Long-and short-term controls on the spriana rockslide (Central alps, Italy)

Deep-seated rockslides in alpine valleys involve huge volumes and evolve over a long time under the action of multiple triggers. Scenario assessment and early warning systems based on monitoring activities are often the only effective ways to mitigate related risks, and require a sound understanding of complex interacting controls. We discuss the Spriana rockslide, affecting the left-hand flank of Val Malenco (Italian Central Alps). Documented rockslide activity dates back to 1912, with major acceleration stages in 1960 and 1977-1978 and later minor reactivations. The rockslide is a compound slide involving up to 50 Mm3of slope debris and fractured rock, with a basal failure zone up to 90 m deep and two main scarps. Rock mass characterisation based on laboratory and field analyses provided inputs to 2D Finite-Element modelling of long-term slope evolution. The results allowed re-evaluation of the mechanisms of the Spriana rockslide, accounting for both long-term controls related to valley deglaciation and the short-term complexity of groundwater response to rainfall inputs. We suggest that modelling long-term slope evolution may be required to correctly understand large rockslides in changing geomorphic systems.