Abstract
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). At the NSEC, each event was usually preceded by Strombolian activity, increasing in intensity with time, and climaxed with powerful lava fountains, often accompanied by lava overflows from the crater rim and by the development of ash plumes that spread several kilometres above and hundreds of kilometres away from the crater. In turn, the ash plume caused fallout and often disruption to airports and traffic on the motorways well beyond the area of the volcano itself, impacting the stability of buildings and caused public health issues. The four episodes at VOR were more intense and of greater magnitude compared to the NSEC events, resulting in a higher ash plume, and were produced by a deeper source region. 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 paroxysmal explosions using geophysical monitoring data, characterise the episodes, and analyse all available data statistically, with the aim of recognising the eruptive processes and extracting common parameters that may prove useful for hazard assessment and risk mitigation.
Highlights
Lava fountains are a mixture of liquid clots and droplets and magmatic gases (H2O, CO2, SO2, CH4, N2O, HCl, height of the lava fountain (LF) (HF), and CO, in order of decreasing abundance; Allard et al, 2005)
To obtain a more robust dataset, we used the values obtained from ECV measurements, when height of the plume (HP) was less than 9 km in height, and for other cases (HP > 9 km) we considered the value from MODIS and alternatively, if this was not available, the value of SEVIRI (Table 4)
For the LF of 12 January 2011, we used the plume height reported in Calvari et al (2011); for the LF of 23 October 2011, we considered the plume height measured by SEVIRI and reported in Guerrieri et al (2015); for the LF of 23 November 2013, we considered the height inferred by Corradini et al (2016) by using a multi-sensor approach considering different satellite instruments such as Meteosat, MODIS and SEVIRI, and for the four events of the VOR of 3–5 December 2015, we used the plume heights reported in Vulpiani et al (2016), obtained by three radar systems operated by the Italian Department of Civil Protection (Table 4)
Summary
Lava fountains are a mixture of liquid clots and droplets (the pyroclasts) and magmatic gases (H2O, CO2, SO2, CH4, N2O, HCl, HF, and CO, in order of decreasing abundance; Allard et al, 2005). In January 2015, ash plume emissions started from the Voragine crater (VOR), after 16 years quiescence at this crater (Corsaro et al, 2017; Cannata et al, 2018) Explosive activity from this crater increased in intensity and became almost regular since 27 October, climaxing with a sequence of four paroxysmal events between 3 and 5 December (Vulpiani et al, 2016; Bonaccorso and Calvari, 2017; Neri et al, 2017).
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