Share on Facebook Share on Twitter Email
Answers.com

firn

 
Dictionary: firn   (fîrn) pronunciation
Home > Library > Literature & Language > Dictionary
n.
Granular, partially consolidated snow that has passed through one summer melt season but is not yet glacial ice. Also called old snow.

[German, from German dialectal, of last year, from Old High German firni, old.]


Search unanswered questions...

Enter a question here...
Search: All sources Community Q&A Reference topics

Geography Dictionary: firn
Top
Home > Library > Science > Geographical Dictionary

Ice formed when falls of snow fail to melt from one season to another. As further snow accumulates, its weight presses on earlier snow, compacting and melting it to a mass of globular particles of ice with interconnecting air spaces. Further snow fall, and further compaction, drives out the air spaces and turns the firn to pure ice. Where temperatures are around 0 °C, snow can turn to firn within five years. The process takes much longer in very cold conditions. An alternative term for firn is névé. The firn line is the line at which firn forms, and is close to the equilibrium line. This line varies with aspect; it is notable that former glaciers descended lower on the eastern than on the western slopes of Mount Ruwenzori, for example.

Wikipedia: Firn
Top
Home > Library > Miscellaneous > Wikipedia
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 (from German Firn with the same meaning, cognate with for) 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.

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.

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

Stub icon This glaciology article is a stub. You can help Wikipedia by expanding it.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

 
 

 

Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Geography Dictionary. A Dictionary of Geography. Copyright © Susan Mayhew 1992, 1997, 2004. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Firn".  Read more