A review of the stratigraphy of the Ischia harbor (Southern Tyrrhenian Sea, Italy) and the relationships with coastal and marine hazard assessment

A review of the stratigraphy of the Ischia harbor is presented, aimed at the identification of possible solutions for coastal monitoring and marine hazard. Previous papers have shown that the coastal and marine hazard of Naples Bay is high and is mainly concentrated in three areas, including the Dohrn and Magnaghi canyons, the southern Ischia canyon system, and the southern offshore of the Sorrento Peninsula. In this paper, we demonstrate that the Ischia harbor is a complex volcanic area whose stratigraphy has been controlled by important volcanic eruptions, corresponding with significant tephra deposits, according to previous literature. The most important tephra deposits are represented by the Ischia Porto Tephra, observed in a limited number of outcrops around the Ischia harbor, and studied in nine stratigraphic sections. It consists of a succession of pyroclastic layers, reflecting a complex eruptive sequence, typified by a set of explosions, that generated phenomena with a variable impact on the surrounding land. Important data on coastal and marine hazards in the Ischia harbor are provided by the geoarchaeological data, showing that the Ischia Porto eruption has generated a set of phenomena with variable degrees of impact on the surrounding landscape. In a volcanic setting, the reconstruction of the stratigraphic framework allows for the evaluation of a reliable chronostratigraphic framework and opens the door to the study of the stratigraphic relationships between sedimentary and volcanic seismostratigraphic units. A crucial component in assessing the hazard of a coastal volcanic area is the ability to more accurately predict the areal distribution of the major Holocene volcanic units due to their onshore-offshore association.