Reconstructing the Gorte and Spiaz de Navesele Landslides, NE of Lake Garda, Trentino Dolomites (Italy)

Abstract

We applied a multi-method approach to reconstruct the Gorte rock avalanche (85–95 Mm3) located at the northeastern end of Lake Garda. The combination of field mapping, characterization of bedrock discontinuities, Dan3D-Flex runout modeling and dating of boulders with cosmogenic 36Cl supports the conclusion that the deposits stem from a single rock avalanche at 6.1 ± 0.8 ka. The Gorte event may have triggered the Spiaz de Navesele–Salto della Capra landslide (3.2 Mm3), whose deposits cover the southern end of the Gorte deposits. First-order controls on detachment were the NNE–SSW- and WNW–ESE-oriented fractures in the limestone bedrock, related to the Giudicarie and Schio-Vicenza fault systems, respectively. Dan3D-Flex runout modeling sufficiently reproduced the Gorte rock avalanche, which involved detachment and sliding of a quasi-intact block, likely along marly interbeds, followed by rapid disintegration. The frictional rheology in the source area and the turbulent frictional rheology (Voellmy) in the remaining part best replicate the observed deposit extent and thickness. Heavy precipitation that occurred at that time may have contributed to failure at Gorte. Nonetheless, its timing overlaps with the nearby (<15 km) Dosso Gardene (6630–6290 cal BP) and Marocca Principale (5.3 ± 0.9 ka) landslides, making a seismic trigger plausible.

The Tamins rock avalanche (eastern Switzerland): timing and emplacement processes

“…A better understanding of rock avalanche occurrence and motion requires detailed analysis of a large number of case histories (e.g., Evans et al 1994;Nagelisen et al 2015;Grämiger et al 2016;Ivy-Ochs et al 2017;Singeisen et al 2020). As rock avalanches are infrequent events, studies of pre-historic rock avalanches provide crucial information regarding rock avalanche geomorphology and sedimentology (e.g., Cruden and Hungr 1986;Giorgio et al 1991;Dufresne et al 2016), runout mechanisms (e.g., Evans et al 1994;Nagelisen et al 2015;Castleton et al 2016;Grämiger et al 2016;Aaron et al 2020), and temporal occurrence (e.g., Ivy-Ochs et al 2017;Ruggia et al 2021), especially for the rare extreme volume event. In particular, detailed mapping of prehistoric rock avalanches has revealed that the source zone stratigraphy often remains intact in the highly comminuted deposit (e.g., Strom 2006, Dufresne et al 2016Singeisen et al 2020;Pfiffner 2022).…”