Geographic-information-system-based topographic reconstruction and geomechanical modelling of the Köfels rockslide

Abstract. The Köfels rockslide in the Ötztal Valley (Tyrol, Austria) represents largest known extremely rapid landslide metamorphic rock masses Alps. Although many hypotheses for trigger were discussed past, until now no scientifically proven factor has been identified. This study provides new data about (i) pre-failure and failure topography, (ii) volume porosity of sliding mass, (iii) numerical models on initial deformation mechanism, as well shear strength properties basal zone obtained by back-calculations. Geographic information system (GIS) methods used to reconstruct slope topographies before, during after event. Comparing resulting digital terrain leads estimates deposition 3100 4000 million m3, respectively, a mass 26 %. For 2D investigation distinct element method was applied geomechanical characteristics process (i.e. model runs without zone) determine reconstructed zone. Based numerous varying block joint input parameters, could be plausibly reconstructed; however, exact geometry rockslide, especially view thickness, not fully reproduced. Our results suggest that both blocks shearing along dipping joints moderately east responsible formation or rockslide. progressive may have taken place fracturing loosening advancing from shallow deep-seated zones, development internal localized domains increased failure. simulations further highlighted importance considering dominant structural features mass. Considering back-calculations properties, i.e. friction angle zone, indicated under groundwater flow conditions, an exceptionally low 21 24? below is required promote failure, depending how much allowed. Model resulted approximately 6? higher back-calculated critical angles ranging 27 30?. Such are unexpected mechanical perspective this strong rock, flow, even if high water pressures assumed, able In addition, needed induce implemented significantly lower than those which would classical considerations. Additional conditioning triggering factors such impact earthquakes acting precursors weakening involved causing gigantic