CGRG Bibliography of Canadian Geomorphology
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Author : Cavers, D.S.
Date : 2003.
Title : Copper River and Limonite Creek rock avalanches.
Publication : 3rd Canadian Conference on Geotechnique and Natural Hazards. Sheraton Hotel. Edmonton, Alberta, Canada. June 9 and 10, 2003.
Issue :
Page(s) :
Abstract
There have been two large rock avalanche events in the Zymoetz River Valley (locally called the Copper River) and the extension of the valley to the east (Limonite Creek) in the last 5 years. One event was located in the headwaters of Limonite Creek a short distance west of the Telkwa Pass, approximately 30 km east of Terrace, BC, and the second was located approximately 18 km east of Terrace at KP 15 of the Copper River Forest Service Road. Both events started as toppling failures on the east side of tributary valleys near the crests of the mountain ranges on the south side of the valleys. Both failures, which had estimated volumes exceeding 1 million cubic meters, traveled at high velocity down the tributary valleys, blocked the stream and resulted in failures of the Pacific Northern Gas pipeline that runs from Summit Lake to Prince Rupert and Kitimat. The toppling failures started on west facing valley slopes that had been oversteepened by glacial erosion (one of the failures also had a translational component). Melting of the glacial ice over the last few decades reduced the toe support for the oversteepened slopes, allowing toppling movements to initiate. The toppling failures, which involved large volumes of rock mixed with additional snow or glacial ice, ran downslope to the main tributary valleys where they turned toward the north down the tributary valleys picked up additional snow and meltwater. The failures ran at high velocity down the tributary valleys to the main valley over distances of 3 to 4 km. Both failures temporarily blocked the valley, producing small lakes that have persisted. Both rock avalanches cut the PNG pipeline. The geology conditions that led to the failures, the debris avalanches, and some of the after effects of the debris avalanches are described. Temporary pipelines were dragged across the slide debris dams, which were initially too loose and soft to support foot traffic. Subsequently, the pipeline was rerouted around the failure areas, in one case using an aerial crossing and in one case by crossing to the opposite valley slope. The geological conditions that led to the failures are present in other locations along the south side of the Copper River and Limonite Creek valleys. Loss of glacial ice support of oversteepened valley walls has occurred in other nearby areas that have similar geological conditions and further similar failures may occur in this general area.
Bibliography of Canadian Geomorphology