Volcanic System Research Articles

Regional structural control on the Mont-Dore Plio-Quaternary volcanism (France)

Magma transfer in the upper crust including emplacement at the surface of the Earth, have been regarded as largely controlled by the regional tectonic activity. While this relationship is well highlighted for systems like monogenetic, mostly basaltic, volcanic fields, the tectonic control on the transfer and emplacement of magmas in complex, polygenetic, volcanic systems, remains poorly documented in evolving tectonic settings. The Mont-Dore Plio-Quaternary volcanic complex (4.7 to 0.3 Ma) is one of such polygenetic volcanic fields as it is formed of three successive eruptive cycles: The caldera unit (3.3 to 2.2 Ma); The Aiguiller complex (2.5 to 1.5 Ma) and the Sancy stratovolcano unit (1.5 to 0.3 Ma).Analyzing fractures, fault kinematics and regional lineaments in the Variscan basement, together with attitude of dikes and volcanic centers alignments of the three volcanic units, we document the influence of the brittle structuration of the underlying basement on the volcanism distribution over time while regional stress changed. The late-Variscan N02E0, and secondary N160, striking crustal faults were reactivated since the Oligocene and channeled at depth the magma, while similarly oriented faults and fractures triggered the final storage in the shallow crust and spatial distribution of the volcanic vents. This fault system continued to act from the Miocene to the present-day uplift, associated with new N020E striking, flat-lying, fractures. An exception arises during the upper Miocene while N060E and N135E striking faults enabled the development of the caldera unit in a NW-SE extensional context.The emplacement of the three units from the mid-Pliocene to the end of the Pleistocene while a change in regional stress field conditions emerged at about 2.5 Ma exemplify the control of the brittle Variscan basement on the magmatic activity of the Mont-Dore Plio-Quaternary volcanic complex.

Exceptionally low mercury concentrations and fluxes from the 2021 and 2022 eruptions of Fagradalsfjall volcano, Iceland

Mercury (Hg) is naturally released by volcanoes and geothermal systems, but the global flux from these natural sources is highly uncertain due to a lack of direct measurements and uncertainties with upscaling Hg/SO2 mass ratios to estimate Hg fluxes. The 2021 and 2022 eruptions of Fagradalsfjall volcano, southwest Iceland, provided an opportunity to measure Hg concentrations and fluxes from a hotspot/rift system using modern analytical techniques. We measured gaseous Hg and SO2 concentrations in the volcanic plume by near-source drone-based sampling and simultaneous downwind ground-based sampling. Mean Hg/SO2 was an order of magnitude higher at the downwind locations relative to near-source data. This was attributed to the elevated local background Hg at ground level (4.0 ng m−3) likely due to emissions from outgassing lava fields. The background-corrected plume Hg/SO2 mass ratio (5.6 × 10−8) therefore appeared conservative from the near-source to several hundred meters distant, which has important implications for the upscaling of volcanic Hg fluxes based on SO2 measurements. Using this ratio and the total SO2 flux from both eruptions, we estimate the total mass of gaseous Hg released from the 2021 and 2022 Fagradalsfjall eruptions was 46 ± 33 kg, equivalent to a flux of 0.23 ± 0.17 kg d−1. This is the lowest Hg flux estimate in the literature for active open-conduit volcanoes, which range from 0.6 to 12 kg d−1 for other hotspot/rift volcanoes, and 0.5–110 kg d−1 for arc volcanoes. Our results suggest that Icelandic volcanic systems are fed from an especially Hg-poor mantle. Furthermore, we demonstrate that the aerial near-source plume Hg measurement is feasible with a drone-based active sampling configuration that captures all gaseous and particulate Hg species, and recommend this as the preferred method for quantifying volcanic Hg emissions going forward.

MaxEnt machine learning model predicts high groundwater potential areas in a fractured volcanic aquifer system

Groundwater constitutes a vital resource for public water supply, and thus, it is imperative to recognize the areas of highest potential for increasing availability. The present study employs the MaxEnt model to discern the most favorable areas for locating high-yield wells in Caxias do Sul, Rio Grande do Sul, southern Brazil, where the Serra Geral Aquifer System, a fractured volcanic aquifer, emerges. This aquifer system is characterized by its heterogeneous, discontinuous, and highly anisotropic nature. A dataset comprising 83 wells with high flow rates (≥10 m³/h) was selected from the municipal registry of deep tubular wells, along with 14 factors that influence groundwater occurrence (specific capacity, transmissivity, altitude, slope, horizontal curvature, vertical curvature, relief dissection index, drainage density, distance to drainage, topographic wetness index, distance to lineament, lineament density, precipitation, and soil hydrological group). The model output was a Groundwater Potential Map, which stochastically expresses the probability of obtaining flow rates ≥10 m³/h. The map was validated through cross-validation, resulting in an average accuracy of 65.14%, and by the Receiver Operating Characteristic analysis, resulting in an Area Under the Curve value of 0.911, indicating satisfactory validation. While the MaxEnt model is widely used in ecology to model species distribution, its application in groundwater prediction remains limited, particularly in fractured aquifers associated with volcanic rocks. Apart from optimizing the use of groundwater resources, this study also enhances the understanding of natural phenomena in this type of aquifer.

Efficient Thermoelectric Conversion of Sulfide Chimneys in Submarine Volcanic Systems

AbstractSubmarine volcanos are the most active areas in the deep sea, but the environmental consequences of frequent volcanic activity on the geophysical fields and biogeochemical processes near hydrothermal chimneys have not been fully understood yet. In particular, how continuous high‐flux thermal energy, the most typical form of energy in active submarine volcanic systems, affects electron transport and geoelectric field remains unknown. This study provides the first evidence that thermal energy can be efficiently converted to electrical energy at an extremely small spatial scale of the submarine black chimneys. The Seebeck coefficient of sulfide chimneys can reach more than 200 μV/K, with high electrical conductivity of 104 S/m and low thermal conductivity of 1.0 W/(m·K) within 300–700 K. A maximal potential gradient of 300 mV/cm under a temperature difference of 300–700 K can be generated by the thermoelectric conversion of sulfide chimneys, with a maximum energy converting efficiency up to 1%. The thermoelectric conversion effect of a global‐scale submarine volcanos could enable electroactive bacteria to fix appromaxiately 105–106 tons of carbon per year. In addition, the thermal‐electrochemical experiments indicated sulfides underwent rapid oxidation under thermoelectric effects, which may help explain the intense oxidative weathering of sulfides in some anoxic deep‐sea hydrothermal zones.

Evolution of shallow volcanic seismicity in the hydrothermal system of La Soufrière de Guadeloupe following the April 2018 Mlv 4.1 earthquake

La Soufrière de Guadeloupe volcano is characterized by seismo-volcanic activity dominantly linked to an active hydrothermal system. This microseismicity is shallow, mainly triggered in swarms and characterized by repeating earthquakes. Four recurrent families of Volcano-Tectonic (VT) repeaters have been identified and the main repeater accounts for 80% of detections. Stacking repeating seismic waveforms produces MASTER events with a high Signal-to-Noise Ratio (SNR) and thanks to the deployment of a temporary seismic nodal array, their absolute locations can be better constrained. Because we observe systematic positive residuals of P-wave arrival times at almost all stations, we investigate potential bias in the velocity model in the shallow part of the dome. By increasing the P-wave velocity and decreasing the VP/VS ratio from 1.8 to 1.69, we reduce these residuals and improve the local velocity model. We use this new velocity model to locate each VT event relatively to is own MASTER hypocenter. This procedure offers a new image of the hydrothermal seismic activity that we locate under the acid lake of the summit Tarissan crater, along a sub-vertical conduit. We also define a linear relationship between the logarithm of the peak amplitude of seismic events and their duration to obtain a pseudo local magnitude. The approach enables to accurately and automatically estimate the magnitude during the event detection. We show that after the occurrence in April 2018 of the largest earthquake (Mlv 4.1) since the last phreatic eruption in 1976–1977, the swarm frequency and amplitude increased significantly, and a new family of VT repeater emerges, accounting for up to 14% of detections. We show a quiescence in the main repeaters activity in the month following the April 2018 earthquake, suggesting a significant stress release within the volcanic system, which is likely related to dynamic stress changes rather than static stress variations caused by the earthquake. Moreover, we detect the emergence of a new family of repeaters 3 months after the event, located ∼100 m above the main repeater family, that could be related to a fluid pressure increase induced by the regional hydrological cycle, superimposed to the internal forcing driven by the hydrothermal system. Finally, using a statistical approach, we highlight seasonal periodicities in the number of events and the released seismic moment at La Soufrière de Guadeloupe, with a dominant peak of seismic activity in October–November and a second, less significant, peak of in April.

Three-dimensional resistivity structure in Toya caldera region, Southwest Hokkaido, Japan — Constraints on magmatic and geothermal activities

Southwestern Hokkaido, Japan, is characterized by numerous Quaternary volcanoes and geothermal areas. At the same time, the region hosts various critical infrastructures, and there is a need to assess the impact of volcanic hazards on them. Geophysics could provide scientific clues for the hazard assessment by elucidating the abundance of subsurface magma. To clarify the resistivity structure from the crust to uppermost mantle of the Toya caldera, a representative Quaternary volcanic area, a wideband magnetotellurics survey of 117 points over land, sea, and lake areas, as well as 3D inversion, has been conducted. In combination with petrological and seismological findings, quantitative interpretation of the inverted model has found that conductive bodies in the uppermost mantle (14–68 [Formula: see text]) suggest the presence of melts (0.25 vol%–3.4 vol%) or fluids (0.068 vol%–0.45 vol%). An extremely conductive body (<10 [Formula: see text]) at a depth of approximately 3–14 km in the eastern geothermal area could be interpreted as a hydrothermal reservoir; below this body, the conductive column (1.8–15 [Formula: see text]), rising from the uppermost mantle, suggests fluid upwelling. In contrast, high resistivity (>100 [Formula: see text]) beneath Usu Volcano, the center of active volcanism, suggests that no mobile magma was present. A columnar-shaped region of slightly low resistivity (44 [Formula: see text] at minimum) is observed below the Toya caldera, which was inferred as cooling magma or an altered or heated upper crust attributed to past magma intrusion. A resistivity structure observed below the volcanic edifice is considered to reflect the steady state of the dormant volcanic system in this area, and there is likely no large amount of melt that would be deemed imminent for a caldera-forming eruption. This information could be a valuable scientific contribution to the volcanic hazard risk assessments currently being conducted in Japan.

Hydrothermal fluid circulation within the restless structural frame of Hasandağ volcanic system (Central Anatolia, Türkiye) inferred from Self-potential, CO2, and temperature measurements

Hasandağ is an active composite volcanic system located in the Central Anatolian Volcanic Province (CAVP). A comprehensive field survey was conducted to reveal the hydrothermal activity within the Hasandağ volcanic system, with particular emphasis on Self-Potential (SP) mapping. The Hasandağ system is characterised by the presence of twin stratovolcanoes that arise from pre-existing partially buried calderas. In conjunction with the SP measurements, carbon dioxide concentration (CO2) and surface temperature (ST) measurements were taken. The temperature measurements were elaborated with thermal infrared remote (TIR) sensing methods. The SP results, with a peak-to-peak magnitude of 3.8 Volts, revealed the presence of a significant hydrothermal input in both of the twin cones, characterised by a typical W-shaped anomaly commonly observed in active volcanoes. The highest SP signal coincides with the active fumarole zone at the western flank of G. Hasandağ summit, where we measured ∼70 °C vapour temperatures and relatively high CO2 output (>100,000 ppm). The SP/elevation (Ce) gradient assisted in revealing the hydrothermal and hydrogeological zonation, providing substantial evidence of the relationship between hydrothermal circulation and the structural frame of the volcano. Integrated evaluation of SP, CO2, and temperature data revealed the structural control on the hydrothermal and hydrogeological circulation, with the contribution of Hasandağ, Karacaören, and Karkın Faults as major structural components. The partially buried rim of the Hasandağ caldera was revealed through the detection of a ‘double Ce-low’ signal, providing valuable insights on the dimensions of the structure and its role in the hydrogeological cycle of the system. The extent and magnitude of the hydrothermal activity observed, the Holocene eruptive history of the volcano, and its proximity to populated areas denote the requirement of further geophysical and geochronological research and the necessity of hazard assessment and instrumental monitoring.

Evolution of the magma system at Makushin volcano, Alaska, from 2004 to 2021

Located in the northeast of Unalaska Island in the central part of the Aleutian, Alaska, Makushin volcano is one of the more active volcanoes in the United States, with the most recent eruption occurred in 1995. Pre-eruptive inflation and post-eruptive deflation were identified from 1993 to 1995 and 1996 to 2000, respectively, and were interpreted as volume changes associated with magma movement within the plumbing system. In this study, we investigate the surface deformation of Makushin from 2004 to 2021 to evaluate its present-day activity, using Synthetic Aperture Radar (SAR) interferometry technique. SAR images acquired from C-band Envisat and Sentinel-1, X-band TerraSAR-X, and L-band ALOS-2 satellites are analyzed using an advanced multiple temporal Interferometric SAR (InSAR) algorithm. The produced deformation time series are then used to track the temporal evolution of the volcanic system with Ensemble Kalman Filter (EnKF) assuming Mogi sources. The results show that Makushin is characterized by time-varying deformation episodes including quiescence, and inflation/deflation cycles at varied rates since 2004. The derived deformation histories can be well reproduced by a spatially stationary pressure source located to the east-northeast of the summit, at a depth about 6 km beneath the sea level (BSL). The inflation/deflation cycles with distinct temporal patterns are interpreted as results from volatile-dominated volume accumulation/loss in the magmatic reservoir. A secondary reservoir connected to the main magma chamber is revealed from the deformation time series. No surface displacement associated with the large earthquake swarm in 2020 is identified from the InSAR-derived deformation. The cumulative volume change in the magma reservoir is about −6×106m3 from 2004 to 2021, indicating a volume/pressure deficit in the magma plumbing system.

Magmatism at an ultra-slow spreading rift: high-resolution geomorphological studies of a Red Sea Rift segment in Hadarba Deep

The mid-ocean rift in the Red Sea is one of the youngest rifting systems on Earth. Only recently, state-of-the-art methods and modern deep-sea instruments have been used to explore this young and unique volcanic system. During the first autonomous underwater vehicle surveys of the Red Sea Rift in Spring 2022, we collected multibeam bathymetry, backscatter, sub-bottom profiler data, and water column data over a 9 km long ridge segment in the Hadarba Deep between 22.49°N and 22.56°N to investigate the volcano-tectonic processes of this ultra-slow spreading segment (12 mm/year spreading rate). The high-resolution hydroacoustic data was used to (1) delineate and quantify the geometry of tectonic structures and individual lava flows, (2) define lava flow morphology and eruption style, (3) estimate relative ages of flows and features, and (4) retrace the evolution of the volcanic activity. In addition, the geochemistry of several young lava flows provides information on the relation between the different magma that supply these eruptions. About 90 eruptive units with variable sedimentary cover have been identified within the 43 km2mapped region. The oldest lava flows are buried under 3 to 4.2 m of sediment, indicating ages of up to ~30 ka based on average sedimentation rate estimates (~14 cm/ka), while the youngest eruptions are covered by<10 cm of sediment, and are thus younger than 700 years. Three volcanic phases have been identified based on changes in flow morphology and distribution, and tectonic pattern. All three axial phases have an average eruptive frequency of ~100-250 years. The segment displays an overall low tectonic extension (<10% of the total extension) and low vertical offset. Our geomorphological maps, analyses, and statistics reveal a moderately faulted, ultra-slow spreading MOR segment in the Red Sea with a surprisingly large amount of magmatic extension, implying that the segment has been underlined by a large magma supply for at least 15 ka. All these observations provide valuable implications for the formation history of the Red Sea Rift and the formation of ultra-slow spreading crust.

Seismicity near Mayotte explained by interacting magma bodies: Insights from numerical modeling

Mayotte island experienced a large volcanic eruption 50 km offshore in 2018–2021, creating the submarine volcano “Fani Maoré”. The eruption was accompanied by intense seismicity at mantle depths (20–45 km), divided into a “proximal” and a “distal” cluster centered 10 and 30 km east from the island, respectively. Previous studies suggest that two separate magma reservoirs may lie at the top and bottom of the proximal cluster. Here, we assess whether two reservoirs are a mechanically viable explanation for the proximal cluster's truncated conical shape. We developed finite-element models of pressurized magma reservoirs in a 2D axisymmetric domain, modeling the reservoirs as compliant elastic ellipsoids embedded in an elastoplastic host rock. We find that, at these depths, extremely low friction is required to generate failure at realistically low reservoir pressures. This implies in turn that mechanical weakening must occur at these depths. The weakening could be induced by fractures or pore fluid overpressure in the volcanic system. We find that two superimposed reservoirs can generate a plastic domain between them, if they are spatially close enough. Several reservoir geometries (from spherical to sill-like) are plausible. A conical fracture domain is more likely to appear for reservoirs with opposite pressure loads (i.e. one inflating, one deflating). Given the geometrical match with the proximal seismicity cluster at Mayotte, we suggest that the shallower (Moho-depth) reservoir is inflating, creating a potential hazard for Mayotte island.

Constraints of boron and oxygen stable isotopes on dehydration fluids, sediment-derived melts, and crustal assimilation of the Toba volcanic system (Indonesia)

Abstract Arc magmas are produced from the mantle wedge, with possible addition of fluids and melts derived from serpentinites and sediments in the subducting slab. Identification of various sources and their relevant contributions to such magmas is challenging; in particular, at continental arcs where crustal assimilation may overprint initial geochemical signatures. This study presents oxygen isotopic compositions of zoned olivine grains from post-caldera basalts and boron contents and isotopes of these basalts and glassy melt inclusions hosted in quartz and clinopyroxene of silicic tuffs in the Toba volcanic system, Indonesia. High-magnesian (≥87 mol% Fo [forsterite]) cores of olivine in the basalts have δ18O values ranging from 5.12‰ to 6.14‰, indicating that the mantle source underneath Toba is variably enriched in 18O. Olivine with <87 mol% Fo has highly variable (4.8–7.2‰), but overall increased, δ18O values, interpreted to reflect assimilation of high δ18O crustal materials during fractional crystallization. Mass balance calculations constrain the overall volume of crustal assimilation for the basalts as ≤13%. The processes responsible for the 18O-enriched basaltic melts are further constrained by boron data that indicate the addition of <0.1 wt% fluids to the mantle, >40% of the fluids being derived from serpentinites and others from altered oceanic crust and sediments. This amount of fluids can increase δ18O of the magma by only ~0.02‰. Approximately 6–9% sediment-derived melt hybridization in the mantle wedge is further needed to yield basaltic melts with δ18O values in equilibrium with those of the high-Fo olivine cores. The cogenetic silicic tuffs, on the other hand, seem to record a higher proportion of fluid addition dominated by sediment-derived fluids to the mantle source, in addition to crustal assimilation. Our reconnaissance study therefore demonstrates the application of combined B and O isotopes to differentiate between melts and fluids derived from serpentinites and sediments in the subducted slab—an application that can be applied to arc magmas worldwide.

Environmental challenge of landslide in geothermal areas: an introductory study

Landslides in geothermal areas are one of the environmental challenges that are attributed to their volcanic and hydrothermal systems. However, the inventory of landslides in geothermal areas remains considerably limited. This may implicate pitfalls, where characterisation of historical events is an essential practice in disaster risk management. Accordingly, this exploratory study aims to characterise landslide events in 19 geothermal areas with historical landslides. This introductory study was sourced from electronic news, scientific publications, and authoritative institutions. The collected records were cross-examined and integrated into comparable attributes. The resulting characteristics display the physical features, environmental factors, and mitigation measures as follows: (1) landslides commonly occur in small to extremely large volumes. However, serious tolls may be caused even by small-to modest-sized landslides. (2) Landslides may not be preceded by triggering factors but by their gradually weakened environment. (3) Although there are scattered sources and unclear information related to underreported landslides and understudied mitigation, respective authorities conduct rapid measures following the landslide event. Correspondingly, it is highly recommended to further improve and establish a landslide inventory database in geothermal areas that constitutes a more comprehensive overview for better risk management.

Isotope Composition of Gases of Magmatic and Sedimentary Volcanic Systems: A Review and Comparative Analysis

Isotope Composition of Gases of Magmatic and Sedimentary Volcanic Systems: A Review and Comparative Analysis

Geological significance of the spatial clustering and alignment of vents in zones of distributed volcanism: A critical review

The spatial distribution of volcanic activity has been the subject of scientific enquiry for more than 350 years. Nevertheless, it has been only until recently that modern techniques of analysis started to be used to characterize such distribution. As a result, in the past 40 years many methods were devised, or adopted from other fields of study, aiming to achieve that purpose. Ironically, the plethora of now available methodologies has made problematic the selection of one method of study to characterize the spatial distribution of volcanic vents. In addition, given the diversity of methods, and their underlying assumptions, there are issues concerning the form in which the results of any specific method should be interpreted in a volcanic context. In this work I make emphasis on the relationship between the embedded assumptions of several common methods of study with the concept of a “natural partition”. Throughout this work it is remarked that 1) it is extremely important to gain conscience about the several assumptions implicit on each method of analysis, 2) never loose sight that not all volcanic systems are equal, and 3) that it is a myth that any quantitative method can provide reliable information about any system. The convenience of assessing more than one conceptual model to explain the formation of a cluster-subcluster structure is also mentioned. Overall, it is shown that the complexity of volcanic phenomena cannot be encapsulated by using a single method of study, or an automatized selection of parameters. Thus, given the complexity and diversity of volcanic phenomena, there is no particular method, nor set of methods, that can be recommended to be used on every situation of interest. Yet, as a golden rule, it is suggested that more than one method of analysis is used at every location of study, looking for congruency of results within a range of spatial scales.

Remobilization and eruption of an upper crustal cumulate mush at the Singkut caldera (North Sumatra, Indonesia)

Understanding the conditions and timescales of storage and remobilization of magma bodies in the upper crust is key to interpreting the signals of potential reawakening at active volcanoes. In this paper, we provide the first volcanological and petrochronological characterization of the Singkut caldera, a young volcanic system located in northern Sumatra (Indonesia), in close proximity to Medan, one of the country's most popoluous cities. Singkut formed at ∼44 ka during a VEI 6 explosive eruption that deposited at least ∼26 km3 of tephra (dense rock equivalent, DRE). The cataclysmic eruption was preceded by >200 ky of mostly effusive pre-caldera activity and followed by effusive to mildly explosive post-caldera activity. The lavas and pumices have high crystallinity (up to 62% crystals) with andesitic to dacitic bulk-rock composition and rhyolitic glass. Mineral textures and matrix glass compositions indicate resorption of quartz, plagioclase and zircon. Zircon crystallization ages show a complete overlap with the eruption ages in pre-caldera lavas, while a time gap in zircon crystallization (>50 ky) is identified in the caldera-forming tuff and post-caldera lavas. Ti-in-zircon thermometry shows that the Singkut magma body experienced a temperature increase starting approximately upon eruption of the pre-caldera lavas (∼254 ka). Such thermal perturbation determined progressive melting of mineral phases in the cumulate crystal mush, caused the resorption of the youngest zircon domains before the caldera-forming eruption, and hampered zircon crystallization between the caldera-forming eruption and the effusion of the post-caldera lavas (∼16 ka). Our data demonstrate how cumulate melting processes played a key role in leading the volcanic system towards a caldera-forming eruption and controlled the transitions in eruptive style between the effusive phases and the explosive climactic eruption.

The Holocene silicon biogeochemistry of Yellowstone Lake, USA

Silicon (Si) is an essential macronutrient for diatoms, an important component of lacustrine primary productivity that represents a link between the carbon and silicon cycles. Reconstructions of lake silicon cycling thus provide an underexploited window onto lake and catchment biogeochemistry. Silicon isotope geochemistry has potential to provide these reconstructions, given the competing source and process controls can be deconvolved. The silica-rich volcanic and hydrothermal systems in Yellowstone National Park are a great source of dissolved silicon into Yellowstone Lake, a system with high silicon, and thus carbon, export rates and the formation of diatom–rich sediment. Yellowstone Lake sediments should be an archive of past silicon biogeochemistry, although the effect of sublacustrine hydrothermal activity or hydrothermal explosion events is unclear.Here, we analysed lake water, tributaries, and hydrothermal vent fluids from Yellowstone Lake for their dissolved Si concentrations, isotope composition (δ30Si) and Ge/Si ratios to evaluate the sources of variability in the lake's Si cycle. Bulk elemental composition and biogenic SiO2 (bSiO2) content, together with δ30Si and Ge/Si ratios from a single diatom species, Stephanodiscus yellowstonensis, were analysed in two sediment cores spanning the last 9880 cal. yr BP. We investigate these datasets to identify long term Holocene changes in hydrothermal activity and effects of large and short-term events i.e., hydrothermal and a volcanic eruption.Combinations of bSiO2, δ30Si and Ge/Si with XRF and lithology data revealed that Yellowstone Lake has a resilient biogeochemical system: hydrothermal explosions are visible in the lithology but have no identifiable impact on bSiO2 accumulation or on the δ30Si signature. Both cores show similarities that suggest a stable and homogeneous dSi source across the entire lake. A narrow range of δ30Si and Ge/Si values suggests that the productive layer of the lake was well mixed and biogeochemically stable, with consistently high hydrothermal inputs of Si throughout the Holocene to buffer against the disturbance events. Variation in bSiO2 concentration through time is weakly correlated with an increase towards younger sediment in the δ30Si fossil diatom record in both cores. This increase mirrors that seen in ocean records, and follows changes known in summer insolation, summer temperatures and lake water-column mixing since the deglaciation. This suggests that climate forcing, and soil formation ultimately govern the silicon isotope record, which we suggest is via a combination of changes in weathering stoichiometry, diatom production, and relative proportion of dSi sources.

Geostatistical and multitemporal InSAR method and elastic deformation model for detailed characterizations of topographic change and magma reservoirs: Application to the Tangkuban Parahu Volcano, Indonesia

This study proposes the entire detection of the surface deformation of a volcanic area using interferometric synthetic aperture radar (InSAR) with geostatistics to specify the locations and shapes of the sources causing the deformation. We selected the Tangkuban Parahu area, West Java, Indonesia, as our study site and used a Sentinel-1 dataset. In this study, we combine persistent scatterer and small baseline subset InSAR with a geostatistical technique, i.e., turning bands simulation. This combination can compensate for undetected displacement pixels and decompose the line-of-sight displacement into vertical and horizontal east–west displacements using both the ascending and descending mode results and the least-squares method. This two-dimensional geostatistics and multitemporal InSAR approach is referred to as 2D GMT-InSAR. A detailed displacement pattern is revealed by 2D GMT-InSAR for undetected pixels in low-coherence areas. Then, the vertical displacement pattern in the study period from 2014 to 2019, mainly uplift with local subsidence, is reproduced via the joint use of the Mogi and Okada models for circular and rectangular parallelepiped sources of the deformation, respectively. Via a Bayesian inversion, one circular source, equivalent to a magma reservoir, and one dyke source are identified. The displacement pattern is likely caused by pressure increases in the magma reservoir, associated with the volcanic activation, and in the dyke, associated with the gas and fluid flows from the reservoir, which induced a phreatic explosion in July 2019. A connection of the dyke with the old Sunda volcanic system is found; this new finding is a result of the caldera collapse during the Sunda volcanic eruption.

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.

Constraining the volatile evolution of mafic melts at Mt. Somma–Vesuvius, Italy, based on the composition of reheated melt inclusions and their olivine hosts

Abstract. Mount Somma–Vesuvius is a stratovolcano that represents a geological hazard to the population of the city of Naples and surrounding towns in southern Italy. Historically, volcanic eruptions at Mt. Somma–Vesuvius (SV) include high-magnitude Plinian eruptions, such as the infamous 79 CE eruption that occurred after 295 years of quiescence and killed thousands of people in Pompeii and surrounding towns and villages. The last eruption at SV was in 1944 and showed a Volcanic Explosivity Index (VEI) of 3 (0.01 km3 of volcanic material erupted). Following the 1944 eruption, SV has been dormant for the past nearly 79 years, with only minor fumarolic and seismic activity. During its long history, centuries of dormancy at SV have ended with Plinian eruptions (VEI 6) that signal the beginning of a new cycle of eruptive activity. Thus, the current dormancy stage demands a need to better understand the mechanism involved in high-magnitude eruptions in order to better predict future eruption magnitude and style. Despite centuries of research on the SV volcanic system, many questions remain, including the evolution of magmatic volatiles from deep primitive magmas to shallower more evolved magmas. Developing a better understanding of the physical and chemical processes associated with volatile evolution at SV can provide insights into magma dynamics and the mechanisms that trigger highly explosive eruptions at SV. In this study, we present new data for the pre-eruptive volatile contents of magmas associated with four Plinian and two inter-Plinian eruptions at SV based on analyses of reheated melt inclusions (MIs) hosted in olivine. We correct the volatile contents of bubble-bearing MIs by taking into account the volatile contents of bubbles in the MIs. We recognize two groups of MIs: one group hosted in high-Fo olivine (Fo85–90) and relatively rich in volatiles and the other group hosted in low-Fo olivine (Fo70–69) and relatively depleted in volatiles. The correlation between volatile contents and compositions of host olivines suggests that magma fractionation took place under volatile-saturated conditions and that more differentiated magmas reside at shallower levels relative to less evolved/quasi-primitive magmas. Using the CO2 contents of corrected MIs hosted in Fo90 olivine from SV, we estimate that 347 to 686 t d−1 of magmatic CO2 exsolved from SV magmas during the last 3 centuries (38–75 Mt in total) of volcanic activity. Although this study is limited to only few SV magmas, we suggest that further study applying similar methods could shed light on the apparent lack of correlation between the volatile contents of MIs and the style and age of eruptions. Further, such studies could provide additional constraints on the origin of CO2 and the interaction between the carbonate platform and ascending magmas below SV.

182W and 187Os constraints on the origin of siderophile isotopic heterogeneity in the mantle

Major and trace element abundances, including highly siderophile elements, and 187Os and 182W isotopic compositions were determined for ca. 89 Ma mafic and ultramafic rocks from the islands of Gorgona (Colombia) and Curaçao (Dutch Caribbean). The volcanic systems of both islands were likely associated with a mantle plume that generated the Caribbean Large Igneous Provence. The major and lithophile trace element characteristics of the rocks examined are consistent with the results of prior studies, and indicate derivation from both a chemically highly-depleted mantle component, and an enriched, or less highly-depleted mantle component. Highly siderophile element abundances for these rocks are generally similar to rocks with comparable MgO globally, indicating that the major source components were not substantially enriched or depleted in these elements. Rhenium-Os isotopic systematics of most rocks of both islands indicate derivation from a mantle source with an initial 187Os/188Os ratio between that of the contemporaneous average depleted mid-ocean ridge mantle and bulk silicate Earth. The composition may reflect either an average lower mantle signature, or global-scale Os isotopic heterogeneity in the upper mantle. Some of the basalts, as well as two of the komatiites, are characterized by calculated initial 187Os/188Os ratios 10–15 % higher than the chondritic reference. These more radiogenic Os isotopic compositions do not correlate with major or trace element systematics, and indicate a mantle source component that was most likely produced by either sulfide metasomatism or ancient Re/Os fractionation. Tungsten-182 isotopic compositions measured for rocks from both islands are characterized by variable μ182W values ranging from modern bulk silicate Earth-like to strongly negative values. The μ182W values do not correlate with major/trace element abundances or initial 187Os/188Os compositions. As with some modern ocean island basalt systems, however, the lowest μ182W value (−53) measured, for a Gorgona olivine gabbro, corresponds with the highest 3He/4He previously measured from the suite (15.8 R/RA). Given the lack of correlation with other chemical/isotopic compositions, the mantle component characterized by negative μ182W and possibly high 3He/4He is most parsimoniously explained to have formed as a result of isotopic equilibration between the mantle and core at the core-mantle boundary.