Debris cone in landslide-hit Blatten over 100 metres high in places

Debris cone in Blatten VS is over 100 metres high in places Keystone-SDA

According to the head of the Valais Natural Hazards Office, the cone of debris from the landslide in Blatten is over 100 metres high in places. Raphaël Mayoraz told the media that no cracks or major collapses of the pile of rubble have been detected so far.

However, this could change as soon as the ice begins to melt, Mayoraz said in an interview with the newspapers Walliser Bote, Le Nouvelliste and ArcInfo on Monday. The debris cone consists of six million cubic metres of rubble and debris. In addition, there are three million cubic metres of ice, he said.

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If the ice melts, mudflows could occur, said Mayoraz. However, he was confident that the Ferden dam wall further down the valley would be able to absorb them. Simulations have shown this. However, should several events occur simultaneously, the villages of Gampel and Steg would also have to be evacuated, he said.

The Lonza River poses a further risk. If the water carves a new path through the debris cone, so-called “water pockets” could form, said Mayoraz. These accumulations of water are not visible. But even in this scenario, the head of the Natural Hazards Department of the canton of Valais was optimistic. The Lonza is currently flowing in a relatively controlled manner and is slowly eroding.

Precipitation announced

As far as the predicted precipitation is concerned, “we don’t have to expect the worst”, added the geologist, basing his assessment on simulations. The water level of the lake that has formed behind the debris cone has dropped by around one metre.

Meanwhile, the Kleine Nesthorn above Blatten remains in motion. “Around 100,000 cubic metres of material are still unstable,” said Mayoraz in the interview. According to Mayoraz, there is practically no danger from the glacier as it has largely collapsed.

The opposite slope of the Kleiner Nesthorn also harbours a potential danger. Material up to ten metres high has been piled up there, Matthias Ebener from the municipal management staff told a reporter from the Keystone-SDA news agency on site on Sunday. This is unstable and due to the rain forecast for next week, there is also a risk that the rock masses on the opposite slope could slide down again.

The site is being monitored day and night, said Mayoraz. The observers from the fire brigade, army and civil defence will raise the alarm if, for example, they see that the level of the Lonza is rising or the dammed lake is draining faster. This allows them to react accordingly to developments down the valley at the debris cone or on the mountain.

Last Wednesday afternoon, the Birch Glacier above Blatten and the debris deposited on it fell from the Kleine Nesthorn into the valley. The village in the Valais Lötschental was largely buried. A lake formed behind the debris cone, which flooded houses that had been spared from the collapse.

>> Watch the collapse of the Birch Glacier above Blatten in southern Switzerland on May 28, 2025:

The glacier collapse had been preceded by a collapse on the Kleine Nesthorn. Around 300 people had been evacuated in advance. One person is missing after the collapse.

Blatten before and after the landslide: on November 3, 2024, and May 29, 2025 (move slider right/left to compare):

Adapted from German by DeepL/ac

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