Volcanic System Research Articles

Research for the classification of volcanic caves in the Central Highlands

Volcanic caves in Central Highlands have been discovered since 2007. This is a volcanic cave system with the largest scale, length and uniqueness in Southeast Asia. The discovery has opened up many new research directions (specialised, interdisciplinary earth science and life science), with many scientific and technological projects at different levels... Since the volcanic cave system in the Central Highlands was discovered, there have not had any publications on the taxonomy of Vietnamese volcanic caves. In the practice of studying volcanic caves, there are many methodologies to classify caves depending on the purpose and requirements of use, such as origin, formation mechanism, distribution characteristics, morphology, or a mixture of the above classifications. In this study, the authors classified the Central Highlands volcanic caves according to the mixture of the above classifications and other uses, such as scientific caves, mass caves, prehistoric caves, adventure cave, etc.

Physical and chemical characteristics of active sulfur flows observed at Lastarria volcano (northern Chile) in January 2019

Molten sulfur is found in various subaerial volcanoes. However, limited records of the pools and flows of molten sulfur have been reported: therefore, questions remain regarding the physicochemical processes behind this phenomenon. A suite of new sulfur flows, some of which active, was identified at the Lastarria volcano (northern Chile) and studied using satellite imagery, in situ probing, and temperature and video recording. This finding provides a unique opportunity to better understand the emplacement mechanisms and mineral and chemical compositions of molten sulfur, in addition to gaining insight into its origin. Molten sulfur presented temperatures of 124–158°C, with the most prolonged sulfur flow reaching 12 m from the source. Photogrammetric tools permitted the identification of levees and channel structures, with an estimated average flow speed of 0.069 m/s. Field measurements yielded a total volume of 1.45 ± 0.29 m3 of sulfur (equivalent to ∼2.07 tons) mobilized during the January 2019 event for at least 408 min. Solidified sulfur was composed of native sulfur with minor galena and arsenic- and iodine-bearing minerals. Trace element analysis indicated substantial enrichment of Bi, Sb, Sn, Cd, as well as a very high concentration of As (>40.000 ppm). The January 2019 molten sulfur manifestations in Lastarria appear to be more enriched in As compared to the worldwide known volcanoes with molten sulfur records, such as the Shiretoko-Iozan and Poás volcanoes. Furthermore, their rheological properties suggest that the “time of activity” in events such as this could be underestimated as flows in Lastarria have moved significantly slower than previously thought. The origin of molten sulfur is ascribed to the favorable S-rich chemistry of fumarolic gases and changes in host rock permeability (fracture opening). Molten sulfur in Lastarria correlates with a peak in activity characterized by high emissions of SO2 and other acid species, such as HF and HCl, in addition to ground deformation. Consequently, molten sulfur was framed within a period of volcanic unrest in Lastarria, triggered by changes in the magmatic-hydrothermal system. The appearance of molten sulfur is related to physicochemical perturbations inside the volcanic system and is perhaps a precursor of eruptive activity, as observed in the Poás and Turrialba volcanoes.

A decade of successful magnetotelluric surveys for delineating shallow geothermal reservoirs beneath nonvolcanic hot springs in Thailand

Magnetotelluric (MT) applications to probe the shallow reservoirs of nonvolcanic hot springs in Thailand have become ever more convincing during the past few decades. In 2013, the first modern MT survey was deployed over the Mae Chan hot spring. A shallow hot water reservoir within a network of fractured granite was imaged as a low-resistivity zone beneath the hot spring surrounded by a resistive granite heat source. With the success of the first MT deployment, in 2014 and 2015, MT measurements were expanded to five hot springs with the objective of 1 km deep drilling where the Muang Rae hot spring was chosen out of these five hot springs to assess the volume of hot fluid for a future geothermal power plant. The conductive zone was again detected at a depth of 200–600 m beneath the Muang Rae hot spring, which our team interpreted as a shallow hot fluid reservoir. However, others interpreted it as just the clay cap with no hot fluid inside, which occurs in most volcanic systems. Therefore, a 1 km well was drilled next to the conductor, instead of through it as we suggested. The well did not find any hot water flowing. In 2018, an MT survey with densely spaced stations was used around the Mae Chan hot spring to validate the shallow conductive zone beneath the hot spring through which five wells (<200 m) were drilled. The depth positions where the hot fluid was found match well with the conductor location at most wells. This is a good indicator that in the Thailand nonvolcanic system, the conductive zone beneath the hot spring is genuinely the shallow reservoir, and not the clay cap zone as in the volcanic systems.

Developing an Integrated Petrogenetic Model for Understanding REE Deportment of the Ampasibitika Intrusion and Associated Ion Adsorption Deposits

Abstract Alkaline–peralkaline igneous systems are promising sources of rare earth elements (REEs). Preservation bias has resulted in a gap in the geological record for alkaline–peralkaline magmatic systems, with the hypabyssal plumbing system linking magma chambers to extrusive volcanic rocks poorly represented. Large plutonic varieties of these systems are often proposed to have fed (now eroded) volcanoes, and current peralkaline volcanic systems obscure the plutonic system at depth. The alkaline to peralkaline Ampasibitika Intrusion in Madagascar is a rare example where the magmatic–volcanic interface between a deeper level magma reservoir and its genetically related caldera volcano is exposed. This c. 24 Ma sub-volcanic intrusive system comprises silica-undersaturated to silica-oversaturated units, of peralkaline to metaluminous and peraluminous characters, with varying styles of REE mineralisation, including supergene ion adsorption-style REE occurrences in the overlying weather profiles. There are two main intrusive suites: (1) the concentric Marginal Dyke Swarm (MDS) formed of quartz–microsyenite and peralkaline granite dykes (PGDs), and (2) the Ampasibitika Ring Dyke (ARD) comprising alkali feldspar syenites and subordinate nepheline syenites, trachytes and phonolites. We present new field observations and geochemical data to indicate that the MDS was emplaced as a series of low-viscosity, volatile-rich melt batches, which coalesced in the magma reservoir roof zone and intruded prior to caldera collapse, whereas the ARD was emplaced into the ring fault as a heterogeneous mix of variably evolved syenitic crystal mushes and phonolitic to trachytic-melt batches. As such, we suggest the MDS represents the residual melt fraction of the magma reservoir, whereas the ARD contains portions of the fractionating, silica-neutral to silica-undersaturated syenite, cumulate assemblage. In this revised framework, we assess the major and trace element geochemistry of amphibole- and clinopyroxene-group minerals to gain insight into the magmatic evolution of the Ampasibitika Intrusion and partitioning of REE between early cumulate and residual melt phases. Ultimately, the most REE-enriched units, the PGDs of the MDS, are identified as the product of the most volatile-rich, highly evolved melts from the roof zone of the magma reservoir. However, although REE enriched, the mineralogy does not always enable efficient release of REE for ion adsorption-style mineralisation; instead, lower REE-content protoliths with REE-host phases more amenable to decomposition release a greater proportion of REE.

Hydrogeochemistry of trace and rare earth elements in the Caviahue-Copahue Volcanic Complex

The Caviahue-Copahue Volcanic Complex is one of the most studied active volcanic systems in the South American Andean range, and yet little research has focused on trace and rare-earth elements of waters, especially during an eruptive cycle. In this study, we sampled and investigated natural waters from 23 sites (involving the crater lake, hot springs, streams, rivers, and bubbling pools) in two campaigns in 2017 and 2018, using physicochemical parameters, major, trace and rare-earth elements concentrations. With this novel dataset, it was possible to identify, characterize and compare three groups of waters with distinctive hydrofacies. Indeed, the normalization of water compositions against host rock concentrations showed a particular trace element pattern for each group of waters. Although the absolute concentrations of the elements in each sampling site changed from 2017 to 2018, the normalized patterns did not. Boron, As, Cd, Tl, Se, and Te, commonly recognized as volatile, are the main trace elements that magmatic gases supply to the system headwaters, whereas elements such as Ca, K, and Ba are affected by precipitation of secondary minerals (gypsum, anhydrite, barite, jarosite, and alunite). Furthermore, the main river draining the summit volcano shows a steep decrease in As, Cr, and V concentrations correlated to the precipitation of Fe and Al hydroxysulfates (schwertmannite and basaluminite, respectively). Moreover, it is the first time that a comparison between the different water groups is made using the patterns of the rare-earth elements, allowing us to identify and separate depletion patterns due to dilution processes from those due to precipitation processes.

Tracking volcanic explosions using Shannon entropy at Volcán de Colima

The main objective of this work is to show that Shannon Entropy (SE) calculated on continuous seismic signals can be used in a volcanic eruption monitoring system. We analysed three years of volcanic activity of Volcán de Colima, México, recorded between January 2015 and May 2017. This period includes two large explosions, with pyroclastic and lava flows, and intense activity of less energetic explosion, culminating with a period of quiescence. In order to confirm the success of our results, we used images of the Visual Monitoring system of Colima Volcano Observatory. Another of the objectives of this work is to show how the decrease in SE values can be used to track minor explosive activity, helping Machine Learning algorithms to work more efficiently in the complex problem of distinguishing the explosion signals in the seismograms. We show that the two big eruptions selected were forecasted successfully (6 and 2 days respectively) using the decay of SE. We conclude that SE could be used as a complementary tool in seismic volcano monitoring, showing its successful behaviour prior to energetic eruptions, giving time enough to alert the population and prepare for the consequences of an imminent and well predicted moment of the eruption.

Investigation of deep-seated heat source through 3-D Magnetotelluric inversion in Arjuno-Welirang volcanic complex (East Java)

Arjuno-Welirang is a volcanic complex with quaternary ages in East Java Province, Indonesia. Various geothermal systems in the area might exist, from inactive to still-active hydrothermal systems and even volcanic (magmatic) hydrothermal systems. To differentiate the status of geothermal systems to be useful for further exploration programs, it is necessary to investigate the deep-seated heat source responsible for supporting heat to the existing geothermal systems. To achieve the objective, Magnetotelluric (MT) is used to image the subsurface resistivity variation down to about 20 km. A total of 117 MT stations have been included to fill the coverage area, especially in the eastern and southern regions of the research area. A series of data processing has been conducted to improve the quality of MT data, and 3-D inverse modeling has been applied after processing. In addition, the exploration is also focused on identifying the extension of the high-temperature reservoir with benign fluid. Based on the 3-D inversion of MT data, the updome of resistivity structure at the deeper level below Mt. Welirang is identified as a deep-seated heat source indication supporting the main upflow reservoir zone. A possible reservoir extension to the western side of Mt. Welirang–Mt. Kembar complex is more prominent as indicated by the resistivity pattern, supported by the Cangar and Coban hot springs occurrence as an indication of an outflow zone. This extension zone could be one of the focused areas for further exploration drilling to avoid magmatic fluid that probably exists at the main upflow zone.

The evolution of depletion zones beneath mud volcanoes

Depletion zones are the least well understood component of mud volcanic systems. They are generally difficult to image using reflection seismic data, and have only rarely been identified and described in the subsurface. This study documents 277 mapped depletion zones in the western Nile Cone, offshore Egypt, of which the dimensions and stratigraphic characteristics of a sub-set of 86 depletion zones associated with mud volcanoes of early Pliocene to Recent age are recorded. The primary database used is a large (4,300 km2) 3D seismic survey in which depletion zones can be confidently interpreted using a set of simple criteria. The sub-set of 86 depletion zones were selected for morphometric analysis by virtue of the quality of seismic imaging. The depletion zones are characterised by circular to elliptical planforms with a bowl or conical geometry. They exhibit truncational stratal relationships with their parent stratigraphic unit, which in this area is the Mid-Late Miocene aged OM2 unit, and which occurs directly beneath the Messinian Evaporites. This geometry implies a top-down formation mechanism. Their diameters and relief range from is 600 m–3300 m, and 100 m–740 m, respectively, with a modest scaling relationship between diameter and relief. Flank angles of bowls and cones range from 11⁰ to 41⁰, with a crudely normal distribution, with median and mean values of 26⁰. A model for the evolution of depletion zones in the study area is based on two previous models developed for single source layer plumbing systems and invokes mobilisation of the source layer by sediment collapse and shear-induced liquefaction following initial seal failure by hydraulic fracturing of the evaporite seal. This mechanism may be more widely applicable to mud volcano systems than currently appreciated.

Extreme seismic anisotropy indicates shallow accumulation of magmatic sills beneath Yellowstone caldera

Understanding the distribution and mobility of crystal mushes within modern magmatic systems is crucial to volcanic hazard assessments as distinct pockets of mobile magma may become interconnected and lead to melt accumulation on shorter time scales than magma that is broadly distributed in a homogeneous mush. Here, we reveal that Yellowstone's upper-crustal magma reservoir in the top 20 km is heterogeneous in both melt concentration and texture. We exploit ambient noise in an unprecedented dense temporary seismic network to jointly constrain vertically- and horizontally-polarized shear wave speeds to create enhanced 3D isotropic and anisotropic shear velocity models. Our models show an exceptionally low-velocity (>20% reduction) layer 4–7 km beneath the surface, situated near the top of the reservoir previously-imaged by earthquake P-wave tomography. The presence of strong radial anisotropy (20%) within this layer indicates the uppermost portion of the modern Yellowstone reservoir is organized as a sill complex, with up to 28% of melt fraction in horizontally-elongated volumes at depths where rhyolite was commonly stored before past eruptions. The findings demonstrate that high-resolution anisotropic imaging through a dense seismic network can constrain both magma distribution and reservoir texture, which are important to understand the evolution and hazard assessment of volcanic systems like Yellowstone.

Blooming of a microbial community in an Ediacaran extreme volcanic lake system

Ancient aquatic sediments are critical archives for studying early microbial life and the types of environments in which they thrived. The recently characterized Amane Tazgart microbialites in the Anti-Atlas, Morocco, are a rare and well-preserved non-marine deposit that evolved in an alkaline volcanic lake setting during the Ediacaran Period. A multiproxy geochemical toolbox reveals evidence pointing to spatio-temporal ecosystem organization and succession related to changing lake water chemistry. This is marked by secular transition from a cold/dry climate, hypersaline alkaline thermophilic and anoxic–oxic community, to a stable state warm/wet climate fully oxygenated fresh to brackish water ecosystem, predominated by oxygenic stromatolites. Extreme dissolved Arsenic concentrations suggest that these polyextremophiles required robust detoxification mechanisms to circumvent arsenic toxicity and phosphate deficiency. We propose that self-sustaining and versatile anoxic to oxic microbial ecosystems thrived in aquatic continental settings during the Ediacaran Period, when complex life co-evolved with a rise in atmospheric oxygen content.

Two-stage emplacement mechanism and symmetrical differentiation process of mafic-ultramafic sills in an arc setting: A case study of the Middle Tonian rock assemblage from the Fanjingshan area

The emplacement and differentiation mechanisms are significant parts of understanding the evolution of a magmatic system. There is debate regarding the emplacement mechanism of long-distance lateral transport of magma. And the differentiation mechanisms mainly target the rock assemblage in mantle plume-related or rift-related settings. As yet, few studies had been followed in the arc setting. In this contribution, the mafic-ultramafic sills formed by long-distance lateral transport of magma in the Fanjingshan area in South China have been selected to decode the magmatic emplacement and differentiation mechanism in an arc system. Voluminous basaltic lava and mafic-ultramafic sills are emplaced, concordant to bedding, within the lower part of the Middle Tonian Fanjingshan Group and laterally extend for tens of kilometers. Some mafic-ultramafic sills display symmetrical lithology and geochemical distribution in vertical sections. We provide a detailed stratigraphy and geochemical analysis of the mafic-ultramafic sills of the Fanjingshan Group. The mafic sills within the underlying strata (the Taojinhe Formation) of the lower part of the Fanjingshan Group were intruded at 832 Ma, which is >8 Ma younger than the basaltic eruptions in the overlying strata (the Huixiangping Formation). Moreover, these mafic sills within the Taojinhe Formation have a positive ɛNd(t) value (+0.9 − +1.6), the lowest Platinum Group Elements (PGE) content and highest Rare Earth Elements (REE) content. Compared with other mafic sills and basalts within different formations (the Huixiangping, Xiaojiahe, and Yujiagou formations), mafic sills within the Taojinhe Formation display a separate field on the principal component analysis diagram, suggesting two stages of mafic magma emplacement with a short interval for the Fanjingshan Middle Tonian volcanic plumbing system. The magma channel of the first stage magma is subsequently used by the second stage magma as suggested by ɛNd(t) values and Nb-Ti anomalies. Although island arc magmas differ greatly from mantle plume magmas in volume, temperature and composition, the calculated dimensionless temperature and dimensionless flux of magma imply that the solidification can affect the formation of mafic-ultramafic sills in the island arc systems. At the same time, the difference in rigidity of the upper and lower strata is not the main reason to control the formation of the mafic-ultramafic sills as suggested by the statistical analysis of the mafic-ultramafic sills occurrence between different wall-rock lithology associations. Through the comparative study of the sills formed by the long-distance lateral transport of magma, it is proposed that the clastic wall-rock provides the first-order control for the sills formed by the long-distance lateral transport of magma. According to the detailed geochemical study of an M-shaped geochemical profile within the Huixiangping Formation, two steps of in situ crystallization model have been suggested. In the first step, minerals crystallizing from the inflowing magma on the floor and roof of mafic-ultramafic sills will become more primitive inwards. In the second step, the magma evolves both downward and upward by uninterrupted in situ crystallization in a closed system that results in the whole-rock becoming more evolved in composition inward.

New insights into geological setting of the summit area of mount Etna volcano (Italy) inferred from 2D gravity data modelling

Gravimetric observations were carried out in 2015, to image the uppermost portion of the volcanic plumbing system of Mt. Etna (Italy). Gravity measurements were performed using two relative gravimeters, along a profile that crosses the summit craters area (elevations between 2,820 and 3,280 m a.s.l.). Accurate positioning of the gravity observation points was determined through GPS measurements. After applying elevation and terrain corrections, the reduced gravity data were used to build a 2D density model of the uppermost part of the volcano edifice. This model was constrained using to-date knowledge of the structural setting of the area and the available volcanological data. We highlighted the presence of low-density material below the summit craters, down to the depth of about 2.1 km, interpreted as highly altered, fumarolized and structurally weakened material. It is also likely that the close presence of the conduits feeding the summit craters of the volcano contributes to the gravity low in the SW half of the measurement profile. Conversely, the gravity low observed at the northern edge of the profile could reflect the high concentration of faults and eruptive fissures in the Pizzi Deneri area, in correspondence of the Ellittico caldera rim.

High resolution magnetic anomalies, volcanism and tectonics of the active “La Fossa” vulcanic system (Vulcano island) and Lipari island (South Italy)

In this paper we present the new high-resolution magnetic anomaly map of the La Fossa Caldera system and Lipari island (Southern Italy), obtained by merging two low-altitude aeromagnetic surveys. In these islands a variegated ensemble of magnetic anomalies develops in the north-south direction. The La Fossa Caldera is characterized by very high-intensity and short-wavelength magnetic anomalies, related to mafic intrusive/effusive sources, mainly aligned along the NNW-SSE and NS faults. Instead, the Lipari island is characterized by lower intensity anomalies related to sources with more evolved chemistry, elongated in the NE-SW, NNE-SSW and EW of the subordinate faults. Both the two sets of structures belong to the Tindari-Letojanni strike slip fault-system, a regional lineament along which the southern side of the Aeolian Archipelago is emplaced. The study identifies three distinctive magnetic zones on the Lipari island: the southern, the central, and the north-western ones. The southern zone is characterized by negative magnetic monopoles in correspondence with the younger rhyolitic domes and a Curie Isotherm upwelling. The central part of the island has an average lower intensity of positive anomalies, corresponding to the less evolved products of the intermediate Lipari volcanic epochs. The north-western side is characterized by higher intensity anomalies related to older volcanic epochs. The interplay among strike-slip tectonics, chemistry of the uprising magmas, and the thermal setting has contributed to the overall anomaly pattern in this sector of the Aeolian Archipelago. This interpretation is supported by the application of digital enhancement to the total intensity magnetic anomaly field and by the spatial correlation analysis of the magnetic and volcano-tectonic features. The obtained insights are useful to better understand the relationship between arc volcanism and tectonics. Moreover, they can also outline new inferences to forecast future eruptions of the active La Fossa volcanic system. In fact, recent unrest signals were registered at La Fossa Cone, which is one of the present-day active volcanoes of the Aeolian Archipelago, along with Stromboli island. Key pointsLa Fossa volcanic system of Vulcano and Lipari islands high resolution aeromagnetic surveys; Strike slip tectonics magnetic anomaly signature; Spatial correlation analysis of volcano-tectonic and magnetic features.

Emplacement dynamics of the plumbing system and lava pile of the Paraná Magmatic Province in Morro da Igreja, Santa Catarina, Brazil

The mechanisms of magma ascent, transport and emplacement of the volcanic pile from LIPs are key issues regarding the understanding of the complex construction of volcanic systems and magma transport through the crust. The integrated approach of morphology of the volcanic and subvolcanic bodies, whole rock geochemistry and ASM data provides a robust tool to unravel the flow dynamics of the volcanic bodies and the sequence of the magmatic events. Such approach allows building up a model of construction of the lava pile considering the role played by the plumbing system. This paper investigates the emplacement mechanism of sill and lava flows of the Serra Geral Group (SGG), in the southern part of Mesozoic Paraná-Etendeka Magmatic Province (PEMP) in Brazil. Geologic and geochemical analysis were integrated with anisotropy of magnetic susceptibility (AMS), anisotropy of anhysteretic remanent magnetization (AARM) and rock magnetism experiments on 14 sampling sites in the Morro da Igreja region, top of the lava pile in Santa Catarina. The area is composed of low-Ti basaltic (with predominance of rubbly pahoehoe) and silicic lava flows, both intruded by a tabular sill that reaches a few hundred meters wide. The mafic lava flows are composed of Gramado, Urubici and Esmeralda magma-type basalts and andesite basalts. The silicic lava flows are massive or foliated, classified as Palmas type dacites. The sill has regular columnar joints and is classified as Esmeralda type. Magnetic mineralogy data suggests magnetite or Ti-poor magnetite as the main magnetic mineral for all the igneous rocks, and AARM results show anomalous fabric for the lava flows and normal or intermediate fabric for the sill. Besides the anomalous fabric sites, AMS data provide reliable directional data to infer flow direction for the sill, with initial propagation towards NE, followed by a preferential SE direction of magma flow. For the silicic rocks, the presence of vertical and inclined magnetic foliation suggest a lava dome geometry. The dynamics of the magmatic flow of the sill and lava flows associated with the compositional characteristics of the rocks allows stablishing the stratigraphy of the magmatic events in the area as well as the proposition of an emplacement model for the sequence.

Toward a Real-Time Analysis of Column Height by Visible Cameras: An Example from Mt. Etna, in Italy

Volcanic plume height is one the most important features of explosive activity; thus, it is a parameter of interest for volcanic monitoring that can be retrieved using different remote sensing techniques. Among them, calibrated visible cameras have demonstrated to be a promising alternative during daylight hours, mainly due to their low cost and low uncertainty in the results. However, currently these measurements are generally not fully automatic. In this paper, we present a new, interactive, open-source MATLAB tool, named ‘Plume Height Analyzer’ (PHA), which is able to analyze images and videos of explosive eruptions derived from visible cameras, with the objective of automatically identifying the temporal evolution of eruption columns. PHA is a self-customizing tool, i.e., before operational use, the user must perform an iterative calibration procedure based on the analysis of images of previous eruptions of the volcanic system of interest, under different eruptive, atmospheric and illumination conditions. The images used for the calibration step allow the computation of ad hoc expressions to set the model parameters used to recognize the volcanic plume in new images, which are controlled by their individual characteristics. Thereby, the number of frames used in the calibration procedure will control the goodness of the model to analyze new videos/images and the range of eruption, atmospheric, and illumination conditions for which the program will return reliable results. This also allows improvement of the performance of the program as new data become available for the calibration, for which PHA includes ad hoc routines. PHA has been tested on a wide set of videos from recent explosive activity at Mt. Etna, in Italy, and may represent a first approximation toward a real-time analysis of column height using visible cameras on erupting volcanoes.

Fluid-Assisted Aggregation and Assembly of Magnetite Microparticles in the Giant El Laco Iron Oxide Deposit, Central Andes

The El Laco iron oxide mineral deposit in the Central Andes of Chile has attracted significant attention because of its uniquely preserved massive magnetite orebodies, which bear a remarkable similarity to volcanic products. To date, the outcropping highly vesicular and porous massive magnetite orebodies have received little attention from a microtextural point of view, limiting our understanding about the role of volcanogenic processes on iron mineralization. Here, we report the chemical composition of vesicular magnetite at El Laco using EPMA and LA-ICP-MS methods and provide detailed 2D and 3D imaging of the internal structure of these texturally complex magnetite ores by combining SEM observations, synchrotron radiation micro-X-ray fluorescence chemical mapping, and high-resolution X-ray computed microtomography. Our observations reveal the presence of abundant magnetite microspheres with diameters ranging from ∼100 to ∼900 μm, as well as dendritic microstructures forming interconnected networks up to a few millimeters in size. Two-dimensional microtextural and geochemical imaging of the microspheres show that these features are formed by multiple euhedral magnetite crystals growing in all directions and occur immersed within a porous matrix conformed by smaller-sized (∼2–20 μm) and irregularly shaped magnetite microparticles. These types of morphologies have been reported in hydrothermal vents associated with hydrovolcanic processes and commonly described in hydrothermal synthesis experiments of magnetite microspheres, suggesting precipitation from iron-rich fluids. A hydrothermal origin for the magnetite microparticles reported here is further supported by their geochemical signature, which shows a strong depletion in most minor and trace elements typical from magnetite precipitated from hydrothermal fluids in ore-forming environments. We propose that decompression, cooling, and boiling of fluids triggered massive iron supersaturation, resulting in the nucleation of magnetite microparticles or colloids, followed by self-assembly into larger and more complex microstructures. Our data from El Laco deposit agree with models invoking magmatic-hydrothermal fluids to explain the origin of the deposit and provide new insights on the potential role of iron colloids as agents of mineralization in volcanic systems.

Nitrate sources, timing, and pathways of a permeable volcanic aquifer system with mixed land use in Jeju Island, South Korea

The occurrence of various N-related human activities increases the difficulty in distinguishing the major sources of NO3− contamination in groundwater, especially in areas with mixed land uses. In addition, the estimation of the timing and pathways of NO3− is necessary to better understand the processes of NO3− contamination in the subsurface aquifer system. This study applied environmental tracers, such as stable isotopes and age tracers (δ15N and δ18O of NO3−, δ11B, chlorofluorocarbons, and 3H), to elucidate the sources, timing, and pathways of NO3− contamination in the groundwaters of the Hanrim area, which has suffered from illegal disposal of livestock wastes since the 1980s, and also characterizes them based on mixed N-contaminant sources such as chemical fertilizers and sewage. The combined use of δ15N and δ11B overcame the limitation of using only NO3− isotopes for the identification of overlapping sources of N and successfully identified the major source of N as livestock wastes. The lumped parameter model (LPM) estimated the binary mixing of the young (age: 23–40 years, NO3-N: 2.55–15.10 mg/L) and old (age: >60 years, NO3-N: <3 mg/L) groundwaters, and explained their age mixing behaviors. The young groundwater was highly affected by livestock-derived N loading during 1987–1998, which coincides with the period of improper dumping of livestock wastes. Furthermore, the young groundwater with elevated NO3-N followed the historical NO3-N curves with younger ages (6 and 16 years) than those derived from the LPM, suggesting the possibility of faster inflows of livestock wastes through the permeable volcanic structures. This study demonstrated that a comprehensive understanding of NO3− contamination processes can be achieved using environmental tracer methods, which enables the efficient management of groundwater resources in areas with multiple N sources.

Elucidating the magma plumbing system of Ol Doinyo Lengai (Natron Rift, Tanzania) Using satellite geodesy and numerical modeling

Ol Doinyo Lengai, located in the southern Eastern Branch of the East African Rift had several eruptive episodes with ash falls and lava flows (VEI 3) that caused damage to the nearby communities between 2007 and 2010. The volcano is remote and access is difficult. Although this volcano has been studied for decades, its plumbing system is still poorly understood, in part, because of the lack of precise observations of surface deformation during periods of quiet and unrest. This study investigates the volcanic plumbing system of Ol Doinyo Lengai and its surroundings using data from the network of permanent Global Navigation Satellite System (GNSS) sites monitoring the volcano (the TZVOLCANO network) around the flanks of the volcano and Interferometric Synthetic Aperture Radar (InSAR) observations. We constrain surface motions using 6 GNSS sites distributed around Ol Doinyo Lengai, operating between 2016 and 2021, and InSAR data covering nearly the same time period. Because of the complex local tectonics, the interpretation of the deformation pattern is not straightforward. We first invert the GNSS deformation and InSAR observations independently to infer potential deformation sources. Then we perform a joint inversion of both GNSS and InSAR datasets to verify our findings. We compare the results from the joint inversion with the results from inverting each dataset independently. The GNSS, InSAR, and joint inversion results point to a deflating source, located east of Ol Doinyo Lengai and southwest of the dormant volcano Gelai at a depth of 3.49 ± 0.03 km (GNSS inversion), 5.2 ± 1.2 km (InSAR inversion) and 3.49 ± 0.06 km (joint inversion) relative to the summit (vent) and with a volume change ∆V of −0.04 ± 0.05 × 106 m3 (GNSS inversion), −0.39 ± 0.29 × 106 m3 (InSAR inversion), and − 0.04 ± 0.01 × 106 m3 (joint inversion). Although this is non-unique modeling of geodetic datasets with small signals, the inversion results suggest that Ol Doinyo Lengai could be fed by an offset multi-reservoir system that includes a shallow magma reservoir (<5 km) east of Ol Doinyo Lengai, possibly connected to a deeper magma reservoir.

Stratigraphy of volcanic memory: Sociocultural dimensions of volcanic risk in the Southern Andes, Chile

AbstractThis article focuses on communities that reoccupy territories affected by volcanic eruptions to extend understanding of people's social appropriation of environments exposed to natural hazards. We take as a case study three rural settlements affected by several eruptions from the Carran‐Los Venados and Puyehue‐Cordón Caulle volcanic systems (Southern Andes, Chile). Using an ethnographic observation scale, we engage with local actors' experiences during volcanic eruptions and quiescence. We identified three factors shaping people's decision to reoccupy volcanic territories: the reproduction of a peasant habitus, a stratigraphy of memories and the acceptability of volcanic risk. The results illustrate the construction of human–volcano interactions built over generations, framed in socio‐volcanic cycles faced from a habitus of precariousness. However, after recalling their past vulnerabilities, the community imagines overcoming the impacts of volcanism from a different habitus based on living as peasants in conditions of greater social equity. From this, we discuss how volcanic imaginaries interrogate the past, motivate a more accurate understanding of volcanic risk and support the projections of communities about their human–volcano coexistence despite exposure to hazards. Finally, we posit the concept of ethnovolcanology to understand the tension between place attachment and disaster risk as a persistent intersection of human and geological forces.

The Capabilities of FY-3D/MERSI-II Sensor to Detect and Quantify Thermal Volcanic Activity: The 2020–2023 Mount Etna Case Study

Satellite data provide crucial information to better understand volcanic processes and mitigate associated risks. In recent years, exploiting the growing number of spaceborne polar platforms, several automated volcanic monitoring systems have been developed. These, however, rely on good geometrical and meteorological conditions, as well as on the occurrence of thermally detectable activity at the time of acquisition. A multiplatform approach can thus increase the number of volcanological-suitable scenes, minimise the temporal gap between acquisitions, and provide crucial information on the onset, evolution, and conclusion of both transient and long-lasting volcanic episodes. In this work, we assessed the capabilities of the MEdium Resolution Spectral Imager-II (MERSI-II) sensor aboard the Fengyun-3D (FY-3D) platform to detect and quantify heat flux sourced from volcanic activity. Using the Middle Infrared Observation of Volcanic Activity (MIROVA) algorithm, we processed 3117 MERSI-II scenes of Mount Etna acquired between January 2020 and February 2023. We then compared the Volcanic Radiative Power (VRP, in Watt) timeseries against those obtained by MODIS and VIIRS sensors. The remarkable agreement between the timeseries, both in trends and magnitudes, was corroborated by correlation coefficients (ρ) between 0.93 and 0.95 and coefficients of determination (R2) ranging from 0.79 to 0.84. Integrating the datasets of the three sensors, we examined the effusive eruption of Mount Etna started on 27 November 2022, and estimated a total volume of erupted lava of 8.15 ± 2.44 × 106 m3 with a Mean Output Rate (MOR) of 1.35 ± 0.40 m3 s−1. The reduced temporal gaps between acquisitions revealed that rapid variations in cloud coverage as well as geometrically unfavourable conditions play a major role in thermal volcano monitoring. Evaluating the capabilities of MERSI-II, we also highlight how a multiplatform approach is essential to enhance the efficiency of satellite-based systems for volcanic surveillance.