Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano

Edmonds, Marie and Humphreys, Madeleine C. S. and Hauri, Erik H. and Herd, Richard A. and Wadge, Geoff and Rawson, Harriet and Ledden, Rachel and Plail, Melissa and Barclay, Jenni and Aiuppa, Alessandro and Christopher, Thomas E. and Giudice, Gaetano and Guida, Roberto (2014) Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano. Geological Society, London, Memoirs, 39 (1). pp. 291-315. ISSN 0435-4052, 2041-4722 DOI 10.1144/M39.16

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Official URL: http://mem.lyellcollection.org/content/39/1/291

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 \textgreater3 wt% H2O are enriched in CO2, suggesting flushing with CO2-rich gases. Intruding mafic magma contains \textgreater8 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
Uncontrolled Keywords: 2014AREP; IA68;
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
06 - Part-III Projects
Journal or Publication Title: Geological Society, London, Memoirs
Volume: 39
Page Range: pp. 291-315
Identification Number: 10.1144/M39.16
Depositing User: Sarah Humbert
Date Deposited: 18 Jul 2014 17:11
Last Modified: 07 Sep 2014 01:36
URI: http://eprints.esc.cam.ac.uk/id/eprint/3081

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