Multi-sensor anatomy of the March 2025 landslide sequence in Poggio Baldi (Northern Apennines, Italy)

On March 14–16, 2025, a sequence of two distinct landslide events affected the Poggio Baldi landslide (PBL) area (43° 54′ 26″ N, 11° 48′ 34″ E, 441 m a.s.l., Northern Apennines, Italy): an earth flow on March 14 involving the debris talus accumulated since 2010, followed by a rock slide on March 16 affecting the right shoulder of the main scarp of the former PBL. Both events were triggered by exceptional rainfall (117.8 mm/day, the second-highest recorded since 2021) and comprehensively documented through the site’s integrated multi-sensor monitoring infrastructure. The earthflow, with an estimated volume of 30,000 m3, occurred 3 h after peak rainfall intensity, demonstrating a rapid response to the meteorological trigger. Pre-, syn-, and post-failure evolution was framed by a combination of remote sensing approaches. Optical Digital Image Correlation and thermal image analyses revealed average velocities of 18.3 cm/h with peaks reaching 100 cm/h. The rockslide (35,000 m3) was preceded by precursory rockfall activity detected by motion-triggered optical cameras and an InfraRed camera, as well as progressively monitored through optical monitoring. Acoustic analysis characterised the collapse as a three-phase event lasting 4 min and 30 s with dominant frequencies at 315 Hz. An Interferometric Arc-SAR monitoring system documented the post-failure evolution of the rockslide debris, showing maximum displacements of 1.8 m, and revealing sudden reactivations to the following rainfall events. An optical satellite analysis confirms the area of the event, approximately 3 ha, and highlights the reactivated part with respect to the older PBL. The combined events mobilised approximately 65,000 m3 of material, with the slope achieving near-stable conditions after 2 months. This case study demonstrates the effectiveness of integrated remote sensing–based monitoring for capturing the complete landslide sequence, from its precursors, triggers, up to progressive stabilisation, providing crucial quantitative data to advance the understanding of complex slope deformation processes that anticipate the ultimate failure. Furthermore, this event proved the applicability of low-budget image-based monitoring systems in early warning applications.