Avalanche-derived rock glaciers in Svalbard

Visual year-round observations have shown that snow avalanches are driving the formation of rock glaciers near the glacier Larsbreen in central Svalbard. Here, avalanches are important suppliers of fresh rock debris, but they also represent the means by which ice is added to the rock glacier interior. During the winter, 1-5 m avalanche snow containing rock debris accumulates, ablating during the following summer, but a gradually accumulating surface layer of released rock debris increasingly reduces the ablation rate. Refreezing of percolating surface water during the ablation season enhances the metamorphosis from avalanche snow into solid ice, assisted by low permafrost temperatures below the avalanche snow. At the end of each summer, a 0-100 cm thick layer consisting of remnant avalanche snow covered by a surface debris layer has been added to the rock glacier permafrost body along the initiation line. Depending upon thickness, slope, relative ice content and temperature, deformation of such thickening layered avalanche deposits eventually leads to the formation of a rock glacier in the run-out zones of snow avalanches in permafrost regions. Avalanche-nourished rock glaciers are expected to exhibit a regional downwind preferred orientation. Copyright (C) 2007 John Wiley & Sons, Ltd.