A ice cap is a tablecloth of ice, a Glacier continental very wide, known also under the more common name of polar icecap .
The word is of origin Danish E and literally means ice of the interior of the country or ice of the back country .
It is considered that an ice cap is a glacier whose surface exceeds 50 000 km 2 .
The current ice caps are thus two:
- the ice cap of the Greenland from which the name comes;
- the ice cap of the the Antarctic (sometimes divided into two with side the Western Antarctic and other the Eastern Antarctic).
The Vatnajökull in Iceland is not regarded as an ice cap because it measures “only” 8 100 km 2 . One will speak about Icecap for the glaciers of very great dimension and having some of the characteristics of the ice caps.
The formation of the ice caps rests on the same principle as that of the glaciers : an accumulation of Neige resulting from an insufficient cast iron causes a compressing of the snow which expels the air that it contains and is transformed into Glace. This ice is sufficiently plastic to become deformed according to gravity or its own weight. In the case of the ice caps, it is the proper weight of the ice which causes its displacement by Fluage, the slope on an island or continent scale large being too weak to cause a gravitating flow. A balance between contribution of snow, weight of the ice and ablation of snow (sublimation, cast iron, production of Iceberg S) is carried out then and masses it of ice stabilizes its thickness and its extent. An ice cap is maintained more by one weak ablation than by a strong contribution of snow.
A cut in profile of an ice cap makes it possible to distinguish several recurring points:
- a concave surface: the edges of an ice cap are sloping and its center is made of several domes very little marked which give the appearance of a plate;
- a layer of very thick ice, in general 2 000 meters thickness, and being able to reach 4 000 meters thickness;
- a rock substrate being able to be under the sea level;
- a overflow on the sea (Sea of Ross and Sea of Weddell in the Antarctic);
- a glacial face being able to make the turn of the many ice caps and producing Digitation S and glacial lobes;
- a production of icebergs:: tabular when they come from the dislocation of the floating ice cap, without particular form when they come from the digitations and the glacial lobes;
- an absence of relief emerging except for the Nunatak S.
The ice caps contain 98% of the Fresh water of planet.
Disappeared glaciations and ice caps
At the time of each Glaciation, the current ice caps were wider and some occupied of the whole portions of continents.
The principal ice caps of the Pleistocene, disappeared today, were located:
- on the Canadian Shield and the Rock;
- in the the Andes on the level of the Bolivia and the Patagonie;
- in Iceland;
- on British Isles, the Europe of north, the north of the Russia and the Siberia;
- in the Altaï;
- in the Mounts Verkhoïansk;
- in the the Himalayas, the Hindū-Kūsh, the mounts Tian Shan and Kunlun.
Ice cap of the Greenland
The Greenlandic ice cap is one of the remainders in the northern Hemisphere of the last glaciation. The ice cap was formed with the average Pléistocène and higher on formerly moderate grounds of which the center-South part was furrowed broad rivers which flowed in the Baie of Disko and whose traces form today channels under the ice and of the depressions under navy. The oldest ice has 250 000 years and is maintained by the annual accumulation of the snow which compensates for the losses by Vêlage and cast iron on the level of the margins.
Its dimensions are impressionnantes : 2 400 kilometers length and 1 000 kilometers broad. Its surface, relatively punt, are of 1 726 000 km and has an average altitude of 2 135 meters. The ice can reach the thickness of 3 000 meters in the center of the ice cap, this represents a total volume of 2 000 000 km of ice, is 10% of fresh water on the surface of the sphere.
In this frozen interior, the Gunnbjörns Fjeld culminates with 3 733 meters.
Ice cap of the Antarctic
The ice cap of the the Antarctic has a surface of 14 000 000 km, an average thickness higher than 2 000 meters and a maximum altitude of 4 000 meters. It is appeared as an immense plate of ice and snow to the edges precipice giving rise to the barriers of Ross and Filchner. The ice cap of the Antarctic east cut into two by an assembly line (the Mounts Transantarctiques) separating the Eastern Antarctic from the Western Antarctic.
See also: the Antarctic
the ice cap of Greenland on GoogleMap
- Animation on the formation of an Ice cap (international polar Foundation)
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