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Firn (; from

Swiss German Swiss German (Standard German: , gsw, Schwiizerdütsch, Schwyzerdütsch, Schwiizertüütsch, Schwizertitsch Mundart,Because of the many different dialects, and because there is no defined orthography for any of them, many different spelling ...

"last year's", cognate with ''before'') is partially compacted

névé Névé is a young, granular type of snow which has been partially melted, refrozen and compacted, yet precedes the form of ice. This type of snow is associated with glacier formation through the process of ''nivation''. Névé that survives a ...

, a type of

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet ...

that has been left over from past seasons and has been recrystallized into a substance denser than névé. It is

ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...

that is at an intermediate stage between snow and glacial ice. Firn has the appearance of wet sugar, but has a hardness that makes it extremely resistant to shovelling. Its density generally ranges from 0.35 g/cm³ to 0.9 g/cm³, and it can often be found underneath the snow that accumulates at the head of a

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...

Snowflake A snowflake is a single ice crystal that has achieved a sufficient size, and may have amalgamated with others, which falls through the Earth's atmosphere as snow.Knight, C.; Knight, N. (1973). Snow crystals. Scientific American, vol. 228, no. ...

s are compressed under the weight of the overlying

snowpack Snowpack forms from layers of snow that accumulate in geographic regions and high elevations where the climate includes cold weather for extended periods during the year. Snowpacks are an important water resource that feed streams and rivers as th ...

. Individual

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macr ...

s near the melting point are semiliquid and slick, allowing them to glide along other crystal planes and to fill in the spaces between them, increasing the ice's density. Where the crystals touch they bond together, squeezing the air between them to the surface or into bubbles. In the summer months, the crystal metamorphosis can occur more rapidly because of water percolation between the crystals. By summer's end, the result is firn. The minimum altitude that firn accumulates on a glacier is called the ''firn limit'', ''firn line'' or ''snowline''.

List of firns

Antarctic Firn The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...

* Daniel Bruun Firn * Dreyer Firn * East Northwall Firn * Rink Firn * Sven Hedin Firn''Sven Hedin Firn'',

Army Map Service The Army Map Service (AMS) was the military cartographic agency of the United States Department of Defense from 1941 to 1968, subordinated to the United States Army Corps of Engineers. On September 1, 1968, the AMS was redesignated the U.S. Arm ...

United States Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

, Greenland 1:250,000 * West Northwall Firn

Other uses

In colloquial and technical language, 'firn' is used to describe certain forms of old snow or harsch: * Old snowfields or

(''Firnfelder''), even if the snow is not yet one year old * the more recent snow layers of a glacier (a 'firned' glacier) * the uppermost, soft layer of snow that is frozen overnight and, as a result of spring sunshine and high air temperatures, forms on an area of old snow or '' harsch'' (a slope ''firns up''; in Switzerland called ''Sulz'', but this term in Germany refers to a certain depth at which skiing downhill is no longer enjoyable)

References

Sources

* * * * {{Ice Glaciology Water ice Montane ecology Mountaineering Snow