ИСТИНА

Massive ground ice, includes polygonal-wedge ice, ice-core of pingos and tabular ground ice, are less common than structure-forming ice, but their influence on the surface dynamics is enormous, since their thawing leads to the activation of dangerous permafrost processes such as thermokarst, thermoerosion, complex of slope processes and so on. The dynamics and nature of changes in permafrost state under natural conditions (without anthropogenic impact) for a certain period of time can lead to activation of permafrost processes, making them dangerous and catastrophic in relation to already existing infrastructure facilities. Dangerous permafrost processes and phenomena are mainly due to the reaction of the upper layers to new formations (aggradation) or the degradation of permafrost as a result of changes in heat transfer conditions on the surface. The growth of annual sums of positive temperatures leads to the activation of thermal denudation in areas with subsurface ground ice occurrence. These processes lead to formation of vast thermokarst depressions, themocirques (or retrogressive thaw slumps) and erosion ravines. Over the past decades, due to the imposition of climatic fluctuations of different durations, the average air temperature in Western Siberia has increased by several tenths of a degree. Modern climate warming leads to an increase of permafrost temperature, and growth of active layer thickness. In Central Yamal, in recent years, an increase in the growth of themocirques has been observed, associated with the thawing of tabular ground ice. New themocirques appear, as well as a new cycle of activation appeared of previously stabilized forms. Studies of the dynamics of the coastal dynamics of Kolguev Island with tabular ground ice exposures show high retreat rates of themocirques in recent years (up to 15 m/year). High retreat rates are also revealed on the coasts of Yugorsky Peninsula. Supported by RFBR grants № 18-05-60080 (destruction rates estimation) and 18-05-60221 (methods of remote sensing data analyzes). https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/489856