High-resolution, UAV-based mapping of the DSGSD scarp at Padauner Berg (Brenner Pass, Austria)

Large-scale landslides pose a significant threat to both population and infrastructure. Among various slope movements, deep-seated gravitational slope deformations (DSGSDs) are landslides affecting large portions of slopes, occurring in several mountain regions in the Alps and worldwide. These processes are evolving in a long-term dynamic, and their kinematics are characterized by relatively low displacement rates (mm-cm/yr) compared to the spatial extent of the affected slope. However, these phenomena should not be neglected when assessing potential hazards in a specific area. Continuous evolution of DSGSDs may cause damages to infrastructure and, in some cases, evolve into secondary, faster landslide processes and invoke a substantial risk for critical infrastructure. This becomes of major importance when the infrastructure is essential for local communities, commuters and cross-border transportation. Therefore, it is important to investigate and better understand ongoing processes.

This study presents preliminary findings from the investigation of a known DSGSD in the bottleneck area of the Brenner Corridor between Italy and Austria. In this region, the occurrence of DSGSDs is controlled by the tectonic setting, combined with the presence of lithologies with structural weaknesses (e.g., schistosity). These slope instabilities not only affect entire valley flanks, potentially involving massive unstable volumes in case of collapse, but also threaten the Brenner corridor, a key transportation route linking northern and southern Europe across the Alps. Our investigation focuses on the characterization of the upper scarp of the Padauner Berg slope (2230 m a.s.l.) in Austria, which shows surface evidence of ongoing deformation. The research combines close-range remote sensing using a commercial UAV device (DJI Phantom 4 Pro) and field observations across an area of 0.10 km². Images captured during the UAV survey were processed using a standard Structure from Motion (SfM) workflow to generate a high-resolution 3D point cloud. The point cloud was georeferenced using ground control points (GCPs), equally distributed across the study area and surveyed with a high-precision GNSS device. Approximately one-third of the GCPs were used as checkpoints to assess the accuracy of the georeferenced point cloud.

The results of this study contribute to identifying terrain morphologies and mapping distinct morphostructures on the slope, such as ridges and uphill-facing scarps. These findings provide a preliminary assessment of the potential extent and enlargement of the slope instability, aiming to bridge the gap between remote sensing outputs and conventional geomorphological analysis to understand DSGSD dynamics at a local scale. Additionally, this study evaluates the possibility of complementing previous DEMs as well as orthoimagery to calculate surface changes and quantitatively assess the temporal evolution of the investigated DSGSD. However, while UAV-based surveys offer a practical solution for spatial representation of potentially hazardous processes in high-alpine areas, the study highlights certain methodological limitations, such as flight altitude and terrain accessibility, that must be considered when planning flight missions to ensure consistent and comparable results across repeated surveys.