NWT RESEARCH DATABASE

Regions: Sahtu Settlement Area

Tags: permafrost, Mackenzie Valley , Natural Hazards

Objective(s): To characterize a large suite of retrogressive thaw slumps and thaw-induced landslides in the basins that have initiated largely in the last decade; and, to characterize ground ice properties and permafrost conditions in the central Mackenzie Valley corridor.

Project Description: This licence has been issued for the scientific research application No. 5935. This work builds on studies over the last several years, including field work in the Mackenzie River valley in 2018 and 2019. The objective of 2021 fieldwork is twofold: 1) characterizing a large suite of retrogressive thaw slumps and thaw-induced landslides in the Redstone, Keele, and Johnson River basins that have initiated largely in the last decade, and 2) characterizing ground ice properties and permafrost conditions in the central Mackenzie Valley corridor. In 2019, the research team observed more than 400 active layer detachment slides, retrogressive thaw slumps, and thaw-induced landslides in the upper Keele and Redstone River areas. These represent the most southern concentration of widespread permafrost slope failure in the western Arctic. The research team have since mapped these mass-wasting features using European Space Agency supported satellite imagery and established that most of these slides (~75%) have initiated in the last 15 years. Additionally, the patterns of accelerated mass-wasting are well-constrained by extents of forest fire activity from the mid to late 1990s. The close association between historic fire and permafrost degradation suggests a legacy influence of thermal disturbance. The team have identified three of these features with debris deposits that have infilled valleys below the slides for up to 3 km, blocking river drainage and forming prominent lakes above the slide debris. The research team will test and measure the specific failure mechanisms of these large permafrost landslides, the degree of legacy fire disturbance on the permafrost table, if this is new form of permafrost-related slope failure, through installing ground temperature boreholes at each of these three slides (with Steve Kokelj and Ashley Rudy, GNWT), and carry out electrical resistivity tomography surveys to map the depth of permafrost along the margins and bases of the slides. These data should provide the necessary observations to test if these failures are being driven by failure at the base of permafrost. Further, cm-scale unmanned aerial vehicle (UAV) mapping (with Jurjen van der Sluijs, GNWT) of these features will be undertaken to map the evolution and failure dynamics of the permafrost landslides. The Mackenzie Valley corridor, poised for continued infrastructure expansion with the proposed Mackenzie Valley highway, includes an abundance of permafrost terrain with high potential for thaw subsidence in fine-grained glacial lake sediments that blanket the region. These areas are sensitive to ongoing and future climate change, but their distribution and properties are not well-anchored in a geologic model. An abundance of geotechnical data exists for the area, but of varying quality, and again lacking a geologic context making regional projections difficult. Over the last several years the team have been revising the Quaternary (Ice Age) geologic framework for the Mackenzie Valley, which includes a much earlier retreat of the last continental ice sheet (starting around 15 thousand years ago) from surface exposure dating. A substantial change is therefore suggested in the evolution of glacial Lake Mackenzie, which occupied the Mackenzie Valley during this time and deposited the aforementioned widespread lake sediments. The focus of this work is to investigate the geological record of glacial Lake Mackenzie in the central Mackenzie Valley and its association to ground ice abundance and permafrost thaw potential. The fieldwork strategy employs a targeted approach to verify and quantify ground ice and permafrost mechanics from remotely-sensed satellite mapping. Field activities are concerned with ground-truthing mapping observations through the collection of shallow permafrost cores, installation of ground temperature data, UAV mapping, and non-destructive geophysical survey methods. Permafrost cores up to 5m depth will be collected at sites exhibiting a high potential for ground ice and permafrost degradation using a lightweight, 2-person Talon Drill system. The uppermost soil profile will be set aside and used to cap the drill holes to mitigate surface disturbance. Cores up to 10 cm in diameter will be retrieved and shipped frozen to the Permafrost Archives Laboratory (U. Alberta) for characterization of physical properties (computed tomography ice contents and structures, radiocarbon dating and paleoenvironmental reconstructions). Ground temperature thermistors will be installed in select boreholes in the upper Keele and Redstone River basins to measure the continued effect of legacy forest fire disturbance on permafrost stability. These thermistors (see research locations) will be revisited in subsequent years to collect data with the assistance from the Northwest Territories Geological Survey. Electrical Resistivity Tomography (ERT) surveys will be undertaken at study sites to characterize the subsurface distribution and physical properties of permafrost and its potential for thaw. This is a non-invasive geophysical method that involves inducing an electrical current through a string of small electrodes at the surface and measuring the electrical resistivity at depth. Lastly, the use of hand-held UAVs for photographing select permafrost disturbances in the upper Keele and Redstone River watersheds will be undertaken by Jurjen van der Sluijs (GNWT). The research team have been in contact with the Sahtu Secretariat about joint research in the Mackenzie Valley highway right-of-way. In February 2020, Froese, following invitation by the Sahtu Secretariat Chair Charles McNeely, travelled and met with their board in Yellowknife, and presented an update on the research to date in the Sahtu region on the impacts of climate change on permafrost in their territory. The research team intend to directly inform Sahtu Secretariat from all works stemming from this research. Copies of all research materials resulting from this project will also be supplied to the Aurora Research Institute and to communities as Aurora thinks appropriate. The fieldwork for this study will be conducted from: August 22 - October 31, 2024