Iannuzzi, Enrico

We report, for the first time, evidence of seismically induced soft‐sediment deformations in the central area of the active Campi Flegrei caldera (southern Italy). We analyzed the marine‐transitional and continental sequences located along the coastal La Starza cliffs and several stratigraphic logs exposed during the excavation of a 1‐km‐long tunnel in the Pozzuoli area. The successions host several soft‐sediment structures including sand dikes and sand volcanoes, which are largely dated within the 4.55‐ to 4.28‐kyr BP interval. The volcano‐sedimentary sequence, deposited within the Campi Flegrei caldera in the last 15 kyr, is schematically formed by the superposition of three layers with different rheological behaviors; from the base progressing upward we recognize (1) a massive tuff, (2) marine‐transitional sands of the La Starza unit, and (3) a dominance of continental volcanoclastics. We envisage that during unrest episodes of the volcano, which included ground deformation and seismic activity, the whole volcano‐sedimentary pile was deformed through brittle mechanisms with the formation of normal faults. However, the intermediate layer, when subject to seismic shaking, behaved locally as a viscous material facilitating liquefaction processes and lateral spreading deformation. Furthermore, new geophysical, stratigraphic, and structural surveys allowed us to model the deformation evolution of this area over the last 15 kyr. The evidence of seismically induced soft‐sediment deformation within the volcano‐sedimentary record suggests that moderate earthquakes could occur during future volcano‐seismic unrests. Consequently, liquefaction and related gravitational mass movements must be considered as a hazard during these unrest and volcanic crises.

Ground deformations are among the main volcanic phenomena occurring within the caldera system and pres- ently 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 This study, which has also benefited of unpublished boreholes stratigraphic data, shows that the most uplifted sector of the Campi Flegrei caldera, presently marked by the morphological structure of the La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 charac- terized 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 al- ternations 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 sig- nificant 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 move- ments. 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.

Campi Flegrei (CF) is an example of an active caldera containing densely populated settlements at very high risk of pyroclastic density currents (PDCs). We present here an innovative method for assessing background spatial PDC hazard in a caldera setting with probabilistic invasion maps conditional on the occurrence of an explosive event. The method encompasses the probabilistic assessment of potential vent opening positions, derived in the companion paper, combined with inferences about the spatial density distribution of PDC invasion areas from a simplified flow model, informed by reconstruction of deposits from eruptions in the last 15 ka. The flow model describes the PDC kinematics and accounts for main effects of topography on flow propagation. Structured expert elicitation is used to incorporate certain sources of epistemic uncertainty, and a Monte Carlo approach is adopted to produce a set of probabilistic hazard maps for the whole CF area. Our findings show that, in case of eruption, almost the entire caldera is exposed to invasion with a mean probability of at least 5%, with peaks greater than 50% in some central areas. Some areas outside the caldera are also exposed to this danger, with mean probabilities of invasion of the order of 5–10%. Our analysis suggests that these probability estimates have location-specific uncertainties which can be substantial. The results prove to be robust with respect to alternative elicitation models and allow the influence on hazard mapping of different sources of uncertainty, and of theoretical and numerical assumptions, to be quantified.

This study focuses on the Solfatara volcano within Campi Flegrei, a volcanic eld located on the Tyrrhenian coast of southern Italy. Volcanism at the Campi Flegrei caldera has included phreatic to phreatomagmatic explosions and both magmatic (ranging from small scoria-producing events to those with Plinian columns) and effusive eruptions. These eruptions have formed tuff cones, tuff rings, minor scoria cones, and lava domes. A detailed stratigraphic, structural, and geo- physical study of the area indicates that the Solfatara volcano is a maar-diatreme structure previously not recognized within the Campi Flegrei caldera. It is characterized by a crater cut into earlier volcanic deposits, a small rim of ejecta, and a deep structure (down to 2–3 km). This maar-diatreme has allowed the gases and uids to ow up to the surface over a long time. A new geological map and cross sections show a complex architecture of different volcano-tectonic features including scoria cones, lavas, crypto- domes, feeder dikes, pipes, ring and regional faults, and explosive craters. Volcanological data were collected with the main aim of characterizing the eruptive activity in a lim- ited sector of the caldera. Fault and fracture analyses, using the scan line methodology, highlight the role of the main structures that accompanied the volcanic evolution within this sector of the Campi Flegrei caldera. To better constrain the subsurface structure of the Solfatara crater, electrical resistivity tomography investigations were integrated with the volcano-tectonic information. All data suggest that the Solfatara area is dominated by a maar-diatreme evolution. Pres- ently, the Solfatara area shows widespread hydrothermal and fumarolic activity that is localized along the major faults. The results allow us to de ne a particular type of vol- canic activity in the recent past, in what is still considered today an area with a higher probability of opening new vents, particu- larly for possible phreatic activity.

Pyroclastic density currents (PDCs) represent one of the most dangerous volcanic hazards for people living in proximity of explosive volcanoes. The zonation of areas potentially affected by this threat is therefore of paramount importance and is the first step needed to set up appropriate mitigation measures. Campi Flegrei (CF) caldera represents a high-risk volcano with a remarkable PDC hazard due to the frequent occurrence of this phenomenon in its eruptive history. Despite the fact that CF caldera has been the object of many studies in recent decades, the mapping of PDC hazard there remains particularly challenging due to the remarkable variability of potential vent locations and eruption scales, and the complex dynamics of PDC propagation over the caldera topography. In this study we have produced, through the application of a doubly stochastic model, quantitative background (also called long-term or baseline) probabilistic maps of PDC invasion able to incorporate some of the main sources of epistemic uncertainty that influence the models for aleatoric (physical) variability. The new method developed combines the spatial probability distribution of vent opening locations, the density distribution of PDC invasion areas, and a simplified PDC model able to describe the main effect of topography on flow propagation. Our results indicate that the entire caldera has the potential to be affected (with a mean probability of flow invasion higher than about 5%) and the central-eastern area of the caldera (i.e. Agnano-Astroni-Solfatara) has invasion probabilities above about 30% (with local peaks of mean probability of about 50% in Agnano). Significant mean probabilities (up to values of about 10%) are also computed in some areas outside the caldera borders. Our findings are quite robust against different assumptions about several of the main physical and numerical parameters adopted in the study. In addition to mean values of probability of PDC invasion, the study provides the estimates of the credible uncertainty ranges associated with such probabilities in relation to some key sources of epistemic uncertainty. From our analysis, uncertainty spreads on invasion probabilities inside the caldera typically range between ±15 and ±35% of the local mean value, with an average of about ±25%; wider uncertainties are found outside the caldera, with an average above ±50% and a significantly larger range of variability from place to place.

Campi Flegrei is an active volcanic area situated in the Campanian Plain (Italy) and dominated by a resurgent caldera. The great majority of past eruptions have been explosive, variable in magnitude, intensity, and in their vent locations. In this hazard assessment study we present a probabilistic analysis using a variety of volcanological data sets to map the background spatial probability of vent opening conditional on the occurrence of an event in the foreseeable future. The analysis focuses on the reconstruction of the location of past eruptive vents in the last 15 ka, including the distribution of faults and surface fractures as being representative of areas of crustal weakness. One of our key objectives was to incorporate some of the main sources of epistemic uncertainty about the volcanic system through a structured expert elicitation, thereby quantifying uncertainties for certain important model parameters and allowing outcomes from different expert weighting models to be evaluated. Results indicate that past vent locations are the most informative factors governing the probabilities of vent opening, followed by the locations of faults and then fractures. Our vent opening probability maps highlight the presence of a sizeable region in the central eastern part of the caldera where the likelihood of new vent opening per kilometer squared is about 6 times higher than the baseline value for the whole caldera. While these probability values have substantial uncertainties associated with them, our findings provide a rational basis for hazard mapping of the next eruption at Campi Flegrei caldera.

Campi Flegrei (CF) is an example of an active, densely populated, caldera with very high risks associated with the occurrence of explosive eruptions. In particular, mapping of pyroclastic density currents (PDCs) hazard is challenging due to the large uncertainty on future vent location and eruption scale as well as the complex dynamics of flows over caldera topography. In this presentation we show how volcanological datasets of different type, mathematical modelling and expert elicitation techniques have been used to produce base-rate probabilistic vent opening and PDC inundation maps. The analysis particularly focused on the reconstruction of the location of past eruptive vents and it allowed the incorporation of additional volcanological datasets, such as the distribution of faults and surface fractures assumed to be representative of areas of crustal weaknesses in the caldera. One key objective was to directly incorporate some of the main sources of epistemic uncertainty relating to an understanding of the volcanic system. We used a formal and structured expert elicitation procedure to quantify uncertainties for the main parameters and evaluate the outcomes through different expert weighting models. A set of probabilistic PDC inundation hazard maps were then produced by the Monte Carlo approach based on a simplified inundation model and incorporating uncertainties on future vent location and event scale.

Campi Flegrei is an example of active and densely populated caldera with a very high volcanic risk associated with the occurrence of Pyroclastic Density Currents (PDCs) produced by explosive events of variable scale and vent location. The mapping of PDC hazard in such caldera setting is particularly challenging due to the complex dynamics of the flow, the large uncertainty of future vent location and the complex topography affecting the flow propagation. Nevertheless, probabilistic mapping of PDC invasion, able to account for the intrinsic uncertainties affecting the system, is needed for hazard assessment. In this study, we show the results of new field work and statistical analysis of past eruptive activity aimed at producing long-term probabilistic maps of vent opening at Campi Flegrei. The field work was focused on the structural and morphological nature of the caldera and particularly on the reconstruction of the location of past eruptive vents as well as of main faults and fissures formed in the last 15 kyrs of activity. One objective of the analysis was to incorporate into the vent opening maps the main uncertainties affecting the system. This was done by adopting appropriate density distributions of the probability of vent opening of the different areas of the caldera and by relying on expert judgement. Then, we used these maps to produce a variety of probabilistic PDC hazard maps of the Campi Flegrei area based on different invasion models and accounting for the uncertainty in vent opening and event size. Invasion models were based on simple correlations derived from field reconstruction of past events, one-dimensional models based on a linear decay of the flow energy (e.g. energy line), and simple energy decay models tuned on transient and 2D numerical simulations of the flow dynamics.

Campi Flegrei is an active volcanic area located in the Campanian Plain, along the Tyrrhenian margin of the southern Apennines (Italy), dominated by the formation of a 12 km large, resurgent caldera. The great majority of the eruptions have been explosive, variable in magnitude and intensity and characterized by the generation of remarkable ash fallout and pyroclastic density currents deposits. In this study we present results of field work and statistical analysis of past eruptive activity aimed at producing long-term probabilistic maps of vent opening at Campi Flegrei. Field work was focused on the structural and morphological nature of the caldera and particularly on the reconstruction of the location of past eruptive vents as well as of main faults and eruptive fissures formed in the last 15 kyr of activity. The statistical analysis performed accounted for the spatial distribution of past vent locations but was flexible enough to incorporate the heterogeneous geological information available, such as the density of faults/fissures or the clue of possible past vents hidden by the more recent activity. One key objective of the analysis was to directly incorporate into the maps the main uncertainties affecting the system. This was done by adopting appropriate density distributions of the probability of vent opening of the different areas of the caldera and by relying on expert judgement. Results allowed to quantify the influence of the different theoretical assumptions and sources of uncertainty on the long-term mapping of vent opening. The distributions obtained represent the starting point for the production of long-term ash fallout and pyroclastic density hazard maps at Campi Flegrei caldera.

Campi Flegrei is an example of active and densely urbanized caldera with a very high risk associated with the occurrence of pyroclastic density currents (PDCs) produced by explosive events of variable scale and vent location. The mapping of PDC hazard in such a caldera setting is particularly challenging not only due to the complex dynamics of the flow but also due to the large uncertainty on future vent location and the complex topography affecting the flow propagation. Nevertheless, probabilistic mapping of PDC invasion, able to account for the intrinsic uncertainties affecting the system, is needed for hazard assessment. In this study we present a variety of probabilistic PDC hazard maps of the Campi Flegrei area based on different invasion models and accounting for the uncertainty in vent opening and event size. Invasion models were based on simple empirical correlations derived by field reconstruction of past events, simplified one-dimensional models based on a linear decay of the flow energy (e.g. energy line), and correlations derived from 2D and transient numerical simulations of the flow dynamics. Field data referred mostly to the third epoch of activity of the volcano (i.e. last 5 kyr) although the analysis was extended to the last 15 kyr. In addition to the uncertainty affecting the vent location the probability invasion maps illustrate some of the uncertainties and features affecting the invasion models adopted. Results show that, consistently with field evidences, the central-eastern part of the caldera (i.e. Agnano-Astroni) is the area most exposed to flow invasion whereas values up to about 5-10% are estimated in some limited areas outside the caldera (e.g. Posillipo Hill). This latter result appears consistent with the outcomes of 3D transient simulations of large-scale PDCs when vent location was assumed in the eastern area of the caldera.