The unusual 28 December 2014 dike-fed paroxysm at Mount Etna: Timing and mechanism from a multidisciplinary perspective

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.