Petrological and volcanological constraints on volcanic sulfur emissions to the atmosphere

Abstract

A review of current knowledge about the physics of volcanic eruptions and the experimental constraints on sulfur behavior in magmas is presented with the aim of evaluating the range of sulfur yields from major explosive eruptions based on petrological and volcanological data. The so-called petrologic method, used to evaluate syn-eruptive melt degassing, is expanded by also considering the role of a pre-eruptive gas phase. It is shown that more than 90% of the atmospheric sulfur loading may come from release of the pre-eruptive gas phase during eruptions of intermediate to silicic magmas at subduction-related volcanoes. In contrast, the role of a pre-eruptive gas phase may be much less important in more mafic magmas erupted in other tectonic settings. Bulk sulfur contents are weakly (spreading-ridges and hot spots) to non-correlated (subduction-zones) with bulk-rock composition. With the exception of some persistently active volcanoes, bulk sulfur contents generally do not exceed 0.5 wt %. The sulfur yields are positively correlated with mass of erupted magma, but the dispersion in sulfur emission for a given erupted mass increases progressively as the erupted mass decreases. The sulfur yields of single eruptive events retrieved from this improved petrologic method are shown to closely agree with independent estimates obtained from analysis of ice cores, optical-depth measurements, and remote-sensing spectroscopic techniques (TOMS and COSPEC).