Coastal Processes
There are three main processes at work in coastal areas, and they will be familiar to anyone who has looked at rivers or fluvial processes.
Waves and wind are very powerful forces olong the coastline and much of the erosion, transportation and deposition is controlled by these two factors. There are other factors involved, such as biological weathering and human intervention, but waves and wind are usually the most important.
Erosion
Erosion, in case you've forgotten, is the wearing away and breaking up of rock. Along the coast this means the wearing away of cliffs, wavecut platforms, boulders, pebbles and shingle on the beaches. Even sand and shells can be broken down by abrasion and attrition.
Destructive waves do the greatest damage, but any wave capable of moving sediment over other sediment will contribute to erosion.
There are four ways in which erosion can take place.
Abrasion:Waves bring with them bits of rock and sand. These help to grind down cliffs.
Attrition:Waves cause rocks and pebbles on the shore to smash into each other and break down.
Corrosion (or Solution):Acids contained in sea water will slowly dissolve certain types of rock.
Hydraulic Action: The constant
force of waves crashing on the shore damages it.
Transportation
Waves don't often hit the coast at right angles to it. This is because wave direction is controlled by the wind. Most areas have a prevailing wind, that means that the wind usually comes from one particular direction. The coastline is rarely straight and at right angles to the wind so waves usually hit it at an angle The swash of the waves carries material up the beach in the direction of the wave, so if the wave moves up the beach with a sideways slant, that's the way the beach sediments will be moved too. The backwash is different though; it always flows pretty much straight back down the beach. This is because once the wave runs out of energy at the end of the swash, the backwash is controlled by gravity. Gravity prefers the most direct route back down the slope of the beach - so the water flows back to the sea in a straight line. Each wave transports the sediment a little further along the beach.Hence the name,transportation.
Where prevailing winds always strike the coast at an angle the constant swash and backwash transports material sideways along the coast in the same direction day after day. The material is transported along the coast and this process is called longshore drift.
Deposition
When the sea loses energy, it drops its load of sand, rock particles and pebbles, that it has been carrying. This is called deposition. Deposition happens when the swash is stronger than the backwash.
Deposition is likely to occur when:
Waves enter an area of shallow water
Waves enter a sheltered area
There is little wind
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