COASTS and SHORELINE NOTES

What is a Coast? * A coast is the strip of land that is met by the water’s edge; it leads to the open ocean. * Coasts are temporary structures, often subject to rapid change. * The location of a coast depends on tectonic activity and the level of water in the ocean. * The shape of a coast is a product of many processes. * Coasts are classified as primary or secondary. * Human interference in coastal processes rarely increases the long-term stability of a coast. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Primary Coasts Younger coast dominated by tectonic influences Essentially the west coast as sea level stabilized after the last ice age Some types of primary coasts: Land erosion coasts Coasts built up by land processes Volcanic coasts Coasts shaped by earth movements © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Primary Coasts Many of the islands of Martha’s Vineyard and Nantucket are examples of a primary coast. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Secondary Coasts Older coasts that have been shaped by marine influences Some processes that shape secondary coasts:  Waves and currents  Stream erosion  Abrasion of wind-driven particles  Freeze/thaw cycles  Slumping © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Secondary Coasts Waves are one of the forces that shape secondary coasts. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Large Scale Features of Secondary Coasts These features are associated with secondary coasts. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Barrier Islands Barrier islands are long, relatively narrow islands running parallel to the mainland, built up by wave action and currents and serving to protect the coast from erosion by surf and tidal surges Barrier Island features: ocean beach, dunes, barrier flats, high and low salt marsh, and lagoons (is a body of shallow sea water or fresh water separated from the sea/ocean by some sort of barrier

Barrier Islands, images

Beaches A beach is a zone of loose particles that covers a shore. Note that larger particles are associated with more sloped beach. (and remember those grain sizes we discussed in class) © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Beaches Features of a beach:  berm crest (highest spot on a berm)  berm (mounds of loose materials)  berm crest (highest spot on a berm)  backshore  foreshore  beach scarp (a nearly vertical slope along the beach caused by waves)  longshore trough (long, wide, shallow channel of the sea floor parallel to the shore)  longshore bars (ridge of sand, gravel or mud built on the seashore by waves and currents, generally parallel to the shore and submerged by high tides, also known as offshore bar) © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Beaches The features of a beach. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Complete your Beach Profile

Coasts formed by Biological Activity Coral Reef Classifications **Coral Reefs are the most dramatic of the coasts formed by biological activity. ** Fringing Reefs cling to the margin of land. Barrier Reefs are separated from land by a lagoon. Atolls are ring-shaped islands of coral reef enclosing lagoons. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Coasts Formed by Biological Activity © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Estuaries 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 - The Chesapeake Bay  Fjords – Milford Sound (New Zealand)  Bar-built – The Albemarle and Pamlico Sounds  Tectonic – San Francisco Bay © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Estuaries The four types of estuaries. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

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. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Coastal Cells Sections of coast in which sand input and sand output are balanced are referred to as coastal cells. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Human Interference on Coastal Processes What are some ways that humans try to influence coastal processes? Groins – A wall built out perpendicular to the beach Jetty - A wall built out perpendicular to the beach next to an inlet Breakwater – A wall built parallel to the beach out in the water Seawalls – a wall built parallel to the beach Importing sand – commonly called “Beach Replenishment” **These methods are largely ineffective in solving beach erosion. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Coasts Summary (right) A few of the many types of measures taken to slow and prevent beach erosion. Some of these methods are actually counterproductive. In many cases these methods help serve as a reminder that shorelines and beaches are constantly changing, and are not under human control. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

3 Ways to Classify Coasts By the process shaping the coast Primary coasts - Young coasts shaped by land processes. Secondary coasts - Older coasts shaped by marine processes. 2. By tectonic activity Active – Lots of tectonic activity (at the leading edge of a plate). Passive – Little tectonic activity (at the trailing edge of a plate). 3. By position relative to sea level Emergent – Rising relative to sea level. Submergent – Sinking relative to sea level. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.