Breakthrough model will transform avalanche prediction

A new 3D simulation tool is helping scientists better predict landslides, rockfalls, and avalanches in the Alps – a region with steep, unpredictable terrain packed with ice, snow, and rock. These conditions have long made hazard forecasting extremely difficult.

Scientists at ETH Zurich and the WSL Institute for Snow and Avalanche Research (SLF) have built a model that can better simulate how these massive natural movements unfold. And it just passed its first real-world test: the evacuation of the village of Brienz in 2023.

Simulating avalanches in 3D

Until recently, most simulations used to forecast mass movements relied on 2D, depth-averaged models. These methods estimate average flow direction, speed, and thickness. They’re fast and helpful for general risk estimates, but their usefulness declines in rugged, highly variable landscapes.

“While classical depth-averaged models are very useful for first-order estimates, many have difficulties when dealing with rugged, irregular terrain like that seen in Blatten, where flow behavior is highly three-dimensional,” explained Professor Johan Gaume of ETH Zurich and SLF.

In 2022, he and his team published a paper outlining a new 3D avalanche model aimed at solving this problem. They accurately recreated several well-known disasters after the fact, including the 2017 Piz Cengalo rock-ice avalanche and the 1963 Vajont landslide.

But those were all simulations run after the events had happened. The real test would be to predict an event before it occurred.

Avalanche prediction proved accurate

In spring 2023, the mountainside above Brienz began to shift. Authorities ordered an evacuation. Without tweaking their model or adjusting any parameters, the ETH and SLF team ran what they called “blind simulations.”

They used surface movement data and conservative estimates from rock lab tests to gauge how much mass might fall and how it would move.

“Our simulation predicted that the resulting avalanche would stop just tens of meters short of the first houses. These results were shared informally with cantonal authorities and ultimately matched the actual extent of the real landslide very closely,” Gaume said.

A tougher avalanche simulation

In May 2025, a new risk appeared. This time, it was the village of Blatten. The hazard was even greater, involving a mix of rock, snow, and glacier ice from the Birch Glacier.

Once again, the ETH and SLF team jumped into action. They weren’t officially commissioned and had no direct contact with authorities, but they saw an opportunity to test their avalanche model against a much more complex challenge.

“Given the dramatic situation in Blatten and the novelty of our modeling approach, we proceeded with great caution and subjected the model to a rigorous verification process to ensure its accuracy and reliability,” Gaume said.

They estimated that the falling mass could be around 10 million cubic meters – a mix of 3 to 5 million cubic meters of rock and 5 million cubic meters of glacier ice. That estimate later proved extremely accurate: a post-event analysis confirmed a total of 9.3 million cubic meters.

For the sliding friction, they used a coefficient of 0.2 – a cautious pick based on past events. Though later tests suggested 0.23 would have been even closer to the final outcome, the match between simulation and reality was striking.

3D shows avalanche shockwaves

Most standard tools in hazard modeling assume the mass always stays in contact with the ground, sliding along the surface. But in Blatten, part of the avalanche flow shot into the air. That “airborne phase” created shockwaves and debris that flew over 100 meters above the terrain. The ETH-SLF model captured that too.

“In contrast, our 3D model allows particles to detach from the surface, reducing ground friction and accurately capturing airborne phases – this is critical for simulating flow behavior and runout in steep or complex terrain,” said Gaume.

The simulation showed a runout of 1.2 kilometers on the southwest valley wall and 700 meters on the northeast side. Those numbers almost exactly matched what actually happened. Most of Blatten was destroyed. Weissenried, nearby, was spared by a narrow margin.

Making the tool widely usable

The ETH and SLF researchers are working to make their 3D tool for avalanches accessible to officials and engineers.

“Our aim is not to replace existing 2D tools, but to offer a complementary solution where classical models may reach their limits. We are actively working to make our model accessible and usable for practitioners and authorities,” says Gaume.

The team emphasized that their simulations were not officially part of the risk management process in Blatten. But the results speak for themselves. They show how much more accurate hazard forecasts could become.

“We now have a reliable, ready-to-use tool that enables us to support the authorities with simulations assessing the potential consequences of impending mass movements,” said Gaume.

Respect for lives and limits

Gaume expressed his respect for the way local officials handled the crisis, praising authorities in the Lötschental and in Brienz for their exemplary management and expressing deep compassion for residents who lost their homes and belongings.

“Tragically, the glacier collapse also claimed one life, which reminds us of the very real human cost behind these natural disasters,” he said.

Looking back, Gaume remembers feeling unsure of the predictions. “The initial results I obtained seemed rather unrealistic, particularly due to the significant upslope flow toward Weissenried.”

“Had I had the opportunity to visit the site before running the simulation, I would likely have found these results even less plausible, given the elevation of the village relative to the Lonza,” he said. “I therefore felt it was essential to discuss them with my colleagues before taking any more formal steps.”

With continued refinement and real-world testing, this new 3D model may help save lives and minimize damage in future avalanches. It marks a shift in how we understand and respond to complex alpine hazards -with more accuracy, humility, and responsibility.

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