Hydraulic action is a process where pounding waves compress trapped air in the rocks, creating an explosive blast which weakens and loosens rock fragments.
Abrasion is a process where rock fragments are thrown against the headland, breaking down the cliff face and wearing away the rock.
Solution is a process where salts in sea water dissolves rock.
Attrition is a process where rock fragments are slowly ground down by friction from waveaction into smaller and rounder pieces which can then be used as an abrasive material.
Rocks contain weak points that are more easily eroded.
Over time, lines of weakness are enlarged and develop into small sea caves.
In some cases, a blowhole can form in the roof of the cave as compressed air is pushed upwards by the power of the waves, causing vertical erosion.
There may be erosion on both sides of the headland due to wave refraction until eventually the sea cuts through the back walls of the caves, forming an arch.
Continued erosion enlarges the arch.
The base of the arch is also undercut by the erosion, causing the arch to become unsupported.
Eventually the arch collapses due to gravity to form a stack.