Monitoring so2 emission at the Soufriere Hills volcano: Implications for changes in eruptive conditions
Correlation spectrometer measurements of sulfur dioxide (SO 2 ) emission rates during the current eruption of the Soufriere Hills volcano, Montserrat, have contributed towards identifying different phases of volcanic activity. SO 2 emission rate has increased from <200 tonnes per day (td −1 ; <2.3 kgs −1 ) in the early stages of dome growth to >550 td −1 (>6.4 kgs −1 ) after July 1996, with the uncertainty associated with any individual measurement ca. 30%. Significantly enhanced SO 2 emission rates have been identified in association with early phreatic eruptions (800 td −1 (9.3 kgs −1 )) and episodes of vigorous dome collapse and pyroclastic flow generation (900 to 1500 td −1 (10.4 to 17.4 kgs −1 )). SO 2 emission rate has proved a useful proxy measurement for magma production rate. Observed SO 2 emission rates are significantly higher than those inferred from analyses of glass inclusions in phenocrysts, implying the existence of a S-rich magmatic vapour phase.