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https://doi.org/10.1029/2011gc003794
Copy DOIJournal: Geochemistry, Geophysics, Geosystems | Publication Date: Mar 1, 2012 |
Citations: 50 |
We report CO2, SO2, and H2S emission rates and C/S ratios during the five months leading up to the 2009 eruption of Redoubt Volcano, Alaska. CO2emission 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 SO2, not the >2100 t/d SO2expected 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 CO2‐rich magmatic gas for at least 5 months prior to eruption, and minimal scrubbing of SO2by near‐surface groundwater. The high C/S ratios observed could reflect bulk degassing of mid‐crustal magma followed by nearly complete loss of SO2in 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.
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