Fate and Hazards of Medium-Size Resurgent Calderas: the Case of Campi Flegrei, Ischia and Pantelleria Structures

Abstract

Assessment of time and space relationships among magmatism, volcanism, and resurgence of mediumsize calderas is a necessary tool to formulate a general model for their dynamics which also permits to forecast their evolution. To define a general hypothesis for the Campi Flegrei caldera, in a persistent state of unrest, the Ischia and Pantelleria medium-size resurgent structures, in variable stages of evolution, have also been investigated. In particular some parameters such as the structural and volcanological evolution, with emphasis on resurgence dynamics and coeval volcanism, and the evolution, present state and role of the magmatic system in resurgence, have been defined. For the Campi Flegrei caldera, the data collected during unrest episodes have also been taken into account, together with those from past eruptions. They corroborate the hypothesis that the unrest episodes are transient short-term events within the long-term deformation related to caldera resurgence. The geometry of the short-term deformation is strictly related to the structural setting of the caldera. The sub-surface processes have been dominated by joint degassing of two magmatic bodies, at 3-4 and 8 (or more) km depth, with the shallower formed by magma ascending from the deeper body. Both bodies contribute to the hydrothermal system, but the shallow magma is fluxed by the continuous upstream of CO2-richer gas released by the deep body. The two-layer degassing magma allows explaining geochemical and petrological features of unrest and volcanism. The joined interpretation of geological, geodetic, and geochemical data on the three calderas is an innovative approach that adds a time-perspective on how resurgent calderas behave. The proposed general hypothesis will help in long- and short-term volcanic hazards assessment and will support Civil Defence Authorities in elaborating actions devoted to volcanic risk reduction.