Sampling the surface of a glacier. There is increasingly denser firn between surface snow and blue glacier ice.

Firn from South Cascade Glacier, 80x magnified.

Firn 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. Firn has the appearance of wet sugar, but has a hardness that makes it extremely resistant to shovelling. It generally has a density greater than 550 kg/m³ and is often found underneath the snow that accumulates at the head of a glacier. Image File history File links Taku_glacier_firn_ice_sampling. ... Image File history File links Taku_glacier_firn_ice_sampling. ... Image File history File linksMetadata Size of this preview: 538 × 600 pixel Image in higher resolution (1346 × 1500 pixel, file size: 530 KB, MIME type: image/jpeg) Firn from South Cascade Glacier Original source (6260 KB); Description site Credit: Erbe, Pooley: USDA, ARS, EMU File links The following pages on... Image File history File linksMetadata Size of this preview: 538 × 600 pixel Image in higher resolution (1346 × 1500 pixel, file size: 530 KB, MIME type: image/jpeg) Firn from South Cascade Glacier Original source (6260 KB); Description site Credit: Erbe, Pooley: USDA, ARS, EMU File links The following pages on... Névé is a young, granular type of snow which has been partially melted, refrozen and compacted. ... Animation of snowcover changing with the seasons Snow is precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. ... Insulin crystals Recrystallization is an essentially physical process that has meanings in chemistry, metallurgy and geology. ... Snowflakes by Wilson Bentley, 1902 Ice is the name given to any one of the 14 known solid phases of water. ... Animation of snowcover changing with the seasons Snow is precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. ... A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity and undergoes internal deformation. ...

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 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. Snowflakes by Wilson Bentley, 1902 A snowflake is an aggregate of ice crystals that forms while falling in and below a cloud. ... Quartz crystal Copper(II) sulfate and iodine crystal Synthetic bismuth crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid...

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.

References

• USGS Glossary of Selected Glacier and Related Terminology
• Fundamentals of Physical Geography