Complex magma dynamics at Mount Etna revealed by seismic, thermal, and volcanological data

Three eruptive episodes during the 2006 summit eruptions of Mount Etna were exceptionally well documented by visual, seismic, and thermal monitoring. The first (16 November) was strongly explosive, with vigorous Strombolian activity and ash emission from multiple vents, lava emission, and phreatomagmatic explosions generating pyroclastic density currents (PDCs). The second episode (19 November) had a rather weakly explosive component, with mild Strombolian activity but more voluminous lava emission. The third (24 November) was a moderately explosive paroxysm, with intermittent lava fountaining and generation of a tephra column as well as lava emission and PDCs. Data recorded by a thermal monitoring camera clearly document the different phases of each paroxysm, weather clouds occasionally hampering thermal monitoring. The images show a rapid onset of the volcanic activity, which during each of the paroxysms reached a peak in eruptive and thermal intensity and then decreased gradually. The stronger phreatomagmatic explosions and PDCs on 16 and 24 November did not yield any seismic signature linked to the opening of new vents nor were they associated with peculiar characteristics of the seismic signal. Nevertheless, eruptive styles (Strombolian activity, lava emission) and different levels in the intensity of explosive activity were generally well reflected in the amplitude and frequency content of the seismic signal and in the source location of the volcanic tremor centroid throughout the three eruptive episodes. This multidisciplinary study, therefore, not only provides a key to distinguish between endogenous and exogenous origins of the phenomena observed but also documents the complex magma dynamics within the volcano.