Changing Permafrost Landscapes

Decadal-scale forest fire effects intensify recent thaw-driven mass-wasting in the central Mackenzie Mountain foothills, NWT

Tuesday, November 19, 2019 - 3:20pm to 3:40pm Theatre Three
(Student abstract)


J.M. Young (Presenting)
University of Alberta
A. Alvarez
University of Alberta
J. van der Sluijs
Northwest Territories Centre for Geomatics
A. McPhee
University of Alberta
B.J. Stoker
Charles University
S.V. Kokelj
Northwest Territories Geological Survey
M. Margold
Charles University
D. Froese
University of Alberta

Hillslope thermokarst mass-wasting encapsulates climate-driven geomorphic processes in glaciated terrains that have the potential to rapidly mobilize large amounts of thawed material into surrounding aquatic ecosystems.  We identify over 400 recent thermokarst mass-wasting features, including retrogressive thaw slumps, active layer detachments, and deeper-seated translational landslides within the upper Keele and Redstone River watersheds (~ 4000 km2) in the central Mackenzie Mountain foothills, NWT, Canada.  This area represents the southernmost concentration of widespread thaw slump related permafrost mass-wasting in northwestern Canada.  The surficial geology consists largely of morainal material up to 20 m thick in plateaued areas, with lacustrine, alluvial, and colluvial sediments typically accommodating lower river valleys.  Several thaw slumps that were visited display headwalls consisting of diamicts from the late Wisconsinan Laurentide Ice Sheet and include meter-scale ice lenses at their bases.  Investigation of satellite imagery (1993-present) shows most of these features have initiated and rapidly expanded in the last 10-15 years.  Increases in disturbance size and growth rate are consistent with regional increases in air and ground temperatures and summer precipitation during this timespan.  The largest retrogressive thaw slump documented initiated post-2005 and can be termed a ‘mega-slump’, with a headwall height of over 25 m and total disturbance area of ~ 25 ha.   Patterns of accelerated mass-wasting are well-constrained by the extents of forest fire activity from the mid to late 1990s.  The close association between historic fire and permafrost mass-wasting suggests a legacy influence of thermal disturbance from forest fires as a primary preconditioning mechanism for the initiation of these permafrost mass-wasting features.  Additionally, the acceleration of such disturbances is also associated with the translocation of large volumes of thawed sediment into underlying river valleys, exceeding river transport capacity and creating distinct valley-fill deposits.  Using ground-truthed satellite and unmanned aerial vehicle (UAV) mapping, in conjunction with novel lab-based permafrost characterization, we aim to provide a basis for evaluating climate-driven trajectories of comparable terrains throughout northern Canada.