Factors of thermal denudation activation and thermicirques activity on central Yamal in 2010–2018

The paper presents research findings of the climatic factors responsible for the activation of thermal denudation processes leading to the formation of thermocirques in the central part of the Yamal Peninsula in the north of West Siberia. Based on a comparison of multi-temporal remote sensing (2010, 2013 and 2018) coupled with climate data, an analysis of the thermocirques activity in 2010–2018 was carried out. Thermocirques are specific topographic forms that arise because of the activation of cryogenic earth flows, the formation of which is caused by an increased seasonal thawing of the upper part of the ground ice on the slopes as compared to the previous years. Analysis of the monitoring data showed that in 2012 and 2013 all the types of surfaces are characterized by a significant increase in seasonal thawing compared to the previous period 1993–2011 (12 % increase on slopes), due to the summer air temperature, the amount of summer precipitation and the increased duration of the warm period. The results of the thermocirques activity analysis are shown on a map. The results of this local study were compared with those of a regional (Yamal and Gydan Peninsulas) remote sensing study of thermocirques. This showed a higher accuracy of the local study based on field monitoring and very-high-resolution satellite imagery. The analysis of the thermocirques activity showed that 1) over the period from 2010 to 2018 thermal denudation activity in the study area increased due to the anomalous climatic conditions in the spring-summer season of 2012, and then gradually decreased; 2) in addition to “classical” thermocirques, which were at different stages of activity in the time periods analyzed (2010, 2013 and 2018), a significant number of embryonic thermocirques were identified. Such thermocirques, just as the majority of small “classical” thermocirques, can only be identified on very-high-resolution satellite imagery.