permafrost

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permafrost

permanently frozen ground on which only a thin layer thaws in the summer, as in the high Arctic and Antarctic.
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There are several types of permafrost: continuous permafrost, where the average yearly temperature is below 23[degrees]F (-5[degrees]C), discontinuous permafrost, where it is between 23[degrees]F and 28[degrees]F (-5[degrees]C and -2[degrees]C), and sporadic permafrost, if it is always above 28[degrees]F (-2[degrees]C).
Internal drainage through taliks connecting newly thawed zones under some large thaw lakes has recently been advanced to explain the reduction in lake surface area in the discontinuous and sporadic permafrost zones of Alaska (Yoshikawa and Hinz-man, 2003).