29 February 2016

Elk City landslide: a very interesting video

Posted by Dave Petley

Elk City landslide video

The Elk City landslide happened on 18th February on State Highway 14 on the South Fork of the Clearwater River near Elk City in Idaho, USA. The landslide was captured in a remarkable video by a member of a road clearance crew who were at the scene at the time.  The Idaho Statesman describes it as follows:

“We were just up there doing some routine road maintenance,” said ITD transportation technician Bret Edwards.  The video initially just shows rocks tumbling down the hillside onto the highway. Then a larger piece of the hill begins to move, and you can hear Edwards shouting as he runs away from the massive landslide. The entire hillside sloughs off and the camera spins around.  When all was done, dirt, rocks and trees covered a 500-foot stretch of the road about 40 feet deep.


The Idaho Transportation Department posted this great image of the landslide on their Twitter account on Monday:
Elk City landslide

Aerial view of the Elk City landslide as captured by the Idaho Transportation Department


This a shallow rockslide, probably in deeply weathered rock.  The really interesting aspect of the video is the way that the final movement event developed, yet again showing an increasing event rate of smaller falls and slides as the underlying landslide mass accelerated.  Even then it was not obvious to the road crew that a major collapse was imminent.  As the image above shows, removing the debris will be a large and expensive task.  It will be interesting to see if the adjacent slopes are suffering from stability issues as well.  And note that the the crown (top) of the landslide there is unstable and displaced material that has yet to fail.  This material will need to be managed as failure would lead to it being deposited on the road once again, and as such it is a significant hazard.