|Title||Geochemical and geophysical investigations of massive ground ice on Herschel Island, Yukon|
|Author||Fox, D; Angelopoulos, M; Pollard, W; Lacelle, D; Clark, I; Couture, N; Lantuit, H; Fritz, M; Schwamborn, G; Cray, H|
|Source||Proceedings of the 41st International Arctic Workshop; 2011 p. 105-107|
|Alt Series||Earth Sciences Sector, Contribution Series 20130150|
|Meeting||41st International Arctic Workshop; Montreal; CA; March 2-4, 2011|
|Lat/Long WENS||-139.5000 -138.9167 69.6667 69.5000|
|Subjects||geochemistry; geophysics; surficial geology/geomorphology; freezing ground; ground ice; ground temperatures; permafrost; geochemical analyses; gravimetric analyses|
|Illustrations||location maps; plots|
|Program||environmental impacts and adaptation in the northern environment, Environmental Geoscience|
|Abstract||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.
|Summary||(Plain Language Summary, not published)|
In certain permafrost areas, under the right conditions, large bodies of almost pure ice may form beneath the ground surface. These bodies of massive
ice can be up to 10s of metres thick and can sometimes extend for kilometres. Should this underground ice melt, the consequences could be severe for people, infrastructure, and the landscape itself, so it is important to know where it is located and
what its exact physical properties are. This study focuses on Herschel Island, Yukon, an area with a great deal of massive ice. We examined ice at three different sites in order to better understand how and where it may form. We used geophysical
techniques to map the top and, where possible, the bottom of the ice bodies, and to assess the actual volume of ice. Various geochemical techniques were used to get information on the water sources (e.g., groundwater, snow, glaciers) and on
conditions under which it froze. The results help to improve our understanding of North American glacial limits and of the recent geological history of the region.