Remote sensing-based deformation monitoring and geological characterisation of an active deep-seated rock slide (Tellakopf/Cima di Tella, South Tyrol, Italy)

Abstract

This study presents a 5-year long field campaign combined with 75 years of remote sensing data on the active, deep-seated Tellakopf rock slide in South Tyrol, Italy. Detailed field data and remote sensing techniques from airborne and terrestrial laser scanning (ALS, TLS) and orthoimages from federal flight campaigns and a helicopter-based monitoring campaign, allowed the development of a geometrical-kinematical rock slide model to investigate the initial failure and temporal-variable deformation mechanisms. The rock compound slide formed in foliated, highly fractured metamorphic rock masses at the SE-facing Tellakopf slope, directly above the commuter-rich national road SS 41. A total volume of approximately 3–4 Mm3 was estimated based on geographic information system (GIS) analysis by comparing the pre-failure surface topography and the reconstructed basal shear zone. Multi-temporal deformation analyses based on orthoimages, ALS and TLS data show alarmingly high velocities of at least 9 m/month during the initial formation phase in 2014, followed by a continuous velocity reduction to the current mean annual values of 1–2.5 m/year. Results indicate internal slab formation along discrete shear zones displayed on surface as main and minor scarps. These slabs show a translational movement behaviour along a fully persistent, slightly curvilinear basal shear zone. Rock mass yielding and fracturing conditions extensive mass loss manifested by high rock fall activity and large rock scree deposits at the rock slide toe. The cause for rock slide formation is attributed to retrogressive processes caused by long-term stress release due to topographical and hydrogeological changes by adjacent rock slides.