<p>Thermal denudation is a combination of the processes responsible for the formation of retrogressive thaw slumps (cryogenic earth flows) and thermocirques. Thermocirques are the depressions with a semi-circle shape resulting from tabular ground ice thaw. Environments characteristic of Сentral parts of Yamal and Gydan peninsulas forming the so called  Kara sub-latitudinal transect, are favorable to activation of thermal denudation. The key factors are continuous permafrost distribution and shallow occurrence of tabular ground ice.</p><p>An increase in ground temperature and active layer thickness in 2012-2013 cause the intensification of thermal denudation along Kara sub-latitudinal transect. Field studies in the area of “Vaskiny Dachi” research station as well as remote sensing of 2018 data demonstrates the presence of both active and stabilized thermocirques during.</p><p>This research presents preliminary results of collecting and analyzing the distribution of more than 400 landforms caused by thermal denudation identified in central Yamal and central Gydan peninsulas. Coastal thermodenudation landforms were not taken into account to exclude the influence of wave erosion in this study. Such work became possible due to free of charge satellite images with a very high spatial resolution available at the service Yandex.Maps (https://yandex.ru/maps/).</p><p>In Yamal peninsula, we identified 63 active and 53 stabilized thermodenudation landforms, in Gydan peninsula, 169 active and 166 stabilized, respectively. Active thermodenudation features concentrate in the western and southern parts of central Yamal, while stabilized dominate in western and central parts. In central Gydan both active and stabilized features of thermal denudation are located at northwestern part and are distributed more evenly compared to Yamal. Northern border of all identified thermodenudation features for both Yamal and Gydan peninsulas is located at 71 degrees North, and the southern border at 69 degrees North. Despite the difficulties of visual interpretation of thermal denudation features, we defined the majority of them as thermocirques, most of which are located along lake coastlines. Such indication was also confirmed by in-situ data collected during multiyear field campaigns in the study area. These results reveal a prevalence of thermal denudation features in the study area and the collected data gives us an opportunity for spatial analysis of their distribution.</p><p>The reported study was partially funded by RFBR according to the research project #18-05-60222 </p>

<p>Retrogressive thaw slumps (RTS, also referred to as thermocirques) are dynamic polycyclic landforms resulting from ground ice melting. Initiation of RTS causes organic carbon emissions into the atmosphere and hydrosphere, as well as changes in topography and vegetation. West Siberia's Arctic zone is characterized by continuous permafrost and the presence of tabular ground ice close to the surface. These factors result in widespread RTS occurrence over the region. Since the majority of RTS studies in West Siberia have been limited to fieldwork at a few key sites, there is still no understanding of true RTS distribution, as well as morphometric and topographical parameters in the region. Remote sensing approaches help gain more knowledge of RTS characteristics over vast areas. This research presents preliminary results of the actual morphometric characteristics of 97 lake-associated RTSs located on the Yamal and Gydan peninsulas. The area of each modern RTS that are possible to identify on Sentinel-2 satellite images taken in 2021 was obtained. Elevation profile for several transects over the digitized RTS were collected using ArcticDEM data. The largest RTS was found in the northern part of the Gydan peninsula with an area of 38 ha. The smallest identified RTS based on the 10 m spatial resolution of Sentinel-2 satellite images was located in central Yamal with an area of 6 ha. The median area was found to be 2,5 ha. Around 70% of RTS had elongated shapes along the coastline with a width larger than the length. This can be caused by either merging neighboring RTSs or by widthwise enlargement. Around 21% of the RTSs were found to have approximately equal width and length. And only 9% of RTS were found to expand inland with a width much less than length. According to our estimates, the average elevation of studied RTS edges was 26 meters above sea level. The smallest difference between the edge and front line heights of the RTS was evaluated at ~ 0,2 meters and the largest appeared to be ~ 5,6 meters. Data collected from the Yamal and Gydan peninsulas enable further analysis of the morphometric parameters of RTSs.</p> <p>This research was funded by the Russian Science Foundation, grant number № 22-27-00644.</p> <p> </p>

The Arctic zone of West Siberia (Yamal and Gydan peninsulas) is an area with continuous permafrost and tabular ground ice close to the surface, active thermodenudation, and related landforms: retrogressive thaw slumps (RTS); in Russian referred to as thermocirques (TC). The dimensions of most TCs have not been determined so far. We use Sentinel 2 imagery to measure each TC area ranging from 0.55 to 38 ha with a median of 2.5 ha. Around 95% of TCs have an area of less than 10 ha. The largest areas are gained due to the merging of several neighboring TCs. The ArcticDEM is used to determine TC edge elevation and slope angle. In general, the Median TC of the Yamal peninsula has an area of 1.8 ha, an elevation of the edge of 17.7 m, and a slope angle of 2.5°. The Median TC of the Gydan peninsula has an area of 2.6 ha, elevation of the edge of 29.4 m, and slope angle of 3°. TCs of the Gydan peninsula occupy higher positions and slightly steeper slopes compared to TCs of the Yamal peninsula. The ranges of the median and the largest TC areas are consistent with the reported RTS dimensions in North America.