1 December, 2000
Snow and Ice
While digging several snow pits I have become acquainted with the nature of snow at Siple Dome. Currently, the snow surface is wind packed due to a recent windstorm and the lack of new snow. The texture of snow changes as you go deeper. The surface snow is composed of very fine crystals or grains. Farther down the snow has recrystalized into larger grains. A couple meters (6.5 ft) down, the snow has a consistency like coarse, crumbly styrofoam. The snow grains are surrounded by small, interconnected air spaces. As the snow grains increase in size so do these pores.
The first time I went out cross-country skiing, I was suddenly startled by the sound of collapsing snow beneath my feet. It wasn't a hidden crevasse but rather a "snowquake." The snow did collapse but only a couple centimeters. The collapse usually travels outward five to ten meters (16 to 33 feet). I've experienced many of these events while walking or skiing around camp but they always come as a surprise.
Snowquakes result from the collapse of a porous level of snow called a hoar layer. Hoar forms when a layer of snow differs in temperature from the adjacent snow or air. This results in very large snow grains separated by large air spaces. These layers have little strength leading to their collapse when stepped on.
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