CGRG Bibliography of Canadian Geomorphology
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Author : Clarke, G.K.C.; Leverington, D.W.; Teller, J.T.; and Dyke, A.S.
Date : 2003.
Title : How large was the glacier outburst flood that triggered the 8,200 BP cooling event?
Publication : Canadian Geophysical Union. Annual Meeting, May 10 -14, 2003. Banff Centre, Banff, Alberta.
Issue :
Page(s) :
Abstract
During the deglaciation of North America (ca. 12,000{8,000 BP), huge proglacial lakes formed along the southern margin of the Laurentide Ice Sheet. Depending on the location of the ice margin, overflow from these lakes was variably directed to the Mississippi, Hudson and St. Lawrence drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events. On at least one occasion the ice dam formed by the Laurentide Ice Sheet was penetrated and a massive outburst °ood was routed from Glacial Lake Agassiz to Hudson Bay and ultimately to the North Atlantic Ocean. The impounded water volume has been estimated as 163; 000 km 3 and the timing of the outburst coincides with the early Holocene cooling event at 8,200 BP. Although the total water discharge is reasonably well constrained by glacial geological observations, the magnitude and duration of the °ood, which have a potential influence on oceanic response, remain matters for speculation. For the Lake Agassiz reservoir there are no data to distinguish whether the °ood mechanism was supraglacial or subglacial so that, in addition to relevant but poorly constrained variables such as water temperature, the release mechanism is itself uncertain. Whatever the release mechanism, the flood path is hundreds of kilometres long and simplifying assumptions that have been applied to modern outburst floods that follow shorter flood paths are clearly inappropriate. To simulate flood hydrographs and other diagnostic outputs for subglacial outburst floods, we adopt a modified version of the Spring and Hutter formulation. To simulate supraglacial outbursts we develop new theory and extend earlier work by Raymond and Noll. For both classes of models we solve equations for the spatio-temporal evolution of hydraulic potential, water velocity, water temperature and channel cross section. An approximate calibration of the hydraulic roughness is obtained by applying the model to well-studied modern floods from "Hazard Lake" and Summit Lake in western Canada and in Iceland. Depending on the assumed release mechanism and other factors, provisional estimates of peak °ood magnitude are in the range 5{12 Sv.
Bibliography of Canadian Geomorphology