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| August 23, 2011 Sunrise 6:29 a.m. |
As snow accumulates its structure changes. Newly fallen snow is very light and porous,with a density from 50 to 300 kg/m³, but as the snow becomes buried by subsequent snowfalls the ice crystals that make up the snowflakes partially melt and sublimate, particularly at the delicate points of the flakes. The vapor then condenses, and over time the flakes change into granular ice crystals called firn, which has a density greater than 500 kg/m³.
As more time passes the firn becomes buried even deeper under more fresh snow and firn, and the weight above it compresses it into solid ice with a density of approximately 900 kg/m³. This is the typical 'blue' ice of glaciers.
The time needed to change snow in to glacial ice in this way depends on several factors such as how warm or cold it is and how much new snow is added each year. In fact, it can take anywhere from 5 years in an ideal site, to over 3000 years.”
