Volcanic, Magmatic and Hydrothermal Gases

Abstract This chapter provides an overview of key aspects of volcanic and hydrothermal gases. It covers sampling and analyses of gases emitted from volcanic vents and determination of soil CO2 fluxes. The chemical and isotopic compositions of volcanic and hydrothermal gases reflect processes related to volatile sources and transport from the magma to the surface. Thermodynamics of gas equilibration allows for the investigation of gas compositional changes as a result of temperature, pressure, and dominant buffer reactions. Noble gases in combination with major gas species, such as CO2 and N2 provide important information on the ultimate sources of volcanic emissions in terms of mantle, crust, and subducted materials. The excess sulfur issue, where significantly more sulfur is emitted than what can be dissolved in the erupted magma, demonstrates the significance of characterizing volcanoes both in terms of their volatiles as measured in melt inclusions as well as in the volcanic plumes.