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TitreOrigins and implications of an ice-rich clay ridge (lithalsa) within the Boundary Creek watershed near Yellowknife, Northwest Territories, Canada
AuteurGaanderse, A J; Wolfe, S A; Burn, C R; Kokelj, S V
SourceCANQUA-CGRG Biannual Meeting 2013, abstracts; 2013 p. 1
Année2013
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130141
ÉditeurUniversity of Alberta
RéunionCANQUA-CGRG Biannual Meeting 2013; Edmonton; CA; août 18-22, 2013
Documentlivre
Lang.anglais
Mediapapier; numérique
Formatspdf (Adobe® Reader®)
ProvinceTerritoires du Nord-Ouest
SNRC85J/10
Lat/Long OENS-115.0000 -114.9167 62.5500 62.5000
SujetsHolocène; pergélisol; glace fossile; caractéristiques périglaciaires; soulèvement par le gel; lentilles de glace; talik; sediments; argiles; silts; sables; dépôts organiques; tourbières; écosystèmes; configurations hydrographiques; lacs glaciaires; antecedents de sedimentation; antecedents glaciaires; déglaciation; retrait de la glace; emersion; eaux de surface; lacs; niveaux d'eau; trous de mine; analyses stratigraphiques; géochimie de l'eau; mouvement des eaux souterraines; etudes isotopiques; isotopes d'oxygène; eaux atmosphériques; Lac glaciaire de McConnell; Calotte glaciaire Laurentide; buttes cryogènes; infrastructure; réseau routier; sédiments glaciolacustres; sédiments lacustres; géologie des dépôts meubles/géomorphologie; géologie de l'environnement; géologie de l'ingénieur; stratigraphie; géochimie; Nature et environnement; Transport; Phanérozoïque; Cénozoïque; Quaternaire
ProgrammeGéosciences de changements climatiques, Infrastructures terrestres
Diffusé2013 08 01
Résumé(disponible en anglais seulement)
Thaw of ground ice may have a major influence on terrain conditions and ecosystems, particularly with respect to ground stability and drainage patterns. It may also be a significant consideration for routing and performance of transportation infrastructure. Newly discovered clay ridges, located within the widespread discontinuous permafrost zone in the region surrounding Yellowknife, Northwest Territories, may be lithalsas. Lithalsas are mineral-based permafrost mounds with high segregated ground-ice in their cores. Geotechnical reports have noted the presence of deep-seated ground ice in the Yellowknife region, but the observed ridges are not currently recognized as potentially ice-rich geomorphic landforms. There is presently no information about their stratigraphy, composition, and formation process.
The ridges are located within glaciolacustrine surficial deposits, originating from glacial Lake McConnell approximately 10,000 years ago, following post-glacial retreat of the Laurentide ice sheet, and from subsequent deposition as water levels receded during the Holocene to the present level of Great Slave Lake. Permafrost aggradation followed emergence of the terrain from the lake. The study examines one large ridge, over 700 m long, located adjacent to Highway 3 within the Boundary Creek watershed, 31 km west of Yellowknife. To examine ground ice conditions in these deposits, samples to depths of 8.4 m were obtained from 15 boreholes along a transect perpendicular to the long axis of the ridge.
Boreholes revealed distinct tilted layers of silts, sands, and dense clays, suggesting they have been heaved, with the same layers observed horizontally beneath the adjacent peatland. Ice lenses between 2 and 6 cm thick were common in samples below 4 m, and alternating layers of ice lenses up to 19 cm thick within clay-rich sediment below 6 m created a deep-seated ice-rich core beneath the ground surface. Ice segregation within the fine-grained sediments has heaved the ground, producing the observed lithalsa. Geochemical results indicate free water movement through the substrate, and variations in concentrations are consistent with defined soil stratigraphic layers. Delta-18O values between -16.6 and -18.4 permille from ice lenses at 4.0 to 8.4 m depth indicate that the ice-based core likely formed from modern meteoric water sources, eliminating buried glacial ice or glacial Lake McConnell water as possible sources.
Detrital organics from sediments below the peatland date to between 1570 and 1770 cal BP, indicating lacustrine deposition at that time, and an age of about 1240 cal BP from the base of the peat deposits indicates terrestrial emergence and probable permafrost aggradation at that time. Detrital organics from sediments below the lithalsa range in age from 3190 to 690 cal BP, implying that lacustrine deposition continued here until at least 700 years ago. Thus, permafrost aggradation accompanied by ice segregation within the lithalsa was initiated within the last 700 years. The primary groundwater source for ice segregation is likely from a talik associated with a pond flanking the north side of the lithalsa. Evidence of the lithalsa's incipient nature includes clays with high unfrozen water contents between ice-lenses at depths below 7 m, suggesting that potential movement of unfrozen water toward the ice-based core by cryosuction may still be occurring. Examination of historical air photos demonstrates that the recent Highway 3 realignment intersects the former edge of the lithalsa. Removal of the active layer and ice-poor near-surface permafrost has made ice-rich materials at depth vulnerable to thaw. As a result, the roadway has subsided nearly one metre from 2007 to 2011. Although the study examines a single lithalsa, there are nearly 1800 raised mounds mapped in the area, indicating the potential for a much larger amount of ice-rich terrain across the landscape than previously understood.
Résumé(Résumé en langage clair et simple, non publié)
La glace de sol peut avoir une incidence majeure sur le terrain et les écosystèmes du pergélisol dans le nord du Canada. Des entités découvertes dernièrement à proximité de Yellowknife semblent être des crêtes d'argile riches en glace, désignées sous le nom de lithalses. Ces entités peuvent menacer la stabilité du sol et les réseaux de drainage (c'est-à-dire par thermokarst), et elles peuvent aussi avoir une incidence importante sur les infrastructures de transport. Dans le cas d'une crête d'argile, on a pu déterminer ses origines riches en glace à partir de nombreuses sources de données issues d'échantillons prélevés par puits de forage jusqu'à 8,4 m de profondeur. Nous avons conclu que l'alluvionnement du pergélisol et la ségrégation de glace ont commencé dans la crête au cours des 700 dernières années. La chaussée d'une route construite sur une partie de cette crête s'est affaissée de près d'un mètre de 2007 à 2011.
GEOSCAN ID292787