The Campi Flegrei volcanic district, in southern Italy, has been uplifted since 1968 by a net maximum of 3 m during the intervals 1968–1972 and 1982–1984. The uplift represents a permanent deformation against a background rate of subsidence of about 17 mm a−1. Previous models have reproduced the observed vertical deformation but not the full pattern of horizontal movements. The 1982–1983 deformation is here reanalyzed in terms of a penny‐shaped sill on its own, with a tabular surface protrusion, or in an extensional stress field. It can be explained best by the intrusion of a sill (of 0.03–0.04 km3 at a depth of 2.75 km) in a crust that is being stretched ESE‐WNW at a strain rate of about 5.6 × 10−5 a−1. The sill's volume is similar to the common volumes of Campi Flegrei's eruptions since the Neapolitan Yellow Tuff (NYT) caldera was formed 15.6 ka ago. This similarity and the permanent nature of the uplift favor magmatic intrusion as the primary source of unrest. Sill formation may thus reflect the spreading of magma at a level of neutral buoyancy or along lateral discontinuities in the crust. The southern part of the caldera has been shielded from post‐NYT eruptions, despite some 33 m of permanent uplift since Roman times. Precursors to eruptions may thus be related not to caldera‐wide uplift but to the preceding conditions that determine whether magma ascends beneath the southern part of the caldera (favoring sill intrusion) or elsewhere (favoring an eruption).

Campi Flegrei caldera, west of Naples in southern Italy, has an exceptional documented record of ground deformation from Roman times onwards. Systematic recording began in the nineteenth century. For earlier dates, information has been obtained from archaeological studies and from contemporary descriptions of the locations of buildings, usually Roman, with respect to sea-level. Especially important have been accounts related to the Serapis, a Roman market-place built in the second century BC and now incorporated within the modern town of Pozzuoli. The long-term patterns of ground deformation have conventionally been investigated on the premise that Campi Flegrei naturally tends to a state of static equilibrium. This study argues that, instead, the area naturally tends to a steady rate of subsidence, at about 17 mm a -~. After this background rate has been removed, the data indicate that a permanent uplift of some 33 m has occurred from Roman times (up until the present day: 2005 at the time of writing), attributable to the intrusion of 1.85 km 3 of magma, of which only 1% has been erupted. Uplift has occurred in three episodes, the third of which is still in progress. The behaviour can be interpreted in terms of the intermittent ascent of magma between a reservoir of c. 102-103 km 3 at depths of 8-15 km or greater, to a much smaller, shallower system at depths of about 34 km. Should the current pattern of deformation follow previous trends, uplift is expected to continue for another 80-90 years, during which time Campi Flegrei will be characterized by an elevated possibility of eruption.

<p>We present a new stratigraphy, inferred from several drillings carried out in the framework of the ICDP Campi Flegrei Deep Drilling Project , for the largest volcanic eruption in Europe since at least the Late Pleistocene. The eruption produced the Campanian Ignimbrite of southern Italy. It is conventionally believed to have triggered collapse of the large Campi Flegrei caldera, which, in turn, has been identified as a source for future ignimbrite volcanism. New borehole and radioisotopic data challenge this interpretation. They indicate that the Campanian Ignimbrite was erupted through fissures in the Campanian Plain, north of Campi Flegrei, and was not responsible for caldera collapse. The results are consistent with ignimbrite volcanism being controlled by a common magmatic system beneath the Campanian Plain. Understanding the dynamics of the whole plain is thus essential for evaluating the likelihood of similar future events.</p>