Spectroscopic observation of HCl degassing from Soufriere Hills Volcano, Montserrat

Abstract

Open-path Fourier transform infrared (FTIR) spectroscopic techniques were employed to study gas emissions from Soufriere Hills Volcano in July-August 1996. Observations were made using both volcanic and artificial sources of infrared energy. Column amounts of HCl fall in the range 1-100 ppmv m but other species expected in the gas phase, notably SO2 are not apparent in the spectra. The minimum detection limit for SO2 in these data indicates that the HCl/SO2 molecular ratio exceeded 10. Scaled against measured fluxes of SO2, the HCl emission rate during this period exceeded 15 kg s-1 (1300 t d-1). Comparison of our results with other geochemical measurements of Soufriere Hills emissions is complicated by inherent differences between the analytical methods employed. While the ability to measure atmospheric concentrations of reactive trace gases at high temporal resolution is of clear use in environmental and medical studies of volcanic effluents, a better understanding of the kinetics of plume chemistry is needed to resolve ambiguities in interpretation of time-series FTIR observations.