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Abstract

We evaluated NOVAC (Network for Observation of Volcanic and Atmospheric Change) gas emission data from the 2015 eruption of Cotopaxi volcano (Ecuador) for BrO/SO2 molar ratios. Statistical analysis of the data revealed a conspicuous periodic pattern with a periodicity of about two weeks in a three 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 two 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. 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 %.