Wednesday, 21 May 2014

Glacier retreat and slope instability, an example from Mount Kazbek, Georgia

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A large landslide close to the Georgia - Russia border this week killed up to eight people, and disrupted construction of a new hydropower diversion tunnel. The landslide was released from approximately 4,100 m on the north-eastern flank of Mount Kazbek, and is estimated to have involved more than 10 mil. m^3 of rock. The site of the landslide release is likely to have been recently deglaciated, and 2010 aerial images from Google Earth indicate there was ongoing instability in the years prior to this failure.  

Aerial image of the landslide release area at 4100 m elevation

In this case the landslide traveled over 10 km downvalley, and the deposit seems to have formed immediately upstream of outlet tunnels for the hydropower diversion. Although this was clearly an energetic event (in particular in terms of the 400 m run-up apparent on the opposite side of the valley), the total fall was almost 3 km, and the travel distance is not unusual for a landslide of this magnitude.

Map of landslide release, travel, and approximate location of the deposits. 
The profile is derived from the white line indicating the path of the rock avalanche. 

While it's terrible to see loss of life as a result of such events, high alpine landslides such as this can provide critical insight into the possible effect of changing climate and glacier retreat in more heavily populated alpine regions. Although minor depressions or crevasses are evident in the glacier surface in the 2010 aerial image, and smaller events have been noted to be regular in the region, such a large event was not predicted. By studying failures such as this one, we can gain important insight into the failure characteristics, and begin to identify additional information required to predict similar events with enough confidence to evacuate communities at risk. As it happens, the diversion tunnel for the Dariali hydropower scheme appears to be well situated to relieve inflows into the lake impounded behind the landslide deposit, and hopefully prevent any further losses downstream.


Interactive map indicating the estimated source (orange), and mapped deposit (grey), as well the aerial photograph of the release area (double click the camera icon to view). The white line denotes the path of the landslide that appears to have descended as a rock avalanche. A .kmz file (including additional aerial photographs) is available as a Google Earth download here