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12 Cards in this Set
- Front
- Back
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What produces regular ocean waves?
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wind; friction between the moving air and water
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wave orbital motion def.
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passing waves cause water molecules to trace circles
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wavelength
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from crest to crest with trough in the middle
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What are longshore currents?
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before backwash returns to sea, next wave arrives and pushes backwash landward. successive waves build up excess water along the shore. the waves. Excess water suddenly flows back out to sea. This flow is perpendicular to the beach.
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What is a rip current?
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Fast surface flows away from the beach after longshore transport. Swim parallel to shore to prevent drowning.
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What are the two ways in which longshore sediment transport takes place.
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1. waves wash sediment up the beach in the direction of wave movement, but wash it back down the beach face perpendicular to the beach. Makes zig-zag "river of sand"
Sand is also carried along the shore as suspended load. each wave suspends lots of sand and carries it forward in the direction of the moving wave.backwash washes it back perpendicular to beach. Suspended sand moves along beach in a spiral. 2. Spits- where 'river' cross estuaries |
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Barrier island beaches def.
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narrow ridges of sand that are separated from the mainland by a body of water (lagoon or sound or complex marsh).
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BIBs are modified by 2 additional processes...
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Overwash - takes place when large storm waves breach the dune ridge and sweep sand over a barrier island. Naturally pushes BIBs landward.
Tidal Inlets - when tide rises, water flows in through the tidal inlets to keep the water level in lagoons matched with that of sea level. flows back out when tide drops. |
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What are the main sediment inputs & outputs of a beach?
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Inputs: river deltas, wave erosion of sea cliffs or glacial deposits made of gravel, sand, silt, clay.
Outputs: sand gets swept down submarine canyons, some gets blown inland, and, along barrier islands, overwash is important. |
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Where does most California beach sand come from? Where does it go? What strategy do they have to destroy beaches?
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River systems = 70-90% of beach sand, rest coming from erosion of sea cliffs or old dunes.
Some sand is swept out to continental shelf but a lot ends up getting swept into submarine canyons where it accumulates in unstable dunes that eventually collapse and send plumes of fluidized sand and mud to bottom of sea floor. Dams trap sediment so the rivers no longer supply sediment to coastal systems but sand is still swept into canyons so beaches get narrower. |
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How do groins impact a beach?
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concrete/rocky structures that jut out from a beach.
sand exported from along the whole beach. longshore currents are forced around the groins and the down current side of groins erodes. |
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How do sea walls affect the width of a beach? Why?
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seawall directs energy toward scouring the sand in front of the wall. backwash carries lots of suspended sand out to sea. beach disappears.
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