| definition
| - 1. (Also called perennially frozen ground, pergelisol, permanently frozen
ground.) A layer of soil or bedrock at a variable depth beneath the surface of
the earth in which the temperature has been below freezing continuously from a
few to several thousands of years. Permafrost exists where the summer heating
fails to descend to the base of the layer of frozen ground. A continuous
stratum of permafrost is found where the
annual mean temperature is below about 5C (23F). <p>2. As limited in
application by P. F. Svetsov, soil that is known to have been frozen for at
least a century. <p>
Muller, S. W., 1947: Permafrost, or Permanently Frozen Ground, and
Related Engineering Problems, <p>
Hare, F. K., 1951: Compendium of Meteorology, p. 958, and map, p.
956. (en)
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