Strombolian eruptions and dynamics of magma degassing at Yasur Volcano (Vanuatu)

Woitischek, Julia and Woods, Andrew W. and Edmonds, Marie and Oppenheimer, Clive and Aiuppa, Alessandro and Pering, Tom D. and Ilanko, Tehnuka and D'Aleo, Roberto and Garaebiti, Esline (2020) Strombolian eruptions and dynamics of magma degassing at Yasur Volcano (Vanuatu). Journal of Volcanology and Geothermal Research, 398. p. 106869. ISSN 0377-0273 DOI https://doi.org/10.1016/j.jvolgeores.2020.106869

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Abstract

Open vent basaltic volcanoes account for a substantial portion of the global atmospheric outgassing flux, largely through passive degassing and mild explosive activity. We present volcanic gas flux and composition data from Yasur Volcano, Vanuatu collected in July 2018. The average volcanic plume chemistry is characterised by a mean molar CO2/SO2 ratio of 2.14, H2O/SO2 of 148 and SO2/HCl of 1.02. The measured mean SO2 flux in the period of 6th to 9th July is 4.9 kg s−1. Therefore, the mean fluxes of the other species are 7.5 kg∙s−1 CO2, 208 kg∙s−1 H2O and 4.8 kg∙s−1 HCl. The degassing regime at Yasur volcano ranges from ‘passive’ to ‘active’ styles, with the latter including Strombolian activity and spattering. Gases emitted during active degassing are enriched in SO2 over HCl and CO2 over SO2 relative to passive degassing, with CO2/SO2 ratios of 2.85 ± 0.17, SO2/HCl of 1.6 ± 0.22, and H2O/SO2 of 315 ± 78.8. Gases emitted during passive degassing have CO2/SO2 ratios of 1.96 ± 0.12, SO2/HCl of 0.50 ± 0.07 and H2O/SO2 of 174 ± 43.5. We use a model of volatile degassing derived from melt inclusion studies (Metrich et al., 2011), combined with our observations of chemical variations in the outgassing bubbles to propose a mechanism for magma degassing in the conduit at Yasur. We envisage a shallow conduit filled with crystal-rich magma, forming a viscous and mobile plug that develops an effective yield strength from the surface to a depth of at least 2000 m, in which bubbles are trapped, grow, ascend towards the surface and burst in a typical Strombolian eruption. Deeper bubbles released during active degassing are enriched in CO2 and SO2 compared to bubbles released during ‘passive degassing’, which are sourced from close to the surface, and are, consequently, HCl-rich.

Item Type:	Article
Uncontrolled Keywords:	2020AREP; IA76
Subjects:	05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions:	05 - Petrology - Igneous, Metamorphic and Volcanic Studies 08 - Green Open Access 12 - PhD
Journal or Publication Title:	Journal of Volcanology and Geothermal Research
Volume:	398
Page Range:	p. 106869
Identification Number:	https://doi.org/10.1016/j.jvolgeores.2020.106869
Depositing User:	Sarah Humbert
Date Deposited:	27 May 2020 00:35
Last Modified:	27 May 2020 00:35
URI:	http://eprints.esc.cam.ac.uk/id/eprint/4749

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