Investigating the ancient eruption histories of the pre-caldera Vitafumo and Miliscola monogenetic volcanoes (southwestern sector of Campi Flegrei, Italy)

To assess the contribution of phreatomagmatism to the Campi Flegrei eruptive history, a detailed study of some monogenetic volcanoes was conducted. This research focuses on the stratigraphic analysis of the well-exposed, pre-caldera, ultra-proximal pyroclastic sequences from two distinct volcanoes: the Vitafumo and Miliscola tuff cones, located in the SW sector of Campi Flegrei volcanic field. The Vitafumo remnant comprises three main pyroclastic sequences, overall thick up to 130 m, separated by two erosional unconformities. The Miliscola succession, resting on a paleosol above the Vitafumo volcanic edifice, is up to 50 m thick. A dated tephra sequence above the Miliscola succession suggests a volcanic activity older than ca 70 ka for the two tuff cones. The Vitafumo and Miliscola sequences mainly consist of thick, poorly sorted, massive or diffuse stratified pumice lapilli deposits containing large blocks and scattered bombs, interbedded with massive or stratified, matrix-supported ash layers. Blackish and reddish stratified scoria beds are also present in the Vitafumo succession. This sequence is mainly unconsolidated but includes thick, lithified units and a thin welded horizon. A wide range of eruptive dynamics has been identified, including ballistic impacts associated with short-lived, buoyant eruptive columns accumulating pumice lapilli and blocks alternating with repeated column collapses emplacing unsteady and non-uniform pyroclastic density currents. Episodes of volcanic conduit erosion were also documented, along with intermittent phreatomagmatic pulses. The study revealed that phreatomagmatic phases, though present, are not dominant. Instead, they are interspersed with magmatic phases, probably resulting from significant destabilisation of the conduit-vent system.