Forty years of geochemical data at Campi Flegrei hydrothermal system

The systematic sampling of the main fumaroles of Solfatara (Campi Flegrei, Italy) started during the bradyseismic crisis of 1983-84. In the late 1990s, diffusive CO₂ emissions measurements also became part of the monitoring activity through systematic campaigns. In these 40 years of investigations almost unique databases were created including thousands of chemical and isotopic analyses of fumaroles and hundreds estimations of the diffuse CO₂ emission. These databases provided the base of numerous geochemical and interdisciplinary scientific works to understand the processes occurring in the hydrothermal-magmatic system of Campi Flegrei, a caldera in unrest since 2005. The main results obtained by this effort indicate the pivotal role of magma degassing in the current crisis of Campi Flegrei. The deep magmatic fluids are injected into the hydrothermal system during episodes of magma degassing. These injections cause pressurization and heating of the hydrothermal systems, earthquakes, ground deformations, changes in fumarole compositions and escalating CO₂ emission at the surface. The expulsion of these fluids constitutes the most energetic process currently occurring at Campi Flegrei; it is, in fact, more energetic than ground deformation and seismic activity. In this work, we present a review of these different aspects.