Depression (geology)

A sink in terms of geomorphology - also referred to in the context of this science depression - is an area on the mainland, which lies below sea level.

Definitions and Terms

The depression or geomorphological Valley is a special case of geographical depression whose base is indeed always lower than the total environment, but may also be higher than the level of the ocean. Geomorphological as well as other geographical sinks are to be distinguished from lowlands, which are only partially surrounded by higher ground so that its bottom is predominantly via the outflow horizon. Only in climates where the rainfall is less than the evaporation, depression may be superficially recognizable as naturally walkable land below sea level. At the lowest point they have a salt marsh or salt lake, the water level is not subject rarely seasonal fluctuations.

If there is, however, deeper than the sea floor situated under the water of a lake, it's called a crypto- depression, so hidden depression. Walk-in depression there is a wet climatic regions only by human intervention. By area, the most significant is located just below mean sea level continuously dehydrated marshland, Abdämmungsdepressionen as the Dutch polders. The tiefreichendsten depression in humid regions are surface mines that are either currently being exploited and drained, or have not yet been completely filled or watered according to their abandoning.

Significant natural depression

The deepest depression are the Jordan Valley to the Dead Sea ( -425 m level currently, ground to -800 m) at the lowest point and the Sea of ​​Galilee ( fresh water levels in -212 m), Lake Assal in Djibouti ( mirror at a minimum - 155 m), the Central Asian Turfan depression with the Aydingkol Lake ( mirror at -155 m), in Egypt, the Qattara Depression ( -133 m) and the Fayyum basin with the Lake Qarun ( mirror from -42 to -45 m), in the Afar triangle, the Koba - sink ( -115 m) and the Danakil depression ( -110 m), the American Death Valley ( Badwater -85.5 m), the Caspian depression to the Caspian Sea ( mirror currently at -28 m, floor to -1023 m), in Tunisia the Chott el Gharsa (-17 m) and in Australia, Lake Eyre, mirrors -11 m (9500 sq km) to -17 m ( empty).

Crypto depression

A sink that is filled with water so that the lake level is above sea level, is called crypto- depression ( cf. Greek kryptos for " hidden "). In humid climates hollow molds are filled to overflowing with lakes. Therefore, there is here except for artificial drainage only crypto depression. This most frequently arisen as a result of Pleistocene glaciation as around the Baltic Sea and at the edge of lakes in the high mountains. In such fjord lakes, glaciers have carved out the valleys to below the sea level. Moraines or rock bolt or many hundreds of kilometers of land mass keep the lake level high and sea water.

The crypto depression in the Alpine region include Lake Garda ( lowest point -281 m slm ), Lake Como ( -228 m slm ), Maggiore (179 m below sea level), the Lake Iseo ( -66 m slm ) and the Lake Lugano ( 17 m below sea level). Crypto depression in northern Germany are the soils of the Arend Lake (27 m below sea level), Lake Plön, Hemmelsdorfer lake ( 39.5 m below sea level) in East Holstein, Ratzeburger, Schaalsees ( 36.5 m below sea level), Lake Schwerin, Malchiner lake, lake Kummerow, Great lake Stechlin and Tollense.

However, the deepest crypto depression often have a tectonic origin and are in grave fractures: is Lake Baikal, the deepest sample world ( mirror 456 m, the deepest point 1,186 m below sea level). Furthermore, it is also of Lake Tanganyika ( mirror 782 m, the deepest point 688 m below sea level) tectonic origin.

Abdämmungsdepression

On shallow seashores and in some estuaries is held by the diking and permanent drainage just below the sea level lying country artificial sea water freely and used as arable land - here we speak of the Abdämmungsdepression. So is more than a quarter of the Netherlands below sea level at mean water level. The 3.54 m deepest below sea level Abdämmungsdepression in Germany is located in New Village Sachsenbande in the district of Steinburg.