High-resolution geological investigations to reconstruct the long-term ground movements in the last 15 kyr at Campi Flegrei caldera (southern Italy)

Abstract

Ground deformations are among the main volcanic phenomena occurring within the caldera system and presently recorded at different volcanoes worldwide including the Campi Flegrei active caldera (southern Italy). A new stratigraphic, sedimentological and paleontological survey carried out in the central sector of the Campi Flegrei caldera both along the already known La Starza succession and through a new excavated tunnel provided new insights into the ground movement episodes occurred in the last 15 kyr. This study, which has also benefited of unpublished boreholes stratigraphic data, shows that the most uplifted sector of the Campi Flegrei caldera, presently marked by the morphological structure of the La Starza cliff close to the Pozzuoli coastline, was characterized by a complex sedimentary evolution. It results from different phases of alternating marine transgressions and regressions, the latter marked by both continental volcanic and/or palustrine/lacustrine sediments. These alternations result from the interplay between (i) subsidence and uplift episodes of the caldera floor and (ii) sea level variations during the Holocene. A rest period of volcanism accompanied by a sea level rise determined a significant submersion phase in about 3000 years between 8.59 and 5.5 ka. This phase was defined by a sea level with a maximum water depth value of 60–80 m and a late stage recording significant episodes of ground movements. Subsequently, between 5.5 and 3.5 ka, a ground uplift of about 100 m occurred, with short subsidence around 4.5 ka following the Plinian Agnano-Monte Spina eruption. The net vertical displacement represents the recorded deformation linked with a volcanism period in which ~2.5 km3 of magma were erupted by different vents within the caldera. It is worth to note as the general trend of ground movement through the time indicates a similarity in the pattern, beyond its scale.