The catastrophic debris flow that struck Nepal and Tibet today was triggered by the collapse of a glacier high in the mountains.
Loyal readers will have seen the footage of the catastrophic debris flow that struck parts of Tibet and Nepal today, 26 August 2026. There is a variety of sources, of which the CCTV footage from Gyirong on the border is probably the most dramatic and horrifying – indeed at this scale the event is close to be apocalyptic:-
Current reports indicate around 400 fatalities, but I think it is reasonable to assume that the cost is going to be higher.
The root cause of this disaster is already known, although there is a lot of misinformation and some uncertainty. On Bluesky, Dan Shugar has posted a video compiled from Planet imagery that shows the initiating event:-
The image above was from 25 August 2926, whist the one below is from 26 August 2026:-
The location is is in the area of [28.2765, 85.5194]. The exact sequence is not clear as yet, but the imagery definitely pins down the location.
There has been some speculation, and indeed official comments, that the trigger was an earthquake. This is likely to be a misinterpretation of the data – the seismic signal is almost certainly the rock ice avalanche and debris flow, not a tectonic event.
A fascinating element of this is the source of the huge volume of water. This may be a combination of ice that converted to water as a result of the release of energy from the initial collapse, water embedded in the sediments that were entrained en route and river water. But I am speculating. There is no evidence that this was a GLOF.
Understanding this event is going to need an international team, as has been the case for similar events in recent years. That team has now got together and has started work.
Finally, this event is going to have profound implications on Nepal. The loss of many people, including a large number of tourists as well as local people, will be extremely painful. The Gyirong border crossing has clearly been destroyed, along with its infrastructure. Houses have been lost and at least two hydroelectric schemes destroyed along the Bhote Khosi river. The true scale of the loss is not yet clear.
I have made the point many times before, but we systematically under-estimate the risk associated with these events in the Himalaya mountains. Investments in large-scale hydropower projects are repeatedly being destroyed by these catastrophic debris flows. Unfortunately, under the conditions that result from climate change, many more of these events will occur in the future.