Fig. 1: Chronogram of CF fumarole compositional evolution from 1982 to 2023.
From: Escalation of caldera unrest indicated by increasing emission of isotopically light sulfur
Data from Supplementary Table 1. Analytical uncertainty at 1 standard deviation (s.d.) of the mean. a, A progression from H2O-rich (hydrothermal (H)) to CO2-rich (magmatic (M)) compositions is observed. b, Deuterium isotope composition (δD, relative to SMOW) of fumarolic steam evolves to progressively more positive signatures, within the magmatic gas range15,16,25. c, H2S concentrations increase since 2018, paralleled by a negative isotopic shift of the sulfur isotope composition. d, Observed (fumaroles) versus modelled (at equilibrium with hydrothermal pyrite; Methods) gas H2S/CO2 ratios. The excess H2S during 2018–present (and in the 1980s) implies H2S fugacity is not buffered by pyrite during accelerating unrest. e, Volcano-tectonic seismicity (monthly number of events, grey bars; data from INGV Osservatorio Vesuviano) versus the estimated H2S flux from the Solfatara area. This flux is calculated by multiplying the diffuse CO2 output from the Solfatara degassing structure32 by the fumarolic H2S/CO2 ratio (panel d).
