永久冻土
永冻土（英语：permafrost)，又译永冻层、永冻土层或多年冻土）是一个地质学个名词，指当冻土层（frost soil）处于水个结冰点以下超过两年个状况。永冻层一般分布拉地下30~40公分处，通常又分为上下两层，上层夏季烊脱，下层仍处拉冰冻状态。
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