ABSTRACT: Paleohydraulic modelling of glacier outburst floods: subglacial and supraglacial release mechanisms and an assessment of research needs.

CGRG Bibliography of Canadian Geomorphology
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Abstract

The largest freshwater flood of the past 100,000 years was that associated with the outburst of meltwater from glacial Lake Agassiz. This gigantic proglacial lake formed along the southern margin of the Laurentide Ice Sheet and around 8450 BP released approximately 151, 000 km3 of water to Hudson Bay. The outburst is thought to have been the trigger for the “8200 BP” abrupt cooling event. Present estimates of the magnitude of this flood, based on a physical model of drainage through an ice-walled subglacial conduit, place the peak discharge in the range 5–10 Sv and the duration at roughly 0.5–1 year. Because of its scale and climate significance, the Lake Agassiz flood focusses attention on the strengths and weaknesses of existing models of outburst flood hydraulics. Although a subglacial drainage routing is the most likelymode of flood initiation, there are good reasons for remaining open-minded about the possibility of supraglacial release. In terms of scale, there are no modern analogues to the Lake Agassiz outburst; thus contemporary experience could be an unreliable guide. Additionally, model results suggest that the subglacial drainage conduit grew so large that its ice roof would have collapsed before the flood terminated. An unroofed subglacial conduit is equivalent to a supraglacial conduit that has cut down to the bed. Thus a supraglacial flood model could have greater relevance to this phase of the flood than a subglacial model. A major shortcoming of existing models it thatthey appear to underestimate the heat exchange between flowing water and ice boundaries, either because the theory has deficiences or because the heat transfer empiricism is flawed. Other areas for improvement include a richer representation of turbulence, possibly by adding k–" physics, and coupling the conduit to a dynamic lake model.

Bibliography of Canadian Geomorphology