Landforms and degradation pattern of the Batagay thaw slump, Northeastern Siberia

Thaw slumps are clear indicators of rapid permafrost degradation. They form preferentially in near-surface ice -rich permafrost of northern high latitudes after initial thermal disturbance by the subsequent interplay of thermal (thawing of frozen deposits and melting of ice) and mechanical (slumping and erosion) processes. The largest known thaw slump on Earth - the Batagay megaslump - has been identified in sloping terrain on the Yana Upland in northern Yakutia. Its initiation began in the 1980s, with a current area of >0.8 km2. It continues to grow and has headwall retreat rates of up to 15 m per year. While various satellite remote sensing studies of the Batagay thaw slump have been undertaken, on-site studies characterizing internal landforms, terrain changes, and geomorphic processes have not yet been conducted. To fill this knowledge gap and to enhance our under-standing of the dynamics of very large thaw slumps, our study employs on-site observations and detailed permafrost sampling combined with unoccupied aerial vehicle data from 2019. The latter were used to generate an orthomosaic, a digital surface model, hypsometric slope profiles and a map of relief types in the thaw slump. Within the Batagay thaw slump, the dynamic relationship between headwall morphology and slump floor is largely determined by the cryolithological structure of the permafrost horizons exposed across the headwall rising up to 55 m above the slump floor. Factors include the thickness and overall high volumetric ground-ice content (up to 87 %) of the cryostratigraphic horizons. Furthermore, the diurnal and seasonal insolation expo-sure of the headwall perimeter superimposes both thermal denudation activity and meltwater transport of eroded material. Thus, recent degradation patterns are linked to permafrost properties. Therefore, the Batagay thaw slump is not only a window into Earth's past as it reveals ancient permafrost, but its modern dynamics highlight that ongoing rapid permafrost thaw under present Arctic warming is directly influenced by its Quaternary geological and permafrost history.