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Recent Advances in Volcanic Gas Science

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Front. Earth Sci. | doi: 10.3389/feart.2019.00132

Variation of the BrO/SO2 molar ratio in the plume of Tungurahua volcano between 2007 and 2017 and its relationship to volcanic activity

 Simon Warnach1, 2*, Nicole Bobrowski2,  Silvana Hidalgo3, Santiago Arellano4, Holger Sihler5,  Florian Dinger1, 2, Peter Lübcke2,  Jean Battaglia6,  Alexander Steele7, Bo Galle4,  Ulrich Platt2 and Thomas Wagner1
  • 1Max Planck Institute for Chemistry, Germany
  • 2Institute of Environmental Physics, University of Heidelberg, Germany
  • 3Instituto Geofísico, Escuela Politécnice Nacional, Ecuador
  • 4Department of Space, Geo and Environmental Sciences, Chalmers University of Technology, Sweden
  • 5Satellite Remote Sensing, Max Planck Institute for Chemistry, Germany
  • 6UMR6524 Laboratoire Magmas et Volcans (LMV), France
  • 7Hazard Centre, University College London, United Kingdom

We present the results of ten years (2007 to 2017) of observation of the bromine monoxide (BrO) to sulphur dioxide (SO2) molar ratio in the volcanic plume of Tungurahua volcano and study the relation to volcanic activity. Following the nearly continuous eruptive activity from 1999 to 2008, Tungurahua showed alternating phases of eruptive activity separated by periods of quiescence between late 2008 and March 2016, after which degassing intensity decreased below the detection limit of the UV scanning DOAS instruments.
Recent long-term observations have suggested a link between changes in the BrO/SO2 molar ratio and the volcanic activity. Nevertheless, understanding of the mechanisms determining this link is still limited due to the lack of studies on volcanic bromine release from the melt into the atmosphere.
This study aims to broaden the global observational database through analysis of BrO/SO2 molar ratios collected from 13 eruptive phases at Tungurahua volcano during 10 years of continuous observations. For this purpose, we combine three different methods to retrieve the BrO/SO2 molar ratio to analyse variations over different time-scales.
We identify a cyclic pattern in BrO/SO2 molar ratios for 11 of the 13 eruptive phases. The phases are initialised by low BrO/SO2 molar ratios between 2 and 6x10-5 coinciding with vulcanian-type activity followed by a strong increase to ratios ranging between 4 and 17x10-5 when eruptive dynamism shifts to strombolian. For 5 phases, we additionally observe a progressive decrease to the initial values of 2 to 5x10-5 towards the end of the phase. This clear pattern indicates a connection between the BrO/SO2 molar ratio and eruptive dynamics. Based on our new data, we propose a conceptual model of the volcanic processes taking place at Tungurahua during the eruptive phases. Our data furthermore indicates that maximal BrO/SO2 ratio observed during each phases could be related to the input of volatile-rich magma into the active part of the volcanic system of Tungurahua.
This study shows that long-term BrO/SO2 ratios can be used as a proxy for the volatile status as well as temporal evolution of the volcanic system.

Keywords: Tungurahua, SO2, BrO, ratio, degassing, volcano, DOAS, NOVAC

Received: 31 Jul 2018; Accepted: 14 May 2019.

Edited by:

Alessandro Aiuppa, University of Palermo, Italy

Reviewed by:

Mattia Pistone, Université de Lausanne, Switzerland
Stefan Bredemeyer, German Research Centre for Geosciences, Helmholtz Centre Potsdam, Germany  

Copyright: © 2019 Warnach, Bobrowski, Hidalgo, Arellano, Sihler, Dinger, Lübcke, Battaglia, Steele, Galle, Platt and Wagner. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mr. Simon Warnach, Max Planck Institute for Chemistry, Mainz, Germany, s.warnach@mpic.de