08 - Coastal Processes .the dynamic natural processes in...

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1 Coastal Processes …the dynamic natural processes in coastal environments (including Great Lakes!) and natural responses to human intervention. Flat sandy beach Rugged rocky coast Coastal classification Erosional vs depositional coasts – Erosional: shoreline is moving landward • land influences: stream erosion, abrasion from wind- driven material, freeze/thaw of water in cracks, plant roots, glacial activity, rainfall, dissolution from soil acids, slumping • sea influences: waves, organisms, sediment in water – rate of erosion depends on: • hardness of rocks • range of tides Attack from the sea is by waves and currents. On high-energy shores, the continuous onslaught of waves does most of the erosional work, with currents distributing the results of the waves’ labor. Erosional features formed by waves: • Wave-cut cliffs • Wave-cut platform • Sea arches • Sea stacks • Several mechanical and chemical effects produce erosion of rocky shorelines by waves- Depends on the geology of the coastline, nature of wave attack, long-term changes in sea-level, tidal ranges, etc. Fig. 12-4a, p. 319
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2 Coastal classification • Erosional vs depositional coasts –Depositional: shoreline is moving seaward • Dominated by beaches- places were sediment (usually sand) is transported to a calm place suitable for deposition • Beaches are in a constant state of change (think of as rivers of sand with continuous sediment transport) A calm depositional shore- sunset on a southern California beach Depositional features formed by waves • Beaches •Sp i ts • Bay-mouth bars • Tombolos • Barrier islands – Depends on the configuration of the original coastline, direction of sediment transport, nature of the waves, and shape and steepness of the offshore underwater slope. 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. October, 1997. Bird's eye view of Point Reyes National Seashore. Image from USGS April, 1998. Same location, 18 months later after El Nino storms. Beaches: Sand on the MOVE! • Breaking waves disintegrate into churning sheets of water called swash that carry sand and gravel up onto the beach. • Each wave brings new sediment and carries some sediment back into the surf zone ( backwash ). • If more sediment is deposited by waves than is carried away, a beach builds up; • If more sediment is removed than is deposited,
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3 Longshore transport • Sediment transported along the beach by waves. • Waves rush onto the beach at a slight angle , but they rush straight back out to sea because of gravity. • Because of this, sediment in the surf zone
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This note was uploaded on 04/29/2008 for the course EAS 104 taught by Professor Brown during the Spring '08 term at Purdue University-West Lafayette.

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08 - Coastal Processes .the dynamic natural processes in...

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