Photo: Before and after the glacier collapse and the flow deposits on May 28, 2025 (source: https://pbs.twimg.com/media/GsDXuO8aUAA8N5k?format=jpg&name=small).
We have followed the dare situation above the Blatten village in central Switzerland since early May 2025 when first reports about potential mountain top collapse and large and frequents rockfalls high above the village started to be reported in media – wisely, due to the threating geological events that followed one another in May 2025, the around 300 villagers and their husbandry were evacuated on time (on May 19, 2025).
What was threatening to may happen in the last few days – a large mountain slope collapse including the glacier collapse – occured in the late afternoon on May 28, 2025 – as a part of a landslide cascading event – that burried almost all of the buildings in the village of Blatten in central Switzerland. After several days of large subsequent rockfalls and bergsturzs (due to their estimated volume of several million m3) from Kleines Nesthorn (a 3341 m high mountain in the west ridge of the Bietschhorn (a 3934 m high mountain) that started to happen in early May 2025 and that temporariliy deposited on the Birch glacier, came down together with the ice masses of the collapsed glacier to the valley floor of the Lötschental valley – the flow velocity was estimated to be well over 100 km/s, the air masses in front of the pulverised glacier avalanche were even much faster – w. The dynamic (inertal) forces pushed the ice and coarse rock debris masses up around 200 meters high on the opposite valley slopes. The debris flow of a mixture of rockfall and bergsturz masses, ice masses from the glacier and eroded earth and vegetation taken by the debris flow along its way down the slope, caused a local earthquake of a magnitude over 3.0 – an evidence of the event magnitude. The real volume of the event (event magnitude) should be determined in the next days by detailed observations to be made in the source area where the collapse was triggered, as it might be over 10 million m3. The volume of the event could have been namely larger due to a further collapse of rock slopes of the Kleines Nesthorn (3341 m a.s.l.) above the Birch glacier on May 28, 2025. This would push the event volume from first estimations of 3 million m3 to potentially well above 10 miliion m3. The event magnitude is very large due to glacier ice masses taken collapsed together with the deposited rockfall masses top on the glacier. What has happened can be described as the-worst-case scenario. But the situation may not be over yet. The whole mountain top threaten to collapse and this might be another gigantic event in this cascading events – even more, as the glacier is not supporting the above mountain slopes at their foots any more. and the slide pathway is “open” to the valley floor after May 28 Landslide/Avalanche event.
![La carte de la zone approximative des dégâts, basée sur les images aériennes à disposition. [RTS - GeoAdmin]](https://img.rts.ch/articles/2025/image/d6irmp-28898220.image?mw=1280)
Photo: An approximate map of the area of damage, based on available aerial images [RTS – GeoAdmin] (Source: https://img.rts.ch/articles/2025/image/d6irmp-28898220.image?mw=1280).
The ice avalanche run-out area is close to 2 km2 – covered by ice and debris deposits several meters high. More than 2 km of the Lonza River are now obstracted and a lake is forming upstream of the landslide dam that covered the valley floor several meters high, possibly over 10 meters (the church in the village is covered/destroyed and not visible anymore). This growing lake of the estimated maximum depth up to 10m may cause a future sudden outbreak flood due to a subsequent dam breach (collapse) when water will start overtopping the landslide dam – this threatens to erode long stretches along the Lonza River in the downstreaming direction all the way to the main Rhone River valley and the village of Gampel. The Lonza River will have high dischares due to ice and snow melt, and during local thunderstorms with high rainfall intensities.
On the Wikipedia webpages for the village of Blatten we already have first information about the 2025 Landslide:
On 28 May 2025, at around 15:30 CEST,[7] approximately 90% of Blatten was lost under a landslide triggered by the collapse of the Birch glacier.[8][9] A 3.1 magnitude earthquake was recorded at the same time, potentially contributing to the event.[9][10]
Debris destroyed large parts of the village and ice, earth and rock partially blocked the Lonza River.[11] One person has been reported missing. Smaller landslides in the preceding days had led to the complete evacuation of the village, which prevented mass casualties.[12]
Our sincere condolences to all Blatten citizens hit by this natural disaster.