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The petrological part of this study was supported by the FIR 2014 research grant to Marco Viccaro from the University of Catania (Italy), grant number 2F119B, title of the project “Dynamics of evolution, ascent and emplacement of basic magmas: case-studies from eruptive manifestations of Eastern Sicily”.

Between 2011 and 2013, there were 43 lava fountain episodes from Mount Etna's New South-East summit crater (NSEC). In 2014, this intense activity was supplanted by sporadic Strombolian explosions and the opening of an eruptive fissure between July and August. The only lava fountaining episode of the year occurred on 28 December; this was characterized by the emplacement of a shallow dike that, at the surface, fed two distinct lava flows from an ENE-WSW trending eruptive fissure. Here we provide a detailed picture of the onset of the dike emplacement, as well as the mechanism driving its migration, using a multidisciplinary data set based on seismic, geodetic, geochemical, and volcanological observations. The dike emplacement was preceded by a pressurization of the magmatic plumbing system recorded from August 2014 on. This pressurization has been modeled as a vertically elongated magmatic source located beneath the summit craters at ~4.5 km below sea level. From September to October, magma rising was also detected by seismic and geochemical data that highlighted pressurization of the shallower portion of the plumbing system. We suggest that the 28 December 2014 dike emplacement resulted from a modification of the preexisting NSEC shallow plumbing system, largely due to drainage of the main shallow conduit during the July–August 2014 eruptive fissure activity. Such a structural modification might have created the conditions for magma emplacement as a dike-like structure.

[1] 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.

This work analyzes temporal variations of seismic velocities at Mt. Etna from August 2018 to February 2019. During this time period, a strong flank eruption accompanied by intense seismicity and ground deformation took place along a fracture that opened on 24 December 2018 at the base of the New South-East summit crater. Furthermore, two moderate earthquakes—the 6 October 2018 ML 4.7 and 26 December 2018 ML 4.8—associated with the volcanic activity were recorded. In this study, we computed cross-correlation functions (CCFs) between windows of seismic ambient noise to identify seismic velocity variations within the volcano edifice. We calculated daily CCFs at 16 stations for 120 interstation pairs using the vertical component in the 1.0–1.5 Hz frequency band. We observe that dv/v starts to decrease rapidly from the beginning of October 2018 and reaches approximately −0.45% in the pre-eruption period. The spatio-temporal distribution of seismic velocities shows that the reduction of dv/v mostly occurs in the vicinity of the summit and close to the flank area and is interpreted to be affected by magmatic intrusion at 0–3 km depth. To infer the source mechanism of this eruption, we compared these observations with volcano-tectonic earthquakes, volcanic tremor, volcanic degassing, gravity, and ground deformation data. Our study suggests that a relationship between magma intrusion and associated crack opening is responsible for the decrease of dv/v.