Geophysical Responses to an Environmentally‐Boosted Volcanic Unrest

The spatiotemporal relationship between geophysical, environmental, and geochemical responses during volcanic unrest is essentially unknown, making their joint use and interpretation for eruption forecasting challenging. Here, Empirical Orthogonal Functions analysis applied to GPS data allows the separation of the dominant deep-sourced inflation from environmentally controlled signals associated with extension at Campi Flegrei caldera. This separation bridges the gap between deformation, seismic and geochemical responses, clarifying the processes underlying the ongoing volcanic unrest. Persistent meteoric forcing during the 2017-2018 hydrological year changed the decadal trend of seismic energy and secondary deformation components, pairing their spatial patterns. The result was a block in the carbon dioxide released in 2018 at Solfatara, the primary stress-release valve at the caldera. The subsequent overpressure weakened the fractured eastern caldera, opening pathways for deep, hot materials to reach the surface. Our results give insight into how environmental forcing can favor volcanic unrest in pressurized calderas.Geophysics and geochemistry are two of the most essential disciplines to understand volcanic unrest and eruptions. Finding the link between deformation signals and their seismic and geochemical counterparts is crucial in understanding how a volcano works; however, a time-resolved 3D analysis of signals sensitive to different processes, from magma migration to environmental forcing, is our best chance to understand how the volcano changes and when an eruption might occur. We borrowed standard oceanic and climatic data analysis techniques and applied them to GPS signals recorded during unrest at Campi Flegrei caldera. The results uncovered small deformation components linked to seismic migrations and variations in carbon dioxide fluxes measured at the Solfatara crater. These components clarify how a drought can weaken the shallowest crust, strengthening ongoing processes generated at depth. A wet hydrological year in the middle of the ongoing drought coincided with decreased emissions of carbon-bearing fluids from Solfatara, the primary stress-release valve of the caldera. This stress was eventually released when deep materials rose in the eastern caldera, producing seismicity. Highlighting small components in deformation signals linked to environmental changes appears essential to mark variations in volcanic behavior, in analogy to what is done by ambient noise interferometry.Advanced deformation analysis detects environmental components linked to seismic migrations and variations in carbon dioxide fluxes A wet hydrological year during a drought closed Solfatara, increasing pressure and breaking the shallow caldera in early 2018 The deep unrest sources cracked the weakened eastern caldera in 2018-2019, causing seismic unrest