Submarine gas burst at Panarea Island (southern Italy) on 3 November 2002: A magmatic versus hydrothermal episode

On 3 November 2002, fishermen observed the sudden appearance at the sea surface of three large whitish plumes 3 km offshore of Panarea Island (Aeolian Islands, southern Italy) caused by the uprising from the seafloor of huge columns of gas bubbles, mixed with sediments and colloidal sulfur. The degassing event partly superimposed an already existing gentle-degassing fumarolic field. Since 12 November 2002, a discontinuous geochemical monitoring program of these new discharging fluids have been carried out. The submarine emissions collected on November 2002 were an emulsion made by a CO2-dominated continuous gas phase with suspended sediments, colloidal sulfur, and water condensate microdroplets acidified by dissolution of compounds such as SO2, HCl, and HF. In the gas phase, light-unsaturated hydrocarbons also occurred, possibly related to relatively high temperature and oxidizing conditions due to local input of magmatic fluids at depth, whose occurrence was also supported by the relative high values of He-3/He-4 isotopic ratio (R/R-air = 4.62) with respect to previously measured values (R/R-air < 4.2). The flux of the submarine emissions significantly decreased in a couple of months together with the almost complete disappearance of the magmatic chemical markers and the decrease of the helium isotopic ratio. Thus the most striking feature of the temporal and spatial evolution in the chemical and isotopic compositions of the submarine fumaroles was the relatively rapid restoration, since January 2003, of the precrisis conditions, i.e., typical of a stationary hydrothermal system.