Permafrost thaw-related slope failures in Alaska’s Arctic National Parks, c. 1980–2019

Abstract

Active-layer detachments (ALD) and retrogressive thaw slumps (RTS) are landslides that occur as a result of thaw in permafrost regions. I mapped the extent of bare soil exposed in these thaw-related slope failures in four study areas with continuous permafrost in Alaska’s Arctic National Parks, on mosaics of aerial photographs from 1977–1985 (sampling episode 1), satellite images from 2006–2009 (sampling episode 2), and satellite images from 2018–2019 (sampling episode 3). In all four study areas the count of ALD and RTS, and the area of bare soil they exposed, was greater during the first or second sampling episode than the third sampling episode, in spite of record high mean annual temperatures in 2014–2019. One study area had frozen debris lobes (FDL) in addition to ALD and RTS. In that study area the bare ground exposed by destabilization and rapid movement of FDL was greatest in the third sampling episode, probably as a result of deep thaw and talik formation. The destabilization of FDL in episode 3 was probably a long-term consequence of warming and permafrost loss, while the observed pulses of ALD and RTS in episodes 1 and 2 were closely tied to short-term deep thaw events in areas where the underlying permafrost remained stable.