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Volume 9, issue 2
Solid Earth, 9, 247-266, 2018
https://doi.org/10.5194/se-9-247-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Solid Earth, 9, 247-266, 2018
https://doi.org/10.5194/se-9-247-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Mar 2018

Research article | 07 Mar 2018

Periodicity in the BrO∕SO2 molar ratios in the volcanic gas plume of Cotopaxi and its correlation with the Earth tides during the eruption in 2015

Florian Dinger1,2, Nicole Bobrowski1,2, Simon Warnach1,2, Stefan Bredemeyer3, Silvana Hidalgo4, Santiago Arellano5, Bo Galle5, Ulrich Platt1,2, and Thomas Wagner1 Florian Dinger et al.
  • 1Max-Planck Institut for Chemistry, Mainz, Germany
  • 2Institute for Environmental Physics, University of Heidelberg, Germany
  • 3GEOMAR, Kiel, Germany
  • 4Instituto Geofísico, Escuela Politécnica Nacional (IGEPN), Quito, Ecuador
  • 5Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden

Abstract. We evaluated NOVAC (Network for Observation of Volcanic and Atmospheric Change) gas emission data from the 2015 eruption of the Cotopaxi volcano (Ecuador) for BrO∕SO2 molar ratios. The BrO∕SO2 molar ratios were very small prior to the phreatomagmatic explosions in August 2015, significantly higher after the explosions, and continuously increasing until the end of the unrest period in December 2015. These observations together with similar findings in previous studies at other volcanoes (Mt. Etna, Nevado del Ruiz, Tungurahua) suggest a possible link between a drop in BrO∕SO2 and a future explosion. In addition, the observed relatively high BrO∕SO2 molar ratios after December 2015 imply that bromine degassed predominately after sulfur from the magmatic melt. Furthermore, statistical analysis of the data revealed a conspicuous periodic pattern with a periodicity of about 2 weeks in a 3-month time series. While the time series is too short to rule out a chance recurrence of transient geological or meteorological events as a possible origin for the periodic signal, we nevertheless took this observation as a motivation to examine the influence of natural forcings with periodicities of around 2 weeks on volcanic gas emissions. One strong aspirant with such a periodicity are the Earth tides, which are thus central in this study. We present the BrO∕SO2 data, analyse the reliability of the periodic signal, discuss a possible meteorological or eruption-induced origin of this signal, and compare the signal with the theoretical ground surface displacement pattern caused by the Earth tides. Our central result is the observation of a significant correlation between the BrO∕SO2 molar ratios with the north–south and vertical components of the calculated tide-induced surface displacement with correlation coefficients of 47 and 36%, respectively. From all other investigated parameters, only the correlation between the BrO∕SO2 molar ratios and the relative humidity in the local atmosphere resulted in a comparable correlation coefficient of about 33%.

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We monitored the bromine monoxide-to-sulfur dioxide molar ratio in the effusive gas plume of Cotopaxi volcano in order to gain insight into the geological processes which control the pressure regime of the volcanic system. We observed a conspicuous periodic pattern with a periodicity of about 2 weeks, which significantly correlates with the Earth tidal forcing. Our results support a possible Earth tidal impact on volcanic activity, in particular for the Cotopaxi eruption 2015.
We monitored the bromine monoxide-to-sulfur dioxide molar ratio in the effusive gas plume of...
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