Geography

Caves

Waves often tend to find any weakness or crack in a rock and widen it by the process of hydraulic action. This often results in the formation of caves on a headland.

Arches

Once the cave has formed, the waves are able to enter and continue eroding back into the headland until they eventually break through to form an arch ( For example Durdle Door, UK ). In time the base of the arch is attacked by the waves and this puts increasing pressure on the roof of the arch.

Stacks and Stumps

Eventually over time the roof will collapse due to continued erosion and weathering leaving a tall isolated stack (For example Old Harry, Dorset coastline). The stack is attacked at the base by the force of the waves (undercutting) and will eventually collapse to form a stump.

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