Assessing the morphological changes of a large landslide using high-resolution UAS and airborne LiDAR data

The Upper Orcia Valley exhibits a high geomorphological susceptibility to denudation processes, which manifest through continuous water erosion and the frequent occurrence of landslides, due to the high erodibility of its clay-rich marine and fluvial Pliocene deposits in a sub-humid environment. A significant landslide event occurred in January 2021 on a badland hillslope, affecting an area of 0.54 km² within the Formone sub-catchment, approximately 6 km northwest of the Radicofani village. The landslide occurred in a badland hillslope, marking a transition from water-driven denudation processes to gravitational mass movements, thus leading to a complete reconfiguration of the hillslope. This study aims to quantify the morphological changes induced by the landslide and analyze the erosion dynamics of complex landslides in clay-rich substrates. UAS photogrammetry (SfM-MVS), available airborne LiDAR, and DGNSS surveys were employed to analyze volumetric changes over a decade (2012–2022), identify the most affected areas, and investigate the internal morphological evolution of the landslide. The results indicate a total displacement of 17302 m³ of material, with a maximum surface lowering of -6.49 m in the landslide scarp and a maximum deposition of +5.01 m in the westernmost section, resulting in a negative sediment balance of 9980 m³. The landslide, which exhibits a complex dynamic, evolved into a debris flow, with secondary erosion processes further reshaping the landscape. Given the region’s susceptibility to denudation and anthropogenic modifications, understanding these processes is crucial for hazard assessment and mitigation strategies. This study highlights the importance of high-resolution topographic surveys for detecting morphological changes and evaluating landslide-prone areas in similar environments