• Permafrost
  • 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).

    2. 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.

Abstract from DBPedia
    In geology, permafrost is ground, including rock or (cryotic) soil, at or below the freezing point of water 0 °C (32 °F) for two or more years. Most permafrost is located in high latitudes (in and around the Arctic and Antarctic regions), but alpine permafrost may exist at high altitudes in much lower latitudes. Ground ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material. Permafrost accounts for 0.022% of total water on earth and exists in 24% of exposed land in the Northern Hemisphere. It also occurs subsea on the continental shelves of the continents surrounding the Arctic Ocean, portions of which were exposed during the last glacial period. A global temperature rise of 1.5 °C (2.7 °F) above current levels would be enough to start the thawing of permafrost in Siberia, according to one group of scientists.

    永久凍土(えいきゅうとうど)とは少なくとも2冬とその間の1夏を含めた期間より長い間連続して凍結した状態の土壌を指す。英語では、permafrost と表記するが、permanently frozen groundの省略語で1945年に S. W. MULLERによって使われた。


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