Coastal erosion is the wearing away of the land by the sea. This often involves destructive waves wearing away the coast (though constructive waves also contribute to coastal erosion).
There are five main processes which cause coastal erosion. These are corrasion, abrasion, hydraulic action, attrition and corrosion/solution.
Corrasion is when destructive waves pick up beach material (e.g. pebbles) and hurl them at the base of a cliff. Over time this can loosen cliff material forming a wave-cut notch.
Abrasion occurs as breaking waves, concentrated between the high and low watermarks, which contain sand and larger fragments wear away the base of a cliff or headland. It is commonly known as the sandpaper effect. This process is particularly effective in high-energy storm conditions.
The video below shows abrasion in action at Flamborough on the Holderness Coast.
When waves hit the base of a cliff air is compressed into cracks. Repeated changes in air pressure are caused by water and air being forced in and out of joints, folds and bedding planes. When the wave retreats the air rushes out of the gap. This causes an explosive effect as pressure is suddenly released. This process is supported further by the weakening effect of weathering. Material breaks off cliffs, sometimes in huge chunks. This process is known as hydraulic action.
Attrition is when waves cause rocks and pebbles to bump into each other and break up.
Corrosion/solution is when certain types of cliff erode as a result of weak acids in the sea.
What factors affect the rate of coastal erosion?
Coastal erosion is greatest when:
- waves have a large fetch e.g. the south-west coast has an 8000 kilometre fetch across the Atlantic Ocean;
- strong winds blow for a long time creating destructive waves;
- an area of coastline has no beach to buffer the waves;
- the cliff material is soft e.g. soft boulder clay along the Holderness Coast means it experiences the highest rate of erosion in Europe;
- cliffs made from rock have many joints;
- a headland sticks out into the sea and waves converge on it (wave refraction).