The Cerro Pabellón geothermal power plant, located adjacent to the Cerro Pabellón Dome (CPD) and the Apacheta–Aguilucho Volcanic Complex AAVC (northern Chile), exploits a high-temperature geothermal system whose connection to regional magmatism and structural controls remains uncertain. This novel monitoring approach and industrial protocol aims to determine whether the Cerro Pabellón reservoir is an isolated system or if it is connected to deeper magmatic and hydrothermal sources within the Pabelloncito Graben. To address this question, the study combines two complementary approaches: (1) Advanced geothermal plant monitoring, integrating fumarolic and production steam geochemistry, gas geothermometry, and noble gas isotope analyses, (2) Updated field and laboratory igneous petrology techniques, including mineral-separate fluid inclusion studies and geothermobarometry datasets. Together, these methods are used within a structural and spatial framework to constrain both regional and local fluid pathways and heat sources at Cerro Pabellón. The results indicate that the reservoir is not a closed blind system. The Apacheta–Aguilucho Volcanic Complex hosts a lateral discharge vent hydraulically connected to a deep graben geothermal cell while maintaining a CO2-rich gas source. Isotopic noble gas chemistry confirms a compositional continuum with regional volcanic monitoring, characterized by low 3He/4He values (Rc ≈ 2.1 Ra). N2/He and He/Ar ratios define fault-controlled groups within the Pabelloncito Graben, indicating structural controls on contamination and fluid sources. Exploration wells located >500 m from major faults exhibit lower air/water contamination and compositions closer to the regional end-member (Rc/Ra = 1.7–2.1). Mineral geothermobarometry and gas geochemistry indicate magma apophyses at depths <3.5 km. Mineral-separate noble gas signatures show CPD values <1.0 Ra and primitive Poruña mafic scoria cone values of 4.0–7.0 Ra, recording a regional mantle source of 6.4–7.9 Ra modified by degassing and polybaric fluid entrapment. Geothermobarometry (0.8–2.0 kb) indicates persistent Pleistocene-to-present magmatic heating, with deeper sources extending to >6.0 kb near the inferred Altiplano–Puna Magma Body (APMB) roof. These findings refine the geothermal model and improve exploration strategies by constraining spatio-temporal fluid transport.

Abstract Geothermal heat extraction at a binary plant, and associated plant lifetime, can be optimized through fluid monitoring of geothermal gases and natural system gas discharges. A novel gas monitoring tool for geothermal exploration and production-stage decision-making is presented, based on research conducted at Cerro Pabellón, Chile, following its internationally celebrated opening in 2017. The gas phase was studied over a period of 5 years using direct gas condensate sampling and an innovative application of principal component analysis combined with the uniform manifold approximation and projection (UMAP) method. Monitoring results show that gas composition varies during cooling of the vapor phase, with oxidation state (RH) increasing as vapor fraction (%) decreases. A subsequent increase in HCO₃2⁻ concentration was detected in condensate liquids measured by ion chromatography, reflecting progressive gas–liquid interaction. According to UMAP clustering and gas composition analysis, the N₂/Ar ratio in gas samples represents an effective pathfinder to monitor geothermal plant physico-chemical parameters. Gas compositional clusters of CO₂-rich gases (> 96.0%), mainly represented by the N₂/Ar ratio (N2/O2:CH4/CO2), show two clear trends in gas mixture fluctuations: cooling associated with a relatively hot (315 ± 45 °C) Apacheta-like gas mixture derived from the hydrothermal reservoir, relatively cooler fluids (Md = 252 ± 78 °C) varying in redox conditions (Md (LogH2/H2O) = − 3.33 ± 0.64 RH). These estimated thermo-redox conditions in tandem with vapor N₂/Ar ratio fluctuate distinctly along each vapor separation line segments (C, F, J, M), correlating strongly on vapor fraction (19–100 vol.%), with progressive cooling until reaching temperatures of 140–160 °C at the plant steam–brine separators. Gas compounds in equilibrium with CO₂-rich fluids represent critical indicators of reservoir and plant-scale processes. Monitoring and control of these gas compounds at geothermal plants can improve long-term maintenance strategies and sustainability of binary power plants through integration of condensate liquid surveillance and improved geostatistical analysis.

The Mombacho is a basaltic-andesitic composite volcano of Nicaraguan Quaternary volcanic chain. As no historical eruption has been recorded at Mombacho, there is no available information is about the depth of potential magma storage zones, or about the evolution of ascending magmatic fluids. However, this information is urgently needed given the current state of the volcano, which is showing signs of unrest. To acquire this knowledge, melt inclusions and pyroxene crystals in various Mombacho tephras were analyzed, along with the volcanic gases emitted by fumaroles in the crater. The major element compositions of the melt inclusions support, to a first order, a magmatic evolution controlled by the fractional crystallisation of olivine, pyroxene, plagioclase and titanomagnetite crystals. However, the compositional variability of the most mafic samples can only be explained by a source heterogeneity. Additional trace element analyses agree with this hypothesis but seem to highlight a migration of the most mobile elements with an aqueous phase. The composition of the clinopyroxene crystals and the H2O and CO2 contents of the melt inclusions reveal the presence of a complex main storage zone between 8.2 +/- 1.6 and 3.1 +/- 0.4 km. Degassing modelling also supports this architecture and indicates that the gases sampled in 2024 in the Mombacho fumarole come from depths similar to this large storage zone. In addition, the 2024 fumarole gas contents in SO2, H2O and CO2 are similar to those sampled around twenty years ago, highlighting the stability of the degassing and therefore of the underlying magmatic system.

The Callaqui volcano (south-central Chile) currently exhibits significant fumarolic activity, and its remains indicate that it has had substantial eruptive activity in the past. However, there is no prior knowledge about the fluids discharged by this volcano, which is critical for volcanic monitoring and subsequent understanding of associated volcanic hazards. This work presents the chemical and isotopic compositions of fumarolic gases from the Callaqui volcano (period 2017–2024) to identify the fluid source(s) and evaluate the physicochemical conditions operating at depth. Gases were collected by direct sampling, using Giggenbach bottles and condensation procedures. The temperature of fumarolic gases ranged from 86.3 to 215 °C, with a composition dominated by water vapor, CO2, and minor amounts of acid species (SO2, HCl, HF). Helium isotope ratios (5.13 to 6.69 Ra) suggest a significant contribution from MORB-like fluids, while δ13C-CO2 isotopes (−10.8 to −9.11‰ vs. V–PDB) suggest assimilation of carbon-bearing crustal compounds. These features suggest a magmatic-hydrothermal origin of Callaqui emissions. The magmatic source corresponds to a degassing magma chamber likely hosted in an intermediate portion of the crust, whereas the hydrothermal system is fed mainly by meteoric waters. Despite the apparent large size of the hydrothermal system, since the volcano is in a rainy and snowy area, magmatically derived species still reach the surface. As a result, partial scrubbing of magma-derived species is assumed at this volcano. Following geothermometric approaches, fumarolic gases indicate the presence of high-temperature magmatic-hydrothermal fluids, with a vapor phase equilibrated at 375–415 °C, as well as super-heated vapors up to 350 °C. Callaqui gases show an increase in the magmatic signal by the end of the study period, consistent with incandescent volcanic episodes and anomalous LP earthquakes reported in late 2021 and early 2022.

Degassing of deep-seated fluids is a key process occurring in orogenic systems, yet its sources and controlling mechanisms remain poorly constrained. The Carpathians represent a major degassing province in Europe, where CO2 emissions are concentrated in the Neogene-Quaternary volcanic arc and carbonate-rich flysch nappes along tectonized suture zones (Magura, Pieniny and Ceahl & abreve;u-Severin suture zone), while CH4 of mostly thermogenic origin dominates in the Outer Flysch belt. We present the first regional geochemical dataset and map of CO2 and CH4 emissions in the Western and Eastern Carpathians, integrating chemical and isotopic analyses with lithological and structural constraints. Helium isotopes reveal variable mantle-crustal mixing: elevated R/R-a values (>3) near long-dormant volcanic centres, especially Ciomadul, reflect persistent deep magmatic reservoirs with 60-70% mantle/magmatic He-3 input, whereas radiogenic He-4 signatures dominate non-volcanic flysch and metamorphic regions, producing low R/R-a values (similar to 0.02). CO2 acts as the primary carrier of mantle He, but metamorphic devolatilization of marls and carbonates at 5-20 km depth provides the principal crustal CO2 source, consistent with "orogenic CO2 degassing" described in other collisional belts. Degassing sites cluster along nappe boundaries and fault zones, where enhanced permeability enables rapid volatile ascent. Carbon isotopes and CO2/He-3 ratios confirm heterogeneous carbon sources of the CO2 gases emitted at the surface, with mantle and crustal inputs at different proportions. In general, the biogenic CO2 contributions are negligible, with the majority of samples plotting along a mantle-limestone mixing line, indicating significant crustal-derived CO2 up to 80-95% for non-volcanic areas, and 40-70% for volcanic areas. The carbon isotopes and CO2/He-3 ratios are variably modified by groundwater interaction (dissolution and precipitation processes). Mantle-derived He flux averages are 1.59 & times; 10(-13) g m(-2) s(-1) for Ciomadul volcano, 8.64 & times; 10(-14) g m(-2) s(-1) for the Eastern Carpathians volcanic area and 3.46 & times; 10(-14) g m(-2) s(-1) for the Eastern Carpathians non-volcanic area. CO2 fluxes show average values of 1.4 & times; 10(6) g km(-2) y(-1) for the Ciomadul volcanic area, 1.18 & times; 10(8) g km(-2) y(-1) for the volcanic area of the Eastern Carpathians and 5.1 & times; 10(7) g km(-2) y(-1) for the non-volcanic area of the Eastern Carpathians. Mantle-derived He fluxes coupled with CO2/He-3 indicates a 4.66 Mt. year(-1) mantle CO2 flux for the Carpathians. These values match with other active orogens, highlighting the Carpathians as a key setting to investigate volatile transport, crust-mantle interactions, and their contribution to the global carbon cycle.

Within the framework of SANTORY (SANTORini’s seafloor volcanic observatorY) project, funded by the Hellenic Foundation for Research and Innovation and with the financial support of the Municipality of Thira, three oceanographic cruises were performed in December 2022 and June and October 2023, with the research vessels PHILIA and AEGAEO of the HCMR at the submarine volcano Kolumbo, 7 km NE of Santorini. Kolumbo is considered to be one of the most active submarine volcanic complexes in the Eastern Mediterranean Sea, while being easily accessible from land.. The oceanographic surveys were mainly aimed at the deployment of a new generation observatory along with several multiple innovative sensors such as temperature sensors, inclinometers, pressure gauges, optical cameras, multispectral and stereo camera, radioactivity sensor gSniffer and the γ-radiation imager. During the surveys, several water column profiles were also performed in order to collect seawater samples for chemical analysis. At the bottom of the Kolumbo crater (500m depth), acidic and slightly reducing conditions prevail, due to the presence of several active hydrothermal vents. This agrees with previous studies and with the data recorded by the deployed observatory. Collected samples have been analyzed for the chemical and isotope (carbon, helium and argon) composition of the dissolved gases as well as for the major, minor and trace element concentrations. The results indicate that the morphology of the crater allows the buildup of persistent anomalies that extend from the bottom up to the lowest crater-rim level at about 250-meter depth. We will discuss the temporal variability of the Kolumbo venting dynamics and the explore in detail the resulting vertical gradients in the crater funnel.

Risk mitigation in long‐dormant volcanic provinces is often hampered by the lack of information about potential eruptive scenarios. It is the case of the Monts Dore volcanic province (France), where the last eruptive sequence occurred about 7,000 years ago in lake Pavin. While the main recent interests focused on potential limnic eruption from the lake due to CO 2 storage in the deep‐water layer, no information is provided about the assessment of lava flow hazards. In this study, an innovative approach is led by coupling geochemical (soil CO 2 degassing) and geophysical (magnetism, electrical resistivity tomography) surveys to identify (hidden) areas and structures marked by fluid circulation and alteration processes. These preferential paths for current fluid ascent may be considered, due to their high permeability, as potential paths for magma ascent in case of volcanic unrest. In such a hypothetical scenario, a priori lava flow modeling can help in discriminating the most exposed infrastructural areas and thus provide new insights to local authorities regarding land use. Our results highlight that, even in long‐dormant volcanic provinces, common tools used on active volcanoes for risk assessment may be applied to improve relevant risk mitigation strategies.

Volcanic eruptions stand as formidable threats to adjacent communities, unleashing a spectrum of hazards such as earthquakes, tsunamis, pyroclastic flows, and toxic gases. The imperative for proactive management of volcanic risks cannot be overstated, particularly in densely populated areas where the potential for widespread devastation looms large. Kolumbo, an active submerged volcano located approximately 7 kilometers northeast of Santorini Island in Greece at 500m depth, serves a pertinent case. Its historical record is marred by an eruption in 1650 AD which triggered a relentless tsunami. The aftermath witnessed havoc on neighboring islands, coupled with casualties stemming from noxious gases in Santorini. Eyewitness accounts mention maximum water run-up heights of 20m on the southern coast of Ios, a staggering 240m inundation on Sikinos, and a disconcerting flooding of up to 2km² of land on the eastern coast of Santorini.Recent studies suggest that a potential future explosive eruption of Kolumbo poses a substantial hazard to the northern and eastern coasts of Santorini. Unfortunately, the absence of a concrete management protocol, leaves these areas vulnerable to an impending threat that demands immediate attention. Therefore, it is recommended that a comprehensive approach be adopted, involving scientific research (active monitoring, hazard maps), community engagement, preparedness planning with government agencies, and the development of timely response strategies to reduce the associated risks, prevent casualties, and mitigate the consequences on the region's economy and infrastructure. Our team has multidisciplinary data from past oceanographic expeditions that will help us to understand Kolumbo’s behavior. These include a) High-resolution multibeam bathymetry data and optical data., b) a dense network of sub-seafloor seismic reflection profiles, c) a series of the seafloor and sub-seafloor samples of microbial mat and sediments, d) CTD data, e) several polymetallic (Au, Ag, As, Sb, Pb, Hg, Mo, Zn, Cu, Tl) CO2 diffuser chimney samples and f) tephra in marine sediment cores. Despite the current knowledge that we managed to obtain, monitoring is needed to efficiently assess potential hazards and create early warning systems and management protocols for an imminent eruption from Kolumbo. In the current context, advanced sensors have been deployed to monitor Kolumbo's active hydrothermal field as part of the SANTORY project. The SANTORY project aims to create innovative communication tools and establish interregional monitoring protocols, providing the scientific community, policymakers, and stakeholders with the means to assess hazard warning codes effectively.

The underwater volcanic activity associated with deep-seated mantle processes represents a primary driver of the chemical and biogeochemical evolution of the global oceans. Hydrothermal activity is often a manifestation of submarine volcanism, where fluxes of heat and magmatic volatiles confer both potential hazard and opportunities of resource exploitation. Despite this, research on shallow submarine arc volcanoes is still in an early stage and only a few continuous seafloor observing infrastructures have been developed until now. The Kolumbo underwater volcano, located in the Aegean Sea, hosts one of the most active and dynamic hydrothermal vent fields, marking it - along with the proximity to the world-known Santorini island - a severe geohazard for a combination of reasons. Within the framework of the SANTORY (SANTORini’s seafloor volcanic observatorY) project, funded by the Hellenic Foundation for Research and Innovation and with the financial support of the Municipality of Thira, between 2022 and 2023, three oceanographic cruises were performed on submarine Kolumbo volcano. The oceanographic surveys were mainly aimed at the deployment of integrated operating sensors of state-of-the-art technology, for in situ monitoring. A new-generation stand-alone multiparametric observatory has been developed at INGV Palermo and deployed at the bottom of the crater (500 meters depth) for the first time in December 2022. The battery powered module has been able to operate autonomously for a 10-month-long period, collecting a dense, heterogeneous dataset able to describe the activity of the hydrothermal reservoir, highlighting its intense dynamic along the time.In June 2023, the observatory was recovered and re-deployed after brief maintenance operations including battery charging and data downloading. Finally, in October 2023, the observatory was definitely recovered.Here we present for the first time a mid-term-long chemical-physical data series acquired (pH, temperature, hydrostatic pressure, turbidity, conductivity, dissolved methane) along with passive acoustic and the preliminary findings of the system evolution within the observing window. A variety of local VT events likely sourced in the deeper portion of the plumbing system, together with several other minor seismic events related to fluid dynamics inside “fluid-filled” cracks and conduits has been revealed by passive acoustic data. Moreover the acoustic sensor recorded all the signals generated by the bubbles along the water column. The obtained results gave back an up to date picture of the ongoing Kolumbo degassing dynamics, hydrothermal and seismic activity.

Forecasting changes in volcano activity requires a detailed understanding of magma plumbing architecture and dynamics in terms of geometry, distribution and connectivity of the magma bodies and magma properties. This is mandatory to apply effective monitoring strategies and deploy appropriate risk mitigations policies. The PGF's multidisciplinary approach, we have adopted over years on several volcanoes, combines the study and monitoring of petrography and mineral chemistry of erupted products, with the composition of fluids trapped in minerals and the study of gas emissions. This framework permits to constrain magma evolution and dynamics within a volcano plumbing system over a very large range of pressure, temperature and compositions, and on a large range of time scales and frequencies of eruptive events. Here we review the most recent results obtained on two active volcanic systems (Piton de la Fournaise and Mayotte) located in the Indian Ocean, formed in distinct geodynamic settings and with very contrasting eruption rates, volumes, and dynamics, but sharing a common feature: an important lateral shift of the magma ascent paths with respect to the eruptive sites and the coexistence of both evolved (phonolite to trachyte) and mafic (basalts to basanite) melts over a large depth range (from mantle to crust). We show that the most effective monitoring is obtained by focusing on the deepest parts of the plumbing system that allow recognizing and following new magma recharges, melt differentiation and degassing and magma lateral drainage. The occurrence already in the mantle and close to the Moho of variably evolved and degassed melts, besides primitive and volatile rich ones need to be carefully considered, in order to provide a robust interpretation of multidisciplinary monitoring datasets.

SANTORY is a state-of-the-art project dedicated to advancing submarine volcanic hazard monitoring and risk mitigation in the Aegean Sea. Located in Kolumbo submarine volcano, northeast of Santorini Island, this groundbreaking observatory employs advanced imaging, geophysical and geochemical measurements, and real-time monitoring technologies to address one of the most significant volcanic threats in the region.Over the past two years, SANTORY has provided unparalleled insights into Kolumbo’s geological dynamics and processes and potential hazards. High-resolution 3D mapping has identified steep slopes, mass-wasting deposits, and hydrothermal vent fields, crucial for assessing seafloor instability and the risks associated with eruptions and submarine landslides. Novel hyperspectral imaging and autonomous video systems have documented persistent hydrothermal venting, bubbling plumes, and environmental changes, offering a comprehensive baseline for tracking volcanic activity and geohazard precursors.Autonomous sensors on the crater floor have continuously monitored hydrothermal outflow temperature, pressure, and fluid chemistry, capturing variations driven by tides and magmatic activity. These continuous datasets are critical for identifying precursor signals of volcanic unrest, such as changes in subsurface permeability and magmatic degassing. Chemical and isotopic analyses of hydrothermal fluids have confirmed the degassing of CO2-rich fluids with a mantle-like 3He/4He signature, underscoring Kolumbo’s potential for hazardous eruptions and its significance as a high-risk volcanic system.SANTORY goes beyond scientific exploration; it is a transformative initiative aimed at improving volcanic hazard assessment and developing mitigation protocols. By integrating cutting-edge technologies and multidisciplinary expertise, the project delivers actionable insights to enhance early warning systems and protect vulnerable coastal communities.

During years 2021–2022, an unusual seismic swarm was recorded at crustal level beneath the Monts Dore volcanic province (France). Complementary field and remote measurements were performed. Together with the time series recorded on the seismological and GNSS national networks, these measurements were fundamental for monitoring the evolution of the seismic swarm and deciphering its origin. Although a potential vertical migration of the seismic events is suggested, the complementary measurements presumably discard the hypothesis of magma intrusion at shallow crustal level. The ascent of a CO2-rich fluid originating from the mantle might instead have reacted with the hydrothermal system beneath the Monts-Dore since at least the summer 2021 leading to the reactivation of pre-existing tectonic structures with known associated seismicity. Feedback on the management of the 2021–2022 seismic swarm prompts for several recommendations that should be considered in future to better face and address at the national level the issues raised at long-dormant volcanic provinces in mainland France.

This dataset provides a comprehensive geochemical characterization of gases emitted across the Romanian segment of the Eastern Carpathians, including both volcanic and non-volcanic areas. It comprises in situ measurements of CO2, CH4, and H2S at 143 degassing sites, including dry vents, bubbling pools, drillings, and mineral springs, supplemented by gas-chromatographic analyses of major components (CO2, CH4, N2) and isotopic measurements (3He/4He, δ¹³C (CO2)) at 50 selected sites. The sampling strategy spans a N–S transect of the region, capturing both CO2- and CH4-rich emissions, and providing detailed coverage of dormant volcanic and non-volcanic geological settings.Field measurements employed a portable Multi-GAS instrument with calibrated IR (for CO2 and CH4) and electrochemical (for H2S) sensors, ensuring high-quality in situ data. Laboratory analyses were conducted at Istituto Nazionale di Geofisica e Vulcanologia (INGV) Sezione Palermo, Italy and at HUN-REN Debrecen, Hungary, enabling robust characterization of gas compositions and isotopic ratios.This dataset represents a high-resolution geochemical resource for the Romanian segment of the Eastern Carpathians, offering extensive information on gas compositions, noble gas signatures, and carbon isotopes. It can be reused by researchers to investigate degassing processes, gas origins, fluid migration, and tectonic controls in dormant volcanic and non-volcanic regions. Furthermore, it provides a reference for comparative studies with other global degassing systems and supports modelling of deep carbon fluxes from dormant volcanic and non-volcanic environments.

The Tolhuaca Geothermal System (TGS) represents a potential 13 MWe geothermal reservoir located on the NW flank of Tolhuaca stratovolcano, in the Southern Volcanic Zone (SVZ) of the Andes. Despite decades of scientific exploration on the chemistry of its high-enthalpy surface geothermal system, the full understanding and connection to the underlying magmatic system has yet to be demonstrated. A novel combined approach studying gas emissions from the plume and fumarole has found that the TGS magma-gas component is dominated by CO2-rich fluids (relatively high CO2/H2S and CO2/CH4) that feed the fumaroles and exploration wells in the Amphitheater structure. Gas measurements near the summit of Tolhuaca show little atmospheric contamination (low CO2/Ar) but higher CO2/H2S ratios relative to fumaroles on the lower flanks, which may be caused by scrubbing effects on H2S within a hydrothermal reservoir at less than similar to 1.5 km beneath the surface (permeable geothermal zone). The atmosphere-corrected He-3/He-4 ratio (Rc/Ra) measured by bulk fluid inclusion (FI) analysis of olivines from the Cono Cancion minor eruptive center (6.40 +/- 0.38 Ra) is similar to other fumarole systems measured in the literature that are <400 m from the vent (6.49 +/- 0.05 Ra). The magma erupted from this center is andesitic to dacitic in composition. In addition, minor amounts of crustal-derived He-4 indicate alteration of the initial 3He-rich magmatic fluids (1.37.10(-9) CO2/He-3). In contrast, fluid inclusions from olivines in the syn-glacial Tolhuaca Fissural eruptive center give values of 8.16 +/- 0.63 Rain (typical SVZ regional MORB signature), corresponding to basaltic-to-basaltic andesite melt which has preserved the magmatic He-3 in fluid inclusions (2.64.10(-8) CO2/He-3). For the first time in this volcano, we use melt inclusions (MI) to investigate the magma-volatile component of a magmatic plumbing system in the context of geothermal exploration (parental melts contain 1.94 wt% H2O, 2496 mu g/g CO2, 142 mu g/g S, and 1095 mu g/g Cl). The volatile dataset from the naturally quenched melt inclusions agrees with decompression and degassing models, interpreted here as resulting from magmatic release of water and oxidized sulfur at depths of 1.08-1.8 km, inferred to be the primitive vapor feeding the geothermal vapor zone. This is a few tens of meters below the water boiling point identified in past exploration well studies at TGS (0.95 km). This new solubility model provides a means of combining geothermal exploration with location of magma depth, and of geochemically characterizing the narrow vertical window between the base of characteristic hydrothermal convection cells and the roof of the underlying magmatic system in other high enthalpy geothermal systems around the world.

Tectonic structures such as faults and fractures act as preferential pathways for gas ascent and their consequent release into the atmosphere. Magma-derived gases are widespread throughout the western Eger Rift (Czech Republic), an intraplate region without active volcanism but with the occurrence of mid-crustal earthquake swarms. Geogenic CO2 discharges from the Počatky–Plesná fault zone (PPZ), Mariánské Lázně Fault (MLF), Bad Brambach (BB), and a deep local fault (DLF) have been sampled since 2021. Gases were analysed for their chemical (CO2, N2, O2, Ar, He, CH4, and H2) and isotopic contents (noble gases, CO2, and CH4). Results showed that CO2 is the dominant gas species (concentrations > 99.4%), with the remaining gases being present in minor amounts. The He isotopic composition for gas samples from the PPZ and MLF is typical for the subcontinental lithospheric mantle (SCLM - with 3He/4He ratios between 5 and 6 RA), while gases from BB and the DLF show a lower mantle input (3He/4He is 3.2 and 2.4 RA, respectively). δ13CCO2 data reflect a SCLM CO2 signature (-4 to -1 ‰ vs. V-PDB). First CH4 isotopic data present values between -52.0 and -47.1 ‰ vs. V-PDB for δ13CCH4 and between -307 and -284 ‰ vs. V-SMOW for δ2HCH4. With the exception of samples collected from the MLF that show a clear thermogenic CH4 origin, all the other samples present isotopic values and CH4/(C2H6+C3H8) ratios that suggest a likely biogenic origin, with secondary processes playing a crucial role on the gases’ isotopic signature. It should be noted that low CH4concentrations (

The Alpehue Hydrothermal Field (AHF) near the Sollipulli Volcano in the Southern Volcanic Zone of Chile shows promise as a significant geothermal resource. A comprehensive geothermal exploration survey was conducted, including the evaluation of hydrothermal gases, geothermometer calculations, and CO2 flux measurements, to assess the AHF's geothermal potential. Our results indicate that the hydrothermal gasses at the AHF primarily originate from primitive, mantle-derived sources, with some contribution from crustal sediments. Two different CO2 populations of fluxes were identified. One corresponds to the background emission related to the soil biological activity (mean ∼7.7 g·m−2·d−1), and the other, much more significant, emanates from an endogenous source related to the Alpehue hydrothermal reservoir (mean ∼461 g·m−2·d−1). Reservoir temperatures were calculated using gas geothermometry yielding average temperatures of 249 °C. The calculated heat flow rate of the AHF is approximately 3.3 MW and the heat flux corresponds to 156 thermal MW⋅km−2, which could be considered a medium geothermal potential comparable to other systems worldwide. Although further studies are needed to fully address its exploitability, this study presents favorable characteristics of the AHF that make it a promising avenue for further exploration.

Abstract Carbon dioxide is a key gas to monitor at volcanoes because its concentration and isotopic signature can indicate changes to magma supply and degassing behavior prior to eruptions, yet carbon isotopic fluctuations at volcanic summits are not well constrained. Here we present δ13C results measured from plume samples collected at Stromboli volcano, Italy, by Uncrewed Aerial Systems (UAS). We found contrasting volcanic δ13C signatures in 2018 during quiescence (−0.36 ± 0.59‰) versus 10 days before the 3 July 2019 paroxysm (−5.01 ± 0.56‰). Prior to the eruption, an influx of CO2‐rich magma began degassing at deep levels (∼100 MPa) in an open‐system fashion, causing strong isotopic fractionation and maintaining high CO2/St ratios in the gas. This influx occurred between 10 days and several months prior to the event, meaning that isotopic changes in the gas could be detected weeks to months before unrest.