Recent Intensification (2004-2020) of Permafrost Mass-Wasting in the Central Mackenzie Valley Foothills Is a Legacy of Past Forest Fire Disturbances

The effects of recent climate change are accelerating permafrost thaw, including ice-rich landscapes of the western Canadian Arctic. However, regional drivers of permafrost slope failure in hillslopes with warm, thin permafrost remain poorly understood. Repeat satellite imagery (1984-2020) indicates rapid increases in retrogressive thaw slumps (RTSs) and deep-seated permafrost landslides (DSPLs) since 2004, indicating a change in slope stability thresholds in an area that otherwise appeared thaw stable. The widespread occurrence of DSPL represents a contrasting geomorphic response to the RTS-dominated ice-rich permafrost landscapes. In this study area, RTS and DSPL occur predominantly in areas that were burned by forest fires in the 1990s, indicating a legacy thermal disturbance that preconditioned permafrost hillslopes for failure. The relations between historic fires and the later development of widespread permafrost slope failures represent an outstanding example of the complex interactions between inherited landscape sensitivity in ice-rich terrain and ongoing climate change.