Deep magmatic degassing versus scrubbing: Elevated CO2 emissions and C/S in the lead-up to the 2009 eruption of Redoubt Volcano, Alaska

Cynthia A. Werner; William C. Evans; Peter J. Kelly; Robert G. McGimsey; Melissa Pfeffer; Michael P. Doukas; Christina A. Neal

doi:10.1029/2011gc003794

USGS · 70193254

Deep magmatic degassing versus scrubbing: Elevated CO2 emissions and C/S in the lead-up to the 2009 eruption of Redoubt Volcano, Alaska

Cynthia A. Werner·William C. Evans·Peter J. Kelly·Robert G. McGimsey·Melissa Pfeffer·Michael P. Doukas·Christina A. Neal

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Abstract

We report CO 2, SO 2 , and H 2 S emission rates and C/S ratios during the five months leading up to the 2009 eruption of Redoubt Volcano, Alaska. CO 2 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 2 , not the >2100 t/d SO 2 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 2 -rich magmatic gas for at least 5 months prior to eruption, and minimal scrubbing of SO 2 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 2 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.

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Source-reported bounding extent: 60.45° to 60.6° latitude; -152.9° to -152.7° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Cynthia A. Werner, William C. Evans, Peter J. Kelly, Robert G. McGimsey, Melissa Pfeffer, Michael P. Doukas, Christina A. Neal. 2012-03-20. Deep magmatic degassing versus scrubbing: Elevated CO2 emissions and C/S in the lead-up to the 2009 eruption of Redoubt Volcano, Alaska. https://doi.org/10.1029/2011gc003794

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