RESUMO
The balance between the amount of gas coexisting with mantle-derived magmas at depth and that emitted during intereruptive phases may play a key role in the eruptive potential of volcanoes. Taking the December 2018 eruption at Mt. Etna volcano as a case study, we discuss the geochemical data streams observed. The signals indicate a long-lasting prelude stage to eruption, starting in 2017 and involving magma-fluid accumulation in the deep (>7 km bsl) reservoir, followed by pressure buildup in the system at intermediate depth (5 to 2 km bsl), 6 to 7 months before the eruption. A brief preeruptive phase marks the pressurization at 2 to 3 km below the craters. By comparing the magma and fluid recharge at depth to the measured volcanic degassing from the plume, we provide evidence that Mt. Etna was in a state of extreme overpressurization in the weeks before the onset of the eruption.
RESUMO
During the reawaking of a volcano, magmas migrating through the shallow crust have to pass through hydrothermal fluids and rocks. The resulting magma-hydrothermal interactions are still poorly understood, which impairs the ability to interpret volcano monitoring signals and perform hazard assessments. Here we use the results of physical and volatile saturation models to demonstrate that magmatic volatiles released by decompressing magmas at a critical degassing pressure (CDP) can drive volcanic unrest towards a critical state. We show that, at the CDP, the abrupt and voluminous release of H2O-rich magmatic gases can heat hydrothermal fluids and rocks, triggering an accelerating deformation that can ultimately culminate in rock failure and eruption. We propose that magma could be approaching the CDP at Campi Flegrei, a volcano in the metropolitan area of Naples, one of the most densely inhabited areas in the world, and where accelerating deformation and heating are currently being observed.
