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Caliro, Stefano
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Caliro, Stefano
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stefano.caliro@ingv.it
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122 results
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- PublicationOpen AccessUnveiling spatial variations in atmospheric CO sources: a case study of metropolitan area of Naples, Italy.(2024-09-03T00:00:00Z)
; ; ; ; ; ; ; ; ; In the lower atmosphere, CO emissions impact human health and ecosystems, making data at this level essential for addressing carbon-cycle and public-health questions. The atmospheric concentration of CO is crucial in urban areas due to its connection with air quality, pollution, and climate change, becoming a pivotal parameter for environmental management and public safety. In volcanic zones, geogenic CO profoundly affects the environment, although hydrocarbon combustion is the primary driver of increased atmospheric CO and global warming. Distinguishing geogenic from anthropogenic emissions is challenging, especially through air CO concentration measurements alone. This study presents survey results on the stable isotope composition of carbon and oxygen in CO and airborne CO concentration in Naples' urban area, including the Campi Flegrei caldera, a widespread hydrothermal/volcanic zone in the metropolitan area. Over the past 50 years, two major volcanic unrests (1969-72 and 1982-84) were monitored using seismic, deformation, and geochemical data. Since 2005, this area has experienced ongoing unrest, involving the pressurization of the underlying hydrothermal system as a causal factor of the current uplift in the Pozzuoli area and the increased CO emissions in the atmosphere. To better understand CO emission dynamics and to quantify its volcanic origin a mobile laboratory was used. Results show that CO levels in Naples' urban area exceed background atmospheric levels, indicating an anthropogenic origin from fossil fuel combustion. Conversely, in Pozzuoli's urban area, the stable isotope composition reveals a volcanic origin of the airborne CO. This study emphasizes the importance of monitoring stable isotopes of atmospheric CO, especially in volcanic areas, contributing valuable insights for environmental and public health management.18 6 - PublicationOpen AccessHydrothermal calcite formation in Campi Flegrei caldera, Italy: unraveling carbon sink processes in alkaline volcanic systems(2024-07-22)
; ; ; ; ; ; ; Understanding carbon dioxide emissions variability in volcanic regions is vital for detecting instabilities in the subvolcanic plumbing system, crucial for managing both volcanic and environmental risks. While changes in magmatic sources drive these variations, non-magmatic processes can complicate signal interpretation, especially in caldera environments. Here, geothermal systems can sequester CO2 within the bedrock through hydrothermal calcite precipitation, significantly impacting surface-level CO2 emissions. Unfortunately, few studies have explored this phenomenon, examining hydrothermal calcite origins and their effects on carbon balances and temporal gaseous patterns in active volcanic settings. Our study developed a specialized methodology for quantifying CO2 sequestered in hydrothermal calcites within alkaline caldera systems. We focused on analyzing hydrothermal calcite in lithics from volcanic deposits of eruptions of varying ages, Volcanic Explosivity Index (VEI), and eruptive vent locations to enhance the representativeness of the entire caldera bedrock. Unlike core samples from geothermal wells, which are infrequent and limited to specific depths, lithics can be easily collected, offering a comprehensive understanding of CO2 sequestration. Through extensive 3D textural characterization and isotopic investigations on hydrothermal calcite within lithic fragments from selected alkaline volcanic deposits in the Campi Flegrei caldera, our findings emphasized the significant influence of calcite sinks on the overall CO2 budget released by volcanoes throughout their evolution.74 17 - PublicationOpen AccessSoil CO2 emission and stable isotopes (δ13C, δ18O) of CO2 and calcites reveal the fluid origin and thermal energy in the supercritical geothermal system of Krafla, Iceland(2024)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The Krafla geothermal system is located within a volcanic center that periodically erupts basaltic lavas, and has recently attracted an economic interest due to supercritical fluids forming near a shallow magma intrusion (~ 2 km depth). Here, we discuss new soil CO2 flux and stable isotope data of the CO2 efflux (δ13C) and hydrothermal calcites (δ13C, δ18O) of drill cuttings to estimate both the current magmatic outgassing from soils and the thermal flows in the geothermal system. Soil CO2 emission is controlled by tectonics, following the NNE-SSW fissure swarm direction and a WSW-ENE trend, and accounts for ~62.5 t/d. While the δ18O of the H2O in equilibrium with deep calcites is predominantly meteoric, both the δ13C of the soil CO2 efflux and of the fluids from which calcite precipitated have a clear magmatic origin, overlapping the δ13C estimated for the Icelandic mantle (–2.5 ± 1.1 ‰). Estimates based on the soil CO2 emission from the southern part of the system show that these fluxes might be sustained by the ascent and depressurization of supercritical fluids with a thermal energy of ~800 MW. Such significant amount of energy might reach 1.5 GW if supercritical conditions extended below the whole investigated area. Finally, we report an increase in the soil CO2 emission of about 3 times with respect to 14 years ago, likely due to recent changes in the fluid extracted for power production or magmatic activity. Pairing the soil CO2 emission with stable isotopes of the efflux and calcite samples has important implications for both volcano monitoring and geothermal exploration, as it can help us to track magmatic fluid upflows and the associated thermal energy.140 25 - PublicationOpen AccessPrincipal component analysis on twenty years (2000-2020) of geochemical and geophysical observations at Campi Flegrei active caldera(2023-10-27)
; ; ; ; ; ; ; ; ; ; ; Campi Flegrei (CF) is an active and densely populated caldera in Southern Italy, which has manifested signs of significant unrest in the last 50 years. Due to the high volcanic risk, monitoring networks of the most sensitive unrest indicators have been implemented and improved over time. Precious database constituted by geophysical and geochemical data allowed the study of the caldera unrest phases. In this paper we retrace the caldera history in the time span 2000-2020 by analyzing displacement, seismicity and geochemical time series in a unified framework. To this end, Principal Component Analysis (PCA) was firstly applied only on geochemical data because of their compositional nature. The retrieved first three components were successively analyzed via PCA together with the geophysical and thermodynamical variables. Our results suggest that three independent processes relay on geochemical observations: a heating/pressurizing of the hydrothermal system, a process related to magmatic fluids injection at the hydrothermal system roots, and third process probably connected with a deeper magmatic dynamic. The actual volcano alert state seems mainly linked to the variation of the hydrothermal system activity. Our approach made it possible to explore the interrelation among observations of different nature highlighting the importance of the relative driving processes over time.52 9 - PublicationOpen AccessExploring microstructure and petrophysical properties of microporous volcanic rocks through 3D multiscale and super-resolution imaging(2023-04-24)
; ; ; ; ; ; ; ; ; ; ;Digital rock physics offers powerful perspectives to investigate Earth materials in 3D and non-destructively. However, it has been poorly applied to microporous volcanic rocks due to their challenging microstructures, although they are studied for numerous volcanological, geothermal and engineering applications. Their rapid origin, in fact, leads to complex textures, where pores are dispersed in fine, heterogeneous and lithified matrices. We propose a framework to optimize their investigation and face innovative 3D/4D imaging challenges. A 3D multiscale study of a tuff was performed through X-ray microtomography and image-based simulations, finding that accurate characterizations of microstructure and petrophysical properties require high-resolution scans (≤ 4 μm/px). However, high-resolution imaging of large samples may need long times and hard X-rays, covering small rock volumes. To deal with these limitations, we implemented 2D/3D convolutional neural network and generative adversarial network-based super-resolution approaches. They can improve the quality of low-resolution scans, learning mapping functions from low-resolution to high-resolution images. This is one of the first efforts to apply deep learning-based super-resolution to unconventional non-sedimentary digital rocks and real scans. Our findings suggest that these approaches, and mainly 2D U-Net and pix2pix networks trained on paired data, can strongly facilitate high-resolution imaging of large microporous (volcanic) rocks.536 28 - PublicationOpen AccessQuantification of CO2 degassing and atmospheric dispersion at Caldeiras da Ribeira Grande (São Miguel Island, Azores)(2023-04)
; ; ; ; ; ; ; ; ; ;; ;; ; ; Caldeiras da Ribeira Grande is one of the degassing areas of Fogo, a trachytic central volcano located at Sa ̃o Miguel Island (Azores archipelago). Recently, new steam emissions, soil CO2 and temperature anomalies developed towards the inhabited area, causing high indoor CO2 values and affecting the vegetation and several small animals that were found dead in depressions and low-ventilated zones. During July–August 2021, a soil CO2 flux survey was carried out on the north flank of the volcano, estimating a soil gas release of at least 40 t d− 1 (excluding the contribution of the fumaroles) over an area of ~0.27 km2. Two populations for the CO2 released were found, highlighting the biogenic and volcanic-hydrothermal origins. General NW-SE diffuse degassing structures (DDS) were identified, in agreement with the tectonic lineaments previously recognized in the area. In this regard, we investigated the passive gas dispersion in the atmosphere at Caldeiras da Ribeira Grande per- forming a model validation aimed to estimate the fumarolic gas flux at source and the potential hazard for human and animal lives posed by CO2. Numerical simulations were carried out with the DISGAS-2.3, a 3D Eulerian advection-diffusion model, and the relative outputs processed through the VIGIL-1.3 workflow able to provide probabilistic long-term CO2 concentration maps, considering a meteorological variability over the last 30 years (1991–2020) taken from the ECMWF ERA5 reanalysis dataset. A best-fit between observed and simulated CO2 concentrations allowed us to estimate the total gas flux of the area (~209 t d− 1) obtained by scaling the soil CO2 gas flux by a factor 30. Such an estimate is composed of ~174 t d− 1 as unknown fumarolic and ~ 35 td− 1 as diffuse contribution, in a good agreement with measurements. Although the present-day CO2 concentration at 0.3 m height cannot be considered to raise serious concerns for human health, we reasonably infer that the death of small animals may be due to local conditions of CO2 accumulation or to the presence of H2S. The current study highlights the relevance of coupling gas flux maps, concentration data, and gas dispersion modeling to obtain robust estimation of gas fluxes, including the fuma- rolic contribution, and identify zones potentially impacted by dangerous concentrations of volcanic gases, which are relevant for land-use planning and hazard assessment in case of renewed escalations of volcanic activity.254 69 - PublicationOpen AccessDiscriminating carbon dioxide sources during volcanic unrest: The case of Campi Flegrei caldera (Italy)(2023-03-02)
; ; ; ; ; ; ; ; ; Large 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 CO2.412 43 - PublicationOpen AccessAscent and decompressional boiling of geothermal liquids tracked by solute mass balances: a key to understand the hydrothermal explosions of Milos (Greece)(2023)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Hydrothermal explosions occur through the sudden expansion of fluids at or near boiling condition with little or no precursors, making any kind of forecast difficult. Here, we investigate the processes occurring within hydrothermal systems in a potential critical state for explosions through a new methodology based on mass balances of thermal water solutes. The usage of this method reveals that the pore water samples of the Paleochori Bay (Milos, Greece; <20 m depth below sea level), chosen as a case study, are binary mixtures of a geothermal component and seawater, from which steam is either added through condensation of underlying, ascending vapors or separates through boiling. This new method enables us to quantify and map both the fraction of the original geothermal liquid in each pore water sample and that of the vapor supplied or separated from the solutions. Furthermore, the method allows us to compute the composition of the geothermal endmember. The map of the fraction of supplied vapor shows that decompressional boiling of ascending liquids predominantly focuses in the central part of the Paleochori Bay. Both the estimated composition and temperature (324°C) of the geothermal liquid endmember overlap those measured in geothermal well fluids at or near-boiling condition, except SO4 and SiO2. The lower SiO2 and higher SO4 content in the pore waters may be ascribed to the current production of an impermeable cap, which enables underlying fluids to accumulate and pressure to buildup. The evidence of liquid at or near boiling conditions and self-sealing processes in the Paleochori Bay suggests that decompressional boiling during abrupt pressure drawdowns might have caused hydrothermal explosions at Milos in historical times, whose occurrence is testified by several hydrothermal craters. Finally, our work shows that similar conditions favoring explosions still affect the hydrothermal system of Milos. The new methodology described in this work can find useful applications in the study of submerged hydrothermal systems and in understanding the physicochemical conditions that favor hydrothermal explosions.78 24 - PublicationOpen AccessStructure and Present State of the Astroni Volcano in the Campi Flegrei Caldera in Italy Based on Multidisciplinary Investigations(2022-11-17)
; ; ; ; ; ; ; ; ; ; ; ; ; Despite its known reconstructed volcanic history, the structural setting and present state of the Astroni Volcano of the Campi Flegrei caldera in Italy are still poorly defined. Through structural, geophysical, and geochemical investigations, we elucidate the structure and present volcanic activity of the Astroni Volcano, which hosts tuff cones, scoriae cones, lava domes, and lakes on the crater floor. A volcano-tectonic analysis focused on the entire volcano edifice, coupled with electrical resistivity tomography of the shallower part of the Astroni crater, revealed the main rock formations, faults, and possible fluid patterns within the first 150 m depth. Two main NE–SW and NW–SE trending fault sets were imaged using electrical resistivity modeling and measurements along the wall of the volcanic edifice; they likely delimit a maar-like structure resulting from the highest nergetic subplinian Astroni 6 eruption event and acted as magma pathways during the late eruptive activity stage. A 3D view of the reconstructed resistivity model revealed both deep root-conduit-like structures and shallower dome-like shapes for volcanic edifices on the crater floor. Gas and carbon compositions in the NNE sectors of the Astroni Lago Grande are similar to those of the Solfatara fumarole fluids, suggesting common hydrothermal origin and a possible link with a deep hydrothermal reservoir. This fluid-emission area along the border of the younger volcanic structure exhibits a +40°C maximum soil-temperature anomaly. The proposed volcano-tectonic architecture should improve the unrest scenarios in case of reactivation in this Campi Flegrei caldera sector and the monitoring strategies for the Astroni Volcano.269 158 - PublicationOpen AccessImpact on air quality of carbon and sulfur volatile compounds emitted from hydrothermal discharges: The case study of Pisciarelli (Campi Flegrei, South Italy)Volcanoes are currently to be regarded as natural sources of air pollutants. Climatic and environmental forcing of large volcanic eruptions are well known, although gases emitted through passive degassing during periods of quiescence or hydrothermal activity can also be highly dangerous for the environment and public health. Based on compositional and isotopic data, a survey on the spatial distribution in air of the main volatile compounds of carbon (CO2 and CH4) and sulfur (H2S and SO2) emitted from the fumarolic field of Pisciarelli (Campi Flegrei, Pozzuoli, Naples), a hydrothermal area where degassing activity has visibly increased since 2009, was carried out. The main goals of this study were (i) to evaluate the impact on air quality of these natural manifestations and (ii) inquire into the behavior of the selected chemical species once released in air, and their possible use as tracers to distinguish natural and anthropogenic sources. Keeling plot analysis of CO2 and CH4 isotopes revealed that the hydrothermal area acts as a net source of CO2 in air, whilst CH4 originated mainly from anthropogenic sources. Approaching the urban area, anthropogenic sources of CO2 increased and, at distances greater than 800 m from the Pisciarelli field, they prevailed over the hydrothermal signal. While hydrothermal CO2 simply mixed with that in the atmospheric background, H2S was possibly affected by oxidation processes. Therefore, SO2 measured in the air near the hydrothermal emissions had a secondary origin, i.e. generated by oxidation of hydrothermal H2S. Anthropogenic SO2 was recognized only in the furthest measurement site from Pisciarelli. Finally, in the proximity of a geothermal well, whose drilling was in progress during our field campaign, the H2S concentrations have reached values up to 3 orders of magnitude higher than the urban background, claiming the attention of the local authorities.
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