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There was another similar flood on the same river about a year or two ago. The problem was the the glacial flooding started in Tibet and affected people just over the border (one of the videos is from the border crossing). There's no international data sharing for this sort of thing between China and Nepal and Nepal can't deploy sensors in Tibet to give sufficient warning.

| But apparently this was a black swan.

What is your definition of black swan? This paper is from 2022 and scientists have been warning about climate change for decades. It's not like this possibility wasn't anticipated. It seems likely we'll see more glacial events as the atmosphere warms.

Perpendicular is not the scientifically best path. 45 degree angle is the best angle if the threat is moving toward you at the same velocity that you can move. As the velocity of the threat increases, the angle gets closer to perpendicular. The size of the threat and distance of course matter as well. I think about this before tree felling. In chainsaw classes they teach you to move at a 45.

I wonder if the river went dry first, like the water receding off into the horizon before a tsunami?

The great flood myths across the world are quite possibly ancestral memories of this kind of flood on a continental scale. Retreating ice age glaciers would make lakes the size of states held at bay by an impromptu dam of various kinds of debris (or more glacier) which then would break dumping great lake amounts of water hundreds of miles into the ocean within days. This kind of thing probably happened in lots of places.

I think the Japan tsunami videos showed as many, but it was spread out over the course of almost 2hrs and happened in slow motion over a large area. You could see some cars speeding to safety while others were washed away. Some stayed in taller structures assuming they were safe and were slowly washed away.

That makes sense. You can see lots of settlements on the hills above the sight of this flood too. I also found this study of the risk perceptions of people living there interesting too. https://www.sciencedirect.com/science/article/pii/S221242092...

it's a popular area for tourists and mountaineers, but also i think it's a lot easier to estimate missing/dead tourists since most of them will be there with tours/companies that have to keep track of exactly where they are.

Syabru Besi is downriver of the border and the starting point for the Langtang valley trek which is probably the third most popular trekking location in Nepal (behind Everest basecamp and Annapurna circuit). I think the tourist data they have is from tourists that are traveling with guides but from my experience many tourists also bypass the official requirements and trek solo so the number could be much higher if the Langtang is affected.

Likely the tourists are better accounted for than the locals. Numbers are likely much higher :(

Nepal is popular for Westerners I think. Maybe for religious reasons?

i understand it as 150 dead, with more people missing, of which 47 are americans.

Down stream of a glacier, in the run off water shed.

As I've heard tell, this was a glacial collapse into and blocking a river, which then built up a head of pressure behind it, bursting to release a hammer blow of river water and debris that travelled a great distance.

Similar things can happen due to landslides into rivers; it depends on the topology of the land, here long narrow valleys carved out by heavy water flows.

The warning being, don't live in a natural "drainpipe".

In mountainous regions that's often not much of an option, there's a lot of vertical sides and valley bottoms.

https://m.youtube.com/watch?v=rIVNeDuCF_k

fixed, but some things are better off wrong perhaps