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TitleLithalsa degradation, thermokarst distribution, and landscape evolution, North Slave region, Northwest Territories
AuthorMorse, P DORCID logo; Wolfe, S AORCID logo; Rudy, A C A
SourceNorthwest Territories Geological Survey, Yellowknife Geoscience Forum Abstract and Summary Volume 2019 p. 64
Alt SeriesNatural Resources Canada, Contribution Series 20200653
PublisherNorthwest Territories Geological Survey
File formatpdf
ProvinceNorthwest Territories
AreaNorth Slave Region
Subjectsenvironmental geology; Nature and Environment; Science and Technology; thermokarst; landscape types
ProgramClimate Change Geoscience Permafrost
Released2019 01 01
AbstractThe Great Slave Lowland and Great Slave Upland ecoregions of the subarctic Canadian Shield are influenced by permafrost that has developed in a time transgressive manner throughout the Holocene with lake-level recession. Thermokarst in the region is commonly associated with the degradation of ice-cored mounds (lithalsas), which are numerous. Here we use site descriptions and air photos to document the distinct geomorphic signatures associated with degrading lithalsas and develop a conceptual model for lithalsa degradation, which builds upon an earlier model of lithalsa formation. Two main processes dominate lithalsa degradation: (i) subsidence indicated by ponded water with partially submerged standing dead trees, and (ii) colluviation of thawed sediments toward the lithalsa margin that results in a rampart. Applying these diagnostic criteria to satellite image analysis, we found that lithalsas were once more widespread at higher elevations (Great Slave Upland), but the majority have degraded. The results suggest that lithalsas have been vulnerable to thaw throughout the Holocene, and explain, in part, the reduction of lithalsa abundance with increasing elevation. The conceptual model suggests that soil hysteresis effects would likely prevent re-initiation of lithalsa formation if permafrost were to re-aggrade in the future. Finally, high counts of intact lithalsas, degraded lithalsas, and thermokarst ponds within 15 m elevation of the Great Slave Lake shoreline indicate that this terrain is the most sensitive to climate warming and should be avoided by new infrastructure development.
Summary(Plain Language Summary, not published)
Permafrost is ground that stays frozen for more than 2 years. It often has ice in it, and when ice-rich permafrost thaws, the ground sinks ("thermokarst"). Under the GSC's climate Change Geoscience Program, this study aims to identify the indicators of thermokarst in the study region, and use these indicators to map out where ice-rich permafrost has thawed in the past. The results were compared to a map of ice-rich permafrost to identify the parts of the study region that are most sensitive to thaw and should be avoided by new infrastructure development.

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