Geological Society of America

T22 Cordilleran Ice Sheet Outburst Floods: From Glacial Lake Missoula to the Hubbard Glacier

Sunday, 22 October 2017
8:00 AM - 12:00 PM
Chelan 5

DRAINAGE OF THE LAST GLACIAL LAKE LONDON, ONTARIO: MAPPING AND HYDRAULIC MODELING

Paper number: T22-12
Program: Technical Sessions
Time: 11:00 AM – 11:15 AM

Authors

Nathaniel Bergman Presenting Author
University of Haifa, Mt. Carmel, Haifa
Nathaniel Bergman Presenting Author
Israel Oceanographic and Limnological Research (IOLR), Migdal
Nathaniel Bergman Presenting Author
Western University, London, ON
Marco J. Van De Wiel
Coventry University, Coventry
Marco J. Van De Wiel
Western University, London, ON
Stephen R. Hicock
Western University, London, ON
Yannick Y. Rousseau
Concordia University, Montreal, QC

Abstract

Glacial Lake London existed when southern Ontario was deglaciated during Glacial Lake Maumee III or Glacial Lake Whittlesey phases - the early ancestral phases of modern Lake Erie. Whether one or several lakes, it was an ice-marginal Laurentide Ice Sheet meltwater lake which was dammed behind convergent Arva and Ingersoll Moraines and was breached in its southwestern part to generate a catastrophic flood. Evidence for this high magnitude flood is a large v-shaped spillway channel downstream of the lake outlet, where the modern Thames River flows, and which is an underfit channel under the current hydro-climatic conditions. This study reconstructs paleolake surface area, depths, and volumes for Glacial Lake London based on contemporary topography, lacustrine stratigraphy found in Medway Creek’s Arva Moraine bluffs, and the upper lake level topographic constraint prior to overtopping.

The resulting flood that drained the lake is also reconstructed using two different approaches: 1) applying a variety of published parametric breaching equations to find the peak discharge (13,000-241,000 m³/s) based on breach geometric characteristics and reconstructed maximum lake volume (9.1 km³); and 2) field mapping of a series of unusual geomorphic features found downstream of the Lake London outlet and attributed to the dam-break flood. These features are used for HEC-RAS step-backwater modeling of water surface slope profiles to calculate peak discharge. Reconstructed peak flood discharges (13,400-75,600 m³/s) are in a similar range as other dam-break floods from relatively small ice-marginal lakes of the Laurentide Ice Sheet and 20 montane moraine-dammed lake outbursts. Our results confirm that contemporary hydrology could not have formed the Thames River valley downstream of the glacial lake outlet and that its formation required extreme discharges one or two orders of magnitude greater than historical maximum gauged floods (~1,500 m³/s).

The study shows that outburst floods and resulting spillway channels originating from moraine-dammed lakes are not only typical of ice-marginal lakes in steep montane environments, or proglacial lakes in front of a glacier, but also occur in subdued deglaciating terrains of a receding ice sheet.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-304159

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