What is permafrost?
Permafrost is permanently frozen soil, a common feature of Polar
regions. There is an "active layer" at the surface of varying depth
which does melt during the summer when the temperature consistently
warms above freezing.
Permafrost is often rich in organic matter due to the slow rate
at which it decomposes in these climates. It also causes problems
for humans who try to build on it, who find that the ground that
supports their structures can shift dramatically underneath them as
the permafrost melts due to the heat generated by the buildings as
well as the warming Arctic.