EPS chapters - Chapter 20: Coastlines and Ocean Basins 1....

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Chapter 20: Coastlines and Ocean Basins 1. Basic Differences Between Ocean Basins and Continents Geologic activity in the ocean is limited to faulting and volcanism at mid ocean ridges instead of deformation, etc…. on the continents. Volcanism and sedimentation are dominant processes. Volcanism makes mid ocean ridges, island groups, and arcs near deep sea trenches. Sedimentation is more rapid than on the continents, and provides a better understanding of the Earth’s past. Subduction of plates occurs every 10 million years, limiting our ability paleogeologic ability. 2. Coastal Processes 2A. Wave Motion: The Key to Shoreline Dynamics Waves are made when air transfers its energy to the surface of the water; height of waves increase as wind speed increases, wind blows for long times, there is a long distance. Waves radiate out of the centers of storms, and as they get farther away they are called swell, travelling hundreds of km. Waves have a wavelength=distance between crests, wave height=distance between crest and trough vertically, and period=time it takes for successive waves to pass. V=L/T. Wave motion is negligible at half the wavelength deep. 2B. The Surf Zone Waves break as they approach shore in the surf zone=an offshore belt along which breaking waves collapse. This causes erosion, weathering, etc… As waves approach shore, water particles get restricted due to the shallow depth. But since the period remains the same, the velocity decreases but height increases. The wave gets so high it can’t support itself so it crashes in the surf zone. Gently sloping bottoms make them crash farther from shore, but steep bottoms make them crash close to shore. Rocks next to deep water make the waves crash directly on the rocks. After the waves crash and become smaller at the surf zone, they approach the shore where they break again. Swash and backwash occur, transporting sediments and sand grains. 2C. Wave Refraction
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Wave refraction occurs when wave crests bend as they approach the shore from an angle, usually parallel to the shore. A wave train gradually slows as it gets to the shore, causing the train to bend toward the shore. Wave action at headlands causes more erosion than at bays because bay water is deeper. Longshore drift occurs as sand grains are carried by swash and backwash by waves. It’s a zig zag pattern of the sand grains. Longshore current : a shallow water current that is parallel to shore. This is the cause of heavy sediment transport, and shoreline features. Rip current= a strong flow of water moving outward from the shore. It happens when a longshore current builds up along the shore until the pileup of water breaks and flows back into the ocean dangerously. 2D. The Tides
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This note was uploaded on 02/04/2010 for the course EPS 50 taught by Professor Staff during the Fall '08 term at University of California, Berkeley.

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EPS chapters - Chapter 20: Coastlines and Ocean Basins 1....

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