Scenario-based and physics-informed forecast of the evolution of 75 years of unrest at Campi Flegrei caldera (Italy)

Campi Flegrei, which last erupted in 1538, has undergone unrest with periods of increased seismicity, gas emission and ground deformation in the 50’s, 70’s 80’s and since 2005. The eventual culmination of this last episode in an eruption, will directly impact on 2 million people living in the region, making it of critical concern for scientists, authorities and the general public. Here, we use existing data, thermal modelling and calculations of the physical properties of magma, to provide plausible future scenarios, under the assumption that magma injection at 4-5 km depth is responsible for the unrest episodes recorded since 1950. We show that the ascent of magma and magmatic fluids from depth is necessary to explain the measurements collected since 1950. Our calculations suggest that potentially eruptible magma is present today at ~4 km depth, but that eruption may be suppressed by the combination of small reservoir volume, magma compressibility, and viscous deformation of the surrounding crust. We conclude that efforts should focus on evaluation of the structural integrity of the crust overlying the shallow magma reservoir.