The model captures shockwave effects
In recent weeks, the team revisited the initial unpublished simulations and noted that using a slightly higher friction value of 0.23 would have improved the match even further. Moreover, it turned out once again that the model is capable of realistically handling cascading processes in complex, steep topography.
“Overall, we have achieved a level of predictive accuracy that enables our model to provide more precise estimates of complex alpine mass movements in the future — both in terms of how far they may extend downslope and how much of the valley floor they might cover,” Gaume states.
“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,” he adds, clarifying that these scientific simulations have not been communicated to the Valais authorities and are not part of the ongoing official investigations and risk management efforts.
As in reality, the simulation results indicate that most of Blatten is destroyed, while the neighbouring area of Weissenried narrowly escapes the falling rock and ice. The model very precisely shows a runout of the collapsed mass of 1.2 kilometers on the southwest side of the valley and 700 meters on the northeast side — values that prove to be highly accurate when compared with the actual disaster.
One key factor in the case of the Birch Glacier above Blatten was the complexity of the terrain: the rock and ice flow began in a relatively open area, narrowed dramatically, and ended in a gorge that was not aligned with the initial direction of movement. This created a shockwave effect that caused part of the descending flow mass to become airborne (as captured in videos of the event) — a phenomenon that traditional models typically fail to capture. Notably, particles were reported to have reached heights exceeding 100 metres above the terrain surface.
Widely used tools in engineering practice for modelling snow avalanches, rock avalanches and debris flows are typically based on 2D depth-averaged methods. These assume that the rock and water flow is shallow and remains in constant contact with the terrain, resulting in continuous friction. “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 behaviour and runout in steep or complex terrain,” Gaume explains.
Towards advanced modelling in hazard management
These models provide more realistic insights into flow dynamics, impact zones, and runout distances —ultimately enabling better-informed decisions and more effective risk mitigation. “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,” Gaume explains.
“We hold the authorities in the L?tschental and in Brienz in the highest regard for the exemplary way in which they have managed — and continue to manage — the situation, and we feel deep compassion for the residents who have lost their homes and belongings,” Gaume emphasises. “Tragically, the glacier collapse also claimed one life, which reminds us of the very real human cost behind these natural disasters.”
This further strengthens Gaume’s resolve to do everything possible to ensure that forecasting and early warning of such events becomes even more effective in the future. Looking back at the early stages of modelling the rock-ice avalanche, Gaume recalls the uneasy awe he felt when the simulations first indicated a possible destruction of the village:
“On my side, 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. I therefore felt it was essential to discuss them with my colleagues before taking any more formal steps.”
With their newly developed model, the researchers from ETH and SLF have taken an important step toward making 3D simulation tools even more accurate for future hazard assessments — especially in complex alpine environments — and, hopefully, helping to reduce the extent of damage and loss in the future.