Coasts Revision Notes

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  • Created on: 07-05-13 19:52
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Coastal weathering and erosion
There are two types of weathering ­ chemical and mechanical
Chemical weathering ­ breakdown of rock by changing its chemical composition
(carbonation happens by chemical weathering in warm, wet conditions)
1) Dissolved in rainwater is carbon dioxide, which makes it a weak carbonic acid
2) Carbonic acid reacts with calcium carbonate rocks (limestone) so rocks get dissolved
slowly by the rainwater
Mechanical weathering ­ breakdown of rock without changing its chemical composition
(freeze-thaw weathering happens most commonly on coasts)
1) Water gets into cracks in rocks on cliff-faces
2) As the water freezes, it expands putting pressure onto the rock
3) As it thaws, it contracts releasing the pressure off the rock
4) After time, this causes large cracks to appear in the rock face and eventually the rock
breaks completely
There are four types of erosion, which wear away the cliff-face ­ hydraulic action, corrasion
(abrasion), corrosion and attrition
Hydraulic action ­ waves compress air inside cracks that get trapped, putting pressure
on the rock. As this repeats, cracks widen and eventually fragments of rock break off
Abrasion ­ small particles in the water bang against the edge of the rock, removing
small parts of rock
Attrition ­ small particles in the water bang against each other, breaking into smaller
fragments and edges of the rocks become rounder
Corrosion ­ carbonic acid, which is weak in the water, dissolves rocks
Destructive waves erode away the coastline. Destructive waves have a high frequency with up to
14 waves hitting the beach every minute. They're high and steep waves. They also have a stronger
backwash than their swash which means more material is moved away from the coastline.
Two factors affect the size and power of these waves:
Wind ­ the force of the wind creates the waves therefore if there's a stronger wind, there
will be more powerful waves
Fetch ­ the distance from which the wind has blown where a greater fetch gives bigger,
more powerful waves
Coastal landforms from erosion
Cliffs retreat due to erosion, weathering and movement
The most erosion is at the foot of the cliff
This forms undercutting which causes unstable rock at the top of the cliff
Above sea level, rock undergoes weathering processes making it more unstable until it
collapses; if a cliff collapses many times, it will retreat
After cliffs retreat, a wave-cut platform is formed underneath sea level usually
The geology of the cliff means it can erode faster or slower; cliffs with soft rock retreat
very quickly but cliffs with harder rock retreat very slowly
If there is much vegetation on a cliff, it is more likely to be stable so erode less and retreat

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Mass movements occur when cliffs collapse; these happen when the force of gravity
becomes stronger than the force supporting it
Slides Slumps Rockfalls
Material moves in straight Material moves in rotation Material moves vertically
When erosion happens differently, headlands and bays are formed. This happens because some
types of rock are more resistant to erosion than others. These form where there are different bands
of rocks along a coast.…read more

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Where there are parallel bands of hard and soft rock, coves are formed. Coves ae wide, circular
bays with narrow entrances. They form when there are bands of hard and soft rock behind.…read more

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Deposition is where material that is being carried is dropped off at the coast. Coastlines build up
when there is a greater rate of deposition than there is erosion. More material is deposited when
there is lots of erosion taking place and there's much transportation of seawater and material into
the area. Waves with little energy bring material to the coast but can't take much material away so
there's lots of deposition but not much erosion.
Constructive waves build up the coastline.…read more

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Wave-cut platforms ­ bumpy edges along coast
Sand beaches ­ pale yellow in colour
Shingle beaches ­ pale yellow or white in colour with speckles
Spits ­ beach carrying out to sea with one bit attached to land
Reasons for protecting coastlines
Human reasons
Social Economic
Deaths ­ coastal landforms have killed many in Loss of tourism ­ tourism brings in lots of money
the past and flooding plus erosion can put people off
coming which puts pressure on businesses that
rely on tourism
Water…read more

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