Structural and climate drivers of the historic Masiere di Vedana rock avalanche (Belluno Dolomites, NE Italy)

Abstract

Abstract. The “Masiere di Vedana” rock avalanche, located in the Belluno Dolomites (NE Italy) at the foot of the Mt. Peron, is re-interpreted as Historic on the base of archaeological information and cosmogenic 36Cl exposure dates. The deposit is 9 km2 wide, has a volume of ~ 170 Mm3 correspondings to a pre-detachment rock mass of ~ 130 Mm3, and a maximum runout distance of 6 km and an H / L ratio of ~ 0.2. Differential velocities of the rock avalanche moving radially over different topography and path-material lead to the formation of specific landforms (tomas and compressional ridges). In the Mt. Peron crown the bedding is subvertical and includes carbonate lithologies from lower Jurassic (Calcari Grigi Group) to Cretaceous (Maiolica) in age. The proximal deposit is made of Calcari Grigi Group limestone, the distal deposit comprises upper Jurassic limestones (Fonzaso Formation, Rosso Ammonitico, and Maiolica), while the middle Jurassic Vajont Limestone dominates the central sector of the deposit. In the release area the bedding, the SSE-vergent frontal thrust planes, the NW-vergent backthrust planes, the NW-SE fracture planes, and the N-S Jurassic fault planes controlled the failure and enhanced the rock mass fragmentation. Cosmogenic 36Cl exposure ages, mean 1.90 ± 0.45 ka, indicate failure occurred between 340 BC and 560 AD. Although abundant Roman remains were found in sites surrounding the rock avalanche deposit, none was found within the deposit, and this is consistent with a Late Roman or early Middle Age failure. Seismic and climatic drivers are discussed. Over the last few hundred years, earthquakes up to Mw 6.3 including that at 365 AD, affected the Belluno area. Early in the first millennium, periods of climate worsening with increasing rainfall are known in the NE Alps. The combination of climate and earthquakes induced progressive long-term damage to the rock. The present Mt. Peron crown shows hundreds of meters-high rock prisms bound by backwall trenches, suggesting a potential landslide hazard for the whole mountain belt north of Belluno affected by the same structural characteristics.

Large landslides in the Alpine valleys of the Giudicarie and Schio-Vicenza tectonic domains (NE Italy)

“…A detailed mapping of their location and the study of their mechanisms are crucial in order to achieve reliable hazard maps and correctly assess their destructive potential (Abdulwahid & Pradhan, 2017;Trigila et al, 2018). For this reason, large landslides in the Alps have been also studied in order to assess their age, in relation with structural setting (bedding, faults, joints), ongoing climatic change, and seismicity (Ivy-Ochs et al, 2017a;Rossato et al, 2020;Stead & Wolter, 2015;Trigila et al, 2007).…”

“…In order to highlight the reason for their frequency in this sector of the Alps, in addition to older studies that mainly focused on deposit extension (Largaiolli, 1990;Oetheimer, 1989;Perna, 1991;Trener, 1924; Figure 2), great effort has been recently put on understanding their mechanisms, timing and drivers (Ivy-Ochs et al, 2017a, 2017bMartin et al, 2014;Spreafico et al, 2018;von Wartburg et al, 2020;Zampieri & Adami, 2013). The prevalence of such rock failures has been suggested to be given by the combined action of different factors, such as extreme relief, tectonic setting, climate, and seismic ground shaking (Ivy-Ochs et al, 2017a;Rossato et al, 2020).…”