Campi Flegrei Caldera Research Articles

New constraints on the Middle-Late Pleistocene Campi Flegrei explosive activity and Mediterranean tephrostratigraphy (∼160 ka and 110–90 ka)

The Campi Flegrei (CF) caldera, in southern Italy, is the source of some of the most powerful Late Pleistocene eruptions of the European sub-continent (e.g., Campanian Ignimbrite, Neapolitan Yellow Tuff eruptions). Although the CF caldera has been continuously and intensively investigated for decades, relatively little is known regarding its earliest volcanic activity. In this work, integrating existing and new tephrostratigraphic data, we provide a comprehensive and updated framework for the CF volcanic activity which has occurred at ∼160 ka and between ∼110 ka and ∼90 ka. The new tephrostratigraphic, geochemical (EMPA + LA-ICP-MS), chronological (40Ar/39Ar dating) and grain-size distribution data relate to CF tephra deposits preserved in mid-proximal (Campanian Plain), distal (Tyrrhenian Sea) and ultra-distal (Lower Danube area) sedimentary archives. Our results allowed us to recognize the presence of at least 13 CF eruptions covering the investigated time frame, with 12 eruptions occurring between 110 and 90 ka. Our high-resolution stratigraphic and chronological investigation also allowed us to recognize that the Triflisco/C-22 tephra, previously considered as a single marker layer, can be actually separated into three different events, sourced from within the CF area in the short time interval of ∼93-90 ka, suggesting a more complex and intense volcanic history than previously thought. Moreover, a Bayesian age-depth model, constrained by previous and new high precision 40Ar/39Ar ages, has led to a reliable estimate of the ages of those undated CF eruptions. Overall, the updated framework on the stratigraphy, chronology, dispersion, and geochemistry of the CF tephra of ∼160 ka and between 110 ka and 90 ka consolidates the notion that the Middle-Late Pleistocene activity in theCF area represents a significant stage of its volcanic evolution, characterised by intense and frequent explosive eruptions.

Clusterisation and Temporal Trends of Heat Flux by UAS Thermal Camera

Analysis of a series of thermal mappings obtained by UAS flights on quiescent volcanoes requires some special techniques to be performed. The main challenge is represented by the difficulty of separating hot and cold pixels in areas where their temperatures are quite similar. This task is indeed much simpler, for example, for lava flows where the temperature differences between the hot lava and the cold soil is rather big. This paper shows various software developed in order to perform this extraction and calculate the trends over time of both the average temperature and the heat flux from the soil. This prototypal implementation used thermal flights performed over a time span of a few years on an area in the Campi Flegrei caldera in southern Italy. Standard image manipulation techniques were used to segmentate and clusterise each thermal mapping in order to reduce the thermal anomalies to some sets of simpler features characterised by their fundamental parameters. The temporal trends of some physical parameters (temperature, heat flux, etc.) were extracted from these sets, and we found interesting results necessary for correlations and for ongoing research with other parameters.

Simultaneous normal and reverse faulting in reactivating caldera faults: A detailed field structural analysis from Campi Flegrei (southern Italy)

Models of volcanic collapses proposed in the literature rely on combining field examples with analogue and numerical modelling to connect superficial observables to sub-surface volcano-tectonic processes. However, the behaviour of such collapses in an already faulted and fractured medium needs to be better explored.We studied a complex array of normal and reverse faults within the central sector of the active Campi Flegrei caldera, where faults with centimeters-to-meters displacements are hosted in the La Pietra tuff (∼13.5 ka) and the overlying pyroclastic succession of the last ∼5.5 kyr. We analyzed the attitude, kinematics and throw of these structures, employing a UAV-based digital outcrop model. The analysis shows that antithetic normal and reverse faults form in the hanging wall of a pre-existing WNW striking, NNE-dipping master normal fault. Moving northward, the strike of the antithetic faults rotates from WNW to NNW directions, with the latter showing a right-lateral oblique component. The simultaneity and coherence of both kinematics and attitudes are verified by the throw analysis. We associated the formation of this array with the caldera-collapse phase of the Agnano-Monte Spina eruption (∼4.55 ka), which caused off-caldera faulting beyond the main collapsed area.Based on field data, we suggest that during peak caldera-forming phases, wider areas beyond the main caldera scarps can be involved in volcano-tectonic collapses in the presence of a pre-existing fault network and complex tapped reservoirs. This highlights the role of inherited structures in weakening the crust above the magma reservoir that can potentially increase the magnitude and duration of caldera-forming eruptions, as they may induce a broader roof rock subsidence, pressurizing wider regions of the sub-caldera magma system.

Geophysical Responses to an Environmentally‐Boosted Volcanic Unrest

AbstractThe spatiotemporal relationship between geophysical, environmental, and geochemical responses during volcanic unrest is essentially unknown, making their joint use and interpretation for eruption forecasting challenging. Here, Empirical Orthogonal Functions analysis applied to GPS data allows the separation of the dominant deep‐sourced inflation from environmentally controlled signals associated with extension at Campi Flegrei caldera. This separation bridges the gap between deformation, seismic and geochemical responses, clarifying the processes underlying the ongoing volcanic unrest. Persistent meteoric forcing during the 2017–2018 hydrological year changed the decadal trend of seismic energy and secondary deformation components, pairing their spatial patterns. The result was a block in the carbon dioxide released in 2018 at Solfatara, the primary stress‐release valve at the caldera. The subsequent overpressure weakened the fractured eastern caldera, opening pathways for deep, hot materials to reach the surface. Our results give insight into how environmental forcing can favor volcanic unrest in pressurized calderas.

Feedback responses between endogenous and exogenous processes at Campi Flegrei caldera dynamics, Italy

Feedback responses between endogenous and exogenous processes at Campi Flegrei caldera dynamics, Italy

Evolution in unrest processes at Campi Flegrei caldera as inferred from local seismicity

Changes in seismicity with time and location are diagnostic signals for understanding the dynamics of volcanic unrest. We used these signals at the Campi Flegrei caldera, in southern Italy, to investigate how structural changes have determined three styles of unrest since 1982, distinguished by a ground uplift (measured at Pozzuoli, near the centre of the caldera) of 178 cm in 1982–84; a subsidence of 93 cm in 1985–2005; and an uplift of 118 cm between 2005 and November 2023. Double-difference seismic locations and concentrations of seismic energy release have revealed impermeable horizons that correspond to the cap rock and self-sealed base of the geothermal system at depths of 1.5 and 3 km, respectively. Most earthquakes have been shallower than 3 km, consistent with the brittle upper crust being stretched over a zone of pressurization below the geothermal system. The 1982–84 uplift decayed after a major seismic swarm on April 1st, 1984, breached the lower impermeable horizon, which increased the flux of escaping gas and reduced the source pressure. Continued gas escape promoted subsidence until the lower horizon had resealed itself and initiated a new episode of uplift while gas from depth re-accumulated beneath. Compared with 1982–84, a greater proportion of recent seismicity has occurred at shallower depths below the actively degassing fumaroles of Solfatara-Pisciarelli, north-east of Pozzuoli. The associated high seismic b‐values, between 1 and 2, are consistent with high fluid pressures and, hence, with locations more favourable to fracturing. Continued uplift may thus persist until fracturing of the shallow crust allows faster rates of gas release and depressurization of the pressure source.

Historical vertical ground movements in the Campi Flegrei volcano: A new transect across the caldera rim

This research focuses on a geoarchaeological study of the coastal sector extending from Fusaro coastal lake to Punta Pennata Islet, located in the western peripheral area of Campi Flegrei Caldera (Gulf of Pozzuoli, Italy), to reconstruct relative sea-level (RSL) oscillations and related vertical ground movements which have occurred since the Roman period. Campi Flegrei Caldera is characterized by sudden vertical ground movements of volcano-tectonic origin (i.e. bradyseismic crisis) which strongly modified the coastal landscape during the Holocene. Despite this, the area has been densely inhabited since the Greek-Roman times, preserving numerous traces of its ancient splendor. Part of these findings can be interpreted as high- or low- precision sea-level markers, helping in the reconstruction of the RSL change history. By using a multi-technique approach made of both direct and indirect surveys, the latter performed at the key-site of Punta Pennata through the use of an unmanned surface vessel prototype (ARGO), we investigated different archaeological sites with a twofold purpose. We reconstructed the RSL change of the study area during the last 2.1 ka and, by comparing the RSL data with site-specific geophysical models, we demonstrated that during the considered period the area went through five different evolutive phases characterized by an alternation of prevailing uplift, stability, and subsidence of volcano-tectonic origin, bringing the RSL from −4 and +5 m MSL, up to its current elevation. Moreover, by comparing the RSL data with the present-day sea level, we observed a differential overall subsidence of almost 1-m between the inner and outer sectors of the caldera at Miseno Cape. This validated the presence of a fault, crossing the promontory in an NNW-SSE direction, previously mentioned by other authors. Moreover, the integration of our data and historic sources enabled reconstructing the palaeo-environmental scenario of this area during the 1st century BC.

The effects of hot and pressurized fluid flow across a brittle layer on the recent seismicity and deformation in the Campi Flegrei caldera (Italy)

The influence of the hydrothermal circulation on seismicity and uplift observed at the Campi Flegrei caldera (Italy) is a topic of great interest to the scientific community. Recently, Thermo-Poro-Elastic (TPE) inclusions were proposed as likely deformation sources. They are suitable to explain the mechanical effects induced by hot and pressurized hydrothermal fluids, possibly exsolved from underlying magma, and pervading an overlying brittle layer. Recent works show that a TPE inclusion located at approximately 2 km depth below the Campi Flegrei caldera significantly contributed to the large and rapid soil uplift observed during the ‘82-’84 unrest phase. In the present work we demonstrate that such a source of deformation is likely playing a role even in the current unrest phase, which is characterized by a much lower uplift-rate with respect to the one occurred in the previous unrest phase. We will show that the time-series of soil uplift observed in the last 18 years can be reproduced by assuming the reactivation of the same deformation source responsible of the ‘82-’84 unrest located within a shallow brittle layer at about 2 km depth. The presence of a brittle layer has been evidenced in the past by tomographic studies and is confirmed by a sharp variation of the b-value at the corresponding depth. We believe that our results provide very important insights and evidences, supporting the existence and the importance of an active thermo-poro-elastic deformation source, which can be useful for understanding the unrest of the Campi Flegrei caldera, from both a scientific and geohazard perspective.

Estimation of the Uncertainties Introduced in Thermal Map Mosaic: A Case of Study with PIX4D Mapper Software

The aim of this study is to analyse problems related to thermal mapping obtained from thermal data acquired from unmanned aerial systems (UAS) equipped with thermal cameras. We focused on an accurate analysis of uncertainties introduced by the PIX4D Mapper software version 4.4.12 used to obtain the surface temperature maps of thermal images acquired using the UAS. To achieve this aim, we used artificial thermal references during the surveys, as well as natural hot targets, i.e., thermal anomalies in the Pisciarelli hydrothermal system in Campi Flegrei caldera (CFc). Artificial thermal targets, expressly created and designed for this goal, are a prototype here called “developed thermal target” (DTT) created by the drone laboratory at Istituto Nazionale di Geofisica e Vulcanologia—Osservatorio Vesuviano (INGV-OV). We show the results obtained through three surveys, and during the last two, thermal targets were positioned on land at different flight heights of the UAS. Different heights were also necessary to test the spatial resolution of the DTT with the used thermal camera as well as possible temperature differences between the raw images acquired via UAS with the thermal mapping obtained from the PIX4D Mapper software. In this work, we estimate the uncertainty that may be introduced by the mosaic procedure, and furthermore we find an attenuation of the measured temperatures introduced by the different distances between the thermal anomaly and sensor. These results appear to be of great importance for the subsequent calibration phase of the thermal maps, especially in cases where these methodologies are applied for the purposes of monitoring volcanic/geothermal areas.

50,000 yr of recurrent volcaniclastic megabed deposition in the Marsili Basin, Tyrrhenian Sea

Abstract Megabeds are exceptionally large submarine deposits interpreted to originate from single catastrophic events. Megabeds are significant components of deep-water basins and are critical for understanding geohazards. We discovered a succession of four megabeds within the upper 70 m of the western Marsili Basin, Tyrrhenian Sea, deposited within the past 50 k.y. The megabeds were imaged as distinctive acoustically transparent units with ponded geometries, 10–25 m thick, separated by parallel-bedded strata. Cores from Site 650 of Ocean Drilling Program Leg 107 revealed that three of the four megabeds are made of alternating volcaniclastic sand and mud, and one is a volcaniclastic debris flow. Abundant shallow-water benthic foraminifera within the megabeds suggest that they were not sourced locally from the active Marsili Seamount, but most likely originated from the Campanian volcanic province to the north. The time interval during which the megabeds were deposited includes the 39.8 ka Campanian ignimbrite supereruption of the Campi Flegrei caldera, Italy, which is among the largest known eruptions on Earth, and the 14.9 ka Neapolitan Yellow Tuff supereruption. Volume (minimum) estimates range from 1.3 to 13.3 km3. However, similar megabeds observed in the neighboring Vavilov Basin to the west suggest that the megabeds in both basins may be correlative, and thus volumes could be much larger. The newly discovered megabeds of the Marsili Basin reveal significant geohazard events for the circum–Tyrrhenian Sea coastlines with a recurrence interval on the order of ~10–15 k.y.

Coping Capacity, Adaptive Capacity, and Transformative Capacity Preliminary Characterization in a “Multi-Hazard” Resilience Perspective: The Soccavo District Case Study (City of Naples, Italy)

An innovative methodology for characterizing Coping Capacity (CC), Adaptive Capacity (AC), and Transformative Capacity (TC) resilience determinants in a multi-hazard territorial context is applied to the Soccavo district (Naples, Italy), located in the Campi Flegrei caldera and exposed to volcanic eruptions, ground deformations (bradyseism), earthquakes, geomorphological processes (landslides, rock falls, erosion), and climate change-related hazards (heat waves, pluvial floods). The method allowed for the identification of the CC, AC, and TC parameters that can be easily converted into qualitative–quantitative variables. Among all parameters, the method focused on multi-stakeholder and civil society engagement, which is representative of TC and variable relating to the risk perception and awareness, the urban space perception, or the people’s ability to activate bottom-up urban transformation processes within resilient development pathways. Therefore, qualitative tools such as collaborative mapping and co-design processes, pertaining to the urban planning and design fields, and quantitative tools such as surveys, from the social science field, were harmonized and combined to collect and analyze data on these site-specific topics. Considering people’s priorities and needs, the study was useful to define shared sustainable and resilient solutions in order to holistically integrate Disaster Risk Reduction/Climate Change Adaptation urban planning and design approaches and simultaneously deliver social, environmental, and economic co-benefits.

Potential for rupture before eruption at Campi Flegrei caldera, Southern Italy

Volcanoes reawakening after long repose must rupture the crust before magma can erupt. Rupture is preceded by repeatable variations in the rate of seismicity with ground movement, which trace the amount of applied stress that is released by local earthquakes. A rupturing sequence has been developing across four episodes of ground uplift at Italy’s Campi Flegrei caldera: in 1950-1952, 1969-1972, 1982-1984 and since 2004. We predicted in 2016 that the approach to rupture would continue after an additional uplift of 30-40 cm at the location of largest movement. We have updated our analysis with new data on changes in the numbers of local earthquakes with amounts of ground movement. Here we show that subsequent events have confirmed our prediction and that the unrest has been changing the structure of Campi Flegrei’s crust. The results provide new constraints for evaluating the volcano’s potential to erupt or to subside without eruption.

Magma Transfer at Campi Flegrei Caldera (Italy) After the 1538 AD Eruption

AbstractShallow magma transfer is difficult to detect at poorly monitored volcanoes. Magma transfer before the last 1538 eruption at Campi Flegrei caldera (Italy) was exceptionally tracked using historical, archeological, and geological data. Here, we extend that data set to 1650 to uncover any magma transfer during post‐eruptive subsidence. Results show two post‐eruptive subsidence phases, separated by a previously undocumented uplift during 1540–1582. Uplift highlights the pressurization of the central (∼3.5 km depth) and peripheral (∼1 km depth) pre‐eruptive sources, suggesting an aborted eruption. The subsidence events mainly require the depressurization of the central source and pressurization of a deeper magmatic layer (∼8 km depth). Therefore, despite the overall post‐eruptive deflation, after 1538 the deeper reservoir experienced continuous magma supply, with magma almost erupting between 1540 and 1582, challenging the common assumption of post‐eruptive deflation. This underlies the importance of monitoring the deeper magmatic systems, also after eruptions, to properly assess their eruptive potential.

On the seafloor horizontal displacement from cGPS and compass data in the Campi Flegrei caldera

Seafloor deformation monitoring is now routinely performed in the marine sector of the Campi Flegrei volcanic area (Southern Italy). The MEDUSA infrastructure is formed by four buoys deployed at a water depth ranging from 40 to 96 m, and equipped with cGPS receivers, accelerometers and magnetic compasses to monitor the buoy status and a seafloor module with a bottom pressure recorder and other onboard instruments. The analysis of the time series data acquired by the MEDUSA monitoring infrastructure system allows to study the seafloor deformation in the Campi Flegrei caldera with geodetic accuracy. In a previous work, we show that the time series acquired by the Campi Flegrei cGPS onland network and MEDUSA over the period 2017–2020 are in good agreement with the ground deformation field predicted by a Mogi model which is widely used to describe the observed deformation of an active volcano in terms of magma intrusion. Only for one of the buoys, CFBA (A), the data differ significantly from the model prediction, at a level of simeq  6.9 sigma and of simeq  23.7 sigma for the seafloor horizontal speed and direction, respectively. For this reason, we devised a new method to reconstruct the horizontal sea bottom displacement considering in the analysis both cGPS and compass data. The method, applied to the CFBA buoy measurements and validated also on the CFBC (C) buoy, uses compass data to correct cGPS positions accounting for the pole inclination. Including also systematic errors, the internal consistency, always within sim  3 sigma for the speed and sim  2 sigma for the angle, between the results derived for different maximum inclinations of the buoy pole (up to 3.5^{circ }) indicates that the method allows to significantly reduce the impact of the pole inclination which, if not properly taken into account, can alter the estimation of the horizontal seafloor deformation. In particular, we find a good convergence of the retrieved velocity and deformation angle as we include in the analysis data from increasing values of the buoy pole inclination. Taking the result derived assuming the maximum allowed cutoff and accounting for statistical and systematic errors, we found a speed v = (3.521 ± 0.039 (stat) ± 0.352 (syst)) cm/yr and a deformation direction angle alpha = (-115.159 ± 0.670 (stat) ± 7.630 (syst))^{circ } (statistical errors at 1 sigma quoted from the rms of their values, main systematic errors added linearly). The relative impact of the main potential systematic (statistical) effects increases (decreases) with the cutoff. Our analysis provides a horizontal speed consistent with the model at a level of simeq  5.2 sigma (stat only) or of simeq  0.5 sigma (stat and syst added linearly), and a deformation angle consistent with the model at simeq  4.3 sigma level (stat only) or at simeq  0.3 sigma level (stat and syst added linearly). Correspondingly, the module of the vectorial difference between the velocity retrieved from the data and the velocity of the adopted Mogi model diminishes by a factor of simeq 7.65 ± 1.23 (stat) or ± 5.78 (stat + syst) with respect to the previous work. A list of potential improvements to be implemented in the system and instruments is also discussed.

Impact assessment caused by bradyseism phenomena in the Campi Flegrei area

Campi Flegrei (Italy) is among the areas with the greatest volcanic explosive risk in the world due to the dangerousness of the expected hazards, the high exposed value (about 500,000 people will be evacuated during the “alarm phase”), and the vulnerability of the urban settlements under the effect of the volcanic phenomena. The last two dramatic bradyseism phases occurred in 1969–1972 and 1982–1984 when Pozzuoli town was affected by rapid ground inflation, which brought an overall higher level of about 3.5 m and caused numerous earthquakes (M ≤ 4.2), with severe damage to buildings. During 1984, the seismicity was intense, with 33 events with 0.5 < M ≤ 3 and six with 3 < M ≤ 3.8. Subsequently, the Campi Flegrei caldera was characterized by general subsidence for about 20 years until 2005, when a new inflation period started and is still ongoing (∼1 m). The areal distribution of the recent uplift is characterized by the maximum vertical displacement in the town of Pozzuoli, with a radial decrease from the caldera center outwards. The need to better understand Campi Flegrei volcanic activity is fundamental to protecting the population from hazards linked to explosive volcanic eruptions and understanding the role of seismicity as a possible precursor of a potential eruption. In this perspective, as part of the activities of the PLINIVS Study Centre (Centre of Competence of Italian Civil Protection Department for Volcanic Risk), the authors developed a procedure, implemented in a web application, that relates the monitoring of the ground deformation with the behavior of buildings to evaluate the level of progressive damage to the ordinary Phlegraean buildings due to bradyseism in near real time. This study describes the models adopted for the three impact/risk factors (hazard, exposure, and vulnerability) used to estimate building damage.

Efficient SOM’s Application to Seismic Fumarolic Tremor for the Detection of Anomalous Hydrothermal Activity in Campi Flegrei Volcano (Italy)

In recent decades, the Campi Flegrei caldera (Italy) showed unrest characterized by increases in seismicity, ground uplift, and hydrothermal activity. Currently, the seismic and hydrothermal phenomena are mostly concentrated in the Solfatara–Pisciarelli area, which presents a wide fumarolic field and mud emissions. The main fumarole in Pisciarelli is associated with a boiling mud pool. Recently, episodes of a sudden increase in hydrothermal activity and expansion of mud and gas emissions occurred in this area. During these episodes, which occurred in December 2018 and September 2020, Short Duration Events (SDEs), related to the intensity of mud pool boiling, were recorded in the fumarolic seismic tremor. We applied a Self-Organizing Map (SOM) neural network to recognize the occurrence of SDEs in the fumarolic tremor of Campi Flegrei, which provides important information on the state of activity of the hydrothermal system and about the possible phreatic activity. Our method, based on an ad hoc feature extraction procedure, effectively clustered the seismic signals containing SDEs and separated them from those representing the normal fumarolic tremor. This result is useful for improving the monitoring of the Solfatara–Pisciarelli hydrothermal area which is a high-risk zone in Campi Flegrei.

A geodatabase of historical landslide events occurring in the highly urbanized volcanic area of Campi Flegrei, Italy

Abstract. The analysis of geological processes threatening people and properties in a populated region should be based on a comprehensive knowledge of historical events and related characteristics. This type of information is essential for predisposing event scenarios, validating prediction models, and planning risk mitigation measures. Such activities may be more complex in some geological settings, where urban settlements are exposed to multi-hazard conditions. This is the case of the densely populated Campi Flegrei volcanic area located in the Campania region, southern Italy. Here, volcanic and seismic hazards are associated with landslides, floods, and coastal erosion, which are playing a relevant role in the landscape modification. The CAmpi Flegrei LAndslide Geodatabase (CAFLAG), here presented, provides information related to 2302 landslides that occurred in the continental, coastal, and insular sectors of the study area during the 1828–2017 time interval. Data associated with the collected landslide events highlight the characteristics of both landslides and of the affected sites. Most of the cataloged mass movements consist of rock falls affecting rocky slopes formed by lithified volcanic rocks, such as tuff or ignimbrite. In addition, rainfall-induced earth and debris slides translating into debris avalanches or rapid flows are widespread along steep slopes mantled by weakly welded pyroclastic airfall deposits, similarly to other areas of the region. The highest density of landslides is concentrated along the coastline, where mass movements are contributing to the retreat of coastal cliffs, and along inland slopes exposed towards the western directions, where most of the storm systems come from. Temporal information shows peaks of landslides in the years 1986, 1997, and 2005. A total of 127 people lost their lives as a consequence of 53 cataloged landslides, with a frequency of deadly events observed however to have decreased since the early 1980s. This information will be useful to analyze mortality and risk conditions still affecting the population of the Campi Flegrei caldera, which should be fully addressed with advanced knowledge and accurate scenarios. The full database is freely available online at https://doi.org/10.4121/14440757.v2 (Esposito and Matano, 2021).

Combined volcano-tectonic processes for the drowning of the Roman western coastal settlements at Campi Flegrei (southern Italy)

The active Campi Flegrei caldera in southern Italy has a remarkably long history of coexistence between volcanism and human settlements, and it is famous for its peculiar slow ground movement called bradyseism, i.e. episodes of inflation and deflation of the caldera floor due to magmatic and/or hydrothermal processes. This natural phenomenon has interacted with the civilization that inhabited this strategic and fertile area, especially in Roman times, when the sinking of the coast hindered the flourishment of Puteoli and Baiae coastal towns. The drowning of a large part of Republic-early Imperial Roman coastal buildings, west of the modern Pozzuoli town, is classically used to illustrate the bradyseism activity. In this paper, we investigate the spatial variability and the role of this phenomenon, demonstrating that the caldera deflation alone cannot account for the submersion of Roman facilities in the western sector where the harbour structures of Portus Iulius and luxury villas of the Baianus Lacus presently lie beneath sea level. On the contrary, the sinking of this area is mainly the result of the activity of volcano-tectonic faults. We restored the topography to 100 BCE using archaeological and high-resolution topographic data. Results show that the several metres of vertical displacement recorded in the Baia area in the last 2100 yr were mainly produced by the activity of normal faults and secondarily by caldera deflation, the former including the long-lived Baia Fault and the younger normal faults associated with the Monte Nuovo eruption at 1538 CE.Graphical

Wavelet-like denoising of GNSS data through machine learning. Application to the time series of the Campi Flegrei volcanic area (Southern Italy)

The great potential of the Global Navigation Satellite System (GNSS) in monitoring ground deformation is widely recognized. As with other geophysical data, GNSS time series can be significantly noisy, hiding elusive ground deformation signals. Several denoising techniques have been proposed to improve the signal-to-noise ratio over the years. One of the most effective denoising techniques has been proved to be multi-resolution decomposition through the discrete wavelet transform. However, wavelet analysis requires long data sets to be effective, as well as long computation times, that hinder its use as a real or near real-time monitoring tool. We propose training by a Convolutional Neural Network (CNN) to perform the equivalent of wavelet analysis to overcome these limitations. Once trained, the CNN model provides answers within seconds, making it feasible as a real-time data analysis tool. Our Machine Learning algorithm is tested on daily GNSS time series collected in the Campi Flegrei caldera (Southern Italy), which is a highly volcanic risk area. Without significant gaps, the retrieved RMSE and R2 values vary in the ranges 0.65–0.98 and 0.06–0.52 cm, respectively. These results are encouraging, as they hint at the possibility of applying this methodology in more effective real-time monitoring solutions for active volcanoes.

Discriminating carbon dioxide sources during volcanic unrest: The case of Campi Flegrei caldera (Italy)

AbstractLarge calderas are among the main emitters of volcanic CO2, which is mainly supplied by the deep degassing of magmatic fluids. However, other sources of non-magmatic CO2 can also occur due to the intense interaction among magmatic fluids, wide hydrothermal systems, and their host rocks. In particular, massive amounts of CO2 are released by calderas during unrest phases and have been often detected before eruptions. An accurate assessment of CO2 sources is thus fundamental to properly understand gas monitoring signals during volcanic crises. We focused on the restless Campi Flegrei caldera, in southern Italy, where CO2 fluxes at the Solfatara-Pisciarelli hydrothermal site have been progressively increasing up to 4000–5000 t/d during the ongoing unrest that started in 2005. Theoretical models of magma degassing have been able to reproduce the CO2-N2-He variations at the Solfatara fumaroles. However, a time-dependent deviation between measured and modeled N2/CO2 and He/CO2, well correlated with the temporal evolution of ground uplift and temperature of the hydrothermal system, has been observed since 2005. We show that these variations are controlled by intense physical-chemical perturbation of the hydrothermal system, which is driving the decarbonation of hydrothermal calcite stored in reservoir rocks. This process is providing large volumes of non-magmatic CO2 during the current unrest, contributing up to 20%–40% of the total fumarolic CO2.