Two probability models to study the history of the Campi Flegrei eruptive activity and provide statistical estimates on its possible future behaviour. To present them, a study signed by INGV, University and Scuola Normale Superiore of Pisa, University of Naples Federico II. The work was published in the Journal of Geophysical Research - Solid Earth, and included in the Research Spotlights of the American Geophysical Union's journal EOS.
Understanding the frequency of the eruptive activity of the Campi Flegrei caldera, through a quantitative analysis of its history. This is the aim of the study, born from the collaboration between researchers of the National Institute of Geophysics and Volcanology (INGV) - Sections of Pisa and Naples-Osservatorio Vesuviano, University of Pisa, Scuola Normale Superiore of Pisa and University of Naples Federico II, published in the Journal of Geophysical Research - Solid Earth, and included in the Research Spotlights of the American Geophysical Union's journal EOS (https://eos.org/research-spotlights/when-might-the-campi-flegrei-caldera-erupt-again). At the center of the research, two probability models to statistically study the past of this volcanic system and therefore be able to provide probabilistic estimates on its possible future behavior.
“The Campi Flegrei”, explains Augusto Neri, director of the INGV Volcano Structure, “are an active volcanic caldera which includes part of the city of Naples. The volcano consists of a large topographic depression with a diameter of about 12 km with a large portion of the southern half extending into the Gulf of Pozzuoli. The emerged part contains numerous volcanic craters, tuff and scoria cones and lava domes. Over the past 15.000 years, the entire caldera has been affected by intense and mostly explosive volcanism, with more than 70 known eruptions. These eruptions have concentrated over time within three eruptive epochs lasting a few centuries or millennia, alternating with periods of quiescence that lasted millennia. Often the eruptive events close in time have formed groups or clusters of events that are also geographically close, mainly along the edges of the caldera and in its central-eastern area. The most recent eruption is that of Monte Nuovo, which took place in 1538 AD after more than 3.000 years of quiescence. It could represent the beginning of a new sequence of eruptions, even if almost 500 years have passed since that event without activity”.
The first probability model describes the temporal evolution of the volcano's eruptive rate, also considering the uncertainty that influences the knowledge of the eruptive sequence over the last 15.000 years. This model shows that spatio-temporal clusters of eruptions occurred in all three epochs, with higher activity (more frequent eruptions and larger magma volumes) in the east sector of the caldera than in the west sector, and that the two epochs longer ones (ie the first and the third) showed a lower eruptive rate in their initial part. The second probability model, on the other hand, aims to reproduce the sequence of eruptive events that took place in the caldera to study its spatio-temporal distribution and make predictions about its possible future activity.
"The sequence of eruptions is modeled with a stochastic process which includes the possibility of having close events in space and time as well as processing data characterized by uncertainty", adds Andrea Bevilacqua, a young researcher who developed the probability models in the field of own thesis at the Scuola Normale Superiore of Pisa with a scholarship financed by INGV.
The combination of the two models made it possible to highlight similarities and differences between the three eruptive epochs and to estimate the basic eruptive rate of the caldera, i.e. the temporal frequency with which new clusters of eruptions form instead of individual eruptive events, as well as the duration and prolificacy of such eruption clusters.
“Assuming that the Monte Nuovo eruption marked the beginning of a new caldera eruptive epoch, the models provide an average estimate of just over a century of the waiting time before the next event calculated from today, but with a large variability of the estimate. In particular, the waiting time can vary from several years up to a few hundred if we consider the effect of the various uncertainties involved. Conversely, these estimates grow significantly, even reaching waiting times of more than a millennium, if one assumes that the Monte Nuovo event does not represent the beginning of a new eruptive epoch or in any case has not reactivated the eastern sector of the caldera" explains Neri .
The results of the study make it possible to obtain the first quantitative estimates on the frequency of eruptive activity, as well as on the probability of a future event, of the Campi Flegrei caldera, also considering the effect of some uncertainties involved.
“The estimates made are of a statistical nature and based exclusively on knowledge of the volcano's eruptive history, on the assumption that its behavior in the last 15.000 years is representative of its future. The results obtained clearly highlight the intense eruptive activity of this volcano and therefore its high danger. These estimates are complementary to the short-term forecasts of future activity which are instead possible through the continuous monitoring of the volcano and the study of the processes that govern the ascent of magma underground”, concludes Augusto Neri.
Abstract
After the large-scale event of Neapolitan Yellow Tuff (~15 ka BP), intense and mostly explosive volcanism has occurred within and along the boundaries of the Campi Flegrei caldera (Italy). Eruptions occurred closely spaced in time, over periods from a few centuries to a few millennia, and were alternated with periods of quiescence lasting up to several millennia. Often events also occurred closely in space, thus generating a cluster of events. This study had two main objectives: (1) to describe the uncertainty in the geological record by using a quantitative model and (2) to develop, based on the uncertainty assessment, a long-term subdomain specific temporal probability model that describes the temporal and spatial eruptive behavior of the caldera. In particular, the study adopts a space-time doubly stochastic nonhomogeneous Poisson-type model with a local self-excitation feature able to generate clustering of events which are consistent with the reconstructed record of Campi Flegrei. Results allow the evaluation of similarities and differences between the three epochs of activity as well as to derive eruptive base rate of the caldera and its capacity to generate clusters of events. The temporal probability model is also used to investigate the effect of the most recent eruption of Monte Nuovo (AD 1538) in a possible reactivation of the caldera and to estimate the time to the next eruption under different volcanological and modeling assumptions.
Panorama of the Campi Flegrei caldera seen from the Camaldoli hill (photo by Roberto Isaia, INGV-OV)