Volcanic emissions can also have significant impacts on the terrestrial environment, atmospheric composition, climate, and human health at various temporal and spatial scales. For instance, sulfur dioxide emissions can cause acid rain and influence aerosol formation, and if an eruption column reaches the stratosphere, it causes global dimming and a lowering of the Earth’s surface temperatures that may last for years. Similarly, halogens can dramatically affect proximal ecosystems, influence the oxidation capacity of the troposphere, and alter the stratospheric ozone layer.
Understanding the physicochemical processes underlying volcanic eruptions has improved tremendously through major advances in computational and analytical capabilities, instrumentation and monitoring networks, thereby improving the ability to reduce volcanic hazards. This session focuses on all aspects of volcanic volatile degassing in the Earth’s system through case studies and theoretical and multidisciplinary approaches. We invite contributions discussing how novel measurement techniques, field measurements, direct and remote ground and space-based observations, and modeling studies of volcanic degassing can provide new insights into volcanic and atmospheric processes at local and global scales.
Finally, but significantly, we strongly encourage critical contributions that offer alternative explanations and viewpoints, willingness to consider new ideas supported by evidence, and with the potential to improve the ability to forecast eruptions.
Orals: Tue, 5 May, 14:00–15:45 | Room -2.21
The growing use of hydroacoustics to study magmatic degassing underwater is providing increasingly powerful insights in topics as varied hazard monitoring and microbial evolution. This talk will discuss the use of marine acoustics to study magmatic degassing and present two case studies, 1) Dziani Lake (Mayotte) a Precambrian analogue where variations in magmatic degassing may be driving microbial adaptation , and 2) Lake Kivu (Rwanda) where deadly limnic eruptions may be triggered by newly discovered gas blowouts.
Hydrophones record the sound emitted by gas bubbles at the moment of their release into the water column. The frequency and power of these signals tells us about their number and size. By applying Passive Acoustic Flux Inversion techniques, bubble oscillation spectra can be inverted to passively quantify gas flux continuously, regardless of water quality or depth. This approach enables long-term monitoring of degassing dynamics that are inaccessible using traditional geochemical or visual methods.
Dziani Dzaha Lake undergoes persistent magmatic degassing and is considered one of the best modern analogues for Precambrian environments. A better understanding of what drives adaption in the microbial population of Dziani provides a better understanding of what drove Precambrian evolution. A month long observation reveals strong temporal variability in gas flux, with rapid increases potentially preceding local seismic activity. These observations provide the first quantitative constraints on magmatic gas input to the lake and may suggest a tentative link between volcanic activity and early life.
At Lake Kivu, a hydrophone deployed during the 2021 Nyiragongo dyke intrusion provided the first direct acoustic observations of lakebed degassing. Analysis reveals highly variable degassing behaviour, including pulsed bubble releases, long-period signals associated with subsurface gas migration, and previously undocumented explosive gas blowout events on the lakebed. These high-energy events have the potential to trigger limnic eruption but were not detected by the regional land-based seismic network, highlighting critical gaps in current monitoring strategies. Although no limnic eruption was triggered, the observations demonstrate that potentially hazardous degassing processes can occur silently and episodically, challenging assumptions of steady gas input used in existing limnic hazard forecasts.
Together, these case studies demonstrate the growing potential of hydroacoustics to study magamtic degassing and will hopefully inspire future studies incorporating the use of hydrophones to study magmatic degassing.
How to cite: Roche, B., Barrière, J., Ader, M., and Caudron, C.: Bubbles: A matter of life and death, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7378, https://doi.org/10.5194/egusphere-egu26-7378, 2026.
Dissolved H₂O significantly governs the eruptive behavior of magmas, as the formation and growth of fluid vesicles increase magma volume, potentially triggering an eruption. Some explosive eruptions, such as the 1875 Askja eruption in Iceland(1), result from the injection of basaltic magma into a volatile-rich rhyolitic magma chamber, suggesting enhanced vesicle formation in these systems.
A recent experimental study(2) investigated the melt injection of a hydrous basaltic melt into a hydrous rhyolitic melt. The authors demonstrated that continuous decompression of bimodal hydrated rhyolitic and basaltic melts enhances vesicle formation within the evolving, alkali depleted rhyolitic hybrid melt. Expanding their experimental approach, we synthesized a glass with the composition of the highly vesiculated hybrid melt and conducted H2O solubility experiments using an internally heated argon pressure vessel (IHPV). For the subsequent combined hydration and decompression experiments, we hydrated the hybrid melts with 5.7 wt. % H2O in an IHPV for 96 h at 1523 K and 200 MPa and equilibrated at 1323 K for 1 h prior to continuous decompression at 0.17 and 1.7 MPa·s-1 to final pressures of 60–100 MPa.
The decompression rate-dependent vesicle number densities (VND) and vesicle sizes, together with polymodal vesicle size distributions indicate that H2O-phase separation proceeds in the thermodynamic field of metastability via nucleation. Although the present study confirms the general mode of H2O-phase separation observed in the melt injection-study(2), pronounced textural deviations occur between the homogeneous hybrid melt and a hybrid melt generated during magma mixing. In comparison, the hybrid melts produced during melt injection require substantially reduced supersaturation pressures for the onset of vesiculation and smaller pressure intervals to obtain high VND. These differences demonstrate that chemical disequilibrium and diffusion processes during melt injection substantially enhance vesiculation. Consequently, the comparison of the two experimental series shows that H2O degassing depends not only on the melt composition, but also on geological processes operating within the magma reservoirs, in this case magma mixing and the associated shift out of equilibrium, generated by rapid depletion of the alkali components Na2O and K2O. As H2O solubility of rhyolitic melts is decisively controlled by the alkali content(3), its depletion amplifies H2O supersaturation, further enhancing vesicle formation in the hybrid zone.
(1) Sparks, R. S. J. (1978) Geoth. Res., 3(1-2), 1-37.
(2) Marks, P. L. et al. (2023) Mineral., 35(4), 613-633.
(3) Allabar A. et al. (2022) Petr., 177(52).
How to cite: Luenenschloss, L., Marks, P. L., and Nowak, M.: Experimental Constraints on H2O Vesiculation in the Hybrid Zone of a Bimodal Rhyolitic-Basaltic Melt System., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13725, 2026.
Dormant volcanic areas are defined by long periods of quiescence often exceeding 10 ka since the last eruption. Although these systems may appear inactive, a prolonged dormancy does not imply volcanic extinction, and this misconception can obscure the true eruptive hazard. The eruption of the Laacher See volcano represents the most recent volcanic activity in the East Eifel volcanic field (13 ka BP) and resulted in the formation of a caldera lake. The most prominent indicators of ongoing activity are the continuous release of gases in the form of mofettes and soil degassing, as well as strong gas seepages at various depths (8 – 52 m) within the lake, some of which reach the surface. Previous studies have shown that the gas consists of ≈ 99% CO2 and that the gases originate from the upper mantle, as indicated by elevated helium isotope ratios (>5 Ra).
Although Laacher See is a holomictic lake, events such as earthquakes, landslides or a drop in the water level can cause a sudden release of gas stored at depth. This poses a particular risk from spring until late autumn when the lake is stratified and the region is visited by many tourists. For this reason, three CO2 flux campaigns covering the entire lake surface have been conducted in summer (June/August 2024) and in winter (February 2025) to obtain an initial estimate about the total amount of CO2 released by the lake. Results indicate that winter CO2 emissions are an order of magnitude higher than those measured in summer, suggesting substantial accumulation of dissolved CO2 in the hypolimnion during the stratification period. In parallel to that, summer water column profiles of the dissolved inorganic carbon (DIC) and its respective δ13C signature show gradients from up to 10mM (deep waters) to 6mM (surface waters), with a correspondent water signature from 4 to 8 mUr VPDB, independently supporting our interpretations. In temperate climate zones such as the Eifel, lake stratification persists for approximately eight months. Based on our CO2 flux output calculations, we estimate that 1.6 x 109 moles of CO2 accumulate in the hypolimnion during the stratification period. We therefore discuss possible scenarios under which the gas pressure can exceed the hydrostatic pressure resulting in the sudden release of gas stored at depth.
Alongside the CO2 flux measurements, we sampled the free gas phase directly from gas emission points at different depths to determine the origin of gases using δ13C-CO2 and noble gas isotopic ratios. For this purpose, we tested our newly developed gas sampler mounted on a remotely operated vehicle. Helium ratios range from 4.9 up to 5.3 RA, while δ13C-CO2 range between -1.7 and -0.17‰. The methods presented here are part of an ongoing monitoring study for Laacher See that aims to understand changes in the magmatic plumbing system related to increased volcano-tectonic activity in the region.
How to cite: Jentsch, A., Knornschild, N., Roeser, P., Niedermann, S., Boehrer, B., Kämpf, H., Böttcher, M. E., Brehme, M., and Brune, S.: Volcanic degassing and risk implications at the dormant Laacher See volcano in the East Eifel, Germany, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9335, 2026.
The Campi Flegrei caldera is a restless, resurgent volcanic system located within the densely populated metropolitan area of Naples, southern Italy. Long-term monitoring indicates that the caldera entered a new unrest phase in 2004, characterized by ground inflation correlating with shallow seismicity and intense hydrothermal activity, such as fumarole and soil CO2 degassing. Here, we present the results of monitored soil fluxes from Campi Flegrei from 1998 to 2026 to better understand the dynamics of the current unrest. Crucially, this extends the previously published record (1998–2016) by ten years, offering new insights into recent dynamics. The dataset consists of 41 campaigns (~400 measurement points each) in an extended area—including Solfatara di Pozzuoli and Pisciarelli hydrothermal site—and 220 monthly campaigns over 63 fixed points in a target area of Solfatara. Modeling these datasets through Sequential Gaussian Simulation (sGs) reveals that both the spatial extent of degassing and total emission of CO2 into the atmosphere have increased since 2004. Analyzing temporal variations over distinct areas reveals a significant shift starting in 2018, where escalating emissions became focused specifically within the Solfatara crater. These escalating fluxes correlate with increased soil temperatures, variations in fumarole gas chemistry, ground deformation, and number of earthquakes. These coupled geochemical and geophysical signals suggest that the current unrest is linked to pulses of magmatic fluid injection, leading to progressive pressurization and heating of the hydrothermal system and ultimately triggering shallow seismicity and ground uplift.
How to cite: Bini, G., Avino, R., Carandente, A., Cuoco, E., Iovine, R. S., Minopoli, C., Rufino, F., Santi, A., Ricci, T., Sciarra, A., Tamburello, G., Tieri, M., Caliro, S., Chiodini, G., and Cardellini, C.: Escalating soil CO2 degassing from Campi Flegrei during the ongoing unrest (2004–2026), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17833, 2026.
Active volcanic degassing often includes puffing activity, i.e., the repeated emission of pressurized gas slugs, with inter-event duration of few seconds. Puffing may generate volcanic vortex rings (VVRs), which are toroidal vortices of volcanic gases moving through the surrounding ambient air. This study presents the first systematic attempt to characterise VVRs, aiming at better constraining the mechanisms of magma degassing and conduit dynamics in the shallow plumbing system. During summer 2023, the degassing activity of a new pit crater at Bocca Nuova (Mt. Etna, Italy) was monitored and recorded by means of the user-friendly and easy portable SKATE device. Thermal and high-speed videos were analysed to investigate the evolution and behaviour of VVRs over time. Both manual analysis in ImageJ and automated analysis in MATLAB were applied, the latter based on the brightness temperature of individual pixels of the thermal video imagery. Two classes of VVRs were identified according to their physical characteristics: shape, outer radius (rout), distance from the emitting vent (h), residence time in air, vertical rise velocity (vrise), radius expansion rate. Class 1 rings are well-defined and stable (h > 50 m; initial rout = 6 - 12 m; initial vrise = 8 - 20 m/s), while Class 2 rings are irregular shaped and short-lived (h < 50 m; initial rout = 3 - 9 m; initial vrise < 12 m/s). An automated statistical analysis confirmed the existence of these two clusters and assessed the relative probability of occurrence of each cluster. Class 2 rings dominate the sequence, while Class 1 rings are less frequent. The probability that a Class 1 ring follows a Class 2 ring is 0.10, roughly half the probability that it follows another Class 1 ring (0.24). The statistical analysis of their emission frequency may potentially provide additional insights into magma degassing processes. Given that vortex rings are well defined in the literature (e.g. fluid engineering, medical science, biology), both theoretically and experimentally, the minimum conditions required for VVRs formation at volcanic vents were investigated. Vortex rings were experimentally reproduced using a device consisting of a cylinder, a piston and a spring. The bursting of gas slugs of varying volumes was simulated under different piston accelerations. Comparison between field and experimental data allowed estimation of the source parameters (e.g. L/D, magma depth) associated with VVRs formation. Characterizing volcanic vortex rings provides a unique opportunity to better understand the source conditions at the surface of the magma column, degassing processes, gas flux and conduit dynamics during active degassing of volcanoes.
How to cite: Iezzi, F., Taddeucci, J., Palladino, D. M., Biensan, C., Pennacchia, F., and Scarlato, P.: Characterization of volcanic vortex rings: comparison between field observations and experimental simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10403, 2026.
Quantifying volcanic sulfur dioxide (SO2) emissions is essential for understanding magmatic processes and improving eruption forecasting. We present a four-day, multi-platform investigation of SO₂ emissions at Mt Etna, Italy, spanning 15–18th July 2024 and capturing the build-up, climax, and recovery from a major paroxysmal lava-fountaining eruption at the Voragine crater on 15th July. Spectra were acquired using ultraviolet spectrometers mounted on a car and a custom vertical take-off and landing uncrewed aerial system (UAS). This was complemented with spectra from the permanent FLAME scanning network, and by satellite-derived emission rates from TROPOMI imagery analysed using the PlumeTraj analysis toolkit.
All ground-based and airborne spectra were analysed using the iFit intensity-fitting algorithm, enabling consistent SO₂ slant column density retrievals and correction of light dilution effects using the dual-waveband approach. Wind speeds used in flux calculations were derived from Pitot tube measurements from the UAS when available. Across the integrated dataset, SO2 emission rates increased from steady background levels of ~6 kg s⁻¹ on the morning of 15th July to >40 kg s⁻¹ several hours before the onset of lava fountaining, at which point daylight-dependent ground and airborne measurements ended. Analysis of the TROPOMI imagery provides an average SO₂ emission rate of 270 ± 80 kg s⁻¹ during the 6-hour fountaining phase, corresponding to a total emitted mass of 5.7 ± 1.7 kt of SO2.
Volcanic tremor amplitude rose concurrently with the pre-eruptive increase in SO₂ flux, showing strong correlation prior to fountaining (Spearman rank correlation, ρ = 0.85), but alters during the eruption, likely reflecting a shift in the dominant tremor source. Following the eruption, all platforms recorded greatly reduced quiescent emissions on 16–17th July (<2 kg s⁻¹), before partial recovery by 18th July (<5 kg/s).
Each platform contributed complementary strengths: UAS measurements provided high signal-to-noise ratios and light-dilution quantification; car traverses most easily captured complete plume cross-sections; scanners resolved short-term degassing variability; and satellite observations quantified eruptive emissions inaccessible to the other methods. Together, these results demonstrate that coordinated, multi-platform SO₂ monitoring is essential for resolving rapid degassing dynamics across an eruptive cycle and for enhancing eruption-forecasting at persistently active volcanoes.
How to cite: Riddell, A., Burton, M., Esse, B., McCormick Kilbride, B., Di Grazia, G., La Spina, A., Salerno, G., Crann, V., and Wood, K.: SO2 flux measurements from ground, air and space before, during and after a lava fountain on Mt Etna , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22166, 2026.
Teide volcano (Tenerife, Canary Islands) is an active stratovolcano characterized by persistent low-temperature degassing (81–83 °C) at its summit crater, associated with a hydrothermal system dominated by meteoric steam and deep magmatic inputs. This study presents results from a permanent MultiGAS station operating in continuous mode at the summit crater, designed to monitor the main chemical ratios in the fumarolic gas emissions in situ, to characterize their temporal variability and to look for significant changes that could be related to possible future volcanic unrest periods. The instrument enabled continuous and simultaneous measurements of key gas species, including CO₂, H₂S, SO₂ and water vapour. The data indicate a gas composition dominated by H₂O, followed by CO₂, minor concentrations of H₂S and negligible SO₂ contents, consistent with hydrothermally dominated gas emission. Since the installation of the instrument in the summer of 2025, the H2O/CO2 molar ratio has shown big fluctuations, ranging between 2 and 18, likely affected by meteorological inputs. The CO₂/H₂S molar ratio has shown a more stable value around 1,900. The absence of SO₂ supports the interpretation that the current degassing regime of Teide is decoupled from an open magmatic conduit and is governed by hydrothermal conditions.
The continuous MultiGAS monitoring provides high–temporal resolution data that complement other geochemical surveillance techniques, such as diffuse soil CO₂ emission surveys. This study contributes to a better understanding of the present state of the Teide volcano–hydrothermal system and highlights the value of continuous gas monitoring as a key tool for volcanic activity assessment and for the early detection of potential precursory changes.
How to cite: Di Nardo, D., Padrón, E., Hernández, P. A., D. Padilla, G., V. Melián, G., González Suarez, N., Sánchez Acosta, A., and M. Pérez, N.: MultiGAS measurements of fumarole gas emissions from the summit crater of Teide volcano, Tenerife, Canary Islands , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9913, 2026.
Mercury (Hg) is a volatile and highly toxic metal released into the environment from both natural and anthropogenic sources. Volcanic activity represents one of the major primary natural contributors to atmospheric Hg, with previous estimates of global annual volcanic emissions ranging from approximately 50 to 700 t·a-1 (e.g., Nriagu and Becker, 2003; Pyle and Mather, 2003). The main sources of uncertainty of the total emission of volcanic Hg are rooted in a lack of measurements from volcanic eruptions, due to the logistical challenges of collecting gaseous Hg samples from actively erupting plumes. One potential method to quantify volcanic Hg emission from eruptions is through the analysis of Hg adsorbed to the surface of volcanic ash particles, which can readily be sampled on the ground downwind of eruptions.
The purpose of this study is to estimate mercury emissions from the 2021 Tajogaite eruption at Cumbre Vieja volcano (La Palma, Canary Islands), a record-breaking event characterized by exceptionally high volatile output, with CO2 and SO2 emissions of 28 ± 14 Mt (Burton et al., 2023) and 1.6 ± 0.1 Mt (Esse et al., 2025), respectively.
Mercury degassing during the Tajogaite eruption was estimated using Hg/SO2 molar ratios derived from sulphate (SO42-) concentrations in ash leachates and mercury content in dried volcanic ash samples. Volcanic ash from the eruption was collected almost daily at five monitoring stations located at varying distances from the vents. Sulphate and Hg analyses were performed via ion chromatography and mercury-specific atomic absorption spectrometry (AAS-Hg) using a RA-915 Mercury Analyzer. In terms of analytical performance, an adequate linear factor adjustment (R2= 0.99) and linear range (0.3-30 ng Hg) were achieved for the quantification of Hg in ash samples.
The average sulphate concentration in the ash leachates was 3.49 × 104 µg·kg⁻¹, ranging from 1.21 × 104 to 8.48 × 104 µg·kg⁻¹, while the average Hg content in the dried ash was 1.69 × 103 µg·kg⁻¹, ranging from 0.28 × 103 to 9.40 × 103 µg·kg⁻¹. These measurements yield an estimated average Hg/SO2 molar ratio of 1.55 × 10-5, with a range from 0.76 × 10-5 to 3.54 × 10-5. Considering an SO2 emission of 1.6 Mt from the Tajogaite eruption, the corresponding estimated mercury emission is 77.6 t on average, with a range of 3.8 to 177 t.
References
Burton, M., Aiuppa, A., Allard, P. et al. (2023). Exceptional eruptive CO2 emissions from intra-plate alkaline magmatism in the Canary volcanic archipelago. Commun. Earth Environ. 4, 467. https://doi.org/10.1038/s43247-023-01103-x
Esse, B., Burton, M., Hayer, C. et al. (2025). Forecasting the evolution of the 2021 Tajogaite eruption, La Palma, with TROPOMI/PlumeTraj-derived SO2 emission rates. Bull. Volcanol. 87, 20, https://doi.org/10.1007/s00445-025-01803-6
Nriagu, J. and Becker, C. (2003). Volcanic emissions of mercury to the atmosphere: global and regional inventories. Sci. Total Environ. 304, 3–12.
Pyle, D.M. and Mather, T.A. (2003). The importance of volcanic emissions for the global atmospheric mercury cycle. Atmos. Environ. 37, 5115–5124.
How to cite: Lodoso, E., Pérez, N. M., Melián, G. V., Coldwell, B. C., Perdomo-Sosa, Ó., Hernández, P. A., Asensio-Ramos, M., Padrón, E., and Padilla, G. D.: Mercury emission from the Tajogaite eruption La Palma, Canary Islands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10762, 2026.
The 2021 Tajogaite eruption on La Palma, Canary Islands, was a prolonged event characterized by high intensity and significant emission of volcanic gases. Water vapor (H2O), the most abundant volcanic volatile, is often significantly under-measured due to challenges associated with plume measurement and atmospheric entrainment. This study applies and validates a novel methodology using a portable thermal infrared (TIR) camera combined with a mass and energy conservation model to quantify the H2O mass flux throughout the 85-day eruption. We estimate the total H2O released at 597.9 ± 24 Mt, classifying Tajogaite as one of the highest sustained high-flux tropospheric degassing events recorded globally. An exceptional peak rate of 156 Mt/d was observed on September 22, 2021, shortly after the eruption onset. The temporal evolution of the H2O flux shows a strong correlation with long-period (1–5 Hz) seismic tremors, suggesting a direct link between shallow magmatic/fluid processes and gas release dynamics. We calculate an H2O/CO2 mass ratio of 21.3, which is consistent with the high CO2 signature of the island's intra-plate alkaline magmatism (Burton et al., 2023). However, the resulting H2O/SO2 ratio (373.7) is significantly higher than previous estimates and global basaltic analogues (e.g., Miyakejima approx 10), underscoring the dominance of a shallow, hydrothermal-driven H2O component, which decoupled from the exponentially decaying SO2 flux in the final stages of the eruption.
How to cite: Hernández, P. A., Lev, E., Padilla, G. D., Birnbaum, J., Asensio-Ramos, M., Padrón, E., D'Auria, L., and Pérez, N. M.: Sustained High-Magnitude H2O Flux: Quantifying Exceptional Water Vapor Emission and Shallow Fluid-System Dynamics at the 2021 La Palma Eruption, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11164, 2026.
The 2021 Tajogaite volcano eruption on La Palma created a persistent geohazard due to diffuse volcanic carbon dioxide (CO₂) emissions in the inhabited areas of Puerto Naos and La Bombilla. Elevated indoor and outdoor CO₂ concentrations have restricted access to these zones, highlighting the need for improved tools to characterize gas migration processes and support long-term risk management. This study assesses the risk associated with CO₂ migration by analyzing subsurface gas pressure gradients, proposed as an effective physical proxy to identify preferential advective gas flow pathways. Integrating this approach with geochemical monitoring can improve hazard maps and long-term risk management strategies.
To improve the assessment and reduction of this persistent hazard, a pressure gradient investigation has been conducted in Puerto Naos and La Bombilla. The main aim was to delineate pressure gradient patterns to detect areas dominated by advective gas transport. For this purpose, ten field surveys were performed between November 2024 and October 2025, covering approximately 274 measuring sites, including paved (184-204) and unpaved (70) zones of Puerto Naos, and one survey with 32 sampling sites at La Bombilla (unpaved). Measurements were done by means of an own-developed device that records the pressure difference between the shallow subsurface (40 cm) and the atmosphere, allowing calculation of the pressure gradient (Pa·m⁻¹) following Natale et al. (2000). Surveys were integrated with simultaneous diffuse CO₂ efflux measurements at the unpaved zones to assess the relationship between pressure-driven flow and gas emission intensity. At both zones, soil gas samples were sampled at 40 cm depth to analyze the He, H2 and CO2 concentration and isotopic composition of d13C-CO2.
Results reveal significant spatio-temporal variability, with markedly higher-pressure gradients during periods of enhanced advection. Maximum gradients exceeded 700 Pa⋅m−1 in paved areas of Puerto Naos, where two persistent anomalous zones were identified. Notably, these values significantly exceed the maximum gradients of approximately 319 Pa⋅m−1 reported by Natale et al. (2000) at Izu-Oshima volcano, suggesting a more potent advective driving force in La Palma’s post-eruptive system, potentially exacerbated by the "sealing effect" of urban pavement. The anomalous zones correlate spatially with elevated CO2 effluxes, confirming a coupling between pressure gradients and emission intensity, consistent with the physical principles observed in previous volcanic studies. Conversely, reduced degassing periods showed near-zero or negative gradients, indicating diffusion-dominated transport. Isotopic analysis confirms a volcanic-hydrothermal origin for the gas.
These findings demonstrate that subsurface pressure gradients are a sensitive and reliable proxy for identifying active advective migration in volcanic urban environments. Integrating this physical approach with traditional geochemical monitoring significantly enhances hazard mapping and supports dynamic access management in populated regions affected by persistent degassing.
REFERENCES
NATALE G., HERNÁNDEZ P.A., MORI T. AND NOTSU K. (2000). Pressure gradient measurements in volcanic diffuse gas emanations. Geophysical Research Letters 27(24):3985-3988. DOI:10.1029/2000GL008540.
How to cite: Padilla Hernández, G. D., Di Nardo-Méndez, D., Ramírez, J. D., Herrera, D., Hernández, P. A., Pérez, N. M., González, A. M., De Los Ríos-Díaz, H., Afonso-Falcón, D., Leal-Moreno, V. J., Asensio-Ramos, M., Méndez-Pérez, C., Padrón, E., Melián, G. V., González, P., Carballa, O., Cabrera, D., Pérez, D., Rodríguez, N., and Rodríguez-Rocha, R.: Pressure gradient and chemical-isotopic characterization of diffuse gas degassing at Puerto Naos, La Palma, Canary Islands , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12193, 2026.
Mt. Etna has long been considered one of the major sources of volcanic gases worldwide. Variations in degassing activity have been therefore considered as precious indications about the activity status of the volcanic system. Though most of the gases are released by open-conduit degassing through the summit craters, a significant part of the gases diffuses through the flanks of the volcano interacting with groundwater. Acquisition of physico-chemical parameters in groundwater for volcanic surveillance purposes started on Mt. Etna nearly 40 year ago. While in the first years only periodic sampling, generally with a monthly frequency, was made, in recent years automatic monitoring stations with higher acquisition frequency (hourly) and data transmission were implemented in several groundwater sampling sites.
Moreover, the complex geodynamic situation of the eastern flank of the volcano, with tectonic and volcano-tectonic activity and flank sliding, will also have some influence on the acquired signals at the groundwater monitoring stations.
In this framework, important results are expected from monitoring of the high-frequency oscillations of water level of aquifers, a powerful tool in studying stress and strain conditions in the crust. The present experiment will represent the first time that this portion of the spectrum of the water level signal will be explored in the attempt to recognize possible precursory patterns. Given the peculiarity of the area, we will focus on episodes of magma migration, volcano tectonic events and degassing, as recognized by ground deformation, seismicity and geochemical signals, which cause the propagation elastic energy in the aquifer and can thus produce high-frequency pressure signals. The presence on the area of a well-developed network for measurement of ground deformation will allow in fact to relate our hydrological signals to inflation, deflation of the edifice and sliding of its eastern flank.
A prototype station for measurement of high-frequency (from 0.1 to 50 Hz) variation of pore pressure with an innovative absolute pressure sensor in 2.5mm case with 24bit resolution and 0-2 or 0-4 bar range has been implemented. The station acquires also the following parameters: water temperature, pH, electric conductivity. For the necessary tests, the station will be placed soon in an abandoned well with limited anthropogenic interference in the surrounding area on the eastern flank of Mt. Etna.
How to cite: D'Alessandro, W., Schiera, G., Pisciotta, A. F., and Bellomo, S.: High frequency data acquisition of physico-chemical parameters in groundwater on Mt. Etna volcano (Italy) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7528, https://doi.org/10.5194/egusphere-egu26-7528, 2026.
The La Fossa volcano on the Island of Vulcano, Italy, represents a critical case study for managing volcanic gas hazards in populated areas. Following the prolonged passive degassing phase subsequent to the 1888–1890 vulcanian eruption, the volcano exhibited signs of renewed energetic fumarolic–solfataric activity during 2021. This study characterizes some geochemical evidences and consequences of this "crisis", focusing on the anomalous degassing zones at the base of the volcanic cone (i.e., Palizzi, Faraglione, and Vulcano Porto), which exist in close proximity to inhabited settlements.
While the crater cone typically accounts for approximately 90% of emissions, diffuse degassing in the basal zones accounts for over 10% of total output, posing significant risks to indoor and outdoor air quality. During the 2021 unrest, we observed distinct variations in gas output. Soil CO2 flux (φCO2) in these anomalous zones increased from an average of 74 g m-2 d-1 in September 2021 to 370 g m-2 d-1 in November 2021. These values represent deviations of 27% and 538%, respectively, above the statistical background established since 1988 (φCO2 ≈ 58 g m-2 d-1). To constrain the impact of these emissions on ambient air quality, we conducted five stable isotope surveys δ13C-CO2 and δ18O-CO2 of airborne CO2 between August 2020 and November 2021, using a mobile laboratory equipped with a laser-based analyzer. By exploiting the distinct isotopic signature of volcanic CO2 versus atmospheric background, we developed an isotopic mass balance model to partition the carbon sources. The results demonstrate that volcanic injections, modulated by local atmospheric circulation, significantly drove CO2 concentration anomalies in the inhabited area of Vulcano Porto.
Using both φCO2 and carbon isotope composition, we tracked a dramatic raise in total volcanic φCO2 output, rising from 9.97 · 104 kg d-1 to 101.15 · 104 kg d-1. These estimates suggest that the instability of a deep magmatic body drove the transition from background activity to an unrest event. This escalation resulted in tangible hazards, necessitating the temporary displacement of the population from Vulcano Porto due to elevated gas concentrations. Our results demonstrate that synchronous monitoring of φCO2 and outdoor air CO2 concentration and stable isotopes δ13C-CO2 and δ18O-CO2 of airborne CO2 are essential for the early detection of magmatic transients and the mitigation of gas exposure risks in the populated zones of Faraglione and Vulcano Porto.
How to cite: Gurrieri, S., Di Martino, R. M. R., and Camarda, M.: Magmatic Unrest and Gas Hazard at La Fossa Volcano (Italy): Insights from the 2021 Degassing Crisis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16865, 2026.
El Hierro is the westernmost, smallest, and youngest island of the Canary archipelago (Spain). The island is shaped by three rift zones, with the last eruption taking place in the submarine extension of the southern rift in October 2011. This study aimed to characterize volcanic activity on El Hierro Island. To this end, soil CO2 degassing and temperature were determined at 182 sites covering the 268.7 km2 surface of the island during a five-day field campaign in May 2025. Soil CO2 fluxes were measured using the accumulation chamber method, and soil temperature was recorded at a depth of 10 cm. We also characterize the carbon isotopes composition of CO2 (δ13C-CO2) to infer its origin and the potential processes occurring during its accumulation within the soil and subsequently release to the open atmosphere. In addition, we analysed the spatiotemporal evolution of diffuse thermal anomalies, i.e., subtle (~1 °C), month-to-years, and large-scale (~km2) brightness temperature, over the past 20 years using MODIS spectroscopic products processed with the software SSTAR1 (Subtle Surface Temperature Anomalies Recognizer). We found that diffuse thermal anomalies on El Hierro are temporally associated with periods of increased volcanic activity in the Canary archipelago and frequently occur above the three main rift-zones (west, northeast, and south). Soil CO2 fluxes measured in May 2025 were slightly higher along the western and northeastern (~15 g m−2 d−1) compared to the rest of the island (~4 g m−2 d−1), consistent with background levels. The δ13C-CO2 values suggests that the CO2 emitted through the soil has mainly a biogenic origin, mixing in the accumulation chamber (for gas flux measurements) with the atmospheric component. The results also indicate the fractionation of the carbon isotopes during the molecular diffusion of CO2. Despite CO2 fluxes being biogenic and at low levels, their spatial distribution correlates with the location of the most prominent diffuse thermal anomalies recorded over the last two decades, suggesting interactions between volcanic and biological processes. Based on the geochemical survey and the spatiotemporal thermal analysis, we conclude that El Hierro Island is currently in a quiescent state.
References:
1 Girona, T., & Brenot, L. (2026). SSTAR: A user-friendly framework for detecting and monitoring subtle precursors to volcanic eruptions – application to Shishaldin, Alaska. Earth, Planets and Space (In Review).
Funding
This research was supported by the Spanish Ministry of Science and Innovation (MICIU) through the LOTEAN project (PID2022-139990NB-I00) and a pre doctoral fellowship (FPU20/05157). Additional support was provided by the Canary Islands Smart Specialisation Strategy (RIS3 Extended 2021–2027) through the NEVA2 project (Ref. ProID2024010012), funded by the Canary Islands Agency for Research, Innovation and Information Society (ACIISI) of the Government of the Canary Islands and co‑funded by the European Union under the Canary Islands ERDF Programme 2021–2027; and by the grant RYC2023-043480-I, funded by MCIU/AEI/10.13039/501100011033 and by the FSE +.
How to cite: Benavente, D., García-Martínez, N., Girona, T., Fernandez-Turiel, J.-L., Perez-Torrado, F. J., Rodriguez-González, A., and Fernández-Cortés, Á.: Soil CO2 degassing and diffuse thermal anomalies on El Hierro Island (Canary Islands, Spain), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2138, https://doi.org/10.5194/egusphere-egu26-2138, 2026.
Freshwater carbonate deposits such as travertine and tufa serve as valuable archives of past hydrogeological and volcanic processes. On oceanic volcanic islands, their formation is frequently associated with magmatic CO₂ degassing, although this relationship remains insufficiently constrained. The Barranco de Azuaje in northern Gran Canaria contains the most significant Holocene travertine–tufa deposits in the Canary Islands, located near the lava flows of the Montaña Doramas eruption. Past inconsistencies in dating these carbonates compared to the underlying lava questioned a genetic link, leading to hypotheses that deposition was climate-driven. Resolving this controversy is essential for understanding volcanic effects on groundwater systems and for evaluating geosites of high scientific and conservation value.
To address this, we carried out detailed field mapping, anthracological analysis, and geochronological studies using nine radiocarbon-dated charcoal samples and sixteen U–Th dated carbonate samples. Bayesian modelling integrating stratigraphic constraints allowed us to establish a robust chronological framework. Results show that the Montaña Doramas eruption took place at 3107 [3164, 3068] cal BP, and carbonate deposition started immediately afterwards, lasting around 865 years. The absence of a temporal gap, combined with the stratigraphic evidence of carbonates directly resting on fresh scoriaceous lava surfaces, supports a cause–and–effect relationship between volcanic activity and carbonate precipitation. Hydrothermal alteration of groundwater, increased temperature, and magmatic CO₂ input likely triggered rapid carbonate deposition in perched springs and fluvial backwaters, in both cases showing high abundance of both imprints of plant macrofossils (land plants and liverworts), and plant microfossils (pollen, spores, diatoms).
This research shows that volcanic eruptions can trigger localised freshwater carbonate formation on rejuvenated volcanic islands, providing insights into past volcanic degassing and palaeoenvironmental conditions. Besides its scientific importance, the study highlights the fragility and rarity of these deposits—now less than 10% of their original volume—emphasising the urgent need for conservation and dissemination efforts. Understanding these processes benefits hazard assessment, groundwater management, and geoconservation strategies in volcanic areas.
This research was supported by the Canary Islands Smart Specialisation Strategy (RIS3 Extended 2021–2027) through the NEVA2 project (Ref. ProID2024010012), funded by the Canary Islands Agency for Research, Innovation and Information Society (ACIISI) of the Government of the Canary Islands and co funded by the European Union under the Canary Islands ERDF Programme 2021–2027. Additional support came from two projects granted by the Cabildo de Gran Canaria (2018 and 2019). PVM acknowledges an IJC2020 043481 I Grant funded by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. SEM analyses were funded by project PID2021 125055NA I00 (MCIN/AEI/10.13039/501100011033 and ERDF). CR was supported by the National Biodiversity Future Centre – NBFC (Code CN_00000033), funded by the European Union – NextGenerationEU under the Italian NRRP. Institutional support was provided by the ULPGC research group GEOVOL, included in iUNAT.
How to cite: Rodriguez-Gonzalez, A., Perez-Torrado, F. J., Cabrera, M. C., Marrero-Rodríguez, Á., Ravazzi, C., Vidal-Matutano, P., and Fernandez-Turiel, J. L.: The link between volcanism and travertine-tufa formation at Barranco de Azuaje in Gran Canaria, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3049, https://doi.org/10.5194/egusphere-egu26-3049, 2026.
Characterization of the emitted volcanic gas composition provides crucial information about the processes that affect the volatile magmatic constituents during the degassing process. In the present study, we compare measurements collected from the Etna volcanic plume with simulations of the chemical evolution of the outgassed volatiles. To simulate the composition of the volcanic plume for the COHS system, we developed a numerical model that reproduces the different steps of volatile outgassing from the silicate melt to the atmosphere. First, we identify the possible initial volatile contents using data from melt/fluid inclusions from the literature and we simulate the solubility of the volatile species by considering different pressures, temperatures and redox states of the system. Once the volatiles are exsolved, we determine their chemical speciation assuming thermochemical equilibrium between the melt and the gas phase. In the final step of our simulation, we model the chemical evolution during the mixing of the hot volcanic plume with atmospheric air based on high-temperature reactions. To evaluate the oxidation state of the volcanic plume, we compare the CO/CO2 ratio of measured and simulated compositions. We note that the final outgassed composition could mirror the oxidation state and the temperature of the host melt but it could also be affected by chemical conversions at the magma-atmosphere interface in the first seconds after gas release. By using this approach, we reconstruct the potential chemical evolution of the volatile composition during the entire volcanic degassing process, linking the simulated and measured compositions of the Mt Etna volcanic plume.
How to cite: Ortenzi, G., Bobrowski, N., Kuhn, J., Gorojovsky, L., Nies, A., Roberts, T., Boucher, L., Schuck, T., Degen, J., Giuffrida, G. B., Engel, A., Geil, B., Métais-Bossard, M., and Hoffmann, T.: Comparison of volcanic outgassing simulations and measurements from the Mt. Etna volcanic plume, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4513, https://doi.org/10.5194/egusphere-egu26-4513, 2026.
Volcanic gases carry information about subsurface processes. Decoding this information in gas measurements is essential for volcano hazard monitoring and fundamental geochemical research. Volcanic gas measurements are often interpreted under the assumption that these gases remain chemically inert upon emission to the atmosphere. Measurements of bromine oxide (BrO) in young volcanic plumes however contradict this interpretation since it is an oxidation product of hydrogen bromide (HBr) emissions.
We present model simulations of the high-temperature interface between magmatic gases and the atmosphere and simulate the plume evolution from emission into the first hours downwind. We refer to the early-stage plume evolution where magmatic gases enter the atmosphere and cool and dilute to atmospheric temperatures as the magma-atmosphere interface. For that purpose, we use a two stage box model based on chemical kinetics and a physical mixing and dilution parameterization. The mechanism simulates C-H-O-N-S chemistry and has sub-mechanisms for reactive halogens (Cl-Br) and mercury. The first stage exploits the analogs between combustion chemistry and early hot volcanic plumes and the second stage focusses on the multi-phase formation of BrO in the young plume (up to several kilometers downwind distance from the emission source).
The model is able to reproduce BrO observations in minutes old plumes from Mt Etna, which crucially depends on radical formation in the high-temperature plume stage only milliseconds after magmatic gas release to the atmosphere. The magma-atmosphere interface, also affects oxidation chemistry of other reduced trace gases emitted by the volcano such as molecular hydrogen (H2) and carbon monoxide (CO), modifying thereby the magmatic gas redox state. This process is critically controlled by the magmatic gas emission temperature upon entering the atmosphere. The model furthermore explains the co-existence of reduced gases (H2 and CO) with reactive halogens such as BrO as it is observed for example in the plume of Mt Etna. This evidences that magmatic gases are likely emitted several hundred Kelvin below the magma temperature.
How to cite: Nies, A., Roberts, T., Dayma, G., Fischer, T., and Kuhn, J.: Near-source observations of bromine oxide indicate oxidation of magmatic gases at the magma-atmosphere interface, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9719, 2026.
Volcanic fissure eruptions can produce voluminous gas emissions, posing a risk to local and distal populations and potentially impacting global climate. Quantifying the emission rate and altitude of injection of these emissions allows forecasting of impacts and provides key insights into the magma dynamics driving eruptions. Daily global observations from satellite instruments such as TROPOMI combined with trajectory modelling with PlumeTraj deliver these emission rate and altitude data. Here, we report satellite-derived SO2 emissions from the 2022 eruption of Mauna Loa, which lasted only 13 days but produced an SO2 plume that circled the globe, displaying a highly variable emission rate and injection altitude. Three key discoveries were made: we detect precursory SO2 emissions up to 3 hours before the eruption start; peaks in emission rate are correlated with onset and cessation of activity at different fissures; and the SO2 injection altitude was modulated by the available moisture content of the ambient air. We suggest that alignment of the fissure geometry with the wind direction could potentially explain how the initial emissions reached 14 km asl, approaching the tropopause. The total SO2 measured from this eruption is 600 (± 300) kt. These results demonstrate how satellite measurements can provide new insights into eruptive and degassing mechanisms and highlight that better constraints on the SO2 emissions from fissure eruptions globally are needed to understand their impact on climate.
How to cite: Esse, B., Burton, M., Brenot, H., and Theys, N.: Insights into eruption dynamics from TROPOMI/PlumeTraj-derived SO2 emissions during the 2022 eruption of Mauna Loa, Hawaiʻi, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11559, 2026.
Volcanic gas emissions provide important insights into magmatic processes beneath the Earth's surface and play a crucial role in assessing volcanic hazards. Depending on their solubility in magma and the respective pressure conditions, volcanic gases are exsolved and released at different depths of a volcanic vent.[1] To study behavior prior to an eruption in hazardous locations, unmanned aerial vehicles (UAVs) offer a safer measurement platform. To increase monitoring frequency, reduce manual labor and the associated risk for the researcher, this work aims to develop a drone station capable of autonomous measurement flights near the volcanic crater. The sensor system consisting of a SO2 and CO2 sensor was developed in-house and can be attached to the drone.[2]
To ensure reliable and robust measurement results, a dedicated calibration station was designed and built that allows for easy, repeatable, and automated calibration of the sensor system. The system comprises a pressurized gas container with a calibration gas mixture that connects to a capillary acting as a flow limiter as well as dilution air controlled by a mass flow controller that can be adjusted to a defined concentration for sensor calibration at ambient conditions (p, T, RH).
In order to capture the dynamic behavior of volcanic gas plumes, the UAV-based point measurements are supplemented by a lightweight spectrometer based on a mobile DOAS system.[3] This combination is intended to enable spatially resolved measurements of gas concentrations and fluxes in rapidly changing plume geometries. In the long term, the installation of an autonomous drone docking and charging station at Mount Etna is planned, allowing repeated automated measurement flights and near real-time data acquisition.
[2] N. Karbach, N. Bobrowski, T. Hoffmann, “Observing volcanoes with drones: studies of volcanic plume chemistry with ultralight sensor systems” Sci Rep 2022, 12, 17890.
[3] J. Kuhn, N. Bobrowski, T. Wagner, U. Platt, “Mobile and high-spectral-resolution Fabry–Pérot interferometer spectrographs for atmospheric remote sensing” Atmospheric Measurement Techniques 2021, 14, 7873–7892.
How to cite: Rabe, A., Karbach, N., Bobrowski, N., and Hoffmann, T.: Development of a drone-based measurement system for real-time monitoring of volcanic gas composition at Etna volcano, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12856, 2026.
