ABSTRACT
As noted in the introduction to Part 1, frozen soils include temporarily frozen soils (lasting hours, days), seasonally frozen soils (lasting months) and permafrost (persisting for at least two consecutive years, often hundreds and even thousands of years). Between these categories of frozen soils can be intermediate forms. For instance, seasonally frozen soils which do not melt during a given summer and persist for several years are called pereletok in Russia. The area of distribution of frozen soils is called the cryolithozone ( temporal, seasonal and perennial ). The depth of soil freezing depends on thermal and ground conditions and reaches from a few centimetres to hundreds of metres. Permafrost thickness increases with a decrease in the mean annual air temperature (MAAT). Areas of temporarily and seasonally frozen ground are usually continuous and extend downwards a short distance from the ground surface (centimetres to metres). Permafrost occurs within the upper layers of the ground, below the zone of seasonal freezing and thawing (the active layer).
