It is generally accepted, but not experimentally proven, that a quantitative prediction of volcanic eruptions is possible from the evaluation of volcanic gas data. By discussing the results of two years of real-time observation of H 2 O, CO 2 , and SO 2 in volcanic gases from Mount Etna volcano, we unambiguously demonstrate that increasing CO 2 /SO 2 ratios can allow detection of the pre-eruptive degassing of rising magmas. Quantitative modeling by the use of a saturation model allows us to relate the pre-eruptive increases of the CO 2 /SO 2 ratio to the refi lling of Etna's shallow conduits with CO 2 -rich deep-reservoir magmas, leading to pressurization and triggering of eruption. The advent of real-time observations of H 2 O, CO 2 , and SO 2 , combined with well-constrained models of degassing, represents a step forward in eruption forecasting.

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[1] Constraining fluxes of volcanic bromine and iodine to the atmosphere is important given the significant role these species play in ozone depletion. However, very few such measurements have been made hitherto, such that global volcanic fluxes are poorly constrained. Here we extend the data set of volcanic Br and I degassing by reporting the first measurements of bromine and iodine emissions from Mount Etna. These data were obtained using filter packs and contemporaneous ultraviolet spectroscopic SO 2 flux measurements, resulting in time-averaged emission rates of 0.7 kt yr À1 and 0.01 kt yr À1 for Br and I, respectively, from April to October 2004, from which we estimate global Br and I fluxes of order 13 (range, 3-40) and 0.11 (range, 0.04-6.6) kt yr À1 . Observed changes in plume composition highlight the coherent geochemical behavior of HCl, HF, HBr, and HI during magmatic degassing, and strong fractionation of these species with respect to SO 2 .

Since the second half of the 1990s, the eruptive activity of Mount Etna has provided evidence that both explosive and effusive eruptions display periodic variations in discharge and eruption style. In this work, a multiparametric approach, consisting of comparing volcanological, geophysical, and geochemical data, was applied to explore the volcano's dynamics during 2009–2011. In particular, temporal and/or spatial variations of seismicity (volcano‐tectonic earthquakes, volcanic tremor, and long‐period and very long period events), ground deformation (GPS and tiltmeter data), and geochemistry (SO2 flux, CO2 flux, CO2/SO2 ratio) were studied to understand the volcanic activity, as well as to investigate magma movement in both deep and shallow portions of the plumbing system, feeding the 2011 eruptive period. After the volcano deflation, accompanying the onset of the 2008–2009 eruption, a new recharging phase began in August 2008. This new volcanic cycle evolved from an initial recharge phase of the intermediate‐shallower plumbing system and inflation, followed by (i) accelerated displacement in the volcano's eastern flank since April 2009 and (ii) renewal of summit volcanic activity during the second half of 2010, culminating in 2011 in a cyclic eruptive behavior with 18 lava fountains from New Southeast Crater (NSEC). Furthermore, supported by the geochemical data, the inversion of ground deformation GPS data and the locations of the tremor sources are used here to constrain both the area and the depth range of magma degassing, allowing reconstructing the intermediate and shallow storage zones feeding the 2011 cyclic fountaining NSEC activity.

[1] The Total Volatile (TV) flux from Mount Etna volcano has been characterised for the first time, by summing the simultaneously-evaluated fluxes of the three main volcanogenic volatiles: H 2 O, CO 2 and SO 2 . SO 2 flux was determined by routine DOAS traverse measurements, while H 2 O and CO 2 were evaluated by scaling MultiGAS-sensed H 2 O/SO 2 and CO 2 /SO 2 plume ratios to the UV-sensed SO 2 flux. The time-averaged TV flux from Etna is evaluated at $21,000 tÁday À1