from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Granular, partially consolidated snow that has passed through one summer melt season but is not yet glacial ice. Also called old snow.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A type of old snow which has gone through multiple thaw and refreeze cycles and thus is made of numerous small icy grains, though it is not nearly as saturated with water as snow-cone slush is; can be hard or somewhat soft depending on recent and current weather conditions.
from The Century Dictionary and Cyclopedia
- n. A name given to snow accumulated in the highest parts of mountain ranges on which glaciers occur, while such snow is in a granular condition, and before, in its downward movement, it has been fully consolidated into ice.
The line that separates these two areas is called the firn limit or snow line.
Thus we must discriminate between two distinct parts of the ice fields; that is, first, the snow which originally fellcalled firn in Switzerlandabove the snow line, covering the slopes of the peaks as far as it can hang on to them, and filling up the upper wide kettle-shaped ends of the valleys forming widely extending fields of snow or firnmeere.
The glaciers that make up this alpine cryosphere are actually constantly moving "rivers of ice" that begin in their "accumulation zones" high on mountainsides, where snows fall and are compressed into "firn," the blue ice that gives glaciers their air of frozen purity.
Three or four awkward bits were circumvented; a couloir or gully full of snow mounted; and then there was a long climb up a moderate slope toward where a ridge of rocks stood out sharply, with snow sloping down on either side, the ridge running up far into the mountain; but before they could get to this a deep bed of old snow -- "firn" Melchior called it -- a great sheet, like some large white field, had to be passed.
The critiques of Jaworowski on the shift were addressed by Hans Oeschger 1995, who pointed out that the ice core record shift was done in accordance with theoretical estimates of the rate of diffusion in gases in firn, and that these theoretical estimates were confirmed by isotopic enrichment in line with theory.
Water is also stored in permanent snowfields and firn (compact, granular snow that is over one year old) fields, perched lakes (lakes that are raised above the local water table by permafrost), and as permafrost itself.
Accumulation then causes a further increase in density, modifying the firn into glacier ice, as the lower layers of firn are compressed by the weight of the layers above.
When this process happens year after year, a number of layers of firn can accumulate.
If the névé survives the ablation that occurs during the summer months it is called firn.
This is incredibly difficult and a lot of effort is going in to characterising how gas behaves in the firn layer and the processes that occur during final closure and entrapment of gas into the ice.
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