GeoTopics @ GeoNet

Waves

Coastal Erosion
Cliff Recession
Erosion of a headland

There are four main processes which cause coastal erosion. These are corrasion/abrasion, hydraulic action, attrition and corrosion/solution.

Corrasion/abrasion is when waves pick up beach material (e.g. pebbles) and hurl them at the base of a cliff.

When waves hit the base of a cliff air is compressed into cracks. when the wave retreats the air rushes out of the gap. Often this causes cliff matrial to break away. 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.

Cliff Recession

Erosion is greatest when waves break at the foot of a cliff. This causes erosion at the base of the cliff. This creates a wave-cut notch in the base of the cliff. As the notch increases in size the weight of the cliffs above become too much and the cliff collapses. This material will provide temporary protection for the cliff behind. However, once it has been removed by the sea this process will occur again. Where cliffs are made of more resistant material, wave cut platforms will be created.

Erosion of a headland

A headland is an area of hard rock which sticks out into the sea. Headlands form in areas of alternating hard and soft rock. Where the soft rock erodes bays are formed either side of the headland. As the headland becomes more exposed to the wind and waves the rate of its erosion increases. When headlands erode they create distinct features such as caves, arches, stacks and stumps.

The diagram below shows the sequence in the erosion of a headland.

	Stage 1 Waves attack a weakness in the headland.
	Stage 2 A cave is formed.
	Stage 3 Eventually the cave erodes through the headland to form an arch.
	Stage 4 The roof of the arch collapses leaving a column of rock called a stack.
	Stage 5 The stack collapses leaving a stump.