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Show The importance of graupel ( Figure le) to soft slab formation has long been noted. At times a shallow layer of coarse graupel deposited at relatively low temperatures ( under - 6° C.) may occur as cohesionless pellets which offer poor anchorage to subsequent snowfalls and thus serve as the lubricating layer of a soft slab avalanche. More commonly, graupel forms a dense, cohesive slab layer. When such a layer reaches 20 to 30 cm in thickness, dangerous avalanches are common. The high density of newly- deposited graupel ( up to 0.25 g cm" 3) in relation to its relatively low tensile strength causes readily- fractured soft slabs. Probably just as important is the high viscosity associated with effective grain sizes up to 8- 10 mm, for this would inhibit stress relaxation. The type of new- fallen snow loosely described as " granular" also contributes to soft slab formation. Stabilizing loose- snow sluffs are rare. Deposited new snow density tends to be above 0.10 g cm" 3. Layers more than 25- 30 cm thick have a notable tendency to avalanche if deposited in the presence of wind. Microscopic examination of this snow type shows it to consist of small crystals or fragments or large ones, all heavily rimed but lacking the dense structure of large graupel pellets ( Figure Id). Soft slab layers built up from strongly rimed but still recognizably stellar crystals ( Figure 1c) retain some of the avalanching characteristics of those formed from graupel or " granular" snow. Under favorable circumstances ( adequate wind, precipitation intensity, and new snow depth), large soft slab avalanches may be released. Tension cracks originate readily in mechanically disturbed slab layers of such snow, although they |