Outgassing during the 1669 Monte Rossi Eruption of Mt Etna, Italy

We present a study of magma differentiation and outgassing during a unique and little studied eruption of Etna from the parasitic Monti Rossi cone in 1669, which was the most destructive event in historical times. We show that the large lava effusion rate and areal extent of the lava flows from this eruption may have caused the convective penetration of sulfur-rich gas clouds high into the atmosphere, which would have caused regional environmental effects. The eruption was highly unusual for Etna: it occurred low on the flanks (800 m.a.s.l.) and involved 607±105 ×106 m3 lava erupted over 3 months, which overran many settlements, including the city of Catania. The average lava effusion rate was 58±10 m3/s , but peak of 640 m3/s was reached in the first days of activity; the flow field covered a total area of ∼40×106 m2 in only 4 months [Branca et al., 2013]. It is the widest and longest lava field (∼17 km) produced by Etna volcano both in historical and in prehistoric times. We have carried out a detailed study of melt inclusion trace and volatile element geochemistry to reconstruct melt differentiation and degassing processes prior to eruption. We estimate the sulfur output of the 1669 eruption and we find that > 3 Mt sulfur may have been produced over the 3 months of activity which, given the large area and high mass flux of the lava flows, may have been lofted into the upper troposphere by thermal convection. The sulfur loading would have caused extensive regional perturbations to atmospheric chemistry and environmental hazards. Effusive basaltic eruptions of this size and style are common in the geological record yet infrequent enough such that they are rarely observed using modern volcano monitoring methods. As a consequence, their impact and potential environmental consequences are poorly understood. Branca, S. et al., 2013. Bull Volcanol. 75: 694.