Thermokarst

Thermokarst is a type of terrain characterised by very irregular surfaces of marshy hollows and small hummocks formed when ice-rich permafrost thaws.

Small domes that form on the surface due to frost heaving with the onset of winter are only temporary features.

Some ice lenses grow and form larger surface hummocks ("pingos") which can last for many years, and sometimes become covered with grasses and sedges, until they begin to thaw.

These domed surfaces eventually collapse – either annually or after longer periods – and form depressions which become part of the uneven terrains included under the general category of thermokarst.

Continued thawing of the permafrost substrate can lead to the drainage and eventual disappearance of thermokarst lakes, leaving them, in such cases, a geomorphologically temporary phenomenon, formed in response to a warming climate.

[20] Oriented morphology of lakes can take on shapes such as "elliptical, egg-shaped, triangular, rectangular, clam-shaped, or D-shaped",[5] and commonly occur in terrain with sandy sediments.

Grosse et al. (2013)[5] summarize endogenous and exogenous elements that are key factors in orientation including: Before complete drainage, lake edges recede through retrogressive thaw slumps (RTS) and subaerial debris flows.

[5] Lakes stop growing once drainage is initiated, and eventually depressions are filled by sediments, aquatic plants or peat.