Spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas

• Published in: Nature Vol. 433; no. 7024; pp. 407 - 410
• Main Authors: Allard, Patrick, Burton, Mike, Muré, Filippo
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 27-01-2005; Nature Publishing Group
• Subjects: Basalt; Carbon dioxide; Crystalline rocks; Degassing; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fourier transforms; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Infrared spectroscopy; Lava; Scientific imaging; Volcanic eruptions; Volcanic gases; Volcanoes; Southern Europe; Italy; Sicily Italy; Mount Etna; Italy, Sicilia, Messina, Mt. Etna; carbon dioxide; sulfur dioxide; models; Fourier transformation; degassing; accumulation; Europe; volcanic rocks; eruptions; igneous rocks; chlorine; volcanology; lava; provenance; basalts; sulfur; craters; gases; absorption spectra; infrared spectroscopy
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature03246

Lava fountains are spectacular continuous gas jets, propelling lava fragments to heights of several hundred metres, which occasionally occur during eruptions of low-viscosity magmas. Whether they are generated by the effervescent disruption of fast-rising bubbly melt or by the separate ascent of a bubble foam layer accumulated at depth still remains a matter of debate. No field measurement has yet allowed firm discrimination between these two models. A key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase. This composition should differ markedly depending on whether the magma degassing occurs before or during eruption. Here we report the analysis of magmatic gas during a powerful (250-600 m high) lava fountain, measured with Fourier transform infrared spectroscopy on Mount Etna, Sicily. The abundances of volcanic gas species, determined from absorption spectra of lava radiation, reveal a fountain gas having higher CO2/S and S/Cl ratios than other etnean emissions, and which cannot derive from syn-eruptive bulk degassing of Etna basalt. Instead, its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1.5 km depth below the erupting crater.