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Costal processes - Coggle Diagram
Costal processes
Erosion
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Attrition - when rocks are thrown against one and other eroding each other whilst becoming smoother and rounder
Hydraulic action - When the fast moving water from waves hits against the land on the shore causing the sand to erode.
Air compression - when water pushes air into the cracks in rocks causing an explosive pressure to widen the cracks or break the rock.
Cliff - Sea cliffs are walls of rock formed where the sea meets the land. these are a feature of erosion. The main types are hydraulic action, abrasion, attrition and compressed air. The combined process of erosion attack the rock at the base of the cliff this is an area of soft rock and is easily eroded. This creates a notch which is a small hole under high tide at the cliffs base. when this hole gets larger the overhang also gets larger, over time debris start to fall from the overhang. These debris build up atop the wave cut platform which is a diagonal area underwater usually as high as low tide.
Deposition
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Sand dunes -
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They form when sand on a beach is dried, dry sand is lighter so the wind blows it inland.
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Marram grass can be planted on sand dunes to stop sand from moving further inland. Marram grass is thick, coarse grass that has deep roots and is resistant to salt and needs very little water. The roots help bind (stick) the grains of sand together and prevent them from blowing further inland.
Some county councils (e.g. Co. Wexford in Rosslare) purposely plant marram grass to encourage deposition and build up sand dunes. This is able to help stop sand being blown more inland causing disturbances for the people. The sand dunes it encourages the build-up of also can become a tourist attraction.
In times of stormy weather, destructive waves will throw much larger boulders and stones to the top of the shore which are left as a storm beach.
E.g. Rosslare, Co. Wexford. Where they were having problems with the processes of costal erosion (abrasion, attrition, air compression, hydraulic action. 5.8 million euro cost. ½ a meter of coastline is being lost every year. They already have timber Groynes from 1950’s and rock Groynes from the 1990’s.
The 5.8 million will be spent on new Groynes, 2km of new sand, 520m of rock armour and 1km raised barrier embark and more
Costal defences (4)
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Sea walls – Built to break the power of incoming waves (erosion), usually curved to push waves back out to sea.
Gabions – steel wire cages filled with stones, stacked like a sea wall and are used to slow down or prevent erosion.
Rock armour – placed at the base of a cliff, sand dune or sea wall to prevent erosion (waves lose energy when they his these boulders).
Transportation
Longshore Drift: movement of sand in a zig-zag pattern from one side of the beach to the other along the coast.
- Waves arrive at an angle because of coastline irregular shapes or prevailing winds.
- Swash moves up shore at an angle pushing sand grains up the beach. Backwash flows straight back down the beach due to gravity, dragging sand grains back with it.
- This happens repeatedly (every wave).
- Over time, sand particles are moved in a zig-zag pattern and can move millions of tonnes per year. E.g. Dooagh beach on Achill Island – disappeared in 2019 due to destructive waves
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