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Variation of the BrO/SO2 Molar Ratio in the Plume of Tungurahua Volcano Between 2007 and 2017 and Its Relationship to Volcanic Activity

2019; Frontiers Media; Volume: 7; Linguagem: Inglês

10.3389/feart.2019.00132

2296-6463

Simon Warnach, Nicole Bobrowski, Silvana Hidalgo, Santiago Arellano, Holger Sihler, Florian Dinger, Peter Lübcke, Jean Battaglia, Alexander Steele, Bo Galle, U. Platt, Thomas Wagner,

Geochemistry and Geologic Mapping

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.