Gas geobarometry applied to evaluate phreatic explosion hazard at Vulcano Island (Sicily, Italy)

By using CO2 , CH4 , H2 and CO contents of gases discharged by Baia di Levante fumaroles, the temporal variations of temperature and pressure (PCO2 and Ptot) of the gas feeding aquifer, have been investigated for the period 1982-1990. The estimates of equilibrium temperatures and total pressures ranges from 180 to 240°C and from 10 to 25 bar respectively. Maximum values refer to June 1985 and to August 1988, when drastic change in the chemical composition of high temperature crater fumaroles and an increase of microseismic activity were observed. In 1985 and in 1988, the sudden inlet of high enthalpy fluids from depth, directly detectable in the crater fumaroles, has affected the Baia di Levante hydrothermal field, producing an increment in T and P of the hot aquifers feeding these surface manifestations. Results show that monitoring of CO, H2 and CH4 contents in gas discharged by Baia di Levante fumaroles represent a contribution to assess the risk of phreatic explosion in this area.