Explain, with the aid of annotated diagrams, the various stages and processes involved in the formation of a stack.

Hydraulic action and constant pounding of the waves against the rock causes faults and weaknesses in the cliff. Overtime, faults are enlarged as the pressurised air cracks the rocks and forms a wave- cut notch, this is further deepened to form caves. Wave refraction inside the caves causes the destructive waves to concentrate on the sides. If both sides of the headland are affected, caves can be eroded on both sides until they become an arch. Eventually, the arch becomes unstable and collapses under its own weight to form a pillar of rock- a stack.Sub-arial weathering such as rain, surface run off and freeze thaw erodes the cliff.The rock face is also affected by biological weathering such as roots from trees and burrowing organisms and also chemical weathering like salt crystalization forming when the sea water evaporates.