Preliminary geochemical characterization of the Mts. Simbruini karst aquifer (Central Italy)

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

The seismic sequence of 30 May - 9 June 2016 in the geothermal site of Torre Alfina (central Italy) and related variations in soil gas emissions

In the framework of a medium-enthalpy geothermal exploitation project, seismicity and soil gas emissions have been monitored in the area of Castel Giorgio-Torre Alfina since 2014. A dedicated local seismic network deepened the knowledge of the natural local seismicity in terms of source mechanisms, high-quality event localization and magnitude estimation. From November 2014 to May 2016, 846 seismic events were recorded, with a magnitude range of Md 0.1-2.8 and hypocentres 4-8 km depth. On 30th May 2016 a Mw 4.3 earthquake occurred near Castel Giorgio, followed by almost 1700 aftershocks; the moment tensor solution depicts a WNW-ESE oriented normal fault. An overview of the epicentral distributions since 2014, highlights that the active tectonic structures are NE-SW and WNW-ESE orientated. The diffuse soil CO2 flux is monitored since 2013 in six target areas located around the future production and reinjection wells, in order to assess the level of background natural degassing. In all target areas the maximum value of soil CO2 flux has been recorded during the 2016 seismic sequence. However, the values of δ13C of the emitted CO2 indicated a shallow biological origin of the gas. At Torre Alfina, the Solfanare natural gas emission, with a CO2 dominated gas, has same composition of the gas hosted in the geothermal reservoir. Here, high values of diffuse soil CO2 flux were recorded. During the 2016 seismic sequence, the Solfanare gas was continuously analysed by an automatic gas- chromatographic station. Results show that apart from small perturbations, no significant compositional variations were recorded. The significant contribution of CLVD and isotropic components suggest a possible opening of fluid cracks below the geothermal reservoir hosted in fractured Mesozoic limestones. The seismo-tectonic scenario indicates that the Solfanare fault was not activated. Kinematics and orientation of the activated faults suggest a relationship with the Bolsena caldera collapsePublishedNapoli, Italy1IT. Reti di monitoraggi

Explosive volcanoes in the Mediterranean area: hazards from future eruptions at Vesuvius (Italy) and Santorini (Greece)

Santorini is the site of the famous Minoan eruption of the late Bronze Age and Vesuvius is the type locality for Plinian eruptions. Hazards from the eruption most likely to occur in the near future at these volcanoes are discussed. Downwind zones of Santorini can be affected by minor ash fallout and gas emission from a Vulcanian eruption of Nea Kameni, the most active post-caldera vent. More dangerous would be a sub-Plinian eruption from Columbus, a submarine volcano located 8 km NE of Santorini, whose eruption in 1649-1650 A.D. caused several casualties in Santorini, mostly by wind transported poisoning gas. Vesuvius last erupted in 1944 and its eruptive history includes periods of long quiescence, lasting centuries or tens of centuries, interrupted by violent Plinian or sub-Plinian eruptions. A sub-Plinian eruption is the reference event in the Civil Protection emergency plan. The scenario includes a Red Zone exposed to the risk of being invaded by pyroclastic flows and that should be entirely evacuated before the eruption onset, together with some nearby areas where there is a high risk of roofs collapse by overloading of fallout tephra (nearly 700,000 persons in total). The Red Zone is encircled by the Yellow Zone exposed to pyroclastic fallout and related risk maps are here commented. Another serious risk is associated with earthquakes of the pre-eruptive unrest phase. Because of the high seismic vulnerability of the buildings within the Red Zone, many of them might collapse before the evacuation order of the Red Zone be issued. Finally, the scientific difficulty of forecasting the time evolution of the eruption precursory phenomena is discussed together with the related civil protection implications

Foreword Special issue: Explosive Eruptions and the Mediterranean Civilizations through Prehistory and History

Since the origin of humanity volcanism and human life have been strictly linked to each other. Despite the hazards posed by volcanoes, humans have always found good reasons for settlement and development around them, at least in temperate zones, because of high soil fertility or for the presence of ore deposits and the abundance of volcanic rocks that are good building materials

Estimation of the geothermal potential of the Caldara di Manziana site in the Mts Sabatini Volcanic District (Central Italy) by integrating geochemical data and 3D-GIS modelling

The Tyrrhenian margin of central Italy is an area characterized by crustal thinning (300 mW/m2), which makes it attractive for medium to high-enthalpy geothermal projects. The main difficulties encountered in the geothermal exploitation of the area are not related to the thermal conditions, but rather to the lack of an adequate rock permeability at depth. The medium-high enthalpy geothermal reservoirs of central Italy are hosted in Mesozoic carbonate-evaporitic rocks. These rocks exhibit secondary fracture permeability, locally reduced by self-sealing processes, especially in areas of low seismicity. Also, a low partial pressure of CO2 (PCO2) may facilitate the complete sealing of the reservoir fractures, preventing the ascent of hot fluids and resulting in a low CO2 flux at the surface. Conversely, a high CO2 flux reflects a high pressure of CO2 at depth, that is suggestive of the presence of an active geothermal reservoir. Despite the possibility that also part of CO2 be dissolved into groundwater, a large amount of this non-condensable gas will reach the surface being emitted into the atmosphere by discrete manifestations (gas vents) or through diffuse soil emissions. This is particularly true in sites -such as Caldara di Manziana, hereafter (CM) characterized by cold-gas emissions, which have CO2 concentrations up to 97 vol. %. In this paper we present the results of a study carried out in the western zone of Sabatini Volcanic District (SVD; north of Rome, Italy) that hosts CM (and also Solfatara di Manziana-SM), one of the most spectacular CO2 gas manifestations of central Italy. This study estimated the temperature and pressure conditions of the reservoir and the depth of its top using geological, geochemical and geophysical data and the TIN (triangulated irregular networks) interpolator provided in the ArcGIS for Desktop software. A new structural setting of the Mesozoic carbonates in the CM site is proposed, and an estimation of its geothermal potential is presented on the base of the total (diffuse and viscous) CO2 release.PublishedWien, Austria6A. Geochimica per l'ambient

The sealing capacity of the cap rock above the Torre Alfina geothermal reservoir (Central Italy) revealed by soil CO2 flux investigations

Torre Alfina is a medium enthalpy (T = 140 °C) geothermal field in Central Italy, hosted in buried fractured Mesozoic limestones, extensively explored in the 1970s and 1980s, but which so far has not been exploited. A detailed diffuse soil CO2 flux investigation (1336 measurements over a surface of 12.6 km2) and the periodic monitoring of soil CO2 flux from target areas indicate that in most of the area, even above a pressurized gas cap existing at the reservoir top, the soil CO2 flux is low and mostly within the background threshold (48 g m−2 day−1) and is likely generated by biological soil respiration. Anomalous values (up to 30.250 g m−2 day−1) are found only in the proximity of a small zone with gas vents whose composition is identical to that of the gas produced by the geothermalwells tapping the reservoir. This is the only zonewhere a fault connecting the deep geothermal reservoir with the surface does exist. These data are compared with those of the near Latera high enthalpy geothermal field (T = 210 °C), where anomalous soil CO2 flux is recorded above the productive reservoir. The difference of soil CO2 release in the two fields is attributed to the differences in the impervious cover (allochthonous flysch deposits) above the carbonate reservoir, which is thin and locally lacking at Latera, and continuous and thick (N400 m) at Torre Alfina. Results demonstrate that soil CO2 flux investigations are useful in geothermal exploration, but only high flux values likely indicate the presence of a geothermal reservoir at depth, whereas low flux values can indicate either the lack of an active geothermal reservoir at depth or the presence of a very effective impervious cover above the reservoir

Faulting and Gas Discharge in the Rome Area (Central Italy) and Associated Hazards

The area of Central Italy around Rome contains natural gas discharging zones and severalothers where quarrying or mining excavation removed the impervious superficial layers allowing a freehazardous discharge to the surface of endogenous gas. These gas manifestations are mostly located aboveburied structural highs of fractured Mesozoic limestones hosting the main regional aquifer and revealed bygravity anomalies. In the last decades, many gas blowouts occurred in this area, from wells whose depthranged from 10–15 to 350 m. The main component of the emitted gas is CO2with minor H2S; only in ablowout offshore of Fiumicino CH4prevailed. Several animals even of large size and two persons were killedby the emitted gas (mostly by H2S), and nearby houses were evacuated because of dangerous indoor CO2concentrations. He and CO2‐carbon isotopes suggest that gas has a deep mantle signature, as indicatedfor Fiumicino gas by N2isotopic composition and N2/36Ar ratios. Gas rising from depthfirst accumulates inthe buried Mesozoic limestone reservoir, and from there it escapes along deep‐reaching faults. On its way tothe surface, the gas dissolves into and pressurizes any encountered confined aquifer, which may thenproduce a gas blowout when reached by wells. The main direction of the gas feeding faults was estimatedthrough the alignment of visible gas emissive points, the shape of the positive anomalies in soil CO2fluxmaps, and new structural‐geological observations,finding that they correspond mostly to the mainorientation of the underlying limestone structural high.Published941-9596V. Pericolosità vulcanica e contributi alla stima del rischioJCR Journa

Data set on monitoring of air CO2 and H2S concentration and environmental parameters continuously recorded at Tor Caldara (Anzio, Rome) in March-July 2012

Istituto Nazionale di Geofisica e VulcanologiaUnpublished6V. Pericolosità vulcanica e contributi alla stima del rischi

Fluid Geochemistry Contribution to the Interpretation of the 2011–2012 Unrest of Santorini, Greece, in the Frame of the Dynamics of the Aegean Volcanic Arc

An edited version of this paper was published by AGU. Copyright (2019) American Geophysical UnionTectonic and magmatic activity may couple at volcanic arcs, even though any relationship is less defined in smaller arcs, experiencing limited activity. Here we use gas geochemistry data collected during the 2011–2012 unrest at Santorini (Greece) to understand better the dynamics of the Aegean Volcanic Arc with regard to its tectonic setting. Since the most recent eruption in 1950 and before the unrest, minor seismicity and CO2 degassing (mainly from the fumaroles of Nea Kameni islet) were observed at Santorini. On January 2011, anomalous seismicity along the NE‐SW trending Kameni Line was accompanied by an inflation north of Nea Kameni. Fumarolic gas composition changed and gas release notably increased. We carried out geochemical study on both Kameni and Thera islands from January 2012 to June 2013. We repeated surveys of diffuse soil CO2 degassing and of in‐soil gas concentration, and we analyzed fumaroles and gas dissolved in thermal waters for chemical and isotopic composition. In agreement with previous studies, our geochemical data, particularly the diffuse soil CO2 flux increase, the increase of H2 content, and of CO2/CH4 and 3He/4He ratios in fumarolic gases, support geophysical data in indicating that unrest was associated with the emplacement of new mafic magma. This unrest had limited effect on the regional setting, with gas emissions focusing along the regional NE‐SW structures, without triggering by any seismic event, conversely to the 1950 eruption, which probably occurred in a frame of general tectonic reorganization of the Aegean microplate.Published1033-10492V. Struttura e sistema di alimentazione dei vulcani4V. Processi pre-eruttivi6V. Pericolosità vulcanica e contributi alla stima del rischioJCR Journa