Shallow landslide generation at La Fossa cone, Vulcano island (Italy): a multidisciplinary perspective
Several shallow landslides occurred at La Fossa cone (Vulcano Island, Aeolian Archipelago, Italy) in the last 30 years, during both unrests and periods of quiet volcanic activity. The main event occurred in 1988, during a volcanic unrest, when a landslide collapsed into the sea from the NE flank of La Fossa cone, producing a small tsunami. Hydrothermal activity has been suggested as a potential trigger for landslide generation in this area. However, no specific investigations were carried out to test this hypothesis. With the aim of filling this gap, we studied the mineralogy and hydraulic conductivity of La Fossa cone deposits, the relationships between shallow hydrothermal circulation and rainfall dynamics and their role in triggering slope failures. We also measured rainfall rate, volumetric soil moisture content and soil suction at two automated stations installed in areas with and without active hydrothermal circulation. We found that hydrothermally altered low-conductivity materials show higher background water contents and lower soil suctions than pristine deposits, and their water content is modulated by impulsive increments following rainfalls. This behaviour is due to the combination of lower permeability and direct condensation of hydrothermal vapour. We conclude that shallow hydrothermal circulation produces conditions for slope failures following transients in soil moisture content caused by rainfall infiltration. These considerations allow to identify the areas immediately NW and SE of the 1988 landslide as the most prone to future mass movements.
KeywordsHydraulic conductivity Hydrothermal alteration Shallow landslides Rainfall Volcano island
This work was carried out with the financial support of the Italian INGV-DPC projects GNV-Pr.15 years 2000–2003, V3 years 2005–20006 and 2012–2015, and of the postgraduate specialisation course “La ricerca geofisica e vulcanologica per il monitoraggio dei rischi naturali e ambientali e per la tutela e la fruizione delle risorse del territorio (VULCAMED)” (PON a3_00278 – Quadro Strategico Nazionale 2007-2013 per le Regioni della Convergenza).
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