Revision:Coastal Erosion

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Erosion by Waves

Wave Quarrying / Pounding

Steep waves have considerable energy. Wave quarrying affects loose and unconsolidated rock fragments. The energy of a wave is proportional to its height. They have pressures of up to 50Kg/cm2. Air is trapped and compressed in a joint or between a breaking wave and a cliff. The increase in pressure over a period of time may break off the rock.

Abrasion / Corrasion

Is the wearing away of cliffs by large boulders like when they are hurled against them by waves. This is the most effective method of erosion.

Attrition

This is when rocks and boulders that have already been eroded from the cliffs are broken down into smaller rounder particles.

Weathering the Coast

Water Layer Weathering

This is to do with the rocks wetting and drying on the shore as the tide rises and falls. Salt crystallisation attacks porous and granular rock.

Corrosion / Solution

This includes the dissolving of the limestone by the carbonic acid in the seawater.

Weathering by Biological Activity

Secretions of weak acids from blue and green algae and limpets help to dissolve the rock.

Human Activity

Building on the tops of cliffs increases the rate of erosion and it also increases the pressure and removes beach material which might have protected the base of the cliff.

What Affects the Rate of Erosion?

Breaking Point of the Wave

Most erosive if it breaks at the foot of a cliff. It is less erosive if it hits the cliff before it breaks and if it breaks offshore then the energy is dissipated across the beach.

Wave Steepness

Very steep destructive waves can be formed locally and therefore these are more erosive. Gentle and constructive waves are less erosive.

Depth of Sea, the Length and Direction of the Fetch, and the Configuration of the Coastline

A steeply (more erosive) shelving beach creates higher and steeper waves than one with a gentle gradient, which causes less erosion. The longer the fetch the greater time available for waves to collect energy from the wind and this equals greater erosion.

Wave Refraction

The headlands with vertical cliffs concentrate erosive energy by wave refraction.

Supply of Beach Material

Supply of beach material needed for there to be more abrasion. The beach will reduce wave energy by absorbing it.

Beach Width

The bigger the beach the more erosive energy lost. The wider the beach gives less erosion and the narrower the beach gives more erosion. A wider beach is where there is a ready available supply of sand. A narrow beach is where there is not a ready supply of sand.

Rock Resistance, Structure, and Dip

The resistance of the rock will affect its rate of erosion. E.g. Less resistant rock like Volcanic Ash, Surtsey in 1963 on the South West coast of Iceland, Unconsolidated ash, protected now by lava.

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