ALBERT

Description: Destruction of arctic permafrost coasts occurs as a result of a complex suite of processes, predominantly thermal abrasion and denudation. Activation of these processes can be particularly observed in case of massive ground ice bodies (ice wedges or tabular ground ice) that become exposed on high bluffs along the coastline. Tabular ground ice is a widespread geological feature on Arctic plains. Thermo-denudation of exposed ground ice includes ice ablation, thaw of enclosed frozen deposits and the development of retrogressive thaw slumps with thermo-cirques or thermo-terraces formation. Due to its high self-enforcing process intensity thermodenudation can be referred to as one of the most hazardous processes of permafrost degradation. We are study the current coastal destruction dynamics in the western (Kolguev Island) and eastern-most (Novaya Sibir’ Island) occurrence of tabular ground ice in the Eurasian Arctic. With higher temporal resolution, studies on Kolguev Island continue earlier research efforts on coastal dynamics, while thaw slumps on Novaya Sibir’ still require a quantitative assessment of their erosion dynamics. Coastal dynamics are analyzed using a whole set of multi-temporal satellite images of high and very-high spatial resolution (GeoEye, WorldView, Alos Prism, SPOT, Formosat, and Kompsat). For orthorectification purposes, the 12 m TanDEM-X DEM has been used. However, since the TanDEM-X DEM is based on averaged bistatic SAR surveys acquired during the period 2010 – 2012. This DEM can be used only for orthorectification of images newer than 2012 to determine the exact position of the coastal bluffs and thermocirque edges. We therefore reconstructed the relief along erosive coastline segments by modifying the initial TanDEM-X DEM through extrapolation of coastal bluffs edge elevation values and restoration of the coastal plain relief at 200 – 300 m towards the sea for orthorectification of images prior to 2012. All raw images were terrain-corrected and georeferenced using a comprehensive block adjustment, resulting in a very high absolute and relative accuracy of all images. On western part of Kolguev Island coastal retreat rates during the 2002 – 2012 period varied from 1.7 to 2.4 m/year. Thermo-cirque growth averaged rates were 2.6 m/year, maximum 14.5 – 15.1 m/year. We are about to extend our observations to more recent high resolution acquisitions. We are currently processing new data on the Novaya Sibir’ Island, where tabular ground ice exposures occur in the northern part of the island in the Mira Bay. This study is carried out in the same way as on the Kolguev Island and will allow to detect commonalities and differences in two contrasting environmental settings with “warm” and very cold permafrost.

Description: Kolguev Island is the most western point in the Russian Arctic with tabular ground ice occurrence. Since the Barents Sea is characterized by strong sea ice decline, it is very interesting to study coastal dynamics in conjunction with cryogenic processes in this region. Ice exposures on coastal bluffs favor the activation of thermal abrasion and thermal denudation. Headwall retreat of retrogressive thaw slumps causes not only thermocirque formation, but also leads to increasing coastal destruction rates. This study on Kolguev Island continues and expands our earlier research efforts on coastal dynamics in the region. As a result of field and remote sensing data analysis, coastline classification and segmentation were done according to the morphodynamics principle. The following types are defined: 1) thermo-abrasion wave exposed cliffs, 2) abrasion (thermo-abrasion) with stabilized cliffs, bordered by beaches or accumulative terraces, 3) sheltered abrasion (thermo-abrasion) cliffs, 4) accumulating coasts and accumulative forms, 5) accumulated coasts with sheltered tidal flats, 6) deltas. Thermo-abrasion cliff coasts are predominantly distributed in the west, north and northeast of the island, and accumulative shores in the south, southeast and east of the island. New data on thermal denudation and thermal abrasion rates for Kolguev Island have been obtained using a whole set of multi-temporal satellite images of high and very-high spatial resolution (GeoEye, WorldView, Alos Prism, SPOT, Formosat, RapidEye and Kompsat) covering the period from 2002 to 2017. For image orthorectification purposes, the 12 m TanDEM-X DEM has been used. However, since the TanDEM-X DEM is based on averaged bistatic SAR surveys acquired during the period 2010–2012. This DEM can be used only for orthorectification of images newer than 2012 to determine the exact coastal bluff position and thermocirque edges. We therefore reconstructed the relief along erosive coastline segments by modifying the initial TanDEM-X DEM through extrapolation of coastal bluff edge elevations and restoration of the coastal plain relief at 200–300 m towards the sea for orthorectification of images prior to 2012. All raw images were terrain-corrected and georeferenced using a comprehensive block adjustment, resulting in a very high absolute and relative accuracy of all images. On the western coast of Kolguev Island, average coastal bluff retreat rates between 2002 and 2012 varied from 1.7 to 2.4 m/year. Within key-sites that included three large thermocirques maximum headwall retreat rates were 1.9-15.1 m/year for 2002-2012 and 2.2-13.5 m/year for 2012-2017 yrs. In comparison, activation of thermo-denudation has been also noted along the Kara Sea coast where rates raised up to 13 m/year and were generally correlated with changing environmental factors, particularly expressed in an increase on the thaw index during recent years. Accumulative forms in the southern part of Kolguev Island are also being eroded. Thus, on Vostochnye Ploskie Koshki (on the south of the island), the retreat of formerly accumulative coasts from 2009 to 2016 in some areas amounted up to 62 m. This study was supported by RFBR grants № 18-05-60080 (coastal destruction rates estimation), 18-05-60221 (method of satellite images orthorectification, based on reconstructed DEM), ERC grant #338335 PETA-CARB, and German Academic Exchange Service (DAAD) with funds from BMBF and EU FP7, grant #605728.

Description: Tabular ground ice bodies are widely spread on Eurasian and North American Arctic plains. Exposed tabular ground ice in coastal bluffs favors the activation of thermal abrasion and thermal denudation, which in turn causes increasing coastal destruction rates. Thermo-denudation under conditions of ground ice exposures includes thawing of ice and frozen sediments along retreating headwalls of retrogressive thaw slumps and their constant enlargement. Thermo-cirques and thermo-terraces are two basic landform types that either feature channelized or broad open outlets, depending on the initial ice body outcrop by the denudation processes inland or in the retreating coastal bluffs. We study key-sites on Kolguev Island (Barents Sea) and on Yugorsky Peninsula (Kara Sea), continuing and extending earlier research efforts on coastal dynamics in the region. New data on thermo-denudation and thermo-abrasion rates for these key-sites have been obtained using a set of multi-temporal satellite images of high and very-high spatial resolution covering the period from 2002 to 2016. For orthorectification purposes of imagery collected prior to TanDEM-X acquisitions, we used an edited version of the 12 m TanDEM-X DEM. Along erosive coastline segments the former relief situation was reconstructed through extrapolation of coastal bluff edge elevation values and restoration of the coastal plain relief towards the sea. On the western coast of Kolguev Island, average coastal bluff retreat rates between 2002 and 2012 varied from 1.7 to 2.4 m/year, while averaged rates of thermo-cirques headwalls retreat were 2.6 m/year. Maximum rates at some sections increased up to 14.5-15.1 m/year in the recent past. High rates of thermo-denudation increase were not only observed on western Kolguev Island, but also on the Yugorsky Peninsula, were rates raised up to 13 m/year in recent years. Activation of thermo-denudation is also noted in other parts of Kara Sea coasts and were generally correlated with changing environmental factors, particularly expressed in an increase on the thaw index during recent years.