A Reverse Dynamical Investigation of the Catastrophic Wood-Snow Avalanche of 18 January 2017 at Rigopiano, Gran Sasso National Park, Italy

The snow emergencies that occurred in Central and South Italy in mid-January 2017 are well-known to the consultants. Probably the most important conditions occurred within the Marche, Abruzzo, and Molise areas the place the recorded snow accumulations have been excessive: ranging from the altitude of 800-900 m above sea degree (asl), the snowpack simply exceeded 300-350 cm. Dramatic emergencies occurred: difficulties in street clearing, absence of electrical energy for days (greater than 100,000 customers have been left with out electrical energy for nearly every week), remoted homes and villages because of the thick snowpack, and so forth. The social and financial prices of the snow occasion within the central Apennines have been very excessive, even with out contemplating the Rigopiano tragedy.

On 18 January 2017, seismic occasions occurred within the morning: they have been distinctly felt on the Rigopiano Gran Sasso Resort & Wellness (abbreviated as “Rigopiano Resort”), spreading panic among the many residents. However, because of the extreme climate situations, the 9-km lengthy entry street (provincial street no. 8) to the resort was blocked by recent snow, and energy provide and telecommunication have been interrupted. Not one of the entrapped 11 staff and 29 company had any probability of both receiving assist from outdoors or of leaving the resort after the seismic shocks.

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At about 15:40 (UTC), from an open slope on the east facet of Mt. Siella at 1969 m asl—Gran Sasso Massif, Italy, latitude 42.430992, longitude 13.782408—a snow avalanche launched, instantly encountered the beech forest and elevated its mass by entraining the timber within the snow circulate, operating down the 2-km lengthy pure channel, then impacted the Rigopiano Resort (at about 1118 m asl) at a terrific stress/velocity and destroyed the strengthened concrete construction. The implications have been catastrophic: the avalanche displaced the constructing downhill by nearly 50 m, tearing the concrete columns, tilting the higher flooring and the roof, and killing 29 individuals. The Rigopiano avalanche was probably the most important tragedy attributable to a snow avalanche because the 1916 White Friday Mount Marmolada occasion (Brugnara et al. 2017) in Italy, and because the string of 1999 avalanches in Europe—Galtur, Austria (Höller 2009); Montroc, France (Rapin and Ancey 2000); and Tacconaz, France (Berthet-Rambaud et al. 2007), by the variety of deaths because of the avalanche impacts on buildings.

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The forensic investigation began solely 9 days later, on 27 January 2017, as a result of within the days earlier than the precedence was to finish the problematic rescue operations geared toward discovering attainable survivors trapped below the particles of the constructing. The search and rescue operations lasted from the early morning of 19 January till the afternoon of 27 January and employed, on common, 347 rescuers and technicians, and a number of other dozens of sorts of equipment that have been used to take away the particles and open up areas for the rescuers.

One of many essential actions of the forensic investigation, during which three of the authors participated, geared toward reconstructing the most probably dynamics of this exceptional avalanche occasion, to interpret and decide the causes of the failure of the resort. The Rigopiano avalanche was a “wood-snow” avalanche—a mix of snow, uprooted and crushed timber, rocks, and particles, however on the identical time introduced many typical options of a quick dry-flowing avalanche. These embody snow entrainment and lengthy runout distances, with solely little damping and slowing impact supplied by the mountain forests.

Right here, the principle elements of the investigation are briefly reported, and the numerical simulation of the avalanche that was carried out with the software program RAMMS (developed by the Swiss Federal Institute for the Examine of Snow and Avalanches—Davos (CH)) is described. This text presents how the circulate dynamic of the occasion and the following impression to the resort have been reconstructed with the in situ observations and the outcomes of the avalanche mannequin. The numerical mannequin simulates the most probably circulate dynamics based on the rules of reverse engineering evaluation—the simulations helped to grasp the causes of the terrific structural collapse of the resort.

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