The Geomorphic Role of Snow∗

Snow is temporally and spatially at least as significant as glacial ice. It forms a geomorphic theme with characteristics of fundamental significance for the pattern of weathering and mass wasting in those regions supporting seasonal snow-cover. Contrasts between snowfall and rainfall regimes must be made in terms of geomorphically effective precipitation, and not in terms of gauge totals. In the absence of comprehensive magnitude and frequency process data, a framework of thresholds may be identified. One threshold is the possibility of snowfall, blowing snow and/or drifting snow corrasion at very low temperatures. A snowpack surface provides another threshold. Comparability between snowcreep forces and those of glacial flow establishes the geomorphic importance of snowcreep, in addition to that of avalanching. Several floristic and faunistic thresholds critical to mass wasting on vegetated debris slopes may be associated with snowpack distribution. Snow-pack presence, depth, duration, and meltwaters are critical controls on freeze-cycle weathering, as is meltwater distribution for chemical weathering. Snowpacks subdivide alpine and arctic tundra into a mosaic of microenvironments, each experiencing quite different geomorphic regimes. As snow accumulation is discontinuous, and oriented by the prevailing wintertime winds, any shift in prevailing wind direction may produce reorientation of the geomorphic processes and forms associated with snowpacks. Overall snow regimes appear to be optimized at high latitudes, as at high altitudes summertime processes associated with convection storms may be of equal importance geomorphically.