Systematic SO2 emission patterns prior, during, and after Mt. Etna’s paroxysmal phases captured by ultraviolet cameras

Abstract

We used two and a half years long SO2 flux record, obtained using permanent ultraviolet cameras, to characterize changes in degassing dynamics at Mt. Etna volcano from summer 2014 to the end of 2016. Volcanic activity at Mt. Etna was characterized by persistent open-vent degassing periodically interrupted by intense paroxysmal lava fountaining events (in August 2014, December 2015, and May 2016). Results revealed systematic SO2 emission patterns prior, during, and after Etna’s paroxysmal phases, allowing us to identify thresholds between pre-syn-and post-eruptive degassing regimes. The SO2 flux typically peaked during a lava fountain: in the 18 May 2016 example, the averaged SO2 degassing rate was ~158 kg/s, the peak emission was ~260 kg/s, and the total released SO2 mass was ~1700 tons (in 3h). Paroxysmal explosive activity at NSE crater on 11-15 August 2014 was also associated with intense syneruptive SO2 degassing (at 30-40 kg/s levels on a daily average), and was preceded by onset in degassing activity at the same crater 4 days before. During paroxysmal activity on 3-5 December 2015, the SO2 fluxes peaked at 54-103 kg/s from VOR crater, and was preceded by a sizable increase from 10 kg/s (end of November) up to 45.5 kg/s, two days before. The May 16-25 2016 paroxysmal activity was characterized by intense degassing ~2 times higher than the 2016 average (~18 kg/s) and preceded by mild but detectable SO2 flux increases more than one month before its onset. Taken together, our observations, when combined with independent geophysical (thermal and seismic) evidence, allow us to fully characterize the Etna’s degassing dynamics and contribute to our understanding of its shallow plumbing system.