Abstract
Abstract. The “Masiere di Vedana” rock avalanche, located in the Belluno Dolomites (NE Italy) at the foot of Mt. Peron, is reinterpreted as historic on the base of archeological information and cosmogenic 36Cl exposure dates. The deposit is 9 km2 wide, has a volume of ∼170 Mm3 corresponding to a pre-detachment rock mass of ∼130 Mm3, and has 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 stratigraphic sequence is preserved in the deposit with the formations represented in the boulders becoming younger with distance from the source area. In the release area the bedding, the SSE-verging frontal thrust planes, the NW-verging backthrust planes, the NW–SE fracture planes, and the N–S Jurassic fault planes controlled the failure and enhanced the rock mass fragmentation. The present Mt. Peron crown still shows hundreds-of-metres-high rock prisms bounded by backwall trenches. Cosmogenic 36Cl exposure ages, mean 1.90±0.45 ka, indicate failure occurred between 340 BCE and 560 CE. Although abundant Roman remains were found in sites surrounding the rock avalanche deposit, none were found within the deposit, and this is consistent with a late Roman or early Middle Ages failure. Seismic and climatic conditions as landslide predisposing factors are discussed. Over the last few hundred years, earthquakes up to Mw=6.3, including that at 365 CE, have affected the Belluno area. Early in the first millennium, periods of climate worsening with increasing rainfall occurred in the NE Alps. The combination of climate and earthquakes induced progressive long-term damage to the rock until a critical threshold was reached and the Masiere di Vedana rock avalanche occurred.
Highlights
Landslides have an enormous impact on landscapes and can be a serious threat to human lives and buildings
The deposit is 9 km2 wide, has a volume of ∼ 170 Mm3 corresponding to a pre-detachment rock mass of ∼ 130 Mm3, and has a maximum runout distance of 6 km and an H /L ratio of ∼ 0.2
Cosmogenic 36Cl exposure ages, mean 1.90 ± 0.45 ka, indicate failure occurred between 340 BCE and 560 CE
Summary
Landslides have an enormous impact on landscapes and can be a serious threat to human lives and buildings. Assessment of the potential for future events is distinctly dependent on knowledge of the conditions under which past failures occurred in the immediate vicinity (Samia et al, 2017). This entails detailed analysis and interpretation of driving factors as well as possible triggers of past events (Eisbacher and Clague, 1984; Nicoletti and Sorriso-Valvo, 1991; Hungr, 2006; Strom, 2006; Hermanns and Longva, 2012). Damage accumulation in rock (fatigue) contributes to the location of failure (Friedmann et al, 2003; Brideau et al, 2009; Parker et al, 2013; Stead and Eberhardt, 2013; Preisig et al, 2015), while seismic shakings (Keefer, 1993; Friedmann et al, 2003; Dunning et al, 2007; Cui et al, 2011; Stead and Eberhardt, 2013) and periods of extreme rainfall (Guzzetti et al, 2008; Tsai and Wang, 2011; Loew et al, 2017; Preisig et al, 2015) can trigger landslides.
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