Volcanic Fluids Research Articles

Volcanic tremor associated with successive gas emission activity at a boiling pool: Analyses of seismic array and visible image data recorded at Iwo-Yama in Kirishima Volcanic complex, Japan

Volcanic tremors are often observed during volcanic activity and volcanic eruptions, and their generation processes provide clues for understanding volcanic fluid activity underground and eruption dynamics. However, tremors are characterized by continuous oscillations that mask P- and S-waves; hence few studies have precisely located the source, which is the most fundamental information for understanding the generation mechanism. In this study, we focus on volcanic tremors excited by continuous gas emissions occurring at a vent called Y2a in Iwo-Yama, the Kirishima Volcanic Complex, Japan, to clarify the source process of the tremor as well as gas emission activity. We simultaneously observed the volcanic tremor by deploying a small aperture array consisting of six seismometers and the gas emission activity by using a newly developed visual IoT system that can be operated without commercial electricity. MUSIC analysis locates the tremor at depths ranging from the ground surface to approximately 200 m beneath the Y2a and Y2b vents, which are approximately 30 m apart, for approximately four months from November 2021 to February 2022. The source locations of the tremors in the 2 Hz (1.2–2.6 Hz), 4 Hz (3–4 Hz), and 5 Hz (4–5.5 Hz) ranges show some differences and changes with time. The source location tends to become deeper when the 2 Hz amplitude is large. The infrasound generated by gas emission activity is dominant in the tremor signals, which are recognized in the wave propagation velocity with an acoustic velocity of 330 m/s when the 2 Hz amplitude is small. The visual IoT system succeeded in detecting long-term changes in the gas emission activity, and we found that the 2 Hz amplitude of tremor was well correlated with the amount of hot water in the boiling pool of Y2a, which was controlled by precipitation and evaporation during non-rainy days. From these observations, we infer that the volcanic tremor is generated by resonance of volcanic gas and hot water in a crack-like structure beneath Y2a. The resonance was triggered by the counterforces of the gas emissions in the boiling pool, and the infrasound was dominant during periods of hot water depletion in the boiling pool. Temporal changes in the source depths may be caused by changes in the fluid properties, configuration of the resonator and/or the strengths of the underground sources and infrasound. Our simultaneous observations of seismic array and visual IoT system clarify that even the continuous gas emission activity that looks stable is controlled by external sources such as precipitation.

Stacking of Distributed Dynamic Strain Reveals Link Between Seismic Velocity Changes and the 2020 Unrest in Reykjanes

AbstractIn this study, we measure seismic velocity variations during two cycles of crustal inflation and deflation in 2020 on the Reykjanes peninsula (SW Iceland) by applying coda wave interferometry to ambient noise recorded by distributed dynamic strain sensing (also called DAS). We present a new workflow based on spatial stacking of raw data prior to cross‐correlation which substantially improves the spatial coherency and the time resolution of measurements. Using this approach, a strong correlation between velocity changes and ground deformation (in the vertical and horizontal direction) is revealed. Our findings may be related to the infiltration of volcanic fluids at shallow depths, even though the concurrent presence of various processes complicates the reliable attribution of observations to specific geological phenomena. Our work demonstrates how the spatial resolution of DAS can be exploited to enhance existing methodologies and overcome limitations inherent in conventional seismological data sets.

Thermal pattern of Tatun volcanic system by satellite-observed temperatures and its correlation with earthquake magnitudes

The land surface temperature (LST) of volcanoes detected from satellite sensors reflects the thermal status of heat sources in the subsurface. Volcanic earthquakes occur as magma and volcanic fluids transport to the surface from depth. Thus, both LST and earthquake magnitude are key parameters to the study of active volcanoes. Here we investigate the volcanic status of Tatun Volcanic Group (TVG) based on LST and seismic observations. The Earth-observing satellites onboard thermal sensor derived land surface temperature, and the seismic records retrieved volcanic earthquake magnitude are used to delineate the past and current pattern of volcanic activity plus the future trend of the TVG. The spatiotemporal distribution of LST and volcanic earthquake magnitude in TVG are analyzed. The high-similarity trends of the 4-decade LST time series and 3-decade earthquake magnitude time series are inspected. The retrieved surface thermal pattern shows the non-steady-state nature of the subsurface thermal sources at this volcanic complex. The LST trend exhibits a rather positive correlation with the energy released from volcanic earthquakes and consequently, the presumption on the connection between LSTs and earthquakes is validated.

Subsurface magma movement inferred from extensometer and tiltmeter records during the early stage of the 2018 Shinmoe-dake eruptions, Japan

We infer the temporal changes in the pressure sources that induced crustal deformation during the 2018 Shinmoe-dake eruption using strain and tilt observations and discern that the deep magmatic activity associated with the early stage of this eruption began approximately 19 h earlier than the previously defined onset of magmatic activity. Distinct tilt changes were observed from around 09:00 on 6 March to 12:00 on 8 March 2018 (JST), coincident with observed lava outflow into the crater and lava dome formation. Existing studies have attributed this tilt change to the onset of the deflation of a spherical pressure source located at ~ 7 km bsl (below sea level) to the northwest of Shinmoe-dake. Here we examine strain and tilt data that were acquired in the Kirishima volcanic group, and we find that the distinct changes in the measured strain at Isa-Yoshimatsu Observatory began at around 14:00 on 5 March. This change can be explained by the deflation of a spherical pressure source, thereby suggesting that the onset of magma ascent was earlier than previously thought. The time variation in the spherical pressure source is estimated using the time-dependent inversion of the Ensemble Kalman Filter; the deflation source ascended from ~ 11 to 7 km bsl during Phase 1 (14:00 on 5 March to 06:00 on 6 March) and descended from 7 to 8 km bsl during Phase 2 (06:00 on 6 March to 12:00 on 8 March). Interferometric synthetic aperture radar analysis suggests that a dike intrusion had occurred just below Shinmoe-dake crater until 5 March, and this inflatable crustal deformation is attributed to the emplacement of residual volcanic fluids from the 2011 eruption. It is also known that the surface eruptive activity increased during Phase 1, including an increase in ash venting from the night of 5 March. These strain and tilt observations, therefore, suggest that magma ascended from ~ 11 km bsl to the magma reservoir at 7 km bsl during Phase 1, followed by a deflation of the magma reservoir during Phase 2 due to the large magma supply to the surface.Graphical

On the Diversity and Formation Modes of Martian Minerals

AbstractA systematic survey of 161 known and postulated minerals originating on Mars points to 20 different mineral‐forming processes (paragenetic modes), which are a subset of formation modes observed on Earth. The earliest martian minerals, as on Earth, were primary phases from mafic igneous rocks and their ultramafic cumulates. Subsequent primary igneous minerals were associated with products of limited fractional crystallization, including alkaline and quartz‐normative lithologies. Significant mineral diversification occurred via precipitation of primary phases from aqueous and atmospheric fluids, including authigenesis, hydrothermal and cryogenic precipitation, and evaporites, including freeze drying during eras of low atmospheric pressures. In particular, hydrothermal mineral formation associated with both volcanic fluids and sustained hydrothermal activity in impact fracture zones may have triggered significant mineral diversification, though as yet undocumented. At least 65 such primary minerals have been identified by flown missions to Mars and from martian meteorites. A host of secondary martian minerals were produced by near‐surface processes related to water/rock interactions, including hydration/dehydration, oxidation/reduction, serpentinization, metasomatism, and a variety of diagenetic alterations. Additional mineral diversity resulted from metamorphic events, including thermal and shock metamorphism, lightning, and bolide impacts. However, several dominant sources of mineral diversity on Earth, including (a) extensive fluid/rock interactions and element concentration associated with plate tectonics; (b) high‐pressure regional metamorphism associated with plate tectonics; and (c) biologically mediated mineralization—are not known to be in play on Mars. Consequently, we estimate the total mineral diversity of Mars to be an order of magnitude smaller than on Earth.

Sulfur origin and flux variations in fumarolic fluids of Vulcano Island, Italy

A sharp increase in volatiles, especially SO2 fluxes from the solfataric plume and diffuse CO2 from the soils of the La Fossa crater area, started in June 2021, and subsequently from the Levante Bay area, suggests renewed unrest at Vulcano Island, Italy. This event has encouraged monitoring activities and stimulated new research activities aimed at understanding the recent evolution of the volcanic system. In this study, the chemical and isotopic composition of fumaroles, thermal waters, and soil gases from the main degassing areas of Vulcano Island with a special focus on sulfur isotopes, are used to investigate the fluid transfer mechanism inside the volcano. Sulfur is one of the most abundant volatile elements present in magmas and volcanic fluids from the La Fossa crater, where it mostly occurs as SO2 and H2S at variable relative concentrations depending on oxygen fugacity and temperature. The isotope composition and the chemical ratio of sulfur species depict a complex hydrothermal-magmatic system. In addition, we utilize the installed SO2 monitoring network that measures the total outgassing of SO2 with the UV-scanning DOAS technique. The SO2 fluxes from the La Fossa crater fumaroles, coupled with the SO2/CO2 and SO2/H2O ratios, were measured to evaluate the total mass of fluids emitted by the shallow plumbing system and its relationship with the status of volcanic activity. Combining the whole chemical composition of fumaroles analyzed with a discrete, direct sampling of high-temperature fumaroles located on the crater summit, the output of discharged water vapor has been estimated (5,768 t·d−1). On the basis of the water output, we estimated the total thermal energy dissipated by the crater during the last enhanced degassing activity (167 MW). This strong and sharp increase in energy observed during the current crisis confirms the long-growing trend in terms of mass and energy recorded in recent decades, which has brought the surface system of Vulcano Island to a critical level that has never been recorded since the last eruptive event of 1888–91.

3-D crustal shear wave velocity model derived from full-waveform tomography for Central Honshu Island, Japan

SUMMARY We present a crustal shear wave (S-wave) velocity model for central Japan that accurately captures the previously mapped geology and lithology of the region. We perform a full-waveform tomographic inversion using a large seismic data volume that was recorded by the dense, permanent seismic monitoring network that spans the Japan Islands to resolve the seismic structure beneath central Honshu Island. The inversion reduces the time–frequency phase misfit by 16.4 and 6.7 per cent in the 20–50-s and 10–30-s period ranges, respectively. We infer that the resolved seismic velocity anomalies in our inversion reflect a range of subsurface features, including volcanic fluids, dehydration fluids from the subducted crust and sedimentary basins. In contrast to previous S-wave velocity models of the same region, which have been based primarily on first-arrival tomography, our S-wave velocity model is based on the explicit computation of the full seismic wavefield. This approach makes our model more suitable for modelling seismic wavefields in the 10–50-s period range and enables high-resolution imaging of the subsurface.

Geological constraints on volcanic-fluid pathways at the Maruyamasawa-Fumarolic-Geothermal-Area, and its relation to the present magmatic-hydrothermal activity in Zao Volcano, Tohoku, Japan

A field survey based on outcrop and hand-dug trench observations was conducted in the Maruyamasawa-Fumarolic-Geothermal-Area (MFG) of the Zao Volcano. Powder X-ray diffraction and microscopic analyses of samples collected from the MFG provide new possible links between underground magmatic–hydrothermal activity and fumaroles in the volcanic system. The MFG is a fumarolic area (solfatara) with evidence of intense geothermal activity, such as hot and cold springs, fumaroles precipitating native sulfur, and ongoing fumarolic alteration. The MFG occurs on a talus slope that mainly comprises detritus from Late Cretaceous granitoids mixed with blocks of the ca. 1 Ma Robanomimiiwa Pyrocalstics (Rmp). The Rmp is well exposed on a cliff behind the talus slope, and it unconformably overlies the granitoids with a NW-striking, SW-dipping contact. The southwestward extension of the Rmp-granitoids unconformity is projected laying approximately 500 m below the Okama crater, which is 800–1000 masl. The mineral assemblages of the MFG altered rocks are mainly 1) cristobalite + native sulfur ± pyrite, 2) cristobalite + quartz + alunite + kaolin-group minerals + smectite, and 3) quartz-only (intensely silicified) rocks. These mineral associations indicate a typical shallow acidic environment between steam-heated and fumarolic alteration zones. Three sandy layers (Layers 1 to 3 from bottom to top) are recognized in the hand-dug trench: Layer 1 is brown, poorly sorted and well-consolidated, Layer 2 is pale gray to gray and moderately sorted, and Layer 3 is pale gray and poorly sorted. The 14C dating of a paleosol underlying Layer 3 constrains the deposition event to around 437 ± 20 yrBP (2σ: 1429–1470). The presence of gray basaltic andesite (Rmp), granitic fragments (granitoids), and altered rocks (MFG constituent) in these layers suggests detrital remobilization from the MFG talus slope by rainfall (snowmelt) that emplaced thin lahar deposits. Furthermore, the detrital cristobalite and alunite in the L1-L3 matrix are minerals of fumarolic origin contained in the MFG altered rocks. These results indicate that the fumarolic activity and alteration of the MFG occurred before the deposition of these layers.Based on this information, we propose the following model for the MFG activity: (1) The Rmp-granitoids unconformity behaves as an open pathway for ascending volcanic fluids and controls the MFG geothermal features. (2) The MFG was formed over 600 years ago, probably during early Okama crater activity at the 1200s CE. (3) Volcanic fluids have ascended through the unconformity over the last several hundred years. Therefore, careful monitoring of the MFG is crucial for detecting surface anomalies that could indicate imminent eruptions of the Zao Volcano.

Relationships between fluid mixing, biodiversity, and chemosynthetic primary productivity in Yellowstone hot springs.

The factors that influence biodiversity and productivity of hydrothermal ecosystems are not well understood. Here we investigate the relationship between fluid mixing, biodiversity, and chemosynthetic primary productivity in three co-localized hot springs (RSW, RSN, and RSE) in Yellowstone National Park that have different geochemistry. All three springs are sourced by reduced hydrothermal fluid, but RSE and RSN receive input of vapour phase gas and oxidized groundwaters, with input of both being substantially higher in RSN. Metagenomic sequencing revealed that communities in RSN were more biodiverse than those of RSE and RSW in all dimensions evaluated. Microcosm activity assays indicate that rates of dissolved inorganic carbon (DIC) uptake were also higher in RSN than in RSE and RSW. Together, these results suggest that increased mixing of reduced volcanic fluid with oxidized fluids generates additional niche space capable of supporting increasingly biodiverse communities that are more productive. These results provide insight into the factors that generate and maintain chemosynthetic biodiversity in hydrothermal systems and that influence the distribution, abundance, and diversity of microbial life in communities supported by chemosynthesis. These factors may also extend to other ecosystems not supported by photosynthesis, including the vast subterranean biosphere and biospheres beneath ice sheets and glaciers.

Molecular distribution and stable carbon isotopic composition of lipid biomarkers of Shin-Yan-Ny-Hu Mud volcanoes in southwestern Taiwan: Implications for the origin and diagenesis

The Shin-Yan-Ny-Hu (SYNH) MVs are typical subaerial mud volcanoes in southwestern Taiwan. The lipid biomarkers and their stable carbon isotopes were firstly examined to delineate the mud breccia sources, depositional environments, thermal maturity, probable source strata and the migration framework of volcanic fluid. The sediment organic matter within active SYNH MVs principally stemmed from the petroleum derivatives, bacteria and terrigenous C3 plants suggested by the following indicators: the CPI of n-alkanes (∼1); the distribution and δ13C values of saturate, fatty acids and the plot of Pr/n-C17 vs. Ph/n-C18 ratios. The Pr/Ph ratios, the plot of Pr/n-C17 vs. Ph/n-C18 and the plot of Pr/Ph vs. O/C30 Hopane ratios implied that the sediment organic matter was deposited in a marine deltaic sedimentary environment under an oxic depositional environment. The C30 βα/C30 αβ, Tmax, 22 S/(22 S + 22 R) ratios of homohopane (C31) and bishomohopane (C32), MPI1, MPI2, F1, F2, Tmax vs. HI and the Pr/n-C17 vs. Ph/n-C18 ratios revealed that the Type III organic material was early thermal maturity and the burial depth of mud breccia matrix was estimated around 4–5 km bsf.

Prototype geochemical towing observation system for detection of coastal seafloor discharge of volcanic fluids and its evaluation of performance at volcanic CO<sub>2</sub> upwelling area

Prototype geochemical towing observation system for detection of coastal seafloor discharge of volcanic fluids and its evaluation of performance at volcanic CO<sub>2</sub> upwelling area

Locating Volcanic Earthquakes and Tremors Using Delay Time and Amplitude Ratio Information from Cross-Correlation Functions

AbstractVolcanic tremors and earthquakes must be monitored to gain insights into volcanic activity. Localization of their sources is often challenging because of the unclear onset of seismic waves, particularly when the volcanic activity increases before and during an eruption. Existing alternative techniques to locate the seismic sources are based on the information on the spatial amplitude distribution or the travel-time difference of seismic waves. Exploring the idea of combining both information for source location determination, we propose a new location method that uses the amplitude and travel-time difference information obtained from the unnormalized cross correlations of seismic data. Evaluation using volcanic earthquakes that occurred in 2020 at Tokachidake volcano, Japan, reveals an improvement in location accuracy compared to existing methods using individual information. Analysis of an episode of volcanic tremors and earthquakes accompanying a rapid tilt change event on 14 September 2020 reveals that during the inflation of the crater area, reliable seismic source locations with an error of ≤1 km become more concentrated at around 0.6 km beneath the 62-2 crater, in which the most recent eruptive activity had occurred. Such changes in source locations are associated with the movement of volcanic gas and hot water from the hydrothermal system below. Our proposed method is useful for locating and monitoring seismic source locations corresponding to volcanic fluid movements.

Hydrogeochemical temporal variations related to the recent volcanic eruption at the Cumbre Vieja Volcano, La Palma, Canary Islands

From October 2017, as a response to the occurrence of several seismic swarms on La Palma (Canary Islands, Spain), we strengthened the volcano monitoring of the Cumbre Vieja system by carrying out periodic hydrogeochemical sampling at different points of interest. Two galleries—Peña Horeb (PH) and Trasvase Oeste (TO)—and one well—Las Salinas (LS)—were selected with this objective. Significant temporal variations in the pH, EC, ion content (HCO3−, F−, Cl−, Br−, SO42-, Na+, Ca2+, and Mg2+), partial pressure of carbon dioxide (pCO2), and isotopic signature of dissolved CO2 (δ13C-CO2) were observed throughout the study period. These changes were observed in both chemical and isotopic compositions and were related to the interaction between deep volcanic fluids and groundwaters. They coincided with the occurrence of different seismic swarms, leading to the final Tajogaite volcano eruption, which occurred in Cumbre Vieja from 19 September to 13 December 2021. This work highlights the usefulness of monitoring the chemical and isotopic composition of the groundwaters related to active volcanic systems as they can provide important information about the magmatic gas input in the aquifers.

Effects of a Volcanic-Fluid Cycle System on Water Chemistry of a Deep Caldera Lake: Lake Tazawa, Akita Prefecture, Japan

Lake Tazawa, the deepest lake (423.4 m depth at maximum) in Japan underwent drastically changed water quality in 1940, because volcanic water from two active volcanos was then drawn into the lake for power generation and irrigation. Thereby, the pH of lake water decreased from 6.7 to 4.2, which exterminated a land-locked type of sockeye salmon, Oncorhynchus nerkakawamurae (locally called Kunimasu trout). Additionally, the mean residence time of lake water changed from 195 years to 8.9 years by rapidly increasing the outflow for power generation and irrigation. In this study, long-term chemical fluxes controlling lake water chemistry were obtained, and a groundwater water cycle system between the lake and the volcano was explored by estimating hydrological and chemical budgets of the lake. In the chemical budget estimate, two ionic species, SO42− and Cl−, in volcanic fluids were chosen and each mass conservation equation was yielded. The hydrological budget estimate gave us the net groundwater inflow at −1.36 m3/s on average over three periods in 2020–2021, and then the simultaneous equation coupled with the chemical budget equation allowed us to separate into groundwater inflow and outflow at 6.01 m3/s and 7.37 m3/s, averaged over the three periods, respectively. The evaluated groundwater inflow and outflow were compared with those of the other crater or caldera lakes. The linear relationship between the lake volume and the magnitude of groundwater inflow or outflow suggests that the groundwater cycle scale in such a lake increases with the magnitude of the volcanic eruption to have formed the lake.

The Thermal Effect of Submarine Mud Volcano Fluid and Its Influence on the Occurrence of Gas Hydrates

Mud volcanoes and other fluid seepage pathways usually transport sufficient gas for the formation of gas reservoirs and are beneficial to the accumulation of gas hydrate. On the other hand, the fluid thermal effects of mud volcanoes can constrain the occurrence of gas hydrates. Current field measurements indicate that fluid thermal anomalies impact the distribution of gas hydrates associated with mud volcanoes. However, due to the lack of quantitative analysis of the mud volcano fluid flow and thermal evolution, it is difficult to effectively reveal the occurrence of gas hydrates in mud volcano development areas and estimate their resource potential. This study took the Håkon Mosby Mud Volcano (HMMV) in the southwestern Barents Sea as the research object and comprehensively used seismic, well logging, drilling and heat flow survey data, combining the principles and methods of fluid dynamics and thermodynamics to study the fluid flow and heat transfer of a mud volcanic pathway. The space framework of the mud volcanic fluid temperature field thermal structure was established, the influence of the HMMV fluid thermal effect on gas hydrate occurrence was analyzed and the distribution and resource potential of gas hydrates in mud volcano development areas were revealed from the perspective of thermodynamics. This study provides a thermodynamic theoretical basis for gas hydrate accumulation research, exploration and exploitation under a fluid seepage tectonic environment.

The Helium and Carbon Isotope Characteristics of the Andean Convergent Margin

Subduction zones represent the interface between Earth’s interior (crust and mantle) and exterior (atmosphere and oceans), where carbon and other volatile elements are actively cycled between Earth reservoirs by plate tectonics. Helium is a sensitive tracer of volatile sources and can be used to deconvolute mantle and crustal sources in arcs; however it is not thought to be recycled into the mantle by subduction processes. In contrast, carbon is readily recycled, mostly in the form of carbon-rich sediments, and can thus be used to understand volatile delivery via subduction. Further, carbon is chemically-reactive and isotope fractionation can be used to determine the main processes controlling volatile movements within arc systems. Here, we report helium isotope and abundance data for 42 deeply-sourced fluid and gas samples from the Central Volcanic Zone (CVZ) and Southern Volcanic Zone (SVZ) of the Andean Convergent Margin (ACM). Data are used to assess the influence of subduction parameters (e.g., crustal thickness, subduction inputs, and convergence rate) on the composition of volatiles in surface volcanic fluid and gas emissions. He isotopes from the CVZ backarc range from 0.1 to 2.6 RA (n = 23), with the highest values in the Puna and the lowest in the Sub-Andean foreland fold-and-thrust belt. Atmosphere-corrected He isotopes from the SVZ range from 0.7 to 5.0 RA (n = 19). Taken together, these data reveal a clear southeastward increase in 3He/4He, with the highest values (in the SVZ) falling below the nominal range associated with pure upper mantle helium (8 ± 1 RA), approaching the mean He isotope value for arc gases of (5.4 ± 1.9 RA). Notably, the lowest values are found in the CVZ, suggesting more significant crustal inputs (i.e., assimilation of 4He) to the helium budget. The crustal thickness in the CVZ (up to 70 km) is significantly larger than in the SVZ, where it is just ∼40 km. We suggest that crustal thickness exerts a primary control on the extent of fluid-crust interaction, as helium and other volatiles rise through the upper plate in the ACM. We also report carbon isotopes from (n = 11) sites in the CVZ, where δ13C varies between −15.3‰ and −1.2‰ [vs. Vienna Pee Dee Belemnite (VPDB)] and CO2/3He values that vary by over two orders of magnitude (6.9 × 108–1.7 × 1011). In the SVZ, carbon isotope ratios are also reported from (n = 13) sites and vary between −17.2‰ and −4.1‰. CO2/3He values vary by over four orders of magnitude (4.7 × 107–1.7 × 1012). Low δ13C and CO2/3He values are consistent with CO2 removal (e.g., calcite precipitation and gas dissolution) in shallow hydrothermal systems. Carbon isotope fractionation modeling suggests that calcite precipitation occurs at temperatures coincident with the upper temperature limit for life (122°C), suggesting that biology may play a role in C-He systematics of arc-related volcanic fluid and gas emissions.

Waveform inversion of the ultra-long-period seismic event associated with ground tilt motion during an eruption of Mount Kusatsu–Shirane, Japan, on January 23, 2018

We conducted waveform inversions of an ultra-long-period (~ 240-s) event associated with the phreatic eruption of Mount Kusatsu–Shirane on January 23, 2018. We used broadband seismic and tilt records from three stations surrounding the eruption site. The horizontal components of the broadband seismic records were severely contaminated by tilt motions. We applied a waveform inversion algorithm to account for both the translational and tilt motions. To reduce the number of free parameters, we assumed a tensile crack source and conducted grid searches for the centroid location and orientation of the crack. The results showed a rapid inflation of 105 m3 of the crack, followed by a slow deflation starting 8–11 s prior to the onset of the eruption. The source location and crack orientation were not uniquely determined. The most likely source is a north–south-opening sub-vertical crack near the eruptive craters. This ultra-long-period event may represent volcanic fluid migration from depth to the surface through a vertical crack during the eruption.Graphical abstract

3He/4He Signature of Magmatic Fluids from Telica (Nicaragua) and Baru (Panama) Volcanoes, Central American Volcanic Arc

Constraining the magmatic 3He/4He signature of fluids degassed from a magmatic system is crucial for making inferences on its mantle source. This is especially important in arc volcanism, where variations in the composition of the wedge potentially induced by slab sediment fluids must be distinguished from the effects of magma differentiation, degassing, and crustal contamination. The study of fluid inclusions (FIs) trapped in minerals of volcanic rocks is becoming an increasingly used methodology in geochemical studies that integrates the classical study of volcanic and geothermal fluids. Here, we report on the first noble gas (He, Ne, Ar) concentrations and isotopic ratios of FI in olivine (Ol) and pyroxene (Px) crystals separated from eruptive products of the Telica and Baru volcanoes, belonging to the Nicaraguan and Panamanian arc-segments of Central America Volcanic arc (CAVA). FIs from Telica yield air corrected 3He/4He (Rc/Ra) of 7.2–7.4 Ra in Ol and 6.1–7.3 in Px, while those from Baru give 7.1–8.0 Ra in Ol and 4.2–5.8 Ra in Px. After a data quality check and a comparison with previous 3He/4He measurements carried out on the same volcanoes and along CAVA, we constrained a magmatic Rc/Ra signature of 7.5 Ra for Telica and of 8.0 Ra for Baru, both within the MORB range (8 ± 1 Ra). These 3He/4He differences also reflect variations in the respective arc-segments, which cannot be explained by radiogenic 4He addition due to variable crust thickness, as the mantle beneath Nicaragua and Panama is at about 35 and 30 km, respectively. We instead highlight that the lowest 3He/4He signature observed in the Nicaraguan arc segment reflects a contamination of the underlying wedge by slab sediment fluids. Rc/Ra values up to 9.0 Ra are found at Pacaya volcano in Guatemala, where the crust is 45 km thick, while a 3He/4He signature of about 8.0 Ra was measured at Turrialba volcano in Costa Rica, which is similar to that of Baru, and reflects possible influence of slab melting, triggered by a change in subduction conditions and the contemporary subduction of the Galapagos hot-spot track below southern Costa Rica and western Panama.

Chemical variability in volcanic gas plumes and fumaroles along the East African Rift System: New insights from the Western Branch

The origin of magmatic fluids along the East African Rift System (EARS) is a long-lived field of debate in the scientific community. Here, we investigate the chemical composition of the volcanic gas plume and fumaroles at Nyiragongo and Nyamulagira (Democratic Republic of Congo), the only two currently erupting volcanoes set on the Western Branch of the rift. Our results are in line with earlier conceptual models proposing that volcanic gas emissions along the EARS mainly reflect variable contributions of either a Sub-Continental Lithospheric Mantle (SCLM) component or a Depleted Morb Mantle (DMM) component, and deeper fluid. At Nyiragongo and Nyamulagira, our study discards a major contribution of a high 3He/4He mantle plume component in the genesis of volcanic fluids beneath the area. High CO2/3He in fumaroles of both volcanoes is thought to reflect carbonate metasomatism in the lithospheric mantle source. As inferred by previous results obtained on the lava chemistry, this carbonate metasomatism would be more pronounced beneath Nyiragongo. This supports the idea of the presence of distinct metasomes within the lithospheric mantle beneath the Western Branch of the rift.

Mud Volcanic Fluids of the Kerch–Taman Region: Geochemical Reconstructions and Regional Trends: Communication 2. Genesis of Mud Volcanic Gases and Regional Geochemical Trends

Mud Volcanic Fluids of the Kerch–Taman Region: Geochemical Reconstructions and Regional Trends: Communication 2. Genesis of Mud Volcanic Gases and Regional Geochemical Trends