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Continental/Cordilleran ice interactions: a dominant cause of westward super-elevation of the last glacial maximum continental ice limit in southwestern Alberta, Canada
Authors:EDWARD C LITTLE  LIONEL E JACKSON Jr  THOMAS S JAMES  STEPHEN R HICOCK  ELIZABETH R LEBOE
Institution:e-mail: , Canada-Nunavut Geoscience Office, PO Box 2319, Iqaluit, NU, XOA OHO, Canada;Geological Survey of Canada, Terrain Sciences Division, 605 Robson Street, Vancouver, BC V6B 1R8, Canada;Geological Survey of Canada, 9860 W. Saanich Road, Sidney, B.C., V8L 4B2, Canada;Department of Earth Sciences, University of Western Ontario, Biological and Geological Sciences Building, London, ON, N6A 5B7, Canada;Bruce Geotechnical Consultants Inc., Suite 210, 1290 Hornby Street, Vancouver B.C., V6Z 2G4, Canada
Abstract:In southwestern Alberta, Canada, a westward-rising last-glacial-maximum continental ice limit has been identified. This limit is defined by the upper elevation of Canadian Shield erratics deposited by last-glacial-maximum continental ice along the flanks of prominent ridges and buttes within the region. The interpolation between ice-limit data points has produced two distinct slope profiles: 2.9 m/km to the east, and 4.2 m/km to the west of Mokowan Butte. Three hypotheses are proposed to explain this westward rise of the last-glacial-maximum continental ice limit: (1) regional tectonic uplift, (2) glacio-isostatic uplift, and (3) continental ice-flow convergence due to topographic obstacles and interaction with montane ice. Inferred long-term rates of tectonic uplift and glacio-isostatic modelling show that these two mechanisms account for less than 25% of the observed absolute elevation increase of the limit between the Del Bonita uplands and Cloudy Ridge in southwestern Alberta. The remaining rise in elevation of the continental ice-sheet margin in this region is thought to result from continental ice-flow convergence due to the combined effects of the regional topography and interaction with montane glaciers to the west. The steeper rise in the former continental ice surface west of Mokowan Butte can be explained by the topographic obstruction and interaction with montane glaciers in the area of the Rocky Mountain front.
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