William C. Evans Peter J. Kelly Robert G. McGimsey Melissa Pfeffer Michael P. Doukas Christina A. Neal Cynthia A. Werner 2012 <p><span>We report CO</span>_2,<span>&nbsp;SO</span>₂<span>, and H</span>₂<span>S emission rates and C/S ratios during the five months leading up to the 2009 eruption of Redoubt Volcano, Alaska. CO</span>₂<span>emission rates up to 9018 t/d and C/S ratios ≥30 measured in the months prior to the eruption were critical for fully informed forecasting efforts. Observations of ice-melt rates, meltwater discharge, and water chemistry suggest that surface waters represented drainage from surficial, perched reservoirs of condensed magmatic steam and glacial meltwater. These fluids scrubbed only a few hundred tonnes/day of SO</span>₂<span>, not the &gt;2100 t/d SO</span>₂<span>expected from degassing of magma in the mid- to upper crust (3–6.5 km), where petrologic analysis shows the final magmatic equilibration occurred. All data are consistent with upflow of a CO</span>₂<span>-rich magmatic gas for at least 5 months prior to eruption, and minimal scrubbing of SO</span>₂<span>by near-surface groundwater. The high C/S ratios observed could reflect bulk degassing of mid-crustal magma followed by nearly complete loss of SO</span>₂<span>in a deep magmatic-hydrothermal system. Alternatively, high C/S ratios could be attributed to decompressional degassing of low silica andesitic magma that intruded into the mid-crust in the 5 months prior to eruption, thereby mobilizing the pre-existing high silica andesite magma or mush in this region. The latter scenario is supported by several lines of evidence, including deep long-period earthquakes (−28 to −32 km) prior to and during the eruption, and far-field deformation following the onset of eruptive activity.</span></p> application/pdf 10.1029/2011GC003794 en AGU Deep magmatic degassing versus scrubbing: Elevated CO2 emissions and C/S in the lead-up to the 2009 eruption of Redoubt Volcano, Alaska article