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The area of Central Italy around Rome contains natural gas discharging zones and several others where quarrying or mining excavation removed the impervious superficial layers allowing a free hazardous discharge to the surface of endogenous gas. These gas manifestations are mostly located above buried structural highs of fractured Mesozoic limestones hosting the main regional aquifer and revealed by gravity anomalies. In the last decades, many gas blowouts occurred in this area, from wells whose depth ranged from 10–15 to 350 m. The main component of the emitted gas is CO2with minor H2S; only in a blowout offshore of Fiumicino CH4prevailed. Several animals even of large size and two persons were killed by 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 indicated for Fiumicino gas by N2isotopic composition and N2/36Ar ratios. Gas rising from depth first accumulates in the buried Mesozoic limestone reservoir, and from there it escapes along deep‐reaching faults. On its way to the surface, the gas dissolves into and pressurizes any encountered confined aquifer, which may then produce a gas blowout when reached by wells. The main direction of the gas feeding faults was estimated through the alignment of visible gas emissive points, the shape of the positive anomalies in soil CO2flux maps, and new structural‐geological observations, finding that they correspond mostly to the main orientation of the underlying limestone structural high. Rome region contains several zones with anomalous and hazardous emission of endogenous gas brought to the surface by deep‐reaching faultsAt least 10 dangerous gas blowouts from shallow wells have occurred in the Rome area in the last 30 yearsAlignment of soil gas anomalies and vents indicates that gas raises along faults controlled by buried Mesozoic carbonate structure

Tectonic 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 CO2degassing (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 CO2degassing 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 CO2flux increase, the increase of H2content, and of CO2/CH4and 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. Extensive and systematic geochemical surveys followed the anomalous degassing during Santorini unrest, both in the caldera center and on the inner caldera wallsGas ratios and isotopic composition indicate deep mafic magma refilling into the shallow dacitic plumbing systemUnrest has limited apparent relations with the longer‐term tectonic evolution of the Arc, conversely to the 1950 eruption

La Fossa quiescent volcano and its surrounding area on the Island of Vulcano (Italy) are characterized by intensive, persistent degassing through both fumaroles and diffuse soil emissions. Periodic degassing crises occur, with marked increase in temperature and steam and gas output (mostly CO2) from crater fumaroles and in CO2soil diffuse emission from the crater area as well as from the volcano flanks and base. The gas hazard of the most inhabited part of the island, Vulcano Porto, was investigated by simulating the CO2dispersion in the atmosphere under different wind conditions. The DISGAS (DISpersion of GAS) code, an Eulerian model based on advection‐diffusion equations, was used together with the mass‐consistent Diagnostic Wind Model. Numerical simulations were validated by measurements of air CO2concentration inside the village and along the crater's rim by means of a Soil CO2Automatic Station and a Tunable Diode Laser device. The results show that in the village of Vulcano Porto, the CO2air concentration is mostly due to local soil degassing, while the contribution from the crater gas emission is negligible at the breathing height for humans and always remains well below the lowest indoor CO2concentration threshold recommended by the health authorities (1000 ppm). Outdoor excess CO2maxima up to 200 ppm above local background CO2air concentration are estimated in the center of the village and up to 100 ppm in other zones. However, in some ground excavations or in basements the health code threshold can be exceeded. In the crater area, because of the combined effect of fumaroles and diffuse soil emissions, CO2air concentrations can reach 5000–7000 ppm in low‐wind conditions and pose a health hazard for visitors. Volcanogenic carbon dioxide plume dispersion is simulated by a numerical codeAir CO2 concentration remains below the recommended threshold in inhabited areaIn the crater area CO2 air concentration may create breathing difficulties