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Oceanography An Invitation to Marine Science, 7th Tom Garrison Chapter 12 Coasts Coasts Are Shaped by Marine and Terrestrial Processes Coastal regions are important because they interconnect sea with land. They are affected by both marine and terrestrial processes. Coasts are indicators of eustatic changes, variations in sea level. Glaciation, global warming, volcanic outgassing, tectonic activity, and weather events all have their affects. Coasts Are Shaped by Marine and Terrestrial Processes Coasts can either be: Erosional- caused primarily by loss of materials. Water, wind, weather, and plants can cause erosion. Depositional- caused by the addition of materials. Accumulation through volcanoes, waves, tides, and rivers can cause deposition. Shorelines Can Be Straightened by Selective Erosion The rate of erosion is dependant on 2 factors: The energy or force of erosion and the hardness of the rock 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. Concept Check 12.1-12.2 1. Name 2 types of marine forces that shape the coasts. 2. Name 2 types of terrestrial forces that shape the coasts. 3. Name the process responsible for raising and lowering sea level. 4. Using fig. 12.2 when did the oceans hit a low point, explain why. 5. Explain the difference between erosional coasts and depositional coasts. 6. Give 2 factors that dictate the rate of erosion. 7. Name 2 types of coastal features formed by erosion. 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 Draw a labeled diagram of a beach in your journal • • • • • • • • Include the following along with definitions: Berm Berm crest Backshore Foreshore Beach scarp Longshore trough Longshore bars Waves Transport Sediment on Beaches A longshore current moves sediment along the shoreline between the surf zone and the upper limit of wave action. Beach textures depend on particle size, wave action, and slope. The flatter the beach, the finer the material. Sand Input and Outflow Are Balanced in Coastal Cells Longshore drift- movement of sand along the coast by wave action. Longshore current- movement of sand along the coast by currents. Coastal sediment transport cells. Sections of coast in which sand input and sand output are balanced are referred to as coastal cells. Coastal configurations… Barrier islands-rises that form and run parallel to the coast • Formed possibly 6000 ears ago by higher sea levels • Susceptible to forces of nature • Provide protection to the mainland (i.e. Miami Beach, West Palm Beach, Atlantic City) Our barrier Island Coastal configurations cont. • Sea islands – like barrier islands, except they were once part of the mainland • Deltas – form as sediment deposit at the mouth of a river Coastal configurations cont… • Reefs – structures made by the deposition of skeletons of coral animals • Water must be clear, well lit, and warm • There are 3 types: – Fringing – Barier – atolls Coastal configurations… • Mangroves – dominated by shallow water where trees can grow in saltwater • Estuaries – sheltered areas which contain a mixture of saltwater and freshwater – The “nurseries” of marine life – Majority of marine life starts here Human dependence • Coastal areas are subject to nature and man. • Nature – weather, tides, waves • Man – overdevelopment, pollution, overuse • Highly prized for tourism, real estate • Should be valued for importance to nature • Constant dredging of sand is expensive 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. 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.