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Zusammenfassung:
Retrogressive thaw slumps (RTS) are spectacular lateral thermokarst features occurring in ice-rich permafrost regions. They develop along streams or coastlines and expand inland to form landslide-like U-shaped scars exceeding a kilometer size in selected locations. These slumps are a major source of sediment, organic carbon and nutrients that have a large effect on the aquatic environment. The consequences of the occurrence of RTS, which have been shown to occur at increased frequencies in the Arctic are not well understood, mostly because they have only been studied over the past ten years. The impact of RTS sediment delivery on coastal ecosystems is even less known, even though RTS contribute quantities of sediment sometimes greater than coastal erosion itself. In this study, we present the results of a systemic multidisciplinary study attempting to understand the structure, the evolution and the fate of RTS on Herschel Island, Yukon Territory, in the southern Canadian Beaufort Sea. Herschel Island for the exceptionally ice-rich nature of the permafrost and the occurrence of multiple RTS. We use information stemming from cryostratigraphic sampling in the ice headwall of the RTS, from cores collected above the headwall and in the slump floor, from sediment and water samples collected in the slump outflow, from timelapse photography, from outflow channel discharge measurements and from geophysics (mostly Direct Current and Capacitive Coupled Resistivity) to describe the structure of the slump. We emphasize the role of ground ice distribution, sea water vicinity and sensible and radiative heat input in dictating the pace at which slump initiate, stabilize and re-activate. We compare this information to past knowledge on slumps to emphasize the transient nature of slump occurrence in the arctic coastal zone and the existence of ?pulses? of slump activity with potentially important impacts on the nearshore ecosystem.
