High-Resolution GNSS and UAS Monitoring of an Active Landslide in the Northern Apennines (Italy): Implications for Early Warning Systems

Landslides represent a major natural hazard worldwide, posing risks to infrastructure and population. Monitoring active landslides is essential for understanding their dynamics and developing effective early warning systems. We integrate Global Navigation Satellite System (GNSS) and Unmanned Aerial System (UAS) technologies to monitor the behavior of a complex, earth-flow landslide in the Northern Apennines of Italy. We deployed a small GNSS network on the crown and upper body of the landslide to investigate its kinematics and assess the feasibility of using GNSS data for early warning purposes. Periodic UAS surveys were conducted to complement the continuous GNSS measurements, providing spatially detailed information on surface displacements. The integrated monitoring revealed that the landslide behaves as a single, coherent body with localized differences in response to triggering events. Its kinematics is characterized by recurrent acceleration–deceleration cycles, leading to both major detachment events and intermittent periods of rest. GNSS data recorded maximum horizontal velocities of 0.03 m/day at the crown and up to 4.862 m/day within the upper body. UAS-derived visual image matching of ortophotos detected higher displacements—up to 13 m/day—downstream of the GNSS stations. Cumulatively, the landslide displaced approximately 41,148 ± 5,723 m³ of material over the monitoring period. Crucially, we demonstrate that once appropriate threshold values are established, GNSS velocities are reliable indicators of impending slope failures, with potential to provide early warning several days in advance. These findings highlight the value of GNSS networks for enhancing operational landslide early warning systems.