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Forensic investigations of the Cima Salti Landslide, northern Italy, using runout simulations

Spreafico, Margherita Cecilia, Wolter, Andrea, Picotti, Vincenzo, Borgatti, Lisa, Mangeney, Anne, Ghirotti, Monica
Geomorphology 2018 v.318 pp. 172-186
forensic sciences, ice, lakes, landslides, melting, Italy
Over the last decades, a movement has begun to reclassify deposits previously misidentified as having origins other than landsliding. The reverse problem of incorrectly assigning deposits a mass movement origin, however, has been addressed less in the landslide community. The Cima Salti Landslide in the Lake Garda region of Northern Italy is a cautionary tale of assuming source areas and volumes. It was traditionally thought to have dammed Tenno Lake in the Middle Ages, and to have a volume of 20–30 Mm³. We show through geological field data and simple runout simulations with the codes DAN3D and SHALTOP (which produced comparable results) that the volume of the landslide was likely significantly overestimated in the past, and that it most likely did not dam Tenno Lake, as has been assumed. We propose that a smaller volume landslide (2–5 Mm³) was deposited on stagnant ice melting in situ in the Lateglacial period, a relatively minor event in the complex history of the Magnone valley. This interpretation emphasizes the importance of careful field investigations and assumption validation, at Cima Salti and in a broader context. It also shows the unique capacity of landslide simulation to guide field observation and discriminate mass emplacement processes.