Erosion happens at all beaches and is a natural process. According to the Waikato, New Zealand, Regional Council, most shorelines go back and forth between periods of sand erosion and sand build-up. The type of erosion known as short-term erosion caused by storms does not change the location of the shoreline, though full recovery can sometimes take decades. The presence of dune grasses aids with recovery. Long-term erosion tends to occur on hard coasts and is a permanent change in the coastline, such as when water levels rise or when cliffs erode. Two main types of erosion identified by the Encyclopedia of New Zealand are: cut and fill erosion, which tends to be short-term, and permanent erosion, which is longer-term as the name implies.
Cut And Fill Erosion
Cut and fill erosion occurs when loose sediment--sand, gravel, and the like--are swept about by actions of the sea. Human activity can influence the rate of coastal erosion. Loss or damage of sand dunes or dune vegetation, and removal of coastal plants, make a coastline less stable and more susceptible to erosion. Human development that is too close to the shoreline contributes to destabilising the coastline. Global warming is also a factor. In areas of cut and fill erosion, the erosion may be cyclical with areas eroding away and later being built back up by the action of waves.
Permanent erosion occurs along rocky, hard coasts. In these locations the material is not replaced. Four processes cause permanent erosion: waves tossing beach material at the base of a cliff, hydraulic action when waves retreat pulling materials out of the cracks in cliffs, rocks and pebbles broken up by wave action and acids in seawater causing erosion in some types of rocky cliffs.
Headland erosion is a special type of erosion. A headland is made of hard rock reaching out into the sea causing areas of alternating hard and soft rock. Erosion of the soft rock causes bays to form alongside the headland. As erosion continues, caves, stumps and other rock features are formed. Creation of these rock features is a multi-stage process. First waves work their way into a weakness in the headland and a cave is formed. The cave may then erode, forming an arch. If the roof of the arch collapses, a stack is created. A stack looks like the desert formation known as a "hoodoo," a lone tower of rock. Finally, the tower may break and a stump barely at the water's surface is all that is left.
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