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TitleLithalsa formation and Holocene lake-level recession, Great Slave Lowland, Northwest Territories
AuthorWolfe, S AORCID logo; Morse, P DORCID logo
SourcePermafrost and Periglacial Processes vol. 28, issue 3, 2016 p. 573-579,
Alt SeriesEarth Sciences Sector, Contribution Series 20150479
Mediapaper; on-line; digital
File formatpdf; html
ProvinceNorthwest Territories
NTS85E; 85F; 85G; 85H; 85I; 85J; 85K; 85L; 85M; 85N; 85O; 85P; 75E; 75L; 75M
AreaGreat Slave Lake
Lat/Long WENS-120.0000 -110.0000 64.0000 61.0000
Subjectssurficial geology/geomorphology; geochemistry; hydrogeology; Nature and Environment; Science and Technology; permafrost; ground ice; lakes; cores; Great Slave Lowland; alluvial sediments; lithalsas; Phanerozoic; Cenozoic; Quaternary
Illustrationslocation maps; photographs; tables; plots; histograms
ProgramClimate Change Geoscience Land-based Infrastructure
Released2016 06 03
AbstractLithalsas (ice-cored permafrost mounds) are common within silty-clay sediments of the Great Slave Lowland, a low-relief bedrock plain extending to about 50 m above Great Slave Lake, N.W.T. Following retreat of the Laurentide Ice Sheet, sediment deposition in the lowland accompanied inundation by Glacial Lake McConnell between about 12 700 and 9300 cal BP, and continued subsequently in ancestral Great Slave Lake. Lake-level recession has occurred locally at about 5 mm/a for the last 8000 years, due primarily to isostatic rebound. Maximum-limiting ages of permafrost and lithalsas in the lowland are elevation-dependent, being least near the modern shoreline and greater at higher elevations. Many lithalsas, which are up to 8 m high and several hundred metres wide, are less than 3000 years old. They are abundant in alluvium of the Yellowknife River deposited within the last 2000 years, with permafrost aggradation and lithalsa formation continuing in historical time.
Summary(Plain Language Summary, not published)
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 from 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) 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 probably developed as permafrost aggraded into saturated sediments, and ground ice has formed within the last 250 years.

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