Retrogressive Thaw Slump Morphology and Dynamics in Saline Permafrost in Northeast Greenland

Abstract Saline permafrost occupies a significant portion of permafrost in the Northern Hemisphere and extends several kilometers inland from the present Arctic coastline. However, its thermal conditions, mechanical degradation and geomorphological impacts are poorly understood. We aim to understand the impacts of saline permafrost on retrogressive thaw slump (RTS) evolution, especially when unfrozen highly saline pockets that persist at subzero temperatures, known as cryopegs, are present. In August 2022, we investigated two RTSs near the Zackenberg Research Station in Northeast Greenland. We combined electrical resistivity tomography, laboratory temperature‐resistivity calibrations, stratigraphic records of exposures and cores, in situ temperature measurements and laboratory analysis of soil properties such as salt content. Our results indicate that the main trigger of RTS development is the exposure of massive ground ice exposed by riverbank erosion during a flood event in 2016. The two RTSs remained highly active between 2016 and 2020, with an overall maximum extent of almost 2,000 m 2 total in 2022. Through geophysical and laboratory data, we prove the existence of cryopegs within marine sediments and hypothesize that they slow down RTS retreat when they become dry. Our results suggest that the evolution of RTSs in saline permafrost is influenced by cryopegs and sensitive fine‐grained sediments. We hypothesize that the cryopegs and the massive ice exposed before RTS initiation and within the headwall extend further beneath the station, making it prone to subsidence and further thaw‐related hazards.