ABSTRACT

Permafrost is defined as ground that remains below 0°C for more than two years. It includes dry rock and soil, as well as all icy substrates including rock glaciers, but excluding true, icy glaciers. Dry permafrost (0°C) is currently only known from Antarctica. There is always a maximum concentration of ice in the sediments immediately below the permafrost table, and the ice content usually decreases with depth. In North America, the unfrozen material below the permafrost base is sometimes referred to as the sub-permafrost talik. The joints in the bedrock complicate measuring the thickness of the active layer in massive bedrock and also provide temperature anomalies in deciding the actual depth of the permafrost table. The difference between the pereletok and relatively "young" permafrost is based on the typical thermal mode for a region and the frequency of their appearance.