Monster Seminar JAM - Mother Nature's Dangerous Dams
Dr. John J. Clague, Simon Fraser University
Dams impounded by glaciers, moraines, and landslides are common in mountain ranges around the world. Most of the dams are unstable and can fail suddenly, releasing their impounded waters in floods orders of magnitude larger than the normal nival and storm-triggered floods in the watershed. 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, floods 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 flows. Outburst floods destroy forest and fish habitat, and alter river planform and floodplain morphology. The effects can persist for decades until the river re-establishes its pre-outburst level and form. Under certain circumstances, outburst floods morph into fast-moving debris flows that bulk up as they travel downstream, adding to the destruction of the event. In this presentation, I discuss how natural dams form and fail; I give examples of catastrophic natural dam failures and discuss the impacts of the outbursts; and I speculate on the relation between outburst floods and recent climate change.
Date and Time:
January 5, 2006,
11:00 am - 12:30 pm