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Coastal Landforms, image, image, image, image, image, image - Coggle…
Coastal Landforms
Caves, Arches,
Stacks and Stumps
- A large crack is opened up in the headland by hydraulic action
- The crack grows into a cave by hydraulic action and abrasion
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- The cave breaks through the headland forming a natural arch
- The arch is eroded and collapses
- This leaves a tall rock stack
- The stack erodes and becomes a stump
Headlands and Bays
- Many coastlines have alternating bands of hard and soft rock
- The coastline is broadly straight until erosion begins on the different rock layers
- Soft rock layers are eroded to form bays while the hard rock layers remain as headlands
- The bays are sheltered and protected by the headlands, meaning little wave energy and so little erosion occurs
- The once straight coastline is changed into a sequence of headlands and bays
- Material eroded off the headlands is carried into the bays and is trapped as beaches
Spits and Bars
- 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 the spit is very sheltered. Silts are deposited here and form salt marshes or mud flats
- Sometimes a spit can grow across a bay, and join the headlands together. This is a bar
- They can trap shallow lakes behind the bar, known as lagoons
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Sand dunes
- Embryo dunes form around deposited obstacles such as wood, rock, rubbish etc.
- These develop and become stabilised by vegetation (marram grass). The roots help bind the sand together and stabilise the dunes, forming fore dunes and tall yellow dunes
- In time, rotting vegetation adds organic matter to the sand making it more fertile so more plants colonise these 'back' dunes
- Wind can form depressions in the sand called dune slacks, in which ponds may form
Beaches
Beaches are deposits of sand and shingle that has been transported from elsewhere and deposited by the sea
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Material is deposited when waves lose energy, eg. in sheltered bays
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