RECENT DEVELOPMENT OF DEEP PERMAFROST LANDSLIDES (MOLARD-TYPE) IN DISCONTINUOUS PERMAFROST FROM THE CENTRAL MACKENZIE MOUNTAIN FOOTHILLS, NORTHWEST TERRITORIES, CANADA

Widespread permafrost warming in hillslope terrain increases the potential for thermokarst mass wasting. These disturbances can damage infrastructure, rapidly degrade aquatic environments, and pose direct and indirect risks to communities. Here, we use repeat satellite imagery to inventory over 280 landslides and retrogressive thaw slumps in the Extensive Discontinuous Permafrost Zone from the central Mackenzie Valley Foothills, NWT. These disturbances have largely initiated in the last 10-15 years and show a close correlation with historic forest fire extents from the 1990s. This association suggests a thermal legacy from fire activity as a primary preconditioning mechanism for these permafrost slope failures. In addition, we complement remote mapping with geological and cryostratigraphic site investigations, and high-resolution UAV imagery. This contribution focuses on three of the largest permafrost landslides in the study area. These three deep-seated landslides collapsed recently (2015-2018), on shallow to moderate slopes in areas of fine-grained diamicts, and range in size from approximately 0.6 km² to 2.5 km². Their debris tongues include the presence of meter-scale conical-shaped mounds, termed molards, which indicate the abrupt translocation of frozen blocks of slide material followed by its subsequent thaw into the distinctive mounds. These large-scale failures leave a distinctive geomorphic signature, associated with the molard-type mounds, but also depositing large volumes of material into downstream valleys forming distinct valley-fill deposits with the potential to dam rivers. The increase in these failures suggests an acceleration of this new form in response to climate warming, potentially from thaw at the base of the permafrost table. Further quantification of the parameters and mechanisms regulating the initiation of these landslides will improve our understanding of the severity to which permafrost hillslope landscapes will respond to increasing climatic and environmental stressors.