Palsas and other Permafrost Features in the Lower Rock Creek Valley, West-Central Alberta

Abstract

Three types of permafrost feature occur in a nearly flat alluvial valley bottom in the Foothills of west-central Alberta. (1) Frozen mineral soil underlies wet sedge meadows and fluctuates in lateral extent from year to year. (2) A number of palsas with cores of mineral soil have developed in sedge/willow fens since 1952, and others seem to be actively forming. (3) Frozen soil exists in mounds under spruce trees on an abandoned and subsiding levee, but it appears to be a consequence rather than a cause of those landforms. A fortuitous combination of environmental features permits permafrost to exist in this site, as an outlier far south of the discontinuous permafrost zone. The valley bottom possesses the prerequisite saturated fine materials for ice segregation and palsa formation, and few floods occur to thaw or bury permafrost. Strong down-valley winds ensure little winter snow accumulation. There is little peat in the valley but local climatic factors maintain low temperatures in summer, especially at night, which limit thaw.