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


Lava fountains are spectacular continuous gas jets, propelling lava fragments to heights of several hundred metres, which occasionally occur during eruptions of low-viscosity magmas1,2,3,4,5. Whether they are generated by the effervescent disruption of fast-rising bubbly melt2,3,4,5 or by the separate ascent of a bubble foam layer accumulated at depth6,7 still remains a matter of debate8. 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 eruption9,10. Here we report the analysis of magmatic gas during a powerful (250–600 m high) lava fountain, measured with Fourier transform infrared spectroscopy11,12,13,14 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 emissions14,15,16,17,18, and which cannot derive from syn-eruptive bulk degassing of Etna basalt19,20. Instead, its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1.5 km depth below the erupting crater.

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Figure 1: OP-FTIR measurement of the 14 June 2000 lava fountain on Etna.
Figure 2: Temporal evolution of volcanic gas concentrations and ratios during and after the 14 June 2000 lava fountain.
Figure 3: Scatter plots of gas amounts measured during lava fountaining.


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We thank F. Barberi and L. Villari for their initial support of the Etna FTIR monitoring project within the Poseidon System (Italian Civil Defence and Sicily Region), and A. Bonaccorso, E. Boschi and S. Calvari for their continued support within INGV. We acknowledge early technical assistance from the Bruker company (Germany) and discussions with N. Métrich (LPS) and our colleagues in INGV-Catania.

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Correspondence to Patrick Allard.

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Allard, P., Burton, M. & Muré, F. Spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas. Nature 433, 407–410 (2005).

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