A New Cycle of Activity At Mt. Etna (Sicily, Italy) During 2009, Revealed from Diffuse CO2 Degassing and Crater Emissions of SO2 and Halogens

Abstract

In 2009, Mt. Etna (Italy) activity was characterised by the end of a long-lasting flank eruption started on 13 May 2008 and by the opening of a new summit degassing vent on the E flank of the South-East crater on 6 November. This was preceded by a sequence of significant anomalies in volcanic degassing, detected by periodic measurements of soil CO2 efflux on the east flank of the volcano, continuous measurements of SO2 flux from five fixed monitoring stations, and periodic FTIR measurements of the SO2/HCl and SO2/HF molar ratios in the volcanic plume. Since April 2009, soil and crater emissions showed a progressive increase marked at least by two major steps, in April-May and September-October. Increases were not observed simultaneously; in fact, they were detected first in soil CO2 emissions and then, a few days/weeks later, in crater SO2 flux. Only minor increases of HCl and HF crater fluxes were observed between November and December. The highest SO2 and halogens fluxes were recorded in coincidence with the opening of the November 6 vent. The degassing behaviour of the volcano in 2009 is consistent with the differential release of magmatic gas species, according to their different solubilities, from a magma body rising from ~5 km depth to the surface. Our results suggest the start of a new phase in Etna’s activity, in which the new vent might reflect improved efficiency in the release of magmatic gas through the main feeding system, supplied by a magma body stored at depths between 4 and 2 km. If degassing at the new vent will remain steadystate, thus forming a stable feeding system, then its opening might represent the eastward migration of the South-East crater activity with the likely formation of a new stable summit cone.