The Ecological Significance of the Coexistence of Sulphur Dioxide and Hydrogen Sulphide in Volcanic Fumaroles

The relative concentrations of hydrogen sulphide and sulphur dioxide in volcanic gases cannot be explained simply by the temperatures and pressures, and appear as the result of the influence of different natural factors. SO 2 is directly related to magma degassing, while H 2 S can be produced by the reaction of acidic solutions on dispersed sulphide minerals. As long as these inputs to the surface environment are of moderate extent, then readjustment of redox conditions to an equilibrium situation will occur; a permanent disequilibrium will result in increased contributions of any component. A wide spectrum of trace elements is normally associated with the presence of sulphur compounds in volcanic areas; their importance can be estimated for any system on the basis of the quantitative relationship between the oxidized and the reduced sulphur species. Extensive polluting effects can be produced by a continuous flow from a deep magmatic source, while minor consequences are associated with a re-circulation in the surface environment of heavy metals from previous volcanic activities.