Dave Petley has on March 29, 2021[i] reported that a massive landslide has occurred along Yarlung Tsangpo river in Tibet, just upstream of Great Bend. (coordinates: 29.815, 94.932, the centre of the landslide source.)
It occurred between March 13 and 28, possibly on March 22, 2021. The massive landslide (estimated volume 100 Million Tons) happened possibly as a result of a seismic event, leading to fall of rock and ice mass (some call it hanging glacier collapse, same difference of opinion as was the case for Chamoli disaster on Feb 7, 2021), from a height of 6600 m to 2700 m or fall of about 3900 m, the landslide temporarily blocked the flow of Yarlung Tsangpo, but it started flowing again and is now reportedly flowing freely. Petley writes, the volume was “detached from the east side of the tributary valley, moving westwards and then to the south. Once again this has formed a catastrophic channelised flow that has travelled down the channel to deposit a large volume in the main channel… Note the huge increase in turbidity of the water downstream of the blockage on the Yarlung Tsangpo… This must be one of the most dynamic landslide locations on Earth.” The location could be the same as the Oct 2018 landslide[ii].
It is not clear what earthquake if any, triggered this. The nearest large earthquake both in terms of space and time was the March 19, 2021 earthquake of 5.7 magnitude located at:
31.906°N 92.899°E, with depth of 10 km is quite far away from the landslide location and possible landslide date.
Some useful tweets:
It’s now eight days since the landslide, but there is no news about it from any of the Indian agencies or local area in Arunachal Pradesh immediately downstream along Siang, not even about change in flow or turbidity.
On April 5, 2021, Claude Arpi wrote that the landslide could have been “due to torrential rains” in the area. He said: The slide is about 50 km downstream of projected giga hydropower plant (HPP) on the Yarlung Tsangpo and it is not presently directly connected with the forthcoming project. The Tibet Autonomous Region Meteorological Bureau announced on March 7 that during the week between March 8 to March 14, the temperature in most parts of Tibet would be high for the season, and it would be raining.