After a period of deflation during the 1991–1993 flank eruption, Mount Etna underwent a rapid inflation. Seismicity and ground deformation show that since 1994, a huge volume of magma intruded beneath the volcano, producing from 1998 onward a series of eruptions at the summit and on the flank of the volcano. The last of these, started on 27 October 2002, is still in progress and can be considered one of the most explosive eruptions of the volcano in recent times. Here we show how geodetic data and seismic deformation, between 1994 and 2001, indicate a radial compression around an axial intrusion, consistent with a repressurization of Mount Etna's plumbing system at a depth of 6 to 15 kilometers, which triggered most of the seismicity and provoked the dilatation of the volcano and the recent explosive eruptive activity.

Lava fountains have a major impact on the local population since they cause ash plumes that spread several kilometers above and hundreds of kilometers away from the crater. Ash fallout is responsible for disrupting airports and traffic on the motorways well beyond the area of the volcano itself, as well as affecting the stability of buildings and causing public health issues. It is thus a primary scientific target to forecast the impact of this activity on local communities on the basis of parameters recorded by the monitoring network. Between 2011 and 2015, 49 paroxysmal explosive episodes occurred at two of Mt Etna's five summit craters: the New South-East Crater (NSEC) and the Voragine (VOR). In this paper, we examine the features of the 40 episodes occurring at the NSEC during 2011–2013, and of the 4 events at VOR in December 2015. We study these paroxysms using geophysical monitoring data, characterize the episodes, and analyse all available data statistically. Our main results are two empirical relationships allowing us to forecast the maximum elevation of the ash plume from the average height of the lava fountain, useful for hazard assessment and risk mitigation. For Etna, and using the examples described in this paper, we can infer that wind speed 10 m s⁻¹ is normally associated with weak plumes, bent-over along the wind direction and reaching lower elevations.

Late on the night of July 17, 2001, a lateral eruption started from the slopes of Mt. Etna. A 7 km long field of ground fractures opened between 13 and 20 July. The eruption ended on August 9, 2001 after emitting a lava volume of approximately 48 · 10⁶ m³. A strong seismic swarm earthquake was recorded between July 12 and 17. The evolution leading up to the July crisis was monitored through continuous tilt and GPS measurements, which constrained the intrusion preceding the eruption in time, and inferred the position and geometry of the uprising dike. We modeled the marked ground deformation changes recorded in the days before the eruption onset. The result shows that a tensile crack with an opening dislocation of ca. 3 m, crossing the volcano edifice slightly southeast of the crater area, can explain the recorded deformation pattern. The location of the modeled tensile source fits the zone of the seismic swarm occurring during the magma uprising. The ground deformation pattern associated with the final uprising and its modeling suggest a very fast dike emplacement which appears different, both in terms of rapidity (only a few days) and source position, with respect to the sources modeled for the other lateral eruptions in the last twenty years.