The 39.8 ka Campanian Ignimbrite (CI) is the largest caldera-forming eruption of the Campi Flegrei during the Quaternary, which had a global-scale impact on the environment and human populations. The cooling following the eruption and the several effects of it strongly affected the paleoenvironment and the migration of hominids in Europe. The volume of the eruption is necessary to constrain the climate model of this area in the past. However, despite a large number of studies, the Dense Rock Equivalent (DRE) volume estimates range from 60 to 300 km3. Here we present a review of the previous volume evaluations and a new calculation of the volume of the ignimbrite. This estimate is constrained by the first total CI isopach map, developed through a method able to reconstruct the paleo-topography during the eruption, which is easily reproducible in all ignimbrites strongly topographically controlled and allows the calculation of well-defined uncertainties. The preserved total bulk extra-caldera volume of the ignimbrite is estimated at 61.5 km3 ± 5.5 km3. The total PDC deposit volume is then corrected for erosion, ash elutriation, the intracaldera deposit volume and the volume of tephra deposited in the sea. The total final volume estimate of the eruption ranges from 165 km^3 – 248 km^3 DRE. This value corresponds to a mass of 4.3 - 6.5 x 10^14 kg, a magnitude (M) of 7.7 and a VEI of 7. This M makes the CI the largest-magnitude Quaternary eruption in the Mediterranean area. The new detailed estimation of CI eruption physical parameters confirms this event has significantly affected human activity and the environment on a large scale at the time of the eruption and, in the future, an event of this size would be cataclysmic.

The Campanian Ignimbrite was emplaced during the 39-ka caldera-forming eruption of Campi Flegrei near Naples, Italy. This eruption deposited a trachytic ignimbrite up to 80 km from the caldera and co-ignimbrite fallout more than 2300 km to the northeast. The pyroclastic density current was dilute and mobile, overtopping kilometer-high mountains up to 60 km from the vent. Stratigraphic units within the proximal and distal deposits of the Campanian Ignimbrite have never been definitively correlated due to their very dissimilar appearances and the lack of medial exposure. Correlation of the ignimbrite, specifically which proximal units formed simultaneously with the majority of the distal deposits, is necessary to understand the events that formed this dilute current. The co-ignimbrite lag breccia (Breccia Museo), which represents the caldera collapse, and an earlier eruptive phase that formed a high-grade ignimbrite (Piperno) are potential proximal correlates to the main distal ignimbrite unit. Juvenile matrix material includes pumice and scoria fragments and bubble-wall shards. A distal outcrop at 970 m asl, thought to represent deposits from the upper transport system of the main pyroclastic flow, is dominated by bubble-wall shards. At all other sites, most juvenile ash shards show textures similar to associated pumice lapilli. We suggest that much of the ash was from abrasion of pumice, but the upper current had few pumice clasts and thus less abrasion-derived ash. Preliminary analyses indicate that early units have limited chemical compositional ranges (predominantly Na2O 4-7% and K2O 5-9%), whereas the Piperno and the dominant distal unit both have a broader geochemical range that extends to roughly 9% Na2O and 2% K2O. The uppermost proximal unit has the most extreme compositions, approximately 2-6% Na2O and 6-11% K2O. These observations are consistent with the source of the eruption being either a large stratified magma chamber that underwent pre-eruptive mingling, or several semi-isolated magma bodies. Proximal deposits include spatter from local vents that may have tapped isolated magma bodies. Study of pyroclasts from the Campanian Ignimbrite allow both correlation of proximal and distal deposits and a characterization of some aspects of the pyroclastic current.