From AMS Glossary
- (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 -5°C (23°F).
see active layer.
- As limited in application by P. F. Svetsov, soil that is known to have been frozen for at least a century.
Muller, S. W. 1947. Permafrost, or Permanently Frozen Ground, and Related Engineering Problems.
Hare, F. K. 1951. Compendium of Meteorology. p. 958, and map, p. 956.