On Wednesday, the glacier known as Birchgletscher collapsed under the weight of rock and debris from rock avalanches on Kleines Nesthorn. In a factsheet, ETH researchers explain the background to the catastrophic collapse that buried the village of Blatten.
In brief
- In terms of the volume and the extent of the damage caused, the collapse of the Birch Glacier is unprecedented for the Swiss Alps.
- Several rock avalanches from Kleines Nesthorn, a mountain located above the Birch Glacier, played a critical role in the collapse. The details are still being investigated.
- The accumulated rock debris increased the pressure on the glacier ice, contributing to the destabilisation of the Birch Glacier- until it finally collapsed.
A collapse of the magnitude of the Birch Glacier, which buried the village of Blatten in Valais on Wednesday, is unprecedented for the Swiss Alps. While a rock-ice collapse at Piz Scerscen in April 2024 did cause a similar amount of ice and debris to fall - estimated at eight to nine million cubic metres - as in the Lötschental valley this week, the collapse in the Engadine region did not result in as much damage as in Blatten.
Daniel Farinotti, Professor of Glaciology at ETH Zurich and the Federal Institute for Forest, Snow and Landscape Research (WSL), asserts that the exact causes of Wednesday's glacier collapse are far from fully understood. In particular, Professor Farinotti states, it is not yet conclusive whether external factors or primarily reactions inside the glacier itself were decisive in ultimately triggering the collapse.
However, since authorities and researchers have been monitoring the glacier for years, there are clear indications that several rock avalanches and terrain movements on Kleines Nesthorn, the mountain above the glacier, were the primary cause behind the glacier's collapse.
"We know there were already several rock avalanches before the collapse on Wednesday and that rock debris accumulated on the glacier as a result," says Professor Farinotti, who has been working with ETH and WSL researchers Matthias Huss and Mylène Jacquemart to compile a factsheet that summarises the current state of knowledge from the perspective of glacier research.
"Our aim is to use this data and our available knowledge to support the authorities, who are doing incredible work in extremely difficult circumstances to maintain an overview of the conditions and improve the situation for the people," explains Professor Farinotti.
The Birch Glacier has been moving for some time
The accumulated rock debris - estimated by the authorities to amount to 9 million tonnes - increased the pressure on the glacier ice and encouraged the formation of meltwater at the base of the glacier. The rising water pressure, together with the incoming rain and the unstable mountain terrain, destabilised the Birchgletscher and accelerated the flow of ice. As a result, the glacier moved deeper and deeper down the valley until it finally collapsed.
The unusual valley movement of the Birch Glacier had already attracted the attention of researchers and authorities some time ago, prompting closer observation of the movements around Kleines Nesthorn.
With glaciers generally retreating throughout Switzerland, ETH researchers - currently documenting glacier developments within the GLAMOS glacier monitoring network together with the universities of Fribourg and Zurich - noticed that the front of the glacier in the lower part of the Birch Glacier had advanced by approximately 50 metres since 2019.
Observational data also shows that ice thickness at the glacier snout advanced by up to 20 metres between 2017 and 2023, while the upper reaches of the glacier thinned. This increase is due in part to the rock debris resting on the glacier, as this prevented the ice from melting at the surface.
Comparison with other ice and rock collapses
Kleines Nesthorn and the Birch Glacier have been under close observation since the 1990s, when two snow and ice avalanches affected part of the local infrastructure. Part of the Birch Glacier's development can also be seen in external page satellite images .
The glacier collapse above Blatten has some parallels to the rock avalanche at Piz Cengalo in 2017, when around three million cubic metres of rock fell onto a small glacier, causing it to be partly swept away and triggering a flow of debris. This caused severe damage to infrastructure in the village of Bondo. Eight people were killed during the incident.
On 2 September 2002, the Kolka-Karmadon glacier collapsed in the Russian Caucasus, resulting in 100 million cubic metres of ice travelling up to 19 kilometres down the valley. The avalanche buried the village of Nizhniy Karmadon and claimed 125 lives. In Valais, systematic surveillance and the precautionary evacuation of the village of Blatten fortunately prevented such a tragedy.
Factsheet on the glacier collapse
The current knowledge on the collapse of the Birch Glacier, compiled by ETH and WSL glacier researchers Daniel Farinotti, Matthias Huss and Mylène Jacquemart, has been compiled in Download this factsheet and is available to download. (PDF, 143 KB)
