Degassing at Anatahan volcano during the May 2003 eruption: Implications from petrology, ash leachates, and SO2 emissions

Sulfur budget calculations based on estimates of pre-eruptive magmatic and residual melt S contents, mass of erupted magma, and total SO2 output fluxes require an additional source of S other than the erupted magma. Multiple lines of evidence, including high SO2 emissions early in the eruption, the presence of accretionary lapilli and hydrothermal minerals in the early eruptive deposits, quenched pumice textures, and cation and anion ratios and abundances in ash leachates suggest that a S-rich free volatile phase exsolved from a large magma body. Magmatic volatiles were stored as components of the hydrothermal system (pressurized gases, hydrothermal fluids, and/or hydrothermal minerals) to be remobilized early in the eruption to contribute to the total SO2 output.