3 August 2020
Yigongxiang: a valley blocking debris flow in Tibet
On 2 August 2020 a Twitter user named Swapna (@swapna_apsrsac), a specialist in remote sensing, tweeted news of a valley-blocking debris flow high in the mountains of Tibet. The location is extremely remote, located upstream of Yigongxiang in Nyingchi, Tibet. This event is reported in the Arunachal Times in some detail. This reports that the landslide was spotted from satellite imagery – if so that was a very shrewd piece of detective work. The article is by Chintan Sheth (@blueczkfox), who suggests that it might have been triggered by recent seismic activity in this area.
This part of Tibet is very difficult to image in August due to extensive cloud cover. It is located at 30.428, 94.547 if you wish to see the location – this is close to the termination of a glacier in rugged mountain terrain. The only optical satellite to have captured it as far as I am aware is an ESA Sentinel 2 image from 27 July 2020:-
The debris flow appears to have come from the western side of the valley. It is large – the barrier appears to be about 500 m wide, and probably over a kilometre long. A lake has developed upstream (to the north). This appears to have been about 1.5 km long on 27 July.
The images are partially obscured by cloud. A better understanding can be gained from a false colour image, in which vegetation shows as red, bare rock as a light brown and water as cyan. Cloud is still white:-
For reference, this is the site on 2 July 2020:-
There is a risk here of a breach of the landslide dam and a subsequent flood downstream. It is not possible to estimate the magnitude of the risk at this site, but further investigation and monitoring is needed urgently.
Quickslide 1: Deadly landslides in South Korea
South Korea is suffering a spell of heavy rainfall that has triggered extensive flooding and landslides. The spell of poor weather is expected to extend into Tuesday.
Quickslide 2: Continued landslide losses in Nepal
The toll from fatal monsoon-induced landslides in Nepal continues to rise in a manner that is alarming. In the most recent incident, eight people appear to have been killed in a landslide at Melamchi in Sindhupalchok.