Formation of refrozen snowpack layers and their role in slab avalanche release

[ 1] In a variety of snow climates, numerous slab avalanches release over crusts consisting of refrozen snow. Slab avalanches sometimes release in weak layers of faceted crystals that developed while underlying wet layers froze into crusts, often within a day. Weak layers of faceted crystals can also develop when less permeable and more conductive crusts alter the temperature and vapor pressure gradients. These processes create interfaces where differences in grain radii can contribute to weak bonding. In western Canada, layers of faceted crystals ( facet layers) on crusts are most common in early and late winter when thaws and rain are more frequent. Also, thin facet layers occur in spring when surface melting by solar radiation is common. Shear strength tests on facet layers show an initial strength loss during faceting followed by a slow strength increase. The spatial distribution of poorly bonded crusts can be interpreted from the interaction of terrain and meteorology that caused the antecedent wet layer.