Fluchthorn
The terrain affected by the Fluchthorn event is particularly notable for its steep release zone. The initial failure involved a largely dry mass that fell onto snow-covered ground composed of ice-rich sediments. A significant portion of the avalanche material was deposited on an upper plateau before the remaining flow descended a steep cliff in multiple arms—the most powerful of which was the northernmost.
Michael Mölk (Head of the Geology Unit, Wildbach- und Lawinenverbauung, Innsbruck) provided critical data on the Fluchthorn avalanche event, which helped constrain the RAMMS::RockIce model parameters.
While much of the avalanche’s energy dissipated on the upper slope, the northern arm continued beyond the cliff, reaccelerating and entraining additional material. It struck a rock wall, which deflected the entire avalanche into the glacier lake, leading to substantial entrainment of lake water. Calculated peak velocities reached over 60 m/s on the upper slope, but the main body of the avalanche lost most of its energy before the cliff. In contrast, the northern arm reaccelerated to approximately 35 m/s after the drop.

Figure 1: Location of water in the Fluchthorn avalanche deposits.
From the saturated deposits at the lake margin, small debris flows were initiated. RAMMS::RockIce simulated this event using a single release zone and three entrainment zones. The uppermost zone represented a mixture of soil and ice-rich sediments with water; the second was defined along the steep cliff; and the third encompassed the lake, modeled as 80 percent water and 20 percent soil sediments.
A unique feature of RAMMS::RockIce used in this case was its capability to define a mountain snow cover (see Figure 2). The snow was modeled as dense, cold, and high-elevation, with near-zero temperatures. Meltwater from this snow cover contributed to fluidizing the avalanche, enabling the northern arm to traverse the flat plateau and descend the cliff.
Video 1: Simulated dynamics of the Fluchthorn rock-ice avalanche.
This simulation captures the complex behavior of the Fluchthorn rock-ice avalanche. The orange-yellow-green areas indicate the extent and location of deposited avalanche material. As the avalanche traverses a broad plateau, it leaves behind a significant volume of debris. However, a portion of the mass continues over a steep cliff, accelerating rapidly and entraining additional material along the way. This highlights the powerful remobilization processes that can occur in mixed rock-ice avalanches, particularly when abrupt terrain transitions are involved.

Figure 2: Snow cover conditions used in the Flüchthorn RAMMS::RockIce simulations. The model allows for the inclusion of a high-alpine snowpack, enabling realistic representation of dense, cold mountain snow. In this event, the entrained snow played a dual role – reducing flow friction and contributing meltwater that helped lubricate and fluidize the avalanche, ultimately influencing its mobility and runout.