凍土 permafrost

Permafrost is any rock or soil material that has remained below 32° F (0° C) continuously for two or more years. The two-year minimum stipulation is meant to exclude from the definition the overlying ground surface layer that freezes every winter and thaws every summer (called the "active layer" or "seasonal frost").

http://www.global-greenhouse-warming.com/permafrost.html

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永凍土溶解與甲烷釋放是因為某些地區原是泥煤礦區（西伯利亞西部一片一萬多年前形成、面積約一百萬平方公里的永凍土，最近開始融化，變成佈滿泥沼和淺湖的破碎地形，有些泥沼和淺湖的直徑甚至超過一公里。）見自由時報94/8/12。