Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano

Edmonds, Marie, Humphreys, Madeleine C. S., Hauri, Erik H., Herd, Richard, Wadge, Geoff, Rawson, Harriet, Ledden, Rachel, Plail, Melissa, Barclay, Jennifer, Aiuppa, Alessandro, Christopher, Thomas E., Giudice, Gaetano and Guida, Roberto (2014) Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano. Journal of the Geological Society, 39. pp. 291-315. ISSN 0016-7649

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Abstract

We use volatiles in melt inclusions and nominally anhydrous phenocrysts, with volcanic gas flux and composition, and textural analysis of mafic inclusions to estimate the mass of exsolved vapour prior to eruption at Soufrière Hills Volcano (SHV). Pre-eruptive andesite coexists with exsolved vapour comprising 1.6–2.4 wt% of the bulk magma. The water content of orthopyroxenes indicates a zone of magma storage at pressures of approximately 200–300 MPa, whereas melt inclusions have equilibrated at shallower pressures. Inclusions containing >3 wt% H2O are enriched in CO2, suggesting flushing with CO2-rich gases. Intruding mafic magma contains >8 wt% H2O at 200–300 MPa. Rapid quenching is accompanied by crystallization and vesiculation. Upon entrainment into the andesite, mafic inclusions may undergo disaggregation, where expansion of volatiles in the interior overcomes the strength of the crystal frameworks, thereby recharging the vapour content of the andesite. Exsolved vapour may amount to 4.3–8.2 vol% at 300 MPa, with implications for eruption longevity and volume; we estimate the magma reservoir volume to be 60–200 km3. Exsolved vapour may account for the small volume change at depth during eruptions from geodetic models, and has implications for magma flow: exsolution is likely to be in equilibrium during rapid magma ascent, with little nucleation of new bubbles.

Item Type: Article
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Pure Connector
Date Deposited: 23 Mar 2016 17:00
Last Modified: 11 Jul 2019 16:31
URI: https://ueaeprints.uea.ac.uk/id/eprint/58020
DOI: 10.1144/M39.16

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