Coastal Systems - Processes of Weathering and Erosion

A process is the mechanism by which change is imposed on a geographical component. The main processes leading to the degradation and break-down of existing features can be classified as those that take place ‘in situ’ leading to rock disintegration (weathering) and those that break up and remove the resultant debris (erosion)

Subaerial weathering processes:

Thermal expansion/extraction: alternating warming (sunshine) and cooling (cold sea water) of rock can lead to expansion/contraction of outer layers of coastal rocks.

Wetting/drying: mineral in rocks may absorb and release moisture as tides rise and fall leading to internal loss of coherence.

Freeze-thaw action: sub-zero air temperatures can cause rain water in surface fissures to freeze and expand. Under extreme conditions, sea water may freeze.

Chemical solution: minerals in coastal rocks are dissolved by chemicals in sea water and by acid rainfall.

Biological weathering: plant roots enlarging rock fissures, nesting sea birds, marine organisms that drill into rock such as the paddock.

Erosional marine processes:

Abrasion/corrasion: under storm conditions rock fragments may be launched from the sea bed by waves at exposed cliff faces, chipping off fragments of rock.

Hydraulic action: heavy vibration of cliff faces can occur as storm waves break against them. The resulting rock fracturing can produce quarrying at the base of cliffs leading to undercutting.

Cavitation: Compression of air in sea-facing joints as waves crash against cliffs can cause sea water to be severely compressed. As the wave recedes the pressure reduces and air comes out of solution in violent ‘fizzing’, enlarging fissures within joints.

Attrition: large angular fragments of rock produced by weathering and erosion are rounded, smoothed and reduced in size by wave friction against other fragments. The smaller pebbles are ammunition for abrasion and may eventually form depositional material.