Thermokarst - (n.)

a range of features formed in areas of low relief in the tundra when permafrost with excess ice thaws. Thermokarst terrain is made of irregular depressions and include features such as mud flows on sloping ground and other forms of thaw settlement that account for many of the engineering problems found in tundra landscapes. Global warming may result in irregular melting of the permafrost, resulting in an increase in this terrain. See also “permafrost.”