Features of coastal erosion
The following illustration shows how cliffs are eroded.
Old Harry chalk cliffs and stacks, Dorset, England
- Cliffs usually form where there is soft rock such as limestone and chalk.
- Wave erosion is strongest where large waves break against the base of the cliff.
- A wave-cut notch is formed when the base of the cliff is eroded by hydraulic action, corrosion and corrasion.
- Continual erosion causes the notch to become larger.
- Eventually, the cliff becomes unsupported and collapses into the sea.
- The cliff moves backs and leaves behind a wavecut platform which can be seen at low tide.
Headlands and bays
The following graphic illustrates how headlands and bays are formed.
A general view of the coastal town of Swanage
- Headlands and bays are created where there are bands of hard and soft rock which meet the coastline at right angles.
- Softer rock is eroded more quickly and erodes backwards to form bays (which may have beaches).
- The harder rocks are more resistant to erosion and jut out into the sea to form exposed headlands.
Caves, arches and stacks
The following illustration shows how caves, arches and stacks are formed.
How did the original headland become eroded to the present coastal landscape?
A number of stages are involved:
- The waves erode along lines of weakness in the headland by hydraulic action, abrasion and solution.
- Lines of weakness get enlarged and form small sea caves.
- The caves are deepened and widened on both sides of the headland.
- Eventually the sea cuts through the headland forming an arch.
- Continued erosion erodes the rock at the top of the arch which makes it unsupported as the arch is enlarged and eventually collapses to form a stack.
- The stack gets eroded until only a stump remains.
- Over time the stump will disappear.