A collapsing glacier in Tibet led to a devastating wall of water and debris roaring through a valley in Nepal, leaving hundreds dead and many hundreds still missing.

Stuart Dunning is a professor of applied geomorphology who researches disaster risk reduction in high mountain a areas nd has closely studied the 2021 Chamoli disaster, a similar event. He’s part of a loose group of 50 or more international experts who come together to pool expertise and provide rapid analysis of events like these.

The Conversation asked him about the science behind this event, and what we can expect in future.

What exactly happened – and how can a collapsing glacier generate such a powerful flood?

The exact sequence of events that sent so much debris and water downstream is something we are still trying to unravel. There are a number of possibilities. One is that a large bedrock landslide took the glacier with it. Another is that a bedrock landslide destabilised the glacier and it fell very shortly after. Another is that the glacier failed first and then the bedrock above failed.

I think the best description is that a rock-ice avalanche began at around 4,800 metres and fell over 1,200 metres. There was enough ice in the initial collapse – and perhaps subsequently picked up – that it could generate the water to turn it into the devastating long runout debris flow. This is far more damaging than a dry rock avalanche.

The flow travelled along the river, so gaining water. It would have been eroding the valley floor and sides as it went. Further downstream, that material........

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