A cliffed coast, also called an abrasion coast, is a form of

coast The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in ...

where the action of marine waves has formed steep

cliff In geography and geology, a cliff is an area of rock which has a general angle defined by the vertical, or nearly vertical. Cliffs are formed by the processes of weathering and erosion, with the effect of gravity. Cliffs are common on co ...

s that may or may not be precipitous. It contrasts with a flat or alluvial coast.

Formation

In coastal areas in which the land surface dips at a relatively steep angle below the water table, the continuous action of marine waves on the coastline, known as abrasion, may create a steep declivity known as a

, 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.Herbert Louis and Klaus Fischer: ''Allgemeine Geomorphologie'', de Gruyter, 4th ed., Berlin 1979, pp. 532-537 The slope is constantly being eroded. The waves attacking the cliff-foot form a wave-cut notch 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 area in front of the cliff by the action of the sea. As the coastal cliffs collapse, the shoreline recedes inland. 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 Mecklenburg (; nds, label= Low German, Mękel(n)borg ) is a historical region in northern Germany comprising the western and larger part of the federal-state Mecklenburg-Western Pomerania. The largest cities of the region are Rostock, Schweri ...

coast in

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

recedes by about 25 centimetres per year, whereas the chalk cliffs of southern England retreat by just ½ a centimetre each year. A cliffed coast is made of a loose bedrock material, such as at the Red Cliff on the German island of

Sylt Sylt (; da, Sild; Sylt North Frisian, Söl'ring North Frisian: ) is an island in northern Germany, part of Nordfriesland district, Schleswig-Holstein, and well known for the distinctive shape of its shoreline. It belongs to the North Frisian ...

, but can also occur in hard rock like the red sandstone cliffs on

Heligoland Heligoland (; german: Helgoland, ; Heligolandic Frisian: , , Mooring Frisian: , da, Helgoland) is a small archipelago in the North Sea. A part of the German state of Schleswig-Holstein since 1890, the islands were historically possessions ...

. There are, however, differences between the former and the latter regarding some peculiarities of the coast line. In the case of the large and widespread coastal cliffs of Atacama Desert the modern cliffs originated from a process of

scarp retreat Scarp retreat is a geological process through which the location of an escarpment changes over time. Typically the cliff is undermined, rocks fall and form a talus slope, the talus is chemically or mechanically weathered and then removed through ...

of a

fault scarp A fault scarp is a small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other. It is the topographic expression of faulting attributed to the displacement of the land surface by movement a ...

, thus at present the cliffs does not follow any geological fault.

Rocky cliffed coast

On a rocky cliffed coast made up of material which is relatively resistant to erosion such as sandstone, limestone or granite, a flat rocky

wave-cut platform A wave-cut platform, shore platform, coastal bench, or wave-cut cliff is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by erosion. Wave-cut platforms are often most ob ...

or abrasion platform is formed in front of the cliff. It represents the foot of the cliff preserved at and below the level of water table. If there is a

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

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. On a cliffed coast made up of material which is only fairly or even hardly resistant to erosion no wave-cut platform but a beach is formed in front of the sea cliff. If waves carve notches at a narrow point on both sides of a promontory on the rocky cliffed coast, a

natural arch A natural arch, natural bridge, or (less commonly) rock arch is a natural landform where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion ...

may be formed. When the arch collapses as the coastline recedes further a stack is left behind on the wave-cut platform. The best-known example in Germany is the

Lange Anna Lange Anna ("Tall Anna"), is a high sea stack of Buntsandstein in the North Sea island of Heligoland, Germany. Its local name is ''Nathurn Stak'' ("Northern Stack").Maren Lindstaedt, Thomas Kersten: Ein virtueller Klon für Helgolands Lange Anna d ...

, while, in England, a prominent example are

Old Harry Rocks Old Harry Rocks are three chalk formations, including a Stack (geology), stack and a stump, located at Handfast Point, on the Isle of Purbeck in Dorset, southern England. They mark the most eastern point of the Jurassic Coast, a UNESCO World H ...

Dorset Dorset ( ; archaically: Dorsetshire , ) is a county in South West England on the English Channel coast. The ceremonial county comprises the unitary authority areas of Bournemouth, Christchurch and Poole and Dorset. Covering an area of , ...

Furthermore, on a rocky cliffed coast wave action is not the only driving force for coastline retreat. General weathering of the bedrock is almost equally important.

Living and dead cliffs

"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

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 The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...

a few kilometres inland. These show the former coastline from which the sea retreated as the level of water in the North Sea fell.

Other processes

Steep sea cliffs can also be caused by catastrophic debris avalanches. These have been common on the submerged flanks of ocean island volcanos such as the Hawaiian Islands and the

Cape Verde Islands , national_anthem = () , official_languages = Portuguese , national_languages = Cape Verdean Creole , capital = Praia , coordinates = , largest_city = capital , demonym ...

.Mitchell, N. (2003) Susceptibility of mid-ocean ridge volcanic islands and seamounts to large scale landsliding. Journal of Geophysical Research, 108, 1-23.

References

External links

Collapse and retreat of a cliff edge captured on video
{{Coastal geography ! Erosion Hydrology Coastal and oceanic landforms