The ratio between fumarole gas species of predominant magmatic origin (i.e., CO₂, He) and CH₄, which is typically produced in the hydrothermal environment, is a powerful indicator of the upflow of magmatic fluids towards the surface. The analysis of time series of fumarolic composition from different dormant volcanoes (e.g., Campi Flegrei, Vesuvius, Vulcano, Panarea, Nisyros, Mammoth Mt) reveals similar anomalous peaks of the CO₂/H₂O, CO₂/CH₄, and He/CH₄ ratio during unrests, suggesting recurrent events of magma degassing. The sudden upflow of deep magmatic fluids causes pressure buildup and heating of the hydrothermal systems, earthquakes and ground deformations, which precede the fumarole gas compositional anomalies. These anomalies, once normalized to the time and to the amplitude of the curve, show the same shape: a rapid increase in the geochemical indicator followed by an exponential decrease.

An intriguing consideration based on these examples (almost all the volcanoes for which a long time series of fumarolic compositions are available) is that episodes of magma degassing probably reflect the normal background activity of volcanoes, making the interpretation of volcanic unrests challenging. Concurrently with magma degassing events, a significant increase in the CO₂ degassing process was either measured or qualitatively observed in these systems. A better knowledge of these degassing episodes is needed to improve our understanding of the volcanic behavior and to better constrain the release of CO₂ from quiescent volcanoes.  

How to cite: Chiodini, G., Bini, G., and Caliro, S.: The hidden activity of volcanoes: magma degassing events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4308, https://doi.org/10.5194/egusphere-egu23-4308, 2023.

The Nisyros caldera is located in the easternmost part of the South Aegean Volcanic Arc (SAVA), which formed in the seismically active region of the Aegean and has been site of violent explosive eruptions in the last 160 ky. Two 2–3 km³ dense-rock equivalent silicic explosions caused the collapse of the Nisyros volcanic edifice 60 ka, and were followed by effusive eruptions until 20 ka. More recently, the interplay between an upper-crustal magma reservoir and an active hydrothermal fluid circulation has led to hydrothermal explosions (the most recent in 1887), concurrently with periods of enhanced seismicity. In 1996–1997, a cluster of earthquakes at shallow depth (<10 km) affected the Nisyros area, growing concern for new hydrothermal/volcanic activity. Here, we compare new fumarole chemical and isotopic compositions (2018–2021) with previous data to gain new insights into the state of the magmatic-hydrothermal system and reconstruct its dynamics during the 1996–1997 seismic crisis. New N₂, He, and Ar contents and isotopes show that Nisyros gases are mixtures of magmatic fluids typical of subduction zones, groundwater (or air saturated water, ASW), and air. The composition of the magmatic endmember is calculated through reverse mixing modeling, and shows N₂/He = 31.8 ± 4.5, N₂/Ar = 281.6, δ¹⁵N = +7 ± 3‰, ³He/⁴He = 6.2 Ra (where Ra is air ³He/⁴He), and ⁴⁰Ar/³⁶Ar = 552 ± 20. Although N₂/He is significantly low with respect to typical values for arc volcanoes (1,000–10,000), the contribution of subducted sediments to the SAVA magma generation is reflected by the positive δ¹⁵N values of Nisyros fumaroles. Hence, we suggest that the low N₂/He ratio is not ascribed to the absence of subducted sediments, as previously thought, but to a N₂-depletion due to solubility-controlled differential degassing of an upper-crustal silicic (dacitic/rhyodacitic) reservoir at high-crystallinity. N₂, He, and Ar data reveal clear additions of both magmatic fluid and ASW during the unrest. In the same period, fumarolic vents display a significant increase in magmatic species relative to hydrothermal gas, such as CO₂/CH₄ and He/CH₄ ratios, an increase of ~50 °C in the equilibrium temperature of the hydrothermal system (up to 325 °C), and greater amounts of vapor separation, estimated through the H₂O-H₂-CO-CO₂-CH₄ gas system. These variations reflect an episode of magmatic fluid expulsion during the seismic crisis. The excess of heat and mass supplied by the magmatic fluid injection is then dissipated through boiling of deeper and peripheral parts of the hydrothermal system, without culminating in hydrothermal eruptions. Gas chemistry and reverse mixing modeling of N₂, He, and Ar have therefore important implications for monitoring magmatic-hydrothermal systems, as enable us not only to better understand the state of upper-crustal magma reservoirs, but also to track episodes of magmatic outgassing.

How to cite: Bini, G., Chiodini, G., Caliro, S., Tassi, F., Vaselli, O., Rizzo, A., Mollo, S., Vougioukalakis, G., and Bachmann, O.: Tracking episodes of outgassing from upper-crustal magma reservoirs through fumarole gas chemistry: the case of the Nisyros caldera (Aegean Arc, Greece), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4205, https://doi.org/10.5194/egusphere-egu23-4205, 2023.

Monitoring the volcanic activity of Teide, the only active stratovolcano in Tenerife, the largest island of the Canary Islands, is extremely important for the prevention and reduction of the volcanic disasters of the island. As part of the geochemical monitoring of the Teide volcanic activity, during the last three decades the volcano has been the subject of a geochemical monitoring of the fumarole discharges, characterized by low flux emission of fluids with temperatures of ∼83°C, located at the Teide summit crater (Pérez et al., 1992 and 1996; Melián et al., 2012). Teide fumaroles show chemical compositions typical of hydrothermal fluids, i.e., meteoric steam dominates the gas composition, followed by CO₂, N₂, H₂, H₂S, HCl, Ar, CH₄, He, and CO (Pérez et al., 1992). The temporal variations in fumarole gas chemistry at Teide volcano was useful to detect significant changes in the chemical composition of the Teide fumarole, including the appearance of SO₂, and increases in the HCl and CO concentrations, one year before a seismic crisis that occurred in Tenerife Island between April and June 2004, what suggested that the associated temporal changes in seismic activity and magmatic degassing indicate that geophysical and fluid geochemistry signals in this system are unequivocally related (Melián et al., 2012). The average of the air-corrected ³He/⁴He ratio during the period 1991-2022 was 6.80 R_A (being R_A the atmospheric ratio), with the maximum value of the time series (7.57 R_A) measured in August 2016, when an input of magmatic fluids triggered by an injection of fresh magma and convective mixing took place beneath Teide volcano (Padrón et al., 2021). After such input of magmatic fluids, increases in the CO₂/H₂O, C/S and He/CO₂ ratios, a decrease in the CO/CO₂ ratio were observed together with a significant increase in the seismic activity recorded in the island of Tenerife. This work highlights the important role of volcanic gases in the monitoring of volcanic activity, paying attention to different chemical and isotopic species in the fumarolic discharges.

Melián G.V. et al., (2012), Bull. VolcanoL. 74, 1465–1483.

Padrón E. et al., (2021), J. Geophys. Res. 126, e2020JB020318.

Pérez N.M. et al., (1992), Actas de las sesiones científicas. III Congreso Geológico de España, 1, 463–467.

Pérez N.M. et al., (1996), Geophys. Res. Lett. 23(24), 3531–3534.

How to cite: Padrón, E., Melián, G. V., Asensio-Ramos, M., Hernández, P. A., Pérez, N. M., Rodríguez, F., Amonte, C., Martín, A., D'Auria, L., and Sumino, H.: Temporal variations in fumarole gas chemistry at Teide volcano, Tenerife, Canary Islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5995, https://doi.org/10.5194/egusphere-egu23-5995, 2023.

Gas-sensor-based monitoring stations (aka MultiGAS) near degassing volcanic vents sensibly increased the sampling rate of gas composition measurements. In particular, the CO₂/SO₂ gas molar ratio was demonstrated to be a good indicator of magma depth thanks to the CO₂ and SO₂ contrasting solubilities in magma. Numerous high CO₂/SO₂ gas transients recorded days before an effusive/explosive eruption have been reported in the literature (e.g. Etna, Villarrica, Masaya, Poas). The successful detection of a precursor gas signal in these volcanoes has been favoured by the presence of open or highly permeable closed-conduit (as in the case of Poas) and the instrument’s vicinity to a high-flux degassing vent (high signal/noise ratio). Volcanic gas monitoring in Stromboli represents a particular case. Stromboli is characterised by degassing from multiple vents, which exhibit simultaneous different molar gas ratios during quiescent degassing. The gas emissions during transient strombolian explosions are also different, with higher CO2 contents. Stromboli occasionally exhibits major explosions and paroxysms of greater energy which have often shown a substantial variation of the gas bulk composition weeks before their onset. Finally, the safest sites for a monitoring station in Stromboli are located hundreds of meters from the crater terrace, implying that the detected gas concentrations depend on the wind direction and speed. All these features make the analysis and interpretation of the volcanic CO₂/SO₂ challenging. This work presents a 2-year-long CO₂/SO₂ time series recorded at the Stromboli’s summit. We discuss different types of analysis that can be performed to enhance the variations before major and paroxysmal eruptions. We apply an iterative algorithm to estimate the time, number and magnitude of abrupt changes within the CO₂/SO₂ time series and discuss the origin of such variations. We use an algorithm for finite mixture models on the whole dataset to characterise the source of different gas phases. Finally, we compare the measured CO₂ and SO₂ concentrations with the wind parameters obtained for the area of Stromboli from the ERA5 reanalysis dataset. Hence, we determine the best conditions for gas ratio measurements and how meteorological conditions may affect the measurements' quality.

How to cite: Tamburello, G., Bitetto, M., Delle Donne, D., and Aiuppa, A.: Insights from  CO2/SO2 gas molar ratio variations and distribution at Stromboli volcano, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14757, https://doi.org/10.5194/egusphere-egu23-14757, 2023.

Nyiragongo Volcano is located in the western branch of the East African Rift, in eastern Democratic Republic of Congo (DRC). Nyiragongo has gained fame thanks to its long-lived lava lake and the significant hazards it presents to the >1.5 million people living within <30 km, particularly the inhabitants of Goma (DRC) and Gisenyi (Rwanda).  These hazards include fast-moving lava flows produced during effusive eruptions (e.g., in 1977, 2002, and 2021) and regional environmental and health impacts from the persistent volcanic gas plume.

Continuous gas emissions at Nyiragongo present an opportunity for geochemical monitoring of the volcano during changes in activity, such as the recent 2021 flank eruption.  From late 2019 to the present (early 2023), we monitored plume H₂O-CO₂-SO₂-H₂S compositions at the summit and at the May 2021 flank vent using a portable multi-GAS (multiple Gas Analyzer System). Pre-eruption measurements from 2019 on the crater rim of Nyiragongo reveal two geochemical end-members: the lava lake gas plume characterized by CO₂/SO₂ ratios of 50-60 and crater fumaroles characterized by CO₂/SO₂ ratios up to 300 and a trace of H₂S. Overall, the bulk composition of the summit gases was 39.31-70.34% H₂O, 29.52-59.93% CO₂ and 0.14-0.76% SO₂, within the range of plume compositions reported by Gerlach (1979). At the May 2021 eruptive vent, located ~3 km from the summit on the volcano’s southern flank, measurements in August 2021 (after the eruption had ceased) reveal more C-poor gases with a CO₂/SO₂ ratio of 21.90 and a bulk composition of 95.41% H₂O, 4.35% CO₂ and 0.32% SO₂. The reappearance of the lava lake in the main summit crater in late September 2021 was accompanied by a decrease in the CO₂/SO₂ ratio to 5 at the May 2021 eruptive vent.  These results show that measuring the changes in plume composition by multi-GAS improves monitoring of Nyiragongo. In the future, we plan to deploy a permanent multi-GAS station at the summit of Nyiragongo to carry out much needed continuous geochemical monitoring. 

Key words: Nyiragongo Volcano, volcanic gases, volcano monitoring, multi-GAS, Plume chemistry

How to cite: Balagizi, C., Mashagiro, N., Kasereka, M., and Kelly, P.: Pre- and post-eruptive gas composition measurements at Nyiragongo Volcano, East Africa, using a portable Multi-GAS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16823, https://doi.org/10.5194/egusphere-egu23-16823, 2023.

Tenerife is the largest (2,034 km²) and highest (3,718 m) island of the Canarian archipelago and is the only one hosting an active stratovolcano (Teide-Pico Viejo volcanic system). Its structure is controlled by a volcanotectonic rift-system with NW, NE and NS directions, with the Teide-Pico Viejo volcanic system located in the intersection. The last eruption Teide-Pico Viejo volcanic system occurred in 1798 through an adventive cone. Although Teide volcano shows a weak fumarolic system, volcanic gas emissions observed in the summit cone consist mostly of diffuse CO₂ degassing (Hernández et al., 1998; Mori et al., 2001).

More than 200 diffuse CO₂ efflux surveys have been performed in the summit crater of Teide Volcano during the period 1999-2023. During each survey, diffuse CO₂ emission was estimated in 38 sampling sites, homogeneously distributed inside the crater, by means of a portable non dispersive infrared (NDIR) CO₂ fluxmeter using the accumulation chamber method. CO₂ emission rates was estimated after spatial distribution maps constructed by sequential Gaussian simulation (sGs) algorithm. During 23 years of the studied period, CO₂ emissions ranged from 2.0 to 346 t/d. The most remarkable feature of the temporal evolution of diffuse CO₂ emission rate was an important increase that began few weeks after the occurrence of a seismic swarm of long period events was recorded on Tenerife in 2 October 2, 2016, a followed by a general increase of the seismic activity in and around the island (D’Auria et al., 2019). Several geochemical parameters showed significant changes during ∼June–August of 2016 and 1–2 months before the occurrence of the October 2, 2016, long-period seismic swarm (Padrón et al., 2021). Since then, anomalously high diffuse CO₂ emission rates has remained in the crater of Teide. This change might be explained as an input of magmatic fluids triggered by an injection of fresh magma and convective mixing after the 2 October 2016 seismic swarm (D'Auria et al., 2019; Padrón et al., 2021). This work reflects how useful are the diffuse studies to understand the behaviour of the volcanic system and to forecast future volcanic activity. Monitoring the diffuse degassing rates has demonstrated to be an essential tool for the prediction of future seismic–volcanic unrest and has become an important monitoring tool to reduce volcanic risk in Tenerife.

D'Auria, L., et al. (2019). J. Geophys. Res.124,8739-8752

Hernández, P., et al. (1998). Geophys. Res. Lett. 25, (17) 3311-3314

Mori, T., et al. (2001). Chem. Geol. 177, 85–99

Padrón, E., et al. (2021). J. Geophys. Res.126,e2020JB020318

How to cite: Amonte, C., Padrón, E., Melián, G. V., Asensio-Ramos, M., Rodríguez, F., Padilla, G. D., Barrancos, J., D'Auria, L., Hernández, P. A., and Pérez, N. M.: Anomalous diffuse CO2 emission from the summit crater of Teide volcano and changes of seismic activity in and around Tenerife, Canary Islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7410, https://doi.org/10.5194/egusphere-egu23-7410, 2023.

The Cape Verde Islands are a group of 10 intraplate oceanic islands of which 3 show significant levels of recent volcanic activity: Fogo, Santo Antao and Brava. Of these, Fogo is the only historically active volcano with intense activity up to 1725 AD followed by less frequent, mainly effusive eruptions in the last 280 years. The last eruption began on 23 November 2014, and continuing until 8 February 2015. This eruption occurred 19 years after the previous eruptive event, but on the contrary of the 1995 eruption, when there was not monitoring program for the Cape Verde volcanic surveillance, a simple and multidisciplinary volcanic monitoring program, based on a collaborative research volcano monitoring program between Cape Verde and Spanish scientists, was operative to face volcanic unrest such as the 2014 eruption. As part of this volcano monitoring program, from May 2007 to January 2015, forty eight diffuse CO₂ emission surveys were performed at the summit crater of Pico do Fogo, covering homogeneously an area of about 0.142 km². Measurements of diffuse CO₂ emission were performed at the surface environment following the accumulation chamber method. The emission rate was calculated after the construction of spatial distribution maps following the sequential Gaussian simulation (sGs) algorithm. The emission rate showed a first anomalous peak in the diffuse CO₂ emission, suggesting the occurrence of a first magmatic reactivation likely due to a deep magma intrusion beneath Pico do Fogo volcano between November 2008 and February 2009. Diffuse CO₂ emission data suggest the occurrence of a second magmatic intrusion that trigger the eruption process as can be observed by the significant increase of CO₂ emission on March 2014. The increment of the diffuse CO₂ emission rate shows a good temporal correlation with the satellite-based long-wavelength infrared data reported by Girona et al., (2021). The diffuse CO₂ emission data and satellite-based thermal infrared radiance measurements prior the 2014-15 Fogo eruption demonstrate the importance of measuring both parameters to identify and evaluate changes in the volcanic activity of Pico do Fogo volcano.

Girona, T. et al., (2021). Nature Geoscience 14, 238–241.

How to cite: Ortega-Ramos, V., Pérez, N. M., Dinardo, D., Pitti, L., Amonte, C., Asensio-Ramos, M., Pankhurst, M. J., Barrancos, J., Melián, G. V., Hernández, P. A., Silva, S., Montrond, E. J., and Cardoso, N.: Diffuse CO2 degassing and low-temperature anomalies prior the 2014-15 Fogo eruption, Cape Verde, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9895, https://doi.org/10.5194/egusphere-egu23-9895, 2023.

São Jorge is one of the nine islands of the Azores Archipelago. On March 19, 2022, a seismic crisis began in the island, with more than 32,300 earthquakes recorded until May 2022, of which nearly 300 were felt by the population. On April 5, 2022, an INVOLCAN team travelled to the Azores and, in collaboration with CIVISA/IVAR of the Universidade dos Açores, carried out a soil gas and CO₂ diffuse efflux survey to monitor the activity in this volcanic island. The absence of visible volcanic gas emissions (fumaroles, hot springs, etc.) at the surface environment of Manadas volcanic system -the most recent volcanic system in São Jorge- makes this type of studies an essential tool for volcanic surveillance purposes.

Soil CO₂ efflux was measured in 400 observation points on the island following the accumulation chamber method using a non-dispersive infrared LICOR-830 CO₂ analyzer. Soil gas samples were taken at 40 cm depth to study the chemical composition of diffuse emanations. The chemical composition of the gas samples (He, Ne, H₂, CO₂, CH₄, N₂ and O₂) was analyzed daily on the island by means of a micro-gas chromatograph (micro-GC).

The results reported herein are related to the soil He and H₂ degassing. The former has exceptional characteristics as a geochemical tracer while the second is one of the most abundant trace species in volcanic systems and it is fundamental in many redox reactions occurring in the reservoir gas. Mapping He and H₂ soil effluxes may be useful to detect hidden tectonic structures. In addition, detection of significant changes in the diffuse emission of both gases in volcanically active areas, as well as changes in their spatial distribution, is usually linked to movements of magma in the subsoil and/or changes in seismic-volcanic activity. These variations may be excellent early warning signals of changes in the activity of the system.

Spatial distribution maps of the diffuse flow of He and H₂ in the 237.59 km² area of the island were constructed following the sequential Gaussian simulation (sGs) procedure to quantify the diffuse He and H₂ emission from the studied area. He fluxes varied from 0 to 3.7 mg·m^-2·d^-1 (mean value, 0.4 mg·m^-2·d^-1), while H₂ fluxes ranged between 0 and 4.7 mg·m^-2·d^-1 (mean value, 0.15 mg·m^-2·d^-1). He and H₂ diffuse emission was estimated in 101 and 28 kg·d^-1, respectively, with diffuse degassing values of 0.369 and 0.102 kg·km^-2·d^-1.

The principal H₂ flux anomaly is in the central part of the island and coincides with the ground deformation obtained by synthetic aperture radar data acquired by the ESA Sentinel-1 satellite at the beginning of the crisis. He highest fluxes are dispersed in different areas and most of the highest values are located in the Manadas volcanic system, where most of the seismicity focused. The spatial distribution maps of He and H₂ fluxes seem to show the existence of areas that could be acting as preferential zones of vertical permeability allowing the migration of deep source gases, which is very important to follow any seismic-volcanic crisis.

How to cite: Asensio-Ramos, M., Santana, J. M., Smit, M., Matias, D., Pérez, N. M., Viveiros, F., D'Auria, L., Przeor, M., Melián, G. V., Padrón, E., Hernández, P. A., Silva, C., and Rodríguez, F.: Soil He and H2 degassing during the recent seismic crisis of São Jorge Island, Azores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6185, https://doi.org/10.5194/egusphere-egu23-6185, 2023.

The Eastern Carpathians are characterized by CO₂-dominated, intense, cold gas emissions starting from the Neogene to Quaternary volcanic structures, the youngest dormant volcano, Ciomadul, but occurring also quite far away from these, in the Cretaceous flysch units.

The gases are often transported to the surface through groundwater and appear in the form of bubbling mineral water springs. The major components of these cold gas emissions are: CO₂, CH₄, N₂ and sometimes H₂S. This is the most intensive degassing area from Romania. The gas emissions often appear in inhabited areas, representing a natural risk for locals.

In the recent years we performed detailed geochemical surveys, in which the chemical composition of the free gases, the origin of the different gas species and also the quantification of fluxes from diffuse emissions from the soil and dissolved gas was investigated. We have used different approaches and methods, starting with a specially designed Multi-GAS instrument for low-temperature gases, towards different monitoring experiments.

Our results show that the chemical and isotopic compositions of the investigated fluids throughout the Carpathians are strongly influenced by processes that characterize the geotectonic setting of the study area, such as the former volcanic activity and the subduction. In the present the occurrence of the gas emissions and the high flux areas are dependent on the tectonic structures, namely the nappe systems of the Carpathians and related faults, which represent a pathway for the deep fluids towards the surface.

All our investigations gave us a general view on the quantity, flux, geochemistry and origin of the fluids in the study area and helped us to select the most suitable and appropriate sites for future gas monitoring projects.

This work was supported by a grant of the Romanian Ministry of Education and Research, CNCS - UEFISCDI, project number PN-III-P1-1.1-TE-2019-1908, within PNCDI III, contract number TE 63/2020.

How to cite: Kis, B.-M., Caracausi, A., Palcsu, L., Szalay, R., Zsigmond, A.-R., Viveiros, F., Aiuppa, A., Randazzo, P., and Harangi, S.: The volcano-tectonic setting of the Eastern Carpathians: from detailed gas-geochemical surveys towards gas monitoring planning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9703, https://doi.org/10.5194/egusphere-egu23-9703, 2023.

Rainwater samples were collected at Furnas and Fogo volcanoes (São Miguel, Azores) in order to characterize their chemical signatures and to investigate a possible interaction with fumarolic gases. Marine aerosols contribute significantly to the chemistry of the rainwaters. The marine inputs ranges from 17.72 to 100 % for Cl^-, 9.81 to 100 % for SO4^2-, 3.79 to 30.31 % for Ca²⁺, 34.09 to 48.12 % for Mg²⁺ and 17.29 to 81.09 % for K^-. This suggests other sources beyond marine aerosols influencing the hydrochemistry of rainwater, which can be ascribed to two additional components: mineral and volcanic aerosols. The majority of the samples shows an influence of dust particles from North Africa, which can be found in the north Atlantic atmosphere. It is also possible to notice inputs of fumarolic fluids over the hydrochemistry of at least two samples, namely the ones collected near the Caldeiras fumarolic field in Furnas volcano.
Most of the rainwater samples showed ⁸⁷Sr/⁸⁶Sr ratios (0.70849 ± 21 - 0.71027 ± 45) similar to the seawater (⁸⁷Sr/⁸⁶Sr= 0.70918 ± 1), suggesting that sea salts are the main source of the strontium isotopic ratios. The results are within the range of values presented by rainwater in mainland Portugal (⁸⁷Sr/⁸⁶Sr = 0.708965 ± 31 – 0.710345 ± 38). One sample that is exposed to the fumarolic fluids deviates from these values, depicting a lower strontium isotopic ratio (0.70701), confirming the influence of fumarolic fluids already deduced from the major ion hydrogeochemistry.

How to cite: Ferreira, L., Cruz, J. V., Viveiros, F., Durães, N., Coutinho, R., Andrade, C., and Santos, J. F.: Chemical composition and 87Sr/86Sr signatures of rainwaters from São Miguel, Azores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17277, https://doi.org/10.5194/egusphere-egu23-17277, 2023.

The INGV monitoring system operating in the volcano Island since three decades, recorded a new phase of unrest at the La Fossa volcano since September 2021. The main set of the crisis was the central hydrothermal system, deeply affected by the input of heat and chemicals from the magmatic source. The Levante Bay, located northwest of the La Fossa edifice, is a thermal area, where the vapor, coming from a local hydrothermal aquifer, is emitted from several low temperature (100°C) fumaroles along the beach and in the near off shore. The composition of the gas is typical of hydrothermal systems, and indicates equilibrium at temperature close to 200°C. By the onset of the crisis, in September 2021, the composition of the gas emitted from these fumaroles showed a smooth trend of increasing contribution of the magmatic gas. In May 2022, a sudden release of gas occurred in the Levante Bay, which was testified by the whitening of the seawater in the bay, due the formation of sulfur flakes, and by the appearance of typical pockmark structures on the seafloor. The drastic increase of the gas flux from the underwater gas vents, coupled to the presence of the pockmarks, suggested that an explosive emission of gas occurred in May 2022. The chemical and isotopic composition (He and C isotopes) of the gas emitted from the fumaroles revealed the prevailing presence of the magmatic component, closely approaching the composition of the gas emitted from crater fumaroles. This episode drove the attention of the scientific community to this area, currently affected by a significant input of the magmatic vapor, because of the risk related to the huge gas emission and the eventual overpressurization of the local hydrothermal aquifer.

How to cite: Federico, C., Paonita, A., Bellomo, S., Di Martino, R. M. R., Gattuso, A., La Pica, L., Lazzaro, G., Longo, M., Pecoraino, G., Pisciotta, A. F., and Sortino, F.: When a hydrothermal system is shaken by the magmatic fluids: the thermal area of Levante Bay during the 2021-22 unrest of La Fossa volcano (Vulcano Island, Aeolian Archipelago), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15309, https://doi.org/10.5194/egusphere-egu23-15309, 2023.

In summer 2021, a progressive increase of seismic activity and ground deformation was recorded at Vulcano (Aeolian Islands), followed by a strong change in fumarolic gas emission started in September 2021. New gas vents appeared on the crater rim and along the northern outer flank of the La Fossa crater with outlet temperatures up to 350 °C, and a general increase of CO₂ and SO₂ fluxes was measured.

In this study, we report the results of a geochemical monitoring, including gas and water samples collected during 5 field campaigns, carried out from November 2021 to October 2022. The main aim was to verify the evolution of the plumbing system feeding the fluid discharges of the Vulcano summit crater and those located in the Baia di Levante area. The geochemical dataset also includes the chemical and isotopic composition of thermal and cold wells located in the Vulcano Village. The analytical results have shown that in November 2021 and February 2022 the 9 selected crater fumaroles were affected by a strong increase, compared to the previous decade, of the (i) concentrations of acidic gases of marked magmatic origin (SO₂, HCl and HF) and temperature-dependent gases (H₂ and CO) (ii) gas/vapor and (iii) SO₂/H₂S ratios. In this period, the chemistry of waters and dissolved gases from the wells located at the foothill of the volcanic cone, and that of the gas discharges at Baia di Levante did not show significant anomalies.

Since June 2022, the SO₂/H₂S ratios as well as the concentrations of magmatic gases, H₂, and CO decreased, concurrent with a general decrease of the fumarolic flux. At Baia di Levante an opposite evolution was observed mainly consisting of a significant increase in H₂S, H₂, and CO accompanied by a decrease in CH4 concentrations. Such compositional changes were marked by the occurrence of seawater whitening events caused by enhanced emission of sulfur-rich fluids. In this period, the temperature, as well as the SO₄/Cl ratios and the concentrations of dissolved CO₂ in the thermal wells of the Vulcano Village also increased. The chemical-physical evolution of the crater fumaroles, culminated in February 2022, was likely related to a strong pulse of magmatic fluids occurred in summer 2021. The fluid reservoir feeding the discharges at the periphery of the magmatic fluid plumbing system, the latter being directly connected to the crater fumaroles, seems to have buffered the pulse until May 2022, when the heat and magmatic fluids fed by the deep source partially bypassed the hydrothermal aquifer. Further observations related to the continuation of the geochemical and geophysical monitoring of the Vulcano hydrothermal-magmatic system in the next months could provide fundamental insights to confirm the decline of the volcanic crisis as suggested by the recent evolution of the crater gas chemistry.

How to cite: Tassi, F., Capecchiacci, F., Vaselli, O., and Venturi, S.: The 2021-2022 unrest phase of Vulcano Island volcanic system (Aeolian islands): chemical and isotopic evolution of low-to-high temperature fluid discharges and waters from thermal and cold wells., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2291, https://doi.org/10.5194/egusphere-egu23-2291, 2023.

Monitoring volcanic gases have provided valuable information in recognizing variations of the magma outgassing at depth. The increase of magmatic volatile compounds in either crater plumes or fumarole emissions can help in tracking transitions from dormancy to unrest which can progress further in a volcanic eruption. The volcanic degassing has renewed at Vulcano since September 2021 as the result of an increase of the magma degassing at depth. This event created concerns among civil defense authorities because the CO₂ concentration rose in the air, although the unrest has not produced an eruption.

This study examines the air CO₂ at Vulcano Porto from the early summer to autumn of 2021, when the volcanic degassing achieved the climax at La Fossa volcano. Five surveys enabled exploring lateral variations for CO₂ in the air at Vulcano Porto based on measurements for stable isotope compositions of both oxygen and carbon. In addition, the continuous stable isotopes surveying at a fixed point of interest (i.e., the Centro Carapezza - INGV) enabled studying the time variations for CO₂ in the air.

The surveys captured a remarkable increase of the volcanic CO₂ in the air throughout the settled zone of Vulcano Porto from October to November 2021. At Vulcanello, which lies a few kilometers far from the crater cone, the isotopic signature of the air CO₂ revealed also an increased volcanic degassing. Several variations for the volcanic CO₂ in the air occurred during the same period and some estimations of the CO₂ flux from the crater plume were obtained through continuous stable isotope surveying.
The results of this study represent a step forward in providing volcano monitoring techniques that enable estimating the CO₂ emission in the air from active vents.

How to cite: Di Martino, R. M. R. and Gurrieri, S.: Stable isotope surveys reveal variations in the air CO2 during the unrest event at Vulcano, Italy, in 2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11463, https://doi.org/10.5194/egusphere-egu23-11463, 2023.

Here we present methodologies and practices resulting from the integration, comparison, and validation of thermal monitoring data collected on the close conduit volcano (on the Island of Vulcano, Aeolian Archipelago, Italy). The last unrest phases of La Fossa volcano, manifest since September 2021, allowed us to closely follow the time variations of ground surface temperatures, through the permanent monitoring network, operating since 1991. Our ground control data were used to verify the systematic quantification of time and space variation of thermal anomalies retrieved by the Visible Infrared Imaging Radiometer Suite (VIIRS). The ground-based permanent monitoring network generally provides almost continuous time coverage and higher accuracy, but with limited aerial coverage. On the other hand, satellite data are a powerful tool to study surface thermal anomalies, providing a useful way to monitor the thermal evolution of restless volcanoes by remote platforms. The main applications of thermal remote sensing studies are related mostly to active lava flows and explosive eruptions, whereas the first attempts to remotely track the thermal evolution of quiescent volcanoes are generally lacking ground control reference data. For this reason, those former applications may result in more qualitative than quantitative surface effects of endogenous processes, sometimes including the underestimation of biases of external origin.

This near real-time evaluation of the thermal behavior of the close conduit volcano (La Fossa crater) has been based on three series of long-term monitoring data, independently acquired: the time series of ground temperatures measured within the High-Temperature Fumaroles (a); the depth variation of the convective front rising below the diffuse degassing area (b) and the thermal variations tracked from January 2021 onwards, by the VIIRS images (c). The contact sensors registered the intensity and duration of some periodical modulations of surface temperatures and highlighted other intervals of times when the dynamic equilibrium, usually represented by the gentle emission of fluids in the condition of stationary convection, was critically altered. The radiant flux, retrieved by the nighttime images of VIIRS, confirmed the wider extension of the altered thermal state of the La fossa crater, out of the High-temperature fumaroles, registered from June 2021, up to date.

The complementary nature of the two techniques (direct and remote thermal sensing) has been confirmed by the correlation among the time-series of thermal data. Moreover, the radiant heat remotely sensed by the VIRSS, resulted more closely related to the mild thermal anomaly of the steam-heated ground. Many papers have already presented other monitoring data supporting the same evidence of this volcanic unrest, defined by a significant, and long-lasting phase of pressure buildup, driven by the enhanced supply of magmatic gases in the hydrothermal system (e.g. Diliberto 2021; Inguaggiato et al., 2022a, 2022b; Federico et al., 2023).

How to cite: Diliberto, I. S., Ganci, G., Cappello, A., Di Figlia, M. G., and Bilotta, G.: The combined approach to Ground-based and Satellite Monitoring techniques applied on a close conduit volcano (La Fossa cone, Vulcano, Aeolian Islands, Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16462, https://doi.org/10.5194/egusphere-egu23-16462, 2023.

The Active cone of La Fossa caldera is a close conduit volcano affected by solphataric activity, manifested in the hot fluids released from fumaroles and the associated thermal anomalies in groundwater and exposed ground.

The evaluation of the volcanic activity changes are inferred by the near real-time monitoring of soil CO₂ fluxes diffused at the La Fossa Cone and the peripheral areas of Palizzi and Levante Bay and by the discontinuous monitoring of CO₂ fluxes diffused by soil in areas around the CO₂ continuous monitoring stations, La Fossa Cone, Palizzi and Levante Bay. 

In particular, from June 2021 to February 2023 we evaluated in near real time the level and duration of the exhaling crisis affecting the Island of Vulcano, by measuring the changes in mass and energy carried by the fluid release.

The first summit volatiles increase degassing (VSCS station) started in June 2021 reaching in September 2021 the value of 34,000 g m² d^-1 more of one order of magnitude higher respect to the background values (1000 g m² d^-1).

While, the first great increase of CO₂ output in the peripheral area, measured with the soil CO₂ survey, have been recorded at Levante Bay in May 2022 (17 t d^-1) higher respect to the base values recorded in the past (2-4 t d^-1). At November 2022 a new strong increase of soil CO₂ degassing, have been estimated at Levante Bay area, reaching a values of 46 t d^-1.

The strong and deep input of volatiles released from the underlying magma batch strongly modified the chemical composition of the shallow plumbing system, bringing the system to a higher level of CO₂ total pressure than the average background recorded in recent decades.

How to cite: Inguaggiato, S., Vita, F., Inguaggiato, C., Mazot, A., Diliberto, I. S., and Cangemi, M.: Abrupt output increase of soil CO2 emissions from summit and peripheral areas of Vulcano Island 2021-2023, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15112, https://doi.org/10.5194/egusphere-egu23-15112, 2023.

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.

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.

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.

How to cite: Tarchini, L., Carapezza, M. L., Granieri, D., Pagliuca, N. M., Patera, A., Pruiti, L., Ranaldi, M., Rubino, C., and Sortino, F.: Soil CO2 flux monitoring of the ongoing Vulcano crisis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15400, https://doi.org/10.5194/egusphere-egu23-15400, 2023.

Volcanic and/or geothermal gases provide essential information on the activity of a volcanic system, on magma degassing and on the origin and evolution of fluids. Their study represents one of the most powerful technique to understand the dynamics of systems and to monitor the volcanic activity (dormant state, but also unrest and/or eruption phase).

Volcanic/geothermal gases are complex mix of chemical elements and compounds. Starting from the study of their chemical composition, many equilibrium reactions in gas phase were introduced in the past as possible geothermometers and geobarometers, and they actually used to estimate the thermodynamic conditions in deep system (both in volcanic or geothermal area) and in volcanic surveillance. However, depending on the system, known geothermal-barometric reactions are not able to accurately describe the thermodynamic conditions of reservoirs, highlighting the need for new geothermometric reactions. Of course, the opportunity to develop new “geothermometers/geobarometers functions” depends to the availability of analytical techniques able to detect and quantify new chemical compounds of interest, often at low to very low concentration levels (ppb).

The GC-ICP-MS (gas chromatography-inductively coupled plasma-mass spectrometry), one of the most useful hyphenated method (Michalski R. et al., 2006; Easter R.N. et al., 2010), combines the high separation capacity of the GC with the high sensitivity and specificity of the ICP-MS. Chemical compounds containing C, S and O are abundant in volcanic/geothermal gases and they can be detected at low levels via GC-ICP-MS technique. The development of new specific analytical methods for volcanic/geothermal gas analysis (in particular for what concern new compounds) may provide the chance to introduce new gas equilibrium as a “key” to better understand thermodynamic and redox conditions at depth.

Dry gas samples from fumaroles of the La Solfatara di Pozzuoli (Bocca Grande, Bocca Nuova and Pisciarelli) and for crater area in the Vulcano island were analysed, studying the distribution of sulphur-bearing species. The results obtained are very satisfactory in terms of chromatographic separation and detection limits, making the GC-ICP-MS method very promising in the study of volcanic/geothermal gases.

How to cite: Lelli, M., Caliro, S., Dallara, E., Chiodini, G., and Marini, L.: Sulphur trace components in La Solfatara and Vulcano volcanic gases: searching for suitable new geo-indicators, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4492, https://doi.org/10.5194/egusphere-egu23-4492, 2023.