Earth Observation-based Time Series Analysis of Retrogressive Thaw Slump Dynamics in the Russian High Arctic

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While temperatures are rising globally, they are rising more than twice as fast in the Arctic. Landscapes underlain by permafrost are especially vulnerable to this changing climate and experience increased thaw and degradation. The proceeding warming of organic-rich frozen ground is a highly relevant driver of carbon release into the atmosphere. Retrogressive Thaw Slumps (RTSs) are dynamic thermokarst features which develop when ice-rich permafrost thaws and thus are important indices when it comes to the assessment of potential carbon sources in permafrost landscapes. Thousands of RTSs have been inventoried in northwestern Canada. These inventories showed that thaw slumping modifies terrain morphology and alters the discharge into aquatic systems resulting amongst others in infrastructure instabilities and ecosystem changes. Furthermore, recent studies project that abrupt thermokarst processes contribute significant amounts of greenhouse gas emissions. As observed in most arctic regions, RTS activity has increased in the Russian High Arctic, however, little research has been done on RTSs in this region. The objective of this study is to better understand growth pattern and development rates of RTSs in northern Russia during the last decade. The study area consists of five different sites in the Russian High Arctic covering an area of more than 600 km². The sites are located on the Novaya Zemlya Archipelago, Kolguev Island, Bol’shoy Lyakhovsky Island and Taymyr Peninsula in ice-rich permafrost characterized by either buried glacial ice deposits or syngenetically formed Yedoma permafrost. To assess changes in number and extent, a GIS based inventory of manually mapped RTSs was created. The inventory is based on multispectral imagery of high-resolution satellite sensors, including PlanetScope, RapidEye, Pléiades and SPOT. Cloud free images were acquired between 2011 and 2020 and exist for each or every few years depending on their availability. Additional data sets such as ArcticDEM, Esri Satellite base map and Tasseled Cap Landsat Trends were used to support the mapping process. From the extracted individual RTS objects, changes in number and surface area were calculated. Furthermore, for coastal slumps thermal denudation and thermal abrasion rates were computed. The results show that RTS activity was high at the study sites during the investigation period and that the diverse sites revealed different RTS characteristics, with non-coastal RTSs showing a much larger increase in area. At the non-coastal sites, RTS-affected area increased by a factor of 2 (100 %) in West Taymyr, a factor of 4 (400 %) in Novaya Zemlya, and a factor of 33 (3300 %) in East Taymyr, with particularly large increases in more recent years. At the coastal sites, total RTS area increased by a factor of 1.2 (20%) in North Kolguev, remained the same in South Kolguev, and decreased slightly by a factor of 0.95 (5%) in Bol’shoy Lyakhovsky. Headwall and base of the coastal slumps retreated at different rates. However, at all coastal sites, erosion of the headwall and base progressed, demonstrating that RTS activity cannot be determined by area changes alone because coastal RTSs are strongly influenced by thermal abrasion and thermal denudation which diminishes areal changes. Moreover, the number of RTS did not necessarily increase with increasing RTS activity. At all study sites except East Taymyr, increased RTS activity resulted from RTS growth rather than new RTS initiation. In addition, climate analysis revealed that the mean temperature increased significantly, within the last decade at all sites, potentially favouring RTS initiation and growth. The findings of this study contribute substantially to our understanding of regional permafrost thaw in the Russian High Arctic. Nevertheless, further research is needed to quantify volumetric permafrost loss and associated carbon release comprehensively throughout the Russian High Arctic to better understand RTS dynamics and their impact on greenhouse gas release.

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Barth, S. (2022): Earth Observation-based Time Series Analysis of Retrogressive Thaw Slump Dynamics in the Russian High Arctic , Master thesis, Universität Potsdam.

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