A catastrophic landslide on 28th May 2025 resulted in devastating damage to the village of Blatten in Switzerland. About 90% of the village was destroyed or covered with debris, resulting in a major catastrophe.
Seeing Blatten buried again and again, from every angle… Properly staggering! 😮😱
— Melaine Le Roy (@subfossilguy.bsky.social) 28 May 2025 at 19:51
[image or embed]
The damage is pretty catastrophic.
These are approx. 3 M m3 that collapsed from the Birch Glacier! 🧊🌊 The deposit spans 2.3 km of the Lötschental valley floor!
— Melaine Le Roy (@subfossilguy.bsky.social) 28 May 2025 at 20:20
[image or embed]
You can explore Blatten here:
So what happened? Was this because of climate change?
Developing Landslides
Well, we know that this event was anticipated. Which means that the 300 inhabitants of the village of Blatten were evacuated on 19th May, and the inhabitants, bar one person missing, were moved to safety. This is because a rock slope failure was developing on the mountain side of “Petit Nesthorn” (“Kleines Nesthorm”) above Birch Glacier (Birchgletscher), above the valley floor village of Blatten, and a large avalanche of rock and ice was identified as a risk.
A large landslide then occurred around or shortly before 20th May. You can view the landslide here:
Nice timelapse showing the moving rock mass of the Klein Nesthorn landslide yesterday! 😱 Source Geopraevent
— Melaine Le Roy (@subfossilguy.bsky.social) 21 May 2025 at 14:52
[image or embed]
This was a major instability, with a highly mobile rock mass, generating a huge volume of rock falls and rock dust as the mass deformed.
Here is a 3D visualisation of the landslide, created from high resolution drone imagery taken just before and after the landslide.
Overloading Birch Glacier
Landslides continued over the following week, with a series of smaller rockfalls. These rockfalls largely landed on the Birch Glacier surface, which became loaded with glacier debris. Up to 81 m of debris was reported on the glacier surface. This increased the pressure at the base of the ice.
Lidar survey of Klein Nesthorn landslide 🏔️ 🚁 📷 The results acquired last friday by #HelimapSystemSA and #Terradata show that the Klein Nesthorn has lost 101 m in elevation and that 81 m of debris have accumulated on Birch Glacier ! 1/
— Melaine Le Roy (@subfossilguy.bsky.social) 26 May 2025 at 11:49
[image or embed]
On 26th May, the SRF reported that up to 9 million tonnes of debris was sitting on the glacier surface, also reported by ETH.
Glacier acceleration
The Birch Glacier was overloaded with rockfall debris, with the glacier accelerating to move at up to 10 metres per day by the 26th May, according to the SRF. This is a marked acceleration. Lots of cracks started to form in the ice, which is on a steep slope, a sign of the tension in the ice.
Glacier collapse on 28th May
The night of 26th May was warm, and on the 28th May at 15:30 CEST the glacier catastrophically collapsed under the weight of the rock debris that had accumulated on its surface, generating the massive landslide that impacted the village of Blatten.
Essentially, the weight of the rock load on the ice surface overcame the resistive basal friction and longitudinal tension that holds the glacier onto the mountain, causing lots of cracks and catastrophic failure of the ice. The increased pressure on the ice surface may also have contributed to more ice melting under pressure at the base of the ice, reducing basal friction. Additional water input from rainfall and the mechanical action of the rockfall on the glacier may have contributed to the destabilisation of the glacier. Together, this reduced the effective basal shear strength at the base of the glacier and increased the driving stress through increasing the mass of the glacier.
When enhanced driving stresses from the additional weight of the rock exceed friction at the base of the glacier, detachment occurs (Zou et al., 2023).
As the glacier was on a steep slope, the ice and rock mixture cascaded down the mountain, gathering momentum and more material as it went.
Thus this was a cascading disaster that impacted the village. Evacuating the village was a good call.
Absolutely stunning frontal views of the entire path of the #Blatten event! 😮 Numerous debris flow run through the avalanche fan! 🌊 Shot by @ABettmeralp in early afternoon 🙏
— Melaine Le Roy (@subfossilguy.bsky.social) 29 May 2025 at 14:24
[image or embed]
Debris is reported up to 240 m on the facing valley side, showing the dramatic power of the event.
Developing flood risk
To add to the hazard, the rock-debris and ice mixture of the landslide dammed the Lonza River, resulting in the damming of an unstable and growing lake in the valley. This is flooding the village of Blatten, but if the dam fails, could impact downstream communities. As a result, they have had to be evacuated.
See again the useful update from Melaine Le Roy, noting the clearly visible debris up to 240 m up the opposite side of the valley:
Aerial view westward over the Blatten deposit and the newly formed lake upstream! 🧊🌊 📷Via Christian Petit/Linkedin
— Melaine Le Roy (@subfossilguy.bsky.social) 29 May 2025 at 16:55
[image or embed]
Update: 30th May
As the lake continued to grow over 28/29th/30th May, the local authorities prepared by partially emptying a dam lake 6 km down valley. By the 29th May, the lake level was at the height of the tallest roofs, destroying any chalets not buried.
Photomontage showing the flooded buildings in Blatten! 😱🌊 -As they were originally (up Right) -Immediately after the collapse yesterday (low Right) -This afternoon (Left) Montage by jojoski2.bsky.social
— Melaine Le Roy (@subfossilguy.bsky.social) 29 May 2025 at 18:30
[image or embed]
As of 30th May we continue to watch cautiously as the lake level rises, with access to assess and manage the hazard directly currently not possible. The potential for the hazard cascading down-valley if the lake dam fails. It is likely at this stage that the lake will overtop close to the former channel, and hopefully drain into the emptied dams downstream. The high sediment load will likely have impacts downstream for a few years.
Solidarity to the inhabitants of Blatten who have lost their home, and I grieve for their catastrophic loss.
Was this due to climate change?
Birch Glacier collapsed, causing the devastating landslide that impacted Blatten village, because it was overloaded with debris, rather than due to climate change causing more melting. Although glacier detachments do occur as a result of warming resulting in more meltwater reaching the bed of steep mountain glaciers, the situation here is more complex.
However, mountain landslides are becoming more common in a warming climate, and so more large events like this are happening. A warming climate can lead to increased rainfall, melting permafrost and changing the number of freeze-thaw cycles, and this can exacerbate mountain landslides.
In summary, climate change can lead to large landslides and major mountain hazards like this becoming more common. Although it is simplistic to claim that this specific event occurred due to climate change at the moment, these catastrophic events are more likely in a warmer world.
Shrinking glaciers in a warming world
Climate change is causing dramatic changes in mountain glaciers in Europe, and elsewhere. Record glacier melt occurred globally in 2023, according to the WGMS, and Sweden showed the highest melt levels in 80 years of observations. In 2024, the melt from glaciers was again very high. At least one third of European Alps glacier loss will be lost by 2050, even without further warming, and if current emissions continue, two thirds of glacier ice will be lost. The rapidly changing cryosphere, and mountains above mountain glaciers, may result in rapid changes in mountain hazards.
More details and data are available in the 2024 State of the Cryosphere report: https://iccinet.org/statecryo24/
This ongoing glacier recession, firmly attributed to climate change due to increased temperatures driving more glacier melt, had already resulted in the along-flow disconnection between the lower and upper parts of the Birch Glacier. The glacier became disconnected, or separated, in ~2000 AD, and the lower glacier started to advance by about 50 m since 2019, and the ice velocity and terminus thickness increased. This is likely due to the periodic input of the rockfall from above, insulating the glacier from melting and increasing the mass of the glacier through adding rock material. The separation of the glacier may have made it more susceptible to catastrophic detachment, by removing the longitudinal stresses that can support steep mountain glaciers.
This anomalous behaviour, associated with glacier shrinkage, meant that the Birch Glacier was preconditioned to be hazardous, and regularly monitored.
Furthermore, a warmer climate can also increase glacier detachments by encouraging more surface and basal melt in steep mountain glaciers, which can result in catastrophic glacier detachments. More basal meltwater means more lubrication and reduced basal friction.
In summary, climate change likely contributed to a number of factors that preconditioned the glacier to collapse, and made the large scale rock slope failure more likely. However, attributing the specific incidence of the rock fall onto the glacier surface and the resulting ice-rock avalanche down valley, is simplistic.
Further reading:
Dave Petley’s Landslide Blog: excellent, informative and vital source of information.
Big thanks to Melaine Le Roy for daily informative updates! Follow him on Bluesky.
ICCI State of the Cryosphere 2024
Kaab et al., 2021. Glacier detachments.
Zou et al., 2023. Triggers for glacier detachments after ice-rock debris loadings from headwalls.
ABC news, with comment from Bethan Davies, Mathieu Morlighem and Sridhar Anandakrishhan
This is also a great tool for showing just how much of the town was built on ground formed from previous landslides. Living in beautiful places like the ocean front and valleys formed from decaying mountain ranges comes with the increased threat of mother nature changing your living arrangements. Thanks for sharing this great article and geometry dash lite.
This is also an excellent tool for demonstrating how much of the town was constructed on top of previously produced landslides
Thanks!