“The rumbling would have started across Icy Bay at around 8:19 p.m. on Oct. 17, 2015. In the span of about 60 seconds, 200 million tons of rock roared down the side of Alaska’s Taan Fiord valley and crashed onto the toe of Tyndall Glacier and into the water, setting off a local tsunami big enough to register at the nearest tidal gauge 155 kilometers away.”
A interesting story was revealed at a fall 2015 meeting of the American Geophysical Union. Goran Ekstrom and Colin Stark have pioneered a global seismic network to detect very large landslides in remote areas of the world to much success. They announced at the AGU meeting the detection of an enormous landslide at the toe of the Tyndall Glacier that spilled over the ice and into the Taan Fjord, Icy Bay, Alaska. This particular landslide was identified as non-volcanic, though it is located in an area that is volcanically active.
Icy Bay has only formed over the past 100 years and has been carved by the rapid and erosive power of the retreat of the Guyot, Yahtse and Tyndall glaciers. A research paper titled ultra-rapid landscape response and sediment yield following glacier retreat, Icy Bay, southern Alaska and published in the Journal of The Smithsonian/NASA Astrophysics Data System notes what the rapid glacial retreat reveals.
Glacial retreat and opening of Taan Fjord (an arm of Icy Bay, Alaska) in the last two decades drove a base level fall of ˜ 400 m at the outlets of four tributary valleys in the region of the current Tyndall Glacier terminus. Response in the tributary valleys to this base level fall includes evacuation of stored sediment, incision of slot gorges into bedrock, and landsliding on valley walls.
AGU reports:
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:
An island in Taan Fiord, about 10 km from the landslide, shown by satellite in 2014 (left) and a few days after the landslide and tsunami (right). (GeoEye, Colin Stark)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.
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