25 July 2023
The location of the 20 July 2023 debris flow at Ungar in Lhuentse, Bhutan
Yesterday, I posted about a debris flow disaster that occurred on 20 July 2023 at Ungar (also spelt Unger and Unngar) in Bhutan, which is believed to have killed 23 people. Dr Stuart Dunning (@Rock_Avalanches) of the Newcastle University tweeted (or is that Xeeted?) a possible location for the accident, based upon Planet Labs images:-
— Stuart Dunning (@Rock_Avalanches) July 24, 2023
This location is [27.57095, 91.07595]. Looking at the photographs of the site, I think that this is indeed the location. This is a Planet image of the site collected on 15 July 2023:-
This is an image collected on 22 July 2023, showing the aftermath of the debris flow:-
Below is a slider that should allow you to compare the two images:
In the image before the disaster, there appears to be a set of structures in the channel immediately below the confluence of the two tributaries. In the image after the debris flow, these structures have clearly been destroyed. The decision to locate a camp, if that is what happened, in such a vulnerable position is interesting. As I noted previously, there are multiple examples in which landslide hazard has not been properly considered in hydroelectric schemes in the Himalayas.
The source area for the debris flow, to the west of the images above, is shrouded in cloud in the images since the accident. However, this is what the catchment looks like on Google Earth – the pin is the location of the camp:-
This is clearly a very steep, dissected landscape, with multiple small tributaries feeding into the main channel. This is a classic for landscape for small slips combining to create a channelised debris flow. Unfortunately, cloud free images may not become available until the end of the monsoon.
Planet Team (2023). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/