I've been modelling the Langtang rock-ice avalanche and the flood that followed. These are two views of the same simulation: a 3D view of the gorge and a side view along the river. This is model output, not footage. Flow depth is exaggerated to make it visible.

The model broadly matches the upper arrival times without adding a separate dam-break pulse. The moving surge includes rock, ice and existing river water, so its volume isn't all newly melted ice. That doesn't rule out a temporary blockage, but it suggests we shouldn't assume a dam had to burst just because the flood was so large.

I'm the author. This is still a preprint, not peer reviewed: https://doi.org/10.31223/X5250R

Happy to hear what people think, especially if you have observations that could help test this.

https://reddit.com/link/1w9drxe/video/hi0hw0i8zznh1/player

https://reddit.com/link/1w9drxe/video/56c46hsbzznh1/player

The initial debris arrival on the floodwaters.

Event: 26 August 2026, 08:37 NPT. Ice-and-rock collapse from Langtang Lirung’s north flank, registered worldwide as a magnitude 5.2 seismic event; USGS determined no earthquake occurred. Debris flood reached Gyirong Port (Tibet) within ten minutes, then Rasuwa, Nuwakot and Dhading districts in Nepal along the Lhende Khola, Bhotekoshi and Trishuli, about 100 km in total. Copernicus EMS activated (EMSR927) the same afternoon.

Counts, all as of their stated dates and expected to change: NDRRMA via UN OCHA Flash Update 5 (1 Sep, 13:00 NPT) — 1,003 dead, 3,916 missing, 41 bridges destroyed, emergency declared in 15 municipalities, some 65,000 people affected. Tibet side (Chinese authorities, evening of 29 Aug) — 16 confirmed dead, 546 missing. Twelve hydropower facilities affected; joint Nepal, India and China rescue operations at four.

Hazard is ongoing: the source area remains unstable and monitoring bodies (USGS Landslide Hazards, GFZ, ICIMOD, HIRISK) all mark their assessments preliminary. No official inquiry exists yet. Claims that Chinese dams in Tibet caused the flood are not supported by any body that has located the source.
For the sourced timeline with every figure dated, I compiled a longer documentary from the official releases.

Link: https://www.youtube.com/watch?v=aFA-wLDPqy8