Nelson, Frederick E. Department of Geography and Planning, Rutgers University, New Brunswick, New Jersey.
Last reviewed:August 2019
- Ice content and surface features
- Engineering considerations
- Effects of climatic change
- Related Primary Literature
- Additional Reading
Perennially frozen ground. Two classes of frozen ground are generally distinguished: seasonally frozen ground, which freezes and thaws on an annual basis; and permafrost, which is formed when subsurface earth materials remain below 0°C (32°F) for more than a year, without regard to composition, phase, or cementation by ice. Permafrost occurs at most locations where the mean annual temperature at the ground surface is below freezing. Because substantial differences often exist between the temperature at the surface and that measured in the air, climate statistics do not provide a reliable guide to the existence or distribution of permafrost. Although permafrost is ultimately a climatically determined phenomenon, its presence or absence is strongly influenced by local factors, including microclimatic variations, circulation of ground water, type of vegetation cover, and thermal properties of subsurface materials.
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