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A crack in a headland is widened by hydraulic action. Hydraulic action is the force from
the waves pounding water at the cliffs. When the water enters cracks it forces air into
small pockets. This then (when the water goes out) erupts in small eruptions causing weakness
of the cliff and erosion. As the crack widens it forms a cave. Corrasion
and hydraulic action attack the crack and it widens. Corrasion is a form of marine erosion.
It works when rocks from the sea pound against the cliffs damaging both the rocks and the
cliff. Caves and widened and deepened until they
break through the headland to form an arch. The arch is widened due to weathering and
erosion. Weathering is the breaking down of rocks by the action of weather, plants or
chemical action. In happens in situ, meaning without movement.
Due to weathering and sub-aerial processes, the former roof of an arch collapses. It is
also because of the gravitational pull. Sub-aerial processes are processes that attack the face
and the top of a cliff. This leaves a stack. Due to continuous weathering and erosion the
stack erodes down to produce a stump or collapses into the sea.
The erosion of a headland is a continuous process. Because the erosion of a headland
is a continuous process you may see examples of the process occurring further down the
headland. To summarise the process of headland erosion....
A crack in the rock or an area of weakness is attacked by hydraulic action. Hydraulic
action and corrosion make the crack more vulnerable to other types of erosion. As the crack widens
it forms a cave. Because of other forms of marine erosion, the cave widens and deepens,
breaking through to the other side of the headland. Once it has done so it is now an
arch. The former roof of an arch may collapse due to sub-aerial processes and weathering.
This leaves a stack. A stack may erode away or fall into the sea leaving a stump.