Item: Dry-slab density and thickness during major storms
Title: Dry-slab density and thickness during major storms
Proceedings: Proceedings of the 1996 International Snow Science Workshop, Banff, Canada
Authors: Art Mears, 222 East Gothic Ave, Gunnison, CO 81230, USA, artmears@rmiLcom
Abstract: Observations of forest destruction throughout various snow climates suggest that design avalanches (=100-year return periods) usually result from fracture and release of thick, widespread slabs of new dry snow. Such avalanches usually travel the longest distances into runout zones and probably achieve the largest velocities and impact energies. Dry, new snow slab densities and thickness were estimated from analysis of sustained storms of several days duration at eleven sites in the United States. The sites chosen represent continental (Gothic, CO; Yule Creek, CO; Elkton, CO; Wolf Creek, CO) intermountain (Alta, UT; Jackson, WY) and maritime (Mammoth, CA; Alpine Meadows, CA; Paradise, WA; Stevens Pass, OR; Mt. Hood, OR) snow climates. The 18 storms selected for study were all characterized by a steady increase in snowpack depth through the storm period (e.g., accumulation exceeded settlement), were below freezing, and did not have rain associated with the storm. Data were collected at standard high-elevation snow study plots that represent starting zone conditions where wind effects were not important. Mean densities in the new snow layer were estimated by the relationship p = HW/DH where p = average density of the new snow layer, HW = the water equivalent during the storm, and DH = the snowpack depth increase during the storm. The following conclusions result from the storm analysis: (1) mean slab densities and thickness did not vary significantly from one snow climate to another; (2) average daily precipitation rates were greater within the maritime climates, (3) storms were colder and of longer duration in continental climates.
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Keywords: avalanche, design-avalanche, slab, densities, thickness
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