GNGTS 2017 - 36° Convegno Nazionale

190 GNGTS 2017 S essione 1.3 experienced a mild activity. During 2015-2016, paroxysmal eruptions, affected theVoragine Crater (VOR), marking important changes in the eruptive behavior of Mt. Etna. In particular, during 3-5 December four powerful paroxysmal eruptions with columns up to 10-14 km asl took place at VOR. Again, on 18 and 19 May 2016 two lava fountain episodes occurred at VOR, accompanied by the emplacement of short-living lava flows (Corsaro et al. , 2017). Here, we have integrated ground deformation, seismic, infrasonic and petrological data, collected during June 2015 - August 2016 to investigate the volcano internal processes that led to these VOR’s eruptions, casting lights on the modern Etna plumbing system structure and dynamics. Data analysis. Geodetic data. Raw data collected from the permanent GPS network and spanning the 1 June 2015 - 31 August 2016 interval were analyzed by using the GAMIT/GLOBK software and adopting the methodology described in Gonzalez and Palano (2014). By analyzing the daily baseline changes for some selected sites crossing the summit area, we recognized four major ground deformation stages, defining two inflation/ deflation cycles. Modelling of each recognized stage allowed us to infer the presence of a magmatic reservoir located at a depth of ~5.5 km. Seismic and infrasonic data. The following parameters were investigated: i) variation over time of amplitude and source location of volcanic tremor; ii) daily occurrence rate and amplitudes of LP events; iii) daily number of infrasonic events located on each summit crater. The centroids of volcanic tremor were located at depth ranging from the sea level up to the volcano summit, while the infrasonic sources coincided with VOR, NSEC and NEC. Furthermore, on the basis of the evolution in time of volcanic tremor, LP and infrasonic events, variations in the state of the feeding system were inferred. In particular, increases in amplitude of both volcanic tremor and LP events were observed at the same time as inflation cycles, defined by GPS data, suggesting pressurization phenomena of the upper portion of plumbing system, as already observed during 2013 (Cannata et al. , 2015). Petrological data. Air-quenched rheomorphic lava and tephra samples were taken at the end of each paroxysmal eruption occurred at VOR (Fig. 1). They were investigated for whole rock major and trace elements, together with textural and in situ compositions of plagioclase and olivine crystals. Volcanic rocks erupted during the activity of December 2015 and May 2016 at VOR are porphyritic K-trachybasalts with composition very similar in terms of major and trace elements to the products erupted at NSEC during the 2011-2013 paroxysmal eruptions (Giuffrida and Viccaro, 2017). Textural and compositional characteristics of the observed mineral phases resemble those of crystals previously emitted in historical and recent eruptions at Mt. Etna, particularly during the 2011-2013 activity at NSEC (e.g. Giuffrida and Viccaro, 2017). Plagioclase crystals in lava rocks emitted at VOR show at least 5 main textural types: a) Fig. 1 - Map of Mount Etna volcano with the location of the seismic (SS), infrasound (IS) and geodetic (GPS) stations. Note that in the upper portion of the volcano, many of the stations are co-located (see the map legend). The inset shows a zoom.