GNGTS 2018 - 37° Convegno Nazionale

266 GNGTS 2018 S essione 1.3 SO 2 emission in the plume issued by the summit craters. In this study, we present the daily SO 2 flux observed at Mt. Etna throughout the period March 2015 - May 2016. Over the investigated period, Mt. Etna volcano was characterized by three eruptive events, which ranged from weak Strombolian to extremely vigorous lava fountaining. Here, we explore the temporal correlation between the SO 2 flux and the eruptive activity, along the balance between the volumes of degassed vs. erupted magma. Volcanic activity at Mt. Etna during the March 2015 - May 2016. The eruptive activity at Mt. Etna during the considered period was characterized by three major eruptive episodes. The first occurred between 11 and 20 May 2015 at the New South East Crater (NSEC), producing Strombolian activity and lava flow effusion. The second episode started on 19 October 2015 with weak ash emission and intra-crateric Strombolian activity at the Voragine crater (VOR). This weak explosive activity continued until the 3 December 2015, when an astonishing paroxysmal episode took place at VOR. Other paroxysmal episodes occurred on 4 and 5 December (Cannata et al. , 2018). During the VOR activity, even the NSEC and the North East Crater (NEC) have been the place of Strombolian explosions with ash emission and a lava overflow from the NSEC. This activity ended on 7 December 2015. After more than 5 months, eruptive activity resumed at VOR on 16 May 2016 with Strombolian activity at the NSEC and, soon later, also at the VOR and NEC. Even this eruptive activity culminated with energetic lava fountaining at VOR on 18, 19 and 21 May (Cannata et al. , 2018). During the following days, only lava flow effusion and weak Strombolian activity took place at the summit of Mt. Etna until 25 May 2016. Results and discussion. SO 2 fluxes showed rather low values, generally below 5000 tons/ day (t/d), for most of the period during March 2015 - May 2016. Steady increase with values up to 9500 t/d marked especially the onset of eruptive activity. The total volume of degassed magma was calculated assuming an initial sulfur content dissolved in the magma of 3000 ppm and a mean crystal fraction of 30% (e.g., Allard, 1997; Spilliart et al. , 2006). This yielded a volume of degassed magma of 1.4 x 10 5 m 3 and 2.6 x 10 5 m 3 for 1 March 2015 and 31 May 2016, respectively. The uncertainty on the estimated volume ranges from 22% to 36% since it derives from the SO2 flux measurement. The cumulative degassed volume shows marked temporal changes of the slope in correspondence of onset of eruptive activities, a feature attributed to the release of part of the magma from the plumbing system (Fig. 1). The volume of the erupted magma as lava emission during the three eruptive events for the first eruption at the NSEC on May 2015 are estimated at minimum 2.9 x 10 6 m 3 and maximum 3.9 x 10 6 m 3 . The volumes of the December 2015 eruptions consider both lavas and pyroclastics for the VOR activity and instead lava flows for NSEC. Corsaro et al. (2017), reports that the erupted Fig. 1 Volume of the cumulative degassed magma through time and eruptive activity.