Experimental Evidence for the Source of Excess Sulfur in Explosive Volcanic Eruptions

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Abstract
The amounts of sulfur released in explosive volcanic eruptions are often orders of magnitude larger than those expected to result from the degassing of the erupted SiO 2 -rich magma. Experimentally measured fluid/melt partition coefficients of sulfur ranged from 47 under oxidizing conditions (where SO 2 is the dominant sulfur species in the fluid) to 468 under reducing conditions (where H 2 S dominates). Therefore, a few weight percent of hydrous fluid accumulated in the top of a magma chamber may extract most of the sulfur out of the entire magma reservoir and generate sulfur excesses upon eruption.