Intrusion of magma into sedimentary basins leads to devolatilization of the host rock in contact metamorphic aureoles. Hydrothermal vent complexes are formed by fracturing the overburden sediments if sufficient overpressure is developed in the aureoles, releasing hot fluids and gases into the hydrosphere and atmosphere. We have mapped the structure and distribution of hydrothermal vent complexes using extensive 3D seismic reflection surveys (c. 40,000 km²) in the Møre and Vøring basins offshore mid-Norway by a combination of seismic horizon and attribute mapping. The seismic horizons have been tied to exploration wells to constrain the timing of their formation. A shallowly buried vent complex, the Modgunn Vent, was subsequently imaged by high-resolution P-Cable 3D seismic data collected using the R/V Helmer Hansen. The upper part of this vent complex was recently drilled by five holes during IODP Expedition 396. In total, more than a thousand hydrothermal vent complexes have been identified in the two basins. A typical vent complex has a diameter of between a few hundred meters and five kilometers and extends from the tip of a sill intrusion to the paleosurface. The upper part of the vent complexes are commonly eye-shaped, where the lower surface represents the base of a crater and the upper dome-shaped surface represents the top of the crater infill. Overlying reflections are sub-parallel to the upper vent surface, locally associated with discontinuous high-amplitude reflections and minor faulting. The chimney-shaped lower part of the vent complexes are characterized by disrupted reflections, sometimes including bulbous-shaped transparent bodies with high-amplitude reflections at the top and base. Surrounding reflections are often dipping towards the center of the chimneys. The structure of the vent complexes suggest they were dominantly formed by erupting fluids and sediments during the Paleocene-Eocene Thermal Maximum (PETM), about 56 million years ago. The craters were subsequently rapidly infilled by sediments, and later inverted forming domes above the craters. High-amplitude discontinuous reflections above some vent complexes are interpreted as evidence of long-term fluid flow, sometimes lasting until recent times.

How to cite: Planke, S., Manton, B., Berndt, C., Bünz, S., Binde, C. M., Svensen, H. H., and Myklebust, R.: The structure and origin of hydrothermal vent complexes in volcanic basins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12778, https://doi.org/10.5194/egusphere-egu23-12778, 2023.

Mud volcanoes are diapirical structures expression of cold overpressured fluidized fine sediments rising from depths of hundreds of meters. When depositional process was fast enough to hamper dehydratation of buried sediments, isolated geological reservoirs are generated marked by elevated fluids pressure also due to gas produced by decompositional processes affecting trapped animals.  Due to the density difference with respect to surrounding rocks and because of the high fluid pressure, those sediments move upwards by following faults or other mechanical discontinuities. In the last decades such Sedimentary Diapirism has increasingly interested scientific community as possible markers of hydrocarbon reservoirs, as responsible for explosive events and their close connection with regional seismotectonic activity. Many studies, in the last years, tried also to find a solid relationship between mud volcanoes and gases emissions, in particular CO₂ and CH₄, two of the most important greenhouse gases.

Among the Italian mud volcanoes, those of Nirano (north Italy), represent a typical example of mud volcanic field, with small and uneventful surface structures. This natural reserve is marked by three main lined up surface structures along the NE-SW direction, close to small pools with less thick clay materials, called “salse”.

The structure beneath Nirano mud volcanic field has been investigated by several methodologies, such as geoelectrical, gravimetrical and seismic surveys. In the present work, the study of dynamic behaviour of these structures is focused on aiming at monitoring gas outflow and locating eventual ducts and secondary reservoirs at shallow depth. Specifically, seismic signals possibly associated to gas outflow are investigated by deploying seismic arrays and three directional velocimetric stations.

Outcomes of these measurements show that subsonic seismic emissions of these structures present analogies with to those of active volcanoes, possibly due to similar dynamic mechanisms, probably associated to gas bubbling phenomena. Three kinds of seismic activity have been identified: background ambient vibrations, short periodic energy bursts (drumbeats) and high energy paroxysmic phases. All these observed events, compared to that of active volcanoes, present higher frequencies range.

The analysis of these signals, in particular of the drumbeats phases, allow the location of the sources. The final locations appear to be local (limited to a few tens of meters away from instruments) and shallow (around 5-10 m from the surface). If these emissions were actually associated to gas bubbling, this kind of outcomes could represent an effective tool for measuring gas outflow and monitoring outgoing mud volcanoes activity.

How to cite: Carfagna, N., Brindisi, A., Paolucci, E., Piombo, A., and Albarello, D.: Seismic observation at Nirano mud volcanoes, north Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8193, https://doi.org/10.5194/egusphere-egu23-8193, 2023.

Mud volcanoes are distributed throughout the globe, both on- and offshore. Mud volcanism has been widely investigated from the geological, geophysical, and geochemical points of view. The study of mud volcanoes has important implications in energy resource exploration, geohazard identification, and greenhouse gas emissions assessment (mainly CH₄ and CO₂). Mud volcano eruptions are mainly driven by a gravitative instabilities and fluid overpressure, due to the overall low density of clay/water/gas mixtures with respect to surrounding units. The geohazard of mud volcanoes is to date underrated despite the violent eruptive examples occurred in the past. For instance, the eruption of the Piparo mud volcano (1997, island of Trinidad) damaged electrical and water infrastructures and killed animals and livestock. In 2014, the eruption of the Macalube di Aragona (Italy) mud volcano killed two children. The understanding of the mechanisms regulating mud volcanoes is, therefore, important also in terms of hazard evaluation. To date, a physical conceptual model of the Nirano Salse, Italy, ascribes the eruptions to the presence of over-pressurized fluids that are expelled from a main deep reservoir. The latter is put into communication with the surface due to the episodically reactivation of pre-existing faults or pipes. The debate about this conceptual model is still open. To improve our current understanding, a new high-resolution dataset of gravimetric data was acquired. Our goal is to provide an insight about the subsurface structure of the investigated domain. The gravimetric inversion aims to identify the structural setting of Nirano and the presence of gas traps and faults. The gravity inversion results indicate the existence of a low-density zone (1200-1500 m long, 100-200 m wide, 800 m deep) with an almost planar shape aligned along a NW-SE structural trend, typical of the Northern Apennines chain. This zone likely represents the intrusion of mud/gas in the damage zone of a sub-vertical fault, which feeds shallow fluid reservoirs.

How to cite: Nespoli, M., Antonellini, M., Albarello, D., Lupi, M., Cenni, N., Rivalta, E., and Piombo, A.: The ”Salse di Nirano” mud volcanoes: hints from gravity data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13707, https://doi.org/10.5194/egusphere-egu23-13707, 2023.

Fluid migration in sedimentary basins has profound effects on a range of geological processes, including the methane cycle, tectonic and sedimentary geohazards, and microbial communities in the oceans. The Alboran Sea is a tectonically active basin characterized by contourite drifts that host migrating fluids, expressed in places by pockmarks and mud volcanoes, the latter associated with seafloor methane seepage. In this study, we examine the composition and origin of near-seafloor fluids in the Alboran Sea using sediment cores (up to 20 m long) from a pockmark field (site CL06), a nearby background area (site CL04) and a fault zone (site CL55).

We use halogens (Cl, Br, and I) dissolved in interstitial water to understand the origin of fluids in the Alboran Sea. Chlorine is considered a conservative ion in interstitial water geochemistry, its concentration changing with pore water salinity. Iodine has a strong biophilic character and is incorporated in organic matter deposited with sediments, which during burial decomposes in response to geothermal heat or microbial activity to produce methane. Iodine and methane concentrations are strongly correlated and highly concentrated compared to seawater, so that iodine has been used as a methane tracer. Bromide also has a weak biophilic character and behaves similarly to iodine.

Interstitial water was extracted aboard ship using Rhizon samplers. Chloride concentration was determined by ion chromatography (ICS-1600, DIONEX) at the Tokyo University of Marine Science and Technology; iodine and bromine concentrations were determined by Inductively coupled plasma mass spectrometry (ICP-MS Agilent 7500) at Micro Analysis Laboratory, Tandem accelerator (MALT), University of Tokyo.

The results reveal halogen profiles that differ between the pockmark and fault sites, providing evidence of different modes of fluid migration within the contourite drifts of the Alboran Sea:

(1)Pockmark and background sites: surprisingly, halogen profiles are similar at these two sites. Cl concentration decreases with depth from 610 to 590 mM over the 15 m length of the cores, a trend indicating fresher water is present in deeper sediments. I and Br concentrations increase with depth (I: 0 to 70 µM, Br: 760 to 820 µM). I and Br are strongly enriched (up to 8% and 60%, respectively) by a deep fluid source, which may relate to high TOC or evaporated seawater in deeper sediment.

(2)Fault zone site: in contrast to the other two sites, Cl concentration increases with depth from 600 to 610 mM over the 16 m length of the core 55, a trend indicating saline water is dominant in deeper sediments. I and Br concentrations increase with depth (I: 35 to 70 µM, Br: 800 to 830 µM). I and Br concentrations in near-seafloor sediments are usually less strongly affected by organic decomposition, with concentrations as low as seawater; however, at site 55, I and Br are strongly enriched in near-seafloor sediments. This observation suggests vertical fluid migration is active and reaches the seafloor to maintain high I and Br concentrations.

How to cite: Owari, S., Ketzer, M., Suzuki, N., d'Acremont, E., Lafuerza, S., Leroy, S., Praeg, D., and Oliveira de Sa, A.: Halogens dissolved in interstitial water reveal the origin of migrating fluids in sediments of the Alboran Sea (western Mediterranean), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-182, https://doi.org/10.5194/egusphere-egu23-182, 2023.

Mud volcanoes erupt sediment sourced from subsurface, consolidated mudstones via a conductive flow pathway (conduit). A 3-D seismic survey of mud volcanoes in the Eastern Mediterranean shows localised thinning of the source unit in zones at the base of each conduit, interpreted to result from mud depletion [1]. These depletion zones are typically bowl-shaped, suggesting that they grow radially outward from the base of the conduit. Fluidisation, whereby consolidated sediments can be mobilised by migrating pore fluids of a sufficient velocity, has previously been proposed as a mechanism to explain mud volcano formation [2,3]. However, the dynamics of fluidisation during eruptions are poorly understood due to limited subsurface observations. We hypothesise that the sudden opening of the conduit initiates rapid fluid expulsion, inducing porous flow through and fluidisation of the source rock. This is in contrast to previous modelling work, which attributes the flow of mud to plastic failure [4]. We present a novel theoretical model of flow-driven fluidisation, capturing the dynamic interface between the solid and fluidised regions. The solid region is modelled as a poroelastic material and the fluidised region is modelled as a viscous fluid. Our results indicate that fluidisation initiates at the conduit and spreads radially. We demonstrate that fluidisation amplifies the rate of fluid flow and vice versa, leading to nonlinear growth of the fluidised region. We explore the mechanisms that regulate this growth to produce a depletion zone with a characteristic size.

[1] Kirkham, Chris, et al. "The spatial, temporal and volumetric analysis of a large mud volcano province within the Eastern Mediterranean." Marine and Petroleum Geology, https://doi.org/10.1016/j.marpetgeo.2016.12.026

[2] Brown, Kevin M. "The nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems." Journal of Geophysical Research: Solid Earth, https://doi.org/10.1029/JB095iB06p08969

[3] Nermoen, Anders, et al. "Experimental and analytic modeling of piercement structures." Journal of Geophysical Research: Solid Earth, https://doi.org/10.1029/2010JB007583

[4] Mazzini, Adriano, et al. "Strike-slip faulting as a trigger mechanism for overpressure release through piercement structures. Implications for the Lusi mud volcano, Indonesia." Marine and Petroleum Geology, https://doi.org/10.1016/j.marpetgeo.2009.03.001

How to cite: Kearney, L., MacMinn, C., Katz, R., and Cartwright, J.: The dynamics of fluidisation during mud volcano eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9938, https://doi.org/10.5194/egusphere-egu23-9938, 2023.

The behavior and the rheology of mud during the emplacement of terrestrial sedimentary volcanism has been extensively investigated (e.g., [1,2]). In contrast, this is not the case for Mars and other planetary bodies within the Solar System for which sedimentary volcanism has been proposed [e.g., 3]. The propagation behavior of low viscosity mud in a low-pressure chamber, that partly simulated the environment of Mars, was firstly experimentally studied by [4,5]. Their work revealed that bentonite-based mud could flow in a completely different manner in such conditions. On Mars, mud flowing over cold surfaces would rapidly freeze due to evaporative cooling [6] forming an icy-crust leading to the behavior of some of the mud flows in a similar manner to pahoehoe lava on Earth [4]. However, we lack the knowledge how variations of salt types and their content would affect the flow style and finite pattern of such mudflows as a presence of various salts can be natural on Mars as well (e.g., [7,8]). Therefore increased content of salts can strongly affect the P-T-t dependent cooling and at the same time the rheology of mud which can lead to significantly different propagation potential and finite geometry. 

In a set of experiments, performed in the Mars Simulation Chamber (Open University, UK), we tested several selected salts relevant for the Mars environment (namely NaCl, MgSO4, Na2SO4 and CaSO4) and various salinities of these salts (0.5-15 wt%). These experiments were performed in metallic trays infilled with dry and precooled sand to -25 °C (to simulate the martian surface) and which were inclined to 5°. A container filled with 500 ml mud was positioned above the tray. Then we decreased the pressure to 4.5-6 mbar and released mud. Experiments were documented by a system of video cameras situated around the model box. At the same time, referential cooling experiments of binary solutions (water-salt) were performed. 

Results revealed contrasting scenarios of mud propagation which result in a wide range of shapes. We also found several transitional regimes in behavior between current concentrations and various salts. It was confirmed that the high content of salt in a mud or mud composed by different salts can undergo slightly to significantly different cooling according to thermodynamic equilibria which shifts both freezing and boiling point. Thus, the resultant style of flow process and finite morphology of such mudflows can be highly variable. For example, high content of MgSO4 (typically 5-10 wt%) leads to development of long and narrow streams and with increasing content also develops a “ropy pattern” structure, whereas the same behavior occurs for 2.5 wt% of the NaCl.  

References: [1] O’Brien and Julien (1988), Journal of Hydraulic Engineering 114 [2] Laigle and Coussot (1997), J. Hydraul. Eng., 123 [3] Ruesch et al. (2019) Nature Geoscience 12 [4] Brož et al. (2020), Nature Geoscience [5] Brož et al. (2020), EPSL 545 [6] Bargery et al. (2010), Icarus 210(1), Chevrier et al. (2020), The planetary science journal, 1(3) [8] Nuding, et al. (2014), Icarus, 243.

How to cite: Krýza, O., Brož, P., Fox-Powell, M., Pěnkavová, V., Mazzini, A., Conway, S., Hauber, E., Sylvest, M., and Patel, M.: The presence of salts changes the architecture of potential mudflows on Mars - insights from laboratory simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3182, https://doi.org/10.5194/egusphere-egu23-3182, 2023.

Contemporary studies conducted in northern polar regions reveal that permafrost stability plays an important role in the modern carbon cycle as it potentially stores considerable quantities of greenhouse gases. Rapid and recent warming of the Arctic permafrost is resulting in significant greenhouse gas emission, both from physical and microbiological processes. The potential impact of greenhouse gas release from Antarctica is now also being investigated. In Antarctica, the McMurdo Dry Valleys comprise 10% of the ice-free soil surface areas in Antarctica and like the northern polar regions are also warming albeit from lower mean temperatures.

The work presented herein examines a comprehensive sample suite of soil gases (e.g., CO₂, CH₄ and He) concentrations and CO₂ flux measurements conducted in the Taylor Valley during the Austral summer 2019/2020. Analytical results reveal the presence of significant concentrations of CH₄, CO₂ and He (up to 18,447 ppmv, 34,400 ppmv and 6.49 ppmv, respectively) at the base of the active layer. When compared with the few previously obtained measurements, we observe increasing CO₂ flux rates (estimated CO₂ emission in the study area of 21.6 km² ≈ 15 tons day^-1). The distribution of the gas anomaly, when compared with geophysical investigations, implies an origin from deep brines migrating from inland (potentially from beneath the Antarctic Ice Sheet) towards the coast beneath the permafrost layer. These newly obtained data provide a baseline for future investigations aimed at monitoring the changing rate of greenhouse gas emission from Antarctic permafrost, and the potential origin of gases, as the southern polar region warms.

How to cite: Wilson, G., Ruggiero, L., Sciarra, A., Mazzini, A., Florindo, F., Tartarello, M., Mazzoli, C., Anderson, J., Romano, V., and Ciotoli, G.: Permafrost degassing in Taylor Valley, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1791, https://doi.org/10.5194/egusphere-egu23-1791, 2023.

The southern Apennines are affected by great crustal deformation and tectonic activity, where fluids from different reservoirs mix and rise to the surface through fault structures. Tramutola well (TRW) is an old borehole built by ENI, with the occurrence of bubbling gases located in the High Agri Valley (HAV), Southern Italy. The HAV is an inter-montane basin of the southern Apennine chain characterized by complex geological setting and high seismicity, this area hosts also the largest onshore Western European oil field. TRW is about 400 m deep it crosses clays, silicic clays and silicic limestone and is characterized by the continuous emission of thermal water (28°C) and bubbling gas. The water belong to Na-HCO3 hydrofacies.  TRW gases are CH₄-dominated (82,6 %), and low amounts of N₂ (12,9%), CO₂ (1,7%), C₂H₆ (0,3%). The noble gases are used to discriminate the fluids origin (atmospheric, crustal and mantle). The ⁴He/²⁰Ne ratio values are in three orders of magnitude higher that air-one (0,318) and ⁴⁰Ar/³⁶Ar ratio it is about 320 (Air=295.5; Hilton and Porcelli, 2003), this confirm the atmospheric contribution is present. Value Helium isotope (³He/⁴He, expressed as R/Ra) is between 1,13 and 1,26 Ra, and indicate a radiogenic component with a contribution of a mantle-derived helium (~20%). Methane isotope composition indicates a likely microbial isotopic signature (δ¹³C-CH₄ =-63‰, δD-CH₄= −217‰), probably due to either (1) biodegradation processes of thermogenic hydrocarbons or (2) ongoing microbial methanogenesis in the shallow organic‐rich clays hosting the gas. The δ¹³C-CO₂ value between of -3.5‰ and -6‰ VPDB, consistent with a mantle origin. The gases have low CO₂/³He ratios compared to mantle carbon end-member, probably due to secondary processes such as calcite precipitation. In conclusion, at Tramutola well have three gas sources and their possible mixing processes: (1) Shallow source, highlighted by atmospheric gas and rainwater entering the system through water infliltration; (2) crustal sources, CH4-dominant gas sources in correspondence of the hydrocarbon reservoir; (3) SCLM mantle source, mantle-derived fluids uprising through lithospheric normal faults.

How to cite: Zummo, F., Buttitta, D., Caracausi, A., and Paternoster, M.: Geochemical and isotopic study of Tramutola thermal water (High Agri Valley, Southern Italy): Interaction between crustal and mantle fluids, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3908, https://doi.org/10.5194/egusphere-egu23-3908, 2023.