Debris Flows and Ground Deformation at Colli Albani Hills Volcano (Italy)

Colli Albani Hills, a volcanic complex located 20 km SE of Roma (Italy), represents a long-dormant caldera system and its last eruption is dated back ~ 20 ky. It is subjected to seismic swarms, gaseous emissions and ground deformations. The whole volcanic complex is affected by landslides of different typologies and in the past the most frequent were debris flows. In this study, for the first time, the debris flows susceptibility of the complex is mapped through a heuristic approach that combines parameters recognized in literature as the main predisposing factors to slope instability. Such parameters are morphometry elements, lithology and land cover. The resulting map, validated through historical landslides, classifies the entire complex according to five degrees of susceptibility, identifying Tuscolano-Artemisio caldera edge, Mt. Faete, and steep slopes of Nemi and Albano lakes at high and very high susceptibility. The instability of the entire complex is further investigated measuring the ground deformations observed by using InSAR data in the period 2016–2023. InSAR results, validated through GNSS data, show the overall stability of the complex, except a few areas. In detail, an ongoing uplift of about 1.5 mm/yr is recorded in Genzano di Roma municipality. The InSAR results combined with the debris flows susceptibility map and historical landslides highlight the steep slopes of Albano and Nemi lakes and Giulianello locality, outside the caldera, as the areas potentially most predisposed to trigger debris flows as classified at very high susceptibility and affected by both ground deformations and historical debris flows.