the formation of subsidence and collapse landforms and subsurface cavities because of the melting of underground ice or the thawing of frozen ground that, in turn, are the result of an increase in the annual average air temperature or in the range of variation of soil temperature.

Thermokarst is a phenomenon specific to the area of occurrence of permanently frozen rock. It results in the formation of typical landforms, such as lake basins, alasy, sinkholes, minor depressions (bliudtsa), and other negative topographic forms, and in collapse formations and cavities in the subsoil layer (grottoes, recesses, and pits). Thermokarst usually accompanies other processes, such as thermal contraction and gravity displacement of thawed rock; it may be combined with surface and subsoil wash, solifluction, suffosion, erosion, and abrasion. It also develops in regions of stable and even aggrading cryolithozone as a result of disturbances of the dynamic equilibrium in the water and the thermal regimes of the earth’s surface. It may also be caused by industrial and civil engineering construction, deforestation, and numerous other factors of human economic activity.

Among the measures for the prevention and control of thermokarst are (1) the protection of permanently frozen rock and subsurface ice from melting and thawing during the construction and operation of structures, (2) the thawing of frozen, ice-containing beddings before construction, and (3) drainage of areas.