The Tyndall Glacier landslide in Alaska

An interesting story at the 2015 Fall meeting of AGU last month was the announcement by Colin Stark and Goran Ekstrom that they had detected an enormous landslide in Alaska, which I am terming here the Tyndall Glacier landslide. As regular readers know, Stark and Ekstrom have pioneered the use of seismic waves to detect very large landslides, with remarkable success. The Tyndall Glacier landslide occurred at about 8:19 pm local time on 17th October 2015 at the toe of the Tyndall Glacier. The landslide is enormous – Stark and Ekstrom estimate from the seismic data that it had a mass of about 180 million tonnes, which would give a volume in the order of 72 million cubic metres. The landslide flowed into Taan Fjord, triggering a localised tsunami that was detected 155 km away, according to the Lamont-Doherty press release.

Having detected the Tyndall Glacier landslide, Stark and Ekstrom located it with a very high resolution satellite image, which Lamont-Doherty have included in their press release:

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Note the large source area on the left side of the image, the presence of debris on the toe of the glacier, and the sediment charged water of the fjord. Most of the volume of the landslide must now be on the bed of the Taan Fjord.

The location of the landslide at the toe of the glacier is fascinating. As noted in the press release:

In the case of the Taan Fjord landslide, the Tyndall glacier’s retreat from the edge of Icy Bay in 1961 to its current location more than 17 kilometers up the fiord removed buttressing in the valley, leaving the weak rock on the valley wall prone to collapse, Ekström said. The entire valley was once filled with ice as much as 400 meters high, but as the glacier retreated, the ice thinned.

This mechanism of glacial debutressing has long been discussed by landslide scientist, and this appears to be a very clear example of the process. Given that the retreat of the glacier is being driven by the very rapid warming in the high latitudes, this is likely to be a response to global warming.

The press release also includes a before and after image of the tsunami triggered by the Tyndall Glacier landslide:

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The waves triggered by the Tyndall Glacier landslide was clearly both large and very energetic to have caused this level of change. There is no doubt that this is an event that needs detailed investigation in the Spring. We can learn a great deal about both large landslides and landslide tsumani genesis from this event.

Finally, for now, at the time of the Bingham Canyon landslide in Utah we compiled a list of the largest known non-volcanic landslides in North America:

Mt. Stellar AK – Sept 14, 2005 – 50 million cubic metres of rock and ice total, but initial detachment = 10-20 million cubic metres of rock.

Mt. Steele Yukon – July 24, 2007 – between 28 and 80 million cubic metres including a “significant volume of ice”, modeled as 50 million cubic metres deposit.

Mt. Meager BC Canada – 48 million cubic metres – 6 August 2010 – turned into 12 km debris flow, no deaths, ~largest in Canada.

Hope slide BC Canada – 47 million cubic metres, January 9, 1965, 4 people killed – two seismic events noted, previous largest in Canada.

Frank slide NWT Canada – Apr 29, 1903 – 30 million cubic metres – 70-90 deaths – Turtle mountain area today.

Madison River Canyon (Earthquake lake) Montana – Aug 17, 1959 – 28-33 million cubic metres – 28 deaths.

Lituya Mountain AK – June 11, 2012 – 5-60 million cubic metres – no deaths, poor volume estimate from deposit on glacier.

Lituya Bay AK – July 9, 1958 – 30 million cubic metres – 5 killed from tsunami.

Plus Bingham Canyon itself, which had a volume of about 65 million cubic metres.

At about 180 million metric tonnes, this landslide had a volume of about 72 million cubic metres. On this basis the Tyndall Glacier landslide is the largest recorded non-volcanic landslide in North America. What a find!