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HOLOCENE LAKE-LEVEL RECESSION, PERMAFROST AGGRADATION AND LITHALSA FORMATION IN THE YELLOWKNIFE AREA, GREAT SLAVE LOWLAND
Session: John Ross MacKay Symposium - Permafrost II / Symposium John Ross MacKay - Pergélisol II
Stephen Wolfe, Geological Survey of Canada, Natural Resources Canada (Canada)
Peter Morse, Geological Survey of Canada, Natural Resources Canada (Canada)
The Great Slave Lowland occupies the north shore of Great Slave Lake. After glaciation, it was inundated by Glacial Lake McConnell and ancestral Great Slave Lake. Holocene lake-level recession around Yellowknife is determined from accelerator mass spectrometer ages of peat and detrital organics. In the last 8000 years, recession occurred at about 5 mm/year, and permafrost is youngest near the modern shoreline and older at higher elevations. Silty-clay sediments are abundant, and lithalsas (ice-rich permafrost mounds within mineral soils) occurring within 40 m above the present lake level are less than 6000 years old. They are common on Yellowknife River alluvium deposited within the last 3000 years. Lithalsas on this surface are assumed to have developed as permafrost aggraded into saturated sediments, and ground ice has formed within the last 250 years.
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