Guide to Geologic Hazards in Alaska

Thawing permafrost
Thawing of any soil, subsoil, or other surficial deposit, or even bedrock, occurring in the arctic, subarctic, and alpine regions at variable depth beneath the Earth's surface in which a temperature below freezing has existed continuously for a long time (from two years to tens of thousands of years) [Permafrost]. This definition is based exclusively on temperature, and disregards the texture, degree of compaction, water content, and lithologic character of the material. The thickness of permafrost ranges from over 1000 m in the north to 30 cm in the south; it underlies about one fifth of the world's land area. Syn: pergelisol, perennially frozen ground. (Neuendorf, K.K.E. and others, 2005)