IntroductionVulcano Island, in the Aeolian Archipelago (Italy), is affected by recurrent degassing crises during which elevated volcanic gas emissions may pose hazards to residents, visitors, and personnel operating in the active crater area. This study presents a scenario-based probabilistic assessment of outdoor CO2 and SO2 dispersion hazards at Vulcano.MethodsThe assessment integrates long-term meteorological variability, geochemical monitoring data and numerical dispersion modelling. Three representative degassing scenarios were considered: (i) background activity, based on long-term monitoring data; (ii) unrest conditions, representative of the enhanced degassing observed during the 2021–2022 crisis; and (iii) an escalation scenario exploring the effects of a further increase in gas emissions. Atmospheric variability was represented by randomly sampling 1,000 days from 30 years of ERA5 reanalysis data, complemented by local meteorological observations. Hazard and persistence maps were generated using the VIGIL workflow, which couples passive and gravity-driven dispersion models.ResultsThe simulations indicate that SO2 represents the main outdoor gas-dispersion hazard across the investigated scenarios. Under background conditions, hazardous SO2 concentrations remain largely confined to the La Fossa crater area, whereas under unrest and escalation scenarios the affected area expands along the crater flanks and, under specific meteorological conditions, toward sectors frequented by visitors or located near inhabited areas. In contrast, modelled outdoor CO2 concentrations at 2 m above ground level remain below hazardous thresholds under background and unrest conditions, while elevated concentrations are predicted in the escalation scenario, particularly within the crater area.Discussion and ConclusionsComparison with available monitoring data highlights the importance of poorly constrained local fumarolic and diffuse CO2 sources, particularly near Vulcano Porto and Levante Beach. Overall, the proposed probabilistic framework provides a quantitative basis for identifying areas where hazardous gas concentrations may occur or persist under variable atmospheric conditions, supporting future monitoring strategies and preparedness planning during degassing crises.

Geothermal energy represents a renewable energy source exploited for multiple purposes, including electricity, direct use, district heating and heat pumps. One of the most relevant problems in geothermal energy industry is the permeability of the reservoir, both for production and reinjection. Therefore, it is important to assess the fluid circulation in the reservoir and where deep fluids rise. Faults, fractures and active tectonics influence fluid behaviour and fluid-rock interactions in a geothermal context. It is necessary to estimate the role of faults and map as well as their distribution, as tectonic structures could act as barriers to fluid circulation or as preferential conduits. The Acque Albule Basin (AAB) is a case study representing one of the most important hydrothermal manifestations in central Italy. The AAB is a tectonically controlled basin, characterized by a huge hydrothermal manifestation (discharges in the order of m3/s). The deep hydrothermal activity is testified by the presence of a large and thick travertine deposits and several mineralized springs (Tmax at the surface up to 23°C) in which warm fluids rise from the geothermal reservoir. These hot fluids circulate through the Meso-Cenozoic carbonate reservoir, highly affected by dissolution and brittle deformation. In this framework, travertine deposition is mainly controlled by the faults activity. Several geophysical surveys were carried out to evaluate the cap-rock of the geothermal reservoir, beneath the travertine plateau. The exploration provided a clearer view of the stratigraphy of the AAB and revealed the carbonate roof at 300-400 m. The carbonate rocks are overlain by some alluvial sediments and a travertine plateau from 10 m to 90 m. Based on the geophysical investigations, the measurement of diffuse CO2 emissions from the soil was planned to ascertain the faults role in the hydrothermal circulation. Preliminary results show that the fault zone is characterised by an extremely low degassing (5/10 g m-2d-1). The low degassing could be related to the low-permeability of the alluvial and travertine deposits and/or by self-sealing processes through the main shear zone, which obstacle the upwelling of fluids and gases. The model will be improved with further regional CO2 surveys and δC13 analysis of CO2 of gaseous samples taken from the soil.

Airborne CO2 has played a pivotal role in maintaining the Earth's atmospheric temperature at reasonable levels throughout its history. Since the onset of the industrial revolution, the level of airborne CO2 has surged due to the combustion of hydrocarbons, leading to global warming. Hydrocarbon consumption is predominantly concentrated in metropolitan areas, driven by various human activities. Estimations of CO2 emissions into the atmosphere rely on the growth of electrical power generation through hydrocarbon combustion. This study presents the outcomes of direct measurements of stable isotope concentrations in airborne CO2 in the urban area of Rome, Italy. We focused on Rome capital city, because i) it is the most populous municipality in Italy (2.8 millions inhabitants), ii) it is the European municipality with the largest surface of green areas and iii) in its south-east sector it borders the Colli Albani quiescent volcano. The dataset encompasses stable isotope compositions and airborne CO2 concentrations gathered to investigate variations in CO2 emissions across space and time. The spatial survey conducted throughout Rome's urbanized area, on a 250 km long path, aims to pinpoint the relevant sources of CO2 based on the stable isotope signature. Results reveal that the combustion of fossil fuels, stemming from urban mobility and household heating, constitutes the predominant source for the excess of airborne CO2 across a wide area of Rome centre. On the contrary, within the Rome south-east sector, including Colli Albani periphery, the carbon isotopic signature of airborne CO2 discloses the endogenous origin of the gas emissions. Continuous monitoring was carried out by the installation of an isotope analyser in three specific points of interest throughout Rome: the busiest area of the city centre, the woodland urban park of Villa Ada and the endogenous gas emission of Cava dei Selci. Findings unveil cyclic variations in human-related CO2 emissions in the city centre. The highest concentrations of airborne CO2 coincide with rush hours during morning and evening. The urban park is not affected by anthropic CO2 and its trend displays the typical day-night cycle. At Cava dei Selci we found high CO2 concentrations by a volcanic source and variations in the urban area correlate with changes in environmental conditions, such as wind speed and direction.

<p>Repeated flooding episodes occurred from the crater lake of Albano until 398 B.C. These floods were probably caused by sudden injection of gas and warm waters on the lake bottom, or also by the overturn of the lake which would have brought to the surface the deep water rich in CO<sub>2</sub>. Since several years, we have been monitoring the crater lake chemical composition as well as its physico-chemical parameters and dissolved gas content, in order to assess evidences of possible deep fluid input in the lake water. The concentration of dissolved gases, and their isotopic composition (d<sup>13</sup>C<sub>TDIC</sub>, <sup>3</sup>He/<sup>4</sup>He) suggest the presence of deep gases (CO<sub>2</sub> and CH<sub>4</sub>) within the lake bottom layer. However, the total pressure of dissolved gases is presently, at any depth, much lower than the hydrostatic pressure. If, for any reason, a significant volume of deep water should rise to the surface, only limited phenomena of gas exsolution are to be expected. A density variation of shallow lake water due to cooling, in case of heavy rainfall in harsh winters (T<8.5°C), may produce water overturns. Such phenomena, as long as they happen with a certain frequency, would prevent the accumulation of dangerous quantities of CO<sub>2</sub> in the deepest lake water strata. Apart from a volcanic unrest, the most dangerous condition is the occurrence of seismic swarms with hypocentres in the Lake Albano area, which could lead to an increase in the influx of hot gases and fluids in the lake. Currently, the conditions for a rapid release of significant quantities of CO<sub>2</sub> from Lake Albano do not exist. To improve the knowledge of the Lake Albano  water circulation, we investigated also the isotopic <sup>87</sup>Sr/<sup>86</sup>Sr composition of the lake water, comparing the results with those of the rocks hosting the aquifers. Results indicate that Lake Albano water samples well fit a binary mixing of a high <sup>87</sup>Sr/<sup>86</sup>Sr ratios end-member (Colli Albani volcanites) and a low ratio end-member (carbonate basement) in a proportion of 75% and 25% respectively. Moreover, the landslide hazard of the internal slopes of Lake Albano has been assessed using Ordinary Least Squares and Empirical Likehood Ratio modelling functions. The presence of numerous dwellings and recreational activities along the internal slopes of the crater lake, makes the area of potentially-high risk, both because of the inner intense slope instability and for possible secondary effects due to tsunami waves that might be generated by the impact of sliding subaerial masses on the lake surface or by sub-aqueous landslides.</p>

<p>La Fossa volcano on Vulcano island is the type-location for Volcanian eruptions. Last eruption dates back to 1888-’90. Since then, the quiescent state of La Fossa has been affected both by persistent fumarolic activity and by diffuse CO2 degassing either at the crater and in areas on the flanks (Forgia vecchia) at the base (Palizzi) of the cone, but also in inhabited areas of Vulcano porto (Levante beach, Faraglione). Normal quiescence has been punctuated by potential unrest crises mainly characterized by increase in magmatic degassing, in fumarole temperatures and in diffuse CO2 degassing. We have been monitoring the diffuse degassing area of La Fossa crater since 1995 and Palizzi, Levante beach and Vulcano porto zones since 2004.</p> <p>The ongoing crisis started in 2021 and showed a huge unprecedented increase in fumarolic degassing associated to ground deformation and episodic anomalous seismicity. For monitoring purposes, we performed since October 2021 two general surveys at the crater of La Fossa (soil CO2 flux and temperature), monthly surveys of diffuse soil CO2 flux in the areas of Palizzi, Levante Beach, Forgia vecchia and an extensive CO2 flux survey (~1000 measurements over 1 km2) in the inhabitated area of Volcano Porto in October 2021. From this wide survey we identified a new diffuse-degassing structure which was apparently inactive during the most recent unrest crises. Since November 2021, this area has been monthly surveyed too. This degassing structure is associated to shallow aquifer thermalism and the area is spotted by some mofetes. During the 1988-’93 crisis, it has been the site of some lethal accidents to animals caused by exposure to high CO2 concentration in air. There have been accidents during this crisis too, with the death of some cats and many birds caused by lethal concentrations of CO2 inside the yard of a house. Fortunately, there were no human casualties due to the prompt evacuation of the zone.</p> <p>Monthly repetition of soil CO2 flux from the target areas, showed that, at the early stage of the crisis, diffuse CO2 degassing equalled or even exceeded the high-flux rates measured during the previous crisis of 2004-’05 both at the crater area and at the crater base. In 2022-‘23 soil CO2 fluxes have slowly decreased, but the pre-crisis conditions have not yet been reached.</p>

Natural gas hazard was assessed at Cava dei Selci, a residential neighbourhood of Marino (Rome) by a joint study of gas emissions and related health problems. Here a densely urbanized zone with 4000 residents surrounds a dangerous natural gas discharge where, along the years, dozens of animals were killed by the gas. Gas originates from Colli Albani volcano and consists mostly of CO2 with 1 vol

Rome Capital City is located in a high heat flux area of central Italy, suitable for low-enthalpy geothermal exploitation. In the central-northern part of the city, near Tor di Quinto hippodrome close to Tiber River, a wide undeveloped area occurs, which is a possible future urban development site. We present the results of a geochemical and geophysical study aimed at assessing the presence in this zone of a low-enthalpy geothermal aquifer and at evaluating its depth, thickness and the physico-chemical characteristics of the geothermal water. Furthermore the natural CO2 output of this zone has been investigated. A soil CO2 flux survey with 551 measurements over a surface of 3.09 km2 revealed the presence of parallel NW-SE trending positive flux anomalies. The total CO2 output was estimated to 87.77 t*day(- 1), most of which (85%) of endogenous or mixed origin. An Electrical Resistivity Tomography survey, consisting of five parallel 355 m long and 100 m spaced profiles, allowed the reconstruction of the stratigraphy of the underground sediments, which are fluvial deposits of the near Tiber River. The geothermal water is hosted in a low-resistivity layer, corresponding to the Tiber base gravels, which are here 20 m thick and whose top is 40 m below the surface. The water has a nearly constant temperature of 17.5 ?, a relatively high salinity and an appreciable content in dissolved gas. This low-enthalpy resource is suitable for direct uses, e.g. individual and district heating/cooling, sanitary hot water, spa facilities for swimming and bathing.

La Fossa volcano, located in the Vulcano Island of the Aeolian Archipelago, is the type locality of Vulcanian explosive eruptions. It last erupted in 1888-1890 and since then it is affected by an intense fumarolic activity from both the summit crater area and a hydrothermal site (Levante Beach) located very near to the main settlement of the island (Vulcano Porto). In Autumn 2021 a potential volcanic unrest crisis began with a strong increase of steam, CO2 and SO2 emission from the high-T crater fumaroles, ground uplift and episodic anomalous seismicity. Vulcano Porto inhabited area is exposed to gas hazard either from the wind dispersed crater fumarolic plume (mostly CO2 and SO2) and from anomalous diffuse soil gas emissions in Levante Beach and other zones of Vulcano Porto village (mostly CO2 and eventually H2S). The gas hazard of the village was considered so high that in December 2021 Civil Protection prohibited residents to stay at home during the night. In order to improve the monitoring of gas hazard we developed new stations continuously measuring the air concentration of CO2 and SO2. Each of these stations is operating with an electrochemical sensor for the measurement of SO2 and a photoacoustic sensor for the measurement of CO2. Moreover, atmospheric pressure, temperature and humidity are monitored in parallel to the gas measurements. The measured data are sent continuously via mobile data connection to a dedicated server. By this means the measured parameters can be monitored remotely, without the need to access the site personally. Three stations were installed (at 1 m from the ground) in mid-December 2021 in three sites of Vulcano Porto; two of them were located at the base of La Fossa cone in the sector most exposed to the crater gas plume, while a third station was located in the heart of the village, near the church. Results show that CO2 exceeds of few hundreds ppm the normal air value of 400 ppm in all the stations. In some occasions, during night in absence of wind or with light wind blowing from SW, some peaks of both CO2 and SO2 were recorded in all the stations (CO2 max 1500 ppm; SO2 max 2 ppm). Additionally a future server sided extension to our system is planned, which integrates an early warning system, that can send email alerts, if certain thresholds are exceeded.

Abstract Cava dei Selci (CdS) is the main degassing site of the Colli Albani quiescent volcano and since 20 years it is the site of geochemical volcano monitoring. Emitted gas consists mostly of CO2 (≥98 vol.%) with minor H2S, and helium isotopes suggest it has a significant magmatic component. The diffuse soil CO2 flux was monitored in the period 2000–2020, with 55 surveys on a target area. The total CO2 output fluctuates from 5.6 to 24.8 t d−1. The soil CO2 flux per unit surface (average 2.323 kg m−2 d−1) is the highest of 15 Italian actively degassing volcanic and geothermal areas. Soil CO2 flux and environmental parameter data collected over 4‐year of continuous monitoring (2004–2008) were analyzed by stochastic Gradient Boosting Trees regression (sGBT), Multiple Linear Regression, and Principal Component Regression. Only sGBT predicts the entire data set and effectively identifies the relationship between soil CO2 flux and environmental parameters. Residuals indicate two anomalous degassing periods (March‐2005, summer‐2007). Colli Albani area is affected by moderate seismicity (Md ≤ 4). 575 earthquakes occurring from 2009 to 2021 were analyzed determining their location, hypocenter depth, and focal mechanism (of 43 selected events). Evaluation of seismic events occurred across geochemical surveys within 30 km from CdS shows that there is a relationship between CO2 flux, earthquake focal mechanism and depth: shallow strike‐slip hypocenters are associated to low fluxes, deep normal‐faulting hypocenters to high CO2 output.

Colli Albani is an alkali-potassic quiescent volcano of Central Italy that last erupted 36 ka ago. Several lahar generating water overflows have occurred from Albano crater lake, the most recent in Roman times (IV Century B.P.) and the resulting deposits form a surficial impermeable cover on its north-western flank. An important NW-SE trending volcano-tectonic fracture extends from the volcano to the periphery of Rome city. This is a leaky fracture allowing deep magmatic gas to rise toward the surface. In zones where the impervious cover has been removed by excavations, as Cava dei Selci, the gas is freely discharged into the atmosphere creating local hazardous conditions. Elsewhere, the gas dissolves and pressurizes the shallow aquifer confined underneath the impervious cover. Any time this aquifer is reached by a drilling, a dangerous gas blowout may be generated, i.e. a sudden emission of a jet of gas, nebulized water and fine loose fragments of volcanic rocks. Since 2003 four gas blowouts, from ~ 45–50 m deep drillings, have occurred at the boundary between Rome and Ciampino municipalities, a site designed as the Rome gas blowout zone. Dangerous atmospheric CO2 and H2S concentrations killed some animals and several families had to be evacuated because of hazardous gas concentration inside their houses. The emitted gas consists mostly of CO2 (>90 vol.%) and contains a low but significant quantity of H2S (0.3–0.5 vol.%); it has the highest helium isotopic R/Ra value (up to 1.90) of all Colli Albani natural gas discharges. This He isotopic value is similar or even slightly higher than in the fluid inclusions of phenocrysts of the Colli Albani volcanic rocks, suggesting a likely magmatic origin of the gas. Colli Albani volcano is characterized by anomalous uplift, release of magmatic gas and episodic seismic crises. The Rome gas blowouts represent a geochemical window to investigate deep volcanic processes. Should a volcanic unrest occur, gas hazard would increase in this densely inhabited zone, as the input of magmatic gas into the confined aquifer might create overpressure conditions leading to a harmful phreatic explosion, or increase the emission of hazardous gas through newly created fractures.

Mts. Simbruini karst aquifer feeds important springs whose capture contributes to the water supply of Rome City. To improve the geochemical characterization of this aquifer, we analyzed 36 groundwater samples, 29 from springs and 7 from shallow wells, collected in 1996 and 2019. Atomic adsorption spectroscopy, tritration, ionic chromatography and mass spectrometry were the used analytical methods. Ground waters are bicarbonate alkaline-earth type and HCO3 dominance confirms that the aquifer is hosted in carbonate rocks. Total alkalinity vs. cations plot indicates that CO2 driven weathering controls the water chemistry. The probability plots of HCO3, cations and Ca2+ +Mg2+ indicate four groundwater populations with the less represented one (9 samples) characterized by the highest PCO2 values (>0.3 atm). Most anomalous values of the dissolved PCO2 are from springs located near the center of the studied area. Four samples have negative values of d13CCO2 (about -22‰ vs. PDB), indicating its organic origin, but two other samples have positive values (1.6 and 2.6 ‰ vs. PDB), similar to those observed in the CO2 of deep origin discharged at the close Colli Albani volcano. Therefore, geochemical evidence indicates that the Mts. Simbruini aquifer is locally affected by the input of deep originated CO2, likely rising up along fractures, interacting with a recharge of meteoric origin, as evidenced by its d2H and d18O isotopic signatures.

Although groundwater is a strategic source in volcanic islands, most hydrogeochemical research on this topic has been focused on volcanic activity monitoring, overlooking general hydrogeological aspects. The same applies to one of the most studied volcanoes in the world, Stromboli Island (Italy). Here, we provide a hydrogeological scheme of its coastal aquifer, retrieving inferences about its potential use as a water supply source and for optimizing monitoring protocols for volcanic surveillance. Starting from the hydrogeochemical literature background, we analyzed new data, acquired both for volcano monitoring purposes and during specific surveys. Among these, there were saturated hydraulic conductivity measurements of selected rock samples and precise determinations of water table elevations based on GNSS surveys of wells. We identified a ubiquitous thin lens of brackish water floating on seawater and composed of a variable mixing of marine and meteoric components; inlets of hydrothermal fluids to the aquifer are basically gases, mainly CO2. Based on its hydrogeochemical character, the coastal aquifer of Stromboli could be used as a water supply source after desalinization by reverse osmosis, while the wells located far from the seashore are the most interesting for volcano monitoring, because they are less disturbed by the shallow geochemical noise.

A gas blowout during an unauthorized well drilling occurred on June 9, 2020 at the Rome‐Ciampino boundary at the periphery of Colli Albani quiescent volcano. This zone hosts a shallow confined gas‐pressured aquifer, which recently produced further three gas blowouts. Dangerous atmospheric CO 2 and H 2 S concentrations killed some birds, and 12 families were evacuated. The helium isotopic composition indicates that the gas has a magmatic origin. It rises toward the surface along leaky faults, pressurizing the shallow confined aquifer and creating a permanent gas blowout hazard. Colli Albani volcano is characterized by anomalous uplift, release of magmatic gas, and episodic seismic crises. Should a volcanic unrest occur, gas hazard would increase in this densely inhabited zone of Rome city, as the input of magmatic gas into the confined aquifer might create overpressure conditions leading to a harmful phreatic explosion, or increase the emission of hazardous gas through newly created fractures.

Carbon dioxide flux from the soil has been monitored for 20 years at Cava dei Selci, the main degassing site of Colli Albani quiescent volcano. Cava dei Selci gas discharge occurs at the north-western periphery of the volcano, within an old stone quarry crossed by a NW-SE volcano-tectonic lineament. The area around the manifestation has been densely urbanized and lethal accidents by gas inhalation have occurred to a man and to dozens of animals including cows and sheep. Some houses had to be permanently evacuated because of hazardous indoor gas concentrations. Emitted gas is dominated by CO2 (>90 vol.%) with <1 vol.% of H2S. Isotopic composition (δ13C and 3He/4He) suggests a deep magmatic origin. No significant compositional variations have been recorded during the observation period. Surveyed area includes a fixed grid of 130 points, regularly distributed over an area of about 5500 m2, where soil CO2 flux surveys have been carried out 55 times from May 2000 to August 2020 by accumulation chamber. Collected data have been reprocessed by sequential Gaussian simulation. The total diffuse CO2 output is highly fluctuating, with a maximum rate of 24.8 t*d−1 in January 2006 and a minimum value of 5.6 t*d−1 in December 2003; the estimated mean±1σ is 12.1±4.5 t*d−1. All the flux maps show typically a highly emissive area in the internal sector of the investigated grid, with NW-SE elongation. Another anomalous zone, with the same elongation, is found in the SW of the survey area. Diffuse degassing rate (total flux normalized by survey area) is similar to that of active volcanic zones. In the same zone an automatic permanent station continuously measured the soil CO2 flux and environmental parameters (which may influence the soil gas flux) from 2004 to 2008 and from 2019 to present. Results of timeseries processing by Multiple Linear regression and Principal Component analysis, commonly used to filtrate and clear data from atmospheric inferences (for example at Stromboli and Campi Flegrei), were unsatisfying for Cava dei Selci. Therefore, we reprocessed the timeseries by the stochastic Gradient Boosting Trees regression technique. This allowed to explain up to 55 % of the CO2 variance by environmental variations; 45 % of the variance therefore reflects deep-seated processes. This technique looks promising for the regression of soil CO2 flux timeseries. The results of 20 years monitoring confirm that Cava dei Selci is a convenient site for both monitoring a potential unrest of the volcano and assessing the gas hazard in the nearby inhabited zone.

The southeastern zone of Rome city is located at the northwest periphery of the quiescent Colli Albano volcano. This zone is characterized by the presence of a shallow (depth similar to 45-50 m) gas pressurized aquifer that produces gas blowouts when it is reached by wells. Three gas blowouts occurred in this zone in 2003, 2008 (another one was discovered during the present study) and 2016 and in this paper we describe in detail the latter two. The emitted gas consists mostly of CO2 (>90 vol%) and contains a low but significant quantity of H2S (0.3-0.5 vol%) and it has the highest helium isotopic R/Ra value (1.90) of all Colli Albani natural gas discharges, suggesting its likely magmatic origin. In both the described gas blowouts, dozens of families had to be prudentially evacuated from their houses and the emitted gas killed some animals. We monitored, continuously or by discrete surveys, the soil CO2 flux, the indoor and outdoor air concentration of CO2 and H2S, the environmental parameters and we checked whether the cementation of the gas releasing wells had been effective. In both cases, the upper part of the wells had been partly closed with an inflating packer to avoid free gas dispersion in atmosphere; as a consequence gas diffused laterally from the wells into the permeable surficial soil up to reach the nearest houses creating hazardous indoor conditions, particularly for CO2 in some basements. During the well cementation operations, and in one case because of the packer rupture, gas and nebulized water were freely discharged from the wells into the atmosphere, and high air CO2 and H2S concentrations were found. Fortunately gas was quickly dispersed by strong winds. The positive results obtained in all the studied gas blowouts demonstrate that our applied geochemistry approach represents a model of intervention useful for the assessment of the hazard associated to accidental endogenous gas release. This model is of fundamental importance also to overcome the risk problems created by accidental gas blowout from wells in an urbanized environment, up to the safe return of the people in their evacuated houses.

Gas hazard was evaluated at Lavinio-Tor Caldara, the southernmost gas-discharging zone of the quiescent Albani Hills volcano in central Italy. Also this zone, like the other gas discharges of this volcanic complex, is located above a structural high of the buried Mesozoic carbonate basement, which represents the main reservoir for gas rising from depth. All extensional faults affecting the carbonates are leaking pathways along which gas may rise to the surface creating hazardous conditions. Gas is dominated by CO2 (>90 vol%) and the second component at Lavinio-Tor Caldara is H2S that displays the highest content (4.0-6.3 vol%) of all gas manifestations of the Rome region. This H2S enrichment corresponds to a marked decrease in He-3/He-4 (R/Ra) isotopic ratio suggesting that gas was contaminated in an upper crustal environment. The main gas discharge occurs at the natural reserve of Tor Caldara, in zones where past sulphur mining excavations removed the surficial impervious cover, or along a ditch. Comparison of the results of four soil CO2 flux surveys carried out in 2005-2018 at Miniera Grande within Tor Caldara, indicates that the highest soil CO2 release occurs shortly after local earthquakes. Continuous monitoring of CO2 and H2S air concentration and of wind speed has been carried out for four months in twelve anomalous gas realising sites of Tor Caldara. Results indicate that only H2S reaches lethal concentration (>250 ppm) near the soil in no wind nights, explaining the presence of small dead animals. At Lavinio, the main soil gas release occurs near old water wells that likely produced a gas blowout during drilling. A total release of over 20 tons/day from 2.93 km(2) of gas of endogenous origin, has been estimated for the Lavinio-Tor Caldara area by a detailed soil CO2 flux survey (2572 measurement points over an area of 3.65 km(2)). The main structural lineaments of the area have N-S and W-E directions, but also NE-SW and NW-SE directions are well represented. Some sectors of the investigated area are exposed to a severe gas hazard for people and animals and precautionary measures should be adopted. (C) 2020 Elsevier B.V. All rights reserved.

Tor Caldara natural reserve hosts the southernmost discharge of endogenous gas of Colli Albani volcano (mostly CO2 with a relevant H2S content up to 6.3 vol.%). Gas discharges in zones where past sulfur mining removed the impervious surficial cover (e.g. Miniera Grande and Miniera Piccola) and along tectonic fissures. A structural study of the reserve has shown the presence of two zones with different characteristics: prevailing directions N-S and N30 degrees in the northern zone; E-W and N60 degrees in the southern one. In March-July 2012 a geochemical study was carried out, including a soil CO2 flux survey and continuous monitoring (from 2 to 11 days) of air concentration of CO2 and H2S in 12 sites of the reserve. Environmental parameters were also monitored. Total diffuse soil flux of endogenous CO 2 was estimated to 17.48 ton*day(-1) from 1,259 measurements over a 0.47 km 2 surface, with 6.56 ton*day(-1) only from Miniera Grande. This is the second highest value of soil CO2 flux at Miniera Grande, after that of 2005 (9.25 ton*day(-1)) and is significantly higher than in 2009 (1.20 ton*day(-1)). As both the 2005 and 2012 surveys were made shortly after earthquakes with epicentres near to Tor Caldara (max ML= 4.7 in 2005 and 3.5 in 2012), data confirm that soil CO2 flux increases during earthquakes because of seismic rock microfracturing and soil shaking. Hazardous air concentrations have been found only for H2S, up to immediately lethal values (565-1,124 ppm) and with potentially lethal values (>= 250 ppm) long persisting (up to 12h27') in several no wind nights. Instead, the CO2 air concentration remained always well below dangerous levels (maximum recorded value = 2.1 vol.%). The most hazardous gas releasing sites were found in Miniera Grande and in a small pond NE of Miniera Piccola, where the carcasses of mammals and other small animals are frequently found. The killer gas is H2S, and the dangerous sites should be appropriately fenced to prevent access to people and animals.

The Rome region contains several sites where endogenous gas is brought to the surface through deep reaching faults, creating locally hazardous conditions for people and animals. Lavinio is a touristic borough of Anzio (Rome Capital Metropolitan City) that hosts a country club with a swimming pool and an adjacent basement balance tank. In early September 2011, the pool and the tank had been emptied for cleaning. On 5 September, four men descended into the tank and immediately lost consciousness. On 12 August 2012, after a long coma the first person died, the second one reported permanent damage to his central nervous system, and the other two men recovered completely. Detailed geochemical investigations show that the site is affected by a huge release of endogenous gas (CO 2 ≈ 96 vol.% and H 2 S ≈ 4 vol.%). High soil CO 2 and H 2 S flux values were measured near the pool (up to 898 and 7.155 g·m −2 ·day −1 , respectively), and a high CO 2 concentration (23–25 vol.%) was found at 50–70 cm depth in the soil. We were able to demonstrate that gas had been transported into the balance tank from the swimming pool through two hubs connected to the lateral overflow channels of the pool. We show also that the time before the accident (60 hr), during which the balance tank had remained closed to external air, had been largely sufficient to reach indoor nearly lethal conditions (oxygen deficiency and high concentration of both CO 2 and H 2 S).

The Apennines chain is an active Neogene fold-and-thrust belt resulting from the westward subduction of the Adriatic microplate. Starting from the end of the Early Pleistocene, the chain was affected by an increase in regional uplift. Recent GPS data resolved uplift rates of 1-2 mm/yr for the whole Apennines, whereas, in the Adriatic flank, several studies estimated rates between 0.3 and 0.5 mm/yr over the last 1 Myr. A number of works investigated the evolution of the drainage systems along the Periadriatic margin of the Apennines providing long-term incision rates. Studies from the northern part of this sector reported uplift rates varying from 0.2 to 1.1 mm/yr, whereas only few studies concentrated on the central sector of the Adriatic flank of the Apennines, focusing mainly on the evolution of the lower reach of major rivers. This work aims to quantify the long-term rock uplift and incision rates of the eastern portion of the central Apennines through the analysis of the Tronto River basin. Because of its geologic and geomorphological configurations, this basin is an ideal test site to investigate the influence of tectonics and climate on the recent topographic evolution of the central Apennines. The basin extends, with a roughly WSW-ENE direction, from the inner sector of the chain to the Adriatic coast, crossing several tectonic structures such as the Amatrice extensional basin and the Acquasanta and Montagna dei Fiori anticlines. In particular, in the Acquasanta Terme area, the right flank of the Tronto River valley is characterized by fluvial and travertine deposits organized and exposed in several levels. In this work, we investigated the hydrography (river longitudinal profiles) and topography (swath profile, slope, and local relief) of the Tronto River basin coupling these data with field observations and geochronological analysis on the continental sediments (fluvial deposits and travertines) outcropping in the Acquasanta Terme area. To better characterize the nature of travertines, we performed geochemical characterization of three travertine-forming thermal springs obtaining their physico-chemical parameters, the percentage of dissolved gases, and the isotopes content. Finally, we applied a knickpoint celerity model to chronologically constrain the geomorphological evolution of the whole drainage system. The results show the occurrence of a continuous tectonic uplift (similar to 0.5 mm/yr) across the study area since Middle Pleistocene. The uplift, together with climate fluctuations, drove the incision (similar to 0.6 mm/yr) of the landscape and the delineation of the present drainage network. These data are consistent with previous estimates of uplift and incision rates in adjacent areas and provide new constraints on the Quaternary evolution of the central Apennines. This study highlights how the coupling of field surveys with morphometric and topographic analyses of a drainage system is crucial to understand and quantify the influence of tectonic and climate changes in shaping the landscape. (C) 2019 Elsevier B.V. All rights reserved.