A cliffed coast, also called an abrasion coast, is a form of coast where the action of marine waves has formed steep cliffs that may or may not be precipitous. It contrasts with a flat or alluvial coast.
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Cliff is a Romance loanword that has its origins in the Latin forms clivus / clevus ("slope" or "hillside").[1][2]
The continuous action of marine waves on a coastline, known as abrasion, may create a steep declivity known as a cliff, the slope angle of which depends on a variety of factors including the jointing, bedding and hardness of the materials making up the cliff as well as the erosional processes themselves.[3] The slope is constantly being eroded. Waves run up the abrasion platform or rocky shore platform and attack the cliff-foot. Here wave-cut notches are formed by constant abrasion action producing an overhang. This overhang grows in size as the cliff is undercut, until it collapses under its own weight. The loose debris that has broken off is gradually carried away from the platform by the action of the sea. As the coastal cliffs collapse, the shoreline recedes inland. At the same time the abrasion platform grows in size. The speed at which this happens depends, in particular, on the strength of the surf, the height of the cliff, the frequency of storm surges and the hardness of the bedrock. Thus, the Mecklenburg coast in Germany recedes by about 25 centimetres per year, whereas the chalk cliffs of southern England retreat by just ½ a centimetre each year. If there is a tectonic uplift of the coast, these abrasion platforms can be raised to form coastal terraces, from which the amount of uplift can be calculated from their elevation relative to the sea level, taking into account any eustatic sea level changes. If waves carve notches at a narrow point on both sides of a promontory on the coast, a natural arch may be formed.[4] A cliffed coast is often made of a loose bedrock material, such as at the Red Cliff on the German island of Sylt, but can also occur in hard rock like the cliffs on Rügen.
"Living cliffs" are those on a coast that is still active, i.e. that is being eroded and is receding. A "dead cliff", by contrast, is only reached by very high marine waves and is therefore subjected to very little change. A clear indication of a lack of activity at a dead cliff is a covering of vegetation that appears on the cliff as wave action against it subsides.
Well-known coasts with living cliffs in Germany are the Red Cliff (Rote Kliff) in Kampen on the island of Sylt or the chalk cliffs on the Jasmund Peninsula. The Königsstuhl on the island of Rügen is a good example of a dead cliff. Others may be found in the regions of the present-day Wadden Sea coast of the North Sea a few kilometres inland. These show the former coastline from which the sea retreated as the level of water in the North Sea fell.
Some current conditions lead to the formation of stacks that are left behind on the shore platform as the coastline recedes. The best-known example in Germany is the Lange Anna on Heligoland.