A direct line to the magma
The Solfatara crater shows the restless heart of the Campi Flegrei, a supervolcanic caldera near Naples. Its fumaroles, or gas vents, release a cocktail of gases that shows the processes happening deep underground. The most powerful fumarole, Bocca Grande ("Big Mouth"), has been emitting gases for at least 2,000 years, with surface temperatures consistently around 160°C. The gas mixture is primarily water vapor (H2O), making up about 82% of the volume, followed by carbon dioxide (CO2) at 17.5%. The characteristic "rotten egg" smell comes from a much smaller but pungent component: hydrogen sulfide (H2S), at about 0.13%.
Scientists from Italy's National Institute of Geophysics and Volcanology (INGV) continuously monitor these emissions. The ratios between different gases act as geothermometers and indicators of magma activity. For example, the CO/CO2 ratio changes with temperature changes in the hydrothermal system. Isotopic analysis of elements like helium and carbon helps distinguish between gases originating from the Earth's mantle and those released from the crust, revealing that a significant portion of the CO2 comes from a deep magmatic source. The total output of CO2 from the crater is immense, estimated at around 1,500 metric tons per day.