Timing, drivers and impacts 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 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.

Created by the Monte Peron rock avalanche: Lago di Vedana (Dolomites, Italy) and its sediment record of landscape evolution after a mass wasting event

“…The obtained age of 1.9 ±0.45 ka, i.e. between 340 BC and AD 560, represents the historical Roman Empire of the 2 nd century AD (Rossato et al 2020). This age is the mean of six exposure ages from boulders across the Masiere di Vedana ranging from 1.45 ±0.12 to 2.39 ±0.38 ka and excludes one outlier of 3.62 ±0.41 ka.…”

“…The Masiere (Italian: stony ground) di Vedana is best described as a hummocky toma landscape with irregular topography and boulders of all sizes in a matrix of angular rock debris spotted with kettles and knobs (Rossato et al 2020) -a landscape characteristic for mass wasting deposits (cf., More and Wolkersdorfer 2019). These deposits are the result of the Monte Peron rock avalanche, which travelled a distance of 5.9 km and spread across the confluence plain of the Cordevole River and the Vallone Bellunense (Piave River valley) covering an area of 9 km² with a thickness varying from 5 to >30 m and an estimated volume of 0.17 km³ (Rossato et al 2020). On top of these rock-avalanche deposits, Lago di Vedana and todays peat bog Torbe developed as the successor of a landslide-dammed lake that formed immediately after this catastrophic event.…”

“…On top of these rock-avalanche deposits, Lago di Vedana and todays peat bog Torbe developed as the successor of a landslide-dammed lake that formed immediately after this catastrophic event. After deposition of the Masiere di Vedana the Cordevole River valley was blocked with two major consequences: (1) the Cordevole River was diverted and changed its course by 90° forming a river knee towards the Mis River valley in the W and (2) a landslide-dammed lake was formed between todays Cordevole River valley and Torbe peat bog (Rossato et al 2020). This paleolake was much larger than the modern Lago di Vedana causing deposition of lacustrine sediments: proximal gravels and distal silts.…”

“…Moreover, archaeological evidences are weak. Rossato et al (2020Rossato et al ( , p. 2166 argue that the region "was largely and uniformly inhabited by incolae for agricultural aims" but no Roman findings were excavated from the Masiere di Vedana. Evidences for Neolithic and Roman sites only exist from its surroundings.…”

“…Its age was initially estimated to Late Pleistocene (19,200 cal. BP) by , but recently re-evaluated by cosmogenic exposure dating to the 2 nd century AD by (Rossato et al 2020). Time constraints for mass wasting events are rarely unequivocal.…”