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Erosional landforms - Coggle Diagram
Erosional landforms
Wave cut platform
How it is formed
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Eventually the notch is cut so far that the rock above it cannot be supported via friction, so it falls.
As a wave cut platform extends, so much friction occurs between the shallow water on top of the platform and the platform itself, that undercutting ceases.
Erosion is highest at the low and high tide marks as water levels are constant for a while. This forms a ramp at the high tide mark and a cliff at the low tide mark.
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Bays + headlands
Formation
Bays and headlands usually form adjacent to eachother due to bands of rock with different resistances to erosion.
The weaker rocks are eroded faster to form bays and the stronger rock remains between bays as headlands.
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Concordant coasts most often create a straight coast line, protecting weaker rocks from erosion, but small bays or coves can be eroded at points of weakness, like fault lines. Waves erode through the fault lines until it reaches the less resistant rock, which is eroded to form a bay.
Wave refraction
As a wave approaches a coastline, it is slowed by the shallow water off a headland.
At the same time, the crest moves at the same speed as it is not being slowed by friction.
This means the wave refracts/bends around the headland, and the orthogonals (an imaginary line directly perpendicular to the wave energy) curve towards eachother.
Wave energy is concentrated on the headland, so this is where erosion takes place.
In the bays, the energy is more spread out across the bay and the waves also move slower, leading to more deposition.
This leads to the gradual build up of beach sediment, due to longshore movement of eroded material into the bays.
Geos and Blowholes
Formation
Even on coasts with resistant geology, there may be lines of weaknesses like joints or faults.
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Hydraulic action is most prominent in forming these features: forcing air and water into the rock strata.
If the roof of a tunnel - like cave collapses along a master joint, it may form a vertical shaft which reaches the top, which is a blowhole.
In storm conditions large waves may force spray out of the blowhole as white, aerated water.
Caves, arches, stacks, and stumps
Formation
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Due to wave refraction, energy is concentrated on the sides of headlands.
Any points of weakness, like a joint or fault, is exploited by the high wave energy.
Wave attack is concentrated between high and low tide so can form a cave in the headland, at one or either side.
A cave may enlarge by erosion to reach the other side of the headland, forming an arch.
Weathering and further erosion causes the arch to weaken and eventually collapse, leaving an isolated stack.
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