3 July 2016

Lamplugh Glacier rock avalanche: A massive new landslide in Alaska on Tuesday

Posted by dr-dave

Lamplugh Glacier rock avalanche: A massive new rock landslide

The media in Alaska is reporting a find by a local pilot, Paul Swanstrom of Mountain Flying Service, of a huge new landslide, the Lamplugh Glacier rock avalanche, which occurred in Alaska on Tuesday.  This is yet another enormous event in this area of North America – this is an image that he took of the landslide, which is posted on his company Facebook Page:

Lamplugh Glacier

The Lamplugh Glacier rock avalanche via Paul Swanstrom

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Paul estimates that the runout of the landslide is about 6 miles (i.e. about 10 km).  In a KHNS Radio article about the landslide, Colin Stark of Colombia University estimates that the volume is about 150 million tonnes, presumably based upon an initial analysis of the seismic catalogue.  The landslide appears to be recorded in the Alaska Earthquake Center catalogue as a M=2.9 event on 23rd June 2016 at 08:20 local time:

 Lamplugh Glacier

The Alaska Earthquake Center record of the possible seismic event generated by the Lamplugh Glacier rock avalanche

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The landslide appears to be a very deep-seated, ridge crest to slope toe failure of unusually large proportions:

Lamplugh Glacier rock avalanche

The source of the Lamplugh Glacier rock avalanche, via Paul Swanstrom

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The landslide appears to have generated a highly mobile, broad and long landslide deposit on a comparatively low angled slope, probably consistent with flow of debris over an ice bed.  The landslide has developed complex structures at the toe, probably associated with the final creeping stage of movement:

Lamplugh Glacier rock avalanche

Flow structures in the Lamplugh Glacier rock avalanche deposit, via Paul Swanstrom

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This is not an area with particularly good Google Earth imagery, but I think that this is the slope that failed:

Lamplugh Glacier rock avalanche

The probable site of the Lamplugh Glacier rock avalanche, via Google Earth

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The crest of the slope appears to be at about 2030 metres elevation, and the break at the foot of the slope at about 875 m, giving a vertical extent of about 1155 metres. The toe of the deposit is at about 550 metres elevation, which means that the runout lost about 225 metres elevation over 10,000 metres, giving a travel angle of about 1.3 degrees.  This is exceptionally low.

This part of Alaska is now firmly established as the global hotspot for rock avalanche activity. Recent events include the Tyndall Glacier Rock Avalanche, the Ferebee rock avalanche, the Mount La Perouse rock avalanche, the Mount Jarvis Rock avalanche and the Mount Lituya Rock Avalanche.  A detailed study is urgently needed to understand why this area is so active at present.