Observations on hydrological state of volcanic soil covers: The Celario slope case

On November 26, 2022, a persistent rainfall triggered several landslides in volcanic soil covers and tuff rock slopes in the northern part of Ischia Island (Italy). The most destructive event was triggered by the impact of a weathered rock mass falling from an above-standing vertical front, then a mudflow was channelized along an open slope with convex morphology, known as “cava Celario”. The main preparatory factor for this landslide was the rainfall-induced drop in suction throughout the pyroclastic cover. Further insights into the amount of suction evolution at the landslide trigger time were thought to be helpful to define proper mitigation strategies. An on-site monitoring activity was undertaken, aiming at characterizing the evolution of the hydrological state of the deposits, through the monitoring of suction within the still- intact deposit located laterally to the landslide initiation zone of Celario, approximately 50 m below the uppermost triggering zone. The suction measurements were correlated with meteorological variables, hence recognizing that the accuracy of the forecast could be improved by increasing the density of available measurement points and locating additional monitoring instruments at higher elevations.