The Ganderberg landslide (South Tyrol, Italy): Mitigation of residual risk by real-time monitoring

The whole flank of Ganderberg western slope (3.75 km2) (lat. 46°51'12'', long. 11°10'15'') is involved in a Deep Seated Gravitational Slope Deformation phenomenon. The upper part is characterized by several joint surfaces, with possible wedge failure mechanisms. In particular, the northern crown ridge is divided into three sectors with noticeably different indications of subsidence and displacement. The orientation of the joint planes and evidence of vertical movements of a distinct rock block allow a potential rock avalanche to be hypothesized (up to the volume of 4.5 x 105 m3). On the basis of historical archives analysis it was found that the same slope was involved in a rock avalanche event dating back to 1401. The landslide deposits created a 35 m deep lake, damming the Passer Torrent, creating the Passeirer Wildsee or Kummersee. Aim of the study is the evaluation of residual risk scenarios and its mitigation by means of monitoring and data interpretation using Saito and Fukuzono techniques.