1. A Microsoft® PowerPoint® Link Tool An Invitation to Marine Science
Multimedia Manager
A Microsoft® PowerPoint® Link Tool
for
Oceanography
An Invitation to Marine Science
6th Edition by
Tom Garrison

2. Chapter 12 Coasts

3. Look For The Following Key Ideas In Chapter 12
Coasts are temporary structures, often subject to rapid change. The shape of a coast is a product of many processes: uplift and subsidence, the wearing down of land by erosion, and the redistribution of material by sediment transport and deposition.
The location of a coast depends primarily on global tectonic activity and the volume of water in the ocean.
Change in sea level greatly influences coastal processes. For most of Earth's recent history, sea level has been lower than we find it today.
Erosional coasts are new coasts in which the dominant processes are those removing coastal material. Depositional coasts are those coasts that are steady or growing because of their rate of sediment accumulation or the action of living organisms.
Depositional coasts often support beaches, accumulations of loose particles. Beaches change shape and volume as a function of wave energy and the balance of sediment input and removal.
Depositional coasts, especially along subsiding continental margins, often exhibit characteristic large-scale features.

4. Key Ideas Continued…
Deltas form on broad continental shelves where rivers deposit sediment, tidal range is low, and wave and current action generally mild.
Coasts can be extensively modified by the actions of living organisms
Estuaries can form at river mouths where fresh water mixes with seawater. They are among the most complex and biologically productive coasts.
Human interference in coastal processes rarely increases the long-term stability of a coast.

5. Coasts Are Shaped by Marine and Terrestrial Processes
Sea levels past and future. (a) Sea level rose rapidly at the end of the last ice age as glaciers and ice caps melted and water returned to the ocean. The rate of rise has slowed over the past 4,000 years and is now believed to be between 1.0 and 2.4 millimeters per year. (b) Projections of sea level through the year Seven research groups (represented here by colored lines) have estimated future sea level based on historical observations and climate models. Even the most conservative of these predictions estimates a 20-centimeter (8-inch) rise.

6. Coasts Are Shaped by Marine and Terrestrial Processes
(top-left) The southeastern coast of the United States looked much different 18,000 years ago, during the last ice age. Because of lower sea level, the position of the gently sloping southeastern coast has been as much as 200 kilometers (125 miles) seaward from the present shoreline, leaving much of the continental shelf exposed.
(bottom-left) In the distant future, if the ocean were to expand and the polar ice caps were to melt because of global warming, sea level could rise perhaps 60 meters (200 feet), driving the coast inland as much as 250 kilometers (160 miles)

7. Erosional Coasts Often Have Complex Features
Features of an erosional coast at low tide.
Wave erosion of a sea cliff produces a shelflike wave-cut platform visible at low tide.

8. Shorelines Can Be Straightened by Selective Erosion
Wave energy converges on headlands and diverges in the adjoining bays. The accumulation of sediment derived from the headland in the tranquil bays eventually smoothes the contours of the shore.
Marine erosion is usually most rapid on high-energy coasts, areas frequently battered by large waves.
Low-energy coasts are only infrequently attacked by large waves.

9. Beaches Often Have a Distinct Profile
A beach is a zone of loose particles that covers a shore.
What are the features of a beach?
Berm
Berm crest
Backshore
Foreshore
Beach scarp
Longshore trough
Longshore bars

10. Waves Transport Sediment on Beaches
A longshore current moves sediment along the shoreline between the surf zone and the upper limit of wave action.

11. Sand Input and Outflow Are Balanced in Coastal Cells
Coastal sediment transport cells.
(a) The general features of coastal cells. Sand is introduced by rivers, transported southward by the longshore drift, and trapped within the nearshore heads of submarine canyons.
(B) Example of a sand budget. If sediment gains and losses are approximately equal, the nearshore system is in equilibrium. If losses exceed gains, as shown here, the beaches within the cell will shrink and possibly disappear.
Sections of coast in which sand input and sand output are balanced are referred to as coastal cells.

12. Large-Scale Features Accumulate on Depositional Coasts
(above) A composite diagram of the large-scale features of an imaginary depositional coast. Not all these features would be found in such close proximity on a real coast.
A sand spit forms where the longshore current slows as it clears a headland and approaches a quiet bay.
A bay mouth bar forms when a sand spit closes off a bay by attaching to a headland adjacent to the bay.
Depositional coasts can also develop narrow, exposed sandbars that are parallel to but separated from land - known as barrier islands.
A long, shallow body of seawater isolated from the ocean is known as a lagoon.

13. Coasts Are Formed And Modified By Biological Activity
The development of an atoll.
(a) A fringing reef forms around an island in the tropics.
(b) The island sinks as the oceanic plate on which it rides moves away from a spreading center. In this case, the island does not sink at a rate faster than coral organisms can build upward forming a barrier reef.
(c) The island eventually disappears beneath the surface, but the coral remains at the surface as an atoll.

14. Estuaries Are Classified by Their Origins
An estuary is a body of water in which fresh river water mixes with ocean water. Estuaries can be classified by their origin:
Drowned river mouths
Fjords
Bar-built
Tectonic
(a) Drowned river mouths: the mouths of the James, York, and Susquehanna rivers; Chesapeake Bay; Sydney Harbour, Australia.
(b) Fjords: New Zealand’s Milford South; the Strait of Juan de Fuca in Washington state.
(c) Bar-built: Albernarle and Pamlico sounds in North Carolina
(d) Tectonic: San Francisco Bay; Tomales Bay

15. Estuary Characteristics Are Influenced by Water Density and Flow
Types of estuaries in vertical cross sections. The salinity values show the amount of mixing between fresh water and seawater in the various types.
(a) Salt wedge estuary.
(b) Well-mixed estuary.
(c) Partially mixed estuary.
(d) Fjord estuary.

16. The Characteristics of U.S. Coasts
The Pacific Coast - An actively rising margin where indications of recent tectonic activity can be observed.
The Atlantic Coast - A passive margin on the trailing position of the North American plate.
The Gulf Coast - Smaller wave size and a smaller tidal range characterize the Gulf Coast.

17. Humans Have Interfered in Coastal Processes
What are some ways that humans try to influence coastal processes?
Groins
Seawalls
Importing sand
(left) A few of the many types of measures taken to slow and prevent beach erosion.
In many cases these methods help serve as a reminder that shorelines and beaches are constantly changing, and are not under human control.

18. (a) Groin
Groins are structures that extend from the beach into the water. They help counter erosion by trapping sand from the current. Groins accumulate sand on their updrift side, but erosion is worse on the downdrift side, which is deprived of sand.
Current
(b) Seawall
Seawalls protect property temporarily, but they also increase beach erosion by deflecting wave energy onto the sand in front of and beside them. High waves can wash over seawalls and destroy them and property.
(c) Importing sand
Importing sand to a beach is considered the best response to erosion. The new sand often is dredged from offshore, can cost tens of millions of dollars, and can disturb aquatic biodiversity. Because it is often finer than beach sand, dredged sand erodes more quickly.
Figure 12.36: Some measures taken to slow beach erosion.
Stepped Art
Fig , p. 342

19. Humans Have Interfered in Coastal Processes
A map showing shore erosion by region. One example of shore erosion is the lighthouse on Cape Hatteras, which was moved during 1998 and 1999 to protect it from destruction. It was threatened by rising sea levels and a changing shoreline.

20. Chapter in Perspective
In this chapter you learned that the location of a coast depends primarily on global tectonic activity and the ocean’s water volume and the shape of a coast is a product of many processes: uplift and subsidence, the wearing-down of land by erosion, and the redistribution of material by sediment transport and deposition. Coasts are classified as erosional coasts (on which erosion dominates) or depositional coasts (on which deposition dominates). Natural rock bridges, tall stacks, and sea caves are found on erosional coasts. Depositional coasts often support beaches, accumulations of loose particles. Generally, the finer the particles on the beach, the flatter is its slope. Beaches change shape and volume as a function of wave energy and the balance of sediment input and removal. Coral reefs and estuaries are among the most complex and biologically productive coasts. Human interference with coastal processes has generally accelerated the erosion of coasts near inhabited areas.
In the next chapter you will learn that the study of oceanography includes a marvelous variety of living things. The discussion in the next chapter of the general nature and characteristics of marine life will launch us into the biological part of our journey.

21. End of Chapter 12