Fig. 1. (a) Simplified structural map of Campi Flegrei caldera (Italy), including the map view location of the magmatic source (green ellipse, 4 kilometers deep) and hydrothermal source (blue circle, 2 kilometers below the Solfatara volcanic crater) responsible for the post-1980 deformation [Amoruso et al., 2014]. (b) Elevation changes of benchmark 25a (shown in Figure 1a) from 1905 to 2009 [after Del Gaudio et al., 2010] merged with more recent (2009–2012) GPS data [De Martino et al., 2014]; m a.s.l. = meters above sea level. (c) Measured and simulated fumarolic carbon dioxide:water (CO2/H2O) ratio (top), ground deformation (middle), and earthquake magnitudes (bottom); dashed lines refer to times of injection of magmatic fluids into the hydrothermal aquifer [after Chiodini et al., 2012]. Credit: Acocella et al. [2015].