Dynamics of Campi Flegrei caldera (Italy) after the 1538 AD eruption

Understanding how shallow magma transfer occurs at volcanoes is important to have a conceptual model of how a volcano works and, possibly, to forecast where and when an eruptive vent may open. However, shallow magma transfer is difficult to detect at poorly monitored volcanoes, and particularly at calderas, characterized by areal volcanism. Magma transfer before the last 1538 eruption at Campi Flegrei caldera (Italy) was previously studied using historical, archaeological, and geological data. Here, we extend that dataset to 1650, to uncover any magma transfer during overall post-eruptive phase. Results highlight two post-eruptive subsidence phases, separated by a previously undocumented uplift during 1540-1582. Uplift highlights the pressurization of the central (~3.5 km depth) and peripheral (~1 km depth) pre-eruptive sources, suggesting an aborted eruption. The subsidence events are explained by the depressurization of the central source and pressurization of a deeper magmatic layer (~8 km depth). Therefore, despite the overall post-eruptive deflation, after 1538 the deeper reservoir experienced continuous magma supply, with magma almost erupting between 1540-1582, challenging the common assumption of post-eruptive relaxation. This underlies the importance of monitoring the deeper magmatic systems, also after eruptions, to properly assess their eruptive potential.