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Coasts revision, Coastal processes, Coastal landforms, Coastal management …
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Coastal processes
Types of mass movement
Rockfall
Bits of rock fall off the cliff face, usually due to freeze-thaw weathering forming scree at the bottom.
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Erosion
Attrition - this is when rocks that the sea is carrying knock against each other. They break apart to become smaller and more rounded.
Solution - this is when sea water dissolves certain types of rocks. In the UK, chalk and limestone cliffs are prone to this type of erosion.
Abrasion - this is when pebbles grind along a rock platform, much like sandpaper. Over time the rock becomes smooth.
Hydraulic action - this is the sheer power of the waves as they smash against the cliff. Air becomes trapped in the cracks in the rock and causes the rock to break apart.
Transportation
Solution - when minerals in rocks like chalk and limestone are dissolved in sea water and then carried in solution. The load is not visible.
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Types of weathering
Chemical weathering
Rainwater and seawater can be a weak acid. If a coastline is made up of rocks such as limestone or chalk, over time they can become dissolved by the acid in the water.
Biological
Plant roots can get into small cracks in the rock. This causes small pieces of rock to break away. As the roots grow, the cracks become larger.
Threeze-thaw
Water enters cracks in the rock. When temperatures drop, the water freezes and expands causing the crack to widen. The ice melts and water makes its way deeper into the cracks. The process repeats itself until the rock splits entirely.
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Coastal landforms
Headlands and bays
Bands of soft rock are weaker therefore they can be eroded quickly. This process forms bays. A bay is an inlet of the sea where the land curves inwards, with a beach. Hard rock is more resistant to the processes of erosion. When the softer rock is eroded inwards, the hard rock sticks out into the sea, forming a headland.
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Beaches
Beaches are made up from eroded material that has been transported from elsewhere and then deposited by the sea. For this to occur, waves must have limited energy, so beaches often form in sheltered areas like bays
Spits
Sediment is carried by longshore drift. When there is a change in the shape of the coastline, deposition occurs. A long thin ridge of material is deposited. This is the spit. A hooked end can form if there is a change in wind direction. Waves cannot get past a spit, therefore the water behind a spit is very sheltered. Silts are deposited here to form salt marshes or mud flats.
Coastal management
Hard engineering
Sea Walls
Concrete walls that are placed at the foot of a cliff to prevent erosion. They are curved to reflect the energy back into the sea.
Advantages
Sea walls usually have promenades so people can walk along them. Effective at protecting the base of the cliff.
Disadvantages
Waves are still powerful and can break down and erode the sea wall. Expensive - approximately £2,000 per metre.
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Rock armour
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Disadvantages
They look different to the local geology, as the rock has been imported from other areas. The rocks are expensive to transport.
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Groynes
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Disadvantages
By trapping sediment it starves beaches further down the coastline, increasing rates of erosion elsewhere. They look unattractive.
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Soft engineering
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Dune Nourishment
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Disadvantages
Can be damaged by storm waves. Areas have to be zoned off from the public, which is unpopular.
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Managed Retreat
Managed retreat is the controlled flooding of low-lying coastal areas. If an area is at high risk of erosion, managed retreat could be an option.
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Advantage
This is a cheap option compared to paying for sea defences. Salt marshes are diverse ecosystems supporting many species.