Increases in permafrost mass-wasting driven by failure at the base of permafrost in the central Mackenzie Mountain Foothills
Online pre-recordedHillslope mass-wasting in the extensive discontinuous permafrost zone of the central Mackenzie Mountain foothills has significantly increased in frequency and magnitude in the past 15 years. The increase in thaw-driven mass-wasting is largely a function of increasing air and ground temperatures, precipitation, and legacy thermal disturbance from forest fire activity. In contrast to retrogressive thaw slumps, which initiate and develop from the progressive top-down and lateral thaw of permafrost, we identify an increasing frequency and magnitude of deep-seated translational permafrost landslides with failure planes at depths up to 15 meters below the active layer. We identify a suite of thaw-driven processes that involve basal permafrost sliding, thaw-driven fluidized flow, and continued scarp enlargement by retrogressive failure. Thaw-driven detachment of materials at depth produces the capacity to rapidly transport large amounts of frozen material downslope in a blocky manner, often resulting in individual disturbances covering 10s of hectares, and in some instances, damming river drainage. The downstream impacts of rapid large-scale thawing events in this discontinuous permafrost region are not sufficiently understood, but the sediment flux potential is comparable with “mega-slump” thermokarst disturbances. We employ high-resolution satellite and UAV imagery, along with repeat digital elevation models, geological observations, and electrical resistivity tomography surveys to infer that ‘bottom-up’ thaw from the base of the permafrost table is driving the initiation of these features. We present these observations, and put forward a conceptual framework outlining their setting and mechanism of failure at the base of permafrost. Further understanding of the setting and variability of permafrost mass-wasting has implications at all scales, not least of which involves assessing thaw-induced impacts to downstream aquatic systems.