Thermokarst - online puzzles

Thermokarst is a land surface characterised by very irregular surfaces of marshy hollows and small hummocks formed as ice-rich permafrost thaws, that occurs in Arctic areas, and on a smaller scale in mountainous areas such as the Himalayas and the Swiss Alps. These pitted surfaces resemble those formed by solution in some karst areas of limestone, which is how they came to have karst attached to their name without the presence of any limestone. Small domes that form on the surface due to frost heaving with the onset of winter are only temporary features. They then collapse with the arrival of next summer 's thaw and leave a small surface depression. Some ice lenses grow and form larger surface hummocks, which last 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 contribute to uneven surfaces. These are included within the general label of thermokarst.

The Batagaika crater in Siberia is an example of a large thermokarst depression.

Thermokarst lakes

A thermokarst lake, also called a thaw lake, tundra lake, thaw depression, or tundra pond, refers to a body of freshwater, usually shallow, that is formed in a depression formed by thawing ice-rich permafrost. A key indicator of thermokarst lakes is the occurrence of excess ground ice as well as having an ice content with greater than 30% by volume.