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TitreLithalsa distribution, morphology and landscape associations in the Great Slave Lowland, Northwest Territories, Canada
AuteurWolfe, S A; Stevens, C W; Oldenborger, G; Gaanderse, A J
SourceCANQUA-CGRG Biannual Meeting, abstracts; 2013 p. 1
Année2013
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130151
ÉditeurUniversity of Alberta
RéunionCANQUA-CGRG Biannual Meeting; Edmonton; CA; août 18-22, 2013
Documentlivre
Lang.anglais
Mediapapier; numérique
Formatspdf (Adobe® Reader®)
ProvinceTerritoires du Nord-Ouest
SNRC85J/07; 85J/08; 85J/09; 85J/10; 85J/11; 85J/12; 85J/13; 85J/14; 85J/15; 85J/16
Lat/Long OENS-116.1667 -114.2500 62.8833 62.2500
SujetsHolocène; pergélisol; glace fossile; sediments; dépôts organiques; tourbières; sols; caractéristiques périglaciaires; soulèvement par le gel; talik; trous de mine; diagraphie géophysique; diagraphie de résistivité; résistivité électrique; datation radiométrique; datation au radiocarbone; morphologie; eaux de surface; lacs; eau souterraine; végétation; antecedents glaciaires; niveaux d'eau; relèvement isostatique; climat; écologie; buttes cryogènes; sédiments glaciolacustres; sédiments lacustres; sédiments alluviaux; changement climatique; géologie des dépôts meubles/géomorphologie; géologie de l'environnement; géophysique; géochronologie; Nature et environnement; Sciences et technologie; Phanérozoïque; Cénozoïque; Quaternaire
ProgrammeGéosciences de changements climatiques, Infrastructures terrestres
Diffusé2013 08 01
Résumé(disponible en anglais seulement)
Lithalsas 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.
Résumé(Résumé en langage clair et simple, non publié)
Nous avons entrepris la première étude régionale des terrains riches en glace, désignés sous le nom de lithalses, et qui se trouvent dans les terres basses de Great Slave, dans les Territoires du Nord-Ouest. Les lithalses sont des monticules de pergélisol formés par la croissance de lentilles de glace dans les sols minéralisés qui se produisent à l¿intérieur de la zone de pergélisol discontinu. D¿après notre zone d¿étude, les monticules de lithalse peuvent mesurer jusqu¿à 8 m de hauteur et plusieurs centaines de mètres de longueur. Nous en avons cartographiés près de 1 800 dans la zone des terres basses de Great Slave. Les lithalses sont vraisemblablement plus nombreux que ce qui avait été reconnu jusqu¿ici et ils sont importants, car ils représentent des terres potentiellement riches en glace, et sensibles à la fonte, au gel, ainsi qu¿aux perturbations climatiques et environnementales.
GEOSCAN ID292797