Module 2: Coastal Landscapes
Module 2: Coastal Landscapes
Introduction
What is the coastline or shoreline? What is a coast or coastal zone?
For most of you, the terms coast or shore likely bring to mind visions of things such as vacations, waves, wind, sand, sailboats, coastal birds, and, perhaps, very bad cases of sunburn. Regardless of your first thoughts and whether you have ever been to a coast, if you were asked to define it, you would probably recognize that a coast is a location where the solid dry surface of Earth interfaces with the open-ocean environment. It is absolutely reasonable to think of the intersection of the water line with the firm ground as a coastline, but, in this entire course, we will be focusing on the intersection of the open marine/salty water/ocean/sea environment as the coastal zone. As you learned in Module 1, our global society is intrinsically linked to the coasts of the world and, for this reason, there is a wide range of interest in developing a sound scientific understanding of the form of coastal zones and the processes that cause them to change or evolve through time.
Throughout this course, you will hear or see the term coast or coastal zone. This is where an explicit definition becomes a bit more fuzzy and difficult to provide. Most scientists who conduct research within coastal zones would probably agree that the coastal zone, or coast, can be defined as a part of the land that is affected by processes of the open ocean, such as tides or salty ocean water. It includes the land above as well as below the water in these types of locations. On a global basis, coastal zones are highly varied, and a single coastal zone may consist of numerous coastal sub-environments such as marshes and estuaries or may consist of a single type of environment such as a sandy beach at the base of some very high cliffs (the images below show some very iconic coastal zones). Consequently, they may be highly varied in their width, ranging between perhaps only a few hundred meters or as much as several hundred kilometers.
Regardless of the scale of the coastal zone, each coastal zone of the planet is characterized by a unique set of physical, chemical, and biological processes. Physical processes include things such as the daily movement of water and sand grains because of tides or waves. Chemical processes include the formation of small grains of the mineral calcium carbonate as it precipitates out of seawater. Biological processes include things such as the growth of plants in coastal marshes or the formation of small reefs in estuaries by organisms such as oysters. Collectively, all of the physical, chemical, and biological processes of a coastal zone interact to affect how a specific coastal zone looks, the ecosystems that are present there, the natural resources that are present, how it changes through time, and how we as humans interact with the coastal environments.
Finally, because of the diverse range of physical, chemical, and biological processes that exist in coastal zones, a solid scientific understanding of coastal zones requires a very holistic scientific approach with input from oceanographers, geologists, biologists, chemists, and engineers. In this unit, we will take a close look at how we classify coastal zones and the overall morphology and environments of coastal zones.
Classification of Coastal Zones
As humans, we love to be able to categorize things and create nice little compartments or classifications for the natural world around us. For example, think of how we have taken the animal kingdom and created a classification scheme that separates birds from mammals or invertebrates from reptiles on the basis of the differences between these organisms. Classification, regardless of what we are classifying, provides a way for us to organize things and then ultimately compare and contrast the differences between different parts of the natural world so that we can best understand how and why it developed.
During the last century, there have been numerous classification schemes proposed for coastal zones. Each one has had some good and bad ideas embedded in it, but one of the more recent and useful classification schemes of coastal zones relies upon understanding the concept of plate tectonics.
Goals and Objectives
Goals and Objectives
Goals
- Students will gain an understanding of how plate tectonics plays a first-order control on the characteristics of a coast and how other processes such as glaciation, climate, sediment supply, waves, and tides also influence the characteristics of a coast.
- Students will develop an appreciation for the geomorphologic diversity of coastal zones.
- Students will gain an understanding of the differences between emergent and submergent coasts, depositional and erosional coasts, as well as how hydrodynamic regime exerts a strong control on the geomorphology of the coast.
Learning Objectives
By the end of this module, students should be able to:
- examine and show, using Google Earth, the global diversity of coastal zones;
- identify the plate tectonic setting of a coastal zone based on geographic location relative to major tectonic boundaries;
- identify and be able to describe the second-order processes that can act on coastal zones;
- integrate knowledge of coastal geomorphology and understanding of coastal processes to identify the types of processes that create specific coastal geomorphologies;
- evaluate the history of a coast on the basis of the coastal geomorphology.
Module 2 Roadmap
| -- | Assignment |
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| To Read |
In addition to reading all of the required materials, before you begin working through this module, please read the following required article to make sure you are familiar with the content, so you can complete the assignments.
Extra readings are clearly noted throughout the module and can be pursued as your time and interest allow. |
| To Do |
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Questions?
If you have any questions, please use the Canvas email tool to contact the instructor.
Getting Down to Business: Plate Tectonics
Getting Down to Business: Plate Tectonics
What is a collisional margin? What is a passive margin?
We know from a wide range of different studies that the Earth is not a completely solid sphere, but instead consists of a series of different layers ranging in composition that dictates the way they react when forces are applied to them. The outermost layers are very different with regard to composition and density from the innermost layers of the Earth. A generalized segregation of the Earth recognizes these three primary units: crust, mantle, and core.
Earth Structure
Earth Structure
Crust
At the scale of the whole Earth, the crust is a relatively thin, solid outermost layer that ranges in thickness. The thickest part of the crust exists in areas with mountain ranges and may be as much as 100 km thick in some locations but, generally, the crust is between approximately 30 and 35 km. Below the oceans, the crust is much thinner, averaging about 5 km. Two fundamental types of crust are recognized: Continental Crust, which is below continental land masses, and Oceanic Crust, which is below the oceans.
Mantle
Below the crust is a much thicker layer called the mantle. Because of a higher abundance of dense minerals, the mantle is much denser than the crust. At shallow levels just below the crust, the mantle is rigid; whereas at deeper levels, although the mantle is still solid, it has the ability to flow slowly like taffy or putty. Because the rigid part of the upper mantle behaves mechanically like the overlying crust, the two are lumped together and referred to as Lithosphere. It is the lithosphere of the planet that breaks by fracturing, and it is the lithosphere that is broken into a series of tectonic plates. These plates are able to move very slowly across the hotter and partially molten underlying material that deforms by flowing and is referred to as the asthenosphere. It is the flow of the very hot asthenosphere that helps to deform and drive motion of the overlying lithospheric plates.
Core
From a depth of approximately 2,000 km to the center of the Earth at a depth of 6,378 km is the very dense and very hot metallic core.
Plate Tectonics
Plate Tectonics
Plate Tectonics
Take a look at the global base map that shows, and identifies with labels, the different tectonic plates of the Earth. You will notice that the margins of the plates are very irregular and that the boundaries of the plates fit together similar to a jigsaw puzzle. If you look very closely, you will also see that the margins of the plates are sometimes located on the edge of the continents, and sometimes the margins are located in the middle of the oceans. As previously mentioned, these plates are not static, but, instead, move at very slow rates, averaging just a few centimeters per year. In the course of very long intervals of time, such as 100,000 years, these very slow rates of motion can add up to hundreds of meters or kilometers of total motion.
The result of these rigid plates moving around is the creation of one of three different types of plate boundaries: divergent, convergent, and transform boundaries.
Divergent Boundaries
This is a boundary between two plates that are moving apart from one another. For example, if you look at the global base map again, you will see a plate boundary that extends all the way through the middle of the Atlantic Ocean. This is a divergent boundary where the North and South American Plates are moving away from the African and Eurasian Plate. At this location, new oceanic crust is forming (see Illustration of three types of tectonic boundaries) as underlying mantle material flows up through the gap created by the separation of the plates. It is referred to as the Mid-Atlantic Ridge because along this margin the oceanic crust is elevated and creates a ridge. Because the edges of the continents on opposite sides of the divergent boundary are considered tectonically inactive, they are called passive continental margins. Divergent boundaries can also extend across continental crust – such as where the Arabian Plate is moving away from the African Plate and in the process creating the Red Sea Rift.
Convergent Boundaries
Convergent boundaries are those where plates are colliding with one another, forming either a subduction zone or continental collision. There are two types of convergent boundaries: continental-oceanic and continent-continent.
Continental-Oceanic Boundaries: In the case of a continental-oceanic crust collision, the denser oceanic plate will fold or subduct underneath the less dense continental plate. For example, take another look at the global map of the tectonic plates, and you will notice that there is a boundary along the entire length of the western edge of South America. This is a margin where the Nazca Plate is in direct contact with the South American Plate. Earthquakes, volcanoes, and mountains are often associated with convergent margins (see Illustration below of the three types of tectonic boundaries), and all three of these occur along the western edge of South America.
Continent-Continent Boundaries: A continent-continent collision, or orogeny, occurs when two continental plates collide, fold, fault, and uplift, creating mountain ranges. The Himalaya Mountains are actively building as the result of the compressional forces put upon the Indo-Australian Plate and the Eurasian Plate pushing against each other during the last 30 to 50 million years.
Transform Boundaries: Transform boundaries exist where plates are sliding past, or more scientifically stated: shearing past one another. The San Andreas Fault of southern California is one of the most recognized transform boundaries where the Pacific Plate interacts with the North American Plate. During the approximately 30 million years that the San Andreas boundary has been active, there have been approximately 550 kilometers of movement.
A final thing to keep in mind is that plate tectonic interactions generate stresses that can lead to the development of fractures in the lithosphere. If the movement of the lithosphere takes place across these fractures, they are called faults. Three main types of faults are recognized: 1) normal faults, 2) reverse faults, and 3) transform faults. You probably have realized that transform faults, like transform boundaries, are those where opposing sides of the fault slide past one another. In the case of a normal fault, part of the lithosphere slides down past the lithosphere of the opposing side, whereas in the case of a reverse fault, part of the lithosphere moves over the top of the lithosphere on the opposing side of the fault. Understanding faults and faulting will become important later on, in Module 6, when the creation of tsunamis is covered.
For more information on plate tectonics, check out the following links with the U.S. Geological Survey (USGS):
- USGS Historical Perspective: [6] useful information about the history of thought regarding plate tectonics
- USGS Developing the Theory: [7] information regarding how the modern theory of plate tectonics was developed
- USGS Understanding Plate Motions: [8] additional information regarding the types and characteristics of different plate boundaries and how different plates interact with one another
Learning Check Point
Learning Check Point
Please take a moment to think about what you have learned in this section, then answer the question below to test your knowledge.
There is no credit for this activity, but at this point, you should be able to explain/discuss the differences between the layers of the Earth and the different types of boundaries that exist between the plates.
Coastal Zones: The Margins of Continents
Coastal Zones: The Margins of Continents
What are continental margins and what is the morphology of continental margins?
Continental Margins
Before we get too far along in a discussion of plate tectonics and coastal zones, we need to address the characteristics and form of continental margins because this is where the coastal zones that we will be referring to are located. As indicated by the name, continental margins are the edges of the continents and transition into the deep-water environments of the ocean basins. In general, continental margins have several distinct physiographic subenvironments, including the continental shelf, continental slope, and continental rise (see cross-sectional profile).
Continental Shelf
The continental shelf of a continental margin includes the seafloor that extends from the subaerial part of the continent, or shoreline, seaward to what is known as the shelf break. Continental shelves are typically relatively gently sloping surfaces, but a change in the gradient, or slope, of the continental shelf, takes place at what is referred to as the shelf break. There is a wide range of widths and gradients for continental shelves (see global map), but the global average water depth for where the shelf break is located is between 120 to 130 m. The global average width for continental shelves is approximately 75 km, and the average slope of the continental shelves is on the order of 6 to 8 degrees. One fundamental characteristic of continental shelves is that they can represent areas of extensive deposition because of their proximity to continental river systems that supply sediment to the continental margins. In fact, in some places, the continental shelf may be underlain by as much as 10 to 15 km of sediment, representing tens of millions of years of deposition above the granitic crust that forms the foundation of continental margins. On a global basis, the sediment at the surface of the continental shelves can derive from many different sources. Depending upon the location of the continental shelf and the characteristics of the adjacent continent, the sediment can be sourced from river systems, glaciers, and ice sheets, or can be calcium carbonate sediment sourced from organisms that produce shells of calcium carbonate.
Continental Slope
The continental shelves of the world transition into the continental slopes at the shelf break, where a distinct change in the gradient or slope of the seafloor exists. This change in gradient is coincident with a reduction in crustal thickness and a granitic to basaltic change in the composition of the underlying crust. Continental slopes are narrower than continental shelves, with a global average of only 20 km. They extend from the shelf break at approximately 120 m to as deep as 3,000 m with approximately a 4-degree gradient, but may be as high as 20 degrees. Overall, slopes also vary according to the nearby plate tectonic boundary, where slopes are steepest in locations adjacent to geologically young plate tectonic margins with narrow continental shelves. Deposition on continental slopes is predominantly finer-grained than the sediment that is deposited on continental shelves because there is less moving water from waves and tides to carry large sediment particles. One exception, however, is that during past periods of low sea level when rivers extended across continental shelves to meet the low sea level shoreline, relatively larger sedimentary particles were transported to continental slopes by river systems. As a result of the past low sea levels, some continental slopes contain buried deposits with large sedimentary particles such as coarse-sand and gravel. One unique feature about the outer parts of the continental shelves and continental slopes is that they may be the sites of submarine canyons through which sediment and water can be carried out to deeper parts of the ocean basin. Through the years, there has been much speculation as to how these canyons form, but most scientists agree that their origin is a result of erosion by oceanic currents, gravitational forces that cause failures and incision, or are the remnants of river valleys formed during past lowered sea level.
Continental Rise
The continental rises are the most distal parts of the continental margins and represent the transition from the slope to the deeper, flat physiographic regions of the open ocean basins known as abyssal plains. Wedges of sediment that can be several kilometers thick and several hundred kilometers wide developed because of the seaward transport of sediment from the more shallow water continental shelves and slopes. Overall, the gradients of the continental rises are typically less than 1 degree.
For more information on continental margin physiography and morphology, check out this link:
Learning Check Point
Learning Check Point
Take a few minutes to think about what you just learned, then answer the question below to test your knowledge.
There is no credit for this activity, but at this point, you should be able to explain the structure of continental margins and the fundamental differences that exist along a transect from land to the open ocean.
Back to Coastal Zones: Plate Tectonics and Coastal Classification
Back to Coastal Zones: Plate Tectonics and Coastal Classification
What are the characteristics of coastal zones along collision coasts and trailing margins?
The tectonic setting and tectonic history of a continental margin are probably the most important factors that control the character of a continental shelf and coast. You can think of the tectonic setting as a first-order control on the morphology of a coastal zone. There are other factors that certainly are important, such as sediment supply, but we will get to those in later sections.
A very useful and widely recognized classification scheme of a coastal zone is the tectonic coastal classification developed by two scientists. In 1971, Inman and Nordstrom published a scientific paper that linked different types of coastal zones to tectonic characteristics. They suggested that the most important factors in determining the coastal characteristics were:
- location of the coast with respect to plate boundaries;
- tectonic setting of the coastline on the opposite side of the continent;
- time;
- exposure of the coast to open ocean conditions.
- Collision Coasts
Collision coasts face a plate boundary. They occur at the point of subduction zones, on the edge of a plate. These are tectonically active coasts, with frequent earthquakes and volcanic activity. Features found on and near collision coasts include mountains of more than 3,000 meters; deep trenches offshore, into which sediment falls when it reaches the coast. Here the continental shelf is narrow and there are few depositional features to be found. The rivers that drain to collision coasts are relatively small and there are few of them.
Examples of collision coasts are the west coasts of North and South America.
- Trailing Edge Coasts
Trailing edge coasts face a spreading center where new material is added to the oceanic plates (e.g., mid-Atlantic spreading center). Trailing edge coasts are near the middle of a tectonic plate and far from the plate boundary. The characteristics all trailing edge coasts have in common are lack of tectonic activity (no earthquakes or volcanism); There are three types of training edge coasts:
- Amero-trailing edge coasts
Amero-trailing edge coasts occur in the middle of a tectonic plate and face a spreading center. The coast on the opposite side of the continent is a collision coast. Characteristics of Amero-trailing edge coasts include NO tectonic activity; a wide continental shelf and a wide, low coastal plain. There is abundant sediment deposition and therefore numerous depositional features. These features include marshes, barrier islands, spits, mangroves, and deltas. Examples of Amero-trailing edge coasts are the east coast of North America, the east coast of South America, and India.
- Afro-trailing edge coasts
The distinguishing characteristics of Afro-trailing edge coasts are: they face a major spreading center, AND the opposite coast also faces a spreading center. The entire continent is located within a plate. They also have no tectonic activity. The continental shelf can vary in width from wide to narrow. The coast itself can feature cliffs, hills and low mountains, and coastal plains. Sections of an Afro-trailing edge coast can have many depositional features, while other sections have very little sediment deposition, so they are highly variable. Examples of Afro-trailing edge coasts are the east and west coasts of Africa, the coast of Greenland, and parts of coastal Australia.
- Neo-trailing edge coast
This type of coast faces relatively young plate tectonic spreading centers, which means that there has not been enough time for them to develop. There may be some volcanism, and they may be seismically active with rugged, young topography adjacent to them. The continental shelf is very narrow here. There is very little deposition taking place on these coasts, as few rivers enter the ocean. A few pocket beaches form, but no other depositional features. They are backed by cliffs, hills and low mountains. Examples include the Gulf of California, where Baja rifted from mainland Mexico about 20 million years ago (relatively recent in geologic time).
- Amero-trailing edge coasts
- Marginal Sea Coasts
Coasts of this character occur along continental coasts facing an island arc. They are sheltered from the conditions of the open ocean by other land masses, such as island arcs, which were created by the collision of tectonic plates. They feature wide continental shelves and are backed by hilly or low-lying regions. There is no tectonic activity on these coasts. There is high sediment influx from rivers, resulting in depositional features such as deltas. Examples of marginal sea coasts include the coasts of mainland China on the South China Sea, the East China Sea, the Sea of Japan, and the Yellow sea. The Caribbean islands form an island arc that protects the coasts of mainland central and South America on the Caribbean Sea.
Learning Check Point
Learning Check Point
Please take a few minutes to think about what you just learned then answer the questions below to test your knowledge.
There is no credit for this activity, but you should now be able to explain the different types of coastal zones as a function of plate tectonic settings and understand how different tectonic settings influence the type of coastal zone characteristics that may be present.
A Few Notes on Other Types of Coastal Classifications
A Few Notes on Other Types of Coastal Classifications
What is an emergent coast? How does an emergent coast differ from a submergent coast? What is an erosional coast and how is it different from a depositional coast?
As mentioned at the beginning of this module, there have been a number of coastal classification schemes proposed throughout the time of coastal scientific inquiry. There is not enough room in this module to discuss all of these in detail, but here are a few more as food for thought and discussions that will come later in this course.
Emergent and Submergent Coasts
Emergent and Submergent Coasts
The elevation of sea level has not always been constant. It varies locally on a daily basis because of the phenomenon of tides but has also changed across much longer time periods. For example, about 18,000 years ago, when large ice sheets were present on the planet during a period of cooler climate, sea level was approximately 120 meters lower than it is today because a large volume of ocean water was frozen in ice sheets at that time. In this case, sea level was below the current sea level elevation because of actual volumetric changes to the amount of water stored in the ocean basin.
There are, however, other ways to change the apparent elevation of sea level along a coast. Consider, for example, keeping global sea level steady along an active plate tectonic margin where the coast is being uplifted. Because the land surface is being uplifted, there is an apparent fall of sea level elevation, even though the total volume of water in the ocean basins has not changed. When we can observe evidence of a change in sea level elevation, whether it be an increase or a decrease of elevation, we call it a relative sea level change because we may not necessarily know what mechanism actually contributed to the observed change. You will learn a lot more about changes in sea level later in this course; but, for now, keep in mind that many lines of geologic evidence exist for a long history of relative sea level changes. This leads us to recognize two different types of coasts on the basis of whether they have experienced a relative sea level fall or relative sea level rise.
Emergent Coasts
Emergent coasts are a result of local tectonic uplift of the land surface or a fall in the elevation of sea level because of a reduction in the water volume of ocean basins. Quite often, emergent coasts have rocky coastlines with cliffs and nearly flat platforms that extend inland where older coastal plains have been tectonically raised and are now elevated above the modern land and water interface. A very good example of an emergent coastline, because of its proximity to an active plate tectonic margin, is the west coast of North America. Parts of the Scandinavian coastline (Sweden and Norway) are also emergent where the land surface has been rebounding upward due to the removal of the weight of glacial ice that formed during the last Ice Age but has since melted. The images below show typical emergent coastlines.
Submergent Coasts
Submergent Coasts are those that have been flooded by ocean waters because of a relative rise in the elevation of sea level at that location. The rise in sea level can be either the result of an increase in the volume of water in the ocean basins or the result of the land surface sinking, both of which create an apparent rise in the elevation of sea level. A common feature of submergent coastal zones is river valleys or glacially-carved valleys that have been flooded by ocean water. The Chesapeake Bay of the eastern United States is a classic example of a river valley that extended to the edge of the continental shelf during the last Ice Age when ocean waters were stored in the ice sheets. As the ice age ended, ice sheets melted, and sea level rose, the river valley was flooded with marine waters to create the Chesapeake Bay. The images below show the Chesapeake Bay as well the spectacular Sydney Harbor, also formed in a drowned river valley.
Erosional and Depositional Coasts
Erosional and Depositional Coasts
Another approach to coastal classification is to consider whether coastal processes in the coastal zone are primarily contributing sediment to the coastline, or whether they are removing sediment from the coastline. The former of these is recognized as deposition, whereas the latter is known as erosion. Where erosion is the dominant process, the coastline is retreating landward, and where deposition is dominant, the coastline is advancing seaward.
Erosional Coasts
In places where there is an abundance of wave energy or ocean currents and/or a lack of sediment available for deposition, erosion of the coast will be the dominant mechanism of change. Quite often, erosional coasts are narrow and characterized by resilient rocky shorelines that are exposed to high energy waves and supply relatively little sediment to the adjacent shore. This is the case for much of the western U.S. where there are numerous rocky exposures and vertical sea cliffs (see images from Oregon and Washington coasts below). Often, but not necessarily always, erosional coasts are associated with coastal zones along active plate margins where there is a steady uplift of the landform, and few well-developed drainage basins and rivers systems have developed to deliver large quantities of sediment to the coast.
Depositional Coasts
Depositional coasts are characterized by abundant sediment supply that results in the net deposition of sediment and the creation of new coastal landforms despite the energy of the waves and ocean currents. There is a wide variety of landforms along depositional coasts, such as extensive beaches, barrier islands, and expansive coastal wetlands and mudflats (see typical depositional coasts in the images below). They are most common along mature, tectonically inactive continental margins where ample geologic time has passed for large drainage basins and rivers to develop, which can provide large quantities of sediment that can be distributed by waves and tides at the coastline.
Learning Check Point
Learning Check Point
Please take a moment to think about what you have learned in this section, then answer the question below.
There is no credit for this activity, but at this point, you should be able to discuss the characteristics of glaciated coasts, the role of climate in the biological activity and weathering of coasts, as well as the types of storms that can impact coasts.
Second Order Influence on Coastal Zones
Second Order Influence on Coastal Zones
On the basis of the information discussed in the last several sections, it should now be evident to you that that plate tectonics has a strong influence on the characteristics of continental margins and the associated coastal zones. There are, however, several other key secondary influences that also affect how coastal zones evolve. These include:
- sediment supply,
- glaciations (direct and indirect),
- climate,
- hydrographic regime.
Each of these will be discussed individually in the following sections to provide a comprehensive framework of the types of processes that need to be considered when attempting to evaluate coastal characteristics and evolution.
Sediment Supply
Sediment Supply
How is sediment supply related to the tectonic setting of a coastal zone?
The availability and transport of sediment, loose non-cohesive material, within the coastal zone strongly affect the morphology of a coastal zone. Additionally, it turns out that sediment supply to a coastal region is very closely linked to the tectonic setting of the coastal zone.
To understand this better, let us take a look at Afro-Trailing and Amero-Trailing Edge Coasts. Along Afro-Trailing Edge Coasts, relatively little sediment is delivered to the coast when compared to the amount of sediment that is deposited along the Amero-Trailing Edge Coasts. Recall that a characteristic of Amero-Trailing Edge Coasts is large mountain systems inland of the coastal zone and on the opposite side of the continent. These uplifted mountain systems provide a ready source of sediment that can be transported by river systems to the tectonically inactive Amero-Trailing edge of the continent. The opposite side of the continent from an Afro-Trailing Edge coast, however, also has a trailing edge and no substantial uplifted mountainous areas that can supply sediment. The east coast of North America is a somewhat special case because it was once a collision coast, and, therefore, it is drawing sediments from the Appalachian Mountains which were formed during a geologically much older tectonic collision between North America and North Africa.
To put this in context, examine the drainage basin of the Amazon River on the maps below. The Amazon basin extends all the way from the western collisional margin of South America where the Andes Mountains are located to the trailing passive margin of the east coast of South America. The Andes Mountains are geologically young and are the result of tectonic uplift associated with subduction. Because of their elevation and size, they provide a large amount of sediment to the Amazon drainage basin that can be carried by the Amazon River to the Atlantic Ocean. Alternatively, the Niger River on the west coast of Africa has its headwaters in low-lying, (compared to the Andes mountains) very old rocks that provide little loose sediment to the river. As a result, the Niger River carries approximately two orders of magnitude less sediment to the ocean than does the Amazon River (Table 2.1).
| Type | River | Sediment Discharge |
|---|---|---|
| Amero-Type | Amazon River | 2000 x 106 tons yr |
| Afro-Type | Niger River | 20 x 106 tons yr |
Glaciations
Glaciations
What are the direct and indirect effects of glaciations on coastal zones?
Glaciated Coasts
The effects of glacial activity along coastal zones can be broadly broken into two categories. Direct effects would include the shaping of coastal zones in high latitude areas toward the north and south poles of the planet, where glacial ice is in direct contact with the land surface. Indirect effects would include low latitude areas toward the Equator where glacial ice is not a permanent feature in coastal zones.
Direct Effects on Coasts by Glaciation
The New England states of northeastern United States are a good example of where glacial ice has had a direct and obvious impact on the coastal morphology – specifically along the coast of the state of Massachusetts and around the city of Boston. Between approximately 100,000 and 18,000 years ago, a large percentage of the North American continent was covered in a several kilometers thick sheet of ice that progressively advanced southward during this time. As this massive ice sheet advanced, it scoured and scraped the underlying ground. The scoured sediment was transported as the ice sheet advanced into progressively lower latitudes. Sediment was also carried by meltwater streams that existed out in front of the ice sheet. The result is that glaciers and ice sheets such as this can move substantial amounts of sediment and act to create a unique suite of glacial landforms such as terminal moraines and outwash deposits. In fact, it is these types of deposits that formed the surface sediments of famous New England places such as Cape Cod, Martha’s Vineyard, and Nantucket.
Another type of direct effect that ice sheets and glaciers can have along the coast does not involve the deposition of sediment, but rather the erosion of sediment and the creation of features such as valleys. On a global basis, the modern-day fjords were created during the most recent global-wide glacial event that led to the advance and growth of ice sheets and mountain glaciers everywhere. It was during this period of time that the ice carved out what would later become known as fjords. Since 18,000 years ago, ice sheets and glaciers have been melting worldwide, and this extra water in the ocean basins has led to a rise in sea level and flooding of the glacially carved valleys. In fact, famous fjords of places such as Alaska, Chile, and Norway are the direct result of glaciers once extending to the sea from high areas, carving very long and often deep but generally narrow valleys.
Indirect Effects on Coasts by Glaciation
The indirect effects of glaciations are considered to be associated with the lowering of sea level during the last Ice Age and the subsequent rise of sea level that coincided with the melting of the ice-age ice sheets and glaciers. During the period of major ice sheet and glacial expansion, sea level was approximately 120 meters lower than it currently is today. During this period of lowered sea level, rivers systems on a global extent would have extended across the continental shelves, which were subaerially exposed because of the lowered sea level. River valleys cut across the continental shelves as rivers flowed to reach the new elevation of sea level. The valleys were progressively widened and deepened, and during deglaciation melt, water was released back into the ocean basins and sea level progressively rose so that the river valleys became inundated. This indirect process of glacial and ice sheet influence on the coastal zone is evident in the Chesapeake Bay of the eastern United States. The Chesapeake Bay, as well as many other drowned river valleys, provide critical habitat for freshwater, brackish, and marine water species of plants and animals, but are becoming a progressively more endangered habitat because of the influx of agricultural nutrients through runoff and discharge of wastewater into these environments.
For more information on glaciers and ice sheets, check out these links:
Climate
Climate
The climate of a particular coastal area plays a significant role with regard to the biological activity, weathering, and severity of storms that can impact the coast. Read on to learn about the way these factors influence coastlines.
Biological Activity
Biological Activity
Warm, low-latitude climates encourage the growth of lush vegetation in comparison to relatively colder, high latitude climates. For example, in warm coastal climates, thick, extensive platforms of mangrove forests or salt-tolerant grasses can develop if the substrate is suitable for the development of good root zones, and the plants are not exposed to high-energy waves or tidal conditions that can uproot them. Although a wide range of coastal plant species exists even within high-latitude coasts, the species that occupy warm climates will tend to be more organically productive with longer growing seasons.
Along coasts where vegetation is highly productive, this vegetation can constitute a significant contributor to the coastal sediment budget. When plants of the coastal zone die, the fragments of the plant, also known as organic detritus, can accumulate and help incrementally add elevation to the land surface. In some coastal areas, this process of accumulating organic debris derived from the plants has been suggested to be a major contributor to the health of coastal marshes and their ability to maintain a suitable elevation above sea level as sea level rises.
Vegetation plays another important role along some coasts because extensive root systems help to stabilize environments such as coastal marshes and dunes and can reduce the amount of wave and wind erosion that can take place. The presence of extensive coastal plant communities also can help reduce the destructive power of storm surges and tsunamis to inland areas and coastal infrastructure because the plants act to buffer the energy of these phenomena to the more inland areas.
Some coasts are also fringed by coral reefs. The most extensive and largest reefs are located in warm ocean waters because corals are temperature-dependent, with optimal growth of most coral reefs taking place in low-latitude climates where ocean waters are warm. Corals produce their hard structure out of the mineral calcium carbonate, as do shelled organisms such as clams, oysters, and snails. All of these organisms can be broken apart or fragmented by marine currents and ultimately contribute sediment to a coast. In some areas of the world, the beaches wholly consist of broken coral and shells.
Weathering
Weathering
Weathering is a term that is used to describe the breakdown of solid rock into particles of sediment such as boulders, sand, silt, and mud, as well as ions that are dissolved in water. Two types of weathering processes are recognized: physical weathering and chemical weathering. Physical weathering refers specifically to the reduction of a volume of rock and or individual particles of sediment into progressively smaller and smaller sedimentary particles through mechanical processes. These mechanical processes include fracturing and disintegration by freezing and thawing, transport by glaciers, or even rolling along a shoreline by waves. Chemical weathering, on the other hand, refers to the chemical breakdown of minerals in rocks and the production of new minerals from the dissolved ions. Most chemical reactions proceed fastest when temperatures are elevated and also when there is an abundance of water. In warm wet climates, chemical weathering proceeds fastest, so one would expect that the same rock would chemically weather much faster in a tropical rain forest rather than on an arctic tundra. It is also important to note that because of the nature of chemical reactions in warm, humid climates, there is a more significant production of very fine sediment.
Recommended reading for weathering
- Wikipedia article: Weathering [32]: This article gives an explanation of chemical weathering.
- Watch an informative video on chemical weathering.
Video: Chemical Weathering-Hommocks Earth Science Department (4:04)
Storms
Storms
Large storms in coastal settings typically produce strong winds that can create larger than normal waves. Increased wave heights, and thus the energy associated with the waves, can very quickly change the overall morphology of coastal environments that are exposed to the storm. Even relatively smaller-scale storms, such as thunderstorms, can, with strong enough winds, create substantial changes to a beach or other environments within the coastal zone if they occur with a high frequency during the course of several days or weeks.
Wind can also modify coastal environments. For example, strong winds steadily blowing across a fine-grained beach and dune system for several days can lead to the transport of some of that sand from the beach and dunes and its deposition elsewhere. As a result, environments exposed to strong winds during the course of several days can be reduced in elevation through a process known as deflation.
There is a wide range of scale when it comes to discussing storms. Although capable of inducing change, it is not the random small-scale thunderstorm or even weeks of continuous thunderstorms that cause the most modification to coasts. The most powerful storms to potentially impact a coast are tropical cyclones. We will introduce these systems in the following, but also exploring them in more depth in Modules 5 and 6.
Tropical Cyclones
Tropical cyclones are low-pressure rotating weather systems that are created in the atmosphere by the transfer of heat from the ocean basins to the atmosphere. These low latitude systems (23.5 N and S of the equator) spin clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere and are referred to by different names depending on the ocean basin. In the Atlantic Ocean, they are known as tropical storms and hurricanes when the wind speed exceeds 119 km/hr (75 miles/hr), whereas, in the western Pacific Ocean, they are referred to as tropical cyclones and typhoons respectively. In both cases, tropical cyclones have the capability to generate very large, high, waves that have the potential to devastate the natural environments of a coastal zone and any human infrastructure that is present where the storms make landfall. Another critically important component to understand about tropical cyclones is the storm surges, or elevated levels of sea level, that occur as these low-pressure systems move through an ocean basin. Very large storm surges can be created depending upon the morphology of the coast, the gradient and width of the neighboring continental shelf, the strength of the storm, and the rate of forward motion of the storm. For example, a storm surge in excess of 7 m (25 feet) was created along parts of the northern Gulf of Mexico shore by Hurricane Katrina in 2005 and resulted in inland flooding several kilometers from the non-storm-surge shoreline. We will explore these systems in detail in Modules 5 and 6.
Extratropical Storms and Fronts
North of the Tropic of Cancer (23.5 N latitude) and south of the Tropic of Capricorn (23.5 S latitude), extratropical storms and weather fronts dominate as the major storm impact to coastal zones in these regions. Although not capable of packing the full magnitude of punch that a hurricane can produce, some storms outside of the tropics can produce wind speeds equivalent to those of weak hurricanes, resulting in very large waves and storm surges along coastal environments.
Northeasters
Along the east coast of North America, the classic example of an extratropical storm system is the Northeaster, which is a storm that tracks from the Midwest of the United States, northeast along the east coast of the United States and into Maritime Canada before being turned eastward into the northern Atlantic basin. The term Northeaster derives from the fact that the winds of these storms are from the northeast within this irregularly shaped but counterclockwise rotating storm system. They occur between late fall through spring when cold arctic air moving southeast comes in contact with warmer air moving north from more southerly latitudes to create a low-pressure system with a cold center (in contrast to a hurricane with a warm center). Although not as strong as hurricanes, northeasters are larger in diameter and can impact three to four times as much shoreline as a very large hurricane. Further, their frequency of occurrence is higher for the east coast of North America with 20 to 40 annually, although only several of these generate severe offshore wave heights greater than 5 meters (16 feet).
Recommended reading for Northeasters
- Wikipedia article: Nor'easter formation [33]: This article provides details of Nor'easter formation.
- USGS article on Northeasters [34]: This article provides a brief description of northeasters.
Fronts
There are numerous other types of weather systems that can affect coastal zones. The most common along the northern Gulf of Mexico is what is known as a front. A front is a zone between two air masses with different temperatures, different levels of humidity, and densities. In the winter, low humidity cold air systems sweep southward across North America and encounter more humid, warmer air over the Gulf of Mexico. A strong southerly flow (winds blowing from south to north) persists along the northern Gulf in the days prior to the arrival of the cold front. These sustained winds blow as much as 30 to 50 km/hr and can generate large waves in the Gulf of Mexico that then travel northward and impact the shore, leading to erosion, deposition, and overall modification of the pre-frontal morphology. As the front passes, the wind direction shifts to blowing from the north, bringing much colder and dryer air. These north winds can similarly reach sustained speeds in excess of 30 km/hr persisting for a couple of days. Because these winds are from the north, they can generate large waves in the bays on the north side of the shorelines and have been shown to be very effective at eroding the marsh and other features on the north-facing shorelines of barrier islands and marsh platforms.
Hydrographic Regime
Hydrographic Regime
What does it mean to discuss the hydrographic regime of a coastal zone?
What variability exists in the range of tides and the amount of wave energy for different coastal zones?
Hydrographic Regime is a term that is used to describe the relative influence that waves and tides have along coasts, particularly coasts where the deposition of sediment is more dominant than erosion and removal of sediment. This is because waves and tidal currents are responsible for the movement of sediment along depositional coasts and, ultimately, the relative magnitude of these parameters dictates the type of coastal morphology that will develop. In a discussion of hydrographic regime, there are two primary things to consider, waves and tides. The following sections provide a brief background on each of these phenomena.
Waves
Waves
A full description of waves is beyond the objectives of this course, but very rigorous and sometimes complex theories and mathematical models have been developed to explain waves in water. It also turns out that no singular theory or mathematical model adequately describes the full range of waves and wave behavior within water bodies. An equation that perhaps quite adequately describes wave behavior in deep water might be completely useless when attempting to quantify the behavior of shallow-water waves. Because waves are the most common energy source along most coastal zones, understanding them is paramount to understanding how coasts evolve through time.
Fundamentally, a wave can be considered to be a disturbance of the water as energy is passing through the water. In open ocean basins, wind is the source of this energy that is transferred to the body of water as the wind blows across it. Consider what happens when you blow on the surface of a cup of hot tea or coffee to cool it down, the energy of your moving breath is transferred to the surface of the tea or coffee and causes small ripples or waves to develop.
The characteristics of waves are geometrically described by several different parameters including the: 1) wave height or amplitude, 2) wave length, and 3) wave period. As the name implies, the wave height is the vertical distance between the trough of a wave and the top or crest of a wave. Wave length refers to the horizontal distance between successive wave crests or troughs, and the wave period refers to the number of waves that pass a set point within an established period of time (Fig. 2.27).
Overall, the height, length, and period of a wave fundamentally are governed by 1) wind speed, 2) the duration of time that the wind has been blowing, and 3) the fetch or distance across open water that the wind has traveled. Wave height and the steepness of the wave increase through time as the amount of energy transferred from the wind to the water increases. For example, an increase in wind speed will cause more energy to be imparted to the water, and the result is that the wave heights correspondingly increase. A wind-generated wave can however not grow indefinitely in the open ocean; at some point, waves will grow so large that they break, and this is how whitecaps are generated.
Waves have the ability to travel great distances in the open ocean, and some studies have been able to track waves more than 10,000 km in the open ocean after many days of traveling. Importantly, one should keep in mind that the water of the waves does not actually travel with the wave but rather the waveform itself does. Fundamental to this fact is the process of circular orbital motion, wherein the energy of the wave is passed along as individual water particles move in a circle below the water surface. These circles of travel, or orbitals, are stacked on top of one another with the largest orbital diameter at the top and the smallest orbital diameter at the bottom. The diameter of the orbitals becomes negligible at a water depth that is equal to half of the wavelength, and this water depth is known as the wave base of the wave. In water depths that are less than half the wavelength, the orbitals become deformed and progressively evolve from being perfectly circular to elliptical. The speed of the wave decreases towards the coast but other waves moving in behind are still traveling at a speed that was equal to the first wave's speed before it began to slow down. All of the waves, therefore, begin to get crowded together and the height and the steepness of the waves increase. Eventually, the waves become unstable because they are too high relative to the water depth, the front of the wave collapses and the wave breaks onto the coastline to create surf (Fig. 2.28). The energy of the traveling wave is then transferred onto the shoreline either carrying sediment up onto a coastal environment such as a beach or removing sediment and transporting it offshore or alongshore.
Longshore Currents
Very rarely do wave trains approach a shoreline aligned perfectly parallel to the trend of the shoreline. It is much more common for wave trains to arrive at an angle to the trend of the shoreline. The net result of waves breaking at an angle to shoreline is to produce a weak current known as a longshore current (LSC). This current flows parallel to the shoreline. Some of you may perhaps recall swimming in the ocean when the waves were relatively large, and where you entered the water was not where you got out of the water. The reason for this is that the longshore current moved you slowly down the beach. This same wave-induced current, in conjunction with sand being suspended by breaking waves, is responsible for moving sand along the beach (Fig. 2.29). For this reason, beaches have sometimes been referred to as rivers of sand, because there is constant sediment transport as a result of longshore currents. The movement of sand parallel to the trend of the shore results in the development of features you will learn about in the next module such as spits; it can also increase the length of barrier islands and the buildup of sand next to coastal structures such as groins and jetties that you will learn about in Module 8.
Tides
Tides
People have been fascinated with tides throughout history, with various aboriginal legends dating back tens of thousands of years accounting for this phenomenon. One Native American legend tells of a raven who wanted to alter the depth of the oceans to make it shallower and therefore make more food accessible for his people, while Australian Aborigines have legends that speak of the moon filling with water while it was waxing, and how water drained back out of the moon as it waned, demonstrating the understanding that the lunar cycle was associated with water levels of the ocean.
Our current understanding of the tides can be explained using Sir Isaac Newton’s universal law of gravitation. He proved that the gravitational attraction between two bodies is directly proportional to mass and inversely proportional to the square of the distance between them. This is the case with the relationship between the sun, the moon, and the Earth. While the moon is relatively small, it is also relatively close to Earth and exerts a gravitational pull on the Earth’s surface that is stronger than that of the sun, which is much larger but also much further away. It is this gravitational attraction of both the moon and the sun to the Earth that causes the periodic rising and falling of the ocean’s surface that we call tides.
Tidal “Bulge”
The gravitational attraction between the moon and the Earth causes the water in the oceans, which is fluid and mobile, to be pulled towards the moon. This creates a “bulge” in the ocean that is closest to the moon and as the Earth rotates, the location of the waters that are affected, change. Picture the moon as a magnet that draws the water towards it. This movement of water towards the moon is counteracted by the force of inertia, the force that tends to cause a moving object to continue moving in a straight line. This is what balances out the movement of our oceans, but because the gravitational pull is stronger, the resultant force causes our tides. The sun also has this effect, but due to the vast distance from Earth, plays a smaller role.
Spring and Neap Tides
We sometimes hear on the news during a coastal storm that the effects on the shoreline will be more severe due to especially high tides. This is due to the position of the moon and the sun in relation to the Earth and the resulting gravitational attraction at various stages in the lunar cycle.
When the moon is in a position relative to the Earth where it is pulling in a direction that is in the same axis as the sun (new and full moon), both bodies are exerting a force on the Earth that is cumulative. This is called conjunction, and because these forces are both working to pull the Earth’s surface in the same directional axis, we experience higher high tides and lower low tides than we see throughout the month at a given location. This is the period during the lunar cycle that we experience spring tides.
When the moon is in a position that is at right angles to the sun, the gravitational pull of the two bodies is working in opposing directions on the Earth’s surface. This is when the gravitational forces of the sun and the moon are working against each other and we experience moderate changes in water levels. We refer to this period in the lunar cycle as neap tides that occur during quarter moons.
The difference during spring and neap tides is evident in the tide graphs for a tidal gauge in Halifax Harbour shown for Spring tide and Neap tide. This tide gauge is measuring water levels at the same location. However, during a spring tide the high water is almost 6.5 ft while during the neap tide, the high water is approximately 4.8 ft. The low tide during the spring tide is 0.2 ft and during the neap tide is 1.5 ft. The highs and lows during the full or new moon are much more pronounced than they are during the quarter moons. That is why a storm event paired with a spring tide may cause more serious damage along a coastline than a storm event paired with a neap tide.
Tidal Graphs
Tidal Cycles
A tidal cycle is one high tide plus a successive low tide. Due to land masses, the movement of water moving around on the Earth's surface due to tides is impeded. The resulting tidal cycle or pattern, therefore, depends on geographic location. There are three basic types of tidal cycles that are globally distributed.
Semi-diurnal Tides
This is the most common tidal pattern, featuring two highs and two lows each day, with minimal variation in the height of successive high or low waters, and is very common along much of the east coast of North America.
Diurnal Tides
There is only a single high and a single low during each tidal day; successive high and low waters do not vary by a great deal. Such tides occur, for example, in the Gulf of Mexico, the Java Sea, and in the Tonkin Gulf.
Mixed Tides
These are characterized by wide variation in heights of successive high and low waters, and by longer tide cycles than those of the semidiurnal cycle. Such tides occur, for example, along the U.S. Pacific coast and many Pacific islands.
Summary of Waves and Tides
Summary of Waves and Tides
In summary, waves and tides can have a profound influence on the morphology and evolution of a coast. In areas with large waves and thus high wave energy, sediments can be extensively reworked by the erosive energy of the waves and widely distributed by the process of longshore transport. In high-energy coastal areas with strong tidal currents, large volumes of sediment can be transported or reworked by the tidal currents to create deposits that are aligned perpendicular to the coastline but parallel to the flow direction of rising and falling tides. In coastal areas that have large tidal ranges or are low gradient, some parts of the shoreline may be exposed for several hours each day before the next rise in tide, and extensive mudflats can develop for very large horizontal distances.
For more information on tides and waves:
- NOAA movie that discusses wave formation [41]
- Wikipedia website with a discussion of tidal range [42]
- Wikipedia website with a discussion of longshore transport [43]
Video: Longshore Transport (2:19) (Video is not narrated.)
Wave, Mixed Energy, and Tide Dominated Hydrographic Regimes
Wave, Mixed Energy, and Tide Dominated Hydrographic Regimes
Our understanding of waves and tides now sets the stage for a more thorough understanding of how they interact to shape a coastal zone. In the context of the hydrographic regime, there are two fundamental things that must be considered: the wave and tidal energy of a coast.
- Wave energy (E) is a function of wave height (H) with the energy (E) of a wave approximately equal to the square of the wave height (H2).
- Tidal energy can be equated with tidal range because it is the rise and fall of the tides that produce tidal currents. Tidal range (TR) is the vertical difference between high and low tides, which are commonly categorized into three ranges:
Microtidal: TR < 2.0 m
Mesotidal: 2.0 m < TR < 4.0 m
Macrotidal: TR > 4.0 m
The relative dominance of wave versus tidal energy dictates coastal morphology, and three general regimes exist along depositional coasts:
- Wave Dominated Coasts
- Mixed Energy Coasts
- Tide-dominated Coasts
Wave Dominated Coasts
Along wave-dominated coasts, the role of the waves and, thus, longshore transport processes is the dominant factor controlling the coastal morphology. Because longshore transport carries sediment along the shore, these types of coasts tend to have long linear barrier islands and beaches with relatively few inlets or passes between the open ocean and the more interior bays and waterways. The reason for this is that the longshore transported sediment tends to fill in these inlets and passes. Since the tidal currents are relatively weak, there is no energy available to keep the inlets open as a connection between the open ocean and interior waterways.
Mixed Energy Coasts
Mixed energy coasts are a product of both wave and tidal processes and neither process exerts an excessive influence on the coastal morphology, although some mixed energy coasts show tidal or wave dominance. Rarely in nature are processes in equilibrium. These types of coasts typically contain short stubby barrier islands, have numerous tidal inlets and passes, and are separated from a mainland by extensive marshes and an array of tidal creeks.
Tide Dominated Coasts
Tide dominated coasts are those where strong tidal currents act to redistribute sediment along the vector of falling and rising tidal currents, which are orientated perpendicular to the trend of the coastline. Quite often, the highest energy tidal currents develop in locations where large tidal ranges are present in conjunction with a shoreline morphology that accentuates tidal flow by constricting tidal currents into funnel-shaped embayments. Sediment is reworked by the resulting tidal currents to create subaerial and subaqueous tidal shoals and islands that are aligned parallel to the tidal flow direction, perpendicular to the coastline. Moreover, in areas with very large tidal ranges, extensive tidal flats, and marsh or mangrove systems form along the borders of the embayment and can cover large areas.
Learning Check Point
Learning Check Point
Please take a few minutes to think about what you just learned, then answer the question below.
There is no credit for this activity, but this point, you should know that the relative energy of tides and waves along a coast strongly affects how sediment is transported and the morphology of the coast. You should be able to explain how you think different coastal zones look in the context of the relative strength of tides or waves.
Module 2 Lab
Module 2 Lab
In this brief lab, you will record a Google Earth tour of two of the classifications of coastlines described in this module: choose either emergent or submergent for the first, and choose erosional or depositional for the other. So your submission will include two files (see below for more details).
Instructions
- Read the material on emergent and submergent coastlines in the module and choose a location that exemplifies one of these types of coastlines from one or two of the following worldwide locations:
Emergent:
Any of the example locations labeled as emergent on the Emergent and Submergent Coasts page of the Module 2 course material, plus locations on the west coast of the U.S., focusing on the states of Oregon and Washington; and Scotland.
Submergent:
Any of the example locations labeled as submergent on the Emergent and Submergent Coasts page of the Module 2 course material, plus other locations on the eastern coast of the U.S., focusing on the states of Maryland, Virginia, and North Carolina; the Gulf Coast of the U.S.; and Southern China.
Erosional:
Any of the example locations labeled as erosional on the Erosional and Depositional Coasts page of the Module 2 course material, plus other locations on the west coast of the U.S., Southwestern United Kingdom (England), and southern Australia.
Depositional:
Any of the example locations labeled as depositional on the Erosional and Depositional Coasts page of the Module 2 course material, plus other locations on the east coast of the U.S. and the Gulf Coast of the U.S.
Be sure the location you choose for your tour has very obvious features and landforms that are evidence for the classification you are highlighting. - To prepare for your tour, open Google Earth Pro and cruise around that location at about 25- to 30-mile elevation, then zoom in close to about a mile (~5,300 feet or 1.6 km). Zoom in further to see greater detail (~500 ft. or 150 meters). Note morphological features you see that make the coast fit into that classification. Examples: Do you see cliffs or a low-profile shore? Do you see a wide or narrow beach?
- Next, write a brief 100-word script to describe the morphological features (landforms you see) that are evidence of your chosen coastline fitting into that category. Base your description on the information found in the class material, using terminology learned in the reading and other sources. The script can be informal; it will help you remember what to say when you begin recording. Try to be concise, and please limit your recording to 2 minutes or less.
- Next, watch the YouTube video that shows how to record a tour in Google Earth Pro: Learn Google Earth: Recording a Tour [52]. Also, see Googe Earth Help: Record & Play Tours [53] for step-by-step instructions.
- Follow the instructions to (1) record, (2) save, and (3) email the tour kmz file to yourself. Once you receive the emailed file, reopen it and play it in Google Earth Pro to make sure it works. One piece of advice, GE tends to cut off the end of the tour, so try to include some 10-20 seconds of silence after you stop talking before you stop recording.
- Repeat steps 1-4 for the material on erosional or depositional coastlines, choosing to describe either an erosional or a depositional coastline example.
- The finished product for this assignment will have two kmz files that you will submit to the Module 2 Lab (File Uploads). Name the files you upload with the type of coastline you are describing and the location (e.g., “submergent-Grand Isle.kmz).
Troubleshooting Audio Recording Issues
If you have difficulties with your audio after recording your tour, one of these troubleshooting steps may solve the problem.
- In GE Pro, go to Tools> Options - Chache - clear memory and disk cache.
- Tools> Options > 3D view - and change settings as follows:
Summary and Final Tasks
Summary
Throughout this unit, you have been introduced to the global diversity of coastal landscapes. You have learned about the role of plate tectonics in coastal classification as well as other approaches to coastal zone classification such as recognizing whether a coast is emergent or submergent and depositional or erosional. Finally, you have been introduced to an array of other processes that operate in coastal zones and that exert an influence on the overall morphology of the coast, including climate, sediment supply, glaciation, and the relative role of waves and tides. This unit sets the stage for Unit III, which will provide an overview of very specific types of coastal sub-environments such as rocky coasts, sandy beaches, coral reefs, barrier island shorelines, and marshes and mangroves.
Reminder - Complete all of the Module 2 tasks!
You have reached the end of Module 2! Double-check the Module 2 Roadmap (in Goals and Objectives) to make sure you have completed all of the activities listed there before you begin Module 3.