Caves, arches, stacks and stumps

Wave cut notch

Wave cut notches are formed by waves between high and low tide lines. A crack in the cliff surface is widened by the marine erosion processes of hydraulic action and abrasion. This leaves a deep cave in the cliff face. As this becomes deeper as a result of more erosion, the overhang is left more unstable and weak. It is unsupported therefore it collapses. This process continues and the cliff retreats as a result.


Caves, arches, stacks and stumps

An arch is formed when a crack in the cliff surface of a headland is widened. It has to be in a headland otherwise it would not be hollow and would instead form a cave. The crack is widened by the marine erosion processes of hydraulic action, abrasion and corrosion. Over time the cracks will be eroded immensely to form wave cut notches and eventually caves. Weathering processes such as salt crystallisation may erode more cracks. As a result of wave refraction, the walls of caves are eroded greatly and the cave is deepened. As the cave deepens, the support for the top of the headland decreases. Wave refraction affects all three faces of the headland. There may be another cave on the opposite side of the headland. The waves would cut through the cave to form an arch. Wave cut notches at the base of the arch would widen it further. Eventually the lack of support for the top of the headland leads it to collapse: forming a new cliff face and a stack. The bottom of the stack is continuously eroded by hydraulic action and abrasion to form wave cut notches. Weathering such as raindrop action and salt crystallisation may weaken the stack from above also. As a result it becomes unstable and unable to support itself. The stack would then form a stump.