alt Hacker NewsDown 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.
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bamboozled • today at 4:10 AM
It sounds like there may have been some opportunity for warning then? If the thing was more of a "build up" ?
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The rivers in that area are pretty small. You would have to block them for days before there is a risk of a massive flash flood.
From what I've understood, the collapsing glacier either contained enough liquid water or melted enough from the impact that it continued flowing downstream. It covered ~20 horizontal kilometers in about 7 minutes before hitting the border crossing.