Escalating soil CO2 degassing correlates with ground uplift and seismicity during the ongoing unrest of Campi Flegrei (2005–2025)

Abstract

The mechanism driving accelerating unrest at the densely populated Campi Flegrei caldera since 2005 remains debated. Analyzing an unprecedented two-decade geochemical dataset, we show that escalating soil CO2 fluxes closely tracks caldera uplift, revealing magmatic fluid pressurization at 3- to 4-kilometer depth and heating as the fundamental driver of the unrest. A critical magmatic gas pulse occurred between 2018 and 2022 specifically focused this outgassing beneath the Solfatara crater. Thermodynamic modeling demonstrates that an increasing mass of ascending fluid pressurizes the hydrothermal system, forcing vapor condensation within the upper kilometer. This condensation transfers latent heat to the crust. We calculate that this released thermal energy is an order of magnitude greater than that required for the 1.6-meter uplift since 2005. Ultimately, this fluid pressurization and heating drive accelerating deformation and seismicity; alongside the 2021 emergence of seismic sequences with short inter-event times, it directly signals an escalating phreatic or magmatic eruption risk.