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Formation of caves, arches, stacks and stumps
1.) The sea attacks the foot of the cliff and erodes the areas of weakness by the
processes of HACS
2.) The crack get bigger and develops into a small cave
3.) The cave is widened and deepened until it cuts through the headland to form an
4.) Further undercutting causes the arch to collapse. This leaves part of the cliff
detached as a stack. Further undercutting causes the stack to collapse
Erosion of a headland
Headlands are usually made of resistance rocks that have weaknesses like cracks.
Waves crash into the headlands and enlarge the cracks- mainly by hydraulic power along
with abrasion. Repeated erosion and enlargement of the crack causes a cave to form.
Continued erosion deepens the cave until it breaks through the headland, forming an
arch such as Durdle Door. Erosion continues to wear away the rock supporting the arch,
until it collapses. This forms a stack- an isolated rock that's separated from the headland
such as Old Harry.