firn

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Firn is found between the ice of a glacier and the snow on its surface
Firn field on the column corner

As Firn (from Old High German Firni "vorjährig."; Cf. Swiss German "färn") or firn is called in the strict sense of snow , at least one year old and thus ablation survived.

In a broader sense, firn is snow whose finer snow crystals have fused to larger, sleek , granular structures through repeated thawing and freezing . Eight meters of fresh snow turns into around one meter of firn. The density of firn is between 0.4 and 0.8 g / cm³.

Location and origin

The firn limit is the summer lower limit of the continuous snow cover on glaciers . The part of the glacier above the firn border is also called a firn field. The next stage of the transformation process into glacier ice is called firne ice, whereby this transformation process ( metamorphosis ) is mainly caused by pressure.

Old snow

In colloquial and technical language, different forms of old snow and harsh are referred to as firn :

  • Old snow fields ( firn fields ), even if the snow is not yet a year old
  • the newer snow cover of a glacier ( overfirnter glacier)
  • the superficial, soft layer of snow that forms in spring through sunlight and high air temperatures on a harsh surface ( frozen the night before ) (a slope fires up ; in Switzerland this is referred to as Sulz , while Sulz in Germany is usually a thicker, heavy one and consistently soft snow layer means)

Firn bump

The layers of firn on the glacier are constantly compressing to form ice. If the loose layers in between are preserved longer, they can suddenly z. Sometimes they break down over several kilometers, creating the characteristic, rustling, swelling natural sound of the inland ice that ends in a roaring clap of thunder .

See also

  • Firn mirror - a large, thin layer of ice on the snow surface with high reflectivity

literature

Web links

Individual evidence

  1. Ernst Sorge : By plane, folding boat and film camera in the ice fjords of Greenland. A report on the Universal Dr. Fanck Greenland Expedition. Three masks, Berlin 1933