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1.2 Coastal Landforms (Weathering (Chemical: The decay of rock due to…
1.2 Coastal Landforms
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Mass Movement
Rock fall: on cliffs of 40° or more, especially if the cliff face is bare, rocks may become detached from the slope by physical weathering. These rocks then fall to the foot of the cliff due to gravity. Wave processes then remove this material.
Slides: This may be linear, with movement along a straight slip plane. Slumps occur due to undercutting by wave erosion at the base of the cliff which removes support for materials above. Slumping is common in weak rocks.
Wave processes
Erosion
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Attrition: When rocks transported by wave action collide with each other and with the coastal rocks and progressively become worn away. They become smoother and more rounded - form sand
Hydraulic action: When waves break against the cliff face, and air and water trapped in cracks becomes compressed. As the wave recedes, the pressure is released, the air and water expand and the crack is widened.
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Transportation
Solution: Minerals that have been dissolved into the mass of moving water. This is invisible and the minerals remain in the solution until the water is evaporated and they precipitate out of the solution.
Suspension: Small particles of sand, silt and clay can be carried in currents; muddy appearance of water.
Saltation: This is a series of irregular movements of material which is too heavy to be carried continuously in suspension. Turbulent flow may enable sand-size particles to be picked up and carried a short distance only to drop back down again.
Traction: The largest particles in the load may be pushed along the sea floor by the force of the flow.
Deposition
Material is deposited when there is a loss of energy caused by a decrease in velocity/volume of water.
Occurs where:
- The rate of sediment accumulation exceeds the rate of removal.
- When waves slow down immediately after breaking
- At the top of the swash, where for a brief moment the water is no longer moving
- During the backwash, when water percolates into the beach material
- In low-energy environments such as those which are sheltered from the wind and waves.