Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/9882
AuthorsLa Spina, A.* 
Burton, M.* 
Allard, P.* 
Alparone, S.* 
Mure, F.* 
TitleOpen-path FTIR spectroscopy of magma degassing processes during eight lava fountains on Mount Etna
Issue Date19-Jan-2015
Series/Report no./413 (2015)
DOI10.1016/j.epsl.2014.12.038
URIhttp://hdl.handle.net/2122/9882
KeywordsFTIR remote sensing
lava fountains
gas composition
magma degassing
separate CO2transfer
Subject Classification05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions 
AbstractIn June–July 2001 a series of 16 discrete lava fountain paroxysms occurred at the Southeast summit crater (SEC) of Mount Etna, preceding a 28-day long violent flank eruption. Each paroxysm was preceded by lava effusion, growing seismic tremor and a crescendo of Strombolian explosive activity culminating into powerful lava fountaining up to 500m in height. During 8 of these 16 events we could measure the chemical composition of the magmatic gas phase (H2O, CO2, SO2, HCl, HF and CO), using open-path Fourier transform infrared (OP-FTIR) spectrometry at ∼1–2km distance from SEC and absorption spectra of the radiation emitted by hot lava fragments. We show that each fountaining episode was characterized by increasingly CO2-rich gas release, with CO2/SO2and CO2/HCl ratios peaking in coincidence with maxima in seismic tremor and fountain height, whilst the SO2/HCl ratio showed a weak inverse relationship with respect to eruption intensity. Moreover, peak values in both CO2/SO2ratio and seismic tremor amplitude for each paroxysm were found to increase linearly in proportion with the repose interval (2–6 days) between lava fountains. These observations, together with a model of volatile degassing at Etna, support the following driving process. Prior to and during the June–July 2001 lava fountain sequence, the shallow (∼2km) magma reservoir feeding SEC received an increasing influx of deeply derived carbon dioxide, likely promoted by the deep ascent of volatile-rich primitive basalt that produced the subsequent flank eruption. This CO2-rich gas supply led to gas accumulation and overpressure in SEC reservoir, generating a bubble foam layer whose periodical collapse powered the successive fountaining events. The anti-correlation between SO2/HCl and eruption intensity is best explained by enhanced syn-eruptive degassing of chlorine from finer particles produced during more intense magma fragmentation.
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