Hazard assessment of a potential rock avalanche in south tyrol, italy: 3d modeling and risk scenarios

Abstract

A large DSGDS (Deep-Seated Gravitational Slope Deformation) which extends on an area of 3.75 km2 affects the southwest flank of Mount Ganderberg some 40 km north of Bolzano. The gravitational sagging of the slope is generating a wide field of tension cracks in the crown area where a rock slab of about 800.000 m3 shows clear precursory signs of possible detachment. In 1401 a rock avalanche detaching from the same area dammed the Passer River thus creating a 35 m deep lake which through sequential breaching caused many casualties in the villages downstream. Using geomorphological survey and historical analysis it was possible to estimate the volume of the landslide deposit in 2 × 106 m3. In this study the historical event is back-analyzed using the 2D code DAN-W in order to select the proper soil parameters to use in the modelling of the present potential rock avalanche. Then a 3D modelling is carried out using DAN3D software to evaluate the run-out scenario and the shape of the natural dam. Owing to the relevant discharge of the Passer River, a 2 × 106 m3 lake might be quickly filled. This can cause the breaching and subsequent collapse of the landslide dam with great risk and potentially heavy damages for the downstream population.