Thermokarst refers to a pitted land surface that forms as permafrost melts.This typically occurs following removal of vegetation or physical disturbance that removes the active layer. The loss of these insulators facilitates heat transfer and ice meltout.

This example shows poorly planned highway construction on a Gelisol in Alaska. A large block of permafrost was melted by heat transferred from the road bed. This created a large cavity, resulting in the collapse of the highway and a very surprised driver.