UKC

Last week, a major rockslide at Petite Nesthorn sub‑summit forced the evacuation of a whole village (Blatten) in Valois. The mountainside developed a displacement of nearly 17 metres, with up to 5 million cubic metres of unstable mass.

Since then, smaller rockfall events gradually lessened the danger, eroding it in smaller chunks and slides that didn't reach the valley, but unfortunately started accumulating on a hanging glacier, which accelerated its movement to ten metres (!) a day.

Unfortunately, the whole glacier collapsed this afternoon, triggering another massive landslide that reached the valley floor, destroying most of the (empty) village, even running out on the opposite slope and seemingly damming the whole river valley – potentially (hopefully not) making an even more catastrophic glacial outburst lake failure possible downstream in the future, unless mitigated.

youtube.com/watch?v=y0o8jEF4YaQ&

https://eos.org/thelandslideblog/blatten-4

https://www.bbc.com/news/articles/cnv1evn2p2vo

Climate change – the gift that keeps on giving...

No glaciers melting here - Brexit, the gift that keeps on giving ...

What do you think was holding the mountain together which fell on the glacier? Permafrost. Permafrost that is no longer permanent due to climate change.

It'll be interesting to see how much of the debris is 'land' and how much was ice. It'll be interesting to see if they do remove the 'dam', it's a dead-end valley with only a campsite and small hydro powerstation upstream, so mitigating the lake burst risk is probably the only requirement for doing so.

The permafrost has been receding up the hillsides since the ice retreated from the lowlands. Undeniably at an accelerating pace, but it's an overall trend that precedes industrialisation.

Because of Brexit, our permafrost is growing faster than anywhere in the G7

I doubt if there's any question of 'removing' the 'dam' in its entirety or even in large part.  But restoring a river channel through it to ensure continued drainage of the upper Lotschental and to minimise the risk of a dammed-lake surge into the lower valley and beyond is clearly an urgent and vital need. 

The road up the valley has also been cut at Blatten; it may be a dead-end but it does give access to Fafleralp (and then onwards up the Langgletscher into the World Heritage Aletsch glacier complex) and large areas of alp grazing, so presumably it will be restored for agriculture and tourism.   I somehow don't think the Swiss are into large-scale re-wilding by abandonment.

It is (was ?) also part of a classic ski tour from the Jungfraujoch (reached by the Eiger train), crossing Konkordiaplaz & then exiting down to Blatten. Thirty years we bought a special ticket from (I think) Interlaken which included trains to the start point, then post bus & train back to Interlaken. We did this over several days to ski a few hills & cols but some do it as a day trip - lots of downhill for little uphill.

It’s a pretty depressing time for highland snow patches, mind.

My friend's writeup about this after we chatted about it yesterday:

https://www.antarcticglaciers.org/2025/05/birch-glacier-landslide/

From the footage, it does seem to me that the river might carve a path to the opposite valley side of the landslide's crown, there is sort of a lower channel there between the toe or main body and the runout onto the other valley side.

Last I checked, even the army still hasn't declared it safe for them to work on dam mitigation, as there is still a substantial amount of the glacier left hanging there weighted by fallen rock mass.

But if it finds a channel through there quickly on its own, that might be ideal (though IANAG) – much better  than the lake growing even more and bursting the dam en masse.

Nice read, thanks!

From update reports in Le Nouvelliste it seems that, for the time being anyway, the Lonza river is spontaneously establishing a new course across the huge debris field at Blatten without precipitating a major surge or dam breach.  So the villages further down the Lotschental may be spared severe damage.

did you see the timelapse of the mountain shifting a few days earlier. there was talk earlier that a glacier collapse would reduce support for this huge block but seems unliklier now for some reason?

https://youtu.be/RhxAKCwqZOw?si=tYVhTZdrhcltOkx2&t=219

It's my belief from the available footage that most of that mass shown in that video's timelapse had already been deposited onto the glacier gradually days before it's collapse.

In other words, the vlogger seems to me to be conflating (perhaps deliberately) timelapses from a week ago (of a slope which now had already slipped and loaded the glacier until its collapse on thursday). Of course, I'd have to re‑check all the actual historic footage against the post‑slide ones, but I remember enough of them that I can state that with high confidence.

I'd rather keep to official and scientific sources like Dave Petley's (Vice-Chancellor of the University of Hull) highly informative and scientific blog than some utter teenage rando's youtube channel...

https://eos.org/landslide-blog

This is before the collapse, you can see most of the rock mass initially on the move had already collapsed and loaded the glacier below:

https://bsky.app/profile/did:plc:7tatft4f2j4pcpq2653f637f

Also, from the latest coverage I have seen, the authorities are now most concerned (apart from the GLOF) about the runout mass on the opposite valley side to the crown, which narrowly missed a hamlet there, as it might have been deposited on an already steep slope of the 12,000 year old morraine (which might have actually saved the upper hamlet) with quite some force and not be in a stable configuration. That's not to say there won't be some rockfall from the original crown of the rockslide in the days to come, but it should be much smaller.

this looks like the block that came down so plenty left..

https://i0.wp.com/eos.org/wp-content/uploads/2025/05/25_05-Blatten-3.jpg?w=...

'Geologic time includes now'

talking of sliding land, this footage is pretty rare/unique? of a strike slip fault in action..

youtube.com/watch?v=_OeLRK0rkCE&

That's… interesting, to say the least. Quite a rapid slip!

Back to Blatten, prof. David Dobson has a nice short video explaining the Birch glacier collapse in some detail:

youtube.com/watch?v=1oewSPgTFA4&

Their other OneMinuteGeology videos are pretty interesting as well – they are a climber, and there are quite a few videos on UK's various rock types and geological features.

If they are active here on UKC, I just wanted to say thanks, I found the videos great.

Having seen seen the footage of the mountain subsiding, one thing I've not been clear on is whether there remains more waiting to fall.

Most of that is already gone. Some rockfall persists and likely will for weeks, but currently stopping where the glacier was, not making it into the valley.

Yesterday's inspection flight still shows some potentially loose mass still, but the black scar is where the biggest rockfall (that timelapse mountainside you think of) was:

https://bsky.app/profile/subfossilguy.bsky.social/post/3lqna6h7a2s23

"Four days after the rupture of the Birch glacier, the mountain remains in motion. The landslides at the Petit Nesthorn continue, according to Matthias Ebener, head of information of the regional driving staff.

But everything that goes down stops where the glacier was before, Matthias Ebener added Sunday morning. An intervention of specialists with machines on the waste cone is still not possible".

(src: RTS.ch)

This is a rather good overview of the mass loss and gain derived from prior Swisstopo's data and photogrammetry after the catastrophic event – you can see the lower blue scar of major mass loss from the mountainflank (over -100m of elevation!) and above it the blue spot where the glacier fully collapsed, plus the insane amount of mass deposited in the valley below in red:

https://bsky.app/profile/stim3on.bsky.social/post/3lqjxpk6yos2j

At a lesser level, still in Switzerland, the Julierpass and the Klausenpass have both suffered closures due to rockfall / landslides this week:

https://www.srf.ch/news/schweiz/keine-verletzten-julierpass-nach-steinschla...

300k m3 according to the twitter linked above