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B.C. landslide blocks creek

Landslide photos courtesy TVA.
Landslide photos courtesy TVA.

Beverley Ann D'Cruz, staff writer

August 7, 2010 — A creek blocked by landslide debris had officials concerned about the rising water levels, but fears of a flood have now receded.

Hundreds of people are allowed to go home now that an evacuation order has been lifted in the Meager Creek area, where a landslide of rock and snow came crashing down on Friday. The landslide debris came to rest 95km north of Pemberton, British Columbia, in the Pemberton Valley.

Professor John Clague of Simon Fraser University’s Earth Sciences Department explains what could have transpired: “I think what has happened here is that you have had an extended period of warm weather on the south coast and the freezing level is probably way above the elevations of the peaks, and you have snow and ice melting at high elevations. That is producing a lot of melt water that is infiltrating the slopes around Meager and entering cracks in the rocks and entering some of the surface rubble and debris that one finds in that area and destabilizing the slopes as a result.”

Professor Clague says quite a large amount of material was deposited, which completely blocked the flow of Meager Creek. “A lake has been forming in that impoundment above the dam and is growing in size,” he says. The block is upstream of the slide on the southwest side and is posing a threat to rancher's fields nearby. Water levels downstream on the northeast side are already dropping.

Currently, geologists are assessing the site to predict the outcome when the block buckles under the water's weight. “Once you get a slip or slide the water mixes with the fragmenting material and kind of transforms the landslide into a flow,” adds Professor Clague. “I guess a good analogy would be sort of wet cement but with large boulders in it. So it turns into a flow that speeds down the valley and kind of picks up in size. In this case it was quite large. It actually grew in size before it reached the main stem of Meager Creek.”

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