Monday, 1 September 2014

Ongoing instability of the Randa rock slope (Switzerland)

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Ongoing rockfall activity from the Randa rock slope at 1 pm on the 29th of August 2014

Two very large rockfalls in 1991 left an almost 1,000 m high cliff on the western side of the Matter Valley in Southern Switzerland. The valley is one of the most travelled in the Alps as it serves as access to the town of Zermatt and the skifields immediately adjacent to the Matterhorn.

Research into the cause of the 1991 failures and current state of stability has been ongoing for more than 20 years, and the site is now a classic example of alpine rock slope failure. Although regular rockfall is common from the remaining scarp, the event captured on video is one of the larger failures since 1991. Rockfall was ongoing throughout the day, and the event in the video occurred just after midday.

Large failure from near the crest of the remaining rock slope

The video was captured during a scientific workshop with members of the Chair of Landslide Research from the Technische Universität München, and the Geomorphological and Environmental Research Group at the Universität Bonn.

Randa rock slope in early August (05/08/2014)

Close up of the region of current activity (this is estimated to be perhaps 60 m high). Dark red indicates the approximate region of the present failure. Orange indicates a region of rock that may have been destabilised as a result of the activity.

A pre-failure photo taken two weeks prior to the event (12/08/14). The photo was taken by members of ETH Zurich as they descended by helicopter from the Randa in situ rock laboratory (credit: J. Beutel). Inset indicates the approximate failure location, as well as apparently open cracks on adjacent failure planes.