The aim of this session is to gather researchers focusing on under-explored structures and processes, using innovative tools to collect and interpret integrated datasets, and conducting numerical and laboratory simulations with state-of-the-art instruments and workflows. We welcome contributions that present new approaches for improving our understanding of fluid migration systems on Earth and other planets, ranging across: 1) different tectonic settings and parameters controlling subsurface processes and resulting morphologies; 2) geochemical reactions occurring at depth and the surface, including micro- and biological studies; 3) experimental/numerical simulations about fluid flow evolution and propagation; 4) studies showcasing piercement structures and novel data acquisition methods; 5) interaction of fluid flow in sedimentary basins with host rocks and decommissioned wells; and 6) impact of seepage on climate and evolution of life throughout Earth’s history. We particularly encourage abstract submissions from early-career researchers and scientists from groups that are underrepresented in the geosciences.
Posters on site: Wed, 6 May, 16:15–18:00 | Hall X1
Mud volcanoes are sedimentary structures that extrude clay-rich material driven by fluid overpressure. Their subsurface properties, including porosity, permeability, and fluid content, vary laterally and vertically, influencing fluid circulation and eruptive behaviour. Imaging these heterogeneities is essential to assess environmental and geological hazards, such as landslides, sudden gas emissions, and ground deformation.
A multi-method geophysical survey was conducted on the Saribogha mud volcano (Azerbaijan), selected for its numerous small eruptive surface features (pools, salsa lakes, and gryphons). The dataset includes three electrical resistivity tomography (ERT) profiles, 20 time-domain electromagnetic (TDEM) soundings, and a gravity survey covering the entire area.
The data show low noise levels and are consistent with typical mud-volcano responses. The gravity map reveals an anomaly near zero along an east–west axis, with higher positive values to the north and south. A localized negative anomaly occurs to the west along the axis, coincident with an abundance of surface effusive features. This area also corresponds to highly conductive zones in both ERT and TDEM datasets, which, despite differing resolutions, show similar conductivity patterns. At greater depth (~60 m), both methods show a contrast between a less conductive northern sector and a more conductive southwestern sector. Although the geophysical contrasts are weak, positive gravity anomalies and less conductive zones likely reflect sandstone host rock or consolidated mud, while negative anomalies and more conductive areas indicate fluid accumulation and pathways.
We propose a conceptual model in which deep fluids rise vertically from the southwestern sector, possibly from a shallow mud chamber, before spreading laterally beneath the surface. Interaction with a shallow perched aquifer, partly recharged by rainfall, may contribute to the high-water content of surface features. Ongoing gravity modelling aims to test the proposed mud-flow conceptual model by exploring subsurface geometry and density contrasts.
How to cite: Jodry, C., Camerlynck, C., Seoane, L., and Gabalda, G.: Investigating Fluid Flow and Subsurface Structure of Saribogha Mud Volcano Through A Multi-Geophysical Survey, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7364, 2026.
Mud volcanoes are large geological phenomena that can exhibit spectacular mud flows extending for kilometres in length. Traditionally, these flows have been linked to major eruptive events with extensive mud extrusions. Recently it has been suggested that a significant number of such flows are instead formed by creeping flow processes, a mechanism similar to what is observed at warm-based glaciers. The proposed model suggests that the creeping is promoted/accelerated by two main factors: (1) episodic mud effusion that increases gravitational loading and periodically reactivates the mud flow for several months after an eruptions; and (2) a fluid-rich basal layer that lubricates the movement of the whole flow.
Azerbaijan hosts the highest concentration of large-scale mud volcanoes on Earth. To determine the dynamics of the creeping phenomena and their characteristics, we selected 47 large mud volcanoes across onshore Azerbaijan. For each one, we analysed historical satellite imagery from Google Earth and integrated field observations at four different structures.
Our study reveals that 19 of the 47 mud volcanoes show measurable creeping displacements of preexisting and paleo-mud flows. Rates range from a few metres to tens of metres per decade with movements associated with kilometre-sized mud flows. The rate and extent of this movement vary among individual structures and appear to be induced by factors such as eruption frequency, slope gradient, and/or subsurface fluid availability.
Our observations indicate that the most important deformations are prompted by eruptive events, with a substantial decrease, and occasional halting, over time. Our study emphasises that post-eruptive adjustment mechanisms shape the long-term evolution of kilometre-sized mud flows.
Some of the studied mud volcanoes host infrastructures, dispersed settlements, and are located in the vicinity of populated areas, representing geohazards for those communities. Analogous processes are also expected to occur at large mud volcanoes in other settings worldwide as well as in other planetary bodies. These findings highlight the need for broader studies, continuous monitoring, and to greater awareness of the potential risks that this process may represent.
How to cite: Fenske, C., Brož, P., and Mazzini, A.: The Role of Creeping Mud Flows and the Hidden Dynamics of Mud Volcanism. Examples from Azerbaijan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10734, 2026.
Mud volcanoes in subduction-zone forearcs provide direct access to fluids generated at depth, yet their occurrence tens of kilometres landward of the deformation front poses several questions about the origin and nature of such fluids, since most of the fluid sources from sediment compaction and clay mineral dehydration are exhausted within a few 10s of km into the subduction system. Here we present a comprehensive pore-water geochemical and isotopic dataset from 12 submarine mud volcanoes in the Kumano Basin (SW Japan), located 42–85 km landward of the trench. More than 460 pore-fluid samples from gravity cores and seafloor drill cores were analysed for major and minor elements and for Li, B, and Sr isotopic compositions.
Mud volcano fluids are strongly depleted in Cl, Na, Mg, and K and enriched in B and Li relative to seawater, indicating substantial freshening and deep fluid input. Elemental and isotopic systematics define a ternary mixing between seawater, a pristine deep fluid, and a shallowly overprinted deep fluid affected by volcanic ash alteration and ion exchange. Lithium and boron isotopes constrain fluid sources to a combination of sedimentary clay mineral dehydration and a higher-temperature component inconsistent with purely sedimentary origins. Inferred Li isotope compositions of the fluids sources indicate fluid–rock interaction temperatures of ~150–290 °C, exceeding the smectite-to-illite reaction window and pointing to dehydration of altered oceanic crust (saponite) beneath the forearc. Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr ≈ 0.708) further support mixing between sedimentary, volcanic, and crustal sources.
Our results demonstrate that Kumano Basin mud volcanoes are fueled by multiple fluid sources spanning shallow diagenesis, deep accretionary prism dehydration, and subducting oceanic crust. These findings imply that crustal dehydration fluids can migrate into the overriding plate along inherited fault systems and play a major role in forearc hydrogeology. Mud volcanoes thus represent key natural observatories for integrating deep subduction-zone fluid processes beyond the reach of scientific drilling.
How to cite: Menapace, W., Hüpers, A., Kopf, A., Meixner, A., and Kasemann, S.: Pore-water geochemistry of Kumano Basin mud volcanoes reveals multi-source fluids from sedimentary and crustal dehydration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18471, 2026.
In this contribution we present a multidisciplinary investigation that combines geophysics and geological observations to characterize active degassing areas in the Southern Appenines (Italy). Our focus is on two target areas of Contursi-Oliveto Citra and Mefite d’Ansanto (MdA); MdA, in particular, is one of the largest non-volcanic emission sites worldwide with more than 2000 t of CO2 emitted per day.
Both areas have been the subject of several previous studies that have revealed a classic trap-reservoir structure at depth, connected to the surface by a complex network of fractures that control the gas outflows. However, critical uncertainties remain regarding the precise locations of the reservoirs, the volumes of gas involved and the detailed definition of the structural controls on underground gas pathways.
To address these questions, advanced geophysical surveys were carried out as part of the MEFITIS project. In the MdA area a high-resolution 3D Magnetotelluric (MT) survey was conducted alongside a gravimetric campaign. Over 50 new gravity stations, which were co-located with AMT soundings and precisely positioned via GNSS RTK, enabled us the to produce a Free-Air anomaly map. Residual gravity anomalies were computed after calculating the Bouguer anomalies and removing long wavelength trends. Two relevant gravity highs bordering the area of maximum emission were identified and interpreted as depth variations of the basement rocks hosting the reservoir. MT surveys delineated several low-resistivity anomalies linked to fault system and gas-saturated formations and allowed to define key structural traps and leakage pathways. In the Contursi-Oliveto Citra area, a deep 2D MT profile explored the reservoir geometry at depths over of 5 km and was integrated with a novel analysis of gravity anomalies available from the Italian gravimetric map.
Through this multidisciplinary approach we demonstrate how the combination of geophysical measurements and geological observations can provide valuable insights into the storage capacity and leakage potential of these natural CO2 systems. This information is essential for assessing and characterizing the state of the reservoir; sites candidate for CCS, hydrocarbon reservoir systems are analogous contexts that could benefit from a similar combination of geophysical methods.
How to cite: Pivetta, T., Pagliara, F., Carlino, S., Ciarcia, S., De Paola, C., Di Giuseppe, M. G., Francesco, I., Isaia, R., Sposato, M., Troiano, A., and Vitale, S.: Magnetotelluric and gravity surveys for constraining reservoir and fluid pathways in non-volcanic CO2 degassing areas: a study case in the Southern Appenines (Italy), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21753, 2026.
Methane (CH4) is recognised as one of the most powerful greenhouse gases but yet it represents a relevant energy resource. Therefore it is important to decipher the various sources that can provide inputs to the atmosphere (Saunois et al. 2016). To determine the actual need for future emission reductions, a precise quantification of the global CH4 budget is required, however, according to the most recent modelling, significant uncertainties still affect these calculations (Saunois et al., 2020). The most important source of uncertainty is attributable to natural emissions. While the open ocean CH4 emissions are relatively well constrained, the global marine flux appears to be mainly influenced by shallow near-shore environments (0-50 m b.s.l.), where CH4 released from the seafloor could escape to the atmosphere before oxidation (Weber et al., 2019). The factors that govern the magnitude of methane transfer through the water column to the atmosphere remain poorly understood and are highly site dependent, with water depth playing a critical role. Nevertheless, quantifying methane emissions from shallow coastal environments remains a challenge due to the complex thermo-fluid dynamics of bubble-mediated transport.
The present study, within the framework of the NRPP-PRIN project MEFISTO, focuses on advancing passive hydroacoustic techniques to improve gas flux detection and estimation at two distinct Mediterranean sites: the Panarea hydrothermal field ('hot seeps') and a seepage zone off the Marano and Grado lagoon, North Adriatic Sea ('cold seeps'), which exhibit contrasting degassing regimes. A central objective of the research is to enhance the Signal-to-Noise Ratio (SNR) in recorded acoustic data, which is often compromised by ambient coastal noise. We employ innovative acoustic inversion models based on the spectral analysis of bubble formation and detachment (pinch-off) events using a single hydrophone. By characterizing the unique acoustic signatures of individual bubbles and gas jets, and applying spectral denoising and an adaptive thresholding approach to detect non-overlapping individual bubbles, we aim to minimize the masking effects of the soundscape, allowing for a more precise reconstruction of the Bubble Size Distribution (BSD). These hydroacoustic flux estimates are integrated with and validated by water column geochemical investigations. This multidisciplinary approach allows us to track the fate of CH4 from the sediment-water interface to the surface, evaluating how different degassing regimes (hydrothermal vs. biogenic) and physical forcings influence the efficiency of gas transfer to the atmosphere.
The acquired data revealed that different degassing styles are strongly influenced by natural forces driving the temporal evolution of degassing activity, particularly in gentle or low flux emissions.
Preliminary results from four seasonal campaigns demonstrate that the synergy between acoustic monitoring and geochemical tracing significantly reduces uncertainties and provides new insights into gas migration mechanisms through the use of non-invasive techniques, the temporal variability of emissions, and the fate of dissolved methane, ultimately contributing to a more refined marine methane budget for coastal systems.
How to cite: Lazzaro, G., Caruso, C. G., De Vittor, C., De Rosa, G., Douss, N., Esposito, V., Fonti, V., Graziano, M., Iacuzzo, F., Laudicella, V. A., Longo, M., Morici, S., Semprebello, A., and Bazzaro, M.: Improving Underwater Methane Flux Estimation through Passive Hydroacoustic Inversion and Geochemical Data in Shallow Coastal Systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17880, 2026.
Understanding natural methane seepage systems is key to constraining subsurface fluid flow, benthic carbon cycling, and the development of seep-related ecosystems. On the Norwegian continental shelf, methane seepage reflects the coupling between hydrocarbon migration in the subsurface and seafloor expressions such as gas flares, authigenic carbonates, and chemosynthetic communities.
The Sentinel Seep was initially discovered in 2024 during the WELLFATE expedition, when hydroacoustic water-column data revealed active gas emissions in the Norwegian Trench of the northern North Sea. Follow-up investigations during the 2025 WELLFATE expedition aboard RV Kronprins Håkon enabled detailed characterization of the site through ROV-based observations, documenting its geomorphology, geological framework, and associated biological communities.
The seep is located within a pronounced ploughmark in an area where the Holocene sediment cover is anomalously thin. Seismic data indicate that the seep is situated at the seafloor near the southwestern edge of a large (~1,800 km²) amplitude anomaly along the Upper Regional Unconformity (URU), interpreted as shallow gas accumulation.
The seepage field covers an area of approximately 800 m (N–S) by 200 m (E–W) and contains extensive carbonate crusts and mound structures. Active gas release occurs at multiple locations and is associated with widespread microbial mat coverage. The site hosts abundant Lophelia corals, including isolated colonies exceeding 2 m in diameter as well as dense coral clusters.
Numerous fragments of abandoned and entangled fishing gear are present across the area, with some elements extending into the water column and posing operational risks. This debris has likely reduced subsequent trawling activity, unintentionally contributing to the preservation of the habitat. In this way, diffuse methane seepage has promoted carbonate buildup that physically shields the area from fishing disturbance - a protective function that inspired the name Sentinel Seep.
The Sentinel Seep represents a valuable natural laboratory for investigating the links between shallow gas accumulations, fluid migration pathways, authigenic carbonate formation, and the establishment and persistence of seep-associated ecosystems on the Norwegian margin.
How to cite: Ferré, B., Bünz, S., Trivedi, A., Mattingsdal, R., Polteau, S., and Mazzino, A.: Methane Seepage, Carbonate Accretion, and Ecosystem Development at the Sentinel Seep in the Norwegian Trench, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23175, 2026.
The Tampen area, located along the western bank of the Norwegian Channel in the northern North Sea, is a region of significant natural gas venting activity. Understanding seepage mechanisms here, is however challenging due to subsurface lithological heterogeneity caused by glacial erosion and deposition, as well as acoustic disturbances beneath the seepage zones.
To address these challenges, we conducted a detailed subsurface investigation using high-resolution 3D seismic data that revealed bright amplitude anomalies concentrated beneath the seepage sites that relate to two distinct depocenters hosting high-porosity sediments that act as reservoirs for trapped gas.
The primary depocenter exhibits a wedge-shaped geometry, with bright anomalies arranged in a delta-like pattern. The secondary depocenter is associated with a single, large glacial lineation near the bank area, forming a cavity filled with fine to coarse sediments. We propose a conceptual model outlining a series of geological events that began around 30 ka BP. During a relative sea-level low stand (~25–30 ka BP), significant sandy deposits accumulated, which were later submerged during subsequent high stands. This was followed by the advance of ice sheets, which contributed to extensive glacial erosion and deformation of these deposits. Additionally, the sediments infilling the glacial lineation are attributed to an ice-dammed lake outburst event that occurred during the collapse of grounded ice across the North Sea shelf after the Last Glacial Maximum (LGM).
Fluid escape pathways are mainly along the wedge's western boundary, where eastward-dipping sandy beds aid upward migration. Gas seepage is influenced by glacial deformation and the thickness and distribution of lateral moraines.
This study highlights the interplay between glacial processes, subsurface lithology, and fluid migration in shaping natural gas venting in the Tampen area. The continuous seepage in this narrow corridor underscores the importance of understanding its impact on climate change and the risks it poses for drilling in sensitive environments.
How to cite: Trivedi, A., Bünz, S., Plaza-Faverola, A., Winsborrow, M., Patton, H., Polteau, S., and Mazzini, A.: Natural Gas Venting in the Tampen Area, Northern North Sea: Insights from Subsurface and Glacial Interactions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9529, 2026.
During the offshore petroleum production era, thousands of wells were drilled, many in regions characterized by active natural gas seepage. Observations show gas emissions near plugged and abandoned wells, raising key questions about well integrity and the origin of detected seepage. It remains unclear whether such seepage is induced by compromised wells, would occur naturally in the absence of wells, or reflects contributions from deeper reservoirs versus shallow gas accumulations.
In this study, we investigate these questions using fully coupled fluid‑flow and geomechanical modeling. Our simulations incorporate realistic deformation behavior of soft sediments, pressure‑dependent permeability, and two‑phase fluid flow. The study focuses on the Norwegian channel and its western bank in the northern North Sea, which hosts the Heincke and Sentinel natural seep systems. Geological and geophysical data collected during a recent research cruise were integrated into a detailed subsurface model.
We simulate natural fluid migration without wells and compare it with scenarios including a hypothetical well-related seep. The results demonstrate that the presence of a well perturbs natural flow pathways, modifies seepage patterns, and alters both the timing and magnitude of seepage. We quantify seepage rates for natural and well‑influenced scenarios and identify zones where migrating fluids are most likely to reach the seafloor. The modeling further reveals that seepage is inherently intermittent, with rates varying over time due to coupled hydro‑mechanical processes.
How to cite: Wang, L. H., Yarushina, V., and Trivedi, A.: Modeling Natural and Well‑Related Seepage in the Norwegian North Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22695, 2026.
Natural hydrogen present in the subsurface is highly reactive, but a better understanding of the behavior of this molecule is important for developing to successful exploration models. The aim of this contribution is to present the state-state-of-the-art geochemical and microbiological processes that primarily consume natural hydrogen during its migration through the subsurface, and its retention while stored in the reservoir. Our approach combines published information with results from ongoing and past projects. In particular, we aim to investigate how pressure and temperature conditions control the different phase of hydrogen during migration and retention (hydrogen as free gas, microbubbles or dissolved in water). We will further examine how hydrogen's phase influences its reactivity with water and the surrounding rocks, affecting reaction rates and hydrogen consumption. In addition, we present the preliminary results from theoretical calculations of microbial consumption processes occurring at deep surface reservoirs using available data on cell numbers, metabolisms and reaction rates from hydrogen underground storage projects. The values will enable realistic and worst-case scenario of hydrogen consumption, which can be included in hydrogen reservoir stability assessments. The outcomes of this study will serve as constrains for follow up numerical models of natural hydrogen systems within the project H2-QUEST under the Joint Undertaking of the Clean Hydrogen Partnership.
How to cite: Polteau, S., Mazzini, A., Etiope, G., Moga, R., Dopffel, N., Gaucher, E., and Schmidt, D.: Overview of the behavior of natural H2 in the subsurface and the H2-QUEST project, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5785, 2026.
The Norwegian Continental Shelf (NCS) hosts tens of thousands of active and extinct natural occurring methane seeps (NOMS), which support unique ecosystems. As a mature area for oil and gas exploration and production, the NCS contains ~8,000 wells, including ~2,000 that have been plugged and abandoned and over 2,000 slated for decommissioning. When these gas emissions occur at or near wells, they are known as well-associated methane seeps (WAMS). Here we present the first integrated quantification of methane flux from both NOMS and WAMS over a vast area of the NCS.
Our multidisciplinary survey was conducted on the Tampen area west of the Norwegian Channel. We combined 1) a large 800 km2 multibeam and water column survey to locate, identify and classify each individual gas flare in the area and determine its intensity; 2) in situ ROV sea floor observations and gas flux measurements conducted at different seepage intensity sites; 3) gas sampling and individual geochemical analyses to fingerprint the fluids origin.
Nearly 2,000 flares have been mapped, identifying Tampen as potentially the region with the highest flares concentrations in the Norwegian part of the North Sea; 175 of these flares are associated with plugged and abandoned wells. Geochemical analyses show that methane is the main seeping gas with a distinct microbial signature. This suggests a shallow origin of the seeping gas likely trapped in the glaciogenic wedge along the western edge of the Norwegian Channel. The identified flares were categorized into six classes based on height, width, and intensity from the multibeam echosounder water column data. Applying class-averaged flux estimates, we derive a first-order, internally consistent assessment of methane release across the survey area.
These findings provide an unprecedented opportunity to evaluate the environmental consequences of gas emissions from NOMS and WAMS. Until now, it has been difficult to quantify the emissions reaching the atmosphere and their impact on ocean acidification. These new datasets also provide essential insights for mitigation measures and for implementing the design of future CO₂ and hydrogen storage projects in depleted reservoirs on the NCS. Ensuring long-term stability and safety of these systems will support sustainable resource management and compliance with environmental regulations.
How to cite: Mazzini, A., Polteau, S., Mattingsdal, R., Thomsen, P., Buenz, S., and Ferré, B.: Quantifying methane emissions from the Tampen area (Norwegian North Sea), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18149, 2026.
The volcanic island of Nisyros, situated on the South Aegean Volcanic Arc, represents a critical site for studying the interactions between active magmatic-hydrothermal systems and structural tectonics. Following the 1998 seismic crisis and subsequent fumarolic activity, characterizing the island's subsurface has become essential for volcanic unrest monitoring. As part of the DEMETRA research line funded under the INGV ROSE infrastructure project, we present an unprecedented high-resolution 3D electrical resistivity model of Nisyros, reaching depths of 1.5 km.
To overcome the logistical and topographical constraints of this sensitive Geopark environment, we deployed a non-invasive 3D network of 34 IRIS V-Fullwaver receivers, ensuring island-wide coverage from the central Lakki caldera to the volcanic slopes.
Our 3D model provides a first-of-its-kind geophysical visualization of the island's hydrothermal system. Key findings include:
- Aquifer Identification: The detection of several hydrothermal aquifers, directly corroborated by historical geothermal boreholes (1983-1984).
- Structural Control: Precise imaging of the major NNW-SSE and NE-SW normal fault systems. These structures act as the primary conduits for fluid migration, establishing a definitive link between surface geothermal manifestations and deep aquifers.
The success of this study demonstrates that Deep Electrical Resistivity Tomography (DERT) is a powerful and socially accepted tool for investigating sensitive volcanic environments. This 3D model significantly improves our understanding of Nisyros’ first kilometer, providing a robust baseline for future hydrothermal modeling and hazard mitigation.
How to cite: Sfalcin, J., Henry, M., Przeor, M., Cabrera-Pérez, I., Ganas, A., Lupi, M., Mazzini, A., and Sciarra, A.: Unveiling the 3D Hydrothermal Architecture of Nisyros Volcano (Greece) through Island-Wide Deep Electrical Resistivity Tomography (DERT), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10306, 2026.
As our society shifts toward sustainable resources to meet growing energy demands, geothermal systems represent a promising natural resource distributed globally across active magmatic segments or plate margins. These systems refer to any localized geological setting (volcanic or non-volcanic) where a portion of the Earth's thermal energy is extracted from a circulating fluid and transported to a point of use (Williams et al., 2011). While they constitute important sources of heat, strategic volatiles, and ore-forming elements, the storage, migration pathways, and release mechanisms of hot circulating fluids carrying strategic volatiles remain poorly understood. In detail, these fluids typically form through the interaction between convective groundwaters and shallow heat sources, but a wide range of additional physico-geochemical processes may occur and alter both the composition and release of volatiles.
In this study, we focus on Afar Region (Ethiopia), with the aim of evaluating and distinguishing source effects from physical processes by coupling high precision light (He-Ne) and heavy (Ar-Kr-Xe) noble gas isotope systematics in key hydrothermal systems. Free-gas samples were collected from natural bubbling pools in Central Afar (Dubti area) and North Afar (Dallol area) following sampling protocols adapted from Giggenbach and Goguel (1989). Light noble gas isotopes were analysed by conventional static mass spectrometry at the Centre de Recherches Pétrographiques et Géochimiques (CRPG). Ultrahigh precision heavy noble gas isotope analyses were conducted by state-of-the-art dynamic mass spectrometry at the Seltzer Laboratory (WHOI, MA, USA).
While He-Ne analyses can be combined to distinguish deep contributions from crustal and various mantle endmembers (source effects), stable Ar-Kr-Xe isotope systematics provide key information on the dynamics of water-gas interactions in the subsurface (physical processes). The resulting dataset is evaluated using the diffusive transport fractionation (DTF) model of Bekaert et al. (2023) to test how this globally significant process operates in the Afar Region. We also explore the possibility for heavy noble gas isotope systematics to provide complementary insights into source effects once corrected for the isotopic effect of subsurface fractionation. To better constrain volatile distributions within hydrothermal systems, we compare our dataset with a comprehensive literature compilation of volatile data from the East African Rift, shedding light on the influence of crustal age (i.e., cratonic vs. juvenile crust) on He isotopic and elemental compositions.
Our data yield He isotopic ratios ranging from 7.3 to 12.2 ± 0.20 RA, consistent with contributions from deep mantle sources. 20Ne/22Ne ratios indicate a significant influence of an air-like component, with minor deviations from air attributable to source and/or fractionation processes. Xenon systematic are consistent with subsurface fractionation, with small additions of mantle-derived radiogenic and fissiogenic components.
The entire suite of noble gas isotopes provides a powerful means to identify how physical fractionation processes and deep vs. shallow sources of volatiles contribute to producing the complex geochemical signatures observed in surface emissions. The goal of this project will be to ultimately improve our understanding of whether subsurface water–gas interactions can trigger processes capable of modifying and potentially concentrating strategic volatiles along magmatic segments of the Afar Region.
How to cite: Nazha, W. A., Bekaert, D. V., Marty, B., Seltzer, A. M., Ayalew, D., and Pik, R.: Distinguishing source effects from physical processes using the full suite of noble gas systematics across geothermal systems in Afar (Ethiopia), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10938, 2026.
Hydrothermal vent complexes (HTVCs) form when water, carbon dioxide (CO₂), methane (CH₄), and other fluids, along with sediment, are rapidly ejected into the ocean and atmosphere, driven by the expansion and boiling of pore fluids surrounding intrusive magma in sedimentary basins. HTVCs are a common feature of Large Igneous Provinces (LIPs), which host the largest known magmatic intrusions on Earth. Given their nature and chronology, LIPs have historically been linked to major mass extinctions and global climate change, owing to their role in carbon degassing. The North Atlantic Igneous Province (NAIP, 61–58Ma and 56–53Ma) is the youngest large LIP emplacement and hosts hundreds of hydrothermal vents within the Vøring and Møre basins. Due to their timing and potential to emit a large volume of greenhouse gases, the HTVCs within the NAIP have been proposed to play a role in the onset and long duration of the Paleocene-Eocene Thermal Maximum (PETM, ca. 56 Ma). However, several aspects of the formation, timing, and impact of these particular HTVCs formation on the carbon cycle remain poorly understood. Here, we present a detailed stratigraphic and morphological reconstruction of the Modgunn Vent in the Vøring Basin, offshore Norway. High-resolution 3D P-Cable seismic data and borehole observations from the International Ocean Discovery Program (IODP) Expedition 396 reveal a multi-crater architecture, with four sub-craters formed through individual eruptive events, each associated with discrete sill intrusions and sediment infill phases. The four mapped craters present distinct subsidence, infill stratigraphy, and uplift signatures, indicating that, although currently clustered in a single HTVC, they formed independently and later amalgamated. Crater-specific uplift patterns and internal vent deformation features suggest a late-stage reactivation of vent conduits driven by renewed sill emplacement or fluid and mud migration. Biostratigraphic data tie the formation of the youngest crater in the Modgunn vent to the period immediately preceding the PETM. However, our seismic interpretation shows that the other three craters formed earlier. Our findings emphasise isochronous vent activity across the North Atlantic Igneous Province and reinforce a prolonged, dynamic scenario of greenhouse gas release. Further detailed subsurface imaging and stratigraphic analysis are crucial for refining models of vent evolution and, consequently, carbon degassing and its role in rapid climate perturbations.
How to cite: T. Pandolpho, B., Rollwage, L., M. Binde, C., Berndt, C., Planke, S., Bünz, S., H. Svensen, H., Nelissen, M., Frieling, J., and Brinkhuis, H.: Diachronous Evolution of a Multi-crater Hydrothermal Vent Complex in the Vøring Basin, offshore Norway, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15375, 2026.
Hydrothermal systems form when seawater flows through cracks and faults on the seafloor into the deeper layers of the Earth's crust, where it is heated by geothermal sources and reacts with host rocks, forming high-temperature, acidic fluids. These fluids rise and exit through seafloor vents, playing an important part in the Earth's geochemical cycles. During circulation, radium isotopes (224Ra, 226Ra) are enriched in hydrothermal fluids through rock—hydrothermal alteration, making the radium isotopes useful tracers for studying hydrothermal systems.
In previous studies, a method for measuring 224Ra and 228Th activities in sediments based on a delayed-coincidence counting system was developed, and 224Ra depth profiles were modelled using the general diagenetic equation to evaluate material transport processes at the sediment-water interface. Thus, in this study, we used the 224Ra/228Th disequilibrium in sediments to evaluate the impact of hydrothermal activity on the bottom sediments. Furthermore, the same 224Ra/228Th disequilibrium analysis method is applied across general oceanic areas to elucidate differences in radium fluxes caused by various factors in hydrothermal and non-hydrothermal regions.
The 224Ra/228Th disequilibrium analysis of cores collected from the Mienhua submarine hydrothermal system in the southernmost Okinawa Trough showed that 224Raex increases at a depth of 10-15 cm below the surface, then decreases below 17 cm. However, 224Raex decreases downward from the core top, which was collected at the margin of the hydrothermal zone. It is inferred that in the upper layer of cores from the hydrothermal system, numerous gaps created by hydrothermal fluids in the sediments facilitate direct exchange of pore water with seawater, resulting in lower 224Raex values within the top 10 cm of sediments. Whereas cores from the margin of the hydrothermal system show fluctuating 224Raex values in the upper 10 cm due to dynamic changes in the hydrothermal fluid. Additionally, 224Raex results in cores from non-hydrothermal areas showed lower values than those from the hydrothermal area, assuming a rapid depositional environment in these areas, which causes the rapid dissipation of 224Raex.
How to cite: Chang, C.-W., Su, C.-C., and Hsu, F.-H.: Application of 224Ra/228Th Disequilibrium Method for Investigating Benthic Fluxes and Hydrothermal Influence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6536, 2026.
Hydrothermal conditions are commonly found in a variety of terrestrial and extraterrestrial systems, such as deep ocean hydrothermal vents, geothermal basins, magmatic fluids from volcanic activity, and impact craters. Heat increases both mineral solubilities and reaction rates, increasing the likelihood of brine formation and changing dissolved elemental species. Differences in brine chemistries likely result in different secondary mineral assemblages formed during alteration, particularly differences in oxides and clay minerals, and impacts availability of nutrients for potential microbial processes. We further investigate these hydrothermal processes by reacting basaltic materials and glass-rich samples with different endmember brines at 350K to determine what secondary alteration products form. We reacted 20 g of basalt and mafic glass with 200 mL of near-saturated brines of NaCl, MgCl2, Na2SO4, MgSO4, 10% dilutions of each saturated brine,and ultra-pure water (UPW) for 50 consecutive days at 350K, mixing the reactors frequently. X-ray diffraction analyses show that pyroxene, apatite, and amorphous phases showed the largest relative wt% changes. Compared to the unreacted mafic glass, samples reacted with NaCl, MgCl2, and MgSO4 exhibited a relative increase in amorphous content, whereas UPW and Na2SO4 samples showed a slight decrease. Apatite phases decreased below detection limits for most samples except for near-saturated MgSO4. Additional alteration phases such as Fe and Ti oxides formed at low concentrations following reaction with most brine solutions. While aqueous Si concentrations (measured via ICP-OES) increased in most brine samples reacted with basalt and mafic glass, both near-saturated MgSO4 samples, basalt+10% saturated MgCl2, and basalt+10% saturated Na2SO4 exhibited a decrease in aqueous Si. Changes in dissolved Si concentrations were more prominent with mafic glass samples than basalt samples, despite basalt having greater relative amounts of Si-bearing species compared to glass as observed in XRD relative wt%. Despite the commonly assumed trend of increased dissolution at higher temperatures, smaller net changes in dissolved Si in brines were observed at 350K compared to lower temperature brine experiments. While apatite decreased in glass-rich samples during the alteration, aqueous P was not detected in any of the brine samples. Instead, phosphorus adsorption to preexisting mineral surfaces and new amorphous phases may have removed P from solution. The formation of new amorphous phases with higher surface areas likely increases the amount of reactive adsorption sites which results in greater sequestration of aqueous P and other potential biological nutrients in solution. Because amorphous phase content is impacted by differences in brine chemistries, dissolution and phase formation mechanisms that make nutrients available for microbial metabolic functions may therefore differ and suggest potential enhancements or limitations for habitability in extreme and extraterrestrial hydrothermal systems.
How to cite: Barbre, K., Elwood Madden, M., Elwood Madden, A., and Hodges, C.: Changes in Secondary Alteration Mineralogy and Brine Chemistry through Hypersaline Hydrothermal Alteration of Basalt and Mafic Glass, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8561, 2026.
Interactions between magmas and organic matter from host sedimentary rocks may lead to ore mineralization [1], hydrocarbon cracking [2] and thermogenic gas emissions [3], potentially disrupting the global carbon cycle. We reconstructed magma–hydrocarbon interaction processes by studying basaltic melts intruding bitumen- and oil-bearing sandstones in a continental rift setting, combining detailed field observations with geochemical analyses, melt and fluid inclusions study [4]. Our case study is Bile Island in the Oslo Fjord (Norway), where Upper Silurian sandstones are crosscut by a pyrobitumen-bearing sill and several dykes, which date back to the Oslo Rift activity, the northernmost branch of the 300 Myr-old Skagerrak Large Igneous Province [5]. These intrusions represent the magma plumbing system of an adjacent basaltic volcano from the earliest phase of the Oslo Rift, and the sedimentary succession in this area contains oil and bitumen mainly sourced from Cambrian–Ordovician organic-rich shales. Our multi-technique approach characterized the transformation of bitumen and oil into pyrobitumen along with abundant methane (CH4) and ethane (C2H6) emissions. Our geochemical dataset described element exchange and mass transfer between melts, fluids and host rocks, from magmatic to hydrothermal stages, depicting a scenario with magmatic intrusions of a large mafic complex intersecting a pre-existing petroleum system. Bile Island yields an extraordinary record, where magmatic and sedimentary carbon is synchronously released via the same volcanic vent(s), providing a viable explanation for methane emissions in volcanic areas and offering a new paradigm for degassing in the context of Large Igneous Provinces.
[1] Hoggard et al. (2020), Nat. Geosci. 13, 504–510.
[2] Senger et al. (2017), First Break 35, 47–56.
[3] Svensen et al. (2004), Nature 429, 542–545.
[4] Capriolo et al. (2026), J. Geol. Soc. https://doi.org/10.1144/jgs2025-094.
[5] Torsvik et al. (2008), Earth Planet. Sci. Lett. 267, 444–452.
How to cite: Capriolo, M., Callegaro, S., Aradi, L., Ackerson, M., Karlsen, D., and Svensen, H.: Magmatic and sedimentary carbon release from a mafic complex intersecting a petroleum system in the Oslo Rift (Norway), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13564, 2026.
The presence of liquid petroleum trapped within low-permeability vesicular basalt or mafic intrusions is more than a scientific curiosity, as it also challenges the conventional fluid migration and storage models in porous media. Its presence is significant because it may suggest complex primary magmatic porosity development, low temperature alteration and resulting fluid pathways, nano-scale deformation, or other processes leading to secondary porosity development. Thus the cases offer insights into processes controlling hydrocarbon and fluid flow systems in volcanic areas. In this contribution, we present the study of a Permian dolerite dyke at Tvedestrand in Norway and a vesicular basalt sample from West Greenland, both of which contain liquid oil. The Tvedestrand dyke is emplaced in Precambrian gneiss that was previously overlain by Cambrian black shales. The Greenland basalt is part of the North East Atlantic igneous province, underlain by petroleum-bearing sedimentary strata. Organic geochemistry indicates both oils to be immature, hence suggesting migration through these rocks after emplacement and cooling. We also show ultrahigh-resolution photographs in natural and ultraviolet light to show the distribution of petroleum compounds and image the microstructures controlling fluid migration. The parameters controlling fluid migration in tight crystalline rocks are important to constrain, as these are directly relevant to hydrocarbon exploration in unconventional settings and for hydrogen or carbon storage. We discuss the most likely mechanisms enabling fluid migration in these systems and their broader implications.
How to cite: Kihle, J. B., Polteau, S., Yarushina, V., Planke, S., Kiss, D., Svensen, H. H., and Callegaro, S.: Enigmatic occurrences of liquid oil in diabase intrusions and vesicular basalt, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6759, 2026.
The growing interest in natural hydrogen as a low-carbon energy carrier calls for a better understanding of its geological sources and migration pathways, particularly in marine rifted margins. In this study, we document active seepage from pockmarks offshore the Maltese Islands, providing the first evidence of hydrogen-rich emission in the Mediterranean Sea and offering new constraints on the geodynamic controls governing natural H2 circulation. Integrated multibeam bathymetry, sub-bottom profiler, and multichannel seismic data reveal more than 1,000 pockmarks preferentially aligned along NW-SE trending escarpments. These structures appear to be inherited transtensional faults from a Mesozoic Sicily Channel Rift, a rifting system that ultimately aborted prior to full continental break-up. Although no longer seismically active, these faults remain mechanically open and permeable, acting as long-lived fluid conduits that promote upward gas migration. Geochemical analyses of water-column samples collected within active pockmarks show anomalously high dissolved H2concentrations, associated with elevated helium values and systematic relationships with uranium, thorium, and light rare earth elements. These signatures indicate a predominantly crustal hydrogen source, most plausibly generated by radiolytic water splitting and water-rock interactions within the continental crust. We propose that hydrogen release in the study area is controlled by a leakage-dominated system, where structural inheritance from an aborted rift governs present-day fluid circulation in the absence of active tectonic deformation. This study highlights the critical role of fossil rift architectures as persistent pathways for deep-sourced gases and underscores the importance of considering aborted rift systems as prime targets for natural hydrogen exploration and for understanding long-term fluid flow in rifted continental margins.
How to cite: Spatola, D., Caracausi, A., Sulli, A., Hovland, M. T., Stagno, V., and Micallef, A.: Active hydrogen emissions offshore the Maltese Islands: implications for an aborted Mesozoic rift in the Sicily Channel, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7265, 2026.
Posters virtual: Thu, 7 May, 14:54–14:57 | vPoster spot 3
EGU26-1377 | Posters virtual | VPS25
Impact of segmentation pattern of the Pan-African trending strike-slip basement fault on the spatial distribution of hydrocarbon traps in SW IranThu, 07 May, 14:54–14:57 (CEST) vPoster spot 3
Abstract:
Strike-slip basement faults and their related segments are crucial for oil and gas exploration. These faults are considered favorable channels for hydrocarbon migration. The multistage activities of these faults influence the development of hydrocarbon-bearing structures. They can also produce fracture systems that enhance reservoir properties and boost oil and gas production. Understanding how strike-slip fault segments and their associated structures affect hydrocarbon accumulation is essential for geological research and exploration planning. This study aims to characterize the geometry and structural evolution of the strike-slip basement fault with Pan-African or Arabian trends, investigate the relationship between fault segments, and assess their impact on the distribution of hydrocarbon traps. This research focuses on the structural and tectono-sedimentary analyses of the Kazerun fault system based on processing and interpretation of the surface data (e.g., satellite images and aeromagnetic data) and the subsurface data (e.g., 2D and 3D seismic and well data) in the Zagros orogenic belt, SW Iran. The relationship between the segmented strike-slip fault zone and hydrocarbon reservoirs is analyzed through map view patterns and profile features. Results reveal that the Arabian-trending Kazerun fault system comprises segmented dextral strike-slip faults and is considered a transform and wrench fault. These faults display various planar configurations, including linear, en-echelon, horsetail splays, and irregular geometries in the map view. Based on the seismic data interpretation, three structural styles develop along the Kazerun strike-slip fault zone, including vertical or oblique, pull-apart (negative flower structure), and push-up (positive flower structure) segments. Releasing and restraining bends and oversteps formed at the tail end of the Kazerun strike-slip fault segments. In the study area, salt diapirism occurred along the pull-apart segment and the releasing bend. Hydrocarbon traps are developed in the push-up segment and the restraining bend. Fractures are less prominent in the vertical segments but more developed in push-up and pull-apart segments, which act as pathways for fluid migration and improving reservoir quality. The push-up segment and restraining bend exhibit a higher degree of branching fractures, making them the most significant for reservoir development. This research shows that strike-slip fault segmentation (in the form of fault overlapping or stepping) and their lateral linkage control the reservoir distribution and connectivity. Recognizing the growth and lateral connections of strike-slip fault segments is crucial for structural analysis and predicting fault-controlled reservoirs. These findings offer valuable insights into the structural characteristics of strike-slip fault zones and can enhance oil and gas exploration in the Zagros fold-and-thrust belt and other similar regions.
Keywords:
Strike-slip basement fault, Segmentation pattern, Oil/Gas fields, Zagros orogenic belt, SW Iran
How to cite: Soleimany, B., Tajmir Riahi, Z., Payrovian, G. R., and Sepahvand, S.: Impact of segmentation pattern of the Pan-African trending strike-slip basement fault on the spatial distribution of hydrocarbon traps in SW Iran, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1377, 2026.
EGU26-5147 | Posters virtual | VPS25
Soil CO₂ Emissions as Indicators of Fluid Pathways in Volcanic–Tectonic Environments: Insights from Vulcano IslandThu, 07 May, 14:57–15:00 (CEST) vPoster spot 3
Soil CO₂ emission is a key proxy for investigating fluid migration processes associated with volcanic and tectonic activity. In particular, the analysis of the spatial distribution of geochemical anomalies represents an effective tool for identifying active structures and zones of ongoing deformation. Numerous studies have shown that faults and fracture systems play a fundamental role in controlling the localization and evolution of surface geochemical anomalies.
Vulcano Island (Aeolian Archipelago, Italy) is characterized by intense hydrothermal activity and persistent soil CO₂ emissions, providing a natural laboratory to investigate the relationships between fluid circulation and active tectonic structures. In this study, we present an integrated analysis of soil CO₂ fluxes based on results obtained from periodic surveys and continuous soil CO₂ flux records acquired at key sites across the island.
Periodic measurements are performed on fixed spatial grids, allowing the production of soil CO₂ flux maps and the identification of areas characterized by elevated degassing rates. At selected sites, the carbon isotopic composition of gases is analyzed to constrain gas sources.
These spatial datasets provide insights into the structural control exerted by the main tectonic lineaments on gas release at the surface. Continuous CO₂ flux monitoring enables the investigation of temporal variations and transient degassing signals potentially related to seismic and tectonic processes. In particular, the recent volcanic crisis at Vulcano Island, started on 2021, characterized by a marked increase in soil CO₂ flux, allowed a more detailed identification of preferential CO₂ emission pathways, highlighting zones of enhanced permeability associated with fault and fracture systems.
This work is carried out within the framework of the CAVEAT project (Central-southern Aeolian islands: Volcanism and tEArIng in the Tyrrhenian subduction system), which aims to provide a comprehensive understanding of the current geodynamics of the southern Tyrrhenian region.
How to cite: De Gregorio, S., Camarda, M., Capasso, G., Di Martino, R. M. R., Pisciotta, A., and Prano, V.: Soil CO₂ Emissions as Indicators of Fluid Pathways in Volcanic–Tectonic Environments: Insights from Vulcano Island, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5147, 2026.
