14 December 2015

Fort McPherson: a catastrophic mudflow in Canada

Posted by Dave Petley

Fort McPherson mudslide in Canada

In Canada near to Fort McPherson in the Northwest Territories (NWT), a mudslide has been slowly eroding the barrier that retained a small but far from insignificant lake.  This situation has been developing for a number of months, and back in June the NWT Geological Survey released a warning that the lake would fail catastrophically by the end of the year.  This image, taken by Scott Zolkos of the University of Alberta, illustrates rather clearly why this was a site that was causing much concern:-

Fort McPherson mudslide

Fort McPherson mudslide, picture by Scott Zolkos, University of Alberta


Last week it was announced that the landslide retrogressed to the point that the barrier partially breached on 15th July .  The event was reported in some detail in an article this week in Vice News, which notes that:

On July 15, between 8 and 9 pm, the slumping permafrost that held back the unnamed lake finally gave way. The ensuing cascade gushed roughly 30,000 cubic meters of water in a flow that could have filled a dozen Olympic swimming pools. Although remote camera’s captured the event, the extreme isolation of Fort McPherson, which sits roughly 1,800 miles due north of Vancouver, meant that news of the flood would not reach those studying the lake until weeks later.

Interestingly, the movement of the mudslide was captured in time-lapse footage by a web cam at the site.  That footage is now on Youtube:


The mudflow is very interesting, not least the way that the mass accelerates as the water permeates through the debris.  The partial breach has of course greatly reduced the hazard.  However, the main point here is not this comparatively small if dramatic breach event near to Fort McPherson, but the way that warming temperatures is driving increasing amounts of thawing in these glacial deposits, triggering rising numbers of permafrost landslides like this one.  As the Vice News article wisely observes:

Many other slumps throughout the region continue to alter the landscape and are clouding and clogging waterways with loads of sediment that scientists have found to have strong negative effects on aquatic ecology. According to Pisaric, these changes have provoked deep anxiety among the Gwich’ins of Fort McPherson, worries he said are shared among many communities across Canada’s north.

Scott Zolkos has some amazing images of these landslides on his blog.