The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
Over the course of the last few days, I have been blogging about the evolving situation on the slopes above Blatten in Switzerland. I documented that attention slowly transitioned from worries about the stability of the slope on Kleine Nesthorn (Petit Nesthorn in French) to concerns about the stability of the Birch Glacier due to increased loading from the rockslide debris. Yesterday, I outlined three scenarios and emphasised that we were in unknown territory.
On 28 May 2025, the Birch Glacier catastrophically collapsed, generating the massive landslide that had been the source of concern. The move by the authorities to evacuate the village proved to be the correct call, but tragically a 64 year old resident appears to have been buried in the landslide. Assuming that he was indeed in the area, their prospects are bleak.
Others have covered the failure event better that can I, and once again I recommend two Bluesky accounts that have provided amazing insights. First, there is Melaine Le Roy, who has posted this for example:-
And second is Jan Beutel, who is new to Bluesky (a well timed introduction, sir!), who has posted this before and after comparison that is simply awesome:-
These two scientists will be really good sources of information over the coming days. Reuters also has a nice summary news video of the events:-
So, was the final collapse my scenario 1 (a further failure of Kleine Nesthorn that triggered failure of the Birch Glacier) or scenario 2 (a catastrophic failure of the glacier itself)? At this stage, I am not sure. The seismic data will reveal all in due course – this event will have been extremely well captured in this dataset. Jan Beutel posted seismic record soon after the failure – look at the scale of the signal that the landslide generated:-
I am certainly no expert in analysing this data, so I can only speculate, but it is interesting that there was an elevated signal in the two minutes or so before the catastrophic failure began. What was this? Was movement starting to occur in the Birch Glacier, or was there an event on the slope above (or am I misreading the signal)?
So, for now, attention will focus on three things:
First, the valley of the Lonza river is dammed and a substantial lake is starting to develop. This has the potential to inundate the remaining properties in Blatten and, of course, to release a major flood. Two further communities downstream have been evacuated. There is a good Youtube video of this situation:
This will need to be addressed with urgency, but Switzerland is well placed in terms of expertise and resource to mitigate the threat.
Second, attention will need to be paid to the Birch Glacier and the slopes on the Kleine Nesthorn. Is there the potential for a further failure? Massive though this collapse has been, it is unlikely to have included all of the mass on the slope. What is the state of the remaining material? This will be a critical question in terms of the safety of those charged with managing the flood hazard.
And finally, many people have lost their homes, and more may do so in the coming days. This is a devastating event for them, and they will need considerable help.
As a final comment, I have to pay tribute to those individuals who have managed this hazard. The situation was immensely unpredictable, but they acted quickly and decisively. Whilst it is a tragedy that someone is missing, their actions saved many lives.
In due course, I’m sure that there will be a series of papers about this remarkable event. There are many lessons to be learnt from an absolutely amazing case study. As always, please remember that my posts here are provisional and speculative – the definitive analyses comes from the on site experts and from rigorous scientific study in due course.
Text © 2023. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
