Landslides of the Western Dolomites: case studies from the Adige and Sarca Valleys (NE Italy)

The Lavini di Marco, Marocche di Dro and Molveno rock avalanches in Trentino, and the Termeno landslide in South Tyrol are here presented as case studies for the western Dolomites (Adige and Sarca Valleys, NE Italy). Their structural predisposition, run-out and timing are discussed, also in consideration of other evidence for the Alpine region. The detailed geomorphological mapping of deposits and their release area, combined with regional and local structural analysis, isotopic dating, and numerical modelling, have led to updated interpretations of their mechanisms, timing, and triggering/driving forces. In particular, the major role of structural controls is investigated. Intense rock damage and rock fatigue, which are related to tectonic activity along the Southern Giudicarie and Schio-Vicenza fault systems, together with high topographic relief energy and local dip slope, all combine to promote detachment of huge rock volumes. Besides structural predisposition, other factors like glacial erosion/unloading and climate can exert a primary control. Three large rock avalanches occurred between 5-3 ka ago: Lavini di Marco (200 Mm3, 3.0±0.4 ka), Marocca Principale (1000 Mm3, 5.3 ±0.9 ka) belonging to the Marocche di Dro complex, and Molveno (600 Mm3, 4.8±0.5 ka). This period has been recognized as one of enhanced slope failure activity in the Alps, perhaps related to the climatic transition to cooler and wetter conditions at the beginning of the late Holocene. This is particularly valid for the close contemporaneity of the Marocca Principale and Molveno rock avalanches. Conversely, younger ages at the Kas rock avalanche (Marocche di Dro complex; 300 Mm3, 1.1±0.2 ka) likely imply a close relation with seismic forcing.