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

Change log
Masias, P 
Apaza, F 
Barnie, T 

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.

volcanic hazard, Arequipa, outgassing, ASTER, Multi-GAS, Trail by fire
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Bulletin of Volcanology
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NERC (via University of Leeds) (GA/13M/031)
Leverhulme Trust (RPG-2016-218)
This research was conducted as part of the ‘Trail By Fire’ expedition (PI: Y. Moussallam). The project was supported by the Royal Geographical Society (with the Institute of British Geographers) with the Land Rover Bursary; the Deep Carbon Observatory DECADE Initiative; Santander, Ocean Optics; Crowcon; Air Liquide; Thermo Fisher Scientific; Cactus Outdoor; Turbo Ace and Team Black Sheep. We thank Jean-loup Guyot, Sebastien Carretier, Rose-Marie Ojeda, Pablo Samaniego and Jean-Luc Lepennec together with IRD South-America personnel for all their logistical help. We are extremely grateful to Marco Rivera and all OVI personnel for their help and support. YM acknowledges support from the Scripps Institution of Oceanography Postdoctoral Fellowship program. A.A and G.T acknowledge the ERC grant no. 305377 (BRIDGE). CIS acknowledges a research start-up grant from Victoria University of Wellington. C.O. is supported by the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics. The Earth Observing-1 (EO-1) spacecraft is managed by NASA’s Goddard Space Flight Center, Greenbelt, Maryland, USA.