Features of coastal erosion
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Features of coastal erosion
It can be said that these are the most common and important erosional coastal landform, due to their number and the amount of pressure human activity places upon them.
They result from the interaction of a number of processes:
- Human activity.
Cliffs are steep if removal of material at its base is greater than supply.
Cliffs are shallow if the supply of material is greater than removal.
A direct relationship exists between rock type, erosion rate and cliff morphology.
Hard rock cliffs:
Examples include granite and basalt cliffs. They exhibit a slow rate of erosion and tend to be stable.
Soft rock cliffs:
Examples include cliffs comprised of glacial till and clay, such as those found at Fairlight Cove in Hastings.
These cliffs often erode rapidly. In these cliffs, sub-aerial processes can contribute more to erosion than marine processes, leading to mass movements such as sliding, slumping and falls.
The diagram below illustrates this:
Reasons for cliff erosion at Holderness:
The cliffs at Holderness have an average speed of retreat of 2m per year.
- Cliffs are made of soft glacial till.
- Till is easily eroded at base by waves, resulting in instability.
- Rainwater from above enters the till easily, adding to its weight and instability.
- Massive slumps and slides occur.
A similar situation exists at Baton on sea in Hampshire and Beachy Head.
Usually found where less resistant and more resistant rock alternates. The less resistant rock is attacked, first forming bays, and the stronger rock remains as headlands. As wave refraction later occurs, energy becomes concentrated on headlands, leaving them more liable to erosion.
These are gently sloping features, often found extending from the base of a cliff. They consist partly of material removed from the cliff (wave cut notch) as a result of continual undercutting by waves. (See diagram below):
As undercutting increases, the cliff slowly retreats, leaving a platform with an angle of less than 4 degrees. The platform widens to a point, but due to the cliff being attacked less frequently by waves, it is thought that they can only reach a maximum of 0.5km.
All of the above are secondary features occurring during cliff formation. They originate due to lines of weakness such as joints or faults being attacked and made larger by marine erosion. Caves occur where the weakness is at the base of the cliff, and can become a blowhole if the crack extends all the way to the surface.
- Caves formed on either side of a headland may form an arch if the 2 caves join together.
- Stacks are collapsed arches.
- Stumps are stacks that have been eroded and lost height.