The Interface Between Magma and Earth's Atmosphere

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 23; no. 12
• Main Authors: Kuhn, J., Bobrowski, N., Platt, U.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.12.2022; Wiley
• Subjects: Air; Atmosphere; atmospheric chemistry; Chemical kinetics; Composition; Cooling; Earth; Emission measurements; Emissions; Equilibrium; Gases; Geochemistry; Halogens; Hydrogen peroxide; Hydrogen sulfide; kinetic chemistry modeling; Kinetics; Lava; Magma; magmatic redox states; Oxygen; reactive halogen chemistry; Temperature; Thermodynamic equilibrium; Turbulent mixing; volcanic gas emissions; Volcanic gases; Volcanic plumes
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2022GC010671

Volatiles released from magma can form bubbles and leave the magma body to eventually mix with atmospheric air. The composition of those volatiles, as derived from measurements made after their emission, is used to draw conclusions on processes in the Earth's interior or their influences on Earth's atmosphere. So far, the discussion of the influence of high‐temperature mixing with atmospheric air (in particular oxygen) on the measured volcanic gas composition is almost exclusively based on thermodynamic equilibrium (TE) considerations. By modeling the combined effects of C‐H‐O‐S reaction kinetics, turbulent mixing, and associated cooling during the first seconds after magmatic gas release into the atmosphere we show that the resulting gas compositions generally do not represent TE states, with individual species (e.g., CO, H2, H2S, OCS, SO3, HO2, H2O2) deviating by orders of magnitude from equilibrium levels. Besides revealing the chemical details of high‐temperature emission processes, our results question common interpretations of volcanic gas studies, particularly affecting the present understanding of auto‐catalytic conversion of volcanic halogen species in the atmosphere and redox state determination from volcanic plume gas measurements. Plain Language Summary A major fraction of magmatic gas emissions are released into the atmosphere from open vents. The emission processes are characterized by fast turbulent mixing with atmospheric air (within seconds) and associated rapid cooling. Hardly anything is known about the chemical kinetics within this brief mixing and cooling period. We simulate the chemical kinetics during the first seconds of hot magmatic gases in the atmosphere and find severe deviation to common interpretations and central thermodynamic equilibrium assumptions prevailing in volcanic gas geochemistry. Key Points We model the chemical kinetics of high‐temperature volcanic gas emissions within the first seconds of mixing with atmospheric air We identify key chemical processes within the magma‐atmosphere interface and quantify influences on the volcanic plume composition Our results question common assumptions prevailing in volcanic gas geochemistry and refine interpretations of gas emissions from open vents