GEOSCAN, résultats de la recherche


TitreGeochemical and geophysical investigations of massive ground ice on Herschel Island, Yukon
AuteurFox, D; Angelopoulos, M; Pollard, W; Lacelle, D; Clark, I; Couture, N; Lantuit, H; Fritz, M; Schwamborn, G; Cray, H
SourceProceedings of the 41st International Arctic Workshop; 2011 p. 105-107
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130150
Réunion41st International Arctic Workshop; Montreal; CA; mars 2-4, 2011
Lat/Long OENS-139.5000 -138.9167 69.6667 69.5000
Sujetscongélation du sol; glace fossile; températures au sol; pergélisol; analyses géochimiques; analyses gravimétriques; géochimie; géophysique; géologie des dépôts meubles/géomorphologie
Illustrationslocation maps; plots
Programmeadaptation et impacts sur l'environnement, environnement du nord, Géosciences de l'environnement
Résumé(disponible en anglais seulement)
Massive ground ice dominates the permafrost landscape of Herschel Island, Yukon and has a direct and widespread influence on the island's topography, infrastructure, and ultimately the people who use this land. Massive ground ice located in the headwalls of retrogressive thaw slumps on Herschel Island has been analyzed extensively in order to better comprehend the structure, composition, spatial extents and origins or the ice. This report focuses on research which links precise geochemical values with extensive geophysical imagery. This is a novel approach to permafrost research and allows us to identify the origin of massive ice bodies as well as calculate ice volumes. This work is highly relevant for understanding the geomorphic response to past climates and for providing i data forresponsibly developing and managing this landscape in the future.

Located in the southern Beaufort Sea, Herschel Island is the most northern point of the Yukon Territory, Canada. Also referred to as Qikiqtaruk, which in Inuvialuit means 'This is Island', Herschel Island has an area of approximately 108 km2 (approximately 15 km x 8 km) and is characterized by rolling topography A glaciotectonic origin is assigned to Herschel Island; it is an ice-push structure, formed by the westward advance of the Laurentide ice sheet during the Buckland Stage of the Wisconsin Glaciation (Mackay, 1959; Rampton, 1982). The island is composed of mainly fine-grained marine sediments dredged from the Herschel Basin and coarser grained coastal deposits. Post glaciation, this material has been reworked primarily by alluviation, thermokarst, mass wasting and ground ice formation (Rampton, 1982). Permafrost is up to 600m deep along the Yukon Coastal Plain and Herschel Island lies well within the zone of continuous permafrost; ground ice is widespread and underlies most of the island (Pollard, 1990).

This research focuses on units of massive ground ice discovered in the headwalls of retrogressive thaw slumps and along coastal sea cliffs on the south and north shores of Herschel Island (Fig. 1). The largest exposure, referred to as Hawk Slump, is on the southern coast along Thetis Bay and measures 20m high. A vertical transect in the center of the slump was established which bisects the active layer, a modern ice-wedge and four massive ice units including a unique white band which undulates throughout the entire exposure. The second site is a buried snow bank located at Slump C. This is an isolated and relatively small unit of massive ice measuring only 3m in width by 2m in height, located at the upper edge of the retrogressive thaw slump wall. The final site is the Blue Ice site which contains three exposures of massive ice, all of which are blue in colour and are nearly pure ice with an extremely high gravimetric moisture content of more than2000%.

Work in 2010-2011 focusses on geochemical analyses (including stable water isotopes and molar gas ratios) combined with geophysical data collected using ground penetrating radar (GPR) and capacitively coupled resistivity (CCR). Field based studies included initial ground-truthing and crysotratigraphic interpretations at thaw slump exposures to better comprehend the nature of deformed massive ground ice. Examination of molar gas ratios of N2, O2 and Ar is currently being used to differentiate buried glacial ice from intrasedimental ice. Connecting this geochemical data to an extensive and growing set of geophysical data will produce a greatly improved understanding of massive ground ice at Herschel Island.

Gravimetric moisture contents identified massive ground ice units at all exposures, while acidity and conductivity tests give information on water sources and freezing conditions. Stable water isotope values have provided insight as to the origin of massive ground ice and suggest that several previously enigmatic ice units may be derived from meteoric water sources (Fig. 2). Preliminary results suggest that GPR can map the top and occasionally the base of massive ground ice structures on Herschel Island. When CCR data is included in the investigation, relative ice content changes within the structures can be shown. Hence, we can extrapolate our geochemical results over a larger spatial extent.
Résumé(Résumé en langage clair et simple, non publié)
Dans certaines régions pergélisolées, lorsque les conditions sont favorables, d'importantes masses de glace presque pure peuvent se former sous la surface du sol. Ces masses de glace massive peuvent avoir une épaisseur atteignant des dizaines de mètres et s'étendre parfois sur plusieurs kilomètres. Si cette glace souterraine venait à fondre, les conséquences pourraient être graves pour les personnes, les infrastructures et le paysage lui-même. Il est donc important de savoir où se trouvent ces masses et quelles en sont les propriétés physiques exactes. La présente étude porte sur l'île Herschel (Yukon), une région qui renferme de grandes quantités de glace massive. Nous avons examiné la glace à trois emplacements distincts, afin de mieux comprendre comment et où la glace peut se former. Nous avons utilisé des méthodes géophysiques pour cartographier le haut et, si possible, le bas de ces masses de glace, et évaluer le volume de la glace. Diverses méthodes géochimiques nous ont servi à obtenir de l'information sur les sources d'eau (eau souterraine, neige, glacier) et sur les conditions dans lesquelles l'eau a gelé. Les résultats nous aident à mieux comprendre les limites glaciaires en Amérique du Nord ainsi que l'histoire géologique récente de la région.