Le deformazioni gravitative del versante sinistro della Val Ridanna (Alto Adige-Sudtirol, Italia): geologia strutturale e geomeccanica

Two significant deep-seated gravitational slope deformations (DSGSDs) were recognized for the first time in this thesis along the northern slope of the Ridnaun Valley, west of Vipiteno/Sterzing (South Tyrol-Südtirol, Italy). They were named ‘DSGSD of the Wetterspitz’ and ‘DSGSD of the Telfer Weissen’ and are located respectively northwest and southeast of the niche of the post-Glacial Ridnaunvalley rockslide. Field surveys and aero-photo interpretation were carried out in order to clarify the structural, geological and geomechanical setting in which the DSGSDs are developing. The deformations affect both micaschists and gneisses, belonging respectively to the Upper Austroalpine basement of the Schneeberg Unit and of the Ötztal-Stubai Complex, as well as Late Pleistocene and Holocene glacial and slope deposits. Geomechanical investigations were conducted in order to divide the studied area in geomechanical domains, with sufficiently homogeneous properties. For each domain, the mechanical properties of discontinuities and of rocks were defined through field measurements and application of failure criteria (Barton-Choubey and Hoek-Brown criteria). Although the regional schistosity (Cretaceous in age) dips into the northern slope of the valley, the western DSGSD is clearly influenced by the structural setting of the area. N-S and NE-SW trending faults define the limits of the deformed area, whereas relicts of a south-dipping schistosity constitute the hinge zones of largescale folds and therefore act as a favorable factor for sliding. Instead, brittle and ductile settings apparently doesn’t influence the kinematics of the eastern mass movement. The DSGSDs show present-day medium-rate activity, as indicated by polished surfaces of many morphostructures and by interferometric data (courtesy of the ‘Provincia Autonoma di Bolzano’), with the western one more active. The recognized DSGSDs and the Rock Avalanche are interpreted to be three different stage of the same gravitational evolution. In fact, the DSGSD of the Telfer-Weissen is considered to be the initial stage of the deformation, whereas the “Wetterspitz” DSGSD is the expression of an advanced deformative stage. Both of them are leading to a rock avalanche-type slope evolution. More detailed II studies and numerical modeling are needed in the future to entirely clarify the kinematics and dynamics of the recognized ongoing DSGSDs. Keywords: Deep-seated gravitational slope deformation · Schneeberg · Eastern Italian Alps · Structural influence · Geomechanics