MAGMATIC VAPOR SOURCE FOR SULFUR-DIOXIDE RELEASED DURING VOLCANIC-ERUPTIONS - EVIDENCE FROM MOUNT-PINATUBO

Sulfur dioxide (SO2) released by the explosive eruption of Mount Pinat ubo on 15 June 1991 had an impact on climate and stratospheric ozone. The total mass of SO2 released was much greater than the amount dissol ved in the magma before the eruption, and thus an additional source fo r the excess SO2 is required. Infrared spectroscopic analyses of disso lved water and carbon dioxide in glass inclusions from quartz phenocry sts demonstrate that before eruption the magma contained a separate, S O2-bearing vapor phase. Data for gas emissions from other volcanoes in subduction-related arcs suggest that preeruptive magmatic vapor is a major source of the SO2 that is released during many volcanic eruption s.