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TitleLithalsa distribution, morphology and landscape associations in the Great Slave Lowland, Northwest Territories, Canada
AuthorWolfe, S AORCID logo; Stevens, C W; Oldenborger, GORCID logo; Gaanderse, A J
SourceCANQUA-CGRG Biannual Meeting, abstracts; 2013 p. 1
Alt SeriesEarth Sciences Sector, Contribution Series 20130151
PublisherUniversity of Alberta
MeetingCANQUA-CGRG Biannual Meeting; Edmonton; CA; August 18-22, 2013
Mediapaper; digital
File formatpdf (Adobe® Reader®)
ProvinceNorthwest Territories
NTS85J/07; 85J/08; 85J/09; 85J/10; 85J/11; 85J/12; 85J/13; 85J/14; 85J/15; 85J/16
AreaYellowknife; Great Slave Lake
Lat/Long WENS-116.1667 -114.2500 62.8833 62.2500
Subjectssurficial geology/geomorphology; environmental geology; geophysics; geochronology; Nature and Environment; Science and Technology; Holocene; permafrost; ground ice; sediments; organic deposits; peatlands; soils; periglacial features; frost heaving; talik; boreholes; geophysical logging; resistivity logging; electrical resistivity; radiometric dating; radiocarbon dating; morphology; surface waters; lakes; groundwater; vegetation; glacial history; water levels; isostatic rebound; climate; ecology; Great Slave Lowland; lithalsas; glaciolacustrine sediments; lacustrine sediments; alluvial sediments; Climate change; Phanerozoic; Cenozoic; Quaternary
ProgramClimate Change Geoscience
Released2013 08 01
AbstractLithalsas are permafrost mounds formed by ice segregation in mineral soil that occur within the zone of discontinuous permafrost. Nearly 1800 lithalsas were mapped in the Great Slave Lowland, Northwest Territories, Canada, where permafrost is extensively discontinuous under a mean annual air temperature of -4.6°C and mean total precipitation of 281 mm (Environment Canada normals 1971-2000). The Lowland region contains widespread glaciolacustrine, lacustrine and alluvial fine-grained sediments that are susceptible to frost-heaving. Here, lithalsas are up to 8 m high and several hundred metres in length and width. One lithalsa, examined by electrical resistivity and boreholes, rises 4 to 6 m above an adjacent peatland, shows clear evidence of ice-segregation at depth and ground heave ranging between 2.5 to 4.0 m, and is estimated to have formed within the past 700 years based on radiocarbon dating. Regional lithalsa forms include circular, crescentic and linear, and are typically located adjacent to ponds and streams with mature forms vegetated by deciduous (birch) forest or mixed (birch and spruce) forest with an herb-shrub understory and organic layer typically less than 10 cm. Though lithalsas are widespread in the Lowland area, they are most common within the first few tens of metres above the present level of Great Slave Lake. Continued Holocene recession of Great Slave Lake by isostatic uplift infers that many lithalsas are, therefore, late Holocene in age.
Lithalsas may form as a result of three primary conditions; namely, warm but widespread discontinuous permafrost (not limited to organic peatland terrain), a substrate of fine-grained sediment frost susceptible sediment, and available groundwater supplied from nearby taliks. Where these conditions are suitably fulfilled, lithalsas may be widespread, and contain significant volumes of ground ice. Contemporary and also remnant lithalsas may be more common than previously recognized, as they may be widespread within former lacustrine, glaciolacustrine and marine basins with extensive discontinuous permafrost, but may be obscured by forests or other vegetation cover. Recognition of lithalsas is significant as they represent potentially ice-rich, thaw-sensitive, and frost-susceptible terrain.
Owing to the relatively thin organic matter cover, lithalsa terrain in the Great Slave Lowland may be vulnerable to climatic and ecological disturbances. Permafrost in peatlands, where peat is 30 cm thick or greater, may be maintained under relatively warm climatic conditions by a thermal offset. However, the absence of a thick organic cover on lithalsas at first suggests that this terrain could be vulnerable to thawing caused by atmospheric warming. Since the 1940s, annual mean air temperature at Yellowknife has risen by about 0.3°C per decade, and the average for the first decade of the 21st Century was -3.6°C. Thus, ice-rich lithalsa terrain is anticipated to degrade in the coming decades as permafrost responds to these thermal conditions.
Summary(Plain Language Summary, not published)
We undertook the first regional investigation of ice-rich terrain, known as lithalsas, found within the Great Slave Lowland of the Northwest Territories. Lithalsas are permafrost mounds formed by ice lens growth in mineral soil that occur within the zone of discontinuous permafrost. In our study area, lithalsa mounds can be up to 8 m high and many hundreds of metres in length. We mapped nearly 1800 of these in the Lowland area. The recognition of lithalsas is significant as they represent potentially ice-rich, thaw-sensitive, and frost-susceptible terrain that are sensitive to climatic and ecological disturbances.

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