Outline the processes involved in the formation of a stack?

Stacks are an erosional landform that develop as a result of erosional processes such as hydralic action, abrasion and weathering on a headland. Firstly, cracks form in the cliff face as a result of erosion from the waves. As water enters these cracks the rocks are forced apart and gradually, as hydralic action erodes away the rock, a cave is formed. The waves continue to erode the rocks and will eventually break through to form an arch. As the arch becomes bigger, and weahtering acts to erode the top of the headland, the arch becomes unable to support the rock above and will collapse. This results in the formation of a stack, an erosional landform that can be seen at Old Harry in Dorset on the south coast of England. Eventually this stack will be eroded down to form a stump which will dissapear under the surface of the water.