Permafrost Distribution, Zonation and Stability along the Eastern Ranges of the Cordillera of North America

Abstract

Considerable quantities of new data have become available recently regarding the nature and distribution of permafrost along the eastern ranges of the Cordillera. These are used to produce an elevation view of permafrost in the ranges north of the 35°N parallel. In the south, there is a zone of sporadic permafrost up to 1,000 m in vertical extent overlain by continuous permafrost. The zone of discontinuous permafrost (30-80 percent of the surface with permafrost) is only about 70 m in vertical extent. North of 54°N this changes, with discontinuous permafrost encroaching on the sporadic permafrost zone. The apparent permafrost boundaries differ from those of Brown (1967), Péwé (1983a) and Cheng Guodong (1983). Their work was based on considerably less data, and it is clear that the terrain factors of mean winter snow depth, local moisture and ground water conditions, the distribution of the different air masses and cold air drainage have considerable effect locally, causing undulations and abrupt changes in the lower limit of the permafrost boundaries to about 56°N. Farther north, the climatic factors become dominant. The lower boundaries are different for a different latitude in North America and China. Subdivision of the alpine permafrost into stable, metastable and unstable classes is useful in indicating the instability of alpine permafrost (Cheng Guodong, 1983) and shows that most of the permafrost found in mainland Canada and Alaska is unstable or metastable.

Key words: permafrost distribution, permafrost thermal stability, eastern Cordillera of North America, alpine permafrost, permafrost zonation