The January 18th 2017 Rigopiano avalanche disaster in Italy - Analysis of the avalanche dynamics

On January 18th, 2017, a catastrophic avalanche released from Mount Siella (Gran Sasso Massif - Italy) after a 48-hour period of heavy snowfall. The avalanche started at 1900 m asl, flowed through a narrow canyon and then uprooted a beech forest, reaching the Rigopiano area as a "wood avalanche" (a mixing of snow, uprooted and crushed trees, rocks and other debris). The consequences were catastrophic: the avalanche completely destroyed the Hotel Rigopiano and 29 people died. The Rigopiano avalanche presented many remarkable features of snow avalanches. These include how avalanches entrain snow and reach extremely long runout distances with little braking effect from mountain forests. This paper presents part of the simulations carried with the extended software RAMMS, developed by the WSL-SLF, to reconstruct the flow dynamics of Rigopiano event. Chiambretti et al. (these proceedings) describe the multidisciplinary approach to snow engineering and structural and geotechnical engineering, jointly with applied forensic field investigation techniques with different analyses which lead to the choice of the different inputs for the avalanche simulations. In particular, from the data gathered in situ, we observed that the avalanche was a fluidized dry snow avalanche which entrained a warmer snow cover along the path. From the simulations’ results, it seems that the snow cover conditions had a significant effect on the avalanche dynamics (to simulate such long run-out distance), while the mix of wood and snow was the most important factor when analyzing the structural collapse of the hotel. In conclusion, this paper presents the simulation of the catastrophic avalanches and highlights the importanceof making correct specific assumptions when using avalanche dynamic models to reproduce real events. Such considerations must be taken into account and uncertainties have to be considered also when dealing with forensic investigations.