GeoMations and GeoClips

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.