Magmatic gas percolation through the old lava dome of El Misti volcano

Bulletin of Volcanology, May 2017

The proximity of the major city of Arequipa to El Misti has focused attention on the hazards posed by the active volcano. Since its last major eruption in the fifteenth century, El Misti has experienced a series of modest phreatic eruptions and fluctuating fumarolic activity. Here, we present the first measurements of the compositions of gas emitted from the lava dome in the summit crater. The gas composition is found to be fairly dry with a H2O/SO2 molar ratio of 32 ± 3, a CO2/SO2 molar ratio of 2.7 ± 0.2, a H2S/SO2 molar ratio of 0.23 ± 0.02 and a H2/SO2 molar ratio of 0.012 ± 0.002. This magmatic gas signature with minimal evidence of hydrothermal or wall rock interaction points to a shallow magma source that is efficiently outgassing through a permeable conduit and lava dome. Field and satellite observations show no evolution of the lava dome over the last decade, indicating sustained outgassing through an established fracture network. This stability could be disrupted if dome permeability were to be reduced by annealing or occlusion of outgassing pathways. Continued monitoring of gas composition and flux at El Misti will be essential to determine the evolution of hazard potential at this dangerous volcano.

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Magmatic gas percolation through the old lava dome of El Misti volcano

Bull Volcanol Magmatic gas percolation through the old lava dome of El Misti volcano Yves Moussallam 0 1 2 3 4 5 6 Nial Peters 0 1 2 3 4 5 6 Pablo Masias 0 1 2 3 4 5 6 Fredy Apaza 0 1 2 3 4 5 6 Talfan Barnie 0 1 2 3 4 5 6 C. Ian Schipper 0 1 2 3 4 5 6 Aaron Curtis 0 1 2 3 4 5 6 Giancarlo Tamburello 0 1 2 3 4 5 6 Alessandro Aiuppa 0 1 2 3 4 5 6 Philipson Bani 0 1 2 3 4 5 6 Gaetano Giudice 0 1 2 3 4 5 6 David Pieri 0 1 2 3 4 5 6 Ashley Gerard Davies 0 1 2 3 4 5 6 Clive Oppenheimer 0 1 2 3 4 5 6 0 Nordic Volcanological Center, Institute of Earth Sciences , Sturlugata 7 - Askja, 101, Reykjavik , Iceland 1 Observatorio Vulcanológico del Ingemmet (OVI) , Arequipa , Peru 2 Department of Geography, University of Cambridge , Downing Place, Cambridge CB2 3EN , UK 3 Université Clermont Auvergne , CNRS, IRD, OPGC , Laboratoire Magmas et Volcans , F-63000 Clermont-Ferrand , France 4 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo Via La Malfa , 153, 90146 Palermo , Italy 5 Dipartimento DiSTeM, Università di Palermo , Via archirafi 36, 90146 Palermo , Italy 6 School of Geography, Environment and Earth Sciences, Victoria University of Wellington , PO Box 600, Wellington 6140 , New Zealand The proximity of the major city of Arequipa to El Misti has focused attention on the hazards posed by the active volcano. Since its last major eruption in the fifteenth century, El Misti has experienced a series of modest phreatic eruptions and fluctuating fumarolic activity. Here, we present the first measurements of the compositions of gas emitted from the lava dome in the summit crater. The gas composition is found to be fairly dry with a H2O/SO2 molar ratio of 32 ± 3, a CO2/ SO2 molar ratio of 2.7 ± 0.2, a H2S/SO2 molar ratio of 0.23 ± 0.02 and a H2/SO2 molar ratio of 0.012 ± 0.002. This magmatic gas signature with minimal evidence of hydrothermal or wall rock interaction points to a shallow magma source that is efficiently outgassing through a permeable conduit and Highlights • First characterization of plume composition at El Misti volcano • Gas chemistry reveals a clear magmatic signature • Field and satellite observations suggest a stable outgassing pathway through the conduit and old lava dome Editorial responsibility: P. Allard lava dome. Field and satellite observations show no evolution of the lava dome over the last decade, indicating sustained outgassing through an established fracture network. This stability could be disrupted if dome permeability were to be reduced by annealing or occlusion of outgassing pathways. Continued monitoring of gas composition and flux at El Misti will be essential to determine the evolution of hazard potential at this dangerous volcano. Volcanic hazard; Arequipa; Outgassing; ASTER; Multi-GAS; Trail by fire - Istituto nazionale di geofisica e vulcanologia, sezione di Bologna, Bologna, Italy Lava domes are the extruded part of a magma risen through a conduit. Typically associated with silicic (rhyolitic to andesitic) magmas, lava domes are often unstable and capable of generating pyroclastic density currents. Dome collapse events have been documented at volcanoes such as Soufrière Hills (Montserrat; e.g. Watts et al., 2002), Mount Unzen (Japan; e.g. Sato et al., 1992), Mount St. Helens (USA; e.g. Mellors et al., 1988) and Merapi (Indonesia; e.g. Komorowski et al., 2013). Critical in determining whether or not an otherwise gravitationally stable dome will become overpressured and collapse is the nature of magmatic outgassing through either the conduit wall or fracture networks (e.g. Jaupart and Allègre, 1991; Gonnermann and Manga, 2003; Boudon et al., 2015). While such considerations have been explored theoretically (e.g. Sparks, 1997; Melnik and Sparks, 1999, 2005; Hale and Mühlhaus, 2007) the inherent hazard associated with working on active lava domes has limited in situ collection of data on gas compositions, limiting data to that from remote sensing observations (e.g. Oppenheimer et al., 2002; Edmonds et al., 2003; Holland et al., 2011) with only a few direct measurements (e.g Soufrière Hills; Hammouya et al., 1998). El Misti volcano, southern Peru (Fig. 1), is close to Arequipa, the second largest city in the country, with about one million inhabitants. El Misti is a composite stratovolcano composed of four stratocones (Thouret et al., 2001). The youngest, Misti 4, forms the current summit of the volcano and has erupted at least ten times since 11,000 years. B.P producing pyroclastic-surges and lahars that have travelled up to 13 km from the vent (Thouret et al., 2001). The last plinian eruption occurred ca 2050 years ago and produced a widely dispersed pumice-fall deposit extending ≥25 km from the vent (Thouret et al., 1995, 2001; Harpel et al., 2011; Cobeñas et al., 2012). Since then, eruptive activity has been mild, with minor events in 655–865 A.D., 1304– 1398 A.D. (Thouret et al., 2001) and in 1440–1470 A.D. (Murúa, 1946, 1987); episodes of increased fumaroli (...truncated)


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Yves Moussallam, Nial Peters, Pablo Masias, Fredy Apaza, Talfan Barnie, C. Ian Schipper, Aaron Curtis, Giancarlo Tamburello, Alessandro Aiuppa, Philipson Bani, Gaetano Giudice, David Pieri, Ashley Gerard Davies, Clive Oppenheimer. Magmatic gas percolation through the old lava dome of El Misti volcano, Bulletin of Volcanology, 2017, pp. 46, Volume 79, Issue 6, DOI: 10.1007/s00445-017-1129-5