22 August 2018
High resolution imagery of the Pashgor debris flow in Afghanistan
A little before I took some time off to go to Australia on leave with my two teenagers, I posted about a debris flow that struck Pashgor in Afghanistan as a result of a Jökulhlaup event. In a comment on my original post, Juan Pablo Milana provided an explanation for the event:-
Dear Dave, It was a Jökulhlaup (an arid variation!): In this case the collapse of a supraglacial lake over a debris covered glacier, probably by breaking down an ice barrier due to an excess of hydrostatic pressure. It did not happened before probably because the well visible supraglacial hollow that hosted the lake (sometimes described as thermokarst) it is large and only with excessive snow melt could reach the critical depth to overcome the needed pressure to lift the mix of glacier ice and debris. In fact your last image shows that the lake exceeded the size of the hollow that in many older images showed accumulation of water, but with smaller area covered by it. I cannot send you the images that prove this, but I posted a comment in twitter with an image edited showing the glacier characteristics. It is what we locally call complex glacier system as it shows the transition form a ice-exposed part to a debris-covered ice and then into a rock.glacier, which due to its larger debris concentration cannot be floated, but there are case where ice concentration of rock glaciers in Chile reach 99%. regards.
Whilst I was away, Planet Labs kindly collected a high resolution Skysat image of the site, which I have not been able to post until now. This is the full extent of the flow path of the debris flow:-
Most importantly, the image provides an extraordinary level of detail about the site of the glacial lake that formed and then drained to generate this disaster:-
Whilst this is the impact on the village:-
This image was collected on 4th August. At that point the lake was still in present.
Planet Team (2018). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com