Small-to moderate-volume eruptions at caldera systems often involve complex and rapidly evolving dynamics. The Campi Flegrei caldera in southern Italy has experienced >60 small-to moderate-volume eruptions since the last major caldera-forming event at ca. 15 ka. Among these, the ca. 4.3 ka Solfatara eruption provides a particularly valuable case study for investigating the dynamics of explosive activity in calderas hosting hydrothermal systems. In this study, we reconstruct the eruption sequence and dynamics of the Solfatara eruption using field data, componentry, grain size, ash morphology, vesicle texture quantification, and glass geochemistry. We identify three main eruption phases that indicate a clear transition in eruption styles: a gas-driven phase (Phase 0), a transitional phase from gas-driven to magmatic activity marked by phreatomagmatic explosions (Phase 1), anda magmatic-dominated phase (Phase 2), each associated with specific depositional units. Unit 0, deposited during Phase 0, consists of a fine, indurated ash layer with a high content of free crystals and altered lithic clasts interpreted as originating from the sudden decompression of hydrothermal fluids driving a phreatic explosion. Unit 1, deposited during Phase 1, shows alternating fine and coarse ash beds with abundant altered lithic clasts and clear presence of juvenile clasts (similar to 35 wt%), mainly deposited by dilute pyroclastic density currents (PDCs). These were generated through repeated explosions over short periods of time driven by magmatic activity, yet with an important contribution of hydrothermal fluids (magma-water/fluids interactions). In Unit 2, emplaced during Phase 2, the deposits become richer in juvenile clasts (up to 64 wt%) and include juvenilerich lapilli fall beds and proximal lithic-rich tuff breccias alternating with PDC-related ash and lapilli layers, indicating a shift to a magmatic-dominated, volatile-driven explosive activity. We estimate a total erupted volume of 0.053 km(3 )(whole deposit), with similar to 0.013 km(3) dense rock equivalent of juvenile magma erupted. The Solfatara eruption shows the complex behavior and hazard of small-to moderatevolume eruptions, in which transitions from gas-driven to magmatic activity can occur rapidly and produce diverse, hazardous phenomena. These findings have important implications for the reconstruction of eruption scenarios, emergency planning, and hazard assessment at Campi Flegrei and at other active calderas worldwide.

At Stromboli volcano (Italy) the regular, persistent activity is occasionally (2–4 events/year) interrupted by sudden, short-lived and more energetic major explosions, being intermediate in size between regular Strombolian activity and even more powerful paroxysmal explosions. Despite being frequent and hazardous, the magma source depth, the triggering mechanisms and timescales of such major explosions are still poorly understood. Here, we focus on three major explosions which occurred on 3 May, 8 November and 24 November 2009. We present a dataset of major element composition and dissolved volatile contents in olivine-hosted melt inclusions, embayments and glassy groundmass. We combine them with Fe–Mg diffusion profiles in olivine phenocrysts, and with volcanic gas plume and ground tilt measurements. Olivine phenocrysts display Fo69-72 compositions, with reverse zoning (up to Fo83) in the 24 November and to a minor extent in the 8 November eruption. Glassy groundmass of the November events ranges from the more evolved towards more primitive compositions, whereas the 3 May 2009 glassy groundmass has evolved compositions. Dissolved H2O and CO2 in glassy and bubble-free melt inclusions are low, with CO2 below the detection limit and H2O up to 2.3 wt.

A comprehensive understanding of the processes that occur during magmatic storage and pre-eruptive ascent—and of their associated timescales—is critical to identifying potential precursory signals, and to developing robust volcano early-warning systems. Stromboli’s persistent activity comprises continuous degassing and explosive activity that ranges from hourly, low-intensity “normal” activity to occasional, more violent, paroxysmal activity. While the magma source processes that drive normal and paroxysmal activity are reasonably constrained, eruptive activity intermediate in magnitude and intensity (i.e., major explosions) remains elusive in terms of classification, source region, and pre-eruptive timescales. Here, we investigate the 19 July 2020 major explosion that geophysical parameters place at the upper limit of the major explosions field, close to small-scale paroxysms such as the 2003 and 2007 events. The geochemical signatures of matrix glass, olivine, melt inclusions, and embayments—integrated with gas measurements—highlight important differences in eruption source, ascent behaviour, and pre-eruptive timescales of the studied event when compared to paroxysms. Melt inclusion volatile contents identify that magma rise begins from a slightly shallower source (~9.5 km below sea level, b.s.l.) than for paroxysms (11.4 km b.s.l.), with the activation of a shallower ponding zone at 5–6 km b.s.l.. This, in combination with intermediate matrix glass compositions, suggests complex ascent behaviour, characterised by CO 2 buffering in the deep ponding region and magma self-mixing in the shallower zone. Fe–Mg-diffusion modelling in olivine indicates a system perturbation starting ~20–25 days before eruption onset, in agreement with the timescale of volcanic gas CO 2 /SO 2 ratio changes observed in the plume, and significantly shorter than that observed prior to paroxysms (~4 months). The geochemical dataset provides insights into the processes controlling the steady-state conditions and the broad spectra in eruption magnitude and intensity at Stromboli and bears important implications for eruption forecasting.

The island of Ischia, an active volcanic field emerging in the western sector of the Gulf of Naples (Southern Italy), represents an archetypal case of caldera that underwent a very large resurgence related to the intrusion of a shallow magma body. The resurgence culminated with the formation of a structural high in the central sector of the island, i.e., the Mt. Epomeo block. This is bordered by a system of faults along which volcanic activity occurred up to 1302 A.D., and damaging earthquakes were generated in historical and recent time. The seismicity is located prevalently in the northern sector of the island and appears to be correlated with the most recent phase (<5 ka) of ground movement (subsidence), although the mechanism of earthquakes’ generation is still debated. By jointly analyzing offshore and onshore data (seismic profile and stratigraphy wells, respectively) and new petrological and geochemical data related to the most recent phase of volcano-tectonic activity, we develop a geological and structural layout of the northern sector of the island. In particular, we identify the seismogenic fault associated with the historical and recent destructive earthquakes of Ischia. This fault formed in the northern sector of the island during the final stage of the resurgence. We also propose a conceptual volcano-tectonic model of the northern sector of the Ischia Island, depicting the displacement of the fault zones in the off-shore area and the possible mechanism of stress loading and release in the on-shore zone, which is mainly driven by the subsidence of the Mt. Epomeo block. Our results are crucial for evaluating the dynamics of the seismogenic structures in the framework of the general subsidence of the island, as well as the related seismic hazard.

This work is focused on the hydrothermal system developed in the Ischia volcanic field before Mt. Epomeo resurgence, and is based on the investigation of hydrothermally altered lithic clasts present in the volcanic deposits of Secca d'Ischia and Epomeo Green Tuff eruptions. We demonstrate that a wide high temperature hydrothermal system occurred in the Ischia volcanic complex, both in intracalderic and extracalderic areas, at the time of the caldera-forming paroxysmal phase (60-56 ka). This hydrothermal system was characterized by high temperatures ranging from 240 degrees C and 340 degrees C and fluids of marine (similar to 3.5 wt% NaClequiv.) and meteoric origin (<0.5 wt% NaClequiv.). In the intracalderic area, the hydrothermal system was exhumed during the resurgence of Mt. Epomeo; in the extracalderic area of the island the hydrothermal system was at least partially disrupted during the Secca d'Ischia eruption.

Between May 2009 and March 2010, six small scale paroxysms were recorded at Stromboli volcano (Aeolian Islands, Italy). The small scale paroxysm of 21 January 2010 was the only one characterized by a SSE to SW dispersal direction, which allowed access for sampling of the associated bomb-dominated deposit. The quenched marginal portions of twelve bombs were used to perform density, textural and chemical analyses to define the mechanisms operating in the shallow conduit during the explosion. Whole-rock density values span a range of 1100 to 2300 kg/m3 which, using a dense rock equivalent density of 2850 kg/m3, converts to a vesicularity of 20 to 61%. The vesicle volume distribution (VVD) is unimodal, with a mode at 1.8 mm, consistent with a single bubble nucleation event followed by growth, coalescence expansion and/or densification. Crystallinity ranges from 30 to 62 vol%. Vesicle and crystal contents, however, show considerable variation, consistent with the presence of an extremely dense and degassed component in the fragmented magma. Both groundmass glasses and melt inclusions are chemically homogenous, with CaO/Al2O3 in the range 0.40-0.60. Melt inclusion volatile contents (H2O up to 0.47 wt%) are consistent with fragmentation of a shallow magma residing at a depth of about 480 m. We suggest that dense, degassed and crystal-rich magma formed a "soft" rheological plug at the top of the conduit. Under such a condition, bubbles can accumulate under the plug to slowly build the pressure to a threshold point, after which the pressure is enough to cause the fragmentation of the plug.

Geothermal energy is a key renewable energy for Italy, with an annual electric production of 6.18 TWh. The future of geothermal energy is concerned with clarity over the CO2 emissions from power plants and geological contexts where CO2 is produced naturally. The Mt. Amiata volcanic–geothermal area (AVGA) is a formidable natural laboratory for investigating the relative roles of natural degassing of CO2 and CO2 emissions from geothermal power plants (GPPs). This research is based on measuring the soil gas flux in the AVGA and comparing the diffuse volcanic soil gas emissions with the emissions from geothermal fields in operation. The natural flux of soil gas is high, independently from the occurrence of GPPs in the area, and the budget for natural diffuse gas flux is high with respect to power plant gas emissions. Furthermore, the CO2 emitted from power plants seems to reduce the amount of natural emissions because of the gas flow operated by power plants. During the GPPs’ life cycle, CO2 emissions in the atmosphere are reduced further because of the reinjection of gas-free aqueous fluids in geothermal reservoirs. Therefore, the currently operating GPPs in the AVGA produce energy at a zero-emission level.

A volcanological map merging continental and marine areas of the Phlegrean Fields and Procida Island (Southern Italy) is presented at the 1:25,000 scale. The map is based on 1:5,000 field mapping, and marine geology survey carried out during the Italian CAR.G (Geological CARtography, Servizio Geologico d’Italia) project and on bathymetric and seismic data. Geological data are represented on a digital terrain model of the volcano. This allows better visualization of the main morphological, volcanic, and geological features. The legend is organized in seven activity phases identified based on updated absolute ages of eruptions defining periods of high volcanicity and stasis. The geological map highlights the evolutive history of the Phlegrean Fields volcanic field both in the marine and continental portions, and the reconstructed structural framework and evolution of the caldera formed 39.3 Ky ago in its continental and submerged portions.

A volcanological map of the active Somma-Vesuvius volcano is presented at the 1:20,000 scale. The map is based on 1:5000 field mapping carried out during the Italian CARG project. Geological data are represented on a digital terrain model of the volcano. This allows a better visualisation of the main morphological, volcanic, and geological features. The legend is organised in four different panels, which depict the activity of the volcano and caldera development. The geological survey is based on recognition and description of lithostratigraphic units. The geological map highlights the volcanic evolution of the Somma-Vesuvius volcano, and it is propaedeutic for further studies aimed at improving the scientific knowledge and the volcanic hazard assessment of this world-famous volcano.

In the Amiata volcanic-geothermal area, natural soil degassing of CO2 is particularly intense and observed over a wide area, including the volcano complex and its surroundings. A survey systematically and directly measured the natural total soil CO2 flux over the whole area, comprising 2482 measurements over an area approximately 225 km(2). Sequential Gaussian simulations generated CO2 flux maps for the entire survey area. These data, when combined with evidence from concentrated degassing emissions, provided an estimate of the area's total CO2 flux (biogenic plus deep CO2) as 13,350 t/d. This mapping and estimation greatly improve the knowledge and understanding of natural CO2 degassing to the atmosphere from this well-known volcanic geothermal area High values of diffuse CO2 soil flux correspond to both high- and low-enthalpy geothermal areas, confirming the value of the CO2 flux survey methodology to individualize and delimitate geothermal fields and geothermal resources. (C) 2020 Elsevier B.V. All rights reserved.

Shallow, low-temperature geothermal resources can significantly reduce the environmental impact of heating and cooling. Based on a replicable standard workflow for three-dimensional (3D) geothermal modeling, an approach to the assessment of geothermal energy potential is proposed and applied to the young sedimentary basin of Pisa (north Tuscany, Italy), starting from the development of a geothermal geodatabase, with collated geological, stratigraphic, hydrogeological, geophysical and thermal data. The contents of the spatial database are integrated and processed using software for geological and geothermal modeling. The models are calibrated using borehole data. Model outputs are visualized as three-dimensional reconstructions of the subsoil units, their volumes and depths, the hydrogeological framework, and the distribution of subsoil temperatures and geothermal properties. The resulting deep knowledge of subsoil geology would facilitate the deployment of geothermal heat pump technology, site selection for well doublets (for open-loop systems), or vertical heat exchangers (for closed-loop systems). The reconstructed geological–hydrogeological models and the geothermal numerical simulations performed help to define the limits of sustainable utilization of an area’s geothermal potential.

A volcanological map of the active Ischia volcanic field that includes Vivara Island is presented. The volcanological map is at the 1:10,000 scale and is based on 1:5000 field mapping, geological CAR.G data, and new volcanological studies. Geological data are represented on the three-dimensional orographic background digital terrain model of the inland and offshore areas of the volcanic field. This allows a better visualization of the main morphological, volcanic, and geological structures. Six phases were identified on the basis of volcanotectonic events; the 110 volcanic units were arranged following these evolutive phases, and a volcanosedimentary apron unit was introduced. This volcanological map enables visualization of the volcanic evolution of the Ischia volcanic field and could be useful for the evaluation of volcano-related hazards in the area.

Volcanic eruptions are typically characterized by the rise and discharge of magma at the surface through a single conduit-vent system. However, in some cases, the rise of magma can be triggered by the activation of eruptive fissures and/or vents located several kilometers apart. Simultaneous eruptions from multiple vents at calderas, not related to caldera collapse (e.g., ring faults), are traditionally regarded as an unusual phenomenon, the only historically reported examples occurring at Rabaul caldera, Papua New Guinea. Multiple venting within a caldera system is inherently difficult to demonstrate, owing partly to the infrequency of such eruptions and to the difficulty of documenting them in time and space. We present the first geological evidence that at 4.3 kyr B.P., the Solfatara and Averno vents, 5.4 km apart, erupted simultaneously in what is now the densely populated Campi Flegrei caldera (southern Italy). Using tephrostratigraphy and geochemical fingerprinting of tephras, we demonstrate that the eruptions began almost at the same time and alternated with phases of variable intensity and magnitude. The results of this study demonstrate that multi-vent activity at calderas could be more common than previously thought and volcanic hazards could be greater than previously evaluated. More generally we infer that the simultaneous rise of magma and gas along different pathways (multiple decrepitation of chamber[s]) could result in a sudden pressure rise within the sub-caldera magmatic system.

In this paper, we build a subsurface model that helps us to visualize and understand the structural framework and geology, along with their interactions, in the Mt. Amiata geothermal system. Three-dimensional (3D) modeling provides the possibility of interpolating the geometry of structures, and is an effective method for understanding geological features. The 3D modeling approach is crucial for further progress in the reconstruction of the assessment of the geothermal model of Mt. Amiata. Furthermore, this model can be used as the basis for a 3D numerical thermo-fluid dynamic model of the existing reservoir(s). The integration of borehole data and the numerical modeling results allows us to reconstruct the temperature distribution in the subsoil of the Mt. Amiata area.