Soil CO2 flux monitoring of the ongoing Vulcano crisis

La Fossa volcano on Vulcano island is the type-location for Volcanian eruptions. Last eruption dates back to 1888-’90. Since then, the quiescent state of La Fossa has been affected both by persistent fumarolic activity and by diffuse CO2 degassing either at the crater and in areas on the flanks (Forgia vecchia) at the base (Palizzi) of the cone, but also in inhabited areas of Vulcano porto (Levante beach, Faraglione). Normal quiescence has been punctuated by potential unrest crises mainly characterized by increase in magmatic degassing, in fumarole temperatures and in diffuse CO2 degassing. We have been monitoring the diffuse degassing area of La Fossa crater since 1995 and Palizzi, Levante beach and Vulcano porto zones since 2004.

The ongoing crisis started in 2021 and showed a huge unprecedented increase in fumarolic degassing associated to ground deformation and episodic anomalous seismicity. For monitoring purposes, we performed since October 2021 two general surveys at the crater of La Fossa (soil CO2 flux and temperature), monthly surveys of diffuse soil CO2 flux in the areas of Palizzi, Levante Beach, Forgia vecchia and an extensive CO2 flux survey (~1000 measurements over 1 km2) in the inhabitated area of Volcano Porto in October 2021. From this wide survey we identified a new diffuse-degassing structure which was apparently inactive during the most recent unrest crises. Since November 2021, this area has been monthly surveyed too. This degassing structure is associated to shallow aquifer thermalism and the area is spotted by some mofetes. During the 1988-’93 crisis, it has been the site of some lethal accidents to animals caused by exposure to high CO2 concentration in air. There have been accidents during this crisis too, with the death of some cats and many birds caused by lethal concentrations of CO2 inside the yard of a house. Fortunately, there were no human casualties due to the prompt evacuation of the zone.

Monthly repetition of soil CO2 flux from the target areas, showed that, at the early stage of the crisis, diffuse CO2 degassing equalled or even exceeded the high-flux rates measured during the previous crisis of 2004-’05 both at the crater area and at the crater base. In 2022-‘23 soil CO2 fluxes have slowly decreased, but the pre-crisis conditions have not yet been reached.