rafting around on what's underneath, with the ridges at Death Valley being where we started.

Heated rock rises, less dense, cools at the surface of the earth. Then you sink back, and this gives you the completion of the loop. And this gives us action. This gives us motion. This gives us drama.

You pull apart here, it's going to run into something somewhere else. We're going to have rifts and collisions and earthquakes and volcanoes and fun. And so you get ultimately the heat of the earth making this go on. Rising rocks push aside the cool rocks at the surface. The cool rocks travel sideways. And there will be interaction when cool rocks run into other cool rocks, which we have to look at.

Where does the heat come from? A little bit of it may be left over from when the planet formed. There's some other things going on. Mostly it's radioactivity.

If you get a rock, and you put it in a Geiger counter, you'll get occasional action. There's always a little bit of radioactive stuff. Now, not huge amounts. You usually don't get wiped out by the radioactivity in the rocks next to you.

But it's a big planet. There's a lot of radioactivity. There's a lot of rock. That makes heat.

And that heat is ultimately the big source of what drives the planet. There is a little left from the formation of the planet, a little bit from separation of the planet and freezing of things. But mostly it's radioactivity that does it.

As a wonderful story, if you're into history— don't get too bogged down on this— but if you're into history, the physicist Lord Kelvin says, OK, I'm a physicist. I'm smart. I know all this stuff. The earth started melting, and it's cooling off. And I measure how much heat is coming out of it. That tells me how old the earth is, 24 million years.

And the geologists said, oh, no, no, no, no. It's longer than that. It's lots longer than that. It's more than 100. It's— you got to go way back.

And he said, no, no, no, I'm a physicist. I have it right.

Well, he didn't know about radioactivity. He got it completely wrong, because his assumptions were entirely wrong. Darwin as well as the geologists are saying, come on, come on, we need a longer clock than this.

And actually it took the discovery of radioactivity. Marie Curie, who is shown here, and others find the energy source and say, no, there's heat down there. This will work. Your physics was right. Your assumptions were wrong. Something worth— and so geologists, we like this. So those who study the earth like this.

OK, so brief summary. Heat inside the air from radioactive decay, it drives convection cells. The cells move plates. The jigsaw pieces on top, where it's cold, they go rafting around on the surface of the planet. Where they pull apart, you get faults, you get spreading, you may get a little volcanoes leaking up. Death Valley is one. You get ocean spreading centers beyond that.

You're welcome to pause right now and take a deep breath. [BREATHING] If not, we'll go screaming right along. We're going to briefly visit another park.

And we will look at one of the implications of this. You might say, why should I care? Who cares what's going on here?

One of the reasons this matters is occasionally things that are moving get stuck, and then they move again. And when they move, they go fast. And if you're standing on top, your feet get knocked out from under you. And if you're a building, you fall down. And that's not good.

So we're going to go to Yellowstone. And we're going to look at— Yellowstone has everything. It has geysers, and it has bears, and it has beautiful trees and lakes, and it has earthquakes and volcanoes and river erosion.

Yellowstone has everything, the first national park. The first serious European Western exploration. People are there, and they've had earthquakes. The ground shook. That's cool. Sort of everything is here. It must be going on.

Yellowstone itself is a huge volcanic pit, a volcanic caldera left from giant eruptions. And there will be another one someday, with fairly high confidence. It's due, plus or minus 100,000 years, the next one is due. You can count 1.8, 1.2, and now 0.6, but we're due. Not to worry.

Those were big eruptions, really seriously big eruptions. But we're going to visit there and talk about earthquakes. You go to Yellowstone, and if you read into the history, back here a little bit, there was actually a beauty pageant going on at the Old Faithful Inn. I don't think they do this anymore.

And in the middle of the pageant, in the late 1950s, there was an earthquake. And there's this wonderful text you can read about it, in our textbook, about all these people watching the queen walking down the aisle. And the ground starts shaking. And they all screamed and ran out.

What had happened is just west of the park there was a big earthquake. And the picture you're looking at in front of you, the side that I'm standing on taking the picture, the side that the bottom of the tree is on, dropped about 20 feet relative to the other side. And in the middle of the night, it just went PFFT! And it does this huge motion.

Now you can imagine what happens. There's a hill there. And this is a serious hill. This is a couple-thousand foot high hill. And it drops, and it stops.

Well, if I had something balanced precariously on me, and I dropped, it falls down. What happened is the whole hillside fell down, and it killed a bunch of people. It was not very nice.

But there's these dramatic stories. When the hillside fell down, it's just slid across the river, and it pushed the air out of the way in front of it. And there's this story of this guy that had his clothes blown off of him in the middle of the night. He's sitting there in his tent and pfft— the things come. So it was truly an amazing thing.

You can see the pictures here. Those are big pine trees along the edge of that failure. So this entire hillside just fell off. It dammed the river. It bounced up the other side. This rock is towering over me. And this, the rock came down into the valley and several hundred feet up the other side, in the landslide that was caused by this earthquake.

Once it dams the river, it makes a lake. The Army Corps engineer says, boy, we got trouble. Because what happens, the water's going to fill up. It's going to go over the lake, go over the dam.

The dam is loose rocks. It will cut through the dam. There'll be a giant failure. It'll kill people. That happened 100 years ago, just outside the Grand Tetons. And so fortunately, the Army Corps engineers got in there real fast, and they fixed this sucker and things worked. You can still see the damage that was done by this earthquake.

There's great stories of this lady in this house. I think it was this house. The land sort of tilted. And the lake is filling up. And there was another lake just above it that had already been there.

And her house is getting flooded. And the waves are coming at her. And it's the middle of night, and she's running away. She made it. That's all right.

The earthquake shook up Yellowstone. It changed the timing of the geysers. It did all sorts of things.

And so there are earthquakes. And we know they matter. They matter in natural places. They kill people. They cause troubles.

This is a different earthquake. 1964, Alaska had a big one. And you can see one of the things that happened there.

We usually build buildings to stand up against gravity. We make them so they don't fall down. In an earthquake, they shouldn't fall sideways.

And we usually don't build things to be strong against falling sideways. Well, you notice what happened? Things moved, and that bridge truss there just fell sideways— pfft— it fell off. It's an interesting mess.

Here's another one. This one is from the World Series earthquake in California, '87, I believe it was. An again, sort of we build things not to fall down. But it shook, and it sort of slid off, and then it— So this isn't good. You really wouldn't want to drive your car over the middle span of that bridge right now.

And when you shake the ground and things move, you get cracks and that's not good. And it's not good for houses. And this one, the road is a little perched on these little— you put a real strong thing, and it sits on a post. And then you put a road on top of it, and then it shakes and whoop, the post just poked through the road. Whoop, I didn't design it that way, did I?

So earthquakes are a very bad thing when they happen. And this is also the World Series earthquake. You can see the road is not going to be useful for a little while there.

So what's going on with earthquakes? The land moves. We've seen that it pulls apart. If it's pulling apart somewhere, somewhere else it must be running together. And occasionally there's sliding passes that go on.

And so this is a diagram of the West. This is a diagram of what you might see going on for the World Series earthquake, for the San Francisco earthquake, for the San Andreas fault. What you have out there, in fact, is that there's sort of the far-western piece of California is headed for Alaska. And so it's sort of sliding along. And the join between that far western part and the rest of the country is the San Andreas fault.

So let's see if we can walk through this. We're going to see what happens when a fault get stuck and then it breaks. And what happens is it gets stuck for a while, and things sort of bend. And then eventually, they let go. And when they let go, things happen. And so let's see what we can do here with this.

OK, so we have plates. They're moving. The North American plate is probably what you're sitting on. If you're in Pennsylvania, for example, you're on the North American plate.

But the very far western part of California is out on the Pacific plate. There's a lot of motions. Everything is sort of going that way, and then there's a little of this.

But if we just focus on how they're moving compared to each other, the Pacific plate is headed for Alaska and the North American plate is not. And so there's a little of this slide pass going on. The break between them, the San Andreas fault. And so you can just take that blue line as the San Andreas and the Pacific plate moving relative to the North American plate.

Now let's start. You have a fence or a road or a building or something. You build it across the San Andreas fault, and then things are moving. OK?

So what's going to happen is the different sides are trying to move, but that fault is not letting go. You're trying to go. Maybe they're moving a little bit, but they're not going real far.

And so you actually may start things bending. Far away from the fault it's moved. Right at the fault it's stuck. The rocks, they sort of get locked around each other, and they're getting bent.

Well, eventually what's going to happen is that bend that we have circled there, something's going to break. You can't bend rocks forever. And when it breaks, [POP SOUND], OK? There you go.

And so you go, rrr, stop. And that snap is the earthquake. It's been caught on pumps or rumps or jumps in the rock. And then it breaks and it lets loose.

What happens then? If something snaps, these are big chunks of rock. I mean, sort of everything from San Francisco to LA just moved north by 20 feet. Now, if that happens, it sort of elbows its neighbor a little bit. And so other sorts of things are going to be going on with that snap. And it could get very interesting. And it will release energy.

And so when it goes 20 feet north, it shoves what's just north of that, and that shoves what's just north of that. And the truth is, on a big earthquake, the whole planet will get shaken a little bit. It's not just shaking yourself. It's shaking lots of other places.

Where are earthquakes? Well, the red dots here are earthquakes. This happens to be 1978 to 1987, fairly large quakes. And what you'll find is that these quakes actually outline the plates, the big tectonic plates. The jigsaw puzzle pieces moving around on the planet are pretty well outlined by these red dots, as you can see by comparing to this one.

And so if you sort of remember what this looks like and remember what this one looks like, you will be able to see, and you can compare them on your own time. You'll be able to see that the plates are primarily outlined by the earthquakes. The action is mostly at the edge. There's a few places in the middle that get more interesting, but not too many.

We have been looking at a couple things out there, the pull apart at Death Valley, the slide pass. If that is confusing you a little bit, there's sort of a little of both going on. There's a little of this sort of thing. And so, in fact, we're not telling you anything that's wrong, but we don't want to get this too complicated. So we'll try to keep it—

So now, the rocks shake. They shake their neighbors. They shake their neighbors. This sort of pushes things off. And so you get deformations that run away. And this makes waves, and the waves knock down buildings and do other sorts of things.

There's various kinds of waves. If you're hearing me, I am speaking and the sound is going to a microphone. And what I'm doing is essentially compressing and expanding the air. It's called a push wave or a sound wave or a P-wave. It very clearly goes through gases and liquids, as well as through solids. Because you can hear me, because it's going through the air and getting to the microphone.

There's another kind of wave. If you were to grab a rope and shake it, it sort of this kind of thing that— actually, imagine for a moment going to the football game, getting in the stadium, and doing the wave. Now what's a wave do? You're part of the wave. Yay, yay, yay. Your part of the wave is up and down.

But the wave moves around the stadium. So in that case what you're doing and what the waves are doing, you're going in different directions. That kind of wave is called a shear wave or an S-wave.

And it turns out that unless your neighbor really wants to do what you want your neighbor to do, they don't go through liquids or gases. Because if you move— yay— and your neighbor doesn't cooperate, you can't really grab your neighbor and grab your neighbor up. And so it turns out they do not go through liquids or gasses, oddly enough.

So two kinds of waves are generated. The P-wave, compressional push, they will go through liquids or gases. Sound waves, they are squeezing and then expanding. The shear waves don't go through water or air. They're more like doing the wave in the stadium. You go up and down, but the wave goes around.

Now, if you go look in the textbook you find out the earth is layered. And you find out the outer core is liquid. We say so. It's right in there. Why in heaven's name would we say a silly thing like this?

One thing that can happen, as you can see in the diagram down there, you make an earthquake. If you put out a listening device that listens for this kind of waves and this kind of waves, if you put it near the earthquake, you'll hear both kinds. P-waves and S-waves come winging by.

If you put your listening device on the other side of the planet from the earthquake, you won't hear any S-waves. You'll only hear P-waves. And no matter where the earthquake is, as long as your listening device is on the other side of the planet, there's a zone that doesn't get any S-waves. Now, S-waves won't go through liquid.

And so you start looking down there. And you can see the diagram. And what will happen is that any S-wave that hits that outer core disappears. It gets soaked up. It makes heat ultimately.

And so because every earthquake has a zone on the other side of the planet that there's no S-waves, there must be a ball of liquid in the middle of the planet that keeps the S-waves from getting there. So the seismic energy leaves the earthquake. It goes zipping through the planet. And if it's a big earthquake, you will hear it on the other side of the planet.

And we say that the outer core is liquid, because none of these S-waves or shear waves get through it. And we can look at the global map of earthquakes, listen, because now there's listening devices all around the planet. And the other side of the planet never gets one, so there must be a ball of liquid in the way.

S-waves don't go through the outer core which is liquid. Now, the textbook will tell you why we think there's a solid inner core in there that's even a little more complicated. But this much of it basically make sense.

Earthquakes, we talk about earthquakes. We say, wow, that was a nine, that was an eight, that was a seven. And we get really, really excited if it's an eight rather than a seven.

Why? Well, we sort of cheat in the way we do this. Sometimes scientists get lazy, and we really like talking about nine and eight, rather than 100 million and 10,000. And so we sort of play an interesting game in how we scale these things.

When you move up one in how big an earthquake was, that really means that the ground moves 10 times more. We just do that because it's easy. And it turns out that to move the ground 10 times more takes about 30 times more energy.

So if you have a one earthquake, it's not very much. A two earthquake actually is 10 times more ground motion and 30 times more energy. A three is 30 times more energy than two. A four is 30 times more energy than the three. A five is 30 times more energy than a four.

And by the time you get up to these big ones, they're bigger than all the nuclear arsenals of the world. They're really, really, really bad things. And they are out there occasionally.

What this turns out is that most of the action, most of the damage is in those few really big ones. There aren't many big ones, but they are so huge that they really dominate what happens. And so there's thousands and thousands of earthquakes, but you don't hear about them until that one rarity when, oh, the whole world shakes.

So quick summary, earthquakes mainly at plate boundaries, not entirely. Faults get stuck, then they suddenly slip. When that happens, the energy is spread away on waves that cause a lot of [? destruction. ?] You can measure them to get information about how the earth works. When we say that it was a little bit bigger, we mean it was a lot bigger. And most of the action is from the few big events.

And so we're started on this very interesting— interesting to us, I hope to you— this very interesting journey to understand why there are mountains. And what you can see is that the heat of the earth is stirring things. It's moving things around. It's causing things to come up and down, to stick and slip.

There's action. You can surely see that there's more action coming. And we will get to that more action next time.

Hi I'm not Johnny Cash, but I wear the black for all the geoscientists helping us live in harmony with nature. This song is for the seismologists who watch a seismic line to warn about tsunamis, earthquakes, volcanoes, illegal explosions of atomic devices, and to find valuable things that make money. We keep a close watch on the seismic line, we keep our eyes wide open all the time. We have to find that early warning sign, so you're not dying, we watch the line. We find it very, very, easy to pay heed because tsunamis cross the ocean at great speed. For early warning systems, there's a crying need, so you're not dying, we watch the line. When Magma's moving beneath the volcano, the peak is swelling, and it's just about to blow. It shakes the ground, a warning from below, so you're not dying, we watch the line. Sometimes earthquakes make patterns we can see. Locked seismic gaps endanger you and me, but knowing where might stop a tragedy, so you're not dying, we watch the line. Evil dictators test their bombs at night. They think they've fooled us when they're out of sight, but when it shakes the ground we know it right, so you're not dying we watch the line. Things of great value are down there very near. It takes geoscientists to find them, this is clear, and you should know that it makes a great career, so you're not dying we watch the line and that does fine on the bottom line. Keeping you from dying and building up the bottom line.

Hey, groovy cats. Welcome to my pad. This is the G-Side 10 '70s show, in which we're going to talk about vinyl, bell-bottoms, platform boots, and most importantly, lava lamps.

What? You mean you don't have a lava lamp? Run down to Uncle Eli's right now and get one. I'll wait.

So what do lava lamps and G-Side 10 have to do with each other? Well, they're a wonderful analog for this whole first section of G-Side 10. First section, if you remember from looking at the syllabus, is building mountains. And the short story for building mountains is heat from within the Earth.

We're going to talk about tearing down mountains later on, but right now we're talking about building mountains, and the heat within the Earth is what drives that whole process. And a lava lamp is a beautiful example of that. Let's take a look at it.

What we have here is a glass tube with some water in it, and then these globules of a slightly different material, and at the bottom, we just have a light bulb that produces heat and heats up the bottom of this glass bowl.

All right, I'm going to take this apart here, and just take a look on the inside. I don't know if this is going to be too bright for you, but we have a light bulb underneath here, and its only purpose is to produce heat and to light up this glass bulb a little bit.

These green globules in here get heated up at the bottom, and as they get heated up, they get less dense. This is fundamentally what's happening inside the Earth. Rocks get heated up at depth, because there's a lot of heat trapped inside the Earth. As they get heated up, they get less dense, and just like these lava lamp globules, they rise up like this one's doing right now, up to the surface of the Earth.

When they get to the surface they cool off, and then, just like this one, they sink back down into the Earth and the whole process goes on and on again. This inside the Earth we would call a convection cell. In a lava lamp, we call it cool.

Plates shown are as follows:

• Eurasian Plate
• Indian Plate
• Antarctic Plate
• Pacific Plate
• Philippine Plate
• Gorda Plate
• Cocos Plate
• Nazca Plate
• Caribbean Plate
• American Plate
• Arabian Plate
• African Plate

Image 1: A view of Crater Lake from the sky. Crater Lake, which is about 6 miles across, is the big blue circle in the middle of this satellite photograph. A catastrophic eruption from a towering, snow-capped volcano called Mt. Mazama blasted a recognizable layer as far as Nebraska. The remnants of the volcano then collapsed into the hole left behind. As the hole cooled and water collected, Crater Lake formed. This NASA photograph is from the USGS archives. Because logging and other uses continue outside the park but not in, careful examination will show you the outline of the park.

Image 2: Paul Rockwood’s painting of the cataclysmic eruption. Here is artist Paul Rockwood’s reconstruction of how the peak might have appeared 6600 years ago, early in the cataclysmic eruption. Notice the glaciers flowing down the sides. The USGS hosts this image courtesy of the Crater Lake Natural History Association.

Image 3: Two images. Top, an oblique aerial view of lake. Bottom, a close-up view of the lake. After the eruption, this USGS photo by W.E. Scott shows the lake in an oblique aerial view (out the window of a plane). On the right, a close-up view (USGS photo by Ed Klimasauskas) shows the “U”-shaped valley of a former glacier, which flowed down from the peak that is no longer there (the outline flying in the sky emphasizes the “U” shape). Later in the semester, we’ll learn why glaciers make “U”s while rivers make “V”s.

Image 4: Now, we begin some pictures by Prof. Alley. Here is a view looking up one of the valleys that once carried glaciers down from the peak of Mt. Mazama. If we had stood in the same place before the eruption, this whole picture would have been filled by a massive, snow-capped volcano, with a glacier flowing down the valley towards you and to your right, following the magenta arrow.

Image 5: This is Crater Lake from the rim of the crater. The trees are silhouetted against the water, it’s not sky! Crater Lake probably has the cleanest water of any major lake in the country.

Image 6: Another shot of trees against the crystal water of Crater Lake. There are no rivers to carry mud into the lake; the rivers all drain away down the sides of the volcano. Rain and snowmelt evaporate from the lake, or leak through the rocks to emerge as springs on the side of the volcano.

Image 7: A person sliding down a hill of snow at Crater Lake. Crater Lake gets lots of snow, which melts to fill the lake, and contributes to the fun at the park.

Image 8: Crater Lake with Wizard Island in the middle. After the cataclysmic eruption, additional volcanism began building Wizard Island, which rises about half a mile above the bottom of the lake.

Image 9: A wide angle view of Wizard Island in the Lake. Photo by Lyn Topinka.

Image 10: Top of Wizard Island showing the crater left by the “little” volcano that built the island. Zooming in, you can see the crater left by the “little” volcano that built Wizard Island. Although Wizard Island looks small in Crater Lake, and this crater is just a small part of Wizard Island, notice how big the crater is compared to the trees growing on it. How big something looks can sometimes be misleading!

Image 11: Layers of lava from Crater Lake. We call these big, steep volcanoes of the Cascades and the Ring of Fire “stratovolcanoes”, and say that they are made of layers of lava flows and pyroclastic pieces thrown in eruptions. But how do we know what a big volcano is made of inside? Drilling holes is expensive and provides a narrow window. Geophysicists can learn some things, and geologists can watch volcanoes growing or look where streams have eroded volcanoes. But here at Crater Lake, the insides of the volcano are laid bare. This picture is a telephoto shot of a piece of the cliff above the lake, showing lava flows and pyroclastic layers stacked a couple of hundred feet high. These are strata, and this is a stratovolcano.

Image 12: Llao Rock. Not too long before the cataclysmic eruption, a small eruption threw white pumice that covered the floor of a valley running down from the peak. Then, a big lava flow from the peak filled the valley, giving us what is now known as Llao Rock. The white arrow is pointing to the pumice, with Llao Rock outlined in black. Notice the wonderful layering in the volcanic rocks below the pumice, beside the big red “L”. The next picture is the same view, without the labels.

Image 13: Another picture of Llao Rock.

Image 14: Main lava fold visible in a road cut. Here’s one of the lava flows that make up Mt. Mazama, from before the cataclysmic eruption. You can see this one in a road cut on the southeast side of the lake, where the Rim Drive crosses Dutton Ridge. The thick, viscous lava didn’t flow easily, and some parts flowed faster than others, making the interesting folds that you see in the rock. The arrow points to the main fold—let your eye follow the layers at the end of the arrow, and you’ll see that the layers bend around. Looking carefully, you may see wiggles within the wiggles in the layering. We will see later that folds such as this are also found in metamorphic rocks, but the minerals and other things are quite different.

Image 15: Water depths at Crater Lake. Everything above the water is gray-white, all below is garishly colored, with red the shallowest water, then orange, yellow, green, blue, and on to purple/violet in the deepest water (to 1949 feet deep). Minor volcanic activity after the main eruption produced features, including Wizard Island (marked with a “W”), which sticks above the water. A later eruption produced lava flows (the Central Platform, “C”) coming from a small volcanic dome (at the end of the arrow). Another volcanic peak in the crater is evident below the water (Merriam Cone, marked “M”). From the USGS at http://craterlake.wr.usgs.gov/bathy_images.html

Image 16: Dr. Alley's view from Crater Lake, looking along the Cascades Range of similarly explosive volcanoes.

Image 17: The history of eruptions of the main Cascades volcanoes of Washington, Oregon, and northern California over the last 4000 years, as compiled by the USGS. Each volcano icon indicates an eruption or closely spaced series of many eruptions. The record of written observations is especially good to the right of the red line on the far right, but use of tree-ring dating and other techniques makes all of this highly reliable.

Image 18: Lassen Peak, in Lassen Volcanic National Park of northern California. Lassen, shown here reflecting a beautiful sunset, erupted about a century ago. Lassen is quite similar to the other Cascades peaks, and remains capable of eruptions.

Image 19: Another view of Lassen Peak

Image 20: Yet another view of Lassen Peak

Image 21: Bumpass Hell at Lassen Volcanic National Park. This Yellowstone-like, hot-spring-and-sulfur site attests to the volcanic heritage of Lassen.

Image 22: Mt. Ruapehu, New Zealand. If this peak looks like those of the Cascades that haven't blown up to make a lake, you're getting it. Ruapehu is part of the Pacific Ring of Fire, and has the same basic origin as the Cacades.

Image 1: Map of Olympic National Park. Welcome to your Olympic National Park tour! Jutting out into the Pacific Ocean, just west of Seattle in Washington, is this extraordinarily picturesque park, where the Pacific's moisture-laden winds dump rain and snow more rapidly than anywhere else in the lower-48 states. It’s also home to some of the country's greatest old-growth forests (with trees towering up to 300 ft), crystalline streams, cascading waterfalls, rugged coastlines replete with basking sea lions, tidal pools filled with urchins and starfish, and high peaks that sport active glaciers. Known more for its biology than its geology, Olympic is also the home for the largest subspecies of elk in the country, the Roosevelt Elk, which the park exists to preserve (thanks to, you guessed it, the Roosevelt’s). Photos by Richard & Cindy Alley, map by USGS.

Image 2: Seagulls sitting on rock near Kalaloch at the SW edge of Olympic National Park. The Olympic Peninsula features beaches on three sides. Gulls and starfish grace the Pacific Coast near Kalaloch at the southwest edge of the national park, shown here.

Image 3: Fog along the coast of Olympic National Park. Cool waters offshore favor the formation of fog, which reduces evaporation from the trees. Combined with a general lack of hurricanes, tornadoes, and ice storms, this probably contributes to the ability of west-coast temperate-rain-forest trees to grow roughly twice as tall as their east-coast equivalents. Cutting of trees may increase wind flow and reduce fog, making it difficult for tall forests to re-establish themselves in some places, a problem raised with cutting of redwoods to the south.

Image 4: Coast of Olympic National Park with rocks jutting out of the water. The young, rocky coast is attacked by the waves of the Pacific, which exploit cracks and layers in the rocks to carve out interesting shapes.

Image 5: Sea Cave. A strong rock between cracks may be left standing in the waves as the rocks along the cracks are worn away. Continued attack by waves sometimes cuts through the remaining rock to make a sea cave, such as is seen here.

Image 6: Rainforest growth found inland at Olympic National Park.

Image 7: Epiphytes – plants growing on plants found inland. One hallmark of rainforests is the lush growth of epiphytes. This is a very difficult niche in which to live in climates with droughts, because lack of soil leads to lack of water-holding capacity; this difficulty is much smaller in a rainforest.

Image 8: Sol Duc Falls. The abundant rainfall feeds beautiful streams, some of which host important salmon runs. Sol Duc Falls is shown here.

Image 9: Marymere Falls, shown here, is almost ninety feet high. Don’t try to memorize these details--but take the pictures along if you’re going to visit so you know what to see. Instead, look for the big-picture geology, coming soon.

Image 10: The higher peaks in the park host glaciers. Peaks of similar elevation farther to the east do not have glaciers, however; the high snowfall, frequent cloudiness (blocking the sun) and cool summer temperatures cause glaciations to reach to low elevations at Olympic National Park. Melting of glaciers contributes to summertime stream flow, and the glaciers erode valleys more rapidly than rivers do.

Image 11: Mule deer in the forest. When your professor visited Olympic, he wasn't fortunate to see the famed Roosevelt Elk, but this mule deer was napping the day away, and looking remarkably inconspicuous.

Image 12: Two children playing on the dark sand beaches in Olympic. The beaches of Olympic typically have dark sand, eroded from the sea-floor rocks exposed along the coast. Many common dark minerals break down more rapidly than do light-colored minerals, so “old” beaches, such as those of the east coast where the sea has had a long time to interact with the sand, are dominated by light colors, but “new” beaches such as this are dark-colored. The young ladies enjoyed their visit!

Image 13: Layered rocks jutting out of the beach called Turbidites. The layered rocks in the center of the picture are a special type, called turbidites, shown and discussed in the next slide. The layers seen here were almost horizontal when they formed. But, the layers are now tipped up on edge, the result of deformation as the rocks were scraped off the conveyor-belt of the Pacific floor into the Olympic grocery check-out lane.

Image 14: Close up of the Turbidites, with a pocket knife at the bottom for scale. Sediment eroded from the Peninsula is moved by streams to the sea, and then taken farther out beneath the sea by waves. When an earthquake occurs (and sometimes for other reasons), a landslide or flow sometimes develops, carrying the sediment down into the offshore trench. Sand settles out of such a ”turbidity current” first, followed by smaller pieces (silt and clay). Just above the knife, the light-gray rock is sandstone, grading up into the darker siltstone and claystone. The next flow tore up the top of the clay, so there is mixing between the new, light-colored sand and the old, dark-colored silt and clay, followed by another sand layer and then another clay layer. These rocks were then scraped off the downgoing slab and brought to the beach for you to see.

Image 15: Pacific sunset in Olympic National Park

Image 1: Picture of ash in the sky from Mr. St. Helens. The great eruption of Mt. St. Helens in May of 1980 is ancient history for most of you, from before you were born. That is often the way with geological disasters – they are far enough apart that we forget… and the reminder is often unpleasant.

The eruption blasted out at over 300 miles per hour and over 600 degrees F, followed by even hotter blasts at more than 1300 degrees F. Deaths included 57 people, nearly 7000 large animals (deer, elk, bear), countless smaller creatures, and enough trees to supply lumber for 300,000 homes. Most eruptions build volcanoes, but a few really dramatic ones blow the top off—this one lowered the peak by more than 1300 feet.

Photos from USGS, US Forest Service, and Richard & Cindy Alley. We borrowed many captions from the USGS , too, but with changes for you.

Image 2: Mt. St. Helens, before 1980. Before 1980, Mt. St. Helens was the queen of the Cascades, snow-capped, symmetric, and beautiful. But, geologists knew that the peak had also been the most active of the Cascades over many centuries.

Image 3: Mt. St. Helens on April 10, 1980. In winter and spring of 1980, magma moved upwards beneath the volcano. (Magma is melted rock underground.) Small eruptions started, covering much of the snow with volcanic ash, as seen here. Mt. Adams, another Cascades peak, is visible behind and just to the left of Mt. St. Helens. This USGS picture was taken by Donald A. Swanson on April 10, 1980. No need to memorize numbers or dates here, but appreciate the power.

Image 4: Mt. St. Helens on April 27, 1980 shows a ‘bulge’ developing on the N. side. A “bulge” developed on the north side of Mount St. Helens as magma pushed up within the peak. Repeated measurement of the distance to the bulge (as shown here) found growth of up to five feet (1.5 meters) per day. By May 17, part of the volcano's north side had been pushed upwards and outwards over 450 feet (135 meters). You might not be surprised to learn that such a huge blister will tend to rupture and fall down. The view is from the northeast in this April 27, 1980 photo by Peter Lipman.

Image 5: Mt. St. Helens erupting on May 18, 1980. On May 18, 1980, at 8:32 a.m. Pacific Daylight Time, a magnitude 5.1 earthquake shook the peak, and the bulge and surrounding area slid away. The pressure release triggered a major eruption, as the magma bubbled and blew apart to create ash carried aloft by poison gas. The landslide from the bulge buried 24 square miles (62 square kilometers) of valley. Before going up as shown in these photos, the blast first went sideways, gravely damaging 250 square miles (650 square kilometers). Fifty-seven people were killed or are still missing. USGS photos by Austin Post (left) and Robert Krimmel (right).

Image 6: Plume of ash erupting from the mountain. For more than nine hours a vigorous plume of ash erupted, eventually reaching 12 to 15 miles (20-25 kilometers) above sea level. The plume was blown eastward at an average speed of 60 miles per hour (95 kilometers/hour), with ash reaching Idaho by noon. By early May 19, the devastating eruption was over. This May 18 USGS photo of the ash plume is by Donald A. Swanson.

Image 7: Map of the area affected by the May 18, 1980 eruption. Map of the area affected by the May 18, 1980 eruption. North is to the top, and the little scale bar at the bottom is five miles--this was a big deal. The blast knocked over trees across most of the yellow area. Much of the bulge ended up in the black-lined debris-avalanche deposits, while melted snow and ice plus water pushed out of lakes made the brown mudflow deposits. Thick layers of hot ash fell to make the red pyroclastic flow deposits.

Image 8: After the May 18, 1980 eruption, Mount St. Helens' elevation was over 1300 feet lower than before, and the volcano had a one-mile-wide, horseshoe-shaped crater. This photo by Tom Casadevall of the USGS was taken four months after the eruption, on September 16, 1980.

Image 9: Volcanic ash covering the landscape around the volcano. A helicopter is hovering near the ground. For weeks, volcanic ash covered the landscape around the volcano and for several hundred miles downwind to the east. Noticeable ash fell in eleven states. The total volume of ash (before its compaction by rainfall) was approximately 0.26 cubic mile (1.01 cubic kilometers), or, enough ash to cover a football field to a depth of 150 miles (240 kilometers). In this USGS photograph by Lyn Topinka from August 22, 1980, three months after the eruption, a helicopter stirs up ash while trying to land in the devastated area.

Image 10: Mount St. Helens on May 17, 1980, one day before the devastating eruption. The view is from Johnston's Ridge, six miles (10 kilometers) northwest of the volcano. USGS photo by Harry Glicken. The next photo is from nearly the same place, four months later.

Image 11: Mount St. Helens soon after the May 18, 1980 eruption, as viewed from a similar location as the previous photo, at Johnston's Ridge. USGS photo by Harry Glicken on Sept. 10, 1980

Image 12: Mt. St. Helens before the explosion - top of the mountain still intact. The mountain after the explosion showing the resulting crater. The blast lowered the peak by more than 1300 feet. These USGS (bottom) and US Forest Service (top) pictures are not exactly from the same place, but they’re close.

Image 13: Left image is a stand of trees. Second image is taken from the same place but shows no trees, piles of ash and the mountain with a crater after the eruption. Difficult as it may be to believe, these photos are from the same place, looking in the same direction! The trees on the left were obscuring a view of the beautiful snow-capped peak, which has been blown away, along with the trees, in the photo on the right. US Forest Service photos: http://www.fs.fed.us/gpnf/mshnvm/digital-gallery/25yearsofrecoverybefore...

Image 14: Knocked over coniferous trees. They were knocked over by the eruption. These were towering coniferous trees before the eruption, but now are knocked over like matchsticks. Trees in the upper left weren’t knocked over, but were burned to death. USGS photo on Aug. 22, 1980 by Lyn Topinka.

Image 15: A destroyed logging camp including huge pile of logs and multiple full sized logging trucks. Destruction by a flood created by a landslide. The eruption melted glaciers, and the landslide pushed water out of Spirit Lake, together making a huge flood that destroyed many things including this logging camp on the South Fork Toutle River. Those yellow things in the upper-right are full-sized logging trucks destroyed by the flood (the arrow points at one). USGS photo taken on May 19, 1980, by Phil Carpenter.

Image 16: A car buried in lava approximately 10 miles from Mount St. Helens. Reid Blackburn's car, located approximately 10 miles from Mount St. Helens. Reid was a photographer for National Geographic as well as the Vancouver Columbian newspaper. Unfortunately, Reid did not make it out alive. A scholarship is now given by The National Press Photographers Association in Reid Blackburn’s honor. USGS Photograph taken on May 31, 1980, by Dan Dzurisin.

Image 17: Mudflow created by the melting of the glaciers. As noted for previous slides, the Mt. St. Helens eruption melted the glaciers on the peak, and also dumped immense amounts of rock material into Spirit Lake. The water displaced from the lake, and melted from the glaciers, mixed with volcanic ash and mud to make a giant mudflow that raced down the Toutle and Cowlitz Rivers, causing great destruction. This image and the next two, by Dr. Alley and his wife Cindy, show the situation miles downstream.

Image 18: Damage caused by the mudflow that raced down the Toutle and Cowlitz Rivers include a tree broken off a few feet from the ground. Another view of the damage caused by the immense mudflow that raced down the Toutle and Cowlitz Rivers. The broken trees attest to the power of the mud-filled flood.

Image 19: Another view of the mudflow. In this one, a much younger Dr. Alley (this was 1980, remember) is visible in the lower-left of the picture, dwarfed by the high-mud mark on the tree. The tourists on the right are looking at the foundation of what had been a house.

Image 20: Many logs scattered across the landscape 10 years after the eruption. Some bark remains on the trees. In this picture taken about 10 years after the eruption, trees knocked over by the blast are scattered across the landscape. Some bark remains on these; they were slightly shielded by a hill and were not as strongly blasted as some.

Image 21: 10 years after the eruption students walking through a stand of dead trees that were largely shielded from the blast. In this image taken about 10 years after the eruption, members of a geological field trip attended by Dr. Alley take a walk through some standing former trees that were greatly shielded from the blast, which came over the hill from diagonally behind the camera position. Notice the green vegetation flourishing on the far hillside; salmonberry, fireweed and others moved back in quickly.

Image 22: Part of the mountain with no dead trees. Many trees were salvage-logged. This third picture of Mt. St. Helens a decade after the blast shows deep gullying in a region without dead trees. Many dead trees were salvage-logged because of the value of the lumber, but such actions do have consequences for the landscape--without dead trees to dam the flow, rains feed little streams that rapidly wash away the loose soil, making it harder for new plants to grow.

Image 23: Two women collecting vials of ash. Mt. St. Helens was a media star. T-shirts, coffee mugs, and vials of ash were among souvenirs sold to enthusiastic tourists. These ladies realized that people standing ankle-deep in Mt. St. Helens ash were spending $5 for a little vial of Mt. St. Helens ash, and so the ladies decided to gather some of their own. The colorful garb is possibly reflective of the era.

Image 24: Some additional links about the Mt. St. Helens story.

Image 1: Mauna Loa mountain. Mauna Loa (13,679 feet above sea level); Hawaii’s peaks start from 18,000 to 19,000 feet below sea level, making them the tallest mountains on Earth. Mauna Kea (peak at 13,796 feet above sea level, is out of picture to left)

Image 2: Mauna Loa on the left of the picture, Mt. Lassen in the middle and Mauna Kea is off the picture to the right. The hot-spot volcanoes of Hawaii are vigorous enough to kill the unwary, but are much more approachable during eruption than are the steep, explosive stratovolcanoes of the Ring of Fire and elsewhere, such as Mt. Lassen. This slide show gives you an up-close-and-personal visit to this “nicer” Hawaiian lava.

Image 3: Chain of Craters Road, Hawaii Volcanoes National Park. Older flows, now vegetated, are green. Darker flows are either gray pahoehoe (pronounced pa ho ee ho ee; ropy lava from hotter flows) or black aa (pronounced ah ah; broken-up lava from cooler-but-still-really-hot flows).

Image 4: Close up of lava Pahoehoe (sloid) and aa (looks crumbly)

Image 5: View of ocean with steam rising out of the water. The steam shows where lava is entering ocean.

Image 6: Janet and Karen Alley, on what used to be the continuation of Chain of Craters Road, now lost beneath lava flows from the East Rift of Kilauea volcano. The hike to the active lava from here is just enough adventure to be exciting.

Image 7: Chain of Craters Road was lost, along with almost 200 houses and other buildings, when engulfed by lava.

Image 8: Two pictures. Left, Karen and Cindy Alley along the former Chain of Craters Road. Right, a ‘no parking’ sign buried in the lava. The ropy pahoehoe lava is a strange surface for hiking, but can be traversed safely by careful hikers.

Image 9: The “trail” to the active lava showing Pahoehoe. Hot lava is still flowing down the hill in the far upper right of this picture, as you will see in later photos.

Image 10: Lava flows out of tubes in the rock into the sea. You can see the red lava flowing into the sea and the steam rising out of the ocean where the lava enters. We didn’t get down to measure, but the higher “lava fall” probably is more than 30 feet tall.

Image 11: Closer view of lava flowing into the sea from a large rock outcropping.

Image 12: Mile-wide view of lava flowing from the East Rift of Kilauea. On a sunny day, the hillside looks black, but as darkness falls, the glow of the molten lava shows.

Image 13: Slightly closer view of glowing lava

Image 14: Glowing lava.

Image 15: Glowing lava.

Image 16: Glowing lava.

Image 17: At roughly 2000 degrees F, the lava glows in the night. The lava surface chills rapidly in the air, forming a glassy shell, which then crackles and breaks as the sizzling lava moves beneath. You can sometimes watch a new crack appear as you hear the breaking glass. The red arrow points to a tongue of lava that will harden to look like the pahoehoe tongues shown in the next slide.

Image 18: Hardened lava tongues (pahoehoe). Four pictures showing different flow patterns.

Image 19: “Lava Falls”

Image 20: Karen and Janet Alley with hot lava flowing in the background.

Hawaii Volcanoes National Park below the east rift Kilauea, this is the lava headed for the sea. It is 2,000 degrees Fahrenheit or so. This is the innards of the Earth turning inside out, building new land that we're sitting on right now. And this is way cool because it's so hot. You just can't imagine what this is like.

Below us, it is fountaining into the sea and jetting up great bursts of steam. New land being born, this is geology in action, this is the real thing. The breeze blowing over us is a little bit sulfurous, it's a little bit warm-- we're going to get out of here fairly quickly. But we're having a lot of fun, I wish you could be here with us. This is an amazing, amazing sight.

We're in the rain forest on the side of Kilauea, and behind me is a lava tube. A great lava flow came through here in the past, the top freezes first, the sides freeze, the inside-- glowing hot lava-- comes flowing out, and it drains. And you go inside and there'll be stalactites that were little drips that were falling off the ceiling when they froze. And this is the way a lot of the lava gets to the coast. It's that the top will freeze, and the insides will go squirting on out to the sea. And so it's a really interesting place, a very different kind of cave.

The Southwest Rift of Kilauea on Hawaii. There's a vast and fascinating volcanic history sitting here. Layers of rock that were made of pieces that were tossed through the air. Glass that froze in the air as it was thrown as molten little bits from the volcano, and then other sorts of layers.

Then there's been a great cracking here, probably an inflation from underneath as melted rock is moving underneath that sort of bubbles things up and breaks it. Then an eruption happened at some point, and there was actually sort of a waterfall of melted rock, and it was flowing into the crack. And we can see behind me all these places where this stuff has flown down into the crack. Just a wonderful record of the excitement of the geology of this place.

Welcome to G-Sci 10, Geology of the National Parks. My name is Sridhar Anandakrishnan, and I'll be your guide through some of the beautiful parts of the planet. Last time, we talked a little bit about Death Valley, about the spreading, about how Death Valley is going apart. This time, we're going to go slightly further north up along that same coast, go up to Crater Lake National Park, an absolutely gorgeous place, head on up the coast a little bit further, up to Mount St. Helens, go over and take a look at the Olympic National Park, and really understand why these volcanoes, Crater Lake, Mount St. Helens, why those two volcanoes are where they are.

And we're going to actually spread our picture out a little bit beyond that and look at why there are volcanoes in other parts of the world. All right? So, we'll start our talk about making mountains and making volcanoes, why they are where they are, and what they can tell us about the insides of the Earth.

Here is a screenshot that I took on my computer of a program called Google Earth. And I encourage all of you to go out there and download it. It's free. It runs on Macs. It runs on PCs. And it's a wonderful program for just looking at this planet. You can wander around to different parts. You can zoom in, zoom out. And I really encourage you to download it and to use it. It will really give you a good sense of how big this planet is that we live on.

I've circled in those sort of blue squiggly lines. They're not the best pictures in the world. But you can see that there are some places on the West Coast of the US. That's California on the bottom, Oregon in the middle, Washington state on top. And the circles represent the areas that we're going to go to, Crater Lake National Park on the bottom, Mount St. Helens in the middle. And then right up on the top, right up jammed up against the Pacific Coast is the Olympic National Park. So, as I said, go get yourself Google Earth, and you'll be able to zoom in to these spots yourself.

The other thing that you can do is you can go to your website, go onto Angel, and you'll be able to download what we call V-Trips. They're virtual field trips to these places and to other places. And they're just PowerPoint presentations or web page presentations that just have beautiful pictures of these places.

Let me take you to a couple of these places right now. We'll go take a look at Crater Lake. We'll take a look at Mount St. Helens. And then we'll come back and start the lecture proper.

I like to do this to motivate you, to say, man, these are beautiful places. I want to go see those, and I want to understand them. I want to know why there is a volcano there. So, let's hop out of this program real quick and go over and take a look at Crater Lake National Park. As I said, this is on Angel. You can see all this for yourself. I'm going to whip through it quickly. But you can find it on there.

So, this is just a shot looking down from the rim of Crater Lake through all these lovely trees, down onto that blue, blue, blue water. Crater Lake is this volcano way up high on the top of this mountain, up at 6,000 feet. And that water is as clear and as beautiful as anything.

It's just all snow melt that comes down into the crater. There are very few streams that bring in sediments into it, and no industry, no pollution, no agriculture. And so, that water is as blue and as beautiful as they get on this planet.

Here's a picture on the sides. Even though this was late in the summer, you get lots and lots of snowfall. As you can see, our friend there is wearing his T-shirt as he slides down the side of Crater Lake in the snow. Even though it's in the middle of summer, there's still lots of snow.

So, you pull back. Here's a picture of that crater. The bottom of it there is water.

You can see the far side of the crater. We're standing on the near rim. It's an almost circular feature with this little island called Wizard Island rising up in the middle of it. And then there's the far rim that you can see. And if I could pan, if this camera could pan around, you would see that rim continuing around all the way until it came back to where you are.

Absolutely gorgeous place way up high in the mountains, as I said, 6,000 feet. It's a spectacular place to go and see the world. Here's just another picture looking out over that blue, blue, beautiful water.

Here is a very garishly colored picture of the depth of the water. The purples are where the water is very, very deep. And the grey-white parts are the rim.

So, you can see that near-circular crater with Wizard Lake off on the left side there, that little dome that's starting to build. And then over in the top, there's another little dome starting to build. So, this has something to do with volcanoes. So, let's find out more.

And this is just a picture from Crater Lake looking along the Cascade ranges. And you can see in the distance one, two, three, four volcanoes, each of those perfect little cones marching up the coastline. Why? Why are there volcanoes there? Why aren't there any volcanoes here in central Pennsylvania? Why do they have four of them over there in Oregon in Washington?

That seems awfully unfair. They get all the volcanoes, and we don't get any. Let's find out why they've got them.

Here is a map of the California, Oregon, Washington coast. Each of those little triangles is a volcano. Lassen, Shasta, Medicine Lake, Crater Lake, that's the one that we're going to be talking about. And on the right, you have a little graphic depicting when they most recently have erupted.

As you probably might know, Mount St. Helens erupted in 1980. And that's marked on the right over there. Mount St. Helens has been very, very active, erupting many, many times over the course of the last 4,000 years.

And it's actually getting even more active even as we speak. The dome is starting to build today. And it might be due for an eruption in the next few years to tens of years.

Here's just a beautiful peek of Lassen Peak. It's not Crater Lake, but it's another volcanic peak. Whenever you see one of these nice triangular mountains, you should say to yourself, volcano. It's just a beautiful spot. And here's another view of Lassen Peak, looking at it from a slightly different place.

All right, here is a picture of a little car, a little 1980 Chevette going up the road to Lassen Peak. You can see all the snow there, even though it was the middle of August. I encourage you to go on to the website and just take this V-Trip. And it will encourage you to go there.

This, we went a little bit further afield. Those little white dots are sheep. When you think sheep, you should think New Zealand. And this is indeed a shot of Mount Ruapehu in New Zealand, another volcano on the other side of the Pacific Ocean.

All right, enough wandering around the world. Let's learn why those volcanoes are where they are. So, plate tectonics two, making mountains and volcanoes.

Here is a map of the world. And what we're looking at here is North America, and the US in the middle. The Pacific Ocean is on the left. And each of those little red dots is a source of volcanic activity.

And you should be able to see that those dots circle the Pacific Ocean. Sure, there's a few volcanoes in the Atlantic Ocean. Iceland in particular has quite a few. There's a few volcanoes that occur in Africa and Arabia. But most of them are around the circum Pacific, Australia, New Zealand, heading up the coast towards Japan, over to Alaska, and then down the US and Canadian coast, and then down through Central and South America.

Why? Why is it that these volcanoes are where they are? So, here's a graphic showing where all of these volcanoes are. And because all these volcanoes stretch right around the Pacific, we call it the Ring of Fire. It's a nice, evocative name.

There's another thing that happens that goes along with these volcanoes. There was a curious thing that people noticed is that if you were to take the water out of the Pacific, in the same place where you have all these volcanoes, you'd see these really deep ocean trenches. The ocean would go down 10,000, 20,000, 30,000, in some places even more, 40,000 feet. It's an extraordinary thing. It goes way, way down, as deep down into the ocean as mountains are high.

Why? Why are there trenches that go along with volcanoes, but no trenches anywhere else? That's the second thing people notice.

The third was that you get these big earthquakes in the same place. Volcanoes, deep trenches, big earthquakes, how are they all related? How do they all come together? And then the next thing is we're going to take a look at one of the great songs of all time.

[MUSIC PLAYING - "RING OF FIRE" BY JOHNNY CASH]

By the great Johnny Cash.

[MUSIC PLAYING - "RING OF FIRE" BY JOHNNY CASH]

So, I hope you enjoyed that. And you should be grateful that I did not try to sing that for you.

So, the overview that we're going to-- what we're going to try and go over in this class is ocean materials made of spreading ridges. We saw that last time, Death Valley, mid-ocean ridges. So, somehow ocean materials made at these mid-ocean spreading ridges, material comes up, freezes on, spreads off to the side, if you remember that from last time.

It collides with continental crust. So, all this material is being made in the oceans. It runs into the continent, and something's got to happen.

And what happens is one of two things. Either you get subduction, where that continental crust goes over, the oceanic crust goes under the continental crust. This material gets subducted.

Or you get accretion, where the continental crust and the oceanic crust run into each other, and they actually glom together to create new land. All right? So, those are the two things that can happen. Some of the side benefits, if you will, of that collision of either the subduction or the accretion is the creation of volcanoes and mountains and these deep oceanic trenches.

The third thing that we'll talk about this time is hot spots. And I'll get to that in a minute. Let's talk about subduction and accretion first.

To review, this you should remember from last time, the mantle is a deep part of the Earth, way down deep. You have those hot, relatively soft rocks that make up the asthenosphere. The upper part of the mantle and this crust are this rigid, more brittle mass of rocks called a lithosphere.

And the lithosphere, this upper part, is broken into a number of smaller plates. And these plates float over on top of the asthenosphere, and they will occasionally run into each other. Where they run into each other, that's where these mountains are made.

The convection cells, they bring up this mantle material. It freezes at these mid-ocean ridges. And then the ridges push material off to the side. So, the ocean is continually moving its crustal material off to the side.

That stuff has got to go somewhere. We don't live on an infinite plane. We live on this nice, round planet. So, if you push stuff off to the side, eventually it's got to hit something.

And this is my depiction of what the Earth looks like. If I took the Earth and took a great big hatchet and sliced through it, what I would find is I have the outer core, and then I have-- or the outer lithosphere. And then right in the middle of it, we would have the inner core, which was solid, the outer core that was liquid. And then right up at the surface, this is where we live. There's trees and houses and so on and so forth.

Right underneath that, we have the crust, which is part of the lithosphere. Underneath that, we have the mantle, which is this hot, soft rocks. And then right in the middle, you have the core, which is either solid right in the middle or liquid outside of it. So, this is a little bit a review of if I could take this hatchet and slice through the Earth and look at it from this side, this is what we think we would see.

We don't really know. Nobody's ever drilled into the Earth much deeper than a few miles, three or four miles. So, all of this is inferred from other evidence. But we think this is a pretty good picture of it. It's probably grossly simplified, but this is what we think the world looks like.

I'm going to redraw that picture here. Here we have the Earth again, sliced through. The upper part of it is called the lithosphere. Underneath that, you have the asthenosphere.

And that lithosphere is broken up into a number of little plates. I've just labeled them plate one, plate two, plate three, and so on. So, we've taken a cross-section through it. In your head, you have to imagine that this thing is a globe or a sphere, and those plates are all riding on top of the surface of that globe or sphere.

From the interior of the Earth, because of the heat inside of the Earth and the heating of the rocks that makes them low-density, that material rises up through the asthenosphere until it gets to the surface of the Earth, where it cools off and then sinks back down in these convection cells. All right? So, this should all be review if you remember it from last time.

But what goes on as a consequence of these mantle convection cells is that these plates, plate three there, for example, will slide off in one direction. And plate two will slide off in the other direction. And when plate two slides off, what happens to it? It runs into plate one. All right? You can see that plate one is in its way.

Plate two runs into plate one. Something's gotta happen there. And at that collision spot, that's where either subduction or accretion takes place.

So let's talk a little bit about this oceanic crust. We have these mantle convection cells, materials coming up from deep inside the Earth. It's deposited underneath the oceans. And it cools off, gets more dense, gets shoved off to the side. And this mantle material is basically basaltic.

Basalt is a mineral. It's heavy in silica, iron and magnesium. It's dark in color. It's relatively dense compared to continental crustal material.

Density is a key notion that I've talked about a little bit last time. I'm going to talk about it this time. You'll keep running into it over and over again during this class.

When something is dense, for its size, it's relatively heavy. So, if I have a bottle of water here, I can fill it up with water. And it will have a certain weight to it. And if I divide the weight by the volume of this bottle, I have its density.

I could pour this water out, fill it with olive oil, extra virgin olive oil, please, always. And it would weigh different. It wouldn't weigh the same as the water in here because oil has a different density than water does. You know this stuff, but it's worth emphasizing it anyway.

Ocean floor is mostly basaltic, formed at the ridges. Because we know the Earth isn't getting bigger, as this material comes up, it isn't as if there's this material that's coming from somewhere else. It's all being recycled. It comes up, and then it goes back down. The Earth stays the same size.

What is subduction? That's a word that you ought to write down, maybe look it up in a dictionary. To subduct means to go under. "Sub," under, "duct," I'm not quite sure where that "duct" comes from. I'm not an etymologist. But subduction means for oceanic crust, as it gets denser, as it cools down, moves away from the ridge, gets denser, it starts to sink back down into the mantle.

Think of a lava lamp. If you go onto the Angel website, there's a little movie there, it's a little bit goofy, but it's fun, in which I have a lava lamp. And I show you how that material in the lava lamp rises up as it heats up, and then it goes to the top, and then it sinks back down again. The reason it's sinking down again it's getting cool, meaning it's getting dense.

All right? So, that's what's going on there. And this is to remind you, this is the goofy movie that you will find on the website of the lava lamp.

As this cooling oceanic crust moves to the side, it'll run into a continent. It might run into a continent. It sometimes does, sometimes doesn't. But in the case of the western US, it does run into the continent. It runs into California, Oregon, and Washington.

So, this cooling Pacific oceanic crust is heading eastwards. And there, bang, in its way is California, Oregon, and Washington. They're sitting there in the way, and this oceanic crust runs into it.

If it is cold enough, if it is dense enough, if it is so dense that it wants to sink down, then it does sink down and goes underneath the oceanic crust, which is low density. And it bobs up high. The continental crust is low-density and bobs up high, and so, the oceanic crust, which is higher density, will go underneath it.

If it is still relatively warm, if it hasn't had time to cool down, only recently it was formed, and it runs into the continent, it's still buoyant. It still rides high up there, doesn't want to sink down. Then when the oceanic crust and the continental crust meet, then the oceanic crust doesn't sink down. It just stays up high, and you get what's called accretion. And we'll talk about that.

As this ocean crust sinks down, and I'll draw a picture of it for you in a second. But let me get the words out, and then we'll go back and look at this picture. As this ocean crust sinks down, it carries seawater and sediment with it as it goes underneath the continental crust.

As it sinks down, it starts to heat up again. Remember, the Earth is hot inside. What's the reason for it? You know it. We talked about it last time.

The reason it's hot is because of radioactive decay inside the planet. Inside the Earth, there's all of these radioactive atoms that are slowly splitting apart, giving up a little bit of heat. And so, the inside of this planet is warm.

So, as this oceanic crust sinks down, carrying its water, carrying all these sediments as it sinks down, and starts to heat up, this added water, these added sediments help that crust to melt. If all we had was that oceanic crust, you could heat it up. And you'd have to heat it way, way up before it would melt.

But because of all these impurities that have been added, the water and the sediment, that stuff melts really quickly. All right? Most things melt better in the presence of impurities. And this is an example of one of those.

So, let's take a look at a picture of that whole thing. Here's my cross-section through the ocean. I've drawn a mid-ocean ridge.

We have material coming up from underneath. It's being deposited at this mid-ocean ridge. That's that little peak over there.

And as it cools, it gets shoved off to the right. So we have material coming up, and material gets deposited, cools, and gets shoved off to the right. There's more material going off to the left, but lets only worry about the stuff that's going off to the right.

Here's my picture of the ocean. And there's a little boat. And there's a little fishy. So now you know that's the ocean. It's got a fishy in it. And the sea floor there is the black line.

And that material is physically moving off to the right. If I could go there and put a mark in it, I would come back a year later, and that mark would have moved a little tiny bit to the right, maybe half an inch, maybe a tenth of an inch. But it would have moved a little bit.

Now over here on the right, in the green, I've drawn the continent. So this is the coast of California. This is the coast of Oregon.

What's going to happen when that black line runs into that green line? The continent is low-density. The ocean is basalt. It's high-density.

When the two run into each other in this case, because the mid-ocean ridge is way far away, the basalt has had a lot of time to cool down. It's high-density. It wants to sink back down, and it will. It will subduct down underneath the continental crust.

And in the process of subducting-- I'm sorry, I had to draw a new picture here because my last one got so ugly. In the process of subducting, it will carry down material with it. That junction there that I've circled in yellow has water, and it has ocean sediments with it.

So two things happen at that junction. The first is that the continental crust and the oceanic crust get deformed to form these trenches. So without this motion of the oceanic crust going underneath the continental crust, we wouldn't have that little dip that you see, where the black and the green meet. That part would have just gone flat across.

But because of the motion, you can imagine in your head. This, my left hand over here that's wiggling, is the ocean crust. My right hand over here is the continental crust. And as I move my hand down, down, down, it drags and makes this little triangular indentation that is a mid-ocean ridge.

So, that's why we have trenches where we have subduction zones. That's what that is. This is a deep trench in the ocean floor. If that trench is near a continent, near water, near freshwater, rivers, sediment, that trench will fill up quickly with sediments because the continent will just dump all of this material into it. But if that trench is way out in the middle of the ocean, it won't fill up with sediments, and it'll be really, really deep.

Let's draw another picture of this because my pictures tend to get very messy. So, I just erase them and redraw them. Once again, we have this subducting ocean crust going under a continent. At that junction there, you'll have a trench.

But in addition to that, you'll have sediments and water that are carried down with that subducting trench. As that material goes down, it helps that basalt to melt. As it heats up, remember, as it's going down, down, down, it is getting hotter and hotter.

Eventually, it gets so hot that it melts. And when things melt, they get low in density. When things are low in density, they rise.

And that's what those little red circles are. It's molten material that's rising up through the continental crust because now you've melted this combination of basaltic rock, water, and sediment. You've heated it up. It's melted.

It's got nowhere to go because it's low-density, nowhere to go but straight up. And that's what it does. When it gets to the top, it builds a mountain. So, when this material gets the top, it builds a volcano.

That volcano there is Mount St. Helens. That volcano there is Crater Lake. That volcano there is Mount Ruapehu in New Zealand. It's Mount Fuji in Japan. It's Mount Pinatubo in the Philippines.

So, when you get subduction, you get these deep trenches being formed. You get this melt down there that rises up somewhere back from the coast, not right at the coast. But some distance back from the coast, that melt gets hot enough that it can rise up. And when it rises up, it forms a volcano. So, that's why these things go together, subduction, trenches, volcanoes, lines of volcanoes.

You can imagine in 3D that a coastline, that green line, is a cross-section through the west coast of California. But that's just one spot on the west coast of California. If I were to go a little bit down into the screen there, I'd be up in Oregon or up in Washington, and there would be another volcano and another one and another one. And that's why there's this line of volcanoes all up the coast of California, Oregon, and Washington.

And over time, these volcanoes get bigger and bigger because there's more and more material that's continually coming up and being deposited. Now they don't keep getting bigger forever because there's erosion that will continue to make them smaller. And this process continues to make them bigger. And that fight between building mountains and tearing down mountains is what geology is all about. You'll learn all about erosion later on.

So, here we have volcanic mountains at subduction zones. So, I hope this gives you a picture of it. And I know these drawings are very crude. But they're very, very helpful for me. If you want more information, you gotta read the online textbook.

This is Mount St. Helens. This is Lassen Peak. This is Crater Lake. This is Fuji. This is Mount Ruapehu. This is all of these subduction zone volcanoes around the Ring of Fire.

OK. I'm going to draw that 3-D picture for you. I'm not a good artist. But there's some folks at the US Geological Survey that are good artists. And they have shown this process where one plate is subducting under another plate. And now you can see it in 3D.

It isn't just a single spot the way I drew it on my rather crude picture. But it heads all the way up along that suture, that contact. Where those two plates run together, the one goes under, and you just get this series of volcanoes all up and down that contact. And you get these big old trenches along there.

This type of volcanic rock, the rock that comes up at a subduction zone and forms those volcanoes, is called andesitic. it's an andesite. It's named after the Andes Mountains. There's a very noticeable mixture of basalt and these sediments that forms this andesitic rock.

Now remember at the beginning, I said there were three things that go along with subduction zones. One was volcanoes. The second was these deep trenches. The third was earthquakes.

And the reason for the earthquakes is occasionally that that downgoing slab, that downgoing oceanic material, as it's sliding down underneath the continental crust, will get stuck and get stuck. And the downgoing slab is pushing, pushing. And then suddenly, it breaks loose. And you get these huge earthquakes because of the enormous forces.

And unfortunately, you get very tragic consequences. Because one of the things that happens when these earthquakes occur is it they displace a great deal of water in the oceans. And when those water waves hit land, if there's people that are standing there, they can and unfortunately are killed by the hundreds, the thousands, and in the case of that dreadful, dreadful tsunami in December of 2004 in Indonesia, killed by the hundreds of thousands. So, these are very, very dangerous things indeed.

Trenches, we already talked about trenches. When this slab is subducting, it deforms the overriding plate, and then we get these long, linear trenches. If these trenches are near land, they get filled up with sediment because there's lots and lots of junk, if you will, that's being washed off of the coast of Oregon, the coast of Washington, the coast of California.

All those rivers are carrying lots and lots of sediments. And they'll fill up those trenches quickly. But if they're out in the middle of the ocean, then they won't be filled up quite so quickly.

Those trenches in the middle of the ocean are some of the deepest places on the planet. The Marianas Trench is the deepest spot on the planet. It's as deep as Mount Everest is high. So, Mount Everest you know is 28,000 feet high. And the Marianas Trench is actually a little bit deeper than that below the sea floor.

The trenches near continents, because of all this mud that gets washed out, tends to fill up more quickly. Marianas Trench is here, just off of the Philippines. And as I said, it's one of the deepest places on the planet.

There's a little bit of a side note here. I think I remember I mentioned last time this little symbol up in the corner there. That's my universal symbol that the choo-choo train is going off the tracks.

So, whenever you see that, you know that you can not pay attention for a minute. You can stretch. But the first, the best ever science fiction, is Jules Verne's 20,000 Leagues Under the Sea. That was a novel by Jules Verne. 20,000 leagues, that's about 60,000 miles. Jules Verne was referring to the length of the voyage that the submarine, the Nautilus made with Captain Nemo at the helm. It's a great, great read. I strongly urge you to rush off and find it.

OK. So, here is once again our picture of the West Coast of the US. You have in the blue is the Pacific Ocean and the oceanic crust associated with it. It's moving off to the east. And then in the pink, you have the continental crust. And it's staying relatively stationary. And the two will collide. Where you have that collision, you get subduction. Or further up, you get accretion. This is important to remember. Continents are the lowest density, quote, "light." I put that in quotes because it's not the weight that matters, it's the weight of a particular given volume of the material. All right?

So, I can get a pound of feathers, or I can get a pound of gold. But a pound of feathers would fill this room, and a pound of gold would fit in the palm of my hand. So, it's not the total weight of something that matters. It's the weight per unit volume. Sea floor is the denser of the two. The basalt is a more dense material. Mantle is denser still. So, I gotta always remember, it's density that we care about. The core is the densest of all. It's mostly iron.

Accretion occurs when the sea floor runs into the continent, but it's still relatively low in density. It hasn't gotten so dense that it wants to sink down. It's quote, "light." It's low-density. And so, when it runs into the continent, it doesn't sink down. It doesn't give way. It actually smears onto, it's scraped off. Some of this sediment smears onto the continent. Next time, or a little ways down the road, we'll talk about something called abduction, when two continents collide, and man, neither of them really want to give way. And you get huge mountains built that way.

Here, the oceanic crust, it has some slightly higher density than the continental crust. And so, it sort of wants to go down. But it's still buoyant, and so, it kind of scrapes along underneath, just under the bottom of the continental crust. And then all of this sediment gets scraped off and spackled onto the side of the continent. So, it makes this messy, messy story that's really hard to interpret. But that's what geology is.

As a consequence of all of this, the rocks in the bottom of the ocean are never really that old. They're produced, and then they get subducted somewhere else far way. And because they're moving to the side, sure, they're moving slowly. They're only moving this much every year. And so, it takes them a long time to get any distance at all. But we got lots of time. We'll find out later on in this class that the Earth is really, really old. We've had lots and lots of time to do everything we want to do. And so, the ocean, it's produced over here. It's destroyed over there. And it might take 100 million years to do it. But eventually, all of the ocean floor will be destroyed and then recreated somewhere else.

Continents are very different. Continents are very light. They bob up. They stay up there. They never get recycled. Continents can be as old as four billion years. And we'll talk about how we know the age of rocks.

And here is a nice picture that, again, from the USGS, showing how as the Pacific plate goes down underneath the North American plate, some of the material gets scraped off and smeared onto the side. And the Olympic Mountains are produced during that scraping off process.

There's a V-Trip for the Olympics that you can go to and look at on the website. It's a beautiful spot, It rains a lot, as you probably know. It's near Seattle. And Seattle, as you probably know, is a rainy spot. So, it rains a lot over there. But as a consequence, you get lots of beautiful wildlife, lots of beautiful greenery, huge trees. And then you've got these mountains in the background. So, I urge you to go and run this V-Trip and have a look at it.

It's a beautiful thing. As I said before, when seafloor runs into these continents, the sediments get scraped off. And the Olympic National Park, where this V-Trip was taken, is a good example of that.

So, to review, the mantle is hot. The mantle is deep down inside the Earth. It's hot. You make these convection cells. Right up at the top, the upper part of the Earth called the crust and the upper part of the mantle together make up the lithosphere that's broken up into a few, about eight, major plates and one or two or a few smaller ones. And these plates float around on top of the asthenosphere. When plates meet, one of three things can happen. Either the plates run into each other, either the plates are moving away from each other, or the plates are just sliding past each other. And there's different geology that happens at each of those intersections.

What we've been talking about today is where plates run into each other. When they run into each other, if it's an ocean plate running into a continental plate, then you get subduction or accretion. And in other cases, you have other behavior. Heat from radioactive decay drives the whole thing. Thank you.

Welcome to Geosc 10, geologies and national parks. My name is Sridhar Anandakrishnan, and I'll be your guide through volcanoes this time.

This is the second part of building mountains using subduction zone processes. Last time, we talked about what a subduction zone is, what happens when you have oceanic crust running into continental crust— you produce these volcanoes, and trenches, and earthquakes. This time we're going to go into a little bit more detail about those volcanoes. In addition, we're going to talk about a special thing called hot spots— Hawaii's a hot spot. We'll find out what a hot spot is and what's special about them.

All right. So, let's begin with a little bit of a tour of the Pacific Northwest. We saw some beautiful photographs last time of Crater Lake National Park and some of the extraordinary pictures of the destruction that went along with Mount St. Helens. This time, we'll go to a little bit more of a bucolic scene, sea shore, of Olympic National Park. Not quite so violent, but still telling us a lot about the processes that are going on.

What you're seeing on the screen here is a map of the West coast of the US— that's the State of Washington there in the middle. On the left side is Vancouver Island. Vancouver is in British Columbia, which is in Canada. If we zoom in a little bit into the State of Washington, we come close to Seattle where Boeing and Microsoft famously are headquartered. Starbucks is headquartered. I'm sure you all had your triple latte frappuccino this morning. Well, it all started in Seattle.

To the west of Seattle, you have the Olympic Peninsula. That's this big sort of rectangular-shaped mass of rocks, and mountains, and glaciers that is heavily forested, very wet, and just a beautiful place to go hiking or just simply driving around. It's also very, very heavily logged. That's the other thing to the Pacific Northwest is famous for is their logging industry —timber, paper, all those sorts of things are enormously lucrative for the Pacific Northwest. And so, some of these places that look very beautiful from the road, you go walking back a little ways, and then some timber company's clear-cut the place. So, it's a trade-off.

The Olympic Peninsula is an accretionary terrane. The sea floor has scraped off onto the North American coast. As it was scraped off and plastered against the North American coast, it created these mountains, and we're going to take a look at some of those rocks over here.

This is Mount Olympus right in the middle. Those white lines are the mountains and the snow on top of those mountains. And then, you have these deep valleys, river valleys, that cut through them, and you get enormous amounts of rainfall and snowfall there. And surprisingly, it's somewhat temperate. You get almost semi-subtropical types of plants there just because the amount of water. You get a rainforest type of environment going on over there. So, it's an extraordinary place.

We're going to switch now over to look at some photographs from the Olympic Peninsula. Here are some gulls and starfish on a big old beach rock. You can see the rock is kind of dark colored. The beach itself, the sand there is very dark in color. All of this is because the oceanic rocks that make up the Olympic Peninsula are basalts, if you remember that from last time. Basalts are dark in color and slightly higher in density, but the coloration comes from the fact that the Olympic Peninsula is made up of oceanic crust.

Here you can see the Pacific Ocean off in the distance, and all of these big, jagged rocks sticking up underneath. There's some huge cracks that are left behind and the tide smashing up against it and the big waves. You can see a big wave breaking up against that rock. It's just a great spot to wander the beach and do some sea kayaking or simply lie there on the beach.

If you walk a little bit inland, you'll go into the Hoh Rainforest where you get these enormous slugs six, eight inches long-- banana slugs. They're vast, really quite interesting looking things. Some people are repelled by them, some people are fascinated by them. You've got to go see them for yourself. It's very wet. It just rains and rains and rains constantly. You get these ferns, and you get these big waterfalls going through there. It's a lovely spot.

Here's another photograph of all the mosses and lichen hanging off of the trees. And because of all that rainfall, you have all these streams which come cascading off of the big black rocks that make up the Olympic Peninsula, and you have to make sure you take your raincoat and your rain gear and everything else with you because you're guaranteed to get rained upon on the Olympic Peninsula.

Here's another beautiful shot of a nice waterfall and some lichen and moss on it.

This is a photograph pulled back, and now we're looking at the higher peaks in the interior. This is a shot looking up towards Mount Olympus right in the middle. You can see some snow patches. And if you go right up to the top, Blue Glacier is a well-studied glacier. University of Washington folks have had a long-term project. They've got a hut up there and you can hike up to the hut and you can do all sorts of studies on the glaciology of that glacier. And here you have a deer sleeping in the underbrush looking a little suspiciously at the photographer.

Here's some kids playing on the beach. You can see, again, the very black color of the sand, an indication of the basaltic nature of the peninsula. Here you have these lighter colored material, which these are sedimentary rocks. These are material that came off of land, was deposited in the ocean. And then because of these huge forces involved, the collision of the Pacific plate and the Continental plate, these forces have turned these rocks up on their side and deformed them, and tortured them like this— broke them up into— and you see a big crack running through them. It's all very indicative of all the very large forces involved in producing the peninsula.

This is a close-up of some of those rocks. These are a very special type of rock called turbidites where you have material that goes whooshing down and jumbles up all the sands and gravels and so on, and you're left with a very layered rock. It comes out like that. And just the beautiful Pacific sunset with a gull flying off in the distance. Well worth a visit. If you're in Seattle anyway to go to the Space Needle or have a cappuccino at Starbucks, take a drive out to the Olympic Peninsula.

This slide by now should start to make sense to you. It's the first time we've seen it. We hopefully have put everything together by now. This is a cross section, a very idealized cross section, through the ocean on the left, and a continent on the right. You can think of this as the coast of Washington State or the coast of Oregon State, but it really represents a more generalized situation. This could be the Philippines, this could be Japan, it could be Alaska, it could be one of very many places.

In the middle, you have an oceanic spreading ridge where hot rock comes up, meets the surface, cools off, is shoved off to the right and to the left. When that material, that oceanic crustal material, this basaltic material cools off, it gets much, much more dense. As it gets shoved off to the right, it collides with the continental crust, which is much less dense. And during the collision you get subduction of the oceanic crust underneath the continental crust.

In the process of the subduction, some of the seawater and sediments get carried down with the subducting crust, the subducting plate. And as they get carried down, they melt and they come up as a volcano. That's all going on to the right of the screen over there. And we're going to look into this in a little bit more detail.

When basalt, water, and sediments heat up, they melt. The basalts by themselves don't really want to melt, but you mix in this water, you mix in the sediments, and at relatively low temperatures that mixture starts to melt. If you didn't have the seawater, if you didn't have the sediments mixed in with it, that subducting plate would have to go much, much, much deeper before it started to melt. But because the subduction process has taken the seawater, and taken the sediment and grabbed it, and pulled it down along with it, this mixture melts more readily.

And you've seen this yourself when you take snow out on the streets of State College, or whatever town that you're in. You mix salt with it. You mix these impurities in with it. It'll melt at a much lower temperature and you can drive your car over it. So, most materials, if you make them less pure, if you mix in all these other chemicals with it, like the sediments and like the water, they'll tend to melt more readily, and that's what happens with this.

That mixture, once it's molten, now has become much less dense, and it will rise up to form a volcano. That's what's going on in the left of this image over here. This subducting plate has carried seawater and sediments down with it, and at a relatively shallow depth because of that mixture, because of those impurities that are mixed in to basalt, you get melting, and that starts to rise up to form a volcano. That's the material, that's the picture along the right-hand side of the image.

So, as this mixed basalt, seawater, sediment mass has melted and it rises up, it forms andesitic volcanoes. It was named after the Andes Mountains and is just a type of rock that you find in the Andes. It turns out it's the same type of rock that you have in the Cascades, that you have in Mount Ruapehu in New Zealand, that you have in Alaska in the volcanic belts. It's very typical of these subduction zone volcanoes, so, we all call them all andesitic volcanoes.

As this magma rises up, it wants to polymerize— polymerize is a word you need to know. All it means is turning into these long chains or bonds of material. It wants to clump together to turn into this solid material. That's all that rock does as it goes from being molten to being solid is it's polymerizing. It's turning into a solid by making these long chains, these long compounds of the chemicals. It makes these long stringy units, sort of like lumpy oatmeal.

As this magma comes up, it comes up the top, it freezes into these long ropy, stringy lumps. And more material comes up, it comes out the top of the volcano, it immediately freezes on to the side, and you get these very steep-sided volcanoes. I'm going to draw you a picture now. I'm going to switch over and take a look at this process.

This is our subducting slab. On the left, we have the ocean, as I keep saying, and on the right we have continental crust. And the subducting slab is taking along with it some sediments and water. At a relatively shallow depth, this mixture of basaltic rock, which is the slab, of sediments and of water will start to melt. It will melt, become less dense molten rock, and it will rise up. So, this molten rock is rising up to the surface.

When it gets to the surface, it will polymerize, which is simply a fancy word for freeze, turn into a rock, turn solid, turn into a polymer. As more material comes out, it will come out the top of the volcano, and spill down the sides. I'm going to zoom in on this and draw it on the next page. This is the surface of the earth. You have this molten rock coming up. It polymerizes at the surface. It just freezes on. More stuff pushes through that, comes to the surface, spills down, and freezes on. And more stuff pushes through that, spills down the sides, and freezes on. And more stuff. Eventually you build a tall, steep volcano, known as a stratovolcano. V-O-L-C-A-N-O. Stratovolcano means tall, steep volcano. So, this is the process by which all of the subduction zone volcanoes are made.

You have molten rock, which is formed deep inside the earth where that subducting slab off the bottom of the screen there. The subducting slab has melted because of the addition of the sediment and the seawater. You have this molten material. It rises up. Where it breaks through the crust, it freezes on in the air. And when it freezes on, more stuff breaks through that and spills down the side, and over and over and over and over again. And you end up with these tall, steep stratovolcanoes. And this process goes on and on and on.

However, occasionally what happens is you get this stratovolcano. For example Mount St. Helens, and you have some hot, molten material rising up through it. So, this is molten rock. Let's see if we can't spell rock properly. Molten andesitic rock, it's rising up through there. It gets to the top, and there's a cap on top of this volcano that prevents the molten rock from getting out. So this rock is rising up, and for one reason or another you have a hard, impervious cap on top of the volcano, and this molten rock is trapped underneath this cap. And in the case of Mount St. Helens, more and more material is rising up underneath there, and this cap was bulging and getting pressurized.

So, let's switch back briefly to the PowerPoint presentation and we'll discuss how this then leads to those catastrophic Mount St. Helens explosive volcanic eruptions.

The magma, as this molten rock, as it's rising doesn't freeze within the earth. It stays liquid inside the earth. It's only when it gets to the surface that the CO2 and water that's inside escapes up out of the magma, and that's when it freezes on. And that's why you get these steep volcanoes. The stuff has molten all the way up. As it gets near the surface, the water and CO2 are released from it into the atmosphere, and then what's left behind is plain old basalt, and it freezes on, and you have a nice, wonderful steep volcano.

Sometimes the rock forms a cap, and when that happens, the pressure starts to build. You've got this magma coming up inside, you've got a cap over the thing, so the steam, the CO2 can escape, you're starting to build to a disaster. That's what happens with the stratovolcanoes. It's like releasing a cork on a champagne bottle, or on a Coke bottle, if you're under 21. Pressure, the CO2 is dissolved into the Coke. And when you pop the top on that, it fizzes out. It's all liquid in there as long as it's under pressure. You've got a cap on that Coke bottle. As soon as you pop that Coke bottle, it fizzes out all over your hand if you've shaken it up a little bit.

That's a very small example, but that's exactly what goes on with the volcano. You've got a cap on it. The magma's coming up from underneath, the CO2 and the water can't escape, the pressure builds, the pressure builds, the pressure builds. Something happens to crack the cap. In the case of your Coke or Pepsi bottle, you simply pop the pop top and that's it. In the case of Mount St. Helens, a small earthquake cracked the cap, and the CO2 and the water came shooting out, the pressure dropped and everything exploded. Mount St. Helens, 20th of May 1980. Coke bottle writ large. Champagne bottle, disastrous champagne bottle. This is another picture of Mount St. Helens again. Just a massive destructive force.

The magma contains water and CO2. If there's a cap over, it can't get out, the pressure builds, something comes along. A small earthquake that cracks that cap, and now suddenly all of that pressure that's been built up starts to get released. And then it just goes on and on, releases more, which opens the cracks some more, release some more, open the cap some more, and the whole thing takes off and you get this huge explosion.

That's all it is. It's relatively simple. You can't predict perfectly when it's going to happen, but it happened over and over and over again. Mount St. Helen's has exploded a number of times the last 1,000 years. All the Cascade volcanoes have. And so you have this cycle of pressure building up and an explosion. In the case of Crater Lake, that explosion was so enormous it just blew the whole top of that mountain off and all that's left is that big, round lake.

There's a different kind of volcano, one that isn't quite so destructive. These are the hot spot volcanoes. These are the volcanoes of Hawaii. Hawaii's the best example of them. There's a few of them around the world, but Hawaii is the best example of them. It's the one that's easiest to get to, it's the one that has a national park associated with it. Sometimes a plume of magma will come up from deep inside the asthenosphere.

Now, this is not this same as a subduction zone. If you remember, subduction zone volcanoes, the stratovolcanoes, was when you had oceanic crust going down. And at a relatively shallow depth, because of the mixture of water and sediments, that basalt would melt and it would come up. The hot spot volcano's very different. In a hot spot volcano, that material is coming from deep inside, hundreds, maybe even 1,000 kilometers inside the asthenosphere. Maybe even as deep as the core-mantle boundary.

We really don't understand hot spot volcanoes very well. They're one of the really most enigmatic features of the natural system today for volcanologists and for Earth scientists. So, they're really a fascinating thing. Why are they produced so deep inside in those places are not in other places? We don't really know.

But for some reason, deep down inside the asthenosphere, this plume of magma comes up, and this magma, because it comes from so deep inside the Earth, picks up a lot of iron. And that iron also prevents polymerization. It keeps the magma molten. Unlike stratovolcanoes, iron can't escape. With the stratovolcanoes, CO2 and water could escape and magma would freeze instantly. With these hot spot volcanoes, they come up, the iron can't go anywhere. The iron's not going to just evaporate and disappear into the atmosphere.

And so, even after the magma comes up to the surface, you still have it spreading out. It doesn't freeze instantly. You've probably seen pictures of Hawaiian big lava flows that spread for miles and miles, big rivers of lava that just spread for miles and miles. They haven't frozen on. And the reason they haven't frozen is because you have so much iron mixed in with them that they stay molten even at really low temperatures.

So, these lava flows stay molten long, long— even though they're up in the cold air, they still stay molten because of all this iron that's mixed in with them. And in the end, you end up with these broad, gentle sloping mountains known as shield volcanoes. Stratovolcano's are this big, steep ones. Why? Because the magma comes up, water and CO2 escapes, and the magma instantly polymerizes, and you just get these steep volcanoes because the magma can't run very far away from the mouth of the volcano.

In Hawaii, on the other hand, the magma comes up, it's got lots of iron in it because it comes from deep inside the Earth, comes up to the surface, comes into the cold air, and it still runs way off to the side before it finally freezes. And then more comes up and it spreads way off to the side, and you get these gentle, broad, large volcanoes, like a gladiator's shield. That's why they're called shield volcanoes. If you were to look at them in cross section, they'd be broad and rounded.

These hot spots are fixed in location inside the Earth. But as we talked about before, the surface of the earth is moving around all the time. These plates on the surface are sliding to east and to west all the time. But the hot spot itself is fixed. And so as the overriding plates goes by, the positions of volcano changes because the hot spot is fixed and location, but the overriding plate is moving. And so you get these series of volcanoes, one after the other. And I'll show a picture of that here.

What we're looking at in the left picture is a fixed hot spot. The material's just always coming up in the same spot over and over again. But the plate above it is moving. And as that plate moves, a new volcano comes up in a different spot. And then the plate moves again and a new volcano comes up, and the plate moves again and a new volcano comes up. Those older volcanoes slowly get eroded and disappear as they go off to the side.

And that's why Hawaii is this long chain of islands. You have the big island where there's current eruption going on, and then you have this whole chain of islands off to the northwest where older volcanoes have been carried off to the northwest and eroded one after the other. Hawaii is the best-known hot spot, but there's a whole bunch of them around the world. Iceland is another one, and the Galapagos Islands, and so on. So, as I said, they're very poorly understood, but they're very intriguing nonetheless.

This photograph here is showing that chain of islands. Hawaii is in the bottom left, and then you have this long line of volcanoes stretching off to the Northwest known as the Hawaiian Ridge. Midway Island and the emperor seamount chain, that will continue on, off to the north over there. And this is simply showing the Pacific plate as it moved off to the northwest carried volcano after volcano after volcano off into the distance.

So, hazards. Volcanoes are hazardous. We know that. You can see that. All the pictures that I've showed you of the ash, and the heat, and the blast. That's the biggest hazard. Don't be on a volcano. If there's a danger that it's going to explode, go somewhere else. That's the first thing you can do.

The second is you can't just go 100 feet away, or 1,000 feet away, or even 10 miles away, because this blast from the volcano can kill you even if you're 10 miles away. The gases are hot, 300 degrees plus, and that blast is fast— hundreds of miles per hour, it comes shooting down the side of the mountain so it'll knock you over. The gases are heavy, and so they flow along the ground. They don't go straight up. They flow along the ground. It's known as the nuee ardente, a glowing cloud in French.

There's a famous tragic example on the island of Montserrat where one of these clouds came blasting through and killed everybody in the town, except for one guy who was locked up in the basement of the prison, and the heavy, thick walls of it saved him because it didn't get as hot in there. But everybody else in the town was killed.

The second kind of hazard are the ashes and cinder. Those can spread much further away. Those can spread tens of miles, as much as 50 or 70 miles away from the central parts. These are the pyroclastic flows. All of the smaller pieces that spread out they can clog engines, that can bury houses and roads.

Finally, landslide and avalanche. All of the heat generated from this will melt glaciers and then you'll get floods that go along with them. So, these are some of the hazards associated with volcanoes.

Another hazard that's a little bit less well known, but is still quite dramatic, is the CO2. The carbon dioxide that comes up from one of these volcanoes can kill you in high enough concentrations. Lake Nyos in Cameroon in Africa is on a hot spot, and the lake itself was filled up with CO2 until a small earthquake triggered a turnover of the lake. All the CO2 escaped out all at once, and there was a couple of villages near the lake where everybody died because they were suffocated. There was too much carbon dioxide and not enough oxygen in the air, and they just died of suffocation.

So, CO2 seeped into lake. Something disturbed the lake and the CO2 escaped, and it suffocated hundreds of people that were living downhill from the lake. It was quite a tragic event back in the '80s. Nowadays, they just pump the CO2 out to keep it from building up, but this could happen in other places as well.

The third type of hazard, so you have all the hazards associated with living right near a volcano— nuee ardente, pyroclastic flows, those kinds of things. You have the second type of hazard, the CO2, the gases build up. The final type of hazard is a tsunami. A tsunami is a huge ocean wave that occurs when an earthquake occurs under water, and then that earthquake can generate a big ocean wave. A large volcano can also generate one of these huge ocean waves.

There was an island in Indonesia, Krakatoa, that blew up. And when Krakatoa exploded, it created this enormous cloud of dust and debris that travelled around the world. But another thing that happened was when that island exploded, because it was an island, there was a huge wave that was generated that spread out from Krakatoa that killed thousands and thousands of people.

The tsunami that was generated in 2004 was an earthquake-generated tsunami. An earthquake in a subduction zone let loose and generated a tsunami that spread across. We're going to show you a movie now, an animation, of what happens when that tsunami occurs.

This is an animation of the surface of the water in the Indian Ocean in the minutes and hours after that earthquake. As you can see, the effects of it spread outwards from the earthquake location. They do it relatively slowly, it took a couple of hours for it to spread right across the Indian Ocean, but for the island of Sumatra, which is right there— I'm going to run this animation again for you. For the island of Sumatra that's right there, the waves were enormous.

Let's take another look at this. This is right after the earthquake, and as that wave spreads out, it piles up against the island of Sumatra, and you get these huge waves that spread way inland. And this wave also spreads to the west across the Indian Ocean, and there's Indian [? Sulan ?] off to the left of the screen. And if this animation were to run for long enough, you would see that that wave would eventually hit the island of Sri Lanka and the coast of India.

We're going to run it one more time. And you can see the wave as it spreads out. There it goes, it hits the island of Sumatra, and the waves build up on the coast, and that's where 250,000 people died so tragically the day after Christmas, Boxing Day, December 26, 2004. It was a truly monumental disaster.

So, we need to make sure that we prevent these kinds of hazards, these kinds of disasters from happening. What happens is as the wave gets closer and closer to shore, the sea bottom is getting closer and closer to the surface, there's less room left over for that water. So, as this wave comes along, it builds up and builds up and it strikes with great force, flooding out villages, people, roads and infrastructure are gone. And once roads and infrastructure are gone, all the people that survived the direct effect of the wave, now have to deal with disease and hunger. Quite often the water wells are polluted, and so they don't have clean drinking water and it's just a disastrous situation.

So, next time we're going to talk about collision of continents. This time, we were talking about collisions of oceans with continental crust. Next time, we're going to talk about collision of two continents and what happens when two continents collide. Stay tuned.

DR. RICHARD B. ALLEY: Hi. I'm not Johnny Cash. But I have been in a ring of fire.

[MUSIC- JOHNNY CASH, "RING OF FIRE]

(SINGING) Subduction is a burning thing. It feeds a fiery ring. Cold, dense ocean floor will soon retire down through the mantle for a ring of fire.

Subduction scrapes off mud 'round a burning ring of fire. Takes water down, drives the volcanoes higher. Makes light andesite from a ring of fire. A ring of fire. Basalt is born calm and dark at a spreading ridge or Hawaii's hot-spot park. Dangerous stratovolcanoes fountain higher when fed by subduction and a ring of fire. Subduction scrapes off mud 'round a burning ring of fire. Takes water down, drives the volcanoes higher. Makes light andesite and a ring of fire. A ring of fire.

Great earthquakes from the moving load, stick, slip, and plates just might implode.

Eruptions, landslides-- we require Tsunami warnings from the Ring of Fire.

Subduction scrapes off mud 'round a burning ring of fire. Takes water down, drives the volcanoes higher. Makes light andesite from the Ring of Fire. The Ring of Fire. St. Helen's blew high, others blow higher. Go in awe and fear to the Ring of Fire. The Ring of Fire. The Ring of Fire.

[MUSIC PLAYING] PRESENTER (SINGING): Good morning, Mountain. Hello, crater. Lava dome raising its head. Cracks in their showing the molten rock glowing so hot it's orange and red. Behind the new dome, there's a glacier, fed by the massive snowfall. Fire and ice may make you think twice, either can make you feel small.

May on the mountain, 1980, the magma was coming full bore. The poison gas rising, the earthquake surprising, the north slope was bulging out more. Scientists worried, authorities hurried to save everyone if they could. Those few felt the power, but in the last hour, those few feared that everyone would.

The forces of nature dwarf us here as they shape the mighty land. But as we wonder, as we fear, we can understand. But there once was a time when we could not imagine just what it would mean to say, "We saw the biggest eruption in the whole USA."

Morning the 18th came the earthquake, the north slope went sliding to ground, uncorking the bottle that went off full-throttle. "This is it!" the most memorable sound. Almost as fast as sound came fury. 700 degrees in the blast. The forest was leveled, the landscape was beveled, 57 had breathed in their last.

Now we and the mountain live together. We both have a place on this sphere. It gives us new land, and the scenery grand, new soil for the trees and the deer. But bigger ones happened before cameras. Yellowstone was 1,000 times more. And Crater Lake's blast, not that far in the past, sent ash up to Greenland and o'er.

The forces of nature dwarf us here as they shape the mighty land. But as we wonder, as we fear, we can understand. And that helps us prepare for a bigger one coming. But until then we can say, "We saw the biggest eruption in the whole USA!"

St. Helen's will reach you, St. Helen's will teach you, and stay with you when you say, "I saw the biggest eruption in the whole USA!"

Good morning, Mountain.

[MUSIC PLAYING] PRESENTER: (SINGING) Definite chemical composition. Repeating order, each in position, controls the growth of the faces crystalline. Minerals, silicates are commonest here. Silicon plus 4 has a friendly face, gets 4 oxygens to share its space. Then little silicon is really hid in a tetradedral pyramid, SiO4 -4 won't balance out. So put a silicon on the other side, of an O -2 that's nice and wide. Then one extra O electron counts each way, with the O in two tetradedra to stay, sometimes it pays to share, there is no doubt.

But shared oxygen's not the only way to balance out the charge today. Put a +2 ion in between two oxygens from the pyramid scene. Give iron or magnesium a shout. Share all four oxygens, that's great. You've made a tectosilicate. And half of four with each Si makes SiO2 coming by. That's quartz, but crystals don't work at the bar.

But there's lots of aluminum plus 3 that needs a space where it can be. Take four SiO2 then place one Al in an Si space. K or Na plus balance alkali feldspar. Or kick out Si for two Al that happen by, and balance with Ca +2, Na to Ca solid solution, and then that is plagioclase feldspar.

But if your tetradedra just won't share, a nesosilicate is there. When each tetradedron can be found with iron or magnesium all around. SiO4, it's olivine you'll see. Share some oxygens but not each one, so many ways to mineral fun. Share 3 in sheets, the phyllosilicate way, Si2O5s in mica, serpentine, clay, with some other things, gives cleavage that's flaky.

Share one O, tetradedra form a pair. Si2O7 in the equation somewhere. Sorosilicate, epidote, you know, but we've still a little way to go 'cause some other tetradedra want to join up, you'll will see.

Share 2 in a ring, Si6O18, cyclosilicates beryl and tourmaline. SiO3 sharing two in a line, or Si2O6, tha'ts also fine. Pyroxene, single-chain inosilicate, baby. Join two ions sie by side, is it rings or chains? Si8O22 gives you amphibole grains. It's a double-chain inoslicate. Learn the hornblende formula, just can't wait. Half the tetradedra share 2 Os half share three. Neso, soro, ino, cyclo, phyllo, tecto, silicates-o, tetrahedral Si and O form the minerals commonest below with Al, Fe, Ca, Na, K, Mg.

[RUNNING WATER]

Oh, hi. Welcome to the GEOSC 10 Tectonics III Section, Mountain Building. We're going to be talking about how the Appalachians were built, why they're still as high as they are now. And we're gonna talk a little bit about icebergs. Now, what does all that have to do with rubber duckies, and why am I in the bathtub surrounded by rubber duckies? Well, let's find out.

So why are we in a tub with rubber duckies? Imagine that these ducks represent the mountains that surround us right here in Happy Valley. This is Mount Nittany. Here's the Great Smoky Mountains. And these are all the ridges and valleys that spread up and down the east coast of North America, known as the Appalachian Mountains.

About 300 million years ago, North America and what's now Europe and Africa all collided to form a super-continent known as Pangaea. And when these continents collided, because they're both about the same density, neither one subducted beneath the other. In fact, as they crashed together, they formed larger and larger mountains that wrinkled up. And that's what we had 300 million years ago with the Appalachians. This big duck represents the mountains at the end of that mountain building phase.

So after that collision, we have the proto-Appalachians. They were big. They were tall. They were high.

But for the last 300 million years, they've been eroded, and eroded, and eroded. But still, we have mountains around here that are a couple thousand feet high. If you go further down towards Tennessee and Kentucky, there are mountains that are 4,000 or 5,000 feet high. Why are they still high? Well, it has to do with buoyancy.

[RUNNING WATER]

Image 1: Park Service Map of Great Smoky Mountains National Park

Image 2: Thunderstorm over Great Smoky Mountains National Park. The Smokies are the wettest spot in the lower-48 except for the Pacific Northwest, with the high elevations scraping rain out of the sky to water the wonderful forest.

Image 3: A stone bridge over a stream. Caption: Bridge, Great Smoky Mountains National Park. The abundant rainfall in the Smokies feeds numerous beautiful streams, such as seen here and in the next picture; many streams host native brook trout.

Image 4: Close-up view of a stream in the Smokies. There are many large rocks with white water rushing around them.

Image 5: A waterfall in the Smokies. Caption: This photo and the next, from the USGS archives, were taken by W.B. Hamilton in 1954. They show two of the many beautiful waterfalls in the Smokies. A little extra description of waterfalls is inserted between the two.

Image 6: Two waterfalls in the Smokies. Both photos from the USGS archives were taken by W.B. Hamilton in 1954. Caption: Waterfalls usually indicate something interesting in recent geological time; water flows faster and erodes more on steeper slopes, so waterfalls quickly become rapids. Hence, these waterfalls suggest a recent event, perhaps of mountain-building. Yet, the newest scientific studies suggest that conditions have not changed recently. The debate is more than academic; if mountain-building has occurred recently, then the risk of earthquakes is higher than it otherwise would be, with implications for zoning codes and construction practices and emergency services. Although the basic outline of geology is well-known, large and important questions remain!

Image 7: Another Smoky Mountain waterfall photo from the USGS archives, taken by W.B. Hamilton in 1954.

Image 8: Late-autumn view, Great Smoky Mountains National Park. There are evergreens in the foreground, a dark blue ridge directly behind the evergreens, and then many smaller mountain ridges fading into the distance as typical of the Appalachians.

Image 9: Close up of mountain laurel in Great Smoky Mountains National Park. Caption: The ridges of the Smokies are mostly sandstones, metamorphic rocks, and granites, which give rise to fairly acidic soils that are favored by rhododendron, azaleas (next pictures), and Laurel, among others. Limestones in places produce less-acidic soils and host different plants.

Image 10: Flame azalea with orange flowers, Great Smoky Mountains National Park. Caption: About 10,000 species of plants and animals are known to live in the park, and many more are probably present.

Image 11: A stream with rhododendron in the background.

Image 12: Close up of Goat’s-beard, a common wildflower of the Great Smokies. The Goat's-beard has dark green leaves and a plume composed of tiny white flowers.

Image 13: Old-growth forest in Great Smoky Mountains National Park. There are large deciduous trees with smaller evergreens growing below the trees and short undergrowth. Historical (1953) USGS photo by W.B. Hamilton.

Image 14: Metamorphic rocks near Cades Cove, Great Smoky Mountains National Park. Heating caused former muds to change into new minerals, and squeezing caused the prominent folds seen. A rich and varied geological history is recorded in the diverse and beautiful rocks of the Smokies. USGS photo by W.B. Hamilton, 1953.

Image 15: Remote Sensing Image of the folded Appalachians.

Image 16: Remote Sensing Image of the folded Appalachians. The Great Smoky Mountains were raised to their present elevation by obduction, when Africa and Europe collided with North America as the proto-Atlantic Ocean closed. The whole Appalachian chain formed with the Smokies, including the Valley and Ridge Province—the folded Appalachians—in which State College, PA lies. This autumnal NASA photograph shows State College and Mt. Nittany near the top center, as indicated. The ridges appear orange, the valleys white and blue (some of the colorations is “false-color”—NASA takes subtle differences in appearance and makes the differences appear bigger by changing the color scheme), and Lake Raystown is the black body near the center. From NASA’s Remote Sensing Tutorial.

Image 17: Another Remote Sensing Image of the folded Appalachians. The Great Smoky Mountains occupy the lower-right part of this image, with the folded Appalachians across the center and the Cumberland Plateau in the upper left. The false-color image is from the NASA Remote Sensing Tutorial.

Image 18: A crash test car crashed head-on into a wallm with the hood crumpled together. Caption: Obduction, which produced the Great Smokies, the folded Appalachians, the Himalaya, etc., has some things in common with running a car into a brick wall or another car--something long and thin becomes short and thick, with folds and push-together faults. This rather elegant example is from crash-safety testing by the Department of Transportation, Transportation Statistics Annual Report 2000.

Image 1: National Park map of Rocky Mountain National Park. A quick field trip to Rocky Mountain National Park, Colorado. If you want to see elk, bighorns, big mountains, and big marmots, Rocky Mountain is great AND It has some beautiful metamorphic rocks, which we’ll look at in a minute. All photos by Richard Alley; map from the National Park Service.

Image 2: Clark’s nutcrackers (bird) sitting on a rock. Clark’s nutcrackers are well-known moochers at campsites and highway pull-offs. Feeding the animals is not allowed, however.

Image 3: Bighorn sheep standing beside a road. Bighorn sheep are common in the park and often come right down by the road near Sheep Lakes in Horseshoe Park.

Image 4: Close up of an elk eating grass and wildflowers. Elk are also common in the park and make a bit of a nuisance of themselves in nearby Estes Park sometimes. As for students, breakfast is the most important meal of the day for elk.

Image 5: Rocky Mountain peaks with small glaciers rising above Bierstadt Lake.

Image 6: Rocky Mountain peaks with small glaciers rising above a lake. Glaciers carved numerous lakes in the park, to which we will return later. Here is Ouzel Lake (an ouzel, or dipper, is a small gray bird that walks underwater looking for food.)

Image 7: Top of Flattop Mountain. It is crowned by tundra, short plants growing on permanently frozen ground (permafrost), another topic for our next visit to the park.

Image 8: View of Glacier-carved Emerald Lake, between Flattop and Hallets Peaks, from above. The photographer is standing at the top of a cliff, looking straight down into a lake. The lake is surrounded by mountains.

Image 9: View of Horseshoe Park, a glacier-carved valley. You can see trails, a road, and lakes. Trail Ridge Road runs along beaver ponds in the lower-right side. The ridge behind the beaver ponds is a moraine, pushed up by a glacier that filled the valley beyond during the ice age. Sheep Lakes, in the upper left, are frequented by bighorn sheep.

Image 10: Alluvial fan from the Lawn Lake Flood. In 1982, a dam failed far above this site, unleashing a flood that killed three people and left the trail of sand, rock, and debris running down the mountain and ending in a triangular area of debris. The barely visible road crossing the fan shows the great size of the deposit.

Image 11: Close up of a bog orchid. The park has glorious wildflowers such as this bog orchid.

Image 12: Close up of a calypso or fairy-slipper orchid . Calypso or fairy-slipper orchids are common on the forest floor on both the east and west sides of the park; this one is in the Wild Basin, an outstanding hiking destination.

Image 13: A cliff on the side of Hallets Peak that shows dark metamorphic rock and streaks of lighter colored igneous rocks. This cliff on the side of Hallets Peak is several hundred feet high. The darker metamorphic rocks are cut by lighter-colored igneous rocks that were squirted in while melted and then froze.

Image 14: A close-up of a metamorphic rock (called gneiss) shows beautiful layering and folding that formed when the rock was heated almost to melting. Remarkably, this rock started as mud and then recrystallized under heat and pressure.

Image 15: Metamorphic rock with a red garnet in the center. Metamorphic rocks often develop interesting minerals, such as the red garnet in the center of the picture. The rock folded around the harder garnet as it grew from the parent mud.

Image 1: Title page that simply says ‘Tsunamis’. Tsunamis are among the most deadly natural disasters.

Image 2: Map with an arrow pointing to the N. tip of Sumatra. It says Epicenter Magnitude 9.0, Dec 26, 2004, referring to the 2004 Indian Ocean tsunami. The 2004 Indian Ocean tsunami is among the worst natural disasters ever. An immense earthquake (one of the two or three biggest ever) triggered a wave that killed over 300,000 people. Many of the resources shown here are from the United States Geological Survey.

Image 3: Tall tree with branches broken off and bark scraped off up to the height of the tsunami. It has a 1.5 meter stick leaning against the base for reference. Branches are broken and bark is scraped off of trees up to the height of the tsunami. The 1.5 m (5 ft) high stick does not come close to the high-water mark, which is off the top of the picture.

Image 4: Map with an arrow pointing to Lampuuk. At Lampuuk the peak water depth was 28 m (nearly 100 ft) above normal water level, and the huge surge pushed well inland. Imagine the last time you were on the beach, at Atlantic City or Virginia Beach, and then mentally put 100 feet of water over the place where you were sunning.

Image 5: Steel reinforced beams broken at the base and laying across the sidewalk. The inrush of water carrying trees, boats, etc. can have immense force. Here, steel-reinforced beams were broken by the tsunami.

Image 6: A 2 ft deep hole in the sand. The sand was found inland. It was relocated from the shore to Lampuuk by the tsunami. The tsunami eroded the coast, and some of the eroded sand was carried far inland and deposited. Here, at the village of Lampuuk, 73 cm (2 ft) of sand was deposited on the dark soil at the bottom. Excavations in coastal regions can find such records of tsunamis, and help learn how frequent they are.

Image 7: Before and after satellite images showing the coast at Lampuuk. Before = green and has sandy beaches. After = brown and no sand beaches.

Image 8: Aceh, NW Sumatra, Indonesia: BEFORE the tsunami. Images processed by StormCenter Communications, Inc., Captured by Space Imaging Ikonos Satellite, processed by CRISP-Singapore.

Image 9: Aceh, NW Sumatra, Indonesia: AFTER the tsunami. Large parts of the land are under water and all of the land is brown rather than green. Text on the image says "sinking from earthquake motions also affected this area."

Image 10: Another section of Aceh, NW Sumatra, Indonesia: BEFORE the tsunami. It is green and lush.

Image 11: Another Section of Aceh, NW Sumatra, Indonesia: AFTER the tsunami. Now it’s brown and much of it is underwater.

Image 12: Seward, Alaska after the 1964 Alaska earthquake. Houses are leveled and trees are toppled. The great Alaska earthquake of 1964 generated tsunamis from the plate motions and from landslides and the tsunamis caused most of the deaths. Damage in Seward is shown here. 1964. Figure 4-D, U.S. Geological Survey Circular 491. Digital File:aeq00016

Image 13: View of downtown Kodiak, Alaska, before and after the tsunami. The after image has many missing buildings and a boat found inland.

Image 15: Blackstone Bay, Alaska. The wave reached 80 feet above sea level, washing the snow away (trees are 50-75 feet high). ( 1964. Figure 14-A, U.S. Geological Survey Circular 491 )

Image 16: Prince William Sound, Alaska. Man is standing along the coast, surrounded by trees up to two feet in diameter that were splintered by a tsunami from an earthquake-triggered underwater landslide. Since then, the Trans-Alaska oil pipeline was built, ending near here.

Image 17: Man holding a large tire with a two by four sticking straight through the rubber part of the tire near Whittier, Alaska. This shows the strength of the wave and the strange things that happen when a whole lot of energy is let loose.

We've been looking at how spreading ridges under the ocean make seafloor, which moves away from them and eventually gets old and cold and sinks down. And it will be sinking down beneath a continent, often, and it will scrape things off to make the Olympic. And then it will have a big volcanic range such as the Cascades, Mount Saint Helen's, and so on.

And they will be sitting there next to the ocean, which we can draw in. And coming up from below, there will be melt to make seafloor out here. And coming up from below there will be materials that erupt at the volcanoes like that.

Now, that works all fine, but what happens when there is a little bit of a swinging down of the slab? We know that the slab is moving away from the seafloor spreading ridge, as I show here. But the slab really does have a little of this swinging down, as well, in some cases. And the continent moves to catch up with it.

And so pretty soon, the continent is going to end up getting close to the spreading ridge. And the stuff going down is then not going to be cold. It's going to be getting warmer.

And when that happens, we have to erase this, because now the materials don't want to go down anymore. You'll get something that goes more like this, with it running right underneath the edge of the continent and staying high. And where it runs under the continent and stays high, you'll get a lot of rumpling, a lot of pushing happening in this way. And so then you might expect to see something that gets pushed up like this. And we're reasonably confident that that sort of push up is what the Rockies are.

In a few cases, as in the west, where the San Andreas Fault is, in fact, the subduction zone has been pushed all the way out and has run over the spreading ridge. And the subduction zone and the spreading ridge annihilated each other. And then you've got the San Andreas Fault.

Out in the ocean, there's a giant iceberg sitting out here. Big thing threatening the oil platforms floating around. And in the bottom of this very special iceberg, there is a really strange looking, googly-eyed space alien. And you have been given the task to go out there in your little boat sitting here in the water to get the space alien out.

Now, you're a good geosciences 10 student, and you know that all icebergs have about 1/10 above the surface, and they have about 9/10 below the surface. So you know immediately what to do. You take your gimongous chainsaw and you chainsaw off the top of the iceberg and throw it away, because you know what this will cause is that the iceberg will come bobbing up, carrying the space alien with it.

And so after it gets done bouncing up and down for a little bit, you find that the iceberg is almost as tall as it was before. It still has, sitting way down in the bottom of it, the space alien that you're trying to get to. So there's a space alien down here. And it still has about 1/10 of its height above the surface, and about 9/10 of its height below the surface.

But what you find is it's just a little bit shorter than it was, and it doesn't stick down quite as far as it did. Now you wump the top off again, and you keep wumping the top off, and you keep wumping the top off. And after a long time, you get down to a little iceberg that doesn't stick very far down.

Now it still is the same picture, that it has 1/10 above, and it has 9/10 below. And if you're not careful, you're sitting there admiring this lovely fact of science, and the space alien sticks out a giant tentacle, and it grabs your ship and throws it to the bottom of the sea. And so you'd better not do that.

However, there is a scientific piece to this. Suppose instead of space aliens, that we wanted to talk about mountain ranges. Now, we know that mountain ranges stick up above the plains. But you might not have known that they also stick down.

They have a root in the same way that an iceberg has a root that it's sitting on. There's a slight difference in that about 1/7 of a mountain range is up and about 6/7 of a mountain range is down, way down. The rocks have been heated. They've been squeezed. There's all sorts of interesting things going on and new minerals being grown.

And at the surface, the streams are sitting here, busily trying to grind away the mountain range. As the streams grind away the mountain range, why, the deep stuff will come bobbing up towards the surface. And if you come much later and look at it, you'll find that the rocks have barely any mountains left.

There's still a little bit of root with 1/7 up and 6/7 down. But now what you'll find is that the rocks that had been cooked way down, and bent way down, are very near the surface. And you can go see them.

[MUSIC PLAYING]

We're at Capitol Reef National Park, home of the famous Waterpocket Fold. In the background, we can see it. We can see the layers dipping this way from the west, and you can't really see the layers on that side. This is a classic monocline, and it's a 100-mile long flexure in the Earth's crust. And Dave going to help show us how it formed.

This is the Earth's crust. And then 50 to 70 million years ago compressional stress came from the west and caused a bulge. And rocks on the west side were lifted up on along a thrust fault about 7,000 feet higher than rocks on the east side. Later, uplift during the uplift of the Colorado Plateau about 15 to 20 million years ago left it susceptible to erosion and the top part was eroded off. and you got many of the geological features you'll find in the park, like monoliths, and canyons, and arches.

The reason the Waterpocket Fold got it's name is when the younger layers up here were eroded, softer layers beneath were exposed and formed small basins in which water gathered in, which provided a water source for early settlers.

[MUSIC PLAYING]

[MUSIC PLAYING]

This is the most glorious place. Just look at this place. We're sitting on these old rocks, these seriously old, 1.7 billion year old rocks.

Everything around us that's black didn't quite melt. Everything around us that's pink actually did. That was molten magma squirting into cracks. And the stuff that didn't melt was like toothpaste. It was so soft, because it was so hot, that it just flowed and crinkled and folded, and--

It's been bent, and one can follow any of these layers along. And you see that they wiggle, and they come around, and then they come out here and back. And so these rocks were really, really hot. They were almost up at the melting point.

And they were being squeezed. There was mountain building of some sort going on that caused them to have squeezing and to be pushed from here to there. And as they go, very often, you get something like this folding. If you take a phone book and squeeze it, it'll fold. And in the same way, when you squeeze these rocks, you end up folding them.

The other part that's interesting, here, is that we can see these beautiful things so very well because this stream has come over them. And it's eroded them, and it's polished them. And the surface that we're on is very smooth.

But this is the heart of the mountain. This is what it would look like if you could get down in a mountain range somewhere, down there about 5 or 10 miles. And that's what we're standing on.

Migmatite. M-I-G-M-A-T-I-T-E. It's not quite magma. It's migma. Mixed magma. And you'll see all of these awesome morphs and wiggles and the little things through here.

This melted. This didn't. This melted. This didn't.

Oh, this layer-- that's beautiful. These things have been really, really hot.

[MUSIC PLAYING]

So we're just outside of Happy Valley, Penn State, up behind the ski area on the road up to Bear Meadows. And we've stopped beside a pretty little stream to look at an old beach. The rocks behind me here are made of sand glued together with hard water deposits. They're sand stone.

This is an old beach fed by old rivers. It came down from a great mountain range that used to exist up to the east of us. Now, if you go and look at most beaches, the layers are flat. And if you look at the layer behind me, it very definitely are not flat layers.

The layers are tipped way up on edge. They're very steeply slanted. And so something fundamental has happened here to get the slant that we see out of the flat layers that used to be.

What happened here was that there was a great collision, and Africa rammed into North America. The oceans open and close, and the continents drift around, and occasionally one continent runs into another. And when there's a running into, you get a lot of breaking and you get a lot of bending. And so the rocks in this part of the world have been bent in various ways, and you get all sorts of interesting bends.

The rocks that we see behind me are one of these bends. They're the little slant on this side of the bend. And they go up here and over the top of Penn State and down on the other side in a great arch, the Nittany Anticlinorium. And we're seeing a little side of that. And that's why we have mountains in central Pennsylvania.

The same thing as the Smokies. The same thing as the Presidential Range, Mount Washington up in New Hampshire. The entire trend of the Appalachians is a result of this giant collision that bent and folded and broke the rocks.

The Atlas in Africa, the mountains up through Norway are the same thing, this giant collision that bent everything. It's happening today to make the Himalayas. And so when you see these rocks slanting up behind me, this little piece here in central Pennsylvania, it's part of the vast damage and the beauty of a collision that happened long ago.

Welcome. This is Geology of the National Parks, GSCI10. My name is Sridhar Anandakrishnan, and I'm going to be your guide through obduction, it's a word that means collision of continents and what happens when continents collide. So, you're probably watching this somewhere in Central Pennsylvania. Maybe you're not, maybe you're off on holiday somewhere else, but State College here is certainly in the middle of central Pennsylvania. And what is remarkable about this area geologically is the so-called ridge and valley structure that stretches for hundreds and hundreds of miles to the Northeast and to the Southwest. You've seen them. You driven over them. You've had to go long ways along these ridges with Tussey Mountain on this side or Mount Nittany on this side, Bald Eagle Ridge. So, it's a very characteristic structure of this area, and it was created by obduction, by the collision of continents.

So, that's what we're going to do. Let's take a look at some pretty pictures first that will motivate what it is that we're talking about, and then we'll go to the PowerPoint presentation. This is a picture of a thunderstorm over Great Smoky Mountain National Park. Great Smoky is down in the southern US, it's just an absolutely gorgeous place. High mountains, 4,500 feet high, wooded for the most part, except for these wonderful balds that they have there, these tops of mountains that are bare for reasons that I'm not particularly clear on. But you'll be hiking through and then you'll break out into one of these balds, and you can see forever, ridge after ridge after ridge, and there's all these clouds that give it its name, the Great Smokies. And maybe there's a thunderstorm on the next ridge, or maybe it's raining over there. It really is an amazingly dramatic place. It's not that far away. It's a day's travel from here, but there's some lovely scenery in between as well. Well worth a spring break trip. You've don't have enough money to go to Cancun or something like that, time much better spent. Drive down to the Great Smokies.

Great Smokies is where the Appalachian Trail comes through, one of the most extraordinary hiking trails in the world. It goes from Springer Mountain in Georgia right up the Appalachian Mountains right up to Maine, to Mount Katahdin in Maine. And every year, there's a few people, a few hardy souls, that hike the whole thing. They start down in Georgia in the springtime and they follow the spring up through. They come up through Pennsylvania, go right up Harrisburg right up the Susquehanna Valley, and then on into New York, and then finally through the Northeast up into Maine. So, it's a beautiful place. Here's a picture of the Great Smoky Mountain Park.

There's a bridge over one of the many, many streams. You have these mountains that stick up and to the west of the Great Smokies, you've got nothing. You've got these huge planes that stretch out for miles and miles to the west, all the way through the Midwest until you get to the Rocky Mountains. And the winds build, and the weather patterns, the weather systems come down through there, and they have to climb up over the Great Smokies. And as they climb up over it, they dump all their rain down into them.

They do the same around here. We're pretty wet here in Central Pennsylvania, and one of the reasons for it is that these wind patterns and weather patterns bring a lot of water in. When you've got water, you have streams. And here's one of those streams, a close up of one of those raging torrential streams.

You can go online. This is one of our virtual trips, virtual field trips. We call them vtrips, and you can read the captions. This is just a lovely place. And you're hiking along, you'll come across one of these waterfalls. This is two views of the same one. There's some text, they're talking about why those waterfalls are where they are. So, you should have a look at this. All right?

Late autumn, things are starting to thin out a little bit, and the ridges, one after the other. You see that around here, too. One ridge after the other. You climb up on top of one, and there's another one behind it. The early European settlers were quite unsettled by this. They would get up over one ridge, and there was another one that they had to go past. Lots of lovely vegetation, mountain laurel, flame azalea. Lots and lots of animals that live in there.

This is another thing that national parks are wonderful for. They preserve flora and fauna. If we didn't have a national park in Great Smokies, who knows what would be there? Maybe it would have been logged for farmland, or a subdivision, or a highway. So, the fact that it's a national park preserves all of these wonderful critters and plants. Rhododendrons in the background. Just a lovely place. So, you should take a trip down there. So, we're going to find out why the Smokies are important to us, why the Appalachians are the way they are, why the Appalachian Trail stretches up through there.

We're going to switch out to the PowerPoint, we're going to talk about Tectonics Part Three: When Continents Collide. You get obduction — there's how the word is spelled — and we're going to plunge right into it with "Go dog go." If you can see, there's blue dog and yellow dog, and blue dog has run into yellow dog. Yellow dog is chastising blue dog for being such a poor driver. But the important thing is that the hoods of their two cars have scrunched up like an accordion. Neither one gave way. Neither one submarined under the other one. They just smashed into each other, and they accordioned up and crumpled and rumpled up.

And that's what we're seeing over here. Those rumples in the hood of the red car, and those rumbles in the hood of the yellow car, think of those as the Appalachian Mountains. That's how the Appalachians were created. Two continents collided, not go dogs, but two continents collided. And when they collided, neither one gave way. . If you remember from last time, the subduction one, when oceanic crusts and continental crusts collide, one of them gives way. One of them sinks under. And so, you don't have these types of mountains that are produced when two continents collide. When they collide, neither one wants to sink down, and so, they just crumple up, get shortened. And as they get shortened, they rise up in these peaks that we see around us here in Central Pennsylvania and down in the Great Smokies.

Here's a picture of the Appalachians. And this is a perfect shot, ridge after ridge after ridge after ridge, long skinny things. We are sitting on the hood of the blue car looking up along the hood of that car towards one of the drivers. I'm going to go back here real briefly to the go dog picture. Imagine you're sitting at that collision point, looking up along the hood. That's all it is. That's all that these Appalachians are, writ large.

Here's a photograph in West Virginia. There's a road cut where Route 68, I think, goes west through there. Now there's a wonderful visitor center where you can pull off the highway, and there's a wonderful explanation of it. You have these extraordinary curved layers. What used to be nice and flat, during the collision, they got smashed together and got turned up and turned down, and you can see that over here because the road has cut right through there, and so, they've sliced through that part of it.

So, we're going to do a quick review of what we learned last time, or the last few times. And I know we've been throwing a lot of material at you in the last few weeks, but there is a lot of material to be thrown at you. It's all available online. It's on Angel. The text is free, you just have to download it and read it, and it connects to all of this. Tectonics is driven by heat. I've said that over and over again, I'll say it again. If I ever ask you what drives tectonics, you just yell all together, heat. There are a number of plates, the upper lithosphere is broken up into eight or nine plates, and they move about on these convection cells. The convection cells are due to heat. Oceanic plates are made up of basalt, and the continental plates have more silica in them. Silica ridge, they're a lower density, they're more buoyant.

When cold ocean plates collide with buoyant continental plates, the cold ocean plates sink down. They're of high density. They just sink down, you get a subduction. When continental plates collide, that's what we're going to talk about this time. You get the Appalachian Mountain range, that stretches all the way from Newfoundland down to Alabama. In Alabama, it sinks down underneath the coastal sedimentary plane, but the Appalachians actually come up again in Oklahoma. So, they're just an enormous mountain chain.

Continents are rarely destroyed. The story gets really complicated. If you take something and you just keep piling stuff on top of it year after year, you shred it, you munch it, you fold it up, you put in a corner, you take it out, understanding its history becomes really, really difficult. The ocean is easy. It's created, it's destroyed. After 150 million years, 200 million years, all of the ocean is gone because it's been subducted and disappeared. But the continents are old. They're four billion years old. And in that time, they've had lots and lots of things done to them. And so, it becomes really difficult to know what happened in the past.

The analogy that I give is one of my colleagues— not me, of course. I have a very clean office. That's a joke. You should come see my office sometime. But one of my colleagues has a really messy office. He's an older gentleman. He's been working in the department for almost 40 years. I don't think he's thrown a thing away in that time. And you go in there, and it's piles of books and manuscripts, piles and piles of folders and papers, and rocks that he's collected, and instruments that he's collected. And so, they get jumbled up sometimes, because he pulls something out from underneath and he puts it on top. And so, understanding the relationship of these papers to each other is really difficult.

And that's the way the continents are. They've been all jumbled up, and stuff has been piled on top, and stuff has been pulled out from underneath. We're going to give it a try, though. We're going to give it a try and try and tease out the history of the Appalachian Mountains.

Here's a satellite image of the east coast of the US and the eastern Canadian Shield. And you have this very characteristic wiggly line, you can see it there, that stretches right from the southwest right up through central Pennsylvania— I hope you can recognize the Delaware River there and the Chesapeake Bay. That's where Philadelphia is. And then on up into New England, and then right off the map— that's Maine— and then right off the top would be Newfoundland and Canada. You can see that this mountain chain stretches a long, long ways, and it's got these long, linear features to it.

This is the Susquehanna Valley from space. This is looking down at just the region right around here. That's the Susquehanna River, Harrisburg is right in the middle over there. And you can see these ridges, one after the other, stretching up through there, and this river slicing through them, allowing us to work out their history. This is what we're trying to figure out. Why are the Appalachian Mountains here? What's their relationship to the rest of the world?

The Appalachians are a complicated place. They aren't simple. As I said, the analogy that I give is of my colleague who has an office and it's been filled with stuff, and stuff has been removed, and it's very hard to tell the relationship between things. But we're going to give it a try. About 300 million years ago, North America and what's now Africa and Europe collided. These two huge continents— neither of which wants to sink, because they are low density. Neither of them wants to sink under the other. It's like a game of chicken. And the two, neither of them gave way. They smashed into each other. And they crumpled up to form these huge mountain chains, possibly as high as 15,000 feet. We don't really know, but we think some of those mountains might have been as much as 15,000 feet high.

It's similar to what's going on today, right now, in India and Tibet. The Indian continent is running into the Asian continent, and as the two run into each other, you have these enormous mountain chains, the Himalayan Mountain chains. The highest spot on earth, Mount Everest, is 28,000 feet high, and it's because of this collision of India and Asia.

This is a picture of that collision. The Indian land mass was way out in the Indian Ocean 70 million years ago, and it came zooming up over the last 70 million years. And today, it has smashed into the Asian plate. And in the process of those two continental massesIndia is a continental mass, Asia is a continental mass neither one wants to give way. And they just run into each other, and they crumple up, and then the rocks in between have nowhere to go but up, and so you get these huge mountain chains of the Himalayan mountains. This is a photograph of Mount Everest. Sagarmatha is what Mount Everest is called in the Nepali language. And it's an absolutely awe-inspiring sight, first climbed by New Zealander.

So, in the process of these two continents colliding, they get shortened up. It's just like the hood of the two dogs that we saw. That's an analogy, but it's a pretty good one. You take a hood that used to be longer, you accordion it together, now it's shorter. And that's what happened with the North American continent, and presumably with the European/African continent when they collided 300 million years ago.

One of two things could happen. The first is what's known as a thrust fault. This is where, when the two continents collide, you actually do get sliding of one over the other. You don't get subduction. Nothing sinks back down into the earth. But you can think of two sheets of paper that run into each other. One just climbs up and slides over the other one. This is known as a thrust fault. You can shorten up a continent by sliding one part of it over the other. And this is partly what happened in the Great Smokies area.

And one of the reasons that we know that is that there are places where there are young rocks underneath older rocks, and this is a very unusual situation. Usually, the old rocks are on bottom, and you pile younger rocks on top. It's like my colleague with his office. He gets a book, and he puts it on top of an older book. And he gets a newer book, and he puts it on top of an older book. And then he gets a newer book, and he puts it on top of that one. And so you can look at them, and oh, there's a book that he got 30 years ago, and there's a book that he got last week. And that's this normal sequence of things. Occasionally though, he'll go and he'll pull out one of the older books and read it and put it on top of this pile, and so the whole thing gets jumbled up and you don't know the sequence. That's what's happened down in the Great Smokies area, where you have older material that's ridden up on top of younger material.

Further north, around here, the rocks are more wrinkled. They look like a kicked up rug, or a sheet of paper that has been collapsed. We've got a young kitten that we just adopted from the shelter, and boy is he ever active. And he loves our rug. We don't have one of those little rug runners, the little rubber things that keep the rug from sliding around. And so he'll run as fast as he can, and he'll attack the edge of the rug, and he'll slide into it and he'll shove that rug back. And as he does it, he'll form these wrinkles, one after the other. And he doesn't seem to realize that that's a valuable rug, but his enjoyment of it simply comes from rumbling it up.

This is a similar sort of thing that happened over here. These two continents collided. Instead of one sliding under the other, what happened is the continent got shortened, but now by being crumpled and rumpled up like a rug. The rug itself is layered. There's hard layers and soft layers. And as time goes by, you get differential erosion, that we'll talk about next.

This is a cross-section. Remember what I told you a cross-section was. If I could take something and slice it open and look at it from the edge, that would be be a cross-- look at it from the end, that would be a cross-section. This is a cross-section through State College, going from the Northwest side-- the Allegheny Plateau and the Allegheny Front on one side, going down through Bald Eagle, through Mount Nittany, through Tussey Mountain, and heading off to Southeast on the right, down towards Harrisburg and down towards Philadelphia on the right. You should recognize this. If you have ever driven from here to New York City or ever driven from here to Philadelphia, you've seen this. You have to drive up over Seven Mountains and down the other side, and then there's another valley there, and you have to drive up the next one and down the next one, and that's what's going on over here.

But if you're a geologist, you can go and look at the types of rocks that form the different mountains. And what's interesting here is that these layers, what used to be a sequence of nice flat layers, that have now been squeezed together and crumpled up, have eroded in slightly different ways. Where you used to have very hard rocks, were the high places, and those cracked and you went down into the softer material, and those just eroded right down to what are now the valleys. So paradoxically, it's where the very hardest rocks used to be very, very high up, those are what have broken through, and now we have very deep valleys there. And the ridges in between are made up of what used to be the somewhat softer areas.

Eventually, the collision stopped. These things are colliding, they're getting pushed together. Eventually, the collision stopped, and then a spreading began. Similar to what's happening in Death Valley today. Death Valley is a mid-continental spreading ridge, and that's something that also happened in this area. About 150-200 million years ago, you started to have spreading apart of this in similar fashion to what happens in Death Valley. And the Atlantic Ocean was formed. As you started to rip it apart, and then the waters rushed into that low spot that was created where the continent was spread apart.

The mountains stopped being pushed up. You're no longer shoving them together, so you've stopped shoving these mountains up into the air. As soon as you stop doing that, those mountains will start to be eroded downwards. Mountains are very rapidly eroded. This is something we'll talk about more down the road when we're talking about erosion. But when you have these high mountains, the winds blow on, the water rains on them, the glaciers build on them, and they slowly get scraped off. That's what erosion is. Erosion is simply scraping off pieces of this mountain and making it go away, and depositing them in the low spots.

But for some very interesting reasons, the mountains are still fairly fine. There are 2,000, 3,000, 4,000 foot high peaks. They used to be much higher. They used to be 15,000 feet. But even though they're very old, they haven't been scraped down to sea level yet. And we know about rates of erosion, and so we should have been able to scrape down those 15,000 feet to sea level by now, but we haven't These mountains are still up 2,000, 3,000, 4,000 feet. Why is that?

It's something called isostasy. Mountains have very deep roots. When we squeeze those continents together, the continent bulged upwards, but it also bulged downwards. When you squeeze them together, it isn't as if the bottom was flat and it's just the top that bulged up. When you squeezed it together-- think of silly putty. When you squeeze that together, it bulges out in both directions. And that's what happened with the Appalachian Mountains. Some of it bulged upwards, and some of it bulged downwards. And as the mountains are scraped off on top, these roots ride up, scrape off some more. The roots ride up, scrape off some more, the roots ride up.

And so to get this mountain scraped down to sea level, you don't just have to scrape away the stuff above. You've got to scrape away the stuff below. So I'm going to go to the drawing pad and illustrate this notion.

Obduction is the collision of continents. And about 300 million years ago, we had the North American continent, we had the African/European continent, and the two of them collided. They ran into each other. And over time, as they kept pushing against each other, you had to give way. The one had to give way. Neither of them wanted to give way, but something had to happen. And so you've got shortening of the continent, and one of the ways they shortened is that the continent rumpled up like a rug.

This is still Africa here, and this is still North America on the left. They've shoved into each other, and they have rumpled up. But in the process of rumbling upwards-- I'll go to a different color here-- they've also rumpled downwards. Wherever you see a high spot like this, they also have a low spot underneath them. You squeeze them together, and in the process of squeezing them, you squeeze upwards, and you squeeze downwards. So I'm going to zoom in on that and show that in a little bit more detail.

This is a view of one mountain peak. And it has a deep root that might be three times as deep as the mountain is high. So even if the mountain is three miles high, then the roots might be 10 miles deep, or sometimes much deeper even than that. So it depends on the density contrast between crust and mantle. After the collision, you've now created a mountain, let's say 15,000 feet high. But at the same time, you've created this deep crustal root that goes deep down into the mantle, that is squeezed downwards at the same time that the crust has bulged upwards.

Over time, the collision ended, and so the mountain stopped growing. And in fact, erosion took over, and the mountain started to be scraped away. But the mountain isn't gone yet. Even though we've scraped away and scraped away and scraped away, we've kept eroding that mountain away, it's still there. After all this time, it's still there. And the reason for that is as you scrape material away, more material bobs up from underneath. And that's the principle of isostasy. That's what we're going to talk about next.

I'm going to switch back to the PowerPoint very briefly here, and then we'll come back to this picture drawing. As the mountains are eroded, they remain high because the material from below is floating up at the same time. It's like an iceberg floating in water. You probably have heard this expression, 9/10 of an iceberg is below water and only 1/10 is sticking up. And if you remember that movie The Titanic, with Kate Winslet and Leonardo DiCaprio or somebody. The two of them are on the Titanic, they're riding along, and it smashes into the great iceberg and disappears and all of that. It's because only a little bit of it is above water, and a big chunk of it is underwater. Ice is slightly less dense than water, and so it mostly sinks down into the water, but a little bit of it sticks up.

You can do this experiment for yourself. You can go home today, get yourself a glass of water, take an ice cube out of the freezer, and just drop it in. And if you look at it, you'll see most of it is underwater, and a little teeny bit will stick up above water. If you want to do it a slightly different way, you can go up to your bathtub, take a bath, put in lots of hot water, put in some bubbles, get your little rubber ducky out, and put your rubber ducky in. You'll see that the rubber ducky floats way up. A little bit of it underwater, a little bit of it above water.

That's the principle of isostasy. Different things that have different density contrast. An ice cube in water, a rubber ducky in water, a mountain in mantle, a crustal mountain in mantle. Each of these will float in the fluid. A little bit of it will be below water, and a little bit of it will be above water. And the amount that is below water and the amount that's above water depends on the density difference between them. Ice and water have almost the same density, so most of the iceberg or ice cube is below water, and a little bit of it sticks up above water, and the Titanic can run into it because you can't see it. So that's what we're going to talk about.

We're going to show you a picture of what this iceberg looks like. Before we do that, let me review a little bit about plate collisions. We saw in the first week, pull apart, that was Death Valley. Last time or two times ago, we saw subduction. Crater Lake, Mount St. Helens, all of those. We're seeing obduction this time, and we talked about slide past very briefly when we talked about the San Andreas Fault. In slide past tectonics, sometimes these two plates, when they're sliding past each other, they won't slide very smoothly. You'll have a kink in the boundary, and where these two are sliding past each other, you'll get these big mountains being built.

This goes along with the theme of all the action is at the boundaries. It's where the plates are running past each other, it's where the plates are running next to each other, it's where the plates are running into each other. That's where all the action is, that's where the mountains are being built. So we talked about obduction. We've built the Great Smoky Mountains, and we're going to come back to isostasy in a minute.

Let's briefly take a detour to slide past tectonics. If there's a kink where these two boundary plates are running past each other, once again, you'll have these great mountains being built. The San Gabriel Mountains near Los Angeles are a perfect example of that. The San Andreas Fault wants to go straight, but it's got a little kink in it and you get these big mountains being built. All of these are examples of isostasy. Where these mountains are built, you get these high mountains, and you get these deep roots underneath. Any time you've got a high mountain on a continent, you've got a deep root underneath it.

We're going to take a little detour here. If you remember, I told you when you see that little symbol up in the corner, that means we're running off the tracks and we're going to wander off and talk about something slightly different. During World War II, there was a proposal to build an aircraft carrier from an iceberg, because it would be unsinkable. The Germans could come along-- this was an Allied project, a US and British project. The Germans could come along with their submarines and fire their torpedoes at these aircraft carriers which is made out of an iceberg, and it wouldn't sink. It would just float. And this was an actual project. It would be unsinkable.

They thought big during War II, they really did. They were in a struggle for their lives, and for their way of life, and they would do whatever they needed to do to survive. And they came up with what now seems like a perfectly ridiculous idea, but it was actually taken forward quite a ways. It was called project Habakkuk, not quite sure why Habakkuk. There was a small one that was built on Lake Louise. As a glaciologist, I find it very interesting, things that people do with ice. But this was quite a visionary project that never went anywhere.

Back to the track. We're going to talk about the Rocky Mountains next. That's going to be another example of mountains built within a content. We've seen how obduction can create the Appalachian Mountains, how they will rise up high and they'll have deep roots. And as you scrape away the top of the mountain, the bottom will rise up to take its place, and so you've got to scrape away some more, and more and more has to come up. So that was obduction. You can also produce mountains at a kink in a slide past boundary.

So now, I think we've run into just about every type of mountain building mechanism. The last one that we're going to look at is one of the most unexplained, one of the most enigmatic. It's the Rocky Mountains, right in the middle of the continent. Why do we have these mountains way in the middle of the continent? That's what we're going to do next time.

Hi, welcome to GESCI 10, geology of the national parks. This is our section on building mountains, tectonics and building mountains. And we're gonna go to the Rocky Mountain National Park in the middle of the continental US, take a look at it. My name is Sridhar Arandakrishnan, and I'll be your guide through this part of it.

The Rocky Mountain National Parks are an absolutely stunning place. You have to go there. They are very near Denver. You can fly right into Denver, drive up to Boulder where the University of Colorado is. Some of my colleagues work there. And right there, the front range is of the Rocky Mountains and then this magnificent panorama of mountains stretching for thousands of miles, north 1,000 miles, north and south, and hundreds of miles to the east from there, and right to the west from there, and right up onto the Colorado plateau, all right. So it's just a beautiful place, a very dramatic setting. You come from the plains of Kansas and Colorado, and then you come along, and then here's this unbelievable mountain chain. It must have been quite something for those who first saw it.

On the map here, you're seeing a map of the western US. California is right off to the west, and then you have Nevada and Utah that make up the so-called Colorado plateau, Utah and western Colorado. And then right where that Colorado text is is the edge of the Rocky Mountains. That's where Rocky Mountain National Park is, off to the east of that.

It's all plains, very flat, lots of corn, soybeans, wheat. It is classic midwestern plains country. It's nothing like what people imagine Colorado to be. They think of, when they think of Colorado, they think of majestic mountains. Eastern Colorado is very flat. It's western Colorado that has those 12,000 foot mountains, 13,000, 14,000 foot mountains, Pike's Peak, all these amazing places, all right, so all the skiing. When you think of Colorado, most people think of skiing. Well, eastern Colorado doesn't have it. It's all in the west.

We can zoom in a little bit. And you can see the transition from Denver there in the middle. And everything to the east of Denver is all plains country. It's all flat. And you can see as you go to the west from there you get those dendritic valley patterns, those white snow capped peaks, all of the complications that always go along with mountains, you get all of these little mountain valleys with little rivers and glaciers in them.

Rocky Mountain National Park itself is right here in the front ranges. And you can see the transition there even more dramatically up into the Rocky Mountains, all of the snow covered peaks, right. So this is where we're gonna take a trip to. Let's go look at some real pictures rather than looking at satellite maps. It's a place that's easy to get to and well worth the visit.

Lots of fauna there, lots of critters, birds and mammals of many different kinds, you still have wolves up in there, still have bears up in there, lots of elk and bighorn sheep, very common, all over the place. Obviously, it's a national park so hunting is forbidden. And so it's still in very much pristine condition. It is a very popular place, you drive up in there, going to the mountain, going to the Sun Road is one of the roads that goes through there. It's one of the highest roads in the lower 48. It's up at 12,000 feet. And sometimes it's just this solid mass of RVs, and campers, and pickup trucks, and SUVs stretching as far as the eye can see.

Just pull off the road, just park, get out your car, and walk in any direction. And you walk for 10 minutes and I guarantee 90% of the people will disappear, walk for another 10 minutes and 99% of the people disappear. So few people actually get out of their cars and walk, and I don't want you to be one of them. I want you to get out and walk and walk for just a little ways, just for half an hour, 45 minutes, to experience the solitude and the majesty of Rocky Mountain National Park.

All right, here it is, here's one of these Rocky Mountains. And in the foreground you have a glacially carved lake. When the glaciers came down out of the mountains 20,000 years ago they would have covered this whole area. They would have ripped up this area and pulled up this lake, pulled up this big hole. And then when the glaciers retreated water filled in that area. Now we have these lakes. There's a whole series of lakes up, wherever you have glaciers you usually have lakes that they leave behind. Glaciers are really good at digging deep holes. And this is one of them. Here's another picture of [? Usal ?] Lake and looking up at this glacial valley behind it, really a magnificent place.

This is up on top of Flat Top Mountain. You have this classic alpine landscape, this short scrubby bushes, very hardy little shrubs that manage to eke out a living in the permafrost, in the high winds and the cold. The weather can change really dramatically. You start out in the morning, and you have blue sky, and it's 70 degrees, and you get up there then you need a jacket because the storm clouds have come up, as they have in this case.

This is looking down at a little tarn. Tarn is a Scottish word, I think, I'm not sure, for small mountain lake, usually glacial carved lake. These tarns can be just a few hundred feet across. And they have lovely cold water surrounded by all of that glacial moraine material around them, a few trees but not many.

This is a road that runs, a very popular road, that runs up. There's Beaver Ponds there in the lower part of it, and then behind it a moraine, that little ridge that you can see with a little bit of a brown material on it and then some trees on top. That's a moraine. That's what was left behind by a glacier. A glacier came down, pushed up this material and left that. And we'll talk about moraines next time, or not next time but down the road.

Here's an alluvial fan. This is material that's brought down by rivers and sometimes landslides, just comes down these mountain sides, lots and lots of flora, lots and lots of fauna. So I said, all of these pictures are available online on Angel. Go and take a look at these virtual field trips, orchids, and the classic Rocky Mountain rock, this sort of grayish colored, dark gray and light gray colored rocks, metamorphic rocks cut through with igneous rocks. We'll talk about what a metamorphic rock is, what an igneous rock is over the course of this class. All right, so, let's hop over to the presentation and we'll begin our talk.

The Rocky Mountain National Parks, Rocky Mountains are a mountain range. They're quite high, 12,000, 13,000 feet high. But they're in the middle of the continent. They're 1,500 miles from the ocean. Why are they there? We talked about why the Appalachians are here. They're the collision of North America with Africa and Asia 300 million years ago. They created these high mountains. All right, that's straightforward.

We talked about why Mount St. Helen's is there, or why Mount Baker is there, or why Lassen Peak, or all of those. Those were subduction zone volcanoes. The Cascade range is a volcanic arc created when oceanic crust subducted under continental crust. The question is what's on with the Rocky Mountains? Why are they where they are?

Normally, and the short answer is, normally oceanic crust will simply subduct under continental crust. If it's dense enough and cold enough it'll just go straight down and all is well. You will get the classic subduction zone situation that we now have in the Pacific Northwest. You'll get trenches and volcanoes. Occasionally, if that subducting oceanic crust is hot enough, if it was only created recently in the last half a million years or million years, it hasn't had a chance to cool off, then it's still buoyant.

Remember hot rocks are buoyant and low density. It's only when they get cold that they want to sink. So if that oceanic crust was still hot, buoyant, low density, it would go under the continent, but it wouldn't subduct straight down. And as it got pushed off to the side it would continue to scrape underneath. And I'll show you a picture of it here in a minute, but that's, in words, that's what was going on.

I grew up in New York City, and this next cartoon perfectly encapsulates my ignorance of this country as I was growing up. This is a very famous New Yorker cover called New Yorkers View of America. And you have Ninth Avenue, 10th Avenue, all of the buildings in great detail. You have the Hudson River. They might know a little bit about New Jersey. But then the rest of the continent is just this vast blank space. And it might be, you might know, oh, there's a few mountains somewhere in the middle, and there's something off on the other coast, and then there's the Pacific Ocean. So this is a famous picture of what New Yorkers think of the rest of the country.

And to be honest I have to plead guilty to that. And I was in college, I went to school in New York City, I had a friend who had an internship, a summer internship, in Denver. And I had another friend who had a summer internship in San Francisco. And the two of them are flying out, and on the last evening as they were ready to go, I said, oh, boy, you guys are lucky. The two of you will be able to visit each other on the weekends, and I'm gonna be left here all by myself in New York City. Little did I realize that San Francisco and Denver are 1,500 miles apart. And so my ignorance was stunning back then. Hopefully I know a little bit more now but there it is.

This is our picture of how the Rocky Mountains were made. We think this is what went on with them. This is an animation that's available for you online. But the short answer is that an oceanic ridge, one of these mid-ocean ridges where material is coming up from deep inside the Earth, used to be far offshore but was subducted under North America.

But because it was so close to the edge of the continent, it's still warm. And because it was still warm, it didn't sink down. And because it didn't sink down, as it scraped along underneath the western US, it shoved up the Rockies way, way far inland, all right. So even though subduction is supposed to sink down and only produce mountains at the coast as we have in the Cascades, in this case, because that subducting slab was still warm, it went along for a long ways underneath the continent shoving up the Rocky Mountains far in the interior until eventually it got cool enough, and it did sink down far deep inside. This is the leading idea for why the Rocky Mountains are where they are and how they were formed.

We don't really know. It's a little bit embarrassing to say this, but geologists have a pretty iffy understanding of the Rocky Mountains. But this is the leading idea. This is how science works. We come up with a hypothesis, somebody did, they said we think this is what's going on, all the evidence seems to support it. But people are still working hard to try and figure out whether that hypothesis meets all the data, or if somebody can come find some new data that shall know that hypothesis is wrong, in which case we'll throw this slide out, and we'll put in a new slide.

That's the wonderful thing about science is none of these slides are ever carved in stone, if you will. At any time I could just delete this slide and throw it away because somebody comes up and says, nope, I think that's wrong. So as this warm oceanic crust was subducted and slid right underneath North America long deep, deep under the continent, it shoved up the Rocky Mountains even though they're far, far inland. Whoops, sorry, going the wrong way.

The Rocky Mountains are made up of something called metamorphic rock. Metamorphic rocks are rocks that have changed from their original form. There are three main types of rocks, sedimentary rocks, which are rocks that are formed when sediments collect and over time those sediments pile up and get cemented together into a more solid mass. Sandstones, limestones, these are all sedimentary rocks, all right. Igneous rocks are another relatively straightforward type of rock. This is when you have molten material that comes up and freezes at the surface of the Earth and produces an igneous rock. These are made in volcanic zones. They are basically frozen lava and various frozen magma, very straightforward as well, all right.

Metamorphic rocks are the complicated ones. If you take any kind of rock, a sedimentary rock or an igneous rock or another metamorphic rock, and you squeeze it hard enough and you heat it long enough, it'll change its form and turn into a different kind of rock called a metamorphic rock. And where in the world can we find high pressures and high heat, deep inside the Earth, all right. That's the only place that you can get pressures and heat high enough to cook these rocks and to turn them into metamorphic rocks. So whenever you see a metamorphic rock, as we do in the Rocky Mountains and in a few places in the Appalachians, we know that those rocks, at one time, were deep down inside the planet.

[UNINTELLIGIBLE PHRASE]. See, I told you, you gotta have one mess up somewhere, right? There we go. You better cut this Eric. I'll give you money. How's that? Keep rolling.

Whenever we see metamorphic rocks up at the surface then we know that those rocks, at one time, were deep inside the Earth, that some kind of rock, either sedimentary rock or an igneous rock, was carried deep down into the planet, down to miles and miles, maybe tens of miles down into the Earth. And as those depths the heat is high enough and the pressures are high enough that the rocks can be cooked and squeezed until they are a different form called metamorphic rocks. And then they come back up to the surface.

Here's some pictures of these metamorphic rocks. Unlike igneous rocks, which are more even looking, are more regular in their form, these, as you can see, have all of these grains that are growing in them. They've been folded and twisted around because of the huge pressures that squeeze them together and the high temperatures. They can be right overturned and squeezed out like toothpaste, as you've seen, as you can see in the lower one over here.

This, by contrast, are two pictures of igneous rock. And the site we've talked about, and the site quite a bit, those are the rocks that come up in the Andes mountains, and also in Mount St. Helen's, and all of these other subduction zone volcanoes. Pele's hair is a type of igneous rock that you find in Hawaii, where you have the hot spot type of volcanism, very different looking than and very different chemically than metamorphic rocks.

So why are these metamorphic rocks at the surface? As I said the only way to form these rocks is deep inside the Earth. You got to take them, sink them down miles into the Earth where the heat is high, where the pressures are high, you cook them and squeeze them and they turn into metamorphic rocks. So what are they doing up at the surface? In fact, what are they doing up at 12,000 feet up in the Rocky Mountains? How'd they get way up there? And that has to do with isostasy, deeper rocks rise up because of isostasy. So, we're gonna go to the drawing board here and take a look at isostasy again.

Remember what isostasy was, this is a cross section of a mountain. So this is trees here, and this is the very top of the mountain. If you were standing at the top of the mountain, and you were to start to drill a hole down through it, you would go part of the way down and you would be at what's the equivalent of the surface of the Earth. But you wouldn't be to the bottom of the continental crust. The continental crust continues on under there. And, in fact, it continues way, way down into these deep roots, all right. So all of these mountains that stick up high have these deep continental roots underneath them because of the requirement of isostasy.

You have to have the same mass of material above you at any point to have equal pressures. So if you imagine a line somewhere deep down in here, the amount of weight above you is the same anywhere along that red line. That's the principal of isostasy. If you're over here the amount of weight above you is the same as if you were in the middle of the continental crust over there. But because continental material is less dense, crustal material is less dense than mantle material, you need more of it. Remember that.

If you want to have the same weight of two things but one is more dense and one is last dense, then you need more of that less dense material. You need more volume of it to get the same weight, all right. And that's what these roots and this mountain above allow you to have, is you have the same weight above you but because the continental crust is less dense you have to have more of it, which means you need a mountain rising up and the roots going down. So that's the principal of isostasy. It's a little bit subtle, but I encourage you to go and read the section in the book on this because it's an important notion.

But let's see what happens as we erode this mountain. Imagine, if you will, a metamorphic rock that has been formed inside this continental root. This black blob here represents the metamorphic rock. And we have to somehow bring that to the surface. How do we do that? The way we're gonna do it is we're gonna do it by analogy. We're gonna go and look at an iceberg. An iceberg is very much like a mountain and a mountain root. And there is an animation online that represents this, and I'll just do it very briefly here, and then we'll understand how it is that you can bring up this metamorphic rock to the surface.

Imagine, if you will, an ocean and floating in that ocean you have an iceberg. Ice should be white. It's a little hard for me to draw a white iceberg against a white paper here. So we're gonna make it black. The blue, obviously, represents the ocean. Blue is always ocean. So here we have our iceberg floating in the ocean. Because of isostasy a little bit of it, some of it, is above the ocean, about 1/10, and most of it is under the ocean, about 9/10 of it. OK?

That's because water and ice have almost the same density. So, if I need to have the same weight of material above me, I only need a little bit extra ice. I can go over here. I can draw my same line that I did before. I can go here. I can figure out the weight of water above me. I can go to the same point in the iceberg, and I gotta have the same weight of stuff above me. That's the principal of isostasy. And I only need a little bit extra ice, but I do need that extra ice. And so I need about 1/10 more ice because the density of ice is only a little bit less than the density of water. And so I need a little bit more ice to get the same weight, the same total weight, of stuff above me, OK. So that's isostasy once again.

But let's see how this helps us with bringing metamorphic rocks to the surface. Same picture, ocean, iceberg, but this time, for the sake of argument, I'm going to introduce a space alien into this. We're going to take a space alien, and imagine that a long time ago a space alien crashed into Antarctica and got trapped in this iceberg, and more snow fell on it and more snow and more snow, and eventually somewhere down deep inside this iceberg we have a space alien, big eyes, antenna, stuck inside this iceberg. How can we get the space alien out? Well, it's gonna happen naturally anyway. Why? Because as the top of the iceberg melts the iceberg has to bob up to replace it, all right.

Let's follow that through. Let's do a little thought experiment. Let's say I could magically take everything that's above water and simply slice it off and cart it away, all right. So we're gonna just take everything above water and slice it off and cart it away. And this is what we would be left with. And the space alien would be stuck down in here, same as before. Nothing's changed except that because of isostasy this is unstable.

That iceberg will want to naturally bob up. It has to. Because at any given depth the weight has to be the same above that spot. And in this situation the weight here is more than the weight here, all right. Water is more dense than ice. And so if you'll have the same amount of water and ice then the ice has less total weight. And so what happens next is that the iceberg bobs up in the water a little bit. Remember what we did is we just sliced off magically everything above water. Iceberg bobs up, and the space alien who is embedded in here also bobs up with that.

Let's do it again. Let's once again slice off everything that's above water. I'm gonna erase this ocean. And, once again, we slice off everything above water, and the iceberg would bob up again like this, and the space alien would now be at the surface. I hope you understand that that's an analogy. They don't really have space aliens in the Antarctica ice although according to The X Files we do. That was a terrible movie by the way. But nevertheless it did posit the presence of space aliens in the Antarctic ice.

What we do however have is that the Rocky Mountains have blobs of metamorphic rock deep inside them. And erosion slices off the top. So erosion comes along, and erosion removes the top of the mountain. And in the same way that the iceberg popped up, the roots of the Rocky Mountains also pop up. So after erosion removes the top you end up with the Rocky Mountains rising up again and the metamorphic rock along with them.

The mountains as a whole are smaller, but the metamorphic rock is at the surface or nearer to the surface. So in much the same way that glaciers can bring up these supposed space aliens with them, metamorphic rocks come up. The idea of the metamorphic rocks is a little bit more well supported than that of the space aliens, all right. We're gonna hop back to the PowerPoint here for a second, and then we'll wrap up this session.

The rocks cycle is something that is fundamental to geology. All of the rocks on the surface of the planet have been cycled and recycled and brought up. And erosion will take sedimentary rocks, and it will produce sediment which will turn into sedimentary rocks. And then subduction will carry that down. And then that rock will come back up again either as an igneous rock or as a metamorphic rock. And then it will get eroded again and produce sedimentary rock. And so this whole rock cycle says that we're always recycling all of our material on the surface. And we have to work out their history by coming up with these clever ideas and these hypotheses.

To summarize, there are three types of rocks, igneous rock formed by melting and solidification of magma, sedimentary rocks formed by erosion of other rocks and then cementing them together, and finally metamorphic rocks formed by the cooking of rocks, all right. So that's the end of this part of tectonics. We've learned about building mountains, about how you can build them at pull apart boundaries, at pushed together boundaries, and at slide past boundaries. Next time we'll move on to new material.

[MUSIC PLAYING] PROFESSOR RICHARD ALLEY: (SINGING) I came out from the Eastlands, and so no-one made a slip. I showed 'em my intentions with a Brunton on my hip. I came out to where the mountains, cliffs, and mesas tower tall, to read the planet's story written on the hanging wall, on the hanging wall.

[MUSIC PLAYING]

I was hungry, young, and foolish when I started on my quest. But with a hammer, and a field book, and a map that pointed west, I left behind the ridges that the rivers rounded small to learn the truth or perish here hung from the hanging wall, from the hanging wall.

100 million years ago beneath Pacific brine, the Farallon was sinking down subducting smooth and fine 'til the slab of thickened sea floor tried to squeeze through spaces small. And the squeeze is on the westlands that would make the hanging wall, make the hanging wall. Severe Sevier orogeny, a thin-skinned thrusting belt, as the friction of the buoyant, thickened ocean plate was felt. It broke the rocks and thrust from westward raising mountains tall. Older rocks thrust over young to make the hanging wall, make the hanging wall.

[MUSIC PLAYING]

As the thickened crust moved eastward, and then turned to sink anew, the Laramide Orogeny raised domes and arches too. The Black Hills, Water Pocket, and the Kaibab as well, Wind Rivers and Uintas and the great San Rafael Swell, great San Rafael Swell.

From mountains rising in the west, a heavy load was shed, and now basal conglomerate records that river bed. But fining up and liming up soon gave us what it takes to wash the West's interior, Bryce and Green River Lakes, Bryce, Green River Lakes. But the spreading ridge, it hit the trench to make a slab window, a growing space that filled in with a hot, upwelling flow. The squeeze relaxed, the mountains spread, and though it may seem strange, new hanging walls dropped downward, normal faults, basin and range, normal faults, basin and range.

Volcanoes leaked up some new faults, but in other outcrops clear. In the footwalls of young normal faults, old thrust faults now appear. I can read the mighty story and it leaves me feeling small. I lift the map another day safe from the hanging wall, from the hanging wall.

I'm older now and wiser as I head back from my trek. But I won't die with a hempen rope around a stretched-out neck. There's still more to learn tomorrow as it holds me in it's thrall. I'll be back to read what else is written on hanging wall, on the hanging wall. Hanging wall, hanging wall, I'll be back to read what else is written on the hanging wall.

[MUSIC PLAYING] RICHARD ALLEY: (SINGING) I like the way your folded mountains lay, waving smoothly across the land. I want to hike across your thrust faults today, with your ancient rocks on either hand. I get a peaceful, easy feeling, where so much history is shown, while I'm living, and I'm loving in your old obduction zone.

Photo-Atlantic slowly closed long ago, Old World drawing near the New. Subduction zones fed many a volcano, island arcs eruptions blew. See their ashes in your roadcuts, while small collisions sent down sand. And the mighty obduction was drawing close at hand.

I found out a long time ago, continents cannot sink down. But in collisions, they will fold and break. So they make deep roots and a mountain crown. Your roots were heated, metamorphic, while glaciers carved the peaks you'd grown. The Himalaya became the Smokies of your old obduction zone.

hen as the rivers washed the heights away, rocks down deep bobbed up to light. So I can feel them on your ridges today, and hold them in your valleys tonight, because I get a peaceful, easy feeling, so many secrets ours alone, while I'm living, and I'm loving in your old obduction zone.

[MUSIC PLAYING]

Image 1: Sunrise over the Badlands. A first look at breaking rocks to make sediment, and transporting that sediment to make beautiful and informative places.

Image 2: Children sitting on jackalope statue at Wall Drug tourist area in Badlands. Most folks who drive to the Badlands are enticed by the seemingly endless signs for a particularly well-known tourist trap, shown here.

Image 3: Badlands rock landscape. The badlands are muds and sand beds put down by ancient rivers draining the Rockies, together with volcanic ashes blown in on the wind. All of these materials were made by the breakdown of older rocks in the Rockies.

Image 4: Badlands clay landscape. The clays of Badlands soils expand and contract as they wet and dry, tearing out plant roots. Flat areas maintain vegetation, but steep areas are mostly bare sediment.

Image 5: Large weathered rocks in Badlands. Breakdown of rocks to make smaller pieces and new types such as clay minerals is called weathering. Movement of these smaller pieces is called transport. Together, weathering and transport make erosion.

Image 6: Tree roots in Bryce Canyon exposed by soil erosion. Finding evidence of erosion is not hard. This tree, on the rim of Bryce Canyon, started with its roots covered by soil, but the soil has eroded away. The very soft, steep rocks here have eroded by more than a foot in the few decades of this tree’s life.

Image 7: Ancestral Puebloan rock carving showing surface flaking. Arrow points to half-spiral. Petrified Forest National Park. Ancestral Puebloan people carved this rock in Petrified Forest National Park almost a millennium ago. A little of the rock surface has flaked off since then; the artists did not carve a half-spiral on the left (arrow added).

Image 8: Ancestral Puebloan rock carving damaged by fall of rock. Petrified Forest National Park. As in the previous picture, the thousand-year-old artwork of Ancestral Puebloan people has been damaged a little by fall of rock, showing that rocks do change, but slowly.

Image 9: Rock split in two as a result of frost grown in crack. Coast of Greenland. And in a very different environment, in the remoteness of the coast of Greenland, frost growth in a crack has split this rock in two. The rock is in the deposits from about 1850, and most of its surrounding rocks have not been split, giving some insight to the rate of weathering.

Image 1: Two contrasting photos. Top photo of Redwoods, bottom photo of Death Valley. A Contrast in Weather… Redwoods and Death Valley. Some pretty pictures by R. Alley, with a message at the end.

Image 2: Close-up of Sequoia trees in Redwood National Park. Redwood National Park is another of the parks established primarily for biological reasons. Sequoia sempervirens, the ever-living sequoia, will live for two millennia, and then sprout new trees from its fallen trunk.

Image 3: Redwood forest, with ferns, rhododendron and azaleas in the understory. The redwood forest, with ferns, rhododendron and azaleas in the understory, look like a magnified version of an eastern hemlock forest.

Image 4: Rhododendron in Redwoods. The acids in redwood needles help produce soils that favor rhododendron (shown here) and ferns, as well as more redwoods.

Image 5: Sequoia tree standing more than 370 feet tall. Reaching heights of more than 370 feet (well more than a football-field standing on end), the redwoods are the world’s tallest trees.

Image 6: Ocean view at the Redwood coast. The redwood coast is rainy and foggy; the huge trees couldn’t exist in a drier environment. The coast is also beautiful.

Image 7: Giant Sequoias representative of those found in Yosemite, Kings Canyon and Sequoia National Parks. Up the mountains from the redwoods are the giant sequoias of Yosemite, Kings Canyon and Sequoia National Parks. Although not as tall as the redwoods, these trees are more massive--generally considered the largest living things on Earth--and live more than a millennium longer.

Image 8: Close-up of man standing next to Sequoia tree, showing thick bark. The thick bark of the sequoias is nearly fireproof. The trees need fire to clear out faster-growing trees so young sequoias have room to grow, and to trigger sprouting of those young sequoias.

Image 9: Death Valley landscape. At about the same latitude as the sequoias and redwoods, and with the same sunshine above the clouds, is Death Valley and the rest of the Great Basin. This huge weather difference is discussed in the textbook--Death Valley is warmed by tropical sunshine, set loose by redwoods rain.

Image 10: Topographical map showing Coast Redwood range with arrow pointing to Death Valley behind the mountain range. Link: http://data2.itc.nps.gov/hafe/hfc/carto-detail.cfm?Alpha=REDW# At about the same latitude as the sequoias and redwoods, and with the same sunshine above the clouds, is Death Valley and the rest of the Great Basin. This huge weather difference is discussed in the textbook--Death Valley is warmed by tropical sunshine, set loose by redwoods rain.

Image 1: Two contrasting images: Top photo of Grand Tetons. Bottom photo of Gros Ventre slide. (Top) The Grand Tetons--Surely one of the finest views in the west (Bottom) And the Gros Ventre slide--A reminder that the west is ever-changing.

Image 2: The Grand Tetons with evergreens in the foreground. The Grand Tetons. This is real mountain scenery.

Image 3: Close-up of Grand Tetons showing pull-apart-type faulting. Pull-apart-type faulting has dropped the valley and raised the mountains a total of several miles.

Image 4: Close-up of Grand Teton peaks with dark thunder clouds above. Rockfalls are common, especially during intense summer thunderstorms.

Image 5: Mount Moran with Darn Yellow Composites (wildflowers) in foreground. Mount Moran is framed by summer wildflowers (DYCs, or darn yellow composites, because yellow composites are often so hard to identify accurately).

Image 6: Oxbow Bend with view of Mt. Moran and other Tetons in the background. Oxbow Bend is a favorite site for viewing Mt. Moran and the rest of the Tetons.

Image 7: Grand Tetons with lake in the forefront. Numerous lakes, many glacier-carved, dot the park.

Image 8: Gros Ventre slide, near the Grand Tetons. Historical photograph of the Gros Ventre slide, near the Grand Tetons.

Image 9: Cross-section drawings of before Gros Ventre slide, after the slide, and after dam is breached.

Image 10: Valley cross-section drawing showing geological setting of the Gros ventre slide. Valley cross-section showing geological setting of the Gros Ventre slide.

Image 11: Historical photo of lower slide lake shows a person standing on the roof of a submerged building. Historical photo of lower slide lake. Catastrophic drainage of the slide-dammed lake destroyed the town of Kelly, killing six and destroying the hotel, mercantile store, automobile garage, blacksmith shop, livery stable, and homes, but sparing the Episcopal Church and local school.

Image 1: Drawings labeled A through J representing 10 types of mass movements. http://pubs.usgs.gov/fs/2004/3072/images/Fig3grouping-2LG.jpg. There are many types of mass movements, ranging from hundreds of miles per hour to less than an inch per year, and from whole mountains to single grains of sand.

Image 2: Slide Mountain, Nevada. House buried beneath slide, only roof above surface. http://landslides.usgs.gov/html_files/landslides/slides/slide2.htm. Slide Mountain, Nevada. Snowmelt-triggered debris flow, May, 1983, killed one and injured several. USGS had publicly identified the hazard a decade earlier, but good science is often ignored.

Image 3: A car in the mud of a 1994 landslide near McClure Pass, Colorado. http://landslides.usgs.gov/html_files/landslides/slides/slide11.htm Photograph by Terry Taylor, Colorado State Patrol. Landslide near McClure Pass, Colorado, 1994. The driver did not see this nighttime slide in time to stop, but fortunately was not injured

Image 4: 1995 Landslide under the only road to lodge of Zion National Park. http://landslides.usgs.gov/html_files/landslides/slides/slide19.htm. Photograph by R.L. Schuster, USGS Landslide under the only road to lodge of Zion National Park, April, 1995, stranded 100 people for two days. The broken sewer pipe, shown in lower part of photo, didn’t help.

Image 5: Aerial view of 1995 landslide at La Conchita, California along highway 101. http://landslides.usgs.gov/html_files/landslides/slides/slide21.htm. Photo by R.L. Schuster, U.S. Geological Survey. Spring, 1995 landslide at La Conchita, California, south of Santa Barbara along highway 101. Many homes were destroyed, but no one was injured.

Image 6: Home crumbled and destroyed by La Conchita, California slide. http://landslides.usgs.gov/html_files/landslides/slides/slide24.htm Photograph by R.L. Schuster, U.S. Geological Survey Home destroyed by La Conchita, California slide from previous picture.

Image 7: 1981 Winter Park, Florida sink hole opening. Car, truck and destroyed building in the sink hole. Caption: http://landslides.usgs.gov/html_files/landslides/slides/slide10.htm This is the Winter Park, Florida sinkhole, which opened in one day in 1981. We’ll return to sinkholes when we visit caves, which occur with sinkholes.

Image 8: Half-mile-high landslide scar, Tracy Arm/Ford’s-Terror Wilderness Area, Alaska. Caption: Half-mile-high landslide scar, Tracy Arm/Ford’s-Terror Wilderness Area, Alaska. Steep slopes caused by mountain building or rapid erosion (in this case, by glaciers) often fail catastrophically. A slide similar to this made the immense tsunami in nearby Lituya Bay that we discussed last week. Photo by R. Alley

Image 9: Landslide near Sitka, Alaska. Caption: Most landslides don’t make the news, such as this one near Sitka, Alaska. Photo by R. Alley.

Image 10: Numerous landslides on the mile-high, glacially carved cliffs in Milford Sound, New Zealand. Caption: Milford Sound, New Zealand. The numerous landslides down the mile-high, glacially carved cliffs give it the pretty, striped appearance. Photo by R. Alley.

So out here there's the great Pacific Ocean. And the wind comes trucking in from the Pacific Ocean. And it's just going great guns, except at some point it runs into the giant mountain range of the Sierra, which we know goes up over the top and down the other side and down to Death Valley.

And so when the air runs into that, the air has to rise. And you may know that when air has to rise, it expands. And when you have air expanding, whether it be out here on the Pacific or from a bicycle tire, it cools. And when the air cools, that makes nice clouds. And when that makes clouds, that makes rain that comes dripping down. And so sitting underneath that, as you might imagine, you have really wonderful trees called the Redwoods because it rains like crazy on them. And they're really happy with that.

Now the air is cooling, and the cooling rate is something vaguely about three degrees Fahrenheit for each 1,000 feet that the air goes up. It should be five, five is the thermodynamics. But when the cooling causes condensation that makes the rain that we see, condensing actually gives up a little heat. And so you only get a cooling of about three degrees Fahrenheit per 1,000 feet going up.

Now, when the air comes over the top and starts coming down the other side, there's no water in it to evaporate. There's no water there, it's dry. And when air is coming down like that and being squeezed, it ends up warming. And that warming is about five degrees Fahrenheit per 1,000 feet that it comes down.

And so it cools going up at about three degrees Fahrenheit per 1,000 feet. It warms coming down five degrees Fahrenheit per 1,000 feet. And that in turn means that because the mountains are really high, that if the air comes trucking in at something like 70 degrees Fahrenheit, by the time it goes over 15,000 foot high, it's almost 15,000 feet to the top of the Sierra, and the air has to get over, why when it comes back down here to Death Valley, it is 100 degrees Fahrenheit. And you really would be wiser to go visit in the winter rather than in the summer.

Hi, I'm standing here up at the top of Bryce Canyon. And right over here we have a great example of how quickly erosion takes place here. As you can see, the roots of this tree are exposed. And this tree is only about 100 years old, but it looks like it's trying to jump out of the ground. And that's because of the ground that was up here has been washed down the canyon exposing the tree's roots. Luckily for this tree, the roots go very deep into the ground to get all the moisture it can. And that's why it's still able to surviv.

Hey Sridhar, look here.

What's going on there?

The chain that we are using to climb up the hillside here in Zion is actually causing some mechanical weathering. And you can see how everybody that grabs on to the chain as it goes up--

Ah, cool. Check it out.

It carves into here. It actually carves into the sandstone.

It's made these little scallop marks where the chains that are turned in this way go in a little bit deeper. And the chains that are out that way are back a little bit farther.

Yep. It would be just like a rock in a stream or even a glacier pushing stuff along. It's just scooping things up at a constant pressure along the side of the rock.

And so this stuff is actually fairly friable. It breaks apart reasonably easily. This chain's probably only been here 10, 15 years. And already it's cut in, what 1/25 of an inch, an 1/8 of an inch, something like that.

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So the water came along this way and carved out those holes coming around the bend. And then as it started to make the corner, it came down and it swirled around in these big holes. Probably, you can even see down there, there's some pebbles stuck in there and gravel size bits. And in a big flood, it would carry those size rocks and larger, bring them down.

And it's just like my grandmother grinding rice to make dosas and idlis which are these magnificent South Indian dishes, where you take rice, you put them down in a mortar and a pestle, and you just grind them around, add a little bit of water, grind them around. And you get this wonderful flour that comes out of it. That's the exact same thing happening here.

The water comes pounding down, carrying rocks, and it swirls them around because it's making the turn. And it's going fast enough that as it makes a turn it can't just go straight, it's got to curve around. It's just beautiful, it's magnificent. And we can even see some of the rocks left down in there from the last time we have a flood coming through here.

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If you make a canyon, and you deepen that canyon, the sides fall in. And one can see the sides avalanching in there merrily, eating back over time. See waves of adjustment going on. It's really beautiful to see.

I steepen it, and it steepens at the bottom. And then it eats its way back, and then it eats back at the head, eventually. Well, that's exactly what's going on here.

And so we can see across the river. The river is cut down. And then above it, there's that slope of rocks that have fallen off of the cliff. And as the river cuts down, that slope will be lowered and rocks will fall off of it and come avalanching down in exactly the same way as what we're seeing going on here in a very small scale. And you'd see all these little waves and nick points, and there are quite a number of very exciting things going on here.

Good morning. Welcome to GSCI 10, Geology of the National Parks. Now for the next two or three classes, we're going to be looking at how we tear down mountains. For the first part of this class, for the last four lectures, we've been building these mountains.

And just to do a real quick recap, if you remember, it's all driven by heat inside the earth. And where does that heat come from? From radioactive decay. All right, so radioactive decay inside the earth drives the heating or produces the heat, which then drives these convection cycles inside the asthenosphere. So the hot rocks rise up, get to the surface, cool off, sink back down again. And these big cycles go on inside the asthenosphere.

Up at the surface, in the lithosphere, that's broken up into 8 or 10 lithospheric plates. And those plates move around on top of the convection cells. When they move around, they interact with each other because the surface of the earth is a finite space. And so when one plate moves, it's got to do something relative to another plate. It's either moving away from another plate, or it's moving towards another plate, or it's moving parallel to another plate.

Most of the action of building mountains goes on at those places, where the plates are moving apart, like Death Valley. Where the plates are coming together, like here in the Appalachians, like the Himalayan Mountains in India and Tibet. Like the Pacific Northwest, where the subduction zones are producing those beautiful volcanoes and mountains. Like the San Gabriel mountains in Los Angeles where there the plates are sliding past each other, but because of that small kink in the San Andreas fault, we get mountains being built over there.

All right, so all the action is at these plate boundaries, 30 second review of the last four sections.

Now we're going to take the next step. We've built these mountains. They're sitting out there. We know they're not static. We know they're not just sitting there and nothing happening to them. We know that they change. We know they erode over time. They get torn down. They get lowered further and further down.

We actually saw hints of that when we were talking about how the Appalachian Mountains used to be much higher and now they're much lower. They're not as low as they could be because of isostasy, because they're being floated up by these deep roots. Like that iceberg, if you remember that cartoon, the iceberg and the alien embedded in it, and that alien slowly rose up from within the iceberg.

So, we got a little bit of a hint of this when we talked about how the Appalachians were lowered down, how the tops of them were chopped off. That's what we're going to spend the next few minutes talking about, is how that chopping off process goes on.

Here we are in the badlands. Badlands in the Dakotas are a really beautiful place, but there's a reason they're called the badlands. Not very much grows there, except jackalopes. There's a lot of tourist trade through there because that's all they can do. They have a very hard time growing crops. It's one of the poorest parts of the country. The Pine Ridge Indian Reservation that's near here is the poorest county in the country.

Nevertheless, it is a dramatic place. All of these lovely gullies, and beautiful, stark moonscape-like surfaces, they're lovely for us to look at as tourists, not so nice for the people that live there.

Most of the rocks that you see here are sediments that have been washed down from the ancestral Rocky Mountains. The Dakotas are far away from Colorado, and Wyoming, and Montana, but nevertheless, transport of this material can take place over long, long distances. Mix in some volcanic ashes from, for example, the big Yellowstone volcano and you have the soil of the badlands.

Here's another picture of it. It's a very clean, rich soil. And so, as these soils get wet and dry, they expand and contract. And the trees and plants have a really hard time living in that kind of environment. Their roots get ripped up and torn to pieces. The water comes along and washes off the surface layer or cuts these deep gullies. It's a hard place to make a living.

And if you don't have plants, if you don't have grasslands, or you have very minimal grasslands, this is another shot showing some of the lovely landscape, then there aren't that many animals there. And so eventually, it's hard for people to make a living there as well.

Here's an example of erosion. This tree didn't grow that way to begin with. Those roots were deep inside the soil, but the soil got washed away from around them. You can see to the left of that tree there's that deep gully. And as the rains come along, that soil gets washed off and carried down in there.

This is really commonsense stuff. You've seen it. You've seen it in your backyard. It has enormous implications. If you can do it for year after year, after year, after year for millions of years, then you can even take a huge mountain like the ancestral Appalachians or the Rocky Mountains, and you can tear them down to nothing.

Here's an example of the rate at which this goes on. This as a carving that the ancestral Pueblo people did on rock varnish in the desert. This black glaze gets on to these surfaces in the desert where it's really dry. And the ancestral Pueblo people would go and make these carvings in it.

And what you can see in the corner over there is where one of those designs, that spiral design, has broken off. This ancient artist didn't come along and simply end his design at the edge of his canvas, his design continued on to the left and there was probably even more to the left of that. But it broke off, and that front part fell down.

And so that is weathering. The rate of it is slow. This design is from perhaps 1,000 or 2,000 years ago. And you can see some of it is still there and a very little bit of it has torn away. Here's another example of that same thing. At the lower end, you have some designs of animals, some deer and perhaps horses. And those are being torn down.

Here's an example from far afield, from Greenland. This is a rock that has been split open by one of the most powerful processes known on earth for erosion, a simple act of freezing. You take water, you put it into something, you let it freeze, it expands, and it will crack open just about anything. It'll crack open that rock.

It'll certainly crack open your water bottle. Your mom told you when you were a kid, fill up that water bottle and put in the freezer. You didn't fill it right to the top. Because if you filled it right to the top, when the water froze, it would crack that water bottle open. So, you know that.

And the same thing happened here. The water got down into some little, tiny, minute crack and eventually it broke that big rock. It's the size of your head, that nice big rock.

All right, so we've taken some pictures. We've had a look at some of the weathering that goes on in the badlands, and a little bit of it in the desert southwest, a little bit of it in Greenland. Let's take another quick field trip to where the source material is. I said that these rocks, these big mountains get torn down, and then the material gets spread out in the valleys, in the badlands, and then turns into soil. Well let's go take a look at one of those mountains because they are really beautiful places.

This is Grand Teton National Park in Wyoming, near Jackson Hole, Wyoming. Jackson Hole is very famous. Lots of famous and rich people have their ranches there. It has become quite a popular destination. But before that, it was a simple ranching town. And one of the reasons that people went there was for tourism, for some of the really just magnificent scenery that's available there.

These high, sharp peaks, we're looking from the hole, from Jackson Hole Lake, up towards the mountain to the west. You have this relatively low spot and then these mountains rise, soar up, thousands of feet next to you.

There's a large active fault in the earth and these mountains are actually growing along them. As they grow up into the sky, weathering processes, erosion processes work at them and tear them down producing these jagged cliffs, and these sharp edges, and these very steep sides, and these very dramatic looking valleys and gullies. It's because of that process that you have those sharp edges, because of the erosion process. Here's another beautiful shot of it with the sun setting in the background.

There's lots of rain up there. You get these thunderstorms. And those thunderstorms will go up there and there's these big rocks that are lodged up in these gullies. And the water will come down and then these rocks will all cascade down. Gravity is a very irresistible force. Everything wants to head downhill.

It might stay up there for a little while, it might stay jammed into the side for a little while, but eventually gravity will win and things will come down. Now, if you've got a big rock and it's solid, it won't just simply fall apart by itself. It has to be helped along. That's what we're going to talk about there.

Here's a beautiful photograph of Mount Moran with Jackson Lake in the foreground. Another beautiful view of it. As I said, all of these slides are available online.

Back about 20,000 years ago, there used to be huge glacier that came down from the mountains, down into the lake and probably carved out that lake. And now that glacier is gone. We'll talk about that in a couple of sessions.

Here's the Gros Ventre slide in the Grand Tetons. This was a landslide that came down and dammed a river and ended in a catastrophic flood.

So, let's go to the videotape now. Let's move to the drawing and we'll do a quick summary of where we're going to head for the next class.

Tearing down mountains, weathering, wind, and mass movement. What is erosion? Erosion consists of three things. Weathering, all weathering means is taking a rock and breaking it down, either physically breaking it into smaller pieces or chemically breaking it down into some of its constituent minerals. That's all it is, taking a big thing, making it smaller.

Transport is moving those weathered materials, the smaller rocks, the dissolved chemicals, moving them from here to there. Deposition is the end process of that transport. You've weathered something over here, you've transported it over there, and you've deposited. That whole cycle is known as erosion.

If you have enough time, even very slow erosion processes can dramatically modify the landscape. You can take a huge mountain and you can tear it down to nothing if you give it enough time. This was one of the keys that the early geologists used to say that the world must be really old. Because they looked at these mountains and they said, but look, we know that erosion is really slow here, but we've torn down this huge mountain. It must have taken hundreds of millions of years to do this, to produce all of this deposited sediment pile and so the earth must be old.

That's one of the keys that the early geologists used to say that the earth was old. And then, we got more evidence as time went along and we've found newer and better techniques to date the earth. And we'll talk about that later on.

The most important agents for erosion are water, ice, and temperature. You take water, you put it into a rock, you freeze it, that will break the rock apart. You take that same water, you turn it into a river, it will carry the broken-up pieces down river. Where that river gets to a spot where it slows down, where it gets to the plains, where it starts to meander and heads to the ocean, that material will be deposited.

Ice is the same way. Glaciers come along. Glaciers can tear rocks apart. They can move the rocks to a new place and then they'll deposit those rocks and build these beautiful big moraines like Cape Cod. And we'll learn about Cape Cod in a little while.

So, the atmosphere is involved because that's where the rain water and the snowfall comes from for the glaciers. All of that material, that snow or rain, lands on the earth and it works on the rocks to tear them apart.

The erosion agents are, as I said, water in glaciers and simple, old downhill flow of stuff. You've got a hill, you pile up rocks on it, eventually that will start to head downhill. Especially if you break it up and you help it to move down by raining on it or something like that. So, let's take a look at mass wasting first and then we'll talk about the others in a second.

When we talk about mass wasting, think of Teton National Park, those beautiful, big, sharp, jagged peaks. The reason they're like that is that the edges have been sharply torn down and head downhill. That's mass wasting. We'll talk about soils. Think of Badlands National Park with all of this big soil layer that was produced by weathering. And when we talk about rain, we'll talk about Redwood National Park.

Mass wasting is defined as simply masses of debris or bedrock moving downhill. It can be something fast and dramatic and disastrous like a landslide, or it can be something as slow and innocuous, but ultimately far more important, like simple mass creep, it's called. And we'll talk about that.

All of these things are driven by gravity. Gravity is a force that is pulling material at the surface, mass at the surface, towards the center of the earth. And if you give a small slope or a big slope, there is a component of gravity that's pulling it along that slope. And anything on this slope will want to head downhill.

This is the most basic, simple, common sense thing in the world. You live it every day. You live it when you take a slide down a children's plastic slide in the playground. The children go up to the top, they jump on to it, and they slide whooshing down these plastic slides. They don't know it, but what they're doing is they're responding to the force of gravity. But you do know it because now you've grown up, and you've studied this, and we're talking about it here.

This map here is a map of the landslide potential in this country. How much in danger of having a landslide are we in Ohio, or Wisconsin, or Florida? Not very much. How much of a danger are we to having a landslide in Colorado, or Idaho, or Washington state? Quite a bit.

That's what the colors are. The dark greens are high severity of landslides and the white and tans are low or moderate risk of landslides. Why? It's very simple.

You've got these high mountains in Colorado, or Washington, or Idaho, or Montana. And you don't have them in Florida. In Florida, it's all flat. You're not going to have a landslide. Common sense, it's just plain old gravity that's going to grab things and shove them down. So, this is where gravity comes into play with mass movement downhill.

We can classify this mass movement into a couple of different ways. And really, all it comes down to is how fast this stuff is going to swoosh downhill. If it comes really, really fast, then it's a landslide. If it comes really, really slow, then it's called creep. And it can be everything from in between. From 100 kilometers per hour, the stuff comes shooting down the mountain and wiping out houses, and roads, and bridges, and people that are in the way, and it really is quite disastrous and dramatic. Or it can be really slow, this slow creep of soil where just little bits and pieces of soil will head down the hill, year after year. And after 100 years, maybe it's come down a foot, or half a foot, or something like that. In the end, soil creep is the most important because it happens everywhere.

Here's a picture showing the gravity pulling down towards the center of the Earth. And if you've got a slope, then you have a component of gravity that's pointing downhill along that slope. And you put something on that slope, and it will slowly make its way down the slope. If the slope is really steep, maybe it will go shooting down really fast. If the slope is really gentle, then it will move down much, much more slowly. But in the end, it will move down.

And there's a few things that control that rate. If you've got lots of trees and grass on this hillside, then the soil gets bound together by the roots of these trees and grass, and so the soil doesn't want to slowly go creeping down the hill. Whereas, if you don't have any trees holding it back in place, if you don't have any grass holding the soil in place, the first rain that comes along will wash this soil downhill.

You've seen that. You've seen where there's a gully with nothing planted in it, it will erode faster and faster. But if the farmer goes and plants some crops on it, then it will not waste away quite so fast.

The most important of the controlling factors is water. Water inside the soil will bind the grains together. Unless there's too much of it, at which point the grains will be floated apart, and then it will swoosh away.

When you were a kid, you went to the beach, I know you did. And you were given a bucket and a little shovel, and you were told to build a little sand castle. And away you went, and you started playing in the sand and building your sand castle. And you found that if the sand was completely dry and you tried to build a sand castle with it, whoosh, it would just swoosh away, slump away, and you wouldn't get a sand castle. All it would be would be a pile of dry sand.

You knew that if you went down into the surf and you picked up a bucket full of sand that was filled with water from the ocean waves and you tried to make a sand castle out lot of that, flump, it would just slump down and you would just have this pile of wet sand. But if you got the water mixture just right, if you mixed the right amount of sand with a little bit of water, you got these lovely clumps of sand that you could then build your walls, and your turrets, and your towers, and you could put a little flag in it, and put seashells on it for decoration, and all was well.

So, a little bit of water bound the sand together. If there wasn't enough water, then the sand fell apart. If there was too much water, then the sand fell apart. The same thing happens in soils. And the same thing happens with mass wasting. Ice and vegetation can control that. If you've got vegetation that is holding the soil together, then it will help to stabilize the slopes.

We're going to go to the drawing tablet, and we'll go over these controlling factors once again. I have to have this thing come up.

When you have a mountain as we have over here, gravity wants to pull everything towards the center of the earth. But if you've got a rock sitting on the side of this mountain, it can't shoot towards the center of the earth because the hill here is preventing it from doing that. But what it can do is roll along that slope.

And if you have a very shallow slope like this, it's not going to roll very fast. But if you have a steep slope as we have up in here, then these rocks will flow downhill, or roll downhill, more rapidly.

If we zoom in on the soil surface right over here, what we will find is that the soil is made up of lots and lots of small particles or grains. And inside the pore spaces we have water. That water can bind the grains together unless there's too much of it, unless there's too much water. If there's too much water in there then the grains will be floated apart. Or float them apart.

And it really depends on the amount of water in there. And that's why after a rainfall, you will get much more erosion, much more movement of soils downhill. Because all of that water in the rainfall goes down into the soil and it will float the grains apart. And then those grains will simply wash downhill.

Grasses and trees can stabilize a slope because the roots hold the grains in place. And the roots will suck excess water out. That's what trees and grasses do really well, they drink water. So it rains and a lot of that water gets sucked up by the grass and trees, and so it doesn't float them apart.

The way that these smaller grains do move down hill is helped a lot by ice. And let's take a look at that next. Ice plays a major role in erosion in a couple of ways. The most important is in freeze-thaw splitting of rocks.

If we have a rock with a small crack in it, and we fill it with water, and then we let that water freeze, it will expand. You know that. You've seen that many times.

When it expands, here it is down in this crack. It's filled up this crack, the water has, and it starts to freeze. And it's got to expand, it needs more room. What's it going to do? It's going to push against the sides of the rock. I know rocks are hard, I know rocks are strong, but it turns out the ice can be even stronger. Rocks just cannot resist this. When the water freezes, and turns to ice, and starts to jack the sides of this rock apart, that crack gets deeper and deeper until finally the rock splits in two.

Now you have two smaller rocks. And you do it again, and you do it again, and you do it again, and you keep breaking these enormous boulders down into smaller and smaller pieces. Eventually, the pieces are small enough to be washed away by streams and rivers.

Ice also helps this erosion process in a second way. So the first and most important is breaking large rocks into smaller ones. A second way in which ice does its thing is when you've got a slope, and you've got a bunch of grains piled up on this slope, and you have water in the pores in between the grains. When this material freezes in the wintertime, what happens is, when the water freezes in winter, the grains are pushed apart.

And so, you can imagine that we have frozen this material. And I'm just going to erase these pictures and redraw it after it's been frozen. And we'll exaggerate it a little. Now, we have these rocks pushed apart after freezing.

And then, finally, spring comes around, that ice starts to melt and thaw, and it goes back to water, and the water shrinks back down again. And what happens? And we'll erase it again and redraw it a third time. And now, in spring, the ice thaws and the grains fall down. But not to their original position. They have moved a little downhill.

These grains that used to be piled up, nicely pile together uphill. They froze, got pushed apart a little bit. When they thawed, they didn't simply go back to where they were before. The one that got pushed up fell downhill a little bit.

I know it seems like such a minor, tiny process. But you do this over, and over, and over again, and eventually this grain can be moved here, and then here, and then here, and then here, and slowly creep down the hill. This process is known quite descriptively as soil creep. It is the most effective way of eventually tearing down these mountains.

So, you have this big dramatic action of the rocks breaking off into smaller pieces and then breaking up into even smaller pieces. But eventually, when you get down to small grains that are just the size of a grain of sand, for example, or even smaller, that's when this process takes over. And even on very gentle slopes, you can start to move these grains of sand or grains of soil downhill.

We're going to go back to the presentation here and look at some pictures of this action. Here's one of those dramatic examples. This is a hill slope. You can see there's all those tarps that are lying there. The reason there are tarps there is because it was raining. And after the rain, that hill slope failed, fell apart, fell to the bottom of that hill slope there on the right, and these poor houses are left high and dry.

Here's one of my favorite pictures. Here's this poor policeman that took shelter under a highway overpass. And he was sitting there, maybe eating some doughnuts, I don't know, waiting for the storm to pass. And what happened? This big mud slide came by very rapidly and covered up his cruiser. Poor fellow.

Here's one of those dramatic examples. You've got this rock face off on the side of the road. And probably because of freeze-thaw action, one of these big rocks that was held up against the side of the mountain got water in it. It froze, it thawed, it froze, it thawed, it froze, it thawed. And it just jacked those cracks apart until eventually the whole hillside failed.

Here is a picture of a hill slope in Los Angeles. And we have that white scarp or wall that you're looking at. It didn't used to be white like that, it used to be nice, and gentle, and grass covered. And it has failed, probably after a rainstorm. You get these amazing downpours of rain in Los Angeles. And it has just slumped down. And all that material at the bottom is what used to be a big hill slope.

Here's another picture of some dramatic destruction along the coastline in California. The bottom one, you have all these houses that have been torn apart when the hill slope failed.

This is a very dramatic and tragic example from Wales where it was a mining town. And they used to mine up on the hill just above this little town of Aberfan and drop all of the mine tailings. The tailings are the waste products that are left over from the coal mining. They would bring them up to the mouth of the mine and simply pile them up in these big piles. And after a big rainstorm, you had this huge landslide that came down and killed a number of people in this town. And you can see where that landslide has come through and destroyed the houses.

This is in South America and two enormous landslides that have come through and destroyed part of this village.

All of those were the dramatic examples. The most common one, the one that you see around here, even on gentle slopes, are soil creep. Very, very slow flow, even after a year if you were to sit there and very patiently watch one particular piece of soil, after a year it might have moved half an inch. So it doesn't seem like a lot, but you do that for 100 years, you do that for 1,000 years, you do that for 100,000 years, and eventually you've moved a lot of material downhill.

With these very dramatic things, those happen once every 10 years, or 20 years, or 30 years. And you move a lot of material down with those, but this other process of soil creep happens everywhere, all the time, it doesn't matter how steep the slope is. You've got to have some slope, but as long as you've got a little bit of slope, you're going to get some of this process. If you have vegetation, it happens even slower, but it does happen. It's facilitated by water in the soil and it's facilitated by freeze-thaw in colder climates.

Here's that picture that I showed you, again. You have all of the grains that are piled up, it freezes, they all spread apart. When it thaws, some of the grains fall down, farther downhill than they started out. And so the one in the bottom right is the grains after a winter and a summer. And the grains at the top left are before all of that began.

And here's an example of that soil creep. We have this beautiful stone wall along the side of this house. And the person that built this didn't build it with that big dip in it. They built a nice flat stone wall that went all the way along there. And over time, that very gentle slope above that stone wall has managed to slowly slump down and deform that wall that way.

So we've seen mass wasting and the pictures that we saw were in the Teton National Park. Now let's take a look at soils and what's going on with those soils.

Badlands are erosion from the Rockies transported from the Rockies all the way across to the Dakotas and deposited over there. And this soil is very clay rich. Clay minerals are ones that create a really hard surface that channels the water away and washes away plants. You just can't grow stuff in this. When you mix in lots and lots of clays into the soil, you turn what used to be very friable, very workable soil into this hard layer.

You know that. Pots are made out of clay. Clay pots, you go out into your garden and you'll find all of these lovely reddish clay pots there. Those are hard. They're just soil. They're a type of soil called clay. They just happen to be really, really hard.

Now those are obviously put into a potter's kiln, and fired, and so on, and so those become really, really hard. But the same process goes on even in nature, even without a kiln, even without taking those soils up to high temperature. You take these clays, and you spread them through the soil, and they make a really hard layer.

And that's why the badlands are bad lands. Beautiful places, nice jackalopes in them, but very, very hard to grow plants because that hard layer channels the water. You don't get the water sinking down into it. It just runs along the surface and washes away any trees that are in the way.

Weathering is the breakdown of the rocks at the surface. Remember, I said water controls it to a great extent. Changing temperatures are the next thing that we're going to talk about and biological organisms, plants, trees, and earthworms and other burrowing insects.

There are materials removed by erosion. I defined erosion earlier, which was taking big rocks, breaking them up, transporting them somehow, by water, or wind, or glaciers, however you want to do it, and then depositing them someplace. Now, if you just take a nice low, flat spot, and you start working on that soil, you get what's known as in place weathering, without the transport, without the final deposition. And that's how you make soil.

If you just take a chunk of real estate right around here in State College or wherever it is it you live, and you start working on that soil, you start heating it up, and cooling it, and washing water through it, and you'll eventually change it enough to produce soil. And if you have earthworms, they help, if you have insects, they help. All these things go into making soil.

Mechanical disintegration was the one that just tore these rocks apart. And then, we'll talk about soil. OK, I'll have to delete some of those.

Biological organisms, tree roots and trunks, burrowing insects, earthworms, all of these burrow down into the soil and they bring material up. One thing they do is they bring deeper layers up to the surface. But more importantly, they let water trickle down to those deeper layers. And water is one of those really important materials they can operate on these soils to weather them and to break them down even more. So, all of these critters have a huge impact on them. And when we sterilize the soil, when we don't allow the soil to have vegetation and sources of nutrients for these insects, then we make these soils less productive.

Here's a beautiful example of how these biological organisms work. There's a tree growing in a rock. There's just a little crack in that rock and that tree has managed to get its roots down into it. And those roots will allow water to get down in there, and they will allow soil to get down in there, and they will allow organisms to get down in there. And over time, that tree and all the associated processes that go along with it will break that rock down into smaller pieces.

Chemical weathering, or in place weathering, is helped most strongly by these very weak acids that are formed when rainwater falls through the atmosphere, picks up carbon dioxide, and creates something called carbonic acid. And these acids fall down onto the rocks or onto the soil and they basically dissolve little bits of the soil. And the water carries away some of those, and it leaves some things behind.

The acid attacks the rock. It depends on the type of rock, temperature, acidity, so on and so forth. But at the end of the day, if you spend enough time doing this, even this really, really weak acid can break down the rocks. And we'll look at one example that produced the soils in the badlands. And we'll go through it quickly, but it's all in your textbook, and you can take a look at it.

In the rocks of the badlands you have all of these small grains that are made up of pieces of granite that have washed down from the Rockies. The rain falls down on them. This rain falls through a CO2 layer, that's what we have in the air around us. It makes this acid, this really weak acid called carbonic acid, and it attacks the granite.

The granite is made up of the number of things and one of them is iron. And as you know, iron simply rusts. You take a chunk of iron, you leave it out in the air, it's going to rust. And that's what will happen. The iron parts of the granite will oxidize, will rust, they will fall out, and they'll stay in the soil. That's one of the reasons that some of these soils have this reddish tint to them. It's because all of the iron in the rock has been pulled out and it just lies there within the rock.

The aluminum, potassium, and silica are clays and they remain in the soil as well. These don't get washed away. These are minerals that spread out through the soil. And so what you're left with are iron and these clays in the soil of the badlands. There's a few other parts of the granite, they all get washed away. They all disappear and go off with the rainfall.

Calcium, sodium, and magnesium all get dissolved into the water. And they wash away to the ocean. The calcium is used by critters in the ocean to make seashells. And the sodium washes into the sea to make it salty. And the magnesium eventually gets deposited at the bottom of the ocean and gets recycled at spreading ridges.

So, this is one process we've gone through. And we'll draw it out here in a second. Granite comes down from the Rocky Mountains, gets deposited in the badlands, the rainwater falls on it, and then these pieces of granite get weathered or altered in place. It's not physically tearing it apart, it's chemically tearing it apart, pulling out the differences constituent parts of it. The irons and the clays stay there in the soil. The calcium, and the sodium, and the magnesium all get dissolved into the water and get washed away. I'm going to go to the drawing tablet here and we'll draw that process.

Rocky Mountains, badlands, mechanical disintegration. that's that freeze-thaw. That's taking rocks, breaking them up into smaller pieces, all of the things, the trees growing in the cracks, breaking them apart, all these other things, and breaking the rocks into the smaller pieces. Gravity and streams carry material downhill and deposit them in badlands.

All right, so that's the beginning of the process. We've taken granite up in the Rocky Mountains, broken them into pieces, washed them down in the streams, and deposited them in the badlands. Then we have chemical disintegration in the badlands that makes soil. In the case of the badlands, it isn't very good soil, but it's soil nonetheless.

You have chunks of granite in the soil. You have rainfall. And in the air, you have carbon dioxide or CO2. These two mix together to make a weak acid called carbonic acid that attacks these granite grains and pulls iron and clays out and leaves them in the soil. The water dissolves calcium, sodium, and magnesium and washes it away to the ocean. So, you're left with this iron and these clays over there because all the rest have been washed away.

In areas with lots and lots of rainfall, at high temperatures, this process happens really fast. And so a lot of the material gets washed away and the soils are very poor. In areas with moderate rainfall and moderate temperatures, this process is not quite so fast and so you end up with good soils, better soils, ones that have more of these natural products, of these chemical still left in them, and so you have richer soils.

Let's go back to the presentation. And we will finish up this process with a review. More heat and more water, more stuff is washed away and the soil has fewer minerals in it. In very, very dry areas, even the calcium, and the magnesium, and the sodium stay in the soil and you get these really, really salty soils, which are really bad to grow anything in. So, paradoxically, you could have either too much water, in which case all of these things will be washed away, or too little water, in which case all of this material will stay in the soil. And you've got to have just the right amount to make it all happen.

Next time, we're going to look at the rainfall. Where did this rain come from? Rain seems to be so important for both producing the rivers that wash all this material away and for producing this acid that can eat away the water and for washing away all of these other materials into the sea. And that's what we're going to look at next time.

Dr. Alley: (SINGING) Somewhere over the rainbow, raindrops fall. Sun and rain make a rainbow with your eyes in between, that's all. Sun falls straight on the equator, just skims the poles.

So tropical heating is greater. Air rises and sinks in rolls. Air lifted in these currents great expands as it feels lesser weight, brings cooling. Air cooling holds less H20, condenses to rain, clouds, or snow. That fall, no fooling.

When there's evaporation, it takes energy, That is why perspiration drying cools you or me. Equatorial evaporation stores solar heat that's released by cloud condensation. Energy is conserved, pretty neat.

This heat from Condensation slows. Cloud cooling as it upward grows while raining. But when this air comes down, it's dry and squeezing drives its fever high. And you know from your training.

Three degrees F per 1,000 feet upward, cools and rains. Five degrees F per 1,000 feet downward warms up the downwind plains. Somewhere over the rainbow, raindrops fall.

Sun and rain make a rainbow with your eyes in between, that's all. Wet redwoods, cold sierra high above Death Valley set to fry. That's why.

Image 1: Canyonlands to the Grand Canyon; Rivers Roll Rocks, and Dams Get in the Way; All photos by R. Alley from the Penn State CAUSE trip, 2004.

Image 2: Canyonlands, near Moab, Utah, preserves the junction of the Colorado and Green Rivers. The rocks are mostly from the Mesozoic (a couple of hundred million years ago) and include sandstones and shales.

Image 3: Sunrise over the red rocks of Canyonland in the Needles area. Sunrise washes the red rocks of Canyonlands in the Needles area, one of several distinct districts of the park--the rivers are not bridged, so getting from one district to another can take a lot of driving.

Image 4: Sunrise at Needles area campground in Canyonlands with foot of sleeping bag in foreground. Sunrise over sleeping bag, Needles area group campground, Canyonlands.

Image 5: Several students in sleeping bags on the rocks at Needles area campground, Canyonlands. Sunrise over sleeping students, Needles area group campground, Canyonlands.

Image 6: A field of orange mallows at the entrance to Needles area in Canyonlands. A field of mallows, entrance to Needles area, Canyonlands.

Image 7: Close-up of a desert milkweed in Canyonlands National Park. A desert milkweed, Canyonlands National Park

Image 8: Close-up of large uniquely shaped and patterned sandstone in Canyonlands. Rock features, Canyonlands. The sandstones shown here have weathered into fantastic patterns.

Image 9: Panoramic view of Canyonlands and a muddy Colorado River with exposed sandbars, viewed from Dead Horse Point State Park. The Colorado River and Canyonlands, as viewed from Dead Horse Point State Park. Notice the muddy water, the sand bars in the river, and the tree-covered sand bars along the river. This clearly is a river that moves much sediment.

Image 10: The Glen Canyon dam and highway bridge, viewed from a raft on the Colorado River below the dam. The Glen Canyon dam, and highway bridge, viewed from a raft trip on the Colorado River below the dam. Lake Powell, on the other side of the dam, catches the sediment from the river, so that clean water is released from the dam.

Image 11: A young woman and a man with a video camera standing on a rock in the river, at the bottom of the Grand Canyon. Stephanie Shepherd and Topher Yorks filming at the bottom of the Grand Canyon. Notice that the water behind them is nearly free of sediment, so you can see the bottom clearly in the closer parts.

Image 12: Colorado River, below the Glen Canyon Dam, with arrows pointing to an eroding sandbar. The Colorado River below the Glen Canyon Dam. The cliffs are still spectacular, but the sandbar across the center (arrowed) has largely been eroded away by the sediment-free waters released from the dam.

Image 13: Bottom of the Grand Canyon, boulder bar in left foreground and river with clear water in right foreground. Bottom of the Grand Canyon, from the silver bridge that takes the Bright Angel Trail across the river. The water is clear. The left foreground shows a boulder bar, not a sand bar--much of the sand has been washed out of the Canyon by the clean water released from the dam upstream.

Image 1: Aerial view of Mississippi Delta. Mississippi River flows through green marshes to Gulf of Mexico and river’s mud clouds water. Deltas, rivers and floods: living with the moving water. This picture shows the Mississippi River Delta, south of New Orleans. Plants are green, deep water is blue, and the grayish-white is mud carried by the river. A few poofy white clouds are also visible.

Image 2: Aerial view of delta in Mudder Bugt (“Muddy Bay”), east Greenland. Stream at bottom of photo deposits the delta into fjord at top of photo. Delta in Mudder Bugt (“Muddy Bay”), east Greenland. A stream flowing from the bottom of the picture has deposited the delta into the fjord at the top of the picture. Sediment supply is slow enough to allow waves in the fjord to rework the sediment to make the beaches that outline the delta. Helicopter skid is visible in the far lower left.

Image 3: Aerial view of delta near Muddy Bay, Greenland. Stream flows in braided pattern and there are icebergs offshore. A delta near the one in the previous picture. The stream, flowing from the lower left, is braided, and the pattern of sand bars and beaches is quite interesting. This is Greenland, so the objects offshore are icebergs rather than oil tankers or merchant ships.

Image 4: Aerial view of a Greenlandic delta, near Muddy Bay, shows sand bars and braided rivers. Another Greenlandic delta, close to those in the two previous pictures. Some of the bars in the braided river supplying the delta have been stable long enough for tundra vegetation to become established.

Image 5: Aerial view of two side-by-side deltas in Tasermiut Fjord, South Greenland. Deltas are higher on the right, where the streams enter. Two more deltas, Tasermiut Fjord, South Greenland. Careful examination will show that the deltas are higher on the right, where the streams enter, and lower on the left--sediment builds up as well as out.

Image 6: Aerial view of stream Sondresermilik Fjord, S. Greenland. One arrow points to oxbow lake, one points to levees separating stream from lake. Meandering stream feeding Sondresermilik Fjord, South Greenland. Streams flow fastest on the outside of a curve, eroding the curve, until a shortcut forms and leaves an oxbow lake (pink arrow). Low natural levees (white arrow) separate the oxbow lake from the stream.

Image 7: Failed Missouri levee in the Mississippi basin, during the Great Midwest Flood of 1993. http://water.usgs.gov/nwsum/WSP2425/images/levee.jpeg US Fish and Wildlife Service photo, from Effects of the Great Midwest Flood of 1993 on Wetlands, by James R. Kolva, U.S. Geological Survey. This Missouri levee failed during 1993 flooding in the Mississippi Basin. Many (but not all) artificial levees rest on much smaller natural levees.

Image 8: Aerial view of flooded New Orleans after Hurricane Katrina 2005. Rooftops and tree tops surrounded by water. http://www.mvd.usace.army.mil/hurricane/chr.php Miscellaneous Photos coe_5, US Army Corps of Engineers. Flooding from Hurricane Katrina, New Orleans, 2005. Levee failure triggered this disaster.

Image 9: Aerial view of Mississippi River in New Orleans and the levees that held up during Hurricane Katrina. http://www.mvd.usace.army.mil/hurricane/chr.php Miscellaneous Photos coe_6, US Army Corps of Engineers. Flooding from Hurricane Katrina, New Orleans, 2005. The levees held on the waterway shown here; the floodwaters outside came through a different levee, and are actually lower than the water between the levees seen here.

Image 10: Aerial view of Hurricane Katrina flooding in New Orleans. Muddy waters surround homes and businesses. http://www.mvd.usace.army.mil/hurricane/chr.php Miscellaneous Photos coe_17, US Army Corps of Engineers. Flooding from Hurricane Katrina, New Orleans, 2005. A very waterlogged Wendy’s outlet is visible in the left center. The muddiness of the water is also evident.

Image 11: Aerial view of Hurricane Katrina flooding in New Orleans. Oil slick can be seen on water surrounding homes and businesses. http://www.mvd.usace.army.mil/hurricane/chr.php Miscellaneous Photos coe_20, US Army Corps of Engineers. Flooding from Hurricane Katrina, New Orleans, 2005. The colors on the water indicate an oil slick. The floodwaters raced through houses, gas stations, repair shops, chemical plants and more, releasing many toxic chemicals.

Image 12: Aerial view of Mississippi Delta. Mississippi River flows through green marshes to Gulf of Mexico and river’s mud clouds water. The Mississippi River flows from the upper left through green marshes to the blue Gulf of Mexico, where the river’s mud colors the water whitish. Branches of the river have been deepened for shipping; the main channel extends to the southwest (lower left). Deltas come in many forms; this is somewhat different from those we saw earlier in Greenland.

Image 13: Map of Mississippi Delta, showing that most of the delta has sunk beneath the sea over recent decades because of human actions. Orange indicates land loss from the Mississippi Delta between 1956 and 1978, red is loss 1978-1990, yellow shows gain 1956-78 and green shows gain 1978-1990. Losses dominate, although sedimentation has been lengthening the “log flume” of the main shipping channel extending to the southwest (lower left). Loss slowed after 1978 because most of the land was already gone.

Image 1: Cypress trees in a bayou, Barataria Preserve, Jean Lafitte National Historical Park and Preserve, Louisiana. Many trees in wetlands grow “knees”, projections sticking up from the roots, that help stabilize the trees and may help the tree roots “breathe” when they are underwater. You can see such knees on the cypress trees in the bayous of Barataria Preserve, in Jean Lafitte National Historical Park and Preserve on the Mississippi Delta in Louisiana, a great place to see lots of things growing. All pictures in this slide show are by R. Alley unless otherwise indicated.

Image 2: Alligator in the bayou. Of course there are alligators in the bayou! Barataria Preserve, Jean Lafitte National Historical Park and Preserve, Louisiana.

Image 3: View of bayou plants taken from an airboat. Taken from an airboat (you can see the boat in the bottom of the picture), Barataria Preserve, Jean Lafitte National Historical Park and Preserve, Louisiana. There is water under the plants straight ahead, and that is where we went.

Image 4: A green frog sitting on Dr. Alley’s knee . This frog was sitting on my knee after we air-boated through a particularly dense patch of plants. Barataria Preserve, Jean Lafitte National Historical Park and Preserve, Louisiana.

Image 5: Bayou -- water with large trees growing out of it. Barataria Preserve, Jean Lafitte National Historical Park and Preserve, Louisiana.

Image 6: Palmetto plant in the bayou Palmetto. Barataria Preserve, Jean Lafitte National Historical Park and Preserve, Louisiana.

Image 7: Close-up of channels in limestone inside Mammoth Cave. Dragonfly on palmetto plant.

Image 8: White spider lily plant in the bayou White spider lily, Barataria Preserve, Jean Lafitte National Historical Park and Preserve, Louisiana.

Image 9: Dr. Alley’s boot in the bayou water. There is oily “scum” floating on the water. Richard Alley’s boot in water, Barataria Preserve, Jean Lafitte National Historical Park and Preserve, Louisiana. Notice the oily “scum” floating on the water to the upper right of the boot. A place such as this bayou grows LOTS of plants, which die and sink. In the mud, oxygen is scarce. The decaying plants are not “burned” efficiently in the low-oxygen environment, and some of the formerly living material produces oil. Oil mostly comes from dead algae, coal from dead woody material, and natural gas (methane) from both. Most of the oil and gas float up and escape to the surface, as seen here. In some times and places, some of the oil and gas are trapped in mud. We humans are spending a few hundred years using the oil, gas and coal that have been saved up by nature over a few hundred MILLION years, so we’re using them about a million times faster than nature saved them.

Image 10: Bubbles in the bayou. Barataria Preserve, Jean Lafitte National Historical Park and Preserve, Louisiana. Notice the bubbles in the bayou. These are “swamp gas”, which is methane, and is also called natural gas. As described with the previous picture, the gas that is made naturally and doesn’t escape is what is now being “fracked” from shales under Pennsylvania and other states.

Image 1: View looking out of Mammoth Cave with waterfall to the right of entrance and green forest straight ahead. Mammoth Cave: A World Unknown to Daytime--That May Matter to Your Drinking Water Waterfall into historical entrance of Mammoth Cave. National Park Service Photo. All pictures in this slide show are by R. Alley unless otherwise indicated (as for this one).

Image 2: Close-up of small, salmon-colored, eyeless fish in cave waters. http://photo.itc.nps.gov/storage/images/maca/EYELESSF.JPG National Park Service Photo. Many cave creatures are uniquely adapted to their environment, which may seem strange to us but is normal to them.

Image 3: Close-up of cave cricket on limestone ledge in Mammoth Cave. Here, a cave cricket sits on a limestone ledge in Mammoth Cave. (From tip of front leg to tip of back leg, the cricket is about 3 inches long.)

Image 4: Group of people on walkway at Broadway passageway in Mammoth cave, viewing rubble from a roof collapse. http://photo.itc.nps.gov/storage/images/maca/BROADWAY.JPG National Park Service Photo. Broadway of Mammoth Cave is one of the many huge passageways dissolved in the layered limestone of the park. Roof collapses happen occasionally, as shown by the rubble on the right, but are rare, so tourists are considered safe.

Image 5: Two people standing behind a railing in a room in Mammoth Cave. Cindy Alley (who prepared many of the graphics for the course) and friend Sue Croll in Mammoth Cave. The cave is immense; this room is several stories high.

Image 6: Close-up of Gypsum flowers in Mammoth Cave. Gypsum flowers, Mammoth Cave (photo about 6 inches across). Limestone (calcium carbonate) often has a little gypsum (calcium sulfate), which makes formations with this distinctive appearance.

Image 7: Close-up of channels in limestone inside Mammoth Cave. Channels in limestone, Mammoth Cave (photo about 2 feet across), produced by dissolution of limestone in acidic groundwater.

Image 8: Tall narrow passage in Mammoth cave. Passage in Mammoth Cave. This probably started as a vertical crack, which was widened by dissolution of the limestone rock into acidic groundwaters flowing along the crack.

Image 9: Close up of Frozen Niagara section of Mammoth Cave. Frozen Niagara section of Mammoth Cave. More groundwater enters this region than in the rest of the cave, because the sandstone “lid” that covers much of the cave is broken here. The water picks up extra carbon dioxide in soil, dissolves limestone, then loses the extra carbon dioxide to the cave air (which exchanges rapidly enough with the outside to exhaust the carbon dioxide), and deposits the dissolved limestone as cave formations.

Image 10: Close-up of Frozen Niagara. Arrow points to line of hollow stalactites in upper left. Below stalactites is small patch of greenish algae. Water often enters along cracks; a line of hollow stalactites (“soda straws”) is arrowed in the upper left. The greenish color just below that line comes from algae growing where a Park Service light provides a little energy.

Image 12: Close-up of a roughly 20-foot-high cave formation in Carlsbad Caverns. The sandstone cap that prevents collapse of Mammoth and allows the cave’s immense length does reduce drip-water entry and thus cave formations, so other Park Service caves are often prettier than Mammoth. This roughly 20-foot-high feature is in Carlsbad Caverns.

Image 13: Upper image of limestone has arrows pointing at two snail fossils. Lower image has arrow pointing at one snail fossil. http://geology.er.usgs.gov/eespteam/smoky/ResearchAreas/smokys/cadesCove... USGS Photo Fossil snails (gastropods) in limestone, Cades Cove, Great Smoky Mountains National Park. Most caves and sinkholes are in limestone, and most limestone started out as shells or skeletons of marine creatures. Many shells are so broken as to be unrecognizable, but quite pretty fossils can be found.

Image 14: Excavation area in State College, PA shows soil on limestone bedrock. Soil on limestone bedrock in excavation for a basement, State College, PA. The rock layers slope down to the lower right, and are curved a little. Dissolution has enlarged cracks and deepened some places more than others. When the deeper places become big enough, we say a sinkhole has formed.

Image 16: Group of about 20 people standing by sinkhole, near Shenandoah National Park. http://va.water.usgs.gov/karst_img/karst_photo2.htm USGS Photo. Sinkhole near Shenandoah National Park. The center of the hole is just to the right of the right-most person. The ground slopes into the hole from all directions, so rainwater that runs in and does not evaporate must go downward through the bottom of the hole.

Image 17: Tree trunks and branches in a small sinkhole in Cades Cove, Great Smokey Mountains National Park. Sinkhole in limestone, Cades Cove, Great Smoky Mountains National Park. The sinkhole is the dip containing tree trunks in the foreground. Sinkholes most commonly form by dissolution of limestone along joint intersections, but cave-roof collapse also may form sinkholes. Here, tree trunks have fallen in, but in many places people have dumped things in, which go right to the groundwater.

Image 18: Sink holes in forest floor, covered with fall leaves, near Gregory’s Cave, Cades Cove, Great Smoky Mountains National Park. http://geology.er.usgs.gov/eespteam/<br></a>smoky/ResearchAreas/smokys/<... USGS photo Sinkholes in limestone near Gregory’s Cave, Cades Cove, Great Smoky Mountains National Park. Similar scenes are common along the Appalachians in many places. Soil, rocks, leaves, etc. fall into such holes, yet the holes are not full, indicating that materials are sinking toward the groundwater.

We're flying along in our helicopter out over the ocean, and we're looking towards shore at a beautiful beach we just saw there. And we're seeing the pretty waves of the ocean underneath us. And we see a great river coming down to the shore, something like this, meandering along the way some of these great rivers do.

Now if we could somehow hang along in our helicopter and wait for a flood, what we'd notice is that sitting next to the river, there's a bunch of trees that are growing. And when the flood happens, the water would start trucking out of the river into both directions. And as the water came trucking out of the river, it would slow down when it got into the trees.

And as it did so, it would start depositing a layer of mud. And that layer of mud would be thickest very close to the river, and then it would thin on out across the flood plain of the river. And this would be happening on both sides of the river. And so after a while, we would see that the river is contributing to building a natural levee that sits along the river and runs all the way out to the mouth.

Now, if we could keep watching this happen over very long times, over hundreds or thousands of years, we would see that in many places, the ocean is not strong enough to get rid of all the mud that the river delivers. And so the river would start building out into the ocean, and it would just extend its way out there, building a levee. And as it did so-- not a very high one-- but as it did so, the river itself would lengthen. And so it would be coming out in there, and the water would be flowing down to the sea.

And when this is going on, it has to keep going downhill. So it builds up, as we saw earlier, as well as building out. And so you start getting higher walls that hold the river in, on up here, to allow it to flow downhill and run out like that.

And so as the bed of the river is raised, and it gets higher walls, it's like being on the log flume at the amusement park. And at some point, there's a flood, and that wall breaks, and the river takes the short way down to the sea. And then the whole process will start over again. It'll start building a new wall, and building out that way. And eventually, sometime in the future, this one will become big, and then it will do it over again. And so rivers build deltas. They switch from one place to the other as they build out.

So let's take a look, a strange look, at a river. This is going along the river towards the sea. And this river happens to have trees that grow up on the riverbank. So you can get an idea how we're looking at this.

And what we want to do is ask what happens when we build a dam on this river? And we're concerned about the future of a couple of houses that used to be along the river, one just below the dam right down here, and the other one up above the dam up here, sitting along the riverbank. Well, they build the dam, and the dam fills with water, and it doesn't quite take out the house up above.

But the river's carrying mud. It's carrying sediment. And the sediment starts to deposit out into the lake to fill it with a delta.

Now, rivers have to go downhill. So as the lake is replaced with the mud, if the river were to hit a perfectly flat spot like this, you know what it has to do. It has to build up so that it's headed downhill. And so as the river builds the delta out into the lake to fill the lake, why, you have to bury the house, and that makes the person who lives there mad.

Now, at the other side, it's even more interesting. There's no floods anymore, so the river loses the ability to carry gimongous rocks, which might make the homeowner happy. But the water coming out from the dam is clean. It has no sediment in it. And if there's sand below the dam, why, the water will start washing that sand away.

And that will do a number of things. Your house, now, rather than sitting there right next to the riverbank-- you'll look out some morning and you're ready to fall into a giant hole that's been cut. And you get out there and you fall and then you say, oh, no, and you're very unhappy.

You are not nearly as unhappy as the salmon that are trying to come upstream, because as you may know, salmon like to get really amorous around sand and gravel bars. And if the river has washed away the sand, then you can't have fun with your honey and then leave your eggs there to do well. And so you have a big loss in salmon, as well as getting people's houses unhappy. And so putting a dam on a river makes a big difference.

Here's a great tree. And the great tree is standing up on a bluff looking down on the Mississippi River, which sits down in a valley. And the river has a little natural levee-- this, we haven't gotten to human built ones yet-- and it sits down in a valley.

And then, over on the other side, there's another natural levee, and then you go up another bluff to the top. And the river itself sits down in its river valley like this. And it is flowing towards you, which is what the head of this arrow shows.

And the river is sitting on a few miles thickness of mud that have accumulated over the years as the delta has built out into the Gulf of Mexico. And whenever you get a few miles of mud, everything is sinking under its own weight. And that, in turn, means that the surface is sinking, as well.

Now, nature has a way of handling this surface sinking problem, which is that during a big flood, the water spreads out over the flood plain. And mud falls out of the water, and the mud makes a new layer. And so as the surface sinks, more mud is added. And so there's no net change in the elevation. And that's just fine, except for one little problem.

Over here you have a city. And you've built this big city. And you really don't want that flood coming into your city. So you just call up the Corps of Engineers and you say, make a big wall, and make sure that that flood is not going to get into my city.

Well that's just fine, except that doesn't stop the sinking, because the thing is going down. And so if you come back later, what you'll find is that the surface has moved down to a place like this, and your city has moved down to a place like this. I'm using a darker line so you can see where it's gone to from where it was.

And so you tell them to make the wall bigger. But meanwhile, the city is sinking even deeper. And you've gotten up somewhere way down here, now.

And things are getting really nasty, because at this point, there's a really big storm. And it manages to get just over the top, and it fills your city with water. And then you're underwater and you're very, very unhappy. And this happened to New Orleans. And the sinking is not stoppable, so if it's rebuilt, it is likely that it will happen again.

Today we're going to go see one of the most extraordinary manifestations of man's desire to tame the wilderness.

We're looking, standing here above what was once a vast and deep and beautiful canyon and has turned into a wonderfully used lake that people like to go boating on and people like go swimming in. And so we've seen a great change in what happened here from a world that was used by very few who love solitude to a world that's used by many who love running around in motor boats.

Well, I think a lot of the early settlers really wanted to place their mark. They said, we are not going to be defeated by this land that has only a few inches of rain per year. We will live here. And the way to do it is to get lots of money from Washington that we collect out East and bring it out West here and build these dams. And these places just do not belong. They are magnificent creations. They are incredible engineering masterpieces. But they should not be here.

And so it obviously does a tremendous amount of good, and it's very clean. Once you have a dam, once the lake gets here, you don't dirty anything up. You're not running out smoke from your smokestack that will dim the air in the Grand Canyon.

They should not be here. And I think we've learned that over and over again. But you go to India, you go to China, and they're doing the exact same thing. The Three Gorges Dam in China, one of the most enormous, incredible engineering projects, displaced millions of people, is an absolute ecologic disaster.

If you've got hungry people, and you can save that water and ship it to them, it's food. If you've got people who need power to do things, and you can ship them the power then they can use it.

Dams are amazing human achievements, but they have incredible costs associated with them. So to me, it's very much of a bittersweet kind of a thing. As a former engineer myself, I can appreciate the artistry and the mastery that goes into building these. But as a practicing geologist, as a practicing resident of this planet, I find them a little depressing to be quite honest.

We're going to argue this one again on a lot of rivers in a lot of places for a lot of time.

So now we're on the rim of the canyon. The rim of the canyon does not have streams on the surface. When it rains, which is not all that often, but when it rains, what happens is that the water soaks in. So if you had a rainstorm, you see the water start to make a stream, but then it soaks in. What happens to that water? It goes down through the spaces in the rocks until it hits a rock that it can't get through, such as the Bright Angel Shale. Then it runs along laterally and it comes out at those beautiful springs that we see in the canyon.

Now what's happening here is there's more and more people want to live here, and they want to have water, so they drill wells. And after you drill a well, you suck the water out and you use it to water your grass, or your crops, or your golf course, or to drink or flush or what have you, and eventually it evaporates. And so what you're doing is removing the water that should be running to the springs. And there's worry-- it's not happening yet, but there is worry-- that someday, we may start to lose the springs in the Grand Canyon and the unique biota, the wonderful ecosystems, that live down there because of development outside of the park up here.

Good morning. Welcome to G-SCI 10, Geology of the National Parks. We're going to be looking this time at tearing down mountains some more. Last time, we broke them apart using freeze-thaw action, and by chemical action, and made soils. This time we're going to talk a little bit more about the transport of them-- streams and rivers.

My name is Sridhar Anandankrishan, and I'll be your guide through some of the lovely places. And we're going to take a little bit of a detour to look at some of the damage that water can do. So, let's take a quick look at some lovely pictures and then we'll start on the section.

Redwood National Park on the coast of California. You can go fly into San Francisco and drive up the coast from there. And it's just magnificent trees. These trees, there's a famous one that they cut a hole in it and you can actually drive a car through it. These trees are monsters. They're as big around as a small house. And they tower up in the sky. And you can imagine you need a lot of water to keep a critter like that alive, and you do.

Just go over the mountain. Not very far. Maybe a couple hundred miles. Head inland from Redwood and it's dry as a bone. It's Death Valley National Park. Hottest, driest, lowest place on the planet. Why is it that these two places just very close together, a couple hundred miles apart. Redwood National Park over here with these gorgeous, enormous, towering Redwoods that suck up all this water, this huge root system that needs lots of water to keep it alive, cool climate, rainy climate. 200 miles to the east, you go over the mountain, and you're at Death Valley National Park, it's dry as a bone. What's going on? So that's the first thing we're going to look at.

Let's take a look at some pictures over here. Sequoia sempervirens, the ever-living Sequoia. They live for a long time-- couple thousand years, and then they'll fall over-- kawoomph. And then the new trees will sprout from the trunk. And so when you go there you'll see these lines of trees. They weren't planted that way. It's just that when an old tree falls down, a new one comes up from the trunk, and so they'll be a whole line of them where the old one had fallen down. It's quite an extraordinary sight.

All these ferns and rhododendrons, all of that, surrounding the base of them. The Redwood needles help produce these very acid soils that the rhododendrons really like around here. We have that as well up on the tops of the mountains, these beautiful rhododendron forests. They can tower way up, 200, 300, almost 400 feet up into the sky. They are the world's tallest trees. They are the world's most massive organism. The heaviest single living thing.

The Redwood Coast is rainy and foggy. These trees couldn't make it otherwise. And you go inland a little ways and at the same latitude, you've got this amazingly dry landscape. This is a picture pulled straight out of our very first section a long, long time ago on Death Valley National Park.

Now we're going to look at the surface. Before, we were looking at Death Valley to understand something about pull-apart zones, about spreading, all these other tectonic forces. This time, we're going to look at the surface. Why is it dry at the surface?

Here's a map. The Pacific Ocean is to the bottom, North is to the left on this map, not at the top as it normally is. And you can see this coastal Redwood range all up and down the coast. And then, inland you have Death Valley. And, in between, you have the Sierra Nevada mountains, and that's the key. You have these tall mountains in between, and they intervene and somehow prevent the water from getting from the coast inland to Death Valley. So, let's take a look at that.

The first thing we're going to do is look at winds, and I'll come back to this map in a second. Let's go to the drawing tablet here, and we'll take a look at why the Redwood Coast is wet and cool, and the Death Valley is dry and hot.

We're talking about wind and water this time. We have the Pacific Ocean. We have the Sierra Nevada mountain range. And we have, on the left, these towering Redwoods. And on the east, we have Death Valley. Hot, dry, cool, wet. What's going on? Why is the case?

When the winds blow in from the Pacific, they carry water. Water evaporates in the Pacific Ocean, it blows on shore onto land in California, and it hits the Sierra Nevada mountain range. So, these winds have lots of water in them. The winds are heavily laden with water. They blow in from the ocean, they blow onto the coast, they start heading inland, and they hit the Sierra Nevada ranges.

When they do that they have to start climbing up the mountainside to get over. They can't just tunnel right through the Sierras, and there aren't enough passes for all of that air to go through these low passes. So, the winds as they come along have to rise up the mountain, have to go up to get down on the other side.

As they do that, as the air rises, it cools off. So, as this air rises up to the top of the mountain, it cools off. Cool air can hold less water. You just can't have as much water in the air as that air starts to cool off. What's the result? Rain. As that air is climbing up the side of the mountain, it's cooling off, it can't hold all that water. That water's got to go somewhere, and it falls out as rain. And so, you have all of this rainfall on the windward side of the mountain.

And by the time the air gets to the top of the mountain, all of the water has been squeezed out of it. You take that air, you cool it off, cool it off, cool it off as it rises up, and as it cools off, the water rains out of it, rains out of it, rains out of it. It gets to the top, it's cold and it's dry. It doesn't have any water left in it. It gets to the top, starts to sink, but it is dry. There's no more water left in it. No rainfall.

So, you get no rainfall on the backside of these mountains or what's known as the leeward side of these mountains because all of that water has fallen out on the windward side. This is the rain shadow effect. And this explains why it's so dry in Death Valley. Very simple process. It's you've got this nice, wet air coming in from the Pacific, but all that water gets dumped on the windward side of the mountain, and you end up with it being really dry on the leeward side or on the rain shadow side. That still doesn't explain why it's so hot over there in Death Valley, and that's the next thing we'll look at.

Same picture. Pacific. Sierra Nevadas. Redwoods. Sequoias. Here's that same picture. You've got air coming in off the Pacific, it's heading up the slope of the Sierra Nevadas, its cooling off. We talked about how all the water gets squeezed out. It's dry when it gets to the top of the mountain. And now it's sinking down the other side, and as it sinks it'll just heat up naturally. As you get to lower and lower elevations it gets warmer and warmer-- you know that. When you're at the base of the mountain, it's warm. As you go on a hike and you start climbing up the side of this mountain, it'll start to get cooler and cooler and cooler. Until finally you get to the top, and you've got put on your jacket.

Same process as you go down. As you head down the slope of the mountain, you start shedding your jacket, and then your sweater, and then you're in shorts and tee shirt by the time you get to the bottom of the mountain. So, this very natural process. It just gets cooler as you rise, and warmer as you drop. The one difference, though, is that the cooling off as you go up the hill is about three degrees Fahrenheit for every 1,000 feet that you rise up.

So, if you were to take a thermometer and go for a hike and go up Mount Nittany, and as you head up there, you would find that if you climb 1,000 feet, the temperature has dropped about three degrees Fahrenheit if the air is moist. If you have really wet air, if you have really moist air, lots of water in the air, very humid day, and you start to walk up, it'll cool off about three degrees Fahrenheit per 1,000 feet of rise.

On the other hand, as you head down on the rain shadow side, the leeward side, the Death Valley side, the air is heating up. Same way it was cooling off as you went up, now it's heating up. But now it heats up by five degrees for every 1,000 feet of drop. So, every time on the rain shadow side you have 1,000 feet of loss of elevation, the temperature's now gone up by five degrees. And you walk down another 1,000 feet, the temperature's gone up another five degrees if the air is really dry.

So now, we have this very dry air on the rain shadow side and it's heating up faster. And so, you drop down the same distance that you climbed up on the other side of the mountain, and you've heated up way more than you cooled off. And that's all the difference. When you take a packet of air and you raise it up to the top of the mountain, and then you remove all the water from it in that process, and then you bring it down on the other side, you've heated up way, way more than when you started out.

And so, this is why Death Valley is hot. You start out cool on the coast, you end up hot inland. There's an animation online, and you can take a look at that and review that again. Let's go back to the PowerPoint.

Where do these winds come from? We kept talking about these winds blowing in from the Pacific Coast. Why do you have winds coming in from the Pacific Coast? It's a fairly straightforward system. The sun heats the Earth, and hot air rises. That's the starting point for this whole process.

If you took one thing away from the first third of this class, it was the heat deep inside the Earth drives these convection cells, drives all of the mountain building. Take one thing away from this section, it's that the heat of the sun pounds down on the Earth, heats up the air, and that's what makes the winds, and then the winds do everything else. So let's take a look at that process.

Here we have a map of the Earth showing the places where you have these convection cells in the atmosphere. We're not talking about convection in the Earth anymore, but now convection in the atmosphere in very much the same way. You heat up the air, it rises up, cools off, and there's more heated air that's coming up from underneath it. And so this cooled off air gets shoved off to the side.

Let's take a look at this. We're going to go back to the drawing tablet. This is just so much better diagram, so you can keep this map in your head as I'm drawing my very crude pictures, that would be helpful, and then we'll come back to this.

Air circulation is driven by temperature, by heat-- same as convection in the Earth was. But the heat of the sun drives air movement. The equator is warm. The pole is cold. And the reason for that-- this is the Earth, this is the equator, and this is the North Pole where Santa has his workshop. The Earth is spinning around and around. And the Sun is somewhere way over here sending sunlight to the Earth.

If I were to go and look at a chunk, a square of sunlight, as it flies from the Sun to the Earth, I would find that it would smack straight into the equator, head on. The square, I just took a square piece of sunlight from the Sun and I carried it to the equator, and it went straight over there, and it ran straight into the equator.

If I did the same thing at the pole, I took a square of sunlight and ran it towards the pole, I would find that it would be spread out over a huge chunk of the pole. It would be a small part of the equator. All of that Sun is beating right into that small part of the equator because it's head on. But at the pole, that same chunk of sunlight is smeared across a huge chunk of it simply because of the curvature of the Earth. The Earth is curved in such a way that when the sunlight hits it, it hits the equator head on, but it smears across the pole, and so the poles get colder. They get less sunlight.

It's as if you were to take a piece of toast and take a spoonful of peanut butter and spread it across that. Or if you were to take that same spoonful of peanut butter and try and spread it across a huge sheet of plywood, you wouldn't want to eat that plywood. But there wouldn't be very much peanut butter on that sheet of plywood because you've taken the same spoonful of peanut butter and tried to smear right across this huge sheet of area, and there's very little peanut butter on any given spot.

Same thing happens on the Earth. The Sun is beating down on the equator head on, and so, all of the Sun's energy is concentrated in a relatively small area. It's nice and hot. Up at the pole, the same amount of energy's spread across this huge area, so every spot is cold and shivering. That's why the poles are cold and why the equator is warm.

What happens? We'll go back to the Earth, we'll make it bigger now, we have the equator, and we have this heat along the equator. The equator's being heated up because the sun is beating down straight on it. All of the energy is being jammed into a relatively small area.

The air gets warm. And what happens when things get warm? You know that. We've seen it over and over again. When things get warm, air gets less dense. What happens when things get less dense? We've seen that over and over again. Rises. Air rises up, hot air rises. And so all around the equator you have hot air rising upwards into the atmosphere.

As it rises up, somewhere up here, it will cool off. As it rises up it will cool off, but there's more hot air coming up from below.

And so, this cool air can't just sink straight down. This cool air gets shoved off to the side. And eventually it sinks down. When it gets to the bottom, it's heated up again. As it sinks down, it gets hotter and hotter and hotter. And then, it returns to the equator, and the whole cycle begins again. It heats up, goes back to the equator, rises back up, and you have a convection cell.

This whole process is a convection cell in the atmosphere. And this is wind. It's movement of air over the surface. What's that? That's wind. So, this wind is driven by rising air in the equator. It goes up, cools off, sinks back down, and then blows back to the equator. Rises up, goes out, sinks back down, blows back to the equator. In the process of blowing back to the equator, that's wind. Air transport by that.

Let's go back to the map that I showed you on the PowerPoint because that illustrates it so much better than this rather crude diagram. But I hope you get the idea from this.

You're seeing the same thing here, but just more fancily drawn out. This is an image from the USGS. Rising warm, moist air produces what, in this diagram is called a Hadley cell. It's just a convection cell. It was discovered by a scientist named Hadley, so they called it a Hadley cell. Rising warm, moist air. Descending cool, dry air, it gets cooled off, it falls down, and then it rotates back around, blows through the mid-latitudes back to the equator.

And so you have what are called the trade winds. They were called the trade winds because they blew so steadily that sailing ships could use them for trading purposes. They always knew these winds would be there when you needed them, and you could count on them. And so, you could fill up your ship with whatever you wanted, and your sailing ship with these big sails would catch the trade winds, and would be blown from Europe to the new world without any trouble at all. That's why they were called the trade winds.

The North Pole is cold, and you have these secondary Hadley cells, or secondary convection cells, called the Ferrel cell and the polar cell. But really, the idea is the same.

This is a map of the world's deserts. And if you look at them, what you see is you have these deserts at a few degrees north and south of the equator where that convection cell brings that air down again. The air goes up and then it comes down. Where it comes down, you get these deserts. Why? Because there's no moisture in that descending air. All of it is gone. So, rising moist air. You have all this rainfall at the equator because all of that air is rising up, and the rain's all falling out of it.

As it gets colder and colder and colder, the rain's just falling out of it. It goes up there, it goes over, and it comes down in the Sahara. It comes down in Australia. And there's no water left in it. It's all gone.

And so, you get these huge deserts, the Saharan Desert, the great Sonoran and Chihuahuan deserts in the US and Mexico. You get the great Australian deserts, and the Kalahari, and the Namibian deserts in Australia and Africa. It's because of these convection cells.

So now, we've talked about wind, and we've talked about a rain shadows. Now, let's take a look at what happens with that water when it falls out of the air and it makes rivers. You get rain, you get rivers. Let's take a look at those.

Water falls from the sky. It's called rain. Very straightforward. What happens to it when it gets down is far more complicated. About two thirds of it goes straight back up into the air. It mostly is taken up by plants and trees through their root systems.

So, here in State College we get about 40 inches of rain. That's about something like that. Every year. Some of it comes as snow, some of it comes as rain. If I were being pedantic, I'd say we get 40 inches of precipitation, but think of as rain. Two thirds of it, about that much of it goes straight back up into the air. The plants drink it, it goes straight up. The trees drink it, it goes up through their roots, goes out through their leaves, straight up into the air again. Or it just falls down and just collects in puddles and then the Sun comes out and those puddles evaporate and it goes straight up into the air again.

About a third of it, about this much, either sinks down into the Earth and turns into groundwater, or it runs off across a surface, falls into Spring Creek, falls into some other creek, eventually makes its way to the Juniata, the Susquehanna, and then down to Delaware Bay, and then out to the ocean, or to Chesapeake Bay and out to the ocean.

So, about a third of it, about that much actually remains on the surface of the Earth, two thirds of it goes straight back up again. This is known as the hydrologic cycle. Fancy name. All it means is you get evaporation in the ocean, it blows onto land, it rains out because of the processes that we talked about, rains out of it because it cools off as it goes up a mountainside. It can't hold all that water, and you get rainfall. Some of it goes straight back up again, and then maybe rains out again and it goes straight back up again and rains again. And some of it gets trapped in the Earth as groundwater, and some of it flows into streams and rivers and goes to the ocean.

Water is unique to Earth, we think. Everybody's always looking for water in all the outer planets. They go to Mars, they want to look for water. They go to the moons of Jupiter, they want to look for water. They go to the Moon and they want to look for water. It's so cold on the Moon, the water probably is almost certainly in the form of ice.

The key is life needs water. If you're going to have critters, if you're going to have any kind of organisms alive, we think they've got to have water. Water is so important to everything, for life to exist, that people don't look for living organisms on Mars, they just look for water. And they say if we find water, I'll bet you there'll be some critters alive there. And that's probably the case. Anywhere on this planet you go and you look for life, you look in the places where the water is and you'll find something alive there.

The human population of this planet is exploding. We're up to six billion or so, and we're heading towards 10 billion in the next 100 years. We all need water. And all the great wars that will come, a lot of the wars that are going on now are probably, to some extent, about water. People need water, and they'll fight each other for it. So, we need to be careful about watching what we do with it.

Here is Johnstown. Here is Johnstown. The great Johnstown flood. It came through, and it smashed in and destroyed-- there was a dam up river from Johnstown. It was a private dam that collapsed, and all the water behind it took Main Street here, nice, lovely place, some horses going down it, and all of these trees, enormous trees, rammed into the second story of this building. So, water is not a benign material. It can be quite destructive.

It's now the summer of 2006 when I'm filming this material, and just recently, just a few weeks ago, Wilkes-Barre, Scranton, the whole Northeast of Pennsylvania, Elmira, Binghamton were all flooded. These enormous rains came down and flooded out all of those rivers and they rose up over the levees. Luckily, the levees held and so people weren't killed, or not that many people were killed, but it was still quite disastrous.

These streams, when they make their way down, they modify the landscape. They dig holes, basically. Streams are very good at eroding their bed. Streams carry water. Duh. We all know that. But streams also carry sediments. Sediments are simply small pieces of rock, or sometimes bigger pieces of rock. And in the case of streams in the mountains, really big pieces of rock. So, sediments are simply pieces of rocks, and streams and rivers carry that along with the water. And they're really good at washing it away.

And so, all those processes that we talked about last time, mass wasting, a freeze-thaw breaking up all these rocks, you put a stream in there, and it'll just take that material and move it away. And then, these freeze-thaw actions and mass wasting actions will bring more material down to the river valley, and the river will wash that out. And then, more material will come down and that will get washed out.

And you do that for long enough and that mountain is gone. It takes a long time, but eventually it'll be gone. Without the river, you wouldn't have been able to wash all that material out, and so the valley would have filled up, and the mountain would still be there. With the river, you just wash the stuff out, more comes in.

Floods do most of the work. The normal flow of the river just isn't powerful enough to move much. The normal flow of the river will carry a little bit of sediment, but it certainly won't move big boulders. It certainly won't break things up. But then, every so often, just about every year usually, you get these floods, and every 10 years you get big floods, and every 100 years you get these enormous floods, and they're the ones that do the work. They're the ones that move enormous masses of material downstream. We use it. We need it. We've got to have it. We need it for agriculture, we need it for industry, we need it for moving material up and down the rivers, we need it for making hydroelectric power.

So, water is enormously important, and controlling streams has been probably one of the primary industrial motives or the things that we do most of all down through human history. If you look at human settlements, they were always on the banks of rivers because you can get water out of them to water your crops. You can use them to run mills to mill your grain. You can build boats and you can go up and down and trade with your friends up and down the river. So, all human settlements have always been associated with rivers.

Here is Glen Canyon Dam in Arizona. And the river is on the lower part there, the Colorado River is flowing down. And if you were to simply imagine that lower picture, that narrow deep gorge heading up, that's what it would have looked like 100 years ago. But back in the '30s and '40s, that dam was built, and when that dam was built, the flow of the river couldn't get past that dam. It got caught over there. And now, that lake that's above the dam is very useful. People use it for recreational purposes. But they also use that dam for hydroelectric, they generate electricity. That dam is used for irrigating crops all through that area.

So, the hydrologic cycle, as I said before, as water evaporates from the ocean it rains onto the land, and some of it goes into streams, some of it goes into groundwater, but most of it goes straight back up into the atmosphere. Let's follow one of those streams to the ocean, and let's take a look at what happens with it.

Streams are driven by gravity. Just like everything else, water wants to head downhill. And water can head downhill a lot more effectively than rock can. Because you get the soil or this rock up on a hill slope, and it can be nicely cemented in place. It can be happy where it is, especially if it's got lots of trees and grass that's stabilizing the slope. That slope can be fairly stable. You get rain, the rain falls on it, that water's going to head downhill. There's nothing that can hold water back, except things like dams.

Streams are recharged by direct rainfall, and by groundwater springs. So, rain can fall straight into the stream, or onto the banks of the stream and flow into the stream. Or the water can fall on the land far, far away, sink down into the Earth, and then slowly make its way through the earth as groundwater, and then these springs will come out and recharge the streams. And that's why rivers run even after long periods without rain.

Streams carry sediment, and mass wasting delivers sediment to the rivers, and then the rivers carry that sediment out usually in these big floods, but also during the normal processes. When those streams get down to the flat areas where the stream is falling more slowly, than that sediment gets deposited. So, up here in the mountains, mass wasting is bringing material into the stream, the streams are flowing through these very steep valleys, and so they carry lots and lots of water, lots and lots of sediment. And then, they flow out onto the plain out in front of the mountain. The streams slow down because they're going in more shallow slopes. As they slow down, the sediments can't be carried by these streams anymore, and they deposit them.

This is how a stream carries sediment. This is a cross section through a stream. The surface of the stream is at the bottom. And the top of it is where the stream is flowing most rapidly, and the bottom of the stream is where it's flowing less rapidly. And it can slowly move material either by what's known as suspended load, which are really tiny particles that are just floating up in the stream. And if you look at a stream and you see it's brown, it's because it's got all of this junk in it.

Water's blue, you know that. And normally a stream, if it's flowing slowly, is blue. But after a big storm, after it's churning and it's carried all this junk into it, all the sediment into it, it's flowing fast. You look at it, it'll be brown. And why? It's because of the suspended load. All of this dirt basically that's suspended in it-- soil that's suspended in it.

Down at the bottom of the stream, you have what's called bed load. This is the material that bounces along the bottom. The water isn't flowing quite so fast at the bottom, and so it can't carry all this material right up in it, and so it just picks it up and drops it, picks it up and drops it, picks it up and drops it, and stuff bounces along the bottom of the stream bed.

And then, you have bigger boulders, or gravel sized pieces of rock that are down at the bottom, and those usually don't move that much until you get one of those big floods. And then, all those pieces along the bottom will be washed along and moved downstream. Suspended load is the fine stuff, bed load is the bigger stuff that bounce along the bottom breaking up the rocks as they go making smaller rocks. So, this is another way that you have mechanical disintegration. These pieces down at the bottom, you have these rocks bouncing along, and every so often one will hit another rock and break it open. Or it'll just simply scrape off the bottom of the river and break off small pieces that will then be carried away with the river.

Two types of streams. Meandering streams-- this is a classic picture that you have, and we'll see some pictures here where the stream goes around one way and then comes back. Streams never go straight, they always have these big curves to them. If a river has mostly fine sediments, it'll make a deep channel, it will get clogged, and it will just meander. It will stay in its channel for the most part. It will keep breaking out or eroding along the outside of one of these curves and depositing on the inside of one of these curves. And so, the curves will get bigger and bigger, and we'll see a picture of that in a second. And then, it will make another curve and another curve. And here's a photograph of that.

So, you've got the stream that's coming down, and when it goes to the outside of the curve, it will have to speed up to make that curve. And then, it will keep eroding against what's known as a cut bank. And then, on the inner part is where the water's flowing more slowly and it will deposit material there. And so, the river over time will keep migrating inwards.

Eventually, eventually, that neck could get pinched off completely, and that ox bow will be cut off, and you get these ox bow lakes where the river has been cut off from its upper curve and now the river is just going straight. It used to meander around that curve, but over time it just cut across that curve and went straight. And that stranded piece of the curve is called an ox bow lake. It's named after these big yokes that the farmers used to put around oxen, and then that yoke would be hitched up to a cart, and then these oxen would plod along dragging the cart behind them.

A braided stream is a second kind. This is where you have lots and lots of channels that are all intermingled, and you don't know which is the main channel. They all are carrying a little bit. And what happens is you have all these big chunks of rock. They fall into the river and they block a channel, and so the river picks a different one. And then a big chunk of rock falls into that one, it gets blocked, and the river picks a different one.

So, you need big chunks of rock. Where you find big chunks of rock? In the mountains. So, it's mainly in the mountains that you have these braided streams, and it looks like a braid of hair from above, which is where the name comes from. And here's a photograph. You have all of these different channels that you don't know which one is the main one. And we'll go to another picture here. Mainly in mountainous areas where there's lots of big boulders. And one of these channels could get blocked very easily, and the river will pick a different way to go.

Another way to stop the flow of river is to put up a dam. Beavers build dams, natural landslides can create dams, or you can go out with a bulldozer and a great pile of concrete and you can simply stop the river. And that will stop the water temporarily until you get a lake built up. But, eventually, the lake will rise to the height of the dam, and then the water will start to flow again. The engineers will open the valves and the water will flow, but you'll still have a lake behind the dam.

So, the water stoppage is temporary, the sediments get stopped forever. Engineers don't like to have sediments going through their machinery, it clogs them up. And so, they pull water from the upper part of the dam. And all these sediments that we've been talking about, they come down with the river, they don't make it past the dam. They get deposited behind the dam, more sediments come along, deposited, more sediments come along and get deposited. The water keeps going through, but eventually the sediments are going to fill up that dam.

Here's a picture showing that. You have a dam, and over time, the water is filling up behind it, but along with the sediments are filling up. And that deposition is going to slowly, over time, completely fill up that lake, and then you're left with a useless dam, and you're going to have to build another one. And it's happening to many dams around the world. Dams have been-- some of these big dams have been in place for 100 years or more, or 50 to 100 years, and they're starting to fill up. People go out there, they dredge them. They have big machines that try and suck up these sediments. But in the end, these dams are going to fill up.

The river below the dam is clean of sediments. All the sediments have been dumped into the lake above the dam. And so, the river below the dam doesn't have any of those sediments left. Lots of water-- remember, the water's going right through. But that water that's coming out is clean. It doesn't have any sediments in it. What's it going to do? It's going to pick up sediments.

And so, you get extra erosion below the dam that you didn't used to have before. Before the dam was built, the river would come down, sure, there was lots of water coming, but there was also sediment coming. And so, if there was any erosion, there would also be deposition. And then, that was that most of those places would continue to have these gravel and sand bars. You build a dam, all the sediment's up there. You get this clean water rushing out past the dam, and it will enhance the erosion.

So, let's go to the drawing tablet and take a look at that process. This is a cross section of a slope, of a hill slope. Then you have a river that's happily slowing down. So, this is water that is flowing down. And remember, in addition to that, it has sediment that's caught up, and that's being transported down along with the river.

This is the case before I come along and I build a dam. It's a big old concrete wall. As soon as I do that, I put a lake here. What I've also done is I've done away with all the sediments downstream of that dam. All these sediments still coming down, all those red particles still coming down, but they're now filling up the lake upstream of the dam.

Downstream of the dam, I have just this lovely clean, blue water rushing along, and what's it going to do? It's going to start picking up sediment from the riverbed that it would not have picked up before. Before, it had all these sediments it was already carrying. It couldn't carry any more sediments. And so, it left the riverbed alone. But now, it's bright, blue, clean water, no sediments in it, it has lots of ability to carry sediments, and so it does.

Over time, you will erode downwards. Erode below the dam. This would not have happened until you put the dam in. So, you get deposition above the dam, and erosion below the dam.

Back to the slides. These gravel and sand bars below the dam get washed away. Lot of critters live on those bars. They don't have a place to live anymore. All of the beautiful, blue, clean water that's rushing out, now there's all these fish that used to like having this warm, dirty water-- dirty because it had soil in it to live in, and now they're living in this bright, blue, clean water, and they don't know what to do anymore.

They've evolved to hide in this from their predators, and they can't do that anymore. So, there's a lot of fish that go extinct because of that. Eventually, the reservoir above the dam will fill up and you need to build a new one anyway.

Let's follow that river past the damn, past the mountains, out on to the Gulf Coast. So, this river has just flowed from the mountain down onto the plains, and across the plains to the ocean into New Orleans. And we're going to talk about Hurricane Katrina. There are all these levees protecting New Orleans. Why does New Orleans need levees? It does. We'll find out why.

And one of those levees broke, the 17th Street levee, and all this water came rushing into New Orleans because New Orleans is below sea level. Why is New Orleans below sea level? We'll find out. It's below sea level, the levee broke that was protecting the city, and the water rushed in, and you know the disastrous consequences of that.

So, what's happened? Every year, snow melt comes along, extra rains come along in the spring, the rivers can't carry all of this. The rivers come along, and the water goes over the bank and on to the land on either side of the river and it floods. It happens. It happens every year. And it carries water and it carries sediment out onto the fields on either side of the river, and it deposits it there. Why? The river's rushing along, carrying sediment, it floods out onto the sides, the water spreads out, slows down, sediments can't be carried if the water's moving slowly.

Sediments will slowly sink down and be deposited onto the field. The farmers love it. The Nile Delta famously, pyramids, the Sphinx. All that civilization 3,000 years ago depended on the Nile flooding every year bringing this lovely sediment up into the farmer's field and depositing it, and then they could plant their corn and wheat and-- probably not corn. I don't think they had corn. Wheat, and grow it and store it.

And the lands and the farmers fields didn't get played out, they didn't get old because every year there was new material. When the Nile flooded, it would bring new material onto their lands. People built houses by these rivers, and they don't like the river coming into their basement. They don't like it coming into their first floor. They don't like it coming into their second floor sometimes if the flood is big enough. And so, they build levees. They build walls that keep the river from flooding.

"The Big Easy," New Orleans was built on mud from long ago. From when the river used to flood every year. Every year, the river would flood and put all this mud out onto the plains around the Mississippi, and New Orleans was built on that mud. And then, we came along, we put the levees in, and now we don't get anymore mud. But New Orleans was built on this mud. The water is slowly being squeezed out of that. And as it's squeezed out, New Orleans sinks down. It sinks lower and lower and lower. The levees are still there. And now, New Orleans is below the level of the river.

Let's go to the drawing tablet here and take a look at that sequence. I'm going to try and draw a river in cross section. And it's flowing down like this. And on the banks of the river, you've got trees and houses and tractors-- that's supposed to be a tractor-- farm fields. And so, you have everybody happily living their lives over here.

Once a year or a a few times a year, this river will flood. And water and sediments will spread out all along the banks. The sediment will get deposited as a layer on either side. So, you've got this layer of sediments on either side. And the water will slowly seep away or evaporate or whatever happens.

And the next year, you'll get a second layer on top of that. And the next year, you'll get another layer of sediments on top of that. And the next year, you'll get another layer. Now you don't build up to the sky because as you add each new layer, where the older layers sink down. So, the level actually remains the same. So, older layers sink down, new layers are dumped on top of them, they sink down, new layers are dumped on top of them, they sink down. The reason they're sinking is the water is being pulled out of them. Water is being squeezed out. And the soil is compacting.

And we go to a new page here. So, we're going to take a look at that same picture again. You've got a river, and there's the river flowing down. And on the side here, we have layers and layers of sediment. If I build a wall here, build a levee, and drive my Chevy to it, if I build a wall there and prevent the river from flooding-- so we've got this nice, solid wall here, and the river can never get out of its banks anymore. Over time, these sediments sink down because of water squeezing out.

So, they're sinking down because the water's squeezing out, but nothing is replacing it. So, over time, the surface sinks below the river level. And this is what happened in New Orleans. This is what has happened in the Mississippi River and all of Louisiana and in New Orleans. New Orleans has had these wonderful levees built to protect the city from the flooding of the river.

But at the same time, they prevent all this new mud from being spread over the landscape year after year to keep the surface up high, and so the surface has sunk down. And it sunk quite deep. In some places 20, 30, 40 feet below the level of the river.

If you go to New Orleans, you're walking along Poydras Street, or one of those streets in the French Quarter. And up there, somewhere, you'll see the top of the levee and you'll see a barge floating by above your head. It's a very, very strange feeling to be walking around and to see a ship floating by above your head way up there somewhere. But that's what New Orleans has. It's sinking down, and the river's up high. Now, that wall breaks, that water's going to come down at you.

Let's go back to the slide show. "The Big Easy" is built on mud from long ago floods. The water's slowly squishing out, the mud is compacting, New Orleans is sinking, the river's up high. Eventually, "The Big Easy" is lower than "The Big Muddy," which is what the Mississippi River is known as. The stage is set for disaster, and that disaster struck when the big Hurricane Katrina hit last summer.

It's actually even worse than that. Usually rivers do build natural levees, but then they'll break through those levees themselves and take a different path to the sea. And they'll always build these big deltas around where they come out into the ocean because you'll have one path and then a different one and a different one, and you'll just spread everything out over. But in the case of New Orleans, the Mississippi's been in the same place for the last 100 years.

Here's that picture that I drew so crudely with my pen over here, but that's the same thing that we looked at before.

Here is a satellite image of the Mississippi River coming down, and that sort of rounded peninsula is the Mississippi Delta. And then, you can see that big brown smear going out from it. That's all of the mud coming down the Mississippi and spreading out in the Gulf of Mexico. That's what that big smear of mud is. And that's how much mud "The Big Muddy" carries.

That's why the Mississippi-- that's its nickname is "The Big Muddy." It's brown. It's beautiful water, it's beautiful, clean water, but it's just filled with sediments being carried down to the ocean. And normally, the river would go along different paths and make this nice delta at the bottom of the river. But for many, many years, the Mississippi's gone down the same path year after year.

We're going to switch now to talk about groundwater, and then we'll finish up this section. Groundwater is, as the words says, its water that's in the ground. Soil's kind of like a sponge. You can put water down into it and it'll just filter through it. It's not a solid rock where you pour water on and it'll just flow off of it. It's more like a sponge where the water will go down into the little holes.

If you were to take a shovel and start digging around here somewhere, the very top part of the soil would be more or less dry. I mean there might be some water in it, but there'd be water and air. Until you got to what's known as the water table, and below that, every little hole would be filled up with water. You'd have soil particles, grains of soil, and you'd have water and no air. Everything below that is groundwater. And then the surface, they're separating groundwater from the upper part, which has some water and some air is known as the water table.

The rain seeps down into the ground and it slowly filters its way down to the water table and down into the ground water. And because it does it so slowly, any organisms, any bacteria that are living in it will die over time. Plus the little holes that the water has to make its way through are so tiny that the water can make it, but larger organisms can't.

And so the water, eventually when it gets down to the bottom, is actually incredibly pure. You can just-- people used to do this. They would just drill a hole down to the groundwater, pump it out and they would drink it. And it didn't matter. If there was all this agriculture and sheep and cattle and pollutants and everything at the surface, because most of those organisms would be filtered out before the water got down to the groundwater. You could just pump it out and you could drink it. That's true in most places.

That's not true around here in State College because in this area we have these big holes in the ground, caves, all these big sink holes around here because it's a heavily limestone dominated landscape. And so we have these big holes in it, and the water goes in, and boom, it shoots straight down to the groundwater level. It shoots straight down to the water table, and so we have a little more careful around here that we don't pollute the surface and down it goes.

If you pour a chemical into the groundwater, the water is like a sponge and it will take it. And unlike natural organisms, like bacteria, and giardia, an amoeba, which are killed over time, these pollutants like motor oil or the famous case here in State College is dry cleaning fluid. I forget what it's called, but there's a dry cleaning store here right in the middle of State College, and they found some of these dry cleaning fluids in the soil underneath it.

Those things can go down into the groundwater, and there's no killing those. You can't kill motor oil. It will eventually make its way down into there. So, do not pour your motor oil onto the ground. Take it to the recycling center. Take it to a gas station and they'll recycle it for you. Once that stuff gets into the groundwater, it is really difficult to clean it up. Think of the sponge. You add soap to the sponge, you've got to rinse it out over and over again to get it clean again.

In State College, lots of limestone. And limestone is particularly sensitive to that carbonic acid that we were talking about last time. It really breaks it down, eats away at it really quickly, and makes these big caves and caverns around here.

Our high school football stadium is actually built in a sink hole. If you go to it, the roads are all up here, and the stands head down along the walls of the sink hole, and there it is, football stadium, sink hole. The new school, the new Mount Nittany Middle School that we built for a great deal of money recently was actually more expensive than expected because there were all these sink holes underneath it that had to be filled in first and stabilized before the thing goes up.

So, State College has this problem, it's called Karst terrain, named after the region in Yugoslavia that is very similar to this-- has lots and lots of holes. Water seeps down into these cracks, get bigger and bigger, and makes these sink holes. If you put this cave up near the surface, then you can get these big depressions in the surface, or you can put a football stadium in it if you're lucky enough to have it in just the right place.

In areas with lots of limestone, the water doesn't go slowly. It goes foosh, shooting straight down because these big caves make a wonderful conduit down to the bottom into the Earth. And so, you don't have time to kill off all these bacteria. You don't have that natural filtering where the water trickles through these tiny, tiny pores and keeps out the bigger critters.

That doesn't happen here. The pores aren't tiny, tiny around here. They're big, and so the water just goes straight down, and so we're much more sensitive to groundwater pollution around here. But we are sensitive to groundwater pollution everywhere in the world.

So, my conclusion to you is that water is one of the most important substances on this planet. It falls out of the sky, it seems like it's free, it ain't, because it has to be collected in some way, for example in a dam, but that has its problems. It has to be collected down in the ground in some way, and that happens in some places and not in others.

All of the conflicts that are going to be coming up are going to be about water. So, if you do nothing else, teach yourself about the politics of water, the realities of water, and try and conserve this amazingly precious and amazing material. Thank you.

Image 1: Yosemite valley under cloudy skies. Forest in the foreground and mountains in the background. Bridalveil Falls on right in distance. Tracking the Great Glaciers from Yosemite to Greenland and Alaska. Yosemite truly is an incomparable valley. Bridalveil Falls, on the right, is a hanging valley; its small glacier did not cut downward as rapidly as the main glacier. All photos by R. Alley.

Image 2: Yosemite valley under cloudy skies. Bridalveil Falls in the foreground to the right. Closer view of Bridalveil Falls, right. The U-shape of the valley of Bridalveil Creek shows that it was glaciated.

Image 3: Close-up of Bridalveil Falls, Yosemite. Rock cliffs to each side of falls. Green shrubs just above the falls and forest below. Bridalveil Falls, Yosemite National Park. Bridalveil Creek has just started to cut a notch into the U-shaped cross section of the former glacial valley. The rapids at the bottom of the waterfall is running on rocks dumped there by the creek; eventually, the waterfall will be completely transformed into a rapids unless another ice age brings glaciers to re-form the waterfall.

Image 4: Close-up of Lower Yosemite Falls under blue sky, Yosemite National Park. Rock cliffs to each side and large evergreen in right foreground. Lower Yosemite Falls, Yosemite National Park. The numerous waterfalls of the park exist because the ice-age glaciers eroded the tremendous cliffs of the valley.

Image 5: Yosemite Valley, California. The deep, U-shaped valley was carved by glaciers. Half Dome above Yosemite Valley. A glacier flowing to the lower right deepened and widened the valley; see the next slide for a modern example.

Image 6: A valley in east Greenland that is about the same size and shape as Yosemite, but still contains the glacier that is carving it. Glacier draining Greenland Ice Sheet into head of Scoresby Sund, NE Greenland National Park. The scale is similar to that in the previous picture. Yosemite’s glaciers ended on land; this one calves icebergs into the fjord.

Image 7: Ice sheet, NE Greenland National Park. Wave-shaped folds are visible, showing flow of ice. Bright blue meltwater lake visible, top left. Near ice-sheet edge, NE Greenland National Park. The folds show that ice flows. Blue at top is a meltwater lake; such lakes may drain to the bed.

Image 8: Corridoren Glacier, Greenland. Very visible medial moraines, dark and light wavy stripes. Corridoren Glacier, Greenland. The stripes are medial moraines, rock debris picked up from ridges where two tributary glaciers join.

Image 9: Tributary glaciers joining in NE Greenland National Park. Arrows point to accumulation area, lakes in ablation zone, and medial moraine. Several tributary glaciers joining; flow is to right. NE Greenland National Park. Accumulation area in cirque (red arrow), lakes in ablation zone (green arrow) and medial moraine (blue arrow) are visible.

Image 10: Glacier in east Greenland, with high-elevation accumulation zone, low-elevation ablation zone, and older, lower elevation moraines. Accumulation zone in cirques (top), ablation zone (bottom), 150-year-old moraine (red), subtle, 11,500-year-old moraines (blue), NE Greenland Natl. Park.

Image 11: Close-up of glacier in south Greenland. Arrow points to debris-bearing basal ice. Water in foreground. Debris-bearing basal ice (red arrow) of a glacier in south Greenland. Rocks in such ice sandpaper, or abrade, the bedrock beneath as the ice moves.

Image 12: Close-up of a marmot on granite that has been abraded by debris-bearing glaciers, highlands of Yosemite National Park. The granite behind George the marmot has been abraded by debris-bearing glaciers, in the highlands of Yosemite National Park.

Image 13: Close-up of a Rock Ptarmigan on glacially striated granite, east Greenland. Arrows point to striae which are faint lines on rock. Rock ptarmigan on glacially striated granite (striae are faint lines on rock; a few of many are shown by blue arrows), east Greenland.

Image 14: Glacially striated and polished bedrock under blue sky. East Greenland. Glacially striated and polished bedrock, east Greenland. Ice flowed up the cliff from the lower right.

Image 15: Glacially abraded and plucked rock in fjord wall S. Greenland. Arrow shows ice came from left. “S” marks scratched area, “P” plucked area. Glacially abraded and plucked rock in fjord wall, S. Greenland. The ice came from the left, as indicated by the arrow, scratching/abrading (S) some places and plucking (P) others. Picture is about 10 feet across.

Image 16: Several small snow avalanches into a cirque surrounded by layered rock peaks, east Greenland. Small snow avalanches into a cirque, east Greenland. The layered rocks are flood basalts from opening of the Atlantic Ocean.

Image 17: Horn, Stauning Alps, NE Greenland National Park. Several cirques intersect and leave a towering peak. Horn, Stauning Alps, NE Greenland National Park. Several cirques have intersected to leave this towering peak.

Image 18: U-shaped valley in Tracy Arm Wilderness Area, Alaska. Thick cloud cover, highway in foreground. U-shaped valley from glacial erosion, Tracy Arm Wilderness Area, Alaska.

Image 19: Aerial view of moraines around retreating glaciers, Aple Fjord, NE Greenland National Park. Moraines around retreating glaciers, Alpe Fjord, NE Greenland Natl. Park.

Image 20: Aerial view of moraines around retreating glaciers, NE Greenland National Park. Moraines around retreating glaciers, NE Greenland Natl. Park.

Image 21: Deposits of Bjornbo Glacier, NE Greenland National Park. Rock pieces in foreground and mountains in background. Deposits of Bjornbo Glacier, NE Greenland Natl. Park. Ice was here about 1850. Glaciers carry pieces of different sizes, which make till when deposited.

Image 1: Glacier-free cirque under blue sky in Glacier National Park, Montana. Bear Grass blooming in left foreground. Bear Grass (really a lily, not a grass) blooming in a glacier-carved but now glacier-free cirque along Going-to-the-Sun Road, Glacier National Park, Montana. All photos by R. Alley, except for some of the Alaska pictures, which are by either R. Alley, C. Alley, J. Alley or K. Alley, and we’re not sure on some of them because we kept trading cameras.

Image 2: Glacier-carved scenery, Logan Pass, Glacier National Park. Snow-spotted mountains under cloudy skies, water in foreground. Glacier-carved scenery, Logan Pass, Glacier National Park.

Image 3: Comeron Falls, Waterton Lakes, Alberta, Canada. Water falls from different heights and at different angles. Cameron Falls, Waterton Lakes, Alberta, Canada (Glacier-Waterton Lakes International Peace Park). The rocks were folded by mountain-building, and the waterfall follows the bent layers.

Image 4: Female bighorn sheep at driver’s side window of car. Glacier National Park. Female bighorn sheep, Glacier National Park. In search of salt, she was going from car to car, licking steering wheels where perspiring hands had left deposits.

Image 5: Male bighorn sheep among boulders, greenery in background. Canada, near Glacier National Park. Bighorn sheep. This ram was over the border in Canada, but surely has relations in Glacier.

Image 6: Eight mountain goats on mountain side in Glacier National Park. Mountain goats are aptly named. Glacier National Park.

Image 7: Glacier National Park. Valley with green mountainsides and two “paternoster” lakes in view. Glacially carved “paternoster” lakes, Glacier National Park.

Image 8: Cliff in Glacier National Park, that was eroded when it was the side of a glacier that since melted away. Glacially truncated cliff. The ridge on the left was cut off by a glacier that reached at least as high as the sunlit peak, and that flowed over the point where the photographer stands. Glacier National Park.

Image 9: Surface of Greenland Ice sheet with view of melterwater stream entering blue lake at left center. Meltwater stream entering lake, surface of the Greenland Ice Sheet. At higher elevation, the ice-sheet surface is just snow. Such ice sheets now cover 1/10 of the Earth’s land, but during the last ice age covered almost 3 times more.

Image 10: Eight caribou on the dulled white surface of the Greenland ice sheet. Caribou on the surface of the Greenland ice sheet, here about 1 mile from the edge, avoiding mosquitoes. Healed crevasses are evident. This is in the ablation zone, and meltwater plus wind-blown dust have dulled the white snow.

Image 11: Margerie Glacier, Glacier Bay National Park. Blue ice visible in foreground, background glaciers grey. Bald Eagle sits on peak in center. Bald eagle (arrow) on top of Margerie Glacier, Glacier Bay National Park, Alaska. Glaciers can be large. Glacier ice is blue, as seen here, for the same reasons that water is blue (preferential absorption of red by water molecules).

Image 12: Bald Eagle sitting atop a flag pole in Sitka, Alaska, near Glacier Bay National park. Bald eagle, Sitka, Alaska, near Glacier Bay National Park, in case you wanted to know what the bald eagle in the previous picture looks like. Mostly, this is an excuse to stick in a cool picture.

Image 13: Northwest Fjord, east Greenland. Iceberg under blue sky and surrounded by blue water. Float-plane propeller right foreground. Iceberg behind float-plane propeller, Northwest Fjord, east Greenland. The berg reaches about 400 feet above the water, and is close to one-half-mile long.

Image 14: Harbor seal on small iceberg, Glacier Bay national Park, Alaska. Harbor seal on very small iceberg, Glacier Bay National Park, Alaska. Glaciers lose mass either by melting, or by calving icebergs.

Image 15: Cloudy skies and double rainbows over a bright white iceberg in Scoresby Sound, NE Greenland National Park. Rainbow above iceberg, Scoresby Sound, NE Greenland National Park. Icebergs are highly relevant to the study of glaciers and ice ages, but we’re not above sticking in pictures primarily because they’re pretty.

Image 16: A Fulmar in flight over a sea of ice, NE Greenland National Park. Fulmar in front of sea ice, NE Greenland National Park. Sea ice is frozen ocean water, usually less than 10-20 feet thick. Icebergs calve from glaciers formed from snowfall, and can be more than 1000 feet thick and the size of small states.

Image 17: Marble Island, Glacier Bay National Park, Alaska, covered with sea lions. Marble Island, in Glacier Bay National Park, Alaska, was scoured smooth by glaciers, and is now home to numerous sea lions.

Image 18: A bald eagle soars among a large number of sea gulls and ravens at South Marble Island, Glacier Bay National Park, Alaska. An immature bald eagle (arrowed) concerns the gulls and ravens of South Marble Island, a glacially scoured rock in Glacier Bay National Park, Alaska.

Image 19: A humpback whale breaching in the fjords of Glacier Bay National Park, Alaska. The deep, glacially carved fjords of Glacier Bay National Park and surrounding Alaska are home to humpback whales and other charismatic macrofauna (big, cute critters).

Image 20: Small island in Kong Oskar Fjord,Greenland, with raised beaches that formed as the island rose from the ocean. Raised beaches form a bulls-eye on this small island in east Greenland. Melting of ice sheets raised global sea level at the end of the ice age, but some regions that had been depressed under the former ice sheets rebounded faster than the sea rose, raising beaches out of the water.

Image 21: Satellite image of Chesapeake Bay, an old river valley that was flooded by the rising sea as the ice-age sheets melted. Satellite image of Chesapeake Bay. Geological study of the Bay and its surroundings confirms what you can see by inspection: the bay is a drowned river valley, indicating either that sea-level rose or the land fell fairly recently (mud is filling the bay; if the change happened a long time ago, the bay would be filled). Similar features along many coasts, including those being raised tectonically, show that sea level rose rather than the land falling.

Image 1: Snow spotted Rocky Mountains, greens trees in foreground. What do Rocky Mountain, Bear Meadows, and Greenland have in common? Hint: It’s cold up there on top of Rocky Mountain… All photos by R. Alley, maps from USGS and NOAA

Image 2: Three side-by-side close-ups of flowers. On the left, spotted coral-root orchid. Center, Glacier lily. Right , blue columbine. First, some Rocky Mountain wildflowers. left: Spotted coral-root orchid, middle: Glacier lily, right: Blue columbine.

Image 3: Maps of ice-age ice, which covered almost 1/3 of modern land areas, and modern ice, which covers only about 10% of the land area. http://www.ncdc.noaa.gov/paleo/slides/slideset/11/11_177_slide.html National Geophysical Data Center, NOAA, Mark McCaffrey The last ice age was most intense between about 24,000 and 18,000 years ago. This image re-creates the northern hemisphere about 18,000 years ago (left) and today (right). Notice that broad areas now submerged were exposed during the ice age by the lower sea level (e.g., green areas west of Alaska), and that both land ice (white) and summer sea ice (gray) were more extensive then. Southern-hemisphere changes were smaller. Also notice that the ice came close to Pennsylvania.

Image 4: Map showing that ice-age ice extended into the U.S. from Canada. http://www-atlas.usgs.gov/articles/geology/features/glaciallimit.html This map from the USGS uses distinct colors for different geological units. The white line shows how far south ice-age ice came from Canada. The “Driftless Area” in Wisconsin (white outlines and arrow) was missed by ice, which was channeled south along Lake Michigan and west along Lake Superior. Numerous flooded river valleys including the Chesapeake Bay (yellow arrow) are evident. Bear Meadows (pink arrow) and surroundings were beyond the Canadian ice, but must have been very cold when ice was close.

Image 5: Bear Meadows, State College, PA. Water and water grasses in the foreground. Forest in the background. Bear Meadows, above State College, PA, occurs where natural wetlands are rare. Sediment cores indicate that the bog formed during the ice age.

Image 6: Picture from east Greenland of a “striped” hillside because of downhill creep of rocks and plants formed on permafrost. Permafrost enhances mass movement (downhill creep). Direct measurements have documented motion of roughly 1 inch per year. Such downhill motion can move a lot of rocks over time, and might dam a stream occasionally. Shown here is a permafrost hillside roughly 1/2 mile across, in east Greenland, with rocks creeping downhill toward you.

Image 7: Large band of rocks, some with patches of moss, surrounded by fallen leaves. Trunk of small tree is visible to the left. This band of large blocks has moved down to just above Bear Meadows from the ridgetop, most of a mile away. (Is it any wonder that Pennsylvania hikers need good boots to avoid twisted ankles?) Trees growing on some of the rocks show that motion is not occurring now.

Image 8: Patch of stones in Greenland, sorted by size into a unique pattern, as the result of permafrost. Permafrost often sorts stones by size, making fascinating patterns, as here in Greenland. Dr. Alley’s boot toe (bottom center) for scale.

Image 9: Sorted stone circle in central PA, surrounded by fallen leaves. Unfortunately, the best sorted stone circles in central PA are now obscured by leaves. Weak examples are shown here, with coarse clasts circling the finer centers, which are marked by the white “X” symbols in the lower left and right.

Image 10: Side-by-side images of large bands of rocks. Bear Meadows on the left and Greenland on the right. The tendency for moving hillsides in permafrost to align clasts tipped on edge can be seen in Greenland (right), and is evident above Bear Meadows (left).

Image 11: Side-by-side images of large bands of rocks. Bear Meadows on the left and Greenland on the right. Similarities in size and orientation of blocks in flows that have moved downhill are evident in Greenland (right) and above Bear Meadows (left).

Image 12: Three permafrost hillsides. Top, Rocking Mountain National Park. Bottom left, Juniata River, PA. Bottom right, Devil’s Lake State Park, WI. Top: Rocky Mountain National Park – still moving downhill. Bottom Left: Pennsylvania (Frankstown Branch, Juniata River) Bottom Right: Wisconsin, Devil’s lake State Park/Ice Age Trail Below all three images: Present and Past Permafrost Hillsides

Image 1: Muir Glacier, Alaska, 2004. Blue water in foreground, glacier in background, large amount of rock exposed. Are glaciers changing? Yes. Over the last century, and over the last few decades, essentially every glacier on the planet has gotten smaller. Over shorter times, the “fun things” glaciers do (surges, kinematic waves, etc.) have caused some to grow while others shrank, but overall shrinkage is strong. Here are some photo pairs, historical and more recent, assembled by Bruce Molnia of the United States Geological Survey, and archived at the National Snow and Ice Data Center. The lenses used are not always identical, but the photos are taken as nearly as possible from the same spot, and you should be able to see the changes clearly.

Image 2: Muir Glacier, Alaska in 1941. Glacier covers most of photo, no water visible. Muir Glacier, Alaska, August 13, 1941, photo by B.F. Molnia

Image 3: Muir Glacier, Alaska, 2004. Blue water in foreground, glacier in background, large amount of rock exposed. Muir Glacier, Alaska, August 31, 2004, photo by W.O. Field

Image 4: Holgate Glacier, AK, 1909. Glacier covers much of rock, water in foreground. Holgate Glacier, AK, July 24, 1909, photo by U.S. Grant

Image 5: Holgate, AK, 2004. Small amount of glacier visible, large portions of rock exposed, water in foreground. Holgate Glacier, AK, Aug. 13, 2004, photo by B.F. Molnia

Image 6: McCarty Glacier, AK, 1909. Large glacier in center, water in foreground, mountain visible to left in background. McCarty Glacier, AK, July 30, 1909, photo by U.S. Grant

Image 7: McCarty Glacier, AK, 2004. No glacier visible. Water in foreground, mountains in background. McCarty Glacier, AK, Aug. 11, 2004, photo by B.F. Molnia

Image 8: McCarty Glacier, AK, 1906. Rocky water’s edge and water in foreground. Glacier in background, in front of snow capped mountains. McCarty Glacier, AK, Aug. ??, 1906, photo by C.W. Wright

Image 9: McCarty Glacier, AK, 2004. Rocks in foreground, no water, melting glacier in background in front of snow capped mountains. McCarty Glacier, AK, June 21, 2004, photo by B.F. Molnia

So why do hikers in Central Pennsylvania carry so many ace bandages? And the answer is that there's rocks on top of everything. All the trails in Central Pennsylvania are covered with rocks that are sitting up on a edge like this on top of the dirt. Why do the rocks get on top of the soil? And that story's sort of interesting. If you ever have a cat and you buy a bag of kitty litter, and you shake the bag and then you open it, you'll find the big pieces are on top.

You may find this in cereal boxes too that you'll get the big pieces floating to the top. And that's linked to a very simple geometric fact which is that little pieces can fall under big ones. And big ones cannot fall under little ones. If you want to find things like this that are happening today you won't find them here. These trees are not being rolled over by rocks that are moving. Our trees are perfectly happy here.

To find places where things like this are really moving today, you go to the top of Trail Ridge Road in Rocky Mountain National Park. You go to the North slope of Alaska. And there the ground is permanently frozen at some depth. And the rocks are slowly creeping down in the summer on top of that, lining up and turning up as the freezing and thawing move things around.

Here if you thaw the snow, it just soaks down through the rocks. It goes through the spaces. It goes down the river and it's fine. If it's frozen underneath, it can't soak down. And so you get soft mud that's full of water. It can't get rid of its water. It's sitting on top of slippery ice. What's it do? It slides downhill slowly. And so you go to the North slope of Alaska. You go to the top of Rocky Mountain. And all the hillsides are moving. And they're tipping the rocks up on edge and they're lining the rocks up in the direction they're going. And they're making things that look just like this without the trees. And so what we see here is a route of the Ice Age.

So here we are at Bear Meadows, perhaps the biggest and best natural wetland in Central Pennsylvania. Natural wetlands, lakes, bogs, are fairly rare in Central Pennsylvania. And that's because nothing has been making them recently. And nature fills them up. Rocks wash in in streams. Trees fall and leave's fall. And wetlands fill up. So when you see a wetland, you have to say geology made this fairly recently. Or humans made it. And this one's natural.

If we were to go out into this bog and stick a pipe down in the mud about 20 feet and pull it up and split it open, the mud on top has sticks and leaves and twigs of things that live here today. At the bottom it has a remnants of things that live on the North slope of Alaska today. It has evidence of tundra. This formed during the Ice Age. Below that's rocks.

And so it's rocks and then Ice Age and then stuff that lives there today. So this formed when the climate was different. And it formed by those beautiful rivers the rocks that we were looking at just up the hill. When this was tundra, when this was the North slope of Alaska or the top of Rocky Mountain, the hillsides were creeping down in these great rivers of rocks. And one of those dammed the stream. And that made a lake. And since then the lake has been filling in to give us this beautiful wetland that's full of good things all year.

Good morning. Welcome to Geosc 10, Geology Of The National Parks. Today we're going to be talking about my very favorite subject in geology, glaciers. My name is Sridhar Anandakrishnan, and I'll be your guide through some of the most amazing scenery on the planet. And some of the most important geology that we have today, in my opinion. We're going to be talking about glaciers, and ice sheets, and sea level.

And sea level impacts you. You might never see a glacier in your life, but I guarantee that you know about how sea level affects beaches and coastline communities, and your life is going to be affected by that.

So, let's go and first have a quick look at some of these lovely places, and then we'll come back to the presentation.

Today's tearing down mountains. Glaciers are wonderful at destroying mountains. They're one of the best ways we have to both destroy mountains and to make them beautiful. If you didn't have glaciers, these mountains would look very, very different than what they do today.

This is Yosemite National Park in California. It's just up from San Francisco. You can fly into San Francisco, and drive, and you'll be up there in Yosemite in three hours, four hours, something like that. It's one of the most famous places because of people like John Muir, and the amazing photography that has come out there. Some of the history of the place. So, it's something that is almost legendary in conservation circles and in mountain climbing.

This is Bridalveil Falls over on the right over there. And the classic shape of that valley, going up from it, that U-shape for it tells us that this was glaciated. And we'll find out why that U-shape tells us it was glaciated.

And you just look at it way in the back, there. You have Half Dome. And there's probably people that are crawling up the side of it. It's one of the classic climbs of the world.

Here's a close up shot of that Bridalveil and showing that sort of rounded valley heading up from the falls.

Here's Lower Yosemite Falls. There's all these waterfalls all through there. We're on the lee side, the Pacific side of the Sierra Nevada mountains.

Remember last time we talked about, in the Redwood National Parks section, how we talked about when the winds, these wet, cool winds come along, and they start to rise up the mountain, and they get colder and colder, the air gets colder and colder, and then all the water gets squeezed out. Well, here's where it gets squeezed out. It gets squeezed out in Yosemite National Park. And so you've got tons of water pounding down through there. And then, you have these beautiful valleys, and then all the water comes cascading down the sides.

Here's another picture of Half Dome. The glacier was coming right down that valley. You can just imagine 20,000 years ago, if you were standing where this photographer was standing, you'd just see that whole valley filled up with ice all the way to the back, and that ice would be flowing towards you. And as it flowed along, it would be carving out that glacier, making it a deeper and deeper, year after year. And that's why you get these vertical walls.

This is a photograph not in Yosemite, but we've gone off to Greenland at this point. This is Scoresbysund. This is perhaps what Yosemite looked like. You can see there's a similarity. You have this big mass of ice coming down. You've got these huge walls going straight up. 20,000 years ago, instead of this minuscule amount of ice that we have in here— it's an enormous amount of ice, but 20,000 years ago, that ice would have been half a mile or a mile higher up. It would filled up that whole valley.

This is near the edge of the ice sheet. There's a blue pond at the surface. The ice here is perhaps half a mile thick. So, if you were to sit there, and take your shovel, and start digging, digging, digging, you'd have to dig for half a mile before you got to rock. And you can see those big folds where the ice is flowing down. A bunch of cracks and crevasses. If you're trying to travel across that, you could fall very easily into those. Absolutely dramatic, gorgeous.

This is [UNINTELLIGIBLE] glacier in Greenland. And you can see it flowing. Those big stripes coming down towards you, those are individual glaciers that all have come down and merged together. And you can still see those bands where they came together, and then as a valley curves, it comes down.

Here we have a bunch of tributary glaciers where the green arrow and the red arrow are that have come together, and these amazing, huge crevasse. I wouldn't want to be walking across that glacier. You'd just be falling into those holes all the time.

Another photograph of the glacier. Here we have some evidence, just the first beginnings of a clue that glaciers can change their size. The blue arrows are pointing at where the glacier used to sit just a little while ago. About 150 or 200 years ago, that glacier used to be at a different place. And we can tell that because of the color of the rock, and the marks on the rock. And then, the glacier has retreated back from there in the last few hundred years.

This is looking at the side of a glacier, and you have all of these debris bands in the bottom, and that tells us that glaciers aren't just these clean, beautiful, white, ice and snow masses. They also have all of this rock and mud and debris along the bottom. And so, here's a second clue that glaciers can modify the landscape. They can rip out rocks and carry them away, and here's evidence that they do that. And they're very good at doing that.

All the places in this country that have lakes— Minnesota, the land of 10,000 Lakes. The finger lakes in New York. The Great Lakes themselves, Lake Michigan, Erie, Superior. All of them are there because there was an enormous glacier—an ice sheet, really— that sat on top of North America, that filled all of Canada and flowed down into the northern tier of the US, and as it flowed down, it just churned out these big lakes and ripped them up.

Here are some of the critters that live in Yosemite National Park. And here are some more. These are not in Yosemite. This is in Greenland. Then, you can see these striations were the glacier came by. But now, the glacier's gone, and there are ptarmigan wondering across that landscape.

Here's another example of what glaciers can do. Glaciers flow across this, and they just polish it. It's like taking sandpaper and rubbing it for hundreds and thousands of years across this rock. You smooth it and striate it.

Just beautiful. Snow avalanches coming down. Just some of the most dramatic scenery. I've got a confession to make. I'm not really a geologist. I'm an engineer. I started out my life as an engineer, and I worked as an engineer. And then, I got a job to go to Antarctica and work on an engineering project. And I said, man, I got to keep doing this, and I became a geologist, just so I could go and work on glaciers, and understand them, and continue to go to these absolutely beautiful places.

Look at this. Look at that ridge running up there. If there hadn't been a glacier there, you wouldn't have that ridge. The glacier came along and literally chewed away at the side that mountain. And there was another one on the other side of the ridge that chewed away at it, and the two of them formed this sharp ridge that runs up the side of them. And then, where there's two or three of them that come together, you get these sharp horns that go up into these very, very steep peaks. You wouldn't have it unless you had glaciers doing that. This is some of the most beautiful scenery that I've ever seen.

This is in Alaska. Another one of those nice, U-shaped valleys where a glacier had come pounding down that towards us. It's all gone now. Where did it go? Why did it go? That's what we're going to be talking about today.

Here's another one. I can just sit here all day and just show you pictures, and I'd be perfectly happy. Unfortunately, we're going to have to go and talk about why this is important, and we'll do that next. Let me just run real briefly to Antarctica, and we'll see some pictures there. And then, we'll go to the real stuff.

So, this is Antarctica. The reason we want to go here is that Antarctica is the best analog to what Yosemite might have looked like 20,000 years ago. There's still huge glaciers in Antarctica. This is a mountain range that's 10,000 feet high. And that glacier almost fills it right to the top. Yosemite National Park, the mountains there are 6,000 feet high, and the glacier once did almost fill that valley. Same way here, and these glaciers do fill their valley. And so, we can study these glaciers and learn a lot about what Yosemite might have looked like 10,000 years ago or 20,000 years ago.

Here's [? Ketlet's ?] glacier that's coming down towards us. You can see those flow stripes. And as I said, those are enormous mountains, but there's only a little bit of them, maybe 2,000 or 3,000 feet, that are sticking up out of the snow. All the rest of that valley— and you can imagine if you ripped off that glacier, you'd have this two mile deep valley that would be sitting there, and you'd be standing there looking up these two mile high walls.

Here's a valley. This is a dry valley. It's in Antarctica. For fairly complex reasons, the glaciers can't get into this valley. They did at one time. They carved it out, and now they've retreated, and they have these frozen lakes in the bottom of them. But here, you have one of those two mile high valleys. We're flying over it in an airplane and looking down at it. And way in the back, way, way in the back, you have the main Antarctic ice sheet.

Here's the Transantarctic Mountains. You have these beautiful, layered sedimentary structures a long time ago. These were much lower, and then they were raised up over the last 100 million years or 150 million years. And now they stand 10,000, 12,000 14,000 feet high. And then, right behind them, you can see that white area there is the East Antarctic ice sheet flowing down towards us.

Here's one of those glaciers trying to get through the Transantarctic Mountains, coming down and flowing right around through all the rocks, and trying to erode it, and trying to deepen those valleys.

This is Mount Erebus. This is a volcano in Antarctica. You can see the steam rising up out of the top of it. There's a big lava pool up at the top. There's lots of people that go up there and study it. It's 13,000 feet high. And all the sides of it are ice covered. It's so cold in Antarctica that even though it's this huge mountain that is a volcano, and there's this bubbling lava pool at the top of it, you still have this mass of ice that's covering the whole thing.

This is Mcmurdo Station in Antarctica. This is where we do our research. We fly in here. You can see it looks kind of like a mining town. It's a very gritty place. There are no trees there. There's no vegetation there. The soil is all frozen, so you can't dig underneath it to put all your utility lines, and sewer lines, and electric lines. All of those run above.

So, it's just a very gritty place. But you've got to have that to do your research, to have the airplanes fly around, and so on. This is not one of the most beautiful places in the world, but hey.

This is a view looking out from Mcmurdo, out to the ocean. The ocean is frozen there. It's so cold that the ocean simply freezes over. In some years, it never opens up. Some years, it just remains frozen all through the summer. And then the winter comes, and it freezes, and then the ice just thickens. And that might happen for two or three years in a row, but usually that area does open out.

This is one of those distressing photographs. You got to have fuel to fly airplanes. These are big fuel tanks. And then right in the background, you have this absolutely beautiful shot of Mount Erebus rising up above the town.

There's some critters that live in Antarctica. The most famous, of course, are penguins. I've been down there many times, and I still am delighted every time I see one, because they're just such charming little fellows. And here we are, enjoying watching one of them who is looking at us as well.

And here's a close up. This is an Adalie penguin. They're about a foot and a half or so tall, and just as curious and fearless as anything. They have no predators on land, so when they're walking around on the snow here, they are not bothered if anybody walks around.

And he's off. We're not quite sure where he's off to, he or she. And off into the distance.

This is a penguin rookery. The penguins are displaying. They're sitting there sticking their head up. And those little circles of rocks— I don't know if you can see them— those are their nests. There are no twigs here. There's no place to put their eggs, except the only way to protect them is in these little circles of rocks. And so those rocks become really valuable. And they'll steal them from each other, and they'll get into these titanic battles. When the one steals it, they'll go and fight each other, and they'll bounce against each other. And it's quite serious to them. It's quite amusing us.

This is a view of Erebus stretching up above us, and in the foreground, you have a hut from one of the early explorers from 1910. This is Shackleton's hut. This is what he lived in through the winter before he went on his epic journey to try and get to the South Pole. He didn't succeed, but it was quite a story. There's a close up of his hut and one of my colleagues waiting to go into it.

This is a glacier. We're looking at a glacier. It's coming down towards us. The front of it is breaking off and falling down, but you can imagine— you have to imagine, because we're down below— that it just heads up and up and up the side of Mount Erebus for almost 10 miles. It's a huge glacier.

And here's some people for scale. So, there's these people walking around at the base of it. And that's not even all of it. Just as much as there is above, there's probably three times as much as that below the ground, below what we're looking at, below where those people are standing. The scale of these things is so majestic, it's hard to imagine.

There's a close up of it. You can see all the cracks in the face, and where it's going to break off, and the next chunk is going to fall off towards us.

Here's another picture of a glacier flowing down around the curve and coming towards us.

And to give you a scale of that glacier, off in the middle of the screen, there are two huts. Those are actually fairly big houses. They'd be a house that you might see around town over here. A nice, single story Cape Cod or something like that. These aren't Cape Cods, but that's about the scale of it. So, there's a couple of huts over there, and they're just dwarfed by the edge of the glacier, which you can see to the right of them.

And here's one of these glaciers coming down, and all destroyed, and cracked, and broken, and crevassed. And you can't travel over it, which is why it's nice to have helicopters and airplanes.

And here's another shot of it from the air. And a close up of all the huge seracs and crevasses. And another shot.

So, we're going to end this slide show. Here's one helicopters that we use to fly around. And I think I might have a couple more pictures here. Mount Erebus again, and Castle Rock in the foreground.

Even I don't want to end the slide show here, but —and here's how we move around on the surface with these snowmobiles in the storm. This was a pretty bad storm. You can see the wind blowing across the surface. And this is what we live in. Some tents. That's the tent that we spend two or three months in Antarctica, sleeping in and doing our work from. Putting up a bigger tent. It's cold down there. You've got to wear your parka, pull up your hood.

So, we've had a little tour of some lovely places around the planet. And now, we're going to find out what it all means. Why are there glaciers? How do they flow? How do we know that they came and went? Why was Yosemite filled with two miles of snow a long time ago, and it isn't today? Those are the sorts of things that we're going to be talking about. What glaciers are. Erosion by glaciers. How a glacier makes a hole. How did it make Lake Superior? How did a glacier make the finger lakes? How did a glacier make the 10,000 Lakes of Minnesota? Those kinds of things.

And then ice ages. What evidence is there for them, and why do they happen? Why did it get cold, and why did it get warm?

A glacier is very simple. It's a mass of ice and snow that deforms and moves. By deformation, I mean it simply changes its shape. It goes from here to there. It flows across the surface of the landscape. That's all it is. And it does so under the force of gravity. Glaciers flow when snow falls on the surface of the land and it doesn't melt, so it accumulates. If it's cold enough that the snowfall doesn't all melt and disappear, as it does around here, year after year —every year it snows here, too, but we don't have any glaciers. And the reason we don't is all that snow disappears in the summertime.

But if you go to a place where it's cold year round, that snow remains. And then, there's more snow that falls on it the following year, and more snow that falls on it the following year. And eventually, if the ice gets thick enough, then you form a glacier.

Where is it cold? It's cold at the North Pole, and it's cold at the South Pole. Why? If you remember from last time, we talked about that. The sun is shining on the Earth. At the equator, all the sun's rays just slam straight into the equator. And so, all that energy goes right onto the equator. Up at the poles, that same amount of energy is smeared across a larger area because of the curvature of the Earth. And so, it's colder at the polls, warm at the equator. If it's cold at the poles, then that snowfall doesn't melt.

If you go up high mountains, we talked about that last time. As you go higher and higher up, it gets colder and colder. And you get to a point where it's so cold that the snow doesn't melt in the winter time. That's where we could form a glacier.

Or if it just snows so much and the summers are relatively short so we can't melt all that snow in the summer time, then you could form a glacier. For example, in the Olympic Mountains, they just get so much snowfall that even though it's a relatively warm place, these aren't huge mountains, you can still form a glacier.

You have glaciers at the equator. You have glaciers on Mount Kilimanjaro in Africa. And the reason for that is, they're high, and they get a fair amount of snowfall.

If it's cold but you don't get a lot of snowfall, then the ground just freezes and you get what's called permafrost.

Glaciers move and deform because of gravity. Gravity is one of the key forces in geology. I've talked to you about it over and over again, many, many times. We talked about it with mass movement last time. We talked about it with convection cells earlier on. And here it is. It's coming at us again. It's how a glacier moves and deforms.

When you make a pile of anything, the highest spot in that pile will put more weight at the bottom than the lowest spot, or a lower spot, on that pile. So, there's more force under the highest spot and less force under the lowest spot. And like everybody else, glaciers respond to forcing, and they want to move from where there's high force to where there is lower force. And so, the glacier simply moves off to the left.

I'm going to go to the drawing tablet now, and we're going to sort of summarize this part of it.

Here's the ocean. Everything always starts with the ocean. Here's land. And we're going to put some trees on land. And we're going to put some houses on here. And then, we're going to have it snow. We get water that evaporates from the ocean. It gets blown up onto land, and it starts to snow, and we'll show snowfall as these little X's, and down they come. It's snowing on the land.

And if it is cold enough, that snow will make a pile. And if it's cold enough, and the snow doesn't melt, it'll make a bigger pile. And a bigger pile. And a bigger pile, year after year. Until the weight of that pile gets large enough that the glacier wants to start— I'm going to remove these little snowfall marks, because it doesn't snow inside a glacier. It only snows on the outside. So, we'll get rid of some of these things.

So we've got a pile of snow and ice. And if we make that pile big enough, it will start to flow off to the sides. And the reason for it is that the force here is high. Why? Because it's got lots and lots of ice sitting on top of it. Lots of ice.

And the force here is low. Why? Not so much ice on top.

And so, the ice flows from where the force is high to where the force is low. It flows off to the side like this, and it flows off to the side like that.

This sketch has gotten a little messy. I'm going to start it all over again. We'll put the ocean in. We'll put the land in. And we'll put in our glacier. Now we've built this big pile of ice, and it's flowing off to the side. And when it gets to the edge, it will melt. And the water will simply run back into the ocean.

So why doesn't that pile disappear? It's flowing off the side. It's melting. It's going off. And the reason it doesn't disappear is it's still snowing on top. If you remove material off on the edge, if you add material up on top, and you flow from the one to the other, you can keep that glacier at its same size. If you get it just right, if you melt just the same amount as you add on top, and you flow that from the one spot to the other, and you do this continuously over and over again, that mass of ice isn't going to change its size. It's going to stay the same year after year.

This is known as the accumulation zone. That's where snow accumulates. Simple enough.

This is known as the oblation zone. Oblation is a fancy word for removal. To oblate is to remove. The oblation zone is where you remove ice and snow.

And then, the red line indicates flow from the one to the other.

We got to finish this picture out with one more thing, which is evaporation of ocean water followed by transport inland. And then that ocean water deposits as snowfall.

So do you see that cycle? You get evaporation in the ocean. It comes inland. It falls onto the accumulation zone of the glacier. It flows down to the oblation zone. It melts, and it goes back to the ocean. And if you get it just right, the glacier doesn't change its size and the ocean doesn't change its size.

And if the temperature is constant, then the system will come to equilibrium. It will come to a spot where you are removing just as much as you're taking in. And year after year, the glaciers will stay the same. If you change the temperature, if you start to warm things up or to cool them down, then that balance will shift. And that's what we'll talk about.

So this is how a glacier works. It flows from the accumulation zone to the oblation zone, and it does so under the force of gravity.

Glaciers always move from the high to low spot. The high on the surface of the glacier, what do I mean by that? Here we have that mass of ice and snow with the rock underneath it. The rock is relatively flat. The glacier will always flow from where it is high to where it is low.

Not the rock underneath. The rock underneath, you can see, is pretty flat. And the analogy is if you take a bowl or plate, and you start ladling molasses onto it, or you start to ladle pancake batter onto it. As you make a pile, and you keep ladling material into the middle of your plate, what happens? It isn't if your pile just goes straight up in the sky as you ladle onto it. Your molasses just doesn't build up and up and up. It flows off to the side. And which way does it flow? It flows away from where that pile of molasses is high to where that pile of molasses is low. That's all that glaciers do. They flow from where they are high to where they are low.

And in fact, they can even flow— I'm going to go to a new page. Now, we're going to have a glacier sitting in a bowl. The glacier will still flow in that direction even though the rock underneath slopes up. Doesn't matter. Even though that rock slopes up, the glacier will still flow in this direction because the top of the glacier is higher there.

Now, there's a limit to this. If you make the rock really, really steep, then at some point the glacier won't be able to climb that hill. But you have to get pretty steep. You have to get 10 times as steep as the slope at the top of the glacier for the glacier to change direction and head down.

So, this is flow of glaciers. And the balance, the hydrologic balance of evaporation and accumulation and oblation.

We're going to go back to the presentation, and then we'll come back to this drawing tablet in a minute.

Whoops.

Glaciers move from where the surface is high to where their surface is low. "Their" surface. Not the surface of the rock that they're riding over, but their surface themselves. They can even move uphill, like pancake batter flows up the sides of a bowl when you pour it into a bowl. The pancake doesn't all congeal right in the bottom of the bowl. It can actually lap up the sides of the bowl and eventually drip over the edges if you keep pouring more and more into it. The North American glaciers came up into Pennsylvania, and they flowed uphill into the mountains of Pennsylvania because of this process.

And here we have a cross section of a glacier. And you have flow of it from the left, in this case, where it says "Lake Ontario," to the right, where it says "Pennsylvania." Even though Pennsylvania's higher up than Lake Ontario— State College is higher than the bottom of Lake Ontario— when the ice filled it, the ice actually flowed, quote, "uphill." The rock heads uphill, but the glacier itself, the top of it, was sloped from Canada down towards the US. The glacier was higher in Canada than it was in the US, and so it flowed from the high spot of the glacier to the low spot.

When glaciers flow and deform, they don't just move as a mass. They don't just simply have this big fat thing, and the whole thing moves together. They actually deform and change their shape. And that's what's shown in the bottom graph, and I'm going to go back to the tablet and illustrate that.

We'll use that same picture that we had on the presentations. We have the glacier that looks like this. And the bottom of it looks something like that. This is Lake Ontario, and this is Pennsylvania.

If you were to drill a hole down through this glacier, a nice, straight hole— and people do that all the time. They do it to sample what's underneath. They do it to see how thick the glacier is. They do it to sample the ice itself. So, there's lots of reasons for doing it. You drill this hole in the ice, and you come back a year later or two years later, and you measure what that whole looks like. It won't be straight anymore.

If you come back in a year, that hole will look something like that. The top moved a lot. And by "lot," I mean 100 feet, 500 feet. Maybe as much as 1,000 feet after a year, maybe as much as 5,000 feet after a year. So glaciers don't move enormously fast. In a year, they flow anywhere from a few feet to a few thousand feet, but they don't move as fast as you or I could walk, for example.

So, the top has moved a lot. The bottom has moved a little. And there is this curve in between where different places inside of the glacier have moved different amounts.

So, the top is always moved the most. If I were to stand here on the top, I would always move forward, ahead of a marker at the bottom. But it isn't a straight line. It isn't a flat line. It's this sort of complicated curve. And this is a big area of research. People want to know what shape will that hole look like after a year or after 10 years, because it tells us a lot of a glacier flow. But this is a very simple thing, is you have deformation within the glacier that will change the shape of the glacier.

Now, in addition to that, you also have sliding. of the glacier over the base, over the rock. So, glaciers can slide as well. They might slide a little, they might slide a lot. It really depends on how much water there is down there.

And you can have water underneath glaciers. Even though glaciers are ice and snow, and they're very cold at the top, they can be very warm at the bottom because of the heat that's coming up from inside the Earth. And where is that heat coming from? You know, radioactive decay. Remember that. The inside of the Earth is hot. That heat is coming up. It's coming up all around us. If you look down, you'll see heat come up through your feet. You won't be able to measure it. There isn't a lot of it. But there's enough that the bottom of the glacier is warm.

So, you get sliding of the glacier over the base, and that's where the erosion goes on. As a glacier slides along, it rips up the rock, and it destroys the rock. It pulls it up and carries it away, and you have erosion of rock as the glacier slides along.

Let's go back to the PowerPoint.

Glaciers with lots of water at the bottom are good at eroding. If you get lots of water down there, then you get this sliding mechanism. Instead of simply having deformation within the ice, you get sliding at the bottom, and then the glacier can pull up bits of rock and carry them away. "Plucking" is when the glacier literally breaks loose small rocks. You have this big mass of ice. There'll be some small crack in the rock, and it will break off or pluck a piece of rock away and literally carry it off.

"Abrading" is when the glacier drags those small rocks. So, it's plucked one of these small rocks, and it's carrying it away. And as it's carrying it away, that rock acts like sandpaper. It actually scrapes away at the rock that's still underneath the glacier, and then will break off small bits of other rock that will also then be carried away and washed away because of all this water that's down there.

Any water flow under there really helps. If you've ever done any woodworking, you know that your sandpaper will get clogged after a while. You got to clean it off. This is the same thing. So, as you rub at this, if there's water underneath the glacier, that water will simply wash away all the loose material, and then you'll have this clean surface to rub some more. The water will wash away the loose material, rub some more, and the glacier will dig down and down and down, and deeper into the rock underneath.

Here's a picture illustrating that. Both you have plucking on the one side, abrasion on the other side. If you get one of these sort of sloped rocks underneath there, then you can have both of those processes going on. The ice is flowing over these, and it's plucking and abrading. And over time, it will carry that material away, and it will keep digging down deeper and deeper.

And here's an example from the Alps where the glacier would have flowed from right to left across there, and that face we're looking at is where all of the rocks were plucked away and gone. And the glacier, of course, is gone, but this is what the bottom of the glacier would have looked like when it was there. It's smooth on one side where the glacier came from. It's rough on the other side. It's known as a roche moutonnee or rock sheep, that looks a little like a sheep, sort of a rounded thing with this fuzzy edge on the side of it.

The abrasion can be seen. Anywhere there's been glaciers, you get these smooth, polished surfaces with these long, straight lines on them. And the long, straight lines always point in the direction that the glacier was heading. And those long, straight lines are simply from those rocks that it plucked. As they get dragged along the remaining rock, it just leaves these long striations and stripes on there.

The net result of doing all this work of abrading, and plucking, and going on and on, is to build mountains. When the glacier was there, it was just tearing away at the mountains, and it leaves these huge valleys, these deep valleys. And because glaciers are very wide and broad, the valleys that they leave behind are very wide and broad and rounded. And that's why a classic glaciated landscape, like the photographs we saw in the beginning of Yosemite, have this rounding to them.

As you go higher up the valley, and you get to the top, you get to where these glaciers have been chewing away at the side, and you get these very sharp ridges between them. And then if two of these glaciers come together or three of them come together, you get these very sharp-sided features that are diagnostic of glaciated landscapes. U-shaped valleys, hanging valleys, rounded bowls, and sharp ridges and sharp mountains. These are all the things that you'll see if you go up to Glacier National Park, for example.

Glaciers are really, really good at eroding. The finger lakes are there because the glaciers. The Great Lakes are there because of glaciers. The 10,000 Lakes of Minnesota are there because of glaciers.

Streams make a very different landscape. A stream can cut down really sharply where it is, but streams are generally not a mile wide. Streams are usually a few 10s of feet wide, or 100 feet wide, or something like that. You can go out, you can look at your stream that's out there. And they're really good at eroding, too. And they're really good at cutting down. But they're not good at cutting down across broad territories. They'll cut down right here, and then more rocks will fall in and they'll cut down, and more rocks will fall in. And so you get these V-shaped valleys when a stream has been there for a long time.

Any time you drive around here, and you look at the shape of these valleys, and they have these really sharp Vs to them, you know that a stream's been going through there. You go to Glacier National Park, you get these nice, rounded, broad U-shaped valleys.

And here's an example of one of those. Nice, beautiful, rounded valley, broad across the bottom. Now there's a stream running down the middle of it. And if you leave that situation alone, and you let that stream run in the middle of it for 50,000 years, that stream will cut down, and cut down, and it will turn it into a nice V. But because the glacier's only been gone for a few thousand years, it's still rounded and U-shaped.

Here's one of those lakes that's left behind from the glacier. And here's another fjord. This is an arm of the ocean that's come in. The glacier used to flow down through there. The glacier went away and the ocean came running back in.

More, just beautiful, alpine scenery and glaciers. Here's one of those really sharp features where the glacier's eaten away at the side of it and left these sharp ridges.

This is the Matterhorn. Very, very famous mountain in Europe on the French-Swiss border. And the reason it is three-sided like that— there's two that you can see and one more on the side, on the other side— is there were three glaciers on the three sides that were eating away at the side of it. And they kept eating away and making it steeper and steeper, and where those three came together, you get a horn. Beautiful place.

We're going to go back to the drawing tablet now and start to talk about ice ages.

We're back. We'll do this again. We'll make our glacier and land. Our ocean and land. And we'll put a big old pile of ice and snow. And if it gets big enough, we call it an ice sheet. It's no longer a glacier. It really acts like a glacier, but we call it something special, just because it's so big, if it covers a continent.

The size of these is enormous. 2,000 miles, 3,000 miles. All of Canada, all of Antarctica, all of Europe. Something like that. That's how big these ice sheets can be.

Let's make this ice sheet go away. Let's just melt it all. Let's just take a thermostat knob and just heat up the planet. Where is that water going to go? It's going to go to the ocean, right? And when it gets to the ocean, it's going to raise sea level. So, remove ice means you raise sea level. It's as simple as that.

And that has happened over and over again over the last million years. It's actually happened all through the history of this planet, but it has happened very regularly for the last million years that every 100,000 years, the ice grows, sea level drops, the ice disappears, sea level rises. It just happens again and again and again. And when the planet gets cold, there's enough ice that builds up that sea level can drop by more than 300 feet. So, there's a lot of ice that gets built up on Canada, Europe, Antarctica, Greenland, when it gets cold on this planet.

Why does it get cold? Why do we have these cycles? Why is it that every 100,000 years it gets cold, the ice grows, sea level drops, and then it gets warm, the ice shrinks, sea level rises? Back and forth, back and forth. So why ice ages? And really, what evidence for ice ages?

Let's look at the evidence first. We'll go back to the ocean. Ocean with big ice. So, we've got a big old ice sheet. All of North America's covered with ice. Europe is covered with ice. The Antarctic ice sheet is huge. Greenland is huge.

This is where the ocean would sit. It would be at some level. Sea level of the ocean. If I had built a house on the beach over there, I could look out and watch the ocean water lapping up against my house.

This is my ocean level with small ice. I make the ice sheets go away in North America. There's no ice in North America. There's no ice in Greenland. There's no ice in Europe. And sea level's going to rise.

What happens is that in this process of making big ice, you change the chemical composition of the ocean. So, let's take a look at that. I'm going to back up here a second, and we'll come back to this.

In the process of making big ice, you change the chemical composition of the ocean. And the critters that live in the ocean notice that. And when they die and their shells fall to the bottom of the ocean, their shells record that. So, all I have to do is go and find a shell from the time of big ice, and I'll be able to tell how much the ocean had dropped.

What happens is— I'm going to go to the next page over here— in the process of building big ice, we have to evaporate water. You remember that. You got to take water out of the ocean and dump it on these big ice sheets.

It turns out that there are two types of oxygen. Isotopes. Remember what an isotope was? Homer Simpson's favorite team, the Isotopes, the Springfield Topes. These are when you have the nucleus of an atom has a slightly different number of neutrons. It's still oxygen, because that's determined by the number protons. But if you have a different number neutrons, it acts the same way, it's still oxygen, but it just has a slightly different weight to it.

The lighter isotope evaporates more easily. So the ratio of light to heavy changes if we build, quote, "big ice."

So, we build this big old ice sheet. And the way we build it is by preferentially grabbing these light isotopes and dumping them on the ice sheet. So, we grab all of the light isotopes— not all of them, but more of them. Preferentially, grab the light isotopes and dump them onto Antarctica, and Greenland, and Canada. And so, you're left with more of the heavy ones in the ocean.

And the critters notice that. The critters notice that in their shells. Their shells are now built up with a different ratio of light to heavy isotopes, and we can measure that. We can find a shell from 30,000 years ago, pull it out, measure the ratio of light to heavy isotopes, and tell, oh, look. The only way this could have happened is if we pulled out lots and lots of the light isotopes from the ocean. We can take that same critter from today, pick up its shell, take it to the lab, measure its ratio, and know that, oh, there's lots and lots of light isotopes in the ocean today.

So, this is the evidence for it. But why?

Everything in this section of the class, tearing down mountains, is driven by the heat of the sun. Remember that. And glaciers very their size because of variations in sunlight. The amount of sun that hits the Earth changes. Not a lot, but enough over time that you end up with variations in sunlight. It gets cooler, it gets warmer.

I'm going to go back to the slides because there's a nicer picture of it, and I won't be able to sketch those variations as easily as the more professional illustration. We're just going to jump over these.

The heat of the sun drives all of this. The amount of sunlight varies according to three things. The shape of the orbit, and I'll show a picture in a second. You know how the Earth goes around the sun. And it does so in an elliptical orbit. And that ellipse gets more squashed, and more round, and more squashed, and more round every 100,000 years. It goes back and forth. Just wobbling back and forth, like that.

And as it does that wobble, as it does that going from more squashed to more rounded, the amount of sunlight that hits the Earth changes.

The amount of tilt to the Earth's axis. You all know the Earth's axis is tilted. That changes every 40,000 years. It goes back and forth, back and forth. And as it does that, the amount of sunlight that hits the Earth changes.

And finally, the direction of the Earth's axis slowly spins around like a top. And that changes about every 20,000 years. And as that changes, the amount of sunlight hitting the Earth changes.

And let's look at that picture. So on the left, diagram A is showing the orbit of the Earth spinning around the sun. And it's more squashed in blue and more rounded in the black, dashed line. And it goes between those two shapes every 100,000 years, slowly. It takes 100,000 years to do it, but it cycles back and forth, and back and forth

And we can measure this. Astronomers and physicists are really good at this, and they can measure the shape of the Earth's orbit, and they can tell us what it's doing. Similarly, on panel B there, on the right, we have the Earth's orbit tilted over by 23 and 1/2 degrees. And the amount of that tilt changes a little bit every 40,000 years. It goes from 23 and 1/2, down to 21, back to 23. And it takes about 40,000 years to do that.

And then finally, you have that precession, which is the direction of that axis moves around. Today, the Earth's access points at the North Star. You know that. You go out at night, and you can look up, and you can always tell which way is north because all you got to do is look for the Pole Star, right? You all remember how to find the Pole Star? Find the Big Dipper— that's that Big Dipper shaped set of stars— and then follow the end of the Dipper, and you'll go straight to the Pole Star.

And you always know that the Pole Star is where the axis is pointing at. Well, 10,000 years ago, if you had been standing around and you would try to see which way is north, you wouldn't have seen the Pole Star because the Earth's axis was going somewhere else.

So, those things happen over time. And as those three things happen, the amount of sunlight hitting the Earth changes. The sunlight in the Earth changes, the temperature changes, the glaciers grow, and the glaciers shrink.

Milutin Milankovitch predicted this in the 1920s. It's known as the Milankovitch hypothesis. He was a Serbian mathematician. Long before any of these isotopes data were available, he said this ought to happen. The amount of sunlight hitting the Earth is changing. He was an astronomer. He wasn't a geologist. But he calculated that the amount of sunlight hitting the Earth was changing, and he said, I'll bet you that that would have had effects on climate. And he was absolutely correct.

The amount of sunlight in the far northern hemisphere seems to control the ice ages. This is a huge topic of research right now. This is what everybody is really interested in in the climate community. Why? Because we as humans are changing the amount of CO2 in the atmosphere. We're changing the composition of the atmosphere. We're starting to warm the globe because of our activities.

And so it's no longer these solar orbital cycles that are controlling temperature. We as humans are starting to do that. And so we need to understand the natural cycles much, much better, so that we can pull out how much it is that humans are affecting it. And so, this is a huge area, topic of research. And we'll find out more about climate change as we go forward.

Changes in sunlight are relatively small, but have very big effects because of feedbacks. And you'll find out about feedbacks down the road a little bit.

So, I hope you've enjoyed your tour through some of these beautiful places on the planet. You've seen how glaciers are built. You've seen some of the evidence for glaciers changing their size and shape over time. And now, here is a good hypothesis for why those changes take place. It's still an active area of research, and maybe we'll change some of the details, but it seems to be a pretty tight one.

Thank you very much. We'll see you next time when we talk about coastlines, and sea shores, and how the ocean can help to tear down mountains.

DR. RICHARD ALLEY: Oh, snowflake out on a chilly night. Over the ocean of blue and white. Southern Cross as a guiding light and heading for South Pole-Oh, Pole-Oh, Pole-Oh. Southern Cross as a guiding light and heading for South Pole-Oh.

Over the albatross soaring through. Penguins plying the krill-flecked blue, seals and skuas and great whales, too, all playing around South Pole-Oh, Pole-Oh, Pole-Oh. Seals and skuas and great whales, too, all playing round South Pole-Oh.

One flake's a miracle, two a display. Three and you might wreck your car today, but make a two-mile pile and they're on their way flowing from South Pole-Oh, Pole-Oh, Pole-Oh. Two-mile pile and they're on their way flowing from South Pole-Oh.

The physics are simple, all piles spread, water, batter, or cats on a bed, or a continent-wide two-mile pile snow fed and heading from South Pole-Oh, Pole-Oh, Pole-Oh. A continent-wide two-mile pile snow fed and heading from South Pole-Oh.

Slow in the middle, thick and cold, down through the mountains carved and old, picking up speed in the ice streams bold, don't fall in a crevasse-oh, crevasse-oh, crevasse-oh, picking up speed in the ice streams bold, don't fall in a crevasse-oh.

Ice streams at the sea don't make bergs right away, they flow cross the ocean for many a day. As great ice shelves in a rock-bound bay with friction from sides-oh, sides-oh, the sides-oh. A great ice shelf in a rock-bound bay with friction from the sides-oh.

If we raise CO2, warm the air and sea, melt the shelves away and let the piles spread free, it'll raise the oceans towards you and me while it shrinks that two-mile pile-oh, pile-oh, pile-oh, raise the oceans towards you and me while it shrinks that two-mile pile-oh.

Arctic fox on a chilly night by another ocean of blue and white, if we melt their ice, would that be right? Both poles are on the same trail-oh, trail-oh, trail-oh. If we melt their ice, would that be right? Both poles are on the same trail-oh.

Oh, a snowflake out on a chilly night.

Image 1: Landsat image of Cape Cod. One arrow points to the eroding outer beach on the right. Two more arrows point to areas of sand build out to the south and north. NASA Sept. 18, 1999 Landsat image of Cape Cod. The Outer Beach (magenta arrow) along the right-hand side of the Cape is eroding back at a few feet per year. Some of the sand is building out to the south and north (yellow arrows), but some of the sand is being lost to deeper water, so the Cape is shrinking. All pictures in this slide show, except this one, by R. Alley, C. Alley, J. Alley or K. Alley.

Image 2: On the left, a tern perched on a piece of wood. On the right, a tern in flight. One good tern… deserves another.

Image 3: The Nauset Marsh, Cape Cod National Seashore. Water surrounded by green trees, under pale blue sky. Split rail fence in foreground. The great Nauset Marsh, viewed from the back porch of the Salt Pond Visitor Center, Cape Cod National Seashore.

Image 4: Close-up of a bumblebee on a pickerelweed. Bumblebee visiting pickerelweed, which grows in the shallows at the edge of Great Pond, Eastham, Cape Cod. By building a lake-studded outwash plain into the ocean, the glaciers left a rich mix of aquatic habitats.

Image 5: On the left, a herring gull landing in the water. On the right, close-up of herring gull perched. Gulls, such as these herring gulls, are widespread and successful generalists, equally at home along fresh and salt waters, as well as cleaning up messes left by humans.

Image 6: On top, a close-up of three yellowlegs in Nauset Marsh. Below, twelve or more yellowlegs in the marsh. Yellowlegs are well-named, and common in Nauset Marsh.

Image 7: Side-by-side close-up images of a great blue heron standing in the marsh in front of tall water grass. Great blue herons, Nauset Marsh. A fish that doesn’t watch out may realize too late that he blue it.

Image 8: On top, a close-up of a sandpiper on the beach with his beak in the sand. Below, a close-up of a yellowleg standing in the water. Salt marshes are highly productive, and support a diversity of life… including sandpipers (top) and yellowlegs (bottom). Nauset Marsh, Cape Cod.

Image 9: On the left, a close-up of a cormorant perched. On the right, a close-up of a cormorant on a cinder block with his wings spread. Cormorants were not present on the Cape a few decades ago, but now are commonly seen fishing or drying their wings.

Image 10: Large number of people on the beach at Coast Guard Beach, Cape Cod. slide 10 Coasts loom large in our natural psyche, and tens of millions of people each year visit our coasts for recreation and sunburns. These pictures show a cold, gray day at Coast Guard Beach, Cape Cod, and there are still lots of people out.

Image 11: On top, rippled sand, with beach grass in the background. Below, a close-up of rippled sand. Waves and tidal currents move immense amounts of sand, leaving beautiful ripples, as shown in these closeups from First Encounter Beach.

Image 12: Cape Cod sand dune with a thin layer of hardy vegetation. Ocean in background spotted with beach goers. Cape Cod’s beaches may be backed by rapidly eroding bluffs, by sand dunes covered with a thin layer of hardy vegetation that can be damaged easily by human activities (as shown here), or by salt marshes.

Image 13: Nauset Light, lighthouse on Cape Cod. Nauset Light. The light was moved in 1996, just before the rapid erosion of the bluffs along this part of the coastline dropped this historical building into the waves. Everyone with a long memory of the Cape has stories of things that have been lost to the encroaching sea.

Image 14: Family of three sitting atop Great Rock. Great Rock, the Cape’s largest glacial erratic (big rock carried by the glacier) attests to the ability of ice to move pieces of many different sizes. The rock extends below the picture, and then about as far into the ground as above.

Image 15: Bright orange sunset at First Encounter Beach. Herring gulls in the foreground. Herring gulls at sunset, First Encounter Beach, Cape Cod.

Image 16: Sunset at Rock Harbor, Cape Cod. Boats docked on left. Sunset, Rock Harbor, Cape Cod. It isn’t very geological, but it’s pretty.

Image 1: Satellite Image of Rhode Island Acadia and surroundings. Arrow points to the fjord of Somes Sound in Mount Desert Island. Credit: NASA GSFC & Y.Q. Wang at the Laboratory for Terrestrial Remote Sensing, Univ. Rhode Island Acadia and surroundings. The yellow arrow points toward the fjord of Somes Sound in Mount Desert Island. The dotted line marks an area of interest for NASA and the National Park Service, and regions beyond have been blacked out. All pictures except this by C. or R. Alley

Image 2: Lobster pots floating in water in front of large cliffs. Blue skies with puffy white clouds. The old metamorphic rocks (shown here) and granites of Acadia make dramatic cliffs. Floats for a few lobster pots are visible in the water.

Image 3: Beach at Acadia with water in foreground, mountains and cloudy skies in background. This beach at Acadia is one of the few in the area. Most of the sand is calcium carbonate--ground-up shell--because the Gulf of Maine is so amazingly productive of shells to be ground up by waves. The beach is far at the end of an inlet; the rest of the coast is dominated by bare rock.

Image 4: Family on bicycles crossing an arched stone bridge, surrounded by forest. The Rockefeller-constructed carriage roads and their graceful bridges are well-loved at Acadia, which offers wonderful opportunities for bicycling. Dr. Alley and daughters Janet (left) and Karen for scale.

Image 5: Ocean with inlet and forested land in foreground, small islands in the distance. Sailboats anchored in the inlet and sailing in the distance. View of the Maine coast from Cadillac Mountain, Acadia.

Image 6: On left, path leading to Bass Harbor Head Lighthouse. On right, Portland Head Lighthouse, two red roofed buildings, ocean in background. Bass Harbor Head Lighthouse (left) and Portland Head Lighthouse (right), Acadia National Park and vicinity.

Image 7: Two loons in the rain on Seal Cove Pond. Black and white image. Loons in rain, Seal Cove Pond, Acadia. The deep, glacially carved lakes of the island are outstanding for kayaking and canoeing.

Image 8: Blue waters of Jordon Pond with Bubble Mountains in background, under pale blue cloudy sky. Jordan Pond and the Bubble Mountains. The rounded granite summits and U-shaped valleys are clear evidence of past ice.

Image 9: Person standing in the rain on rocky beach, wearing orange rain poncho and blue rain. Water and Evergreens in the background. Even a rainy day can be enjoyable on the shore, as here at Ship Harbor. Notice the “beach” is composed of cobble-sized rocks.

Image 10: People standing on rocks at the coast. Raining and foggy. Acadia National Park. The no-beach granite coast of Acadia National Park in the fog.

Image 11: Close-up of Herring gull standing on granite coast of Acadia. This herring gull is perched on the granite coast of Acadia.

Image 12: Body of water with island in center. Cloudy skies. Arrow at top left points to the right, indicating direction of ice flow. Ice flow as indicated by the red arrow smoothed this island, and plucked rocks off the lee or down glacier side to the right.

Image 1: Satellite image of Cape Cod National Seashore and surroundings. Coasting Down the Coast. Including a bit on sea-level change, some disasters, and some coastal processes, in some beautiful places. All pictures by R. Alley or taken from government Web sites as indicated. The image of Cape Cod National Seashore and surroundings is from Landsat 7.

Image 2: Raised delta, Milne Land, east Greenland. Rock in center foreground. Mountain peaks in background. Raised delta, Milne Land, east Greenland. About 12,000 years ago, a stream flowing to the left from beneath a glacier built the sandy fingers of this delta out into the sea. Then, the ice melted, allowing the land to rise, so the delta is now about 300 feet above sea level (sea is barely visible to the far left).

Image 3: A wall called a jetty built out from the coast in Washington, which has trapped sand on one side but caused erosion on the other side. Washington State Department of Ecology Shore photos--the state photographed their coasts, and makes these pictures available to the public--what a great idea! Two views of the Westport Jetty, Washington. Longshore drift from the right has built up sand to the right but caused erosion to the left of the barrier. Also notice in the left picture that waves are slowed by the shallower waters near the jetty.

Image 4: Hurricane Katrina aftermath. On right arrows point to antebellum and pier house. On left arrows point to where buildings used to be. http://coastal.er.usgs.gov/hurricanes/katrina/photo-comparisons/mainmiss... Before-and-after photos of the aftermath of Hurricane Katrina, near Biloxi, Mississippi. The antebellum house (upper right) and pier house indicated by the red arrows were destroyed.

Image 5: A picture showing tree-covered islands before Hurricane Katrina, and the smaller, treeless islands left after the storm. http://coastal.er.usgs.gov/hurricanes/katrina/photo-comparisons/chandele... Before-and-after photos of the impacts of Hurricane Katrina on the Chandeleur Islands, about 100 miles east of New Orleans. The sites marked by the yellow arrows can be identified in both photos.

Image 6: Hurricane Katrina aftermath. On left houses on Topsail Island, N. Carolina. On right, the same houses are destroyed. Before-and-after photos of the impacts of Hurricane Fran (1996) on Topsail Island, North Carolina. The house indicated by the left yellow arrow largely collapsed, that shown by the right yellow arrow lost its deck, and most of the other houses and much of the road were destroyed.

Image 7: A small stream draining into a Greenland fjord is dammed by sediment transported along the fjord shore. Evidence of longshore drift of sediment, Scoresby Sund, Greenland. The small stream valley flowing from the top (blue arrow) has been dammed by sediment transported along the coast (between the red arrows).

Image 8: Aerial view of delta, arrow points to sediment from stream that formed delta, two arrows point the beaches on each side. Sediment supplied from the stream (blue arrow) formed the delta. Waves have reworked the edge of the delta into the sandy beach (yellow arrows). Much of the area on the delta side of the beach is underwater at high tide, so this is a barrier beach. A helicopter skid is visible in the lowermost left corner.

Image 9: A braided river has wave-formed beaches near the sea; a recent storm moved some beaches well inland. Barrier beach, Mudder Bugt, Milne Land, east Greenland. Sand supplied from the right by the braided river has been reworked into the beaches shown. Storms have breached the beach on the right, washing sand into the lagoon behind and forming secondary beaches (yellow arrows).

Image 10: A delta formed by a braided river is surrounded by beaches and spits formed from the sand carried by the river. Mudder Bugt, Milne Land, east Greenland. The upper picture is a slightly turned close-up of the top part of the lower picture. Sand from the braided stream (lower right) is reworked by waves into the barrier beaches and spits seen, but the beaches are pierced by inlets.

Image 11: Satellite image of North Carolina, showing streams that deliver sand and barrier islands made from that sand. Satellite image of the Outer Banks of North Carolina, from USGS and NASA. Streams flowing from the left (two are indicated by blue arrows) have been flooded by sea-level rise in their lower reaches. Sand from the streams has been built into barrier islands (two shown by yellow arrows). Although the area covered by this picture is much bigger, the features are clearly almost identical to those shown in the previous pictures.

Image 12: Satellite image of Cape Cod. Arrow in upper right points to inlet to Nauset marsh piercing the great barrier beach. NASA Closeup of part of Cape Cod. The great barrier beach on the right is pierced by the inlet to the Nauset marsh (red arrow).

A beautiful, natural morning at Cape Cod. But if you turn to the sea, you can see that the evening revelers were there. I've been to the beaches of Greenland. I've been to the beaches of Antarctica. And everywhere I've been, the flotsam and jetsam of humanity are on the beach.

Oceanographers have traced the currents of the Pacific using shoes and rubber ducks that fell off of ships. More importantly, we've probably taken 90% of the big fish out of the ocean. We don't know what an ocean ecosystem should look like because it isn't natural anymore. We've changed the thing. We've put so much fertilizer into the ocean and places from runoff from farming and pollution and sewers that cause huge poison blooms that essentially kill the life when they rot. And taking care of the ocean is a big deal. And it's a deal we need.

Beautiful morning for a paddle. The tide's coming in, and a really happy professor is going out to see who's running around in the salt marsh, the Nossett Marsh in Eastham on Cape Cod. This is a place for birding. This is a place for shelling. These sand pipers are out getting breakfast.

Salt marshes are remarkably productive places. They are the nurseries of the fish and the shellfish. They're the nurseries of the ocean. They, too, need care.

The outer beach is coming in as the ocean rises. But the inner side is often hardened by humans and not allowed to move. And if we're not careful, we won't have these nurseries.

Great Outer beach of Cape Cod, facing the Atlantic Ocean. Early morning. A lone figure leaving footprints on the sands of time. And you will see that, indeed, the waves move lots of sand. As the waves come in and out, and in and out, they keep moving sand ceaselessly, relentlessly. Notice the foot is on top of the sand when the wave comes in.

The foot is getting really cold, because that water is just straight out of the Arctic Ocean, practically. And now there's sand over the foot. And when the next wave comes, and the one after, you will see that indeed, the waves are moving sand in, out, in, out.

As they do so, they sort it. Little pieces are taken out to deep water and lost. Big pieces are not moved at all. And the in-between ones are swirling around the foot. And then another wave comes in, and then that one is really cold. And the hairy-legged sole here is soon going to be buried under the sand. And you can see how much sand is moved in just a couple of waves.

We're on the outer beach at Cape Cod at Nauset, and we're looking at where the ocean has been cutting back a little bit of the bluffs to reveal what's behind. Now, most of the Cape is sand and gravel. It's outwash from the glaciers from the Ice Age. But what we see here is the filling of a lake. A block of ice fell off the glacier, was buried in sand and gravel, and then melted out to leave a little spot, a lake, which is filled with peat that you see here. The peat is the remains of dead plants. And if you look very carefully, you will see within the peat many of the dead plants.

On top here are grasses of the modern world, but they are not down in the material. Lakes die. They fill with this stuff. When you see a lake on the landscape, you should ask yourself, why is this here? Because something recent has happened to make the lake.

Well, hello. It's a pleasure to be back and chatting with you. As you know, Sridhar and I have been working on this course together. And so, we're playing tag team. I won't actually throw him out of the ring. But we're going to do tag team. And so, now I get to chat with you for a while about some very interesting things. And I hope we have a good time with this.

As you've seen from Sridhar, we've been looking at a big story, a very interesting story, a story that goes a lot of ways. You've watched from Sridhar how the moving continents make big mountain ranges and how some of those mountain ranges explode and give you volcanoes, and how subduction works, and how obduction works, and what happens. You then saw that when you get these big mountain ranges sitting up there, that they have clouds over the top, and rain falls on them. And so, weathering happens and breaks down the rocks.

Then either glaciers come along or rivers come along, and they take the loose pieces of rocks and they head them down towards the ocean. You have seen that if you build a dam on one of those rivers, that you're going to end up trapping sediment behind the dam. And you'll get a big pile of sediment in there.

And if you don't build the dam, if you let the river do what it wants to do, eventually what you're going to find is that the river is headed down to the sea. And it's going to make a giant pile of mud such as the Mississippi Delta. And if you build your cities on top of the giant pile of mud, then they will sink into the mud. And you're going to have problems.

Now you can imagine that eventually we're going to have to close this loop. We don't just build infinite piles of mud that sit there forever. Somehow, that mud is going to make its way down into the deep sea where it can be taken in subduction zones, or it can be squashed in the giant collisions. And it can raise back up in the new mountains and start this over. And so, we're going to now try to close this loop. And we're going to close this loop by going and looking at some coasts for you.

So, let's switch over to some pictures for you. I happen to love coasts. I hope you do. They're very pretty places. They're very interesting to see. And as we're going to see, they are the extra piece that's going to get from the Mississippi Delta down into the deep ocean where eventually its subduction zone can grab something and take it back up.

Here we're going to start with a picture Cape Cod. You might possibly recognize this. It's a very nice coastal place. Cape Cod is going to be a lot of our story. Right now it is a beautiful place. It's a fun place. It is also a place that is disappearing, as we will see.

The magenta arrow sitting out here on the side is pointing at the outer beach. And the outer beach of Cape Cod is marching back. It is being eroded, slowing scratched away at a rate that's sort of that much a year. And if you had coastal property, that means well within your lifetime, it's gone.

Sediment from that, you can see if you look in this picture sort of the whitish stuff down under the sea, say down in here. This is sand that has been washed off of the great outer beach. It's being transported along. It is building the great island of Monomoy down at the bottom. It's also building the Province Lands up at the top. But then, some of it is ending up being dumped into deeper water either that way or that way. And so, eventually, what we're going to see is that Cape Cod is disappearing. It is a pile that is not sustainable. And, in thousands of years, it goes away.

Before it goes away, let's take some pretty picture looks at it because it is a beautiful place. We actually get to summer there sometimes. And we have kayaks. And so, we can go out kayaking and see what you can see. We also have daughters who like puns. So, one good tern does deserve another.

When we go to the Cape to visit, this is at Eastham. It's sort of about there. And when we go, this is the Salt Pond Visitor Center. And we like to stay right over here just out of the picture. And we take our kayaks, and we go out on the great Nauset Marsh which is sitting out here and goes for very long distances. And it's absolutely chock full of birds.

The wetlands are the productive, they're the nurseries of the ocean. They're the things that grow the fish. They grow all sorts of things. And they grow plenty of birds that can take care of them. You'll notice another bad pun, a fish that doesn't wash out may realize too late that he blew it. These are Great Blue Herons, of course, the big wading birds. There are lots of little wading birds around the marsh. Flocks of birds come through. You can just sit there in a kayak and watch for days and just keep seeing new things as they come along.

The marsh is a mixture of sand, a mixture of mud underneath, plants that are growing up, water that is sloshing in with the tides, and bringing in nutrients, and raising young things, and what have you. It's really a wonderful place.

The Cape is changing. This lighthouse, Nauset Light, almost fell into the sea because the outer beach was catching up with it. And they, just in time, hauled it back. They are hauling lights back all up and down the East Coast. Because wherever the lights are sitting on sand, the beach is heading towards them.

The Cape is there because of the glaciers. Sridhar talked to you about the glaciers. Most of the Cape is sand, and gravel, and mud. But it has little rocks like this one. This is Great Rock or Doane Rock. And it is 30 feet high, something like that. And it extends that far down below. The wind did not bring it. A glacier had to bring it there. It is just sitting there in the sand, the giant rock cliff, where the glaciers were. The glaciers made this big pile of sediment, and the ocean is slowly taking it apart. OK, a beautiful, beautiful place, a wonderful beach, a wonderful place to go visit.

Now, I'd like you remember that there's lots of different kinds of coasts. There's muddy coasts. There are rocky coasts. There are fjord coasts and so on. And so, I've got a picture here taken from space of Acadia, which is very, very different place up in Maine. And the yellow arrow that you can see pointing up there is pointing at a fjord. The US doesn't have many fjords on the East Coast. Although we have many on the left. And this sticks up into the heart of Acadia National Park.

Acadia National Park is renowned for the beautiful art that's been done of it. The Hudson River School painters love to go up and paint naturalizing sorts of things up there. The Rockefellers helped preserve this. I love the oil money going back into the public pot. There are these beautiful carriage roads that one can go ride your bicycles on if you ever get there.

Of course, the interest there is still the coast. It is a rocky coast now, not a sandy coast. The glaciers cleaned this off. They took the sand down to Cape Cod, and they left the rocky roots of the old mountain range sticking out where you can see them at Acadia.

Of course, they put the lighthouses on here. But this lighthouse is sitting on rock. And so, this one is actually not having to be moved back from the coast because the rock erodes a little slower than the sand does. And so, it's sitting there fairly happily at this point.

The glaciers carve these beautiful troughs through the mountains. And they're filled with lakes if you get inland and ocean if you get out to the coast. Here's a loon watching you right there. Wonderful, wonderful place.

Again, this is cleaned off by the glaciers. And so, the sand is down making Cape Cod. And you can see that hard rocks sticking out instead. And so, this would be granite sticking out there watching you very clearly right there.

You go down to the beach, there aren't many beaches. It's mostly rock. Where there are beaches they often are a little coarser. So, you'll see fairly large pieces down here. You would not go and sit quietly on the beach and play with the sand running through your fingers. These are rocks. And that's sort of one beach in that area. But there's not much.

And most of the beach at Acadia is more like this This is actually the bare roots of the mountain range, the granite hanging out where the waves are breaking against it and making great blow holes and spray flying when the storms come in. So, this is a very different sort of place.

You can see the tracks of the glaciers. You might remember that glaciers tend to streamline things as the ice goes over. And then, they pluck things loose from the end. And so, the glacier that went over this, and cleaned if off, and taking the sand down to Cape Cod, went the direction of the red arrow. So, you can see what the ice was doing as it came through.

OK. So, that is a little start of some of our coasts. They're beautiful places. They are mostly moving back at this point. Acadia is not. It's hard. It's sitting out there. But Cape Cod is moving back.

And so, let's talk a little bit about how coasts work, and what coasts do, why they tend to be moving back. And then, let's close that loop and show you how the mud of the Mississippi is eventually going to get down into the subduction zone where it can come back and make new volcanoes and come back over again.

To do this, we're going to start talking about waves. The main energy source for the coast now is not gravity. It's not glaciers or rivers going downhill. It's actually the wind-driven waves coming in.

So, let's imagine that you're way out in ocean somewhere, and you're in your boat, and that you have some waves going by. And so, let's do something like this. Here is a wave out in deep water. And you can tell which way is up because you have your boat sitting on top of it. There you go, wonderful boat. And let's say that the wind is blowing towards the shore. And so, the wave is moving this way. What happens when the wave gets to shallow water?

And the answer is that as you get a wave into shallower and shallower water, it starts to have friction with the bottom. It feels the bottom. And as it does that, whenever you run into friction, you sort of slow down. And so, as the wave moves in towards the shore, when it comes towards shallower and shallower water, what happens is the front slows down and the back catches up.

And so, if you were to check this wave later as it's gotten closer and closer to the shore, what you're going to find is it's doing something more like this. Here's a house over on the shore. So, you know you're getting there. And now, your boat is maybe in a more precarious position.

So, what happens is the front slows down, the back catches up, and they pile up. You can see this if you ever go down to the shore. You look out to sea, and you can see little waves coming in. But when they get close to shore, they make big breakers. Well, why? The front slowed, the back caught up. And if you take this long thing and you squeeze it, it gets high. And then eventually the top may fall over. And you get a breaking wave, and you can go surfing. So, at any rate, that's the first thing that one sees as the waves change that way.

Now, there's another important part that goes with this. Suppose instead of looking at the wave coming in and piling up, suppose that you had a helicopter, and you fly over the top in your helicopter. So, let's see if we can draw this. We're going to put the land over here. That's our beach. So, over here is land.

And you're sitting in your private helicopter, wop, wop, wopping over the top. And you're looking at the tops of the waves, or the crests of the waves as they come in. So, let's make waves in blue here.

And, typically, the wind will not be blowing exactly at the shore. It will sort of be coming in at an angle. And so, let's suppose that the top of a wave is sitting out here someplace, and the wind is blowing the top of that wave in. And so, if you had a whole line and surfers that were sitting on this particular wave, they'd be going in the direction of the arrow. They'd all be riding down the face of the wave going something like this. So, this is a top view of a surfer. And so, the surfers are all headed it in that way.

Now, what's going to happen? Remember the rule. Wave gets to shallow water, it slows down. And so, the water, as you might imagine, you're close to land up here, and you're far out down here. That's where the surfer is. OK, so, you're close to land at the top. You're far out down at the bottom. What happens when it's close in? The water is shallow. And when the water is shallow, the wave slows down.

So, on this end, when you look at the wave somewhat later, it's only moved a little. Now on this end, where it's far out, the water is deep. And where the water is deep, the wave is still going fast. So, when you look at this wave later, on this end the wave has moved a long distance. And if it moves a little bit on one end and a lot on the other end, what do you find? It's turned a little bit. And so, we have that.

And so, the wave it is now headed in. This side is still going slower. This side is going faster. If we look at this wave later, it keeps slowing down on the shallow end, and the other end catches up. And by the time it gets close to the land, it's coming in something like this. And the motion of the wave, now, is going almost towards the land, not quite, but almost straight in toward the land. And so, waves almost always turn until they're almost coming straight in.

And this is why you can always go down to the beach, and get on your surfboard, and ride the in and out. You never see anyone surfing down the coast. Because the wave is always coming in because it turns this way.

And so, what we find is that all the waves of the ocean turn. And the waves turn to come almost straight in, not quite though. And that's where this gets more interesting. The fast end never quite catches up because, as it catches up, it gets into shallower and shallower water. And it slows down itself.

And so, there's always a little bit of motion along the shore, not very much, but a little bit. And if you've ever gone down to the shore and sort of not paid too much attention. And you're just sort of riding the waves. And you come in, and you go out, and you come in, and you go out, and you come in, and you go out, and pretty soon the guard's chair is way back over that way. And so, you've got to go trucking across again. And so, there's always a little bit of motion along the shore.

So, you come almost right in. But there is a little bit of motion along the shore. Most of the motion is in and out. So, most in and out and a little bit along. So, that's an interesting thing that we can chat about.

I will show you a couple of pictures in a little bit when we switch over here. There are some seasonal effects in this, which is interesting. If you happen to go to the beach in the winter, you may not recognize it. Many beaches in the winter mostly wash away. The sand gets washed offshore a little bit. And then in the summer the sand gets brought inshore. And the reason is that the winter has bigger breaking waves. And the bigger the braking wave, the more in tends to take sediment offshore.

And this is an interesting thing. This one may not be the least bit obvious. But let's go to a new screen here. And let's see if we can do something like this. Here is now a beach face. Up here is the bathhouse where you go changing. And we have to have blue so that we can do water. And so, we have some water coming in here.

And now let's ask something. What happens if there's a giant breaking wave? OK. There's a giant breaking wave. You've got your surfer on this, crazy people out there. And what happens? The water is coming in through the air. It's not surging up the beach face, it's coming in through the air.

What's it going to do? Well, you know what it's going to do. It's going to turn over. And it's going to crash down. And there's going to be a giant BFFFT! And then the water is going to go out along the beach. Well, what does that mean? If the water comes in through the air, it's not bringing much sand in. When it goes out along the beach, it takes some sand out.

And so, at the end of a giant winter storm, the sand-- let's see if we can make some other interesting color for sand-- at the end of the giant winter storm, some of the sand has been transported out here. It's sitting down in there. And some of it may have gone off the edge into deep water.

In the summer when it's nice and quiet, and people are out there bobbing around with their kids and their little boogie boards, the waves are not so big and crashing. The waves come in more like this. And they'll actually bring some of this sand back on. But the really deep sand they won't. And so, the observation is very often in the winter, beaches will be moved offshore. In the summer, they'll be moved back onshore towards your beach. But some of it will get out to deep water and fall off.

So, just a couple of notes here is that big waves come in through the air. And if you're surfing on that big wave when it comes in through the air, it might be very interesting. And they go out along the surface. And because of that, because they're coming in, breaking through the air, they're going out along the surface, they tend to move sand. A little more sand goes out than comes in. Some comes in. If you stand on a beach facing that big wave, you'll get sand in your teeth. Don't worry. But a little more goes out than comes in. So, more sand out than in with big waves.

But with the little waves, it turns out, they come in just a little faster than they go out. They bring a little more in than they take out. And so, over time, they will build it back up. And so, the big waves coming in through the air out along the surface move more out than they bring in. The little waves bring in more than they take out, just a little bit. If you watch a wave as it surges up that beach towards your feet on a nice day, it'll come in just a little faster than it goes out. And as it comes in a little faster, it will bring in a little more than it takes out.

So, the little waves bring a little more sand than they leave with. And they build the beach back in the summer. So, they take a little more in than they take out. They build beaches. But they can't reach really deep.

Waves cannot go two miles down in the ocean, and grab some sand, and bring it up. So, if those big waves took it out to deep water, it's lost. It's gone over the edge. It's headed down to the deep water, headed down to the trench if there's a trench there. It's headed for the subduction zone. It's headed back to the volcanoes. And so, waves can't reach too deep. They can't reach to the bottom of the ocean. And so, when you get sand out to really deep places, it's lost. You need a subduction zone to bring it back. And so, eventually we're going to close this balance, and we're going to get somewhere.

When we think about these waves coming in, they bring it in on each wave. They take it out on each wave with the sand. They bring a little more in in the summer. They take a little more out in the winter. They lose a little bit more down. But you have this motion along the shore going on because the waves don't come quite straight in. So, there's always this little bit of in and out and drifting along the shore.

And so, we call that drifting along the shore a very technical name. We call it longshore drift. And so, the motion along the shore is longshore drift. Somebody lost the A sometime back in history. So, it is a longshore drift. And you're just drifting along the shore.

What you can think of now, the drift of sand along the shore is a little bit like the sand moving down a river. And so, now you can think of the beach as being a river of sand. So, let's call the beach a river of sand. It's very often used in geology. It gets sand where? From the Mississippi Delta, from lots of places that it can pick up sediment. If it's eroding a little bit, it's getting that sediment. It takes it along the shore, and then, eventually, in these big storms, or when it comes to a really deep spot, it loses that sand down into deep water.

And so, it's going to lose sand from somewhere. It has to pick up sand from somewhere. And so, you have to have a balance. Just like a river is getting sediment from mass wasting delivering it, it's losing the sediment down to the delta, or down to the reservoir, down to the ocean. The beach has to be getting sediment from somewhere. It has to be losing sediment to somewhere else.

And so, the beach loses sediment to deep water. Lose sand to deep water, we've seen that already. And it has to get the sand from somewhere. And it has various choices. It's either delivered by the rivers or the waves are going to take apart what ever is behind them to get that sand. So, it gets sand somewhere.

And so, we're going to look at some pictures here now to show you where you get the sand from. We'll come back. So, let's switch over to a pretty picture time. We're back to Cape Cod. And now, we're going to try to talk a little bit about how beaches work. I'm going to show you a bunch of pictures of different beaches, and what they've done, and how they behave. And we'll see if we end up somewhere.

So, this is a weird beach. You don't have to worry too much about this one. This is a very interesting beach. We are actually in Greenland at this point. And you may possibly remember when Sridhar was telling you about glaciers, that glaciers are very big, and they can be very thick, and they can be very heavy. And we know that the land down underneath, down in the upper mantle is soft.

And so, you put a big weight on the land, and it sinks. And you take that weight off, and the land bobs up. But it's slow. It's like sitting on a waterbed that's full of molasses. It doesn't sink immediately. And so, it's slow.

So, what happens is in places where glaciers melt the land is push down, and the ocean comes in. And you get beaches. And then the land raises up. And those beaches get raised out of the ocean. And so, here way over in the corner you'll just barely see the ocean sitting way over there. And here is the top of the old beach that has now been raised 200 and some feet out of the ocean as the land popped up.

And so, you can actually see this particularly one was sort of a delta/beach combination. And you can see where the sand coming down from the rivers was deposited. And it was growing out in the ocean. And then the land popped up. And here's this beach sitting up there in the middle of nowhere on the edge of Greenland. So, that's sort of cool. I don't know what you'd do with that. But it's cool.

This may be a little more interesting. These are pictures. The state of Washington has actually put pictures of their whole coast on the web. And you can find the website here. And if you want to see a particular cool place along the coast of Washington, they've got pictures of it. And that's all right.

And so, this is a place, the Westport jetty. They built this big, big wall that's sticking out into the ocean here. And there's a number of things that we can learn from looking at the Westport jetty. One of them is this business about how waves behave. You'll remember that when a wave hits friction, when it hits shallow water, it slows down and that in deep water the waves are still going faster.

So, suppose you're a wave. And you come in here, and here comes a wave coming in. And so, there is the top of the wave I've drawn in yellow. And the wave is moving in the direction of the arrow that we're showing.

OK, so what's going to happen to this wave when it hits the jetty? Well it slows down on the shallow end by the jetty. And so, if we watch the wave, you'll see the top of it sort of there. And then you'll see that it starts sort of bending around. It's moving fast out here in deep water. And it's moving slow right there in next to the jetty.

And so, later we look at the thing, and you can see that it's bent a whole lot. And so, it's wrapping around. And you look way in there, and you can see actually wave tops that have bent all the way the other way. They're being held slow against the jetty. They're moving faster elsewhere. And they're trying to turn to come in towards the shore. And so, the waves are always trying to turn to come towards the shore. And we see that happening with the jetty.

There's some other things, though, that happened in this picture. You'll remember that the waves don't quite come straight in. They move sand along a little bit. And so, the waves have just a little bit of motion which is tending to cause the sand to go this way. And so, the net is a little bit of sand moving along this way headed that way.

Now, what happens on a river if you have a dam, and you slow down the water. The river is bringing in sand, and it dumps it right front of the dam, and it fills in the reservoir. What happens if you build a dam on a river of sand that is the beach? Well, it does the same thing. It fills in with sand here. The dam of the jetty is trapping sand. You see it in that picture. You see it in the other picture that we have here. And so, this is the sand that has been trapped as it drifts along, and it comes up to this big dam which is the jetty.

What happens then is that the sand is blocked there. And so, clean water gets around. And that water promptly starts picking up sand. And so, you end up with places like this that are eroding because the clean water passing your dam is going to pick up more sand again. And so, you end up with a deposit on one side and an erosion on the other side out in here.

And so, whenever you put a dam like this up, it makes a big difference to a whole lot of things. If you wanted to save your house, and you put up a dam like this, you'd say, wow, I'm happy. And then your neighbor's house would get eroded. And the neighbor would be very unhappy. And so, whenever you tweak something like this, it matters.

There are other ways that sand moved. It's not always in the winter. It's not always very simple. 2005, Hurricane Katrina comes in. It was not a nice hurricane. It was not nice to New Orleans. It was not nice to very big pieces of the coast. Here are a couple of pictures.

Picture in the upper left here is a September 1998 picture of the coast near Biloxi, Mississippi. And if you notice the sort of building that the red arrow is pointing to with the blue roof over there-- somewhere about there there's a nice blue roof-- if you come back and look at the picture after the hurricane, you'll notice that it's different.

And you'll notice a number of other things. There's a very, very beautiful antebellum mansion in the before picture, that white building. And you'll notice that it isn't actually there in the after picture. Terrible, terrible things that can happen.

Pieces of that are now part of the beach. Some of them get washed inland. Some of them are left there. But some of them are down on the beach. And so, if you compare the look of the beach right here before, and you compare the look of the beach afterwards, you can see that nature really is, when the waves come in, they will get things. They will make a beach. They will erode what's behind them if they can.

These are two more. This is a natural setting now rather than a human setting. These are the same places. It may not be immediately evident. The arrows are pointing to things that are matched. In the far upper left of the before picture over here there's a little lake that is outlined right there that the yellow arrow it was pointing to. And that same lake can still be identified in the after picture.

And I hope it is fairly evident that there is more stuff in the before picture, more plants, more sand, and so on, that are available than there is in the after picture. If you look, you'll see some of the sand in the after picture is down there. It's been moved around. It's been eroded. It's been transporting away. So, it's very clear that when those big waves come in, they grab pieces of the beach, and they take them away.

This is not the same hurricane. There are lots of hurricanes. There are lots of coasts. These are before and after pictures for Hurricane Fran in 1996 on the Outer Banks of North Carolina. There's a yellow arrow in the before picture pointing to somebody's really fancy orange beach house up there. Boy, I bet they liked that thing. And then after they eventually had to tear the thing down because this new stream showed up. The beach was torn apart, and it undermined the house, and it started to fall in.

You'll notice that somebody had a really nice beach house right here in the before picture. And that's it in the after picture. It went away. It was not very nice. And so, you can see that there's a lot of changes when big waves come in and they attack things.

This is evidence of longshore drift in a very much nicer place. You don't have to worry about as much. We're back in Greenland now. And what you'll notice is there's ocean that's sitting out here. The waves are moving along this shore a little bit. Boy, that's not very well written. But here's ocean.

Here, this is actually Scoresby Sund in East Greenland. And what you'll notice is that the sediment has been transported across the mouth of a little stream. And so, this sediment bar has been built up here by sediment being moved along. The sediment is headed for somewhere. It's headed for somewhere deep to fall off into the deep water. But on the way it may pause temporarily and give you interesting things like this.

These are some more pictures in Greenland. You have streams that are bringing sediment down from the glaciers and taking them out to the ocean. So here is a big stream. It's carrying lots of mud and sand. And so, it gets all these bars out there. And you can see the muddiness of the water.

And when it meets the ocean, the waves start to move the sand. And the waves make bars-- outer beaches, if you would. And so, you get these beautiful barrier beaches. All of these things have geologic names that you can learn if you get really excited by this, little tidal inlets and all sorts of other things going on.

And so, you see some very interesting things. And it's obvious that the sand is being affected by the waves where the ocean meets the land and the rivers. You get interesting things going on.

This is the same thing except very much bigger. And so, now we're looking down on the Outer Banks of North Carolina. And you have rivers that are coming out like this. And they're carrying sediment. And the sediment gets down to the sea. And the sea stars banging against it. And it builds these wonderful barrier islands that we know along the coast of North Carolina.

And then behind the coast you get the great embayments that people go sailing in, and they have a good time in, and so on. But these are places that when a giant hurricane shows up, it just goes right over the top. That's very low. And it makes a huge difference to what's behind us. And so, when you look at something like this going on in Greenland, you basically have the same thing on a bigger scale going on on the coast of the US.

OK. So, let us go back. And we're now going to try to draw a few more things for you. And then we'll see if we can get out of here without getting too bored with beaches.

So, what we see is that the beach has a balance. It's getting sediment, it's losing sediment. If it loses too much in the deep water, what's going to happen? Your beach gets skinny. If the beach is skinny, what happens? The waves go over the beach, and they take apart whatever is behind it. They take apart houses. They take apart roads. They take apart natural deposits, whatever is there.

If Acadia, if it's really hard rock, they have trouble taking it apart. And you have no beach. If it's soft stuff, they take it apart and they rebuild the beach. And so, what we have to do then is if the beach gets too little sand, if there's too little sand being supplied to the beach, what you just saw from the hurricanes and other things, if there is a little sand supplied to the beach, then the beach will be narrow. And if the beach is narrow, the waves will come right across the beach, and they will tear apart whatever is behind it.

So, the waves will cross the page, and they will erode what's behind it to get sand. And that sand may start out as your car. It may start out as your house. It may start out as a natural deposit from a glacier. It may start out as granite in Acadia, whatever. The waves don't really care. They're coming across the beach, and they're going to beat up whatever is behind it. And they're going to make enough sand so that the waves can't get across the beach anymore.

And so, we have a balance now. You're supplying sand. You're transporting it. You're losing it into deep water. And you have to ask what tweaks to balance. And we humans keep tweaking the balance. For example, we build dams on rivers.

So, suppose you dam a river. What happens? People did this in Olympic National Park on the Elwha. They make a little power out of the Elwha. It's a beautiful river. It sort of cuts off all the salmon that used to migrate up there. It also cut off the sediment that the river was taking down to the coast.

Well, the next thing that happened is the waves just took the coast away. They eroded right across the beach. And the Native Americans that used to shell fish on the beach there can't do it anymore. The Corps of Engineers is spending a lot of money to shore up the harbor next door because there isn't sediment coming in the longshore drift because the sediment is trapped up in the dams.

So, if you dam a river, you stop the sediment supply to the beach. What does that do? It means that the beach will lose sand in the deep water. It won't get as much supplied. And it will narrow. And then the waves come across, and they take apart your house.

So, one of the things that we humans do that matters is tweaking this, if you would. There are some natural things that feed into this as well. And they're probably worth pointing to as well. If we switch back, for a moment, to the pictures, we're going to try to go back and see a particular slide here if I can make this work. And so, we'll view the slide.

This is along North Carolina. And what one can notice in something like this is that many of the East Coast rivers are flooded way inland. When the sea level rose at the end of the ice age, it flooded river valleys. And so, all up and down the East Coast we have bays. The Susquehanna flows into the Chesapeake Bay. Why is a bay there? The sea level rose at the end of the ice age.

And so, if you now switch back over here for a minute, we will see if we can draw something like this. Imagine, if you would, you're looking down, and you have a river. And the river is running out to the sea. And so here comes some sort of a river, and it comes out to the sea. You're looking on this from your helicopter. So, out here is the sea. And over here is the river. And you know that if you look down on the river valleys, that the river is sort of lower. And around it you'll have hills of some sort or another. And so, let's draw in some hilltops like this. And then something like that.

Now what happens when sea level rises? And when sea level rises, the sea will flood up the river valley. And so, you'll have the sea moving inland, and it will flood up the river valley. And then you have a big bay. And so, the Chesapeake Bay, or the Delaware Bay, or all those bays along the coast of North Carolina are old flooded river valleys.

Well, now what happens? The river brings mud down to the sea. Where is the mud going? Is it getting out to the beach out here? And the answer is no. The mud can't get to the beach out there. And the mud can't get to the beach out there because it's piling up here.

And so, because of the end of the ice age, there is less sediment reaching US beaches than there otherwise would. Because the sediment is trapped way up at the head of the embayments filling them in trying to build out to the beach where it can get there.

And so, if we write this down rather slowly, the ice age ended. And when the ice age ended, sea level rose because the ice melted. Remember, right under the ice it's pushed down. And then it bobs up. But most of the rest of the world was not pushed down by the ice. And so, the water coming from the melting ice sheets fills up the ocean. And it gets higher. So, sea level rose.

And as sea level rose, it flooded the rivers, and it made bays. And so, we have all these beautiful bays up and down the East Coast of the US because the ice age ended. And the rivers are now filling the bays with sediments. Rivers filled the bay with mud, sediment, whatever. We'll write mud. It goes faster.

But because they are filling the bay with the mud, that mud is not getting out to the beach. The sand is not getting out to the beach where it can nourish it. And so, the beach gets eroded. It gets narrow. And the waves take apart what's behind it to get their mud. So, the rivers filled way with mud. It doesn't reach the far out coast. It doesn't reach the beach-- reach the beach-- OK, reach beach. And so, we then see erosion going on at the beaches because they're not being supplied the sediment that they should be. And so, both human activities in damming rivers and natural activities in flooding things at the end of the ice age have contributed to this problem.

Now there's some others floating around. Cape Cod, remember, is a pile that was made by the glaciers. It happens to be a pile that was made by the glaciers in a place that there aren't many big rivers delivering sediment to the coast. And so, you go and look at something like Cape Cod, and it is a pile from the glacier. And it is a pile from the glacier that happened to be made in a place that rivers don't supply much sediment. So, there's nothing replacing the stuff that goes into deep water. OK, so there's no big rivers to supply sand.

And you know if you have a bank account, and you take the money out, but you never put any in, eventually it gets empty. And so, as Cape Cod loses sand to deep water, it is not getting a new supply of sand from the big rivers. And so, Cape Cod eventually, over thousands of years, is a goner. It's going to go away. And so eventually you lose the Cape.

You don't have to run screaming and panicking. It will take a long time for that to happen. Naturally, then, another ice age is supposed to come. The glaciers build the thing back up. And it would be happy again. Whether that happens with human activity will matter.

Another thing that's worth noting is that, in many places, we humans are making things a little worse by pumping water, and oil, and gas out of the ground. And when you pump water, and oil, and gas out of the ground, the surface settles a little bit. And if you're pumping them out from under New Orleans, and the surface settles, now you have a problem because then the sea comes in when you have a hurricane. And then you're very unhappy about this.

And so, pumping oil, and gas, and water out from under the coasts makes them sink. From under the beaches. And we do this in some places. We're getting smarter about this. But we're not real smart yet.

And so, if you're interested in this, and so, the net of all of this, the net of our damming, the net of nature, and the net of sea level rising, and sea level is rising. We will talk about the whys a little bit later in the semester. But sea level actually is rising. Mountain glaciers are melting. The ocean is warming and expanding. And so, sea level is rising.

And the net of all of this is that probably 3/4 of the US coast is moving inland. We're losing land on 3/4 of the coast. And about 1/4 is either holding its own like at Acadia, or maybe advancing a little bit in a few places. And so, the net of all of these different things is sort of 3/4 of the coast is losing. It's coming back. The coastline is being lost at this point.

That's a huge thing because we live, a lot of us, along coasts. We vacation along coasts. We love coasts. Coasts are really expensive, and they're wonderful. And everyone likes to go down to them. And they're busily being gnawed away. And that's not a good thing.

Now people try a lot of things to keep the coast from being gnawed away. They go down, and they dredge sand out of deep water. You spend immense amounts of money. And you pull the sand, and you put it back on the beach. And the next storm takes it back to deep water. And then you go it again. And so, people are trying this.

So, what do you do? OK, one thing is beach nourishment. Go get sand out of deep water and pump it back up on land. That's expensive. And it takes a lot of energy. And it doesn't last very long. And put it on the beach.

People are talking about taking out dams in places. We haven't done much of that yet. But they are actually talking about taking out dams and letting the sediment go back down. We actually bought the Elwha dams in Olympic National Park. And we were going to take them out. But now they're paying money from the hydroelectric power into the government coffers. And we're not taking them out right now. So, people are looking at that.

Some people try to change the shoreline. Remember when we saw that big jetty out along the coast of Washington that it entraps sand. And so, you'll see many people who actually have tried somehow to change the shoreline.

Suppose we get back in our helicopter, and we look down. And over here we have land. And out over here we have ocean. And in the ocean we have some sort of a longshore drift that is running this way.

And so, suppose you are sitting down here, and you say oh, my goodness. I've got this wonderful beach house here. And I love my beach house so much. And I want to save my beach house from being eroded. So, I go, and I build a giant jetty that sticks out into the water. They're also called groynes. So you're going to build a dam, or a jetty, or a groyne. They're all the same thing basically. But you may see all those different names somewhere in your life.

All right, so what's going to happen? You're going to be fairly happy for a little while. Because what's going happen is as the sand comes drifting along the shore on the beach, and it gets to where you are, it will start to pile up. And that will make you happy because now you've got a nice beach, and you're not worried about it. OK.

But the question is suppose you have a neighbor. And your neighbor also has a beach house. And the clean water goes around. So, this goes around without any sand. And what does it do? It starts picking up sand. And so, it starts eroding down here. And your neighbor's house falls in. And then your neighbor sues you.

So, when you do this, you trap sand here. But often-- not always-- but you often end up with erosion on the other side as the clean water gets around the jetty or the dam. And so, you may get erosion here. And if it erodes on this side, then your neighbor's going to sue you. And then it's going to be a real mess.

Geologists have looked at this. And they say, you can do things. You can build things, you can pump things, you can take out dams. In the long term they've said, you know, maybe we should just move back from the beach in some places. Maybe the great outer beach at Cape Cod really is a good national park. And if we just stay off of the beach and let nature play with it, and we go down and enjoy it, if we keep some of these beaches in the national park system, we'll be happier.

Before groundwater pumping, a lens of fresh groundwater extended above and below sea level, floating on deeper salt water. But if enough groundwater is pumped out to lower the water table to sea level, then salt water will rise to sea level, and the well will be pumping salt water.

CARL PILLOT: One.

[BANG]

Two.

[BANG]

A one, two, three.

- RICHARD ALLEY: (SINGING) Near the town where we were born, there's an ocean, not far away. And you know when rocks get worn, they make sand for beaches where we play. Suppose you ride down onto the shore, just to while away your summer day. Splash no beach there anymore.

Could that happen here? What would you say? You'd say, we need more sand, or the beach will wash away. The beach will wash away. The beach will wash away. It guards the land, and the beach can wash away. The beach can wash away. The beach can wash away.

All the waves move sand about, mostly in and then right back out. Some will drift along the shore. Crashing winter breakers take out more. If sand falls too deep, it's gone down into the subduction zone. And it may take 10 million years, eruptions, weathering till new sand appears.

So, we need more sand, or the beach will wash away. The beach will wash away. The beach will wash away. It guards the land, and the beach can wash away. Beach can wash away. Beach can wash away.

If we melt glaciers into mud, sand will disappear beneath the flood. Dams on rivers will impede lots of new sand beaches need. You will not have too much luck making beaches with your rubber duck. Chunks of houses might suffice. But for volleyball, that isn't nice.

So, we need more sand, or the beach will wash away. The beach will wash away. The beach will wash away. It guards the land, and the beach can wash away. The beach can wash away. The beach can wash away.

If beaches fade beneath the sea, you might need a yellow submarine.

[LAUGHTER]

[MUSIC PLAYING]

Image 1: Panoramic view of Bryce Canyon BRYCE CANYON: “A Hell of a Place to Lose a Cow”—quote by Ebenezer Bryce.

Image 2: A 2-inch tall dwarf columbine and a dewy Oregon-grape leaf struggle to grow at Bryce. Although Bryce Canyon is higher, cooler and wetter than many of the nearby parks, life is still tough on the unstable slopes of the canyon. Here, 2-inch-tall dwarf columbine (right) and a dewy Oregon-grape leaf struggle to grow at Bryce.

Image 3: Cedar Breaks National Monument, near Bryce, has the same sort of limestone as Bryce, of the same age. Notice where a small fault has offset the white layer in the upper-right corner.

Image 4: A valley of hoodoos (towers of rock with the harder rocks on top) in Bryce As at Arches, water works wonders widening joints. But the rocks here are not strong enough to hold up arches, instead making hoodoos (towers usually with harder rocks on top).

Image 5: A closer view of some hoodoos shows striations of color Much of the coloration is linked to how rusty the iron is in the rocks. The sedimentary layering is quite evident.

Image 6: Another close view of hoodoos. Guidebooks almost always refer to Bryce as a “fairyland”. The wonders of differential erosion – softer rocks, and rocks along cracks, go faster – really are amazing.

Image 7: A hoodoo named “Queen Victoria” because the top looks like a queen. The Park Service now discourages “naming” rocks, because visitors are so disappointed when erosion then changes those rocks. This one was named Queen Victoria back when naming was condoned. The layered sedimentary rocks are beautiful by any name.

Image 8: Trees in Bryce Canyon.

Image 9: Logs across a stream bed. A decade or so ago, the Park Service put the logs across the stream bed to slow the burial of a trail by sediment. As we’ve seen with dams, rocks filled the space upstream from the logs, and erosion happened downstream. Fast erosion supplied lots of rocks to fill the “lake” above the dam quickly.

Image 10: A close up of a rock at Bryce shows river gravels, conglomerates and clasts and sedimentary rocks. Bryce’s rocks are mostly limestone, but include river gravels such as the conglomerate shown here. Many types of clasts are present; the orange one in the middle is a conglomerate itself, and the clasts in it include several types of sedimentary rocks. This picture shows a long and complex story--try telling it.

Image 1: A rock arch at Arches National Park. ARCHES NATIONAL PARK: Stories in Stone Photos by R. Alley.

Image 2: Dr. Anandakrishnan at Arches with the La Sal Mountains in the background. Dr. Anandakrishnan, Arches National Park. The La Sal Mountains in the background are named for the salt beneath them. The motion of the salt created joints that then isolated the fins that made the arches, such as the one next to Dr. Anandakrishnan’s shoulder.

Image 3: looking down onto the ground at Utah’s Grand Staircase-Escalante National Monument. The ground is white with a grid pattern of green plants. This isn’t Arches, but Utah’s new Grand Staircase-Escalante National Monument. Plants follow water that soaks down into joints in the fossil dunes of the Navajo Sandstone, making the grid pattern in the rocks. Various joint patterns exist; parallel rather than crossing joints are very important in making arches at Arches, as we will see next.

Image 4: End on view of fins at Devils Garden, Arches NP and an angled view of fins at Devils Garden, Arches NP. The tough sandstone has been broken by parallel, vertical joints, and weathering along those joints isolates “fins” of sandstone that then are eroded to make arches.

Image 5: Three images of Delicate Arch. The sandstone of Delicate Arch started as a sand dune (note bedding, top-right picture).

Image 6: Two pictures of arch shaped amphitheaters created by falling fins in sandstone. CAUSE student Raya Guruswami in Glen Canyon (right), and a cliff in Canyon de Chelly National Monument (top). Rock falls from the sandstone cliffs have left arch-shaped amphitheaters. Similar falls from fins help make arches.

Image 7: Two pictures of rocks that have fallen and the arch shaped scars they left in the stone cliff above. (right) an arrow points back up from the fallen rock to its arch-shaped scar. (left) Fallen rocks are gone, but an arrow shows their arch-shaped scar. Two views of fossil sand dunes over redder flood-plain muds, Grand Canyon. Sand fills a gigantic mud crack on the right (yellow arrow). Today, sand dunes encroach on the Nile in a very similar setting. The arch-shaped rock fall scars suggest how arches may form.

Image 8: Landscape Arch is the world’s longest natural stone arch. You can see that numerous large blocks that have fallen from the arch, many since the park was founded, plus joints in the rock that make additional falls likely.

Image 9: CAUSE instructor Eric Spielvogel photographing a lupine near Double Arch. The high desert of Arches is a harsh environment, but surprisingly beautiful flowers appear after the rare, brief rains.

Image 10: Double Arch. You can see dark streaks on the rock. The dark streaks down the rock are desert varnish, mineral deposits formed partly by microorganisms that grow briefly when rainwater runs down the rock.

Image 11: Close up of dark streaks (called varnish) at Double Arch. There is a crack near the top of the arch through which rainwater flows to form desert varnish. Enlargement of the crack will eventually lead to rock fall, changing the arch.

Image 12: Two pictures of men standing close to Double Arch. Rock falls have helped shape the immense cliffs.

Image 13: A rock with a grid like pattern of mud cracks in it. Mud deposited in a small lake near the sand dunes dried and cracked in the sun. More mud washed in and filled the cracks. After the mud hardened, the rocks were split apart, and the upper piece turned over; Dr. Alley’s index finger points to the crack-filling mud.

It's the weekend, and you're baking a cake for the game for the big game. And so you put down a layer of cake like this. And then it's gotta be for the Penn State game. So then you're going to put in a little blue icing, so it's more enjoyable. And you're going to make another layer cake on top of that, still sitting there. Boy, you're a good baker. It's really very impressive.

And we'll put some more Penn State blue icing in the middle. And then you put down one more layer of cake to make the top of the thing. And wow, this is getting to be fairly serious when all is said and done. And then you're going to ice the top of that, and wow, isn't that beautiful.

And then you want to put some candles on. It's going to be Wisconsin game, and Wisconsin's going to get burned. So you better put on some Wisconsin red candles, and they have a little wick sitting out the top of them like that. And then you're carrying the cake across the floor and your big dog comes up and takes a gimungous bite out of your cake, which doesn't necessarily make you entirely happy. And so now your cake is going to look something more like this with this big hole out of it. And the hole goes all the way down, something like that.

Oh dear, what a mess the dog made out of the cake. And you're really very, very unhappy about what your dog did to it because you were carrying the cake while this happened, and you happen to know that if you're carrying the cake while it happens that you may lose your grip, and the cake turns upside-down, which is now a real mess, and the candles gets scrunched, and so they're no longer sticking down the way they're supposed to be. They're actually sort of sticking off to the side the way they get bent over.

Now, if you were to see this, if you were to find this cake on the floor, you would have absolutely no trouble telling what happened, and the sequence of events in which they happened. In the same way, a geologist faced with something such as a rock viewed edge on that has some mud cracks in it like this, there's a crack, says oh, this rock is right-side up, it has not been turned over because we know that when mud cracks, that the cracks go down in the rock, not up.

In the same sense, if the geologist was faced with some sort of a footprint, and let's make a dinosaur footprint here, if you would like to. Do, de-do, de-do. Here's the big footprint. OK. And the footprint is stuck down in the rock, something like that. And so you can see this is how it might have happened somehow. And that's not the world's finest footprint drawing, but you get the idea what we're trying to do. That has been shoved down into a rock so there's a big hole here where the footprint was made.

If you were to happen to find that footprint, and you're going to have to find that footprint as being upside-down, as we can make it very easily with the foot vertically, you wouldn't know that. And so geologists do that. They can put things in order in the same way you that could look a that squished cake and put it in order.

So we've been driving around the West, pointing at rocks-- there's a rock-- and saying, this is a sand dune. This is a lake. This is an ocean. But we haven't spent a lot of effort on, why do we say one is a sand dune, and one is a lake, and one is an ocean? Now in the case of the sand dune, when we looked at it, it was all sand. There were no little pieces, there were no big pieces, it was all intermediate size sand pieces. They had these structures that one sees in modern sand dunes. If you found anything that looked like a fossil, it was little reptile tracks. And so they had all the characteristics that you see in a modern sand dune.

Now here, we're in rocks that are very different. The rocks behind us are sort of washing away and they're making mud that washes down around our feet. And there's a number of characteristics of these, the layers are different, how big the grains are in them is different, sort of everything about them is different. And we can say these were rocks that were underwater. And we can go through the whole list of reasons why we can say they're underwater, but there's one very easy one. If we look down at our feet, and we look around at what's washing out of these rocks, what we find is oysters. And one can be very confident that if you find rocks full of oysters, you're not in the middle of the desert.

[MUSIC PLAYING]

Look at this picture. You've got all these cracks developed over here. Imagine a second flood coming through here, a relatively gentle flood, water slowly flowing in here, a new layer of silt and sand and shales and clays. What's going to happen? All of that new material is going to filter down into these cracks and it's going to solidify in there as the water evaporates out of it.

So now 100 million years goes by. And we come along and we cut this open and we look at this layer and we look at these, and you'll see mud cracks. And we'll be able to tell that that layer of rock was oriented this way, because these mud cracks all start wide at the top and get narrow going downwards. And it quite often happens that these strata of rock, because of the incredible forces of nature of plates coming together, will take these layers and just flap them over upside-down. And we come along and we look at them, and you can't tell which way is up, which way is down until you find one of these mud cracks.

And then, even if the layer's upside-down, then you'll have these mud cracks teepeeing upwards. And you'll say, whoa-ho, this thing must've been flopped over and turned over upside-down. And it's the same processes-- I'm doing a Richard here. It's the same processes that produce these mud cracks, will fill them in, and then maybe after 100 million years, they'll get fossilized, turned into a hard clay layer, and then turned upside-down. But we'll still be able to tell what we call the stratigraphic relationship, the time relationship, which is older, which is younger, because clearly this is older than whatever would lay on top of it.

[MUSIC PLAYING]

Um, maybe. I can kind of break it out.

No, that's a conglomerate, isn't it?

Yeah. It is. Look at that, Dave. That's the conglomerate we were looking for. Just look at that! Isn't that a beauty?

It is.

A conglomerate in a conglomerate. What do you make of the class in the little one?

It looks like sandstone and limestone to me.

Deep time. Deep time!

Very deep.

We got deep time! This is just beautiful.

A conglomerate classed in a conglomerate?

A conglomerate, you have to have sand grains glued together to make sandstone, broken and rolled to round them off, because this is rounded. And you have to have an ocean or a lake that has things living in it, precipitating calcium carbonate to make a limestone, broken loose and rounded off. And then those have to get together in a beach or in a stream channel. They have to be deposited with sand around them, then they have to be cemented together with hard water deposits. Then that has to be broken out, rolled in a stream and rounded, put together with all these other rocks coming from every which way. All of those then have to be glued together with hard water deposits. And then we have to get from the stream or the lake or whatever it was that was making these, up here in the middle of the desert on a cliff. And it's all in that one rock right there. And there's really no other way to explain that rock.

In geology, we often meet people who tell us that we do not know what we're talking about, that the world looks like it is very, very young, that there's nothing in the world older than written history. We never tell those people that they're wrong, that they're false, that they've been led astray. But we can tell these people, it looks old, that the scientific interpretation, the best way to look at these rocks, is that they tell of vast, deep time. So when one looks at a rock like this one that has little tiny remnants of old rocks glued together into a rock which is bounced around in the stream and rounded, that then is glued in with a whole bunch of other rocks into another rock that has been bounced around in a stream and rounded, that is sitting here glued with a bunch of these things on a cliff in the desert-- it is very hard to imagine how this could be something that is only 6,000 years old. And so all we do in science is, what can we observe? What can we test? And what we can observe, what we can test says, really, really old.

What is deep time? Deep time, something very much older than us. Very much older than written history. Something that's old enough to encompass the glorious things that we see as geologists, 4.6 billion years of this planet.

If you go to the Grand Canyon and you look at this great trench holding a river at the bottom of it, and you think that the world is as old as written history, you're very confused. Because how can that river be down there when we can see what the river is doing? We know how rapidly the river is changing the world. People have been coming there for a couple of centuries and writing down what they know about it. And native peoples have been there for a few thousand years. And we know that its changed a little bit in that much time.

And so what's it doing there? Why is it there? If you open the door to deep time, you say OK, a sheet of paper a year, that much erosion, taking a sheet of paper off the rock every year, and you have way more time than is needed to carve that canyon. A sheet of paper a year in a million years, and you have the canyon.

And then you can start to see these greater stories. Because that's the time to cut the canyon. But how long did it take to make the rocks first? And so you see these tremendous stories that are sitting there. And you go out and look at the canyon. If you live in a shallow time, you look at the canyon and you say, isn't that great? It would make a nice picture. It would make a nice post card. And then you go to the visitor center.

And if you live in deep time, there's all these stories. And you can sit there and play in your mind's eye, the beauty of the seas coming and the seas going. And you can imagine what was that lizard that ran up the back of that sand dune, that's fossilized, and that big cliff, the first big cliff down from the rim of the canyon? There were lizards running across sand dunes when that was there. Why were there sand dunes there?

There's these amazing stories. And you stand there for an hour, and you're still thinking about them. And then you got to go walk down in and look at them closer. And rather than running to the gift shop and taking off to Las Vegas to waste your money gambling somewhere, you're lost in deep time. And it's just beautiful.

I do think it's difficult for people to conceive of the age that we have here for a number of reasons. One is that, if you are a literal believer in certain sacred books, you believe that the earth is no older than written history. Now, as a geologist, my predecessors, back mostly in the 1700's, faced this. These were people who really believed in the sacred books and who, at the same time, had to look at the rocks and make sense of them. And some of them ended up, no, I don't believe the rocks.

Some of them ended up actually renouncing their religious beliefs. Many of them said, no, I can be a religious person and I can believe the rocks. But we're going to have to let a day be a little longer than 24 hours in the very beginning. They had to find some compromise between the two. People who absolutely believe, word for word, literal interpretation of certain particular sacred books simply cannot believe the age of the canyon.

I'm a religious person. I won't subject you to my beliefs. I am a religious person. And I belong to a very large religion that has several million members. And we have no problem with the age of the canyon.

If you want to ask, is nature going to undo what we humans are doing to the world-- we're burning fossil fuels. We're taking the carbon out of that and putting that carbon into the atmosphere-- and that's changing things. It's changing how easily plants breathe. It's changing how well shells in the ocean can be made by clams and corals. It's changing the climate. It's changing all sorts of things.

Nature will undo that. How rapidly? And so for that, we have to go back and look at how rapidly has nature done things over deep time.

And we do know. Nature has changed carbon dioxide in the atmosphere a whole lot. The dinosaurs lived in a world that had a lot more carbon dioxide in the atmosphere than we do, and they were fairly happy in that world.

It was a warm world. There were no ice sheets at the poles. It was warm all the way to the poles. There were crocodiles almost to the North Pole, and palm trees in Wyoming, and all sorts of things.

But the change between a low carbon dioxide world and a high carbon dioxide world that nature did is 100 million years, and we're doing it in 100 years. And so, is it likely that nature is going to undo what we're doing rapidly at a time that we would notice it? No. And so one needs to understand how rapidly does the world work by itself, and how rapidly do we change things. And so knowledge of deep time comes into questions like this.

There really are things that matter to you that come out of deep time. That's one reason we have a geosciences department at Penn State. If you've got a job-- you're a geoscientist. You took an undergraduate degree here, you get a job with an oil company, and you're supposed to tell them, should I drill an oil well here or not? We know that oil is made by cooking dead organic material, dead algae for the most part. You know that if you've had oil in your engine and your engine gets too hot, the oil will burn up. Oil is flammable. If rocks have been too hot back in the past, you won't get oil out of them.

And so you need to know, has it been hot enough to cook those rocks? Has it not been too hot to break them down? What happened to them. And so to figure that out, you need to know something about how deeply they've been buried, how long they were down there, how long it took them to come back up, what is their path through time, temperature, space. And that requires knowledge of deep time. Some rocks are not going to give you oil, because it burned up. There's a little bit of carbon, a little bit of graphite, stuck in there, and you're not going to find oil out of that. And so you need to know something about that.

Knowledge of evolution. AIDS was going to happen, something like that. Antibiotic-resistant bacteria are going to happen. Things that are alive are survivors. And things that are alive have ways to adapt if their environment changes. We have to beat that by being smart, because evolution is very slow process. It takes hundreds, thousands of generations. Modern humans have not been around long enough that evolution acts on us very much.

I have bad eyes. This is true. I've probably given my children bad eyes. But physical evolution doesn't matter to that any more. We solve it by being smart. I don't get eaten by a sabertooth tiger, A, because there aren't many sabertooth tigers running around out there, and B, because I have glasses so I can see. And so we outsmart these things, because we don't change fast enough by biological evolution that it matters, but bacteria that reproduce any 20 minutes-- they do.

And so we should know that evolution will happen, that we see the record of it in deep time, and that it matters to us. Because if you don't a really good expert in what bacteria are doing, what viruses are doing, what the flu is doing, how we can beat that when they change-- because they will change-- you're likely to die in the next pandemic. And if you do have really bright people across the street over here who are figuring out the new antibiotics and figuring out the new vaccines and figuring out what we can do about it when that happens, then we can go on being happy and healthy and terrific.

And so these knowledge of deep time things, whether it be oil, whether it be environmental issues, whether it be evolution bringing new diseases that we have to deal with, deep time matters.

Hello. We are going to switch to something different now. You have built mountains with Sridhar. You've torn down mountains with Sridhar, and then you've seen where they go down to the coast with me. And now, we're going to start becoming historians.

A lot of the job of a geologist is to read the past, to find out what it tells us and what we can do with it. As you know, a lot of people make you take history when you're going to school because they believe that, if you know where you came from, that it helps. If it happened, it has to be possible. And so, learning about history is a useful thing.

And so, now we're going to start looking back into history and see if we can tell time, see if we can tell stories, see if we can find out how the environment works. We're going to do a lot of this by looking at sedimentary rocks. We're going to look at what happens to all that sediment that's washed down the river before it gets subducted and erupted again. And we're going to do this by trying to tell time. We're going to try to sort out time.

We're going to start looking at some pretty pictures because we've got to look at pretty pictures. We've got to go to national parks and have fun. And so, we're going to start out with the CAUSE class at Arches National Park.

Arches sits just outside of Moab, Utah. It's a great town, if you're into mountain biking. If you're into a whole bunch of things, you can go to Moab and have a good time. There are national parks just scattered all around the place. And Arches is certainly one of the prettiest ones.

Here's Sridhar, as you'd certainly recognize. And behind Sridhar are the La Sal Mountains. Way up in here are the La Sals.

And La Sal is salt, the salt. And down deep underneath this there are salt deposits from an old sea that dried up. And salt, when you squeeze it, gets soft and it moves.

And so, the rocks in this area have done a little bit of this over time. And by doing a little bit of this, they've given us some very interesting things. And in particular, they've given us the arches.

If you move underneath a really hard rock-- these are hard sandstone rocks from a giant dune field that looked like the Sahara way back when-- if you move underneath really strong rocks, they tend to break. And so, whether you're looking diagonal in the bottom picture or you're looking end-on in the top picture, you can see that, as the salt underneath moved and the rocks flexed, they broke.

Whenever there's a crack, the world can get in. It can go beat up the rocks. It can try to change the rocks.

And in particular, we're now underneath looking up, and you can see the blue sky way up there in the corner. And you can see where a rock has been cracked. The yellow arrow is pointing at it. And I'm going to draw you a red arrow that points at it too. You can see where the rock has been cracked.

And then these funny-looking streaks coming down the side of the rock, water is dripping through the crack. And as it does, it carries sand away. It causes chemical changes. And eventually, the rocks are going to fall off there. And as the rocks fall off, they make these beautiful structures that we know as the arches.

Here you can see a couple of places that arches have started. They haven't broken all the way through, but they've started. You'll see, on the right where Raya is sitting in front of a big stone arch that's arching up over the top of him up there, and the rocks have fallen out of that hole and have fallen down the hill here. These big chunks behind Raya came out of that arch. They fell out.

That one is in Glen Canyon. And on the left is one at Canyon de Chelly where the same thing has happened, except the stream has washed the pieces away. And so, you get this action.

You get cracks. You get weather working down the cracks. You get rocks falling out. And eventually, they break through. And you get glorious, beautiful things.

And you can see Sridhar in the very far, lower left of the left-hand picture sitting down there. And he is looking at Delicate Arch. It's one of the best icons of the National Park Service, sitting up there with the mountains framed behind it, just a glorious place.

If you look closely at the rocks of Delicate Arch, you will see, A, that they're sand, they're sandstone. They're sand that's glued together by hard water deposits. And B, you'll see that they have layers in them. In fact, they look just like a sand dune that's had the sand glued together by hard water deposits. And that is part of the story that we're going to be telling here in a little bit, is how sediment turns into sedimentary rock and then what we can do with it.

This is Landscape Arch. This is the longest natural stone arch in the world. Landscape Arch is probably not that long with us. You'll notice it's getting very, very thin in places such as that one.

You would not want to be under this one if things were shaking and baking just a little bit because, if you look underneath Landscape Arch, you'll see a huge number of bigger rocks that have fallen off. And Landscape Arch is slowly caving in. A very large one fell off of fairly recently, the last couple of decades.

And the scar is shown in the lower right-hand picture. So, down here, on the very far right-hand side, is where a bunch of rocks fell off. And you can see the rocks that fell off sitting down underneath it. And so, the thing is slowly changing. The parks really are active. Geology really does happen.

Now, this is a picture in Hidden Canyon in Zion National Park. It's one of the most beautiful places that you can ever imagine. It's a little bit south and west of Arches.

And you go up in this canyon. And it's just glorious. And you walk back there just a long distance.

And there's sand on the bottom. And the sand has little ripple marks in it from when water flows in the occasional rainstorms. And so, you see things like this. It's loose sand sitting on the bottom with these ripples.

This is sandstone. And all this is is loose sand that's been glued together by hard water deposits. And so, you go from sand to sandstone.

When does it change? Well, there isn't any set line. In just about everywhere, you get a little bit of hard water deposit put down.

At some point, you say, this one's hard enough that I'm going to change the name. But there's no real strong line. We find all sorts of gradations between sediment, sand or mud or something like that, and sedimentary rock. And so, let's go and look at that just a little bit.

So, we will switch over and we'll write a few things. And so, we are going to talk now about sedimentary rocks. You've met metamorphic rocks in Rocky Mountain with Sridhar. You've met igneous rocks belching out of volcanoes. And now, we're going to look at sedimentary rocks.

We tore apart the igneous. We tore apart the metamorphic. We made mud. We made sand and all sorts of things like that. And now, we're going to see what happens to them.

So, you saw that weathering happens. And when weathering happens, which is just weather beating up on rocks, it gives rise to a couple of things. It gave rise to clasts, pieces, chunks. So, clast is a fancy geological word, but chunk will do fine.

And we also saw that it gives rise to dissolved salts, stuff that you can't see that breaks down into individual ions and washes away to make the ocean salty. So, it gave rise also to dissolved salts. And so, these are the two things that come out of weather beating up on rocks.

And so, you can imagine that they don't always go immediately to the ocean, to the subduction zone, to the volcano. They may stop on the way. And so, if they stop on the way, if they're headed from here to somewhere and they end up stopping for a while, then we call it sediment.

So, if they stop somewhere, the stream puts them down, the glacier puts them down, the wind puts them down, whatever, if they stop, we call the pile sediment. We call it sediment. And so, you can imagine that this is going to turn into sedimentary rock at some point.

And to turn into sedimentary rock, you have to make it hard. So, if you take sediment and harden it, hardening sediment makes sedimentary rock. Pardon me, that's not a technical term. We'll give you some technical terms here in just a second. But hardening sediment gives sedimentary rock.

We change the name, nature doesn't. There are all possible gradations between sediment and sedimentary rock. And at some point, we feel compelled to say, that's too hard. I'm going to change the name, OK?

There are several processes that go into this highly gradual transition. And it certainly is a gradual transition, a gradual change that takes one to the others. Up here above where I am, if you take your rock hammer and you hit a sedimentary rock, it goes, boom! It's really hard.

I have a friend that was studying sedimentary rocks that had been scraped off of the slab in Olympic National Park. And what they called rock-- they wanted to study erosion. So, they go out and hammer nails into it and then watch how fast the nails were washed out. And so, theirs are very, very much softer than ours, but they both were called sedimentary rocks.

And so, we have this gradual change of one to the other. And it is achieved primarily in three ways. The easiest one for doing this is how you harden it, so the hardening of sediment. The easiest one to think of is probably hard water deposits.

Most people these days have soft water. And if you have soft water, they've taken most of the rock out of the water. And you don't notice that your pipes get clogged.

But you know something? In an old house, you call the plumber and you say, I need help with my faucets. The plumber doesn't come in with a little screwdriver. The plumber comes in with a big wrench.

And the plumber's got a big wrench because all the pieces are stuck together. And all the pieces are stuck together because, whenever you put water in contact with stuff, it dissolves something here and it puts something down here. And there's usually bugs living in it, microbes that are changing the chemistry.

Anybody that's ever tried to take apart plumbing knows that it's stuck. And it's stuck by hard water deposits. Whenever you've got water going, whenever there's life, there's chemistry. And whenever there's chemistry, you're taking stuff from somewhere and you're putting stuff somewhere else. And eventually, you're going to end up gluing things together or else dissolving things and getting rid of them.

And so, we always see this in human activity. This stuff get stuck together. Nature is the same way.

If you leave a pile of sand long enough and you don't stir it and you let water go through it, eventually, you'll find out that minerals get deposited in the spaces. And it's stuck together. And once it's stuck together, we say, oh, that isn't a sediment any more. Now it's a sedimentary rock.

It's easier if you squeeze it at the same time because that keeps stuff from moving around. And so, you may also see squeezing going on or compaction. If you pick up a handful of sand and you squeeze it, you won't make it stick very well. You're not strong enough to do that.

If you're at the bottom of the Mississippi Delta, it's seven miles of mud on your head. And it's pretty hot down there at the bottom. And you put seven miles of mud on your head, you get squeezed. And so, that will help solidify things.

Way down at the bottom where it's hot and things are getting squeezed, you'll start to see new crystals grow. Things will dissolve. Other things will deposit. You'll get, what we call, recrystallization, or the growing of new minerals.

And you'll be sitting there and say, OK, he's talking about growing new minerals. And he's got a fancy word for that, which is recrystallization. What's the difference between this and metamorphism? And the answer is, nothing.

We humans have to draw lines. And if it looks muddy, we call it recrystallization in a sediment. And if it looks pretty, then we call it a metamorphic rock. And we change the name.

But this grades into metamorphosis. You heat things. You squeeze things. And they start to change.

The biggie for making sedimentary rocks is really, probably, the hard water deposits. We actually have a fancy name for that, as you might imagine. We call it cementation. You're putting cement between the grains. And so, cementation is usually what glues sediments together and makes something different.

OK, now, let us, then, go look at some more sedimentary rocks. So, we'll switch over to the pretty pictures again and see if we can go there. It's so hard to pick a favorite park. They're all so wonderful.

But if you want a beautiful fairyland, wonderful, just unbelievable place, go sit at Bryce for a day. Sit on the rim in the morning. Get up early and watch the sun come up on Bryce. Sit there in the evening and let the sun sink behind you and the shadows lengthen. It is just an amazing place. It's hard to believe that anything can be so pretty.

The flowers are there. The mountain lions are there. All sorts of wonderful things to see up on the rim. They've got prairie dogs and deer and what have you.

You go in the winter and, if you can get in-- the last time I was there in the winter, they were loaning out snowshoes at the visitor's center. And you could put on your snowshoes, and you could go snowshoeing along the canyon. It's just an amazing place.

The scale of it is immense. If you look in the right-hand picture here, you'll see at the bottom a whole bunch of people. I'm circling one of the CAUSE students right here. And I can't even see which one because you'll notice that this is a big place. And yet it looks so delicate. It looks so beautiful.

Now you will notice in all of these pictures that you see layers. The rocks are layered, and that is common in sedimentary rocks. You wash something in, it's put down. You wash some more in, it's put down. And so, you end up getting layers in the sedimentary rocks.

These happen to be from a lake. Today, there's a little lake left in Utah, the Great Salt Lake. During the Ice Age, when there was less evaporation, there were a lot more big lakes that extended across many places in Utah. And as we look back in time, we see the deposits of many lakes. And so, the Bryce Lake-- there's various names given to this-- was this big lake that sat down in Utah.

If you look carefully in many of these rocks, especially some just a little farther north of this, you will find fish fossils. You will find flamingo tracks. You'll find little snails and all sorts of things that say, OK, this was a lake. It was water.

Just glorious, you know? When nature starts beating up on these rocks, it just carves such beautiful things that it's hard to imagine. Here are a couple of our CAUSE students down here, Sam and Sameer, looking at a couple of really big trees that are sitting at the bottom of the canyon. It's hard to imagine how they live there, but they're doing just fine, thank you.

I don't think they do this any more. But you remember we've talked about sediment being carried in rivers and along beaches and so on. Here's a case that a stream is flowing towards you. So, the stream is coming towards you.

Now, there isn't much water in this stream right now. It only flows when it's raining. And the trail was getting buried in sediment, so the Park Service put these big logs across the stream.

And you'll notice what's happened is that sediment has piled up above the logs, it's filled it in, and that there's actually been erosion down here below. It's cut down a little bit. So, you can see the dynamics of sediment. What you've learned in earlier units keeps carrying through.

If this were to sit here a long time, you would get hard water deposits. And it would start to become a rock. It isn't there yet. It's still fairly loose.

This is a very interesting slide. Dave Janesko of the CAUSE class and I had the good fortune to go up and look at this one. And this one feeds into a story that we're going to tell about reading history, about inferring what happened.

We are just outside of Bryce. We're down in Red Canyon and the place they used to shoot a lot of Westerns. And we're up on the same rocks that Bryce is made out of.

Now, Bryce is mostly lake sediments. And you find all these fish fossils and stuff in similar rocks around. And occasionally you'll find such things in Bryce. But if you have a lake, there's probably a river feeding into it. And so, in fact, as you go west out of Bryce, you find the deposits of the rivers.

We know what a river gravel looks like. If you've ever been down to a river that has a little gravel bar in it and looked at the rocks, you know that they sort of look like this picture you see on the left. The rocks tend to be rounded. Rivers break off the hard points. And so, after a while, river rocks tend to be rounded.

The big rocks, cobbles, we call them, or pebbles, will have sand sitting in the spaces between them. This thing just looks like a river deposit. It's shaped like one. It's shooting down from a mountain range to the west, headed down into the lake that was Bryce Canyon.

And so, this is the sort of deposit that the geologist, who has looked at a lot of rocks, will be able to say, rivers make this. And it doesn't look like anything else I've seen. The size, the shape, the arrangement, the rounding, the sorting, all the things you go into this are pointing to this being a river.

What's very interesting, though, is that one of the pebbles in that river, which is this orange one in the middle here, one of the pebbles in that river is itself a river deposit. You can see that this orange one that I'm drawing on over here is made up of little, rounded sedimentary rocks itself. There's a big story in this. And it's a story that you should start thinking in your mind, how will am I going to tell this story?

What is it that has to happen that I can have a piece of an old mountain range and a piece of mud that's been squeezed and a piece of an old beach that have been put together in a river, bounced along, the corners knocked off, had sand deposited around them? Then they've been glued together by hard water deposits enough to make them hard.

Then they've been broken out. They've been bounced around in another river until they get rounded on the outside. They get deposited with pieces of all sorts of other things, old mountain ranges and old beaches and other things. They get glued together by hard water deposits. And they're setting up on a cliff far above any stream on the outskirts of Bryce.

There is a big story in this. And it's a story that, like I say, you want to start thinking about how you would tell that story and what it would mean. So, let's go back over to drawing things that might possibly prove useful. And what we're going to do now is we're going to take a look at sedimentary rocks, such as the ones you were just looking at.

OK, so we saw that sediment is either pieces, it's clasts, or else it's dissolved stuff. It's salts that dissolved. As you might imagine then, the sedimentary rocks that are produced from sediment come in two basic types. They either are pieces or they are the dissolved stuff that is put down. And so, we see chemical precipitates.

If you take a handful of ocean water and you let it evaporate, you will get a handful of salt, a little bit. If you were to wash ocean water into a little, shallow basin next to the ocean and then close it off and let it evaporate, you'll get a layer of salt. If that happens a few times, you'll end up with a lot of salt.

We saw, way back at the beginning, Death Valley early mining was for salts. It was actually a particular salt that had borax in it that had washed out of volcanic rocks. The water is carrying the dissolved stuff.

It goes down in Death Valley. The water evaporates. It leaves the salt. And then people went in and mined that.

And so, the chemical precipitates include things such as salt. It includes things such as the borax that led to the 20-mule teams in the early mining in Death Valley. And so, these things happen. You usually find them in fairly dry places because, when it's wet, the salts tend to wash away.

Other kind of sedimentary rocks, we can do them in a different color to have more fun. The other kind of sedimentary rocks are the ones that are made of clasts or pieces. And so, we call them clastic. And they are classified in various ways, usually by the size of the pieces.

And so, if you go in and you have a bunch of sand and you glue it together, you say, oh, it's a sandstone. This is really highly technical, let me tell you. So, sand gives rise to sandstone, when it gets hard enough that we decide we want to change the name.

A little bit smaller than sand, we have something called silt. And silt gives rise to siltstone. And there are actually very technical definitions for these things that you don't need to know. Silt is 1/16 of 1/256 of a millimeter in diameter, sand is 1/16, yeah, so on.

If you have clay, it gives rise to claystone. That is less than 1/256 of a millimeter in diameter. This is little stuff, although usually, people change the name. They use an old name for claystone. They call it shale. And so, you may possibly have come across that as one that you're familiar with.

If you get things that are bigger than sand, there's granules. People don't usually talk about granule stone. They get pebbles and they call it pebblestone. And they get cobbles and they call it cobblestone.

But usually, if you've got bigger pieces, they say, oh, let's just call that a conglomerate. And we'll not worry about that. And so, you'll end up with these being the main types of sedimentary rocks.

Now, what they are, how big they are, whether they're evaporated or not, whether the corners have been knocked off, a whole bunch of things of these rocks tell you a lot about the environment in which they were deposited. And so, what we can now do is look at it a little bit. And we can say that sediments and the sedimentary rocks that they turn into reveal the environment in which they were deposited.

And now, you can start to see that, if we can read the environment, if we can tell what the conditions were in which it was deposited, then we can read time, which came first and which came later. We can tell history. We can tell what the earth was doing and how it was changing.

For example, suppose that you go down and you find a rock. And you crack the rock open. And there's a fish fossil inside. It's not terribly likely that you're looking at a desert sand dune. You're probably looking at something that had water.

And so, what you can do is you start looking at things such as fossils. And fossils are pretty good indicators of what's there. If you see lizard tracks, you're probably not at the bottom of the sea. And you might be out on a sand dune somewhere. If you see ferns pressed into coal, you're probably not out in the desert where it's too dry for things to grow.

And so, fossils are going to give you a lot of clues as to the environment. And there's a big difference between a fish and a fern and a lizard and so on and so forth. And so, you can recognize these things. And you can start reading them.

There's other stuff. If you see a pile of boulders, the wind did not blow them there. We never see wind quite strong enough that they got boulders and put them there. Now, glaciers can bring piles of boulders. And so, you start saying we can look at what it's made of.

A beach is all sand. It's sorted. All that going in and going out and washing away, the little pieces are washed away fast. The big pieces are left behind until they get broken up. And the beach makes the sand-sized ones, the in between ones.

And so, we start looking at the size, the shape and the sorting, whether they're all the same size or whether some of them have been mixed with other sizes, so the sorting of the sediment. Size, shape and sorting of sediment clearly has clues to what you're looking at. Landslides may include all sizes. Glaciers can carry all sizes.

Wind does not. Wind is very selective. Little, tiny ones get blown far away. In between ones make sand dunes. Big ones are left behind. And so, when you see sand, it's usually wind or it's a beach, something like that. And so, these are pointing to indications of the environment.

Structures in the environment also can give you indications. If you see mud cracks, the mud dries and it cracks, you've got an idea that this was sitting in a place where it could dry so it could crack. And so, when you see mud cracks, you can start to tell a story.

If you see rain drop imprints, the blob that's made when the rain fell on the mud and then more mud washes in and buries it, moraines. If you see the pile left by a glacier and all the scratching and polishing that glaciers do, you're not in the middle of the tropics in a hot place. And so, if you see moraines, that is pointing to something else. And so, we can do environment by looking at the sediments and what is there and what it's doing.

OK, if you can do environment, add time, and you can do history. So, that's where we're headed. We want to tell the history of the planet, what was where.

Where were the continents? Where were the rivers? Where were the glaciers? Was the climate changing? Who was living here?

And so, we're going to try to put time together and we're going to see what we can do. Now, to do that, let me show you a couple more pictures. So, we will flop back over to pretty pictures. And I've got to get a little bit here.

Normally, you dump some mud, you dump some more mud, the younger stuff is on top. Nature doesn't raise the lid and shove mud underneath. It puts layer on top of layer, on top of layer, on top of layer.

If you're on the flood plain of the Mississippi, you build your house and the flood comes in and it puts mud on the grand piano. The mud is younger than the grand piano. The grand piano was there and then the mud is put on top.

So, normally, they pile up, and we can do a story. The young one's on top, and the old one's on the bottom, OK? There is, however, a bit of a tweak to that, which is, occasionally, nature causes trouble.

And you remember, in an obduction zone, you can cram things together. And if you cram things together too much, that they'll start to bend. And if they bend too much, they'll roll over. And if they roll over, now we've got to make sure that we know which way was up originally.

And there's a picture over here that we've got on the left. And if you follow one of these layers, start down at the green place down at the bottom, and then follow that layer around, and whoop, it bends. And now, it's upside down at the yellow place.

And so, geologists can't just say the young one's on top because, occasionally, nature tries to throw us a ringer. Fortunately, we can tell. There's all sorts of things that say this is the direction that was up when I was deposited.

And a geologist reads these. And then they can say, OK, am I down in the green place and I'm still right side up and the young ones are on top? Or am I up in the yellow place and I'm upside down and the young ones are on the bottom? And so, there are many of these indicators.

Something has to be, before you can cut it, you know? I could cut a piece of paper. That's fairly easy. But I can't cut it before it's made.

And so, what we have here is a picture taken in a cliff at Canyon de Chelly. And this is a fossil sand dune. And when there are sand dunes, the wind blows sand. And the sand piles up and makes little layers. And so, you'll see little layers here.

This picture is only about six inches across, but you'll see layers that are piled up. The red is actually hard water deposits. It's rust that's been put in here. And so, the wind was blowing into this picture from the right to the left. And it put down these various layers that you can see in the picture.

Then the wind picked up a little bit and it cut the top off. And so, all the way along the top there, you can see the layers go up, and then they're cut. They just end right there. And then there's more layers deposited on top of them.

And so, this one has to be right side up. The old ones have to be on the bottom because they've been cut. They've been whomped off on the top by the wind that put the next layer down.

Now, I can play games with this. The picture that you just saw is now in the upper left. And the blue arrow shows which way was up, where the sky was when this sediment was deposited.

Suppose that mountain building came in and it started turning things over. And so, you can look to the right of it there. And I've taken the picture and I've flipped it on its side.

And you can look farther down. And I've taken the picture and I've turned it upside down. All of these are possible. Nature can do this.

But you look at it and you say, I know because the cut is still there. And so, I know, if I come to the upper-right picture, I can see where the layers are cut. And so, I know that the layers had to be there before they could be cut. So, I know which way is up. I know what the pointing is.

This is a picture in the wall of the Grand Canyon. You're down at the South Rim. You're headed down to the bottom. And you're going to have a great time.

And you look at that cliff and, oh man, that's such a wonderful cliff. This picture is probably 100 feet high. This is an immense, immense cliff that's sitting there.

On top are sand dune deposits. It's a giant, giant sand sea that came in here. On the bottom is a flood plain deposit. You might think of the Nile River flooding across its vast delta, its vast flood plain and then the desert of the Sahara blowing in over the top.

And so, the bottom rocks are flood plain deposits. You'll find leaf fossils in them. You'll find footprints in them. And then on top, it turns into these sand dune deposits.

Now, you'll notice right under the red arrow that the sand goes down a crack. If you've got mud and then it dries out, and this huge drought arrives, and the mud starts contracting, it'll crack. And when the sand blows in, the sand will fall down that crack.

And you can follow the sand way down this crack. This picture has to be right side up. Sand does not fall up cracks. It does not fall sideways in cracks. It falls down cracks.

And there is the sand. And there's the crack. And there it goes. This picture's right side up.

If we turned it on its side, you'd know that. You're now [? GEOSCI 10-ed. ?] You're geology of the national parks wise. You can figure this out.

These are other mud cracks. These are also right side up. This is from rocks that are just like Bryce, except just a little bit north in the Flagstaff limestone.

The cracks are going down. And so, it cracked. And then more mud will fall in. But we can see down in to these cracks. This one is right side up.

This one is a little tougher because it's a little hard to see. But you'll notice my finger in the picture in the lower left. And you'll notice the shadow of my finger.

And you'll notice the mud cracks up there in the middle. And you'll notice the shadow of the mud cracks right there and right there. So, these are sticking up at you.

This is the stuff that fell down into a crack that was below it. And then we turned the sucker upside down. And so, we're looking at the bottom of this one. And I'll draw this for you in just a minute, after we walk through this. And so, this one's upside down.

We're now out at Sunset Crater, big, beautiful volcano. And the lava came down. And it threw these little rocks.

And the little rocks that it threw actually made mulch for the native peoples that lived there, the Sinagua. And they had wonderful times for a while because their crops didn't dry out because those little rocks held the water.

But in the lava flows, when a lava flow comes down, it's usually bubbling and burping and belching and sorts of things. And the very top will freeze because it's in contact with the air and that freezes it. And the bubbles rise.

And so, if you look at this one, you'll see big bubbles at the top. And when you go down, there's a little bubbles. And then there's not many bubbles at all.

This one's right side up. The bubbles rose and they got trapped under the top. And it doesn't always work, but this one usually works too. And so, this says it's right side up.

If later mountain building turned it over, you would look at that and you'd say, I know what's going on.

OK, so let us draw a couple of those, just so we're on the same page and you're sure. This might prove useful some day. Suppose we start out and we have water. And it washes in some mud.

So, down here, we have mud. And up here, we have water. And you've got a fish swimming in the water, so you know which way is up.

OK, now what happens? The fish swims away, and the mud dries up, OK? So, now, we're going to dry this up. This fish is going off somewhere downstream.

And after the fish swims downstream to safety, then the water dries. And what happens after water dries is, usually, it will crack. And so, you'll get mud cracks.

And so, there we have a picture of some cracks. The cracks go down. They end. They don't go to the center of the earth. And so, the cracks go down and they end.

Now, what's going to happen? We're going to wash in some more mud of some other kind. Let's make blue mud. And so, more water comes.

And the mud comes in. And we get another layer in here. And what does it do? It squirts down in the crack.

OK, if you see this in a cliff, you say, oh, it's right side up. There's no problem. If you happened to come to a cliff and you happened to see something that looked like this-- let me see if I can get this-- suppose that you saw it this way. OK, and it was looking something like this.

You would look at this and you'd say, oh no, mud cracks didn't do that. The mud didn't start with a giant, overhanging cliff with cracks going up into space. This thing has been flipped over. So, this has been flipped, OK? So, this one is right-side up.

And the one down here has been flipped in a very funny way. It's not flipped quite all the way over, but nature doesn't do that. Sometimes it flips it all the way. Sometimes it flips it 3/4 of the way. There's all sorts of possibilities of what nature can do with these things, OK?

The same thing we'd do if you had footprints. If you want to think of as a footprint rather than a mud crack, it's the same sort of picture. And so, footprints do the same. Footprints go down.

Raindrop imprints, if the rain drop falls in mud and it makes a little hole, that goes down. Bubbles rise in lava flows. And they're trapped just below the top because that chills very early. So, they're trapped below the chilled upper layer, the chilled top.

People often look at shells on this. If you go down to the beach-- and this would be interesting for you to do-- this is not 100%, but it usually works. Suppose that you have a shell sitting on the beach. Beach, OK? And this is a shell. And here's a sea gull flying over the shell. OK, big shell.

Now, what happens when the wave comes in? When the wave comes in, it's going to get under this and it's going to rock it. And so, this what you would call your unstable, easy to rock position.

All right, well what's going to happen? It's sitting here and it's going to rock back and forth. And eventually, it's going flip over.

And so, it flips. And now, it's sitting here. And then it gets buried in the beach. And it will stay there.

And if you go down to a beach that has lots of curved shells and you look at them, you'll find that most of them, 80%, 90%, often are in this position. It's stable like this. And so, most shells end up this way.

They get buried. And you can tell which way was up. And so, there's all these things that are sitting there that are telling about it.

Let me try to draw the one I showed you in the cliff of Canyon de Chelly with the way that sand dunes work. And so, let's see if we draw a sand dune. We'll make it a red sand dune.

And so, the wind, we're going to bring in this way. And so, here comes the wind, and what happens? You know how sand dunes are. There'll be a pile here, but they start growing this way.

And so, over time, the sand is blown over the top. And it piles up in the lee of the dune. And so, the dune builds out that way. And so, it grows this way, grows sand there.

Now, what happens is there's usually changes in wind. Sometimes it's stronger. Sometimes it's weaker. And very often what you'll find is that the wind will come through and it will actually scour things off.

Oh, that wasn't what I wanted to do. OK, well let me draw it back in. We'll erase everything. And so, we'll go back and we'll say OK, we've got this sand dune, and it's sitting here. And it grows along like this.

And so, here comes our sand dune, and it's growing. Then the wind will come in and it will basically scour off the top. That gets cut away.

And after that's cut away, you may bury this in another sand dune that's coming through later. And so, now, let's put some more through.

The layers may be nearly horizontal. They may grow like this. But what you'll find is that, where the cut is, these things will always grade in to what's underneath them. They won't be cut, whereas, the ones on the bottom will be cut.

And so, the top ones are not cut. It's got to be there to be cut. And the bottom ones are cut. And so, whenever you see cut and not cut above it, you know which way is up. And so, there's an indicator there that you're dealing with up and not up, OK?

The other thing one notes is that most layers usually start sort of horizontal. These slant, but they don't make cliffs. You'll never go out and see a giant, 100-foot high cliff of sand. You'll see sandstone, but not sand.

And so, what you'll also find is that most layers start out nearly horizontal. And they start out nearly horizontal because of mass wasting. Otherwise, they'd schlump down.

So, that now gives us enough tools to tell stories. We can read environment. We can tell what the deposition was, whether it were a glacier, whether it were a lake, what have you. And we can read time. We can put events in order from oldest to youngest.

If you do that, a very, very remarkable result comes out. And this is something that was developed first by a canal engineer. This canal engineer, William Smith, was out trying to do canals. And he was trying to work in England.

And he found that there's a lot of sheep in England. There's a lot of grass in England. It's sort of hard to find the rocks. And he'd find the rocks in a few places. And he'd look around at the rocks.

And he started realizing that, when he put the rocks in order, that it put the fossils in order, that there were one kind of fossil here and another kind of fossil there. And it also turned out that some of the fossils, actually, he'd find in the dirt. And he could identify from a fossil which rock was underneath.

And so, there was this canal engineer. And his name was Smith, a canal builder named Smith in England. And this happened in the early 17th century. And what we found is, if you put the rocks in order, it puts the fossils in order.

What does that mean? It means that the fossils that are near each other in a pile of rocks are similar, if you do the same environment. Now, let's be very clear. You don't get exactly the same things if a lake turns into a sand dune. You have to compare a lake to a lake.

But if you compare a lake to a lake or an ocean to an ocean or something like that, what you find is the fossils that are near each other are similar. The fossils that are farther apart are more different. The fossils on top are more like the things that are alive today. And the fossils on the bottom are more different from the things that are alive today.

And so, what you find then is that the rocks of similar age have similar fossils. The rocks of very different age have very different fossils, so different age, different fossils. And the rocks on top, the youngest rocks, have fossils that look most like things still alive. And so, the youngest rocks, the youngest fossils, look most like things still alive.

Now, this was done for purely practical reasons. This is an engineer looking for a shortcut. It's to help him identify the rocks that are down underneath all these sheep and the goats and the heather and the what have you. This clearly turned into something much bigger, or it helped contribute to something much bigger, that we're going to talk about. We will come to that in just a little bit.

Right now, we just need to add a couple of things. One is that this gained a name. It was called The Law of Faunal Succession.

Now, this is not a law that was passed in Congress. This is just a rule that is found to work over and over and over again. And after you check it 10 times, you check it 100 times, you check it 1,000 times and it just keeps working, and eventually you say, well this works.

And so, we should give it a fancy name so that people know that we've checked it a whole lot and the thing keeps working. So, they call it a law, but there's no law here. It's just a summary of observations. It is The Law of Faunal Succession.

Another thing that came out of this-- and this will be the last thing we need to get through for today-- is that, when people had put all these fossils in order, they got really tired of talking about, well, you know, the time that I had those big, funky trilobites with the big, giant eyes and then the little horn curls? But not after you showed up with the big, [? iridescent ?] clams.

They needed names. They needed some way to talk about this aside from talking about the big funky eyes of the trilobites. So, they came in and they named everything. And you know that geologists, and scientists in general, have a habit of trying to name a lot of things.

And so, they gave their names-- and if we go from young rocks on the top to old rocks on the bottom, the big names that they gave it, they said, OK, today we're going to call this Cenozoic, all right? Now, you'll recognize in the word Cenozoic, "zo" for life down there. "Ceno" is actually something like new. And so this is the time of new life.

There are lots of things alive today. There are insects and all sorts of things. But the big land critters are more mammals than anything else, so you'll often hear this is called, The Age of Mammals. Although, if you've ever been out in a really mosquitoey place, you begin to wonder about that.

Now, below that, they said, well there's different things. We need another name for that. We don't see mammals dominating all the way back. So, below that, they called the Mesozoic.

And "meso" is middle. So, this is something like the middle life. This is biased for us, big land critter, so this is middle life. And the big land critters were dinosaurs then, so this is what you often hear as, The Age of Dinosaurs.

Now, below that, they had-- you might imagine, if we have new life and middle life, well let's have old life. So, let's call it the Paleozoic. And so this is something like the old life. There weren't a whole lot of land critters until the latter part of this. So, this is old life.

And if you want a catchy name, you could call this The Age of Shellfish because there's lots of marine life that's making shells. And we have good records of that.

Below that, there are a bunch more "zoic" words. If you were taking a course in historical geology, we'd pound them into your head. We're going to use an old term that's a little easier and lumps a whole bunch of them together. We're going to call it the Precambrian.

It turns out that the Paleozoic and the Mesozoic and the Cenozoic have subdivisions. And one of the subdivisions of the Paleozoic is named for Wales, or Cambria, in the United Kingdom. And the rocks that are exposed there have these cute goggle-eyed trilobites.

Since they called that the Cambrian, and then this is older than that, so it's the Precambrian. And if you want, that's just the rocks that are before the Cambrian, so, don't worry about that. And there isn't a lot there, a lot of algae, blue-green algae, cyanobacteria, various other things. So, let's just call this the Age of Algae. That is a little bit loose, but I think it'll get us there.

And so, we have come a fair distance here in a very short period of time. You've seen some beautiful things. I hope that you enjoy seeing these. I certainly enjoyed going there with the CAUSE students to take the pictures.

We have seen that sediment, which is washed down from the hills, which is land-slided down, which is brought by glaciers or what have you, can be glued together by hard water deposits to make sedimentary rock. We can look at those and say, are you a sand dune? Are you from a glacier? Are you from a landslide? Are you from a lake?

We can put them in order. We can tell if nature has tried to fool us by flipping them upside down. And so, we really can say this one's younger and this one's older. We can put the events in order. And once we do that, we are going to start telling histories.

One of those histories is going to involve who lived where, when. Some others are correlating changes in where the continents were. There are going to be changes in all sorts of things in the climate. But one of those stories is going to be who lived when. And we've got a few words now down here that sort of help us summarize who lived when.

Notice that we don't have any numbers on this young and old. And so, we have to go look at putting numbers on the young and old before we can go further. So, that will be our next task is to try to put years on this. And then we're going to tell history.