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 : 2 How large was the 8,200 BP outburst from Lake Agassiz?
Publication : Joint Annual Meeting of the Canadian Quaternary Association and the Canadian Geomorphology Research Group. Halifax, Nova Scotia, June 8-12, 2003.
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 Mackenzie, 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 flood 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 km3 and the timing of the outburst coincides with the early Holocene cooling event at 8,200 BP. Although the total reservoir volume is reasonably well constrained by glacial geological observations; the magnitude and duration of the flood had a potential influence on oceanic response, it remains a matter for speculation. For the Lake Agassiz reservoir there are no data to distinguish whether the flood mechanism was supraglacial or subglacial so that, in addition to relevant but poorly constrained variables such as water temperature and channel roughness, the release mechanism is itself uncertain. 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. Depending on the assumed release mechanism and other factors, provisional estimates of peak flood magnitude are in the range 5-12 Sv. Intriguingly, model results suggest that a single subglacial outbursts could have produced multipulse floods that terminated before the reservoir drained to sea level. The ambiguous Winisk stage of Lake Agassiz could mark the level to which the lake surface dropped rather than a final refilling level.
Bibliography of Canadian Geomorphology