Figure 5

(a) Magma transfer below Campi Flegrei caldera before the Monte Nuovo eruption (orange); magma first propagated laterally from the oblate magma reservoir (OMR) at ~4.7 km depth below the caldera centre, feeding an eccentric reservoir (Monte Nuovo Reservoir, MNR) at ~3.8 km depth; from here, magma propagated vertically (orange) to feed a smaller and shallower reservoir (not shown) and then the Monte Nuovo eruption. The inferred paths (grey) for other representative eruptions of the last 5 ka are also reported; (b–d) General conceptual model for magma transfer below calderas, supported by all recent pre-eruptive unrest: a tabular intrusion, or sill, fed by a dike (red lines) forms at the top of a central magma chamber, possibly resulting from previous stacked tabular intrusions (purple lines) (b); the sill uplifts the caldera centre, where the previously stacked sills may have also promoted resurgence. Stresses (orange lines) focus at the tips of the sill, which propagates laterally following the minimum stress component σ₃ (grey lines, schematically taken from ref. 24) controlled by the unloading promoted by the caldera depression (c); the sill eventually increases its dip and becomes a sub-vertical dike erupting to the side of the maximum uplifted area (black triangle) (d). Black arrows show the propagation direction of the intrusion. Digital Terrain Model by INGV-Osservatorio Vesuviano.