Investigating Retrogressive Thaw Slumps in Saline Permafrost (East Greenland) using Electrical Resistivity Tomography

Retrogressive thaw slumps (RTS), a common type of thermokarst landslide in Arctic permafrost, have been increasing both in number and distribution in recent years. As RTS are characterized by their dynamic behaviour, a main controlling factor is the ice availability and the sediment properties. Most RTS described in previous studies occur within fine grained permafrost sediments, a multi-layered geological setting, as in this study, uncommon for RTS.

The study site is located near the Zackenberg Research in Northeast Greenland, within sediments deposited since the Last Glacial Maximum (LGM), including a salt-rich marine layer. In recent years, two RTS have developed on the eastern riverbank in a multi-facies geological setting. To investigate the RTS, the geological subsurface model, and the threat to the station, five quasi-3D profiles were measured using electrical resistivity tomography (ERT). The surveys were combined with stratigraphic analysis, core drilling and laboratory tests. To better delineate the extent of the marine layer, whose high salt content strongly affects the geophysical measurements, additional ERT calibrations were performed under laboratory conditions. The combined results highlight the significant influence of a saline marine silt on the geomorphology, permafrost state (unfrozen vs. frozen), and the behaviour of RTS.