File:Hydrothermal system.png

English: Conceptual diagram showing sources of water and solutes in a terrestrial hydrothermal system. The diagram depicts groundwater circulation driven by shallow magma at an extensional setting or hot spot. The heated water contains dissolved magmatic gas, including sulfur dioxide (SO2), which can disproportionate into sulfide and sulfate in high temperature aqueous solutions. As the solutions flow toward the surface along faults and joints, decompression boiling can liberate a gas phase enriched in sulfide. As the vapor approaches the surface, exposure to oxic groundwater can cause the sulfide to oxidize, producing sulfate and acid. Springs that primarily receive vapor phase inputs tend to be acidic with low concentration of chloride relative to sulfate. Springs that primarily receive fluid phase inputs tend to have near neutral to basic pH with high concentrations of chloride relative to sulfate. This figure and accompanying text are modified from figure 1 of Colman et al. (2019).