17 December 2015

First news of a rock avalanche on Mount James Turner yesterday

Posted by dr-dave

Mount James Turner rock avalanche

Drew Brayshaw has tweeted this image of a rock avalanche that apparently occurred on Mount James Turner yesterday:

Mount James Turner

Mount James Turner rock avalanche via Drew Brayshaw and Twitter

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Mount James Turner is close to Whistler in British Columbia, western Canada.  This looks to be a large, very mobile rock avalanche event, with a steep upper portion and a long track.  Note the small flow that appears to have left the main flow mid-track, and then rejoined the main flow after descending a step.  There is some evidence of dust on the margin of the landslide.  Drew also tweeted a pre-failure image of this part of Mount James Turner:

Mount James Turner

Mount James Turner via Drew Brayshaw and Twitter

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The landslide appears to have originated from an unsually steep rock cliff on the edge of Fingerpost Ridge and will have had a substantial freefall element.  Based on the image, and correlating with Google Earth, the runout distance that is visible will be about 2 km. However, there may be a longer non-visible component. The top of Fingerpost Ridge is at about 2600 m, whilst the foot of the steep slope is at about 2300 m according to Google Earth.  The toe of the visible part of the landslide is at 1900 m.

Interestingly, at the toe of the landslide there appears to have been a lake – named Berna Lake:

Mount James Turner

Mount James Turner via Google Earth

 

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Is this the snowy apparently-deformed mass that appears to lie at the toe of the landslide in the first image? Canada has a good seismic network, so it will be interesting to see if this landslide has been captured on those sensors.