Firn

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title: "Firn" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["glaciology", "water-ice", "montane-ecology", "snow"] description: "Partially compacted névé" topic_path: "science/biology" source: "https://en.wikipedia.org/wiki/Firn" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Partially compacted névé ::

NOTOC ::figure[src="https://upload.wikimedia.org/wikipedia/commons/e/e9/Taku_glacier_firn_ice_sampling.png" caption="Sampling the surface of a glacier. There is increasingly dense firn between surface snow and blue glacier ice."] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/8/87/Firn_field_on_the_top_of_Säuleck.jpg" caption="Central Alps"] ::

Firn (; from Swiss German firn "last year's", cognate with before) is partially compacted névé, a type of snow that has been left over from past seasons and has been recrystallized into a substance denser than névé. It is ice that is at an intermediate stage between snow and glacial ice. and it can often be found underneath the snow that accumulates at the head of a glacier.

Snowflakes are compressed under the weight of the overlying snowpack. Individual crystals near the melting point are semiliquid and slick, allowing them to glide along other crystal planes and 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
• Daniel Bruun Firn
• Dreyer Firn
• East Northwall Firn
• Rink Firn
• Sven Hedin Firn
• West Northwall Firn

Other uses

In colloquial and technical language, "firn" is used to describe certain forms of old snow, including:

• old snowfields, known as Firnfelder (), even if the snow is not yet one year old
• the more recent snow layers of a temperate, or "firned", glacier
• used in skiing, the uppermost, soft layer of snow that is frozen overnight and, as a result of spring sunshine and high air temperatures, melts and reforms on an area of old snow or harsch (, referring to the snow's rough texture) As in the last context, a ski slope that experiences melting and refreezing into harsch is said to "firn up". In Switzerland, these slopes are called Sulz, but in Germany, Sulz more often refers to a depth at which skiing downhill is no longer enjoyable.

References

Sources

References

1. (3 May 2010). "The Physics of Glaciers". Elsevier.
2. (1 May 2008). "Depth and Density of the Antarctic Firn Layer". Arctic, Antarctic, and Alpine Research.
3. (1 December 2021). "Contemporary Characteristics of the Antarctic Firn Layer (1979-2020)". AGU Fall Meeting Abstracts.
4. "DanielBruun Firn". Mapcarta.
5. "Dreyer Firn". Mapcarta.
6. ''Sven Hedin Firn'', [[Army Map Service]], [[United States Army Corps of Engineers]], Greenland 1:250,000

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