A review of catastrophic drainage of moraine-dammed lakes in British Columbia
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| Authors: | Clague, JJ; Evans, SG |
| Year: | 2000 |
| Journal: | Quat. Sci. Rev. 19: 1763-1783 Article Link (DOI) |
| Title: | A review of catastrophic drainage of moraine-dammed lakes in British Columbia |
| Abstract: | Moraine-dammed lakes are common in the high mountains of British Columbia. Most of these lakes formed when valley and cirque glaciers retreated from advanced positions achieved during the Little Ice Age. Many moraine dams in British Columbia are susceptible to failure because they are steep-sided, have relatively low width-to-height ratios, comprise loose, poorly sorted sediment, and may contain ice cores or interstitial ice. In addition, the lakes commonly are bordered by steep slopes that are prone to snow and ice avalanches and rockfalls. Moraine dams generally fail by overtopping and incision. The triggering event may be a heavy rainstorm, or an avalanche or rockfall that generates waves that overtop the dam. The dam can also be overtopped by an influx of water caused by sudden drainage of an upstream ice-dammed lake (jokulhlaup). Melting of moraine ice cores and piping are other possible failure mechanisms. Failures of moraine dams in British Columbia produce destructive floods orders of magnitude larger than normal streamflows. Most outburst floods are characterized by an exponential increase in discharge, followed by an abrupt drop to background levels when the water supply is exhausted. Peak discharges are controlled by dam characteristics, the volume of water in the reservoir, failure mechanisms, and downstream topography and sediment availability. For the same potential energy at the dam site, hoods from moraine-dammed lakes have higher peak discharges than floods from glacier-dammed lakes. The floodwaters may mobilize large amounts of sediment as they travel down steep valleys, producing highly mobile debris hows. Such flows have larger discharges and greater destructive impact than the floods from which they form. Moraine dam failures in British Columbia and elsewhere are most frequent following extended periods of cool climate when large lateral and end moraines are built. A period of protracted warming is required to trap lakes behind moraines and create conditions that lead to dam failure. This sequence of events occurred only a few times during the Holocene Epoch, most notably during the last several centuries. Glaciers built large moraines during the Little Ice Age, mainly during the 1700s and 1800s, and lakes formed behind these moraines when climate warmed in the 1900s. Twentieth-century climate warming is also responsible for recent moraine dam failures in mountains throughout the world. Warming from the late 1800s until about 1940 and again from 1965 to today destabilized moraine dams with interstitial or core ice. The warming also forced glaciers to retreat, prompting ice avalanches, landslides, and jokulhlaups that have destroyed some moraine dams. (C) 2000 Elsevier Science Ltd. All rights reserved. |
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