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The physiochemical properties of volcanic ash are determined by magma ascent and eruption dynamics and provide important insights into controls on the timing and style of volcanic eruptions. However, linking petrological observations to monitoring parameters remains challenging. Here we investigate the relationships between geophysical, geochemical and satellite remote sensing data with the physiochemical properties of volcanic ash to better understand eruptive dynamics at El Reventador volcano, Ecuador. Between 2016 and 2019, eruptive activity at El Reventador was characterised by frequent explosions interspersed with effusive activity from two summit vents. We found that: (1) periods of predominantly effusive behaviour were defined by ash samples with the lowest proportions of juvenile grains, frequent, more intense thermal anomalies and frequent (ca. every 25 min) but low-energy explosions that produced lower average ash column heights (< 1200 m above the summit) and; (2) periods of predominantly explosive behaviour were defined by ash samples with the highest proportions of juvenile grains and also vesicular juvenile grains, low thermal anomalies and less frequent (ca. every 70 min), higher-energy explosions that produced higher average eruption column heights (> 1500 m above the summit). Our study shows that there are strong correlations between the physiochemical properties of erupted material and the multiparametric monitoring data which in turn link to the type of surface activity observed. As a result, the development of physical conduit models and interpretations of eruptive dynamics are made more robust combining both monitoring data and the physical properties of eruptive products. [ABSTRACT FROM AUTHOR]

Using recycled waste for soil improvement is a sustainable strategy that can reduce resource consumption. In this paper, recycled polyester fiber (RPF) is proposed to improve the engineering performance of red mud- improved volcanic ash (RV). A series of mechanical test were performed for RVs with five different content of RPF. And the microstructure was also investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and mercury intrusion porosimetry (MIP) tests. Results show that RPF significantly reinforces the mechanical strength and toughness of RV and the optimum content of RPF is 0.9%. The Unconfined compressive strength (UCS), cohesion (c) and internal friction angle (φ) of reinforced soil enhanced by up to 122%, 40% and 8% compared to untreated soil at the optimum incorporation and optimum water content, respectively. The failure model of RPF-reinforced RV is converted from brittle to ductile, and the toughness parameters are significantly improved. Microscopic investigations reveal that RPF forms a complex three-dimensional structure within the reinforced soil. Adhesion and friction interactions at the fiber-matrix interface are the main reasons for the enhancement of strength and toughness. However, the performance of composites does not continue increasing with RPF content. Excessive fibers gather and twist to form weak zones, reducing the strength and stiffness of material. In practice, the optimal fiber content needs to be controlled to ensure the best mechanical properties. This eco-friendly soil improvement can promote the harmless utilization of red mud and waste polyester materials contributing to ground improvement techniques in volcanic areas. [ABSTRACT FROM AUTHOR]

Volcanic eruptions can release large amounts of tephra, lava, and gases, drawing attention due to their magnitude, energy, and impact on life and the environment. Among the most documented and sometimes dramatic effects of volcanic ashes are those linked to the input of diverse elements in the environment, which are released as a consequence of ash weathering. Laboratory studies have been conducted to investigate and predict the environmental input of chemical elements from volcanic ashes. This research paper describes the optimization of batch leaching tests used to investigate the release of ions from ashes collected in the Andes Cordillera after the eruption of the Puyehue volcano in 2011. Chemometric multivariate strategies were employed to evaluate the influence of variables affecting the leaching of volcanic ash. The effects of the main variables, namely contact time, the acidity of the leaching agent, the solid/liquid ratio, the particle size, and the stirring speed, were studied in leaching tests. To determine the optimal conditions for selected metal determinations, we employ Darringer's desirability function, which allows for the simultaneous optimization of the selected responses (element concentrations during the leaching process). Multielemental analysis (Na, Mg, Al, Si, P, Cl, K, Ca, V, Cr, Mn, Fe, Ni, Cu, Zn, Sr, Cd, Hg, Tl, and Pb) was quantified by ICP-MS (inductively coupled plasma-mass spectrometry) following adequate dilution of test leaching. These results established the optimal experimental conditions for leaching volcanic ash. The most significant variables were the solid/liquid ratio and the stirring speed, resulting in two groups of elements with an adequate global desirability function (D) value. [ABSTRACT FROM AUTHOR]

This paper presents a method for retrieving optical parameters from volcanic sulfate aerosols from the AHI radiometer on board the Himawari-8 satellite. The proposed method is based on optical models for various mixtures of aerosol components from volcanic clouds, including ash particles, ice crystals, water drops, and sulfate aerosol droplets. The application of multi-component optical models of various aerosol compositions allows for the optical thickness and mass loading of sulfate aerosol to be estimated in the sulfuric cloud formed after the Karymsky volcano eruption on 3 November 2021. A comprehensive analysis of the brightness temperatures of the sulfuric cloud in the infrared bands was performed, which revealed that the cloud was composed of a mixture of sulfate aerosol and water droplets. Using models of various aerosol compositions allows for the satellite-based estimation of optical parameters not only for sulfate aerosol but also for the whole aerosol mixture. [ABSTRACT FROM AUTHOR]

Lahars are hazardous mixtures of rock and water that flow rapidly in the form of debris flows or mudflows. The continuous eruptions at Sakurajima supply volcanic ash to form on the surface, reducing the permeability of the ground. As the surface permeability decreases, surface runoff occurs and eventually lahar starts. Therefore, Sakurajima Island suffers from lahars triggered by heavy rains every year. Sheet erosion by surface runoff decreases the thickness of volcanic ash on the ground and subsequently increases hydraulic conductivity. This cycle continues due to the eruptions of the Sakurajima volcano and the lahars formed by heavy rains. Depending on the lahar type and amount of surface runoff, the flow density and block sizes carried in the lahar vary. In this study, the relationship between the volcanic ash thickness and the hydraulic conductivity of the ground was investigated in the Arimura River basin of Sakurajima volcano between 2015 and 2020. Monthly volcanic ash thickness was measured 2 km from the craters. The dynamic change of volcanic ash thickness due to accumulation and erosion was investigated by the Universal Soil Loss Equation and the newly developed Discharge Dependent Erosion methods. Block sizes of the lahars were estimated by vibrographs and CCTV camera. The hydraulic conductivity of the ground was calculated with a Kinematic Wave Model developed specifically for this study. Based on the relationship between volcanic ash thickness and hydraulic conductivity, a risk assessment chart was created considering the block sizes carried by the lahars. [ABSTRACT FROM AUTHOR]

Volcanic eruption is known as multi-hazards to the surrounding environment and society causing the formation of lahar as the frequent hazards that shortly occurred due to airborne tephra after an eruption. Erosion triggered by rainfall on unconsolidated tephra material, such as volcanic ash, is the primary lahar initiation mechanism. The time and scale of lahars vary based on eruptions and watershed conditions. The variability of the erosion process is driven by a set of local factors including the grain size and spatial distribution of volcanic ash thickness, slope, and rainfall intensity. Laboratory simulation experiments were conducted in a 3.00 m long, 0.75 m wide, and 0.50 m deep flume to study the relationship of volcanic ash erosion rate to three driven parameters, namely slope, rainfall intensity, and volcanic ash thickness. Three slope gradients were selected to represent gentle (14.1%), mild (26.8%), and steep (46.6%) slopes. Meanwhile, the rainfall intensity ranged from 0.65 to 1.85 mm.min-1, and the variations of volcanic ash layer thickness were 1.00 cm; 2.50 cm; and 5.00 cm. The erosion rate model was generated from a dimensional analysis accommodating slope, rainfall intensity, flow discharge, and the ratio of critical and applied boundary shear stress as independent variables. The variable coefficients were obtained by parameter optimization of experiment data through nonlinear regression analysis. The erosion rate model performance was tested using the Nash-Sutcliffe model Efficiency (NSE), Index of Agreement (IOA), and Root Mean Square Error (RMSE). The performance of the volcanic ash erosion rate model was proven to be satisfactory with the NSE>0.75, IOA>0.95, and RMSE values ranging from 0.005 to 0.009. This model has proven applicable better for volcanic ash erosion than other erosion models which are sandy soil material-based experiments because of the specific characteristics of volcanic material itself. The volcanic ash erosion model in this study can be implemented to predict the sediment yield of tephra as part of volcanic disaster mitigation. [ABSTRACT FROM AUTHOR]

This paper considers the propagation of ash during the paroxysmal eruption of Sheveluch Volcano which occurred April 10–13, 2023, and its impact on the water resources of the affected area. We characterize ash thicknesses at various population centers and describe the grain-size composition of the ash. We show that the propagation of ash plumes is primarily driven by the eruption dynamics, but atmospheric circulation actually controls the spatial distribution of deposit thickness. The water-soluble salts contained in the ash and the dynamics of their washing out under natural conditions have been determined. The water-soluble part of fresh ash is dominated by calcium and magnesium sulfates, sodium chloride, with minor amounts of chlorides and fluorides of aluminum, potassium, and ammonium. The first substances to be washed out from ashes are well-soluble chlorides, to be followed by sulfates. As time goes on, the total concentration of soluble salts is decreasing, and their qualitative composition changes: hydrogen carbonates of calcium, magnesium, and sodium begin to dominate. Several months after the eruption, the impact of the ashfall on water resources of the settlements, including open springs at the ground surface, was leveled out. [ABSTRACT FROM AUTHOR]

Portland cement products are extensively used as parent materials in construction projects. However, the production and consumption of these products result in various environmental pollutants, including the emission of carbon dioxide gas and excessive water usage. Geopolymer products have emerged as a promising alternative to Portland cement and its products due to their diverse mechanical and chemical properties. Therefore, in this study, we aim to investigate the potential of geopolymer products as a replacement for Portland cement. To this end, the optimal mixing design was obtained by performing uniaxial compressive strength and flow table tests. Nailing is a commonly used method for stabilizing soil excavations and slopes, often involving the use of Portland cement as grout. Geopolymer is used as a potential replacement for cement grout in this system. Pullout tests were conducted to investigate the interaction between the soil and grout, considering the effect of curing conditions and environmental factors such as temperature, humidity, and overburden pressure for both the geopolymer and cement grouts. The results indicate that, in general, the pullout force of geopolymer samples is lower than that of cement samples. However, raising the temperature in geopolymer samples results in an increase in the pullout force, whereas an increase in temperature in cement samples leads to a decrease in pullout force. It can be concluded that geopolymer samples need to be modified by using an additive, such as sodium silicate, to achieve proper pullout force and suitable interlocking with soil grains. [ABSTRACT FROM AUTHOR]

The color of pyroclasts is fundamental, because it reflects various magma properties and eruption processes, including particle morphology, chemistry, and petrological characteristics. However, deriving the componentry ratio (CR) of pyroclasts for ongoing eruption monitoring remains challenging due to the lack of a robust quantitative standard. The derivation of the CR, as well as other petrological analyses, is too laborious and time-consuming to introduce as a sustainable monitoring method. To address this, we employed spectroscopic colorimetry to rapidly and quantitatively describe eruptive product colors, enabling CR derivation based on clear, objective standards for ash particle classification. Through color spectroscopy of bulk and sieved ash samples, we analyzed the major size fraction for time-series samples during the waxing stage of the 2017–2018 Shinmoe-dake eruption in Kirishima volcano, Southwest Japan. Our findings reveal that the color changes in bulk ash systematically changed with the evolution of componentry. This temporal color change was due to an increase in the amount of vesicular particles with clear glass against dark angular lava particles, as well as a grain size change, which we interpret as an indication of a transition from phreatic/phreatomagmatic to magmatic eruption. Subsequently, the color of the ash changed when the amount of different lava particles increased gradually, coinciding with a shift toward a more dominant effusion of lava. As the lava effusion continued, a slight reddening of the ash, indiscernible to the naked eye, was clearly detected by the spectrometer before the onset of intermittent Vulcanian eruptions. We interpreted this reddening as oxidation resulting from decreased ascent speed and caprock formation, which accumulates overpressure for Vulcanian explosions. These results highlight the potential of rapid, objective color value and componentry derivation for sustainable quasi-real-time monitoring of ongoing eruption materials. [ABSTRACT FROM AUTHOR]

Eruption source parameters (ESPs) are crucial for characterising volcanic eruptions and are essential inputs to numerical models used for hazard assessment. Key ESPs of explosive volcanic eruptions include plume height, mass eruption rate, eruption duration, and grain-size distribution. Some of these ESPs can be directly observed during an eruption, but others are difficult to measure in real-time, or indeed, accurately and precisely quantify afterwards. Estimates of ESPs for eruptions that cannot be observed, for example, due to the remote location of a volcano or poor weather conditions, are often defined using expert judgement and data from past eruptions, both from the volcano of interest and analogue volcanoes farther afield. Analysis of such information is time intensive and difficult, particularly during eruption response. These difficulties have resulted in the production of datasets to aid quick identification of ESPs prior to or during an eruption for use in operational response settings such as those at volcano observatories and Volcanic Ash Advisory Centres. These resources include the Mastin et al. (2009a) ESP dataset and the Catalogue of Icelandic Volcanoes and European Catalogue of Volcanoes aviation tables. Here, we review and compare these resources, which take different approaches to assigning ESPs. We identify future areas for development of these resources, highlighting the need for frequent updates as more knowledge of volcanic activity is gained and as modelling capabilities and requirements change. [ABSTRACT FROM AUTHOR]

Rare-earth silicates are promising environmental barrier coatings (EBCs) that can protect SiCf/SiCm substrates in next-generation gas turbine blades. Notably, RE2Si2O7 (RE = Yb and Ho) shows potential as an EBC due to its coefficient of thermal expansion (CTE) compatible with substrates and high resistance to water vapor corrosion. The target operating temperature for next-generation turbine blades is 1400°C. Corrosion is inevitable during adhesion to molten volcanic ash, and thus, understanding the corrosion behavior of the material is crucial to its reliability. This study investigates the high-temperature corrosion behavior of sintered RE2Si2O7 (RE = Yb and Ho). Samples were prepared using a solid-state reaction and hot-press method. They were then exposed to volcanic ash at 1400°C for 2, 24, and 48 h. After 48 h of exposure, volcanic ash did not react with Yb2Si2O7 but penetrated its interior, causing damage. Meanwhile, Ho2Si2O7 was partially dissolved in the molten volcanic ash, forming a reaction zone that prevented volcanic ash melts from penetrating the interior. With increasing heat treatment time, the reaction zone expanded, and the thickness of the acicular apatite grains increased. The Ca:Si ratios in the residual volcanic ash were mostly unchanged for Yb2Si2O7 but decreased considerably over time for Ho2Si2O7. The Ca in volcanic ash was consumed and formed apatite, indicating that RE3+ ions with large ionic radii (Ho > Yb) easily precipitated apatite from the volcanic ash. [ABSTRACT FROM AUTHOR]

Sulfur-containing ejecta of Plinian-type eruptions can be transported to great distances in gas pores of ash particles. The mean concentration of sulfur in the rhyolite tephra of the ca. 1500 BP Opala eruption is 310 ppm. The maximum concentration can reach 800 ppm. We have found a relationship between sulfur concentration in bulk samples and grain-size composition: sulfur is mostly found in the 0.25‒0.50 mm fraction consisting of elongate ash particles with elongate gas pores 1.0‒10.0 µm long. The most likely cause why sulfur concentration depends on the structure of ash particles consists in the fact that sulfur compounds of the water-soluble complex are preserved inside gas pores; sulfur-containing compounds that have been sorbed on the surface of ash particles were removed by precipitation during the time the tephra resided in continental settings. When ash particles that contain sulfur compounds on the inner surface of gas pores come into bottom sediments during Plinian-type eruptions like that on Opala Volcano ca. 1500 BP, that can affect the geochemistry of lithogeny and rearrange the mineral phases that are sensitive to the presence of oxide-sensitive agents in the sedimentary sequence during diagenesis. [ABSTRACT FROM AUTHOR]

Small-to-moderate explosive eruptions involve VEIs ≤ 3, tephra volumes ≤ 0.1 km3 and often eject a significant amount of ash-sized pyroclastic material. This reduces the preservation potential of associated deposits and leads to an underrepresentation of these low- to mid-intensity explosive eruptions in long-term, frequency-magnitude datasets. Mt. Ruapehu is one of New Zealand’s most active volcanoes, having produced at least 32 small-to-moderate eruptions over the past 1800 years. The largest of these eruptions deposited the widespread T13-sequence and lasted several months to years. The cumulative deposit volume is estimated at 0.15 km3, thus being an order of magnitude larger than the average deposit volumes of the last 1800 years at Ruapehu. The sequence of pyroclastic fall deposits can be subdivided into six depositional sub-units representing at least five eruption phases of variable intensity and magnitude. The ash-lapilli sequence displays variable dispersal, deposit textures and pyroclast characteristics. While the initial phase is characterised by dispersal limited to the proximal 11 km and a tephra volume of 8.5 × 105 m3 (± 3%), the following high-intensity “peak” phase is estimated at 8.8 × 107 m3 (± 37.8%), representing about ⁓60% of the cumulative tephra volume. The combination of deposit characteristics with textural analysis of different types of juvenile clasts suggests that changes in eruption style and intensity were mainly controlled by shallow processes in the conduit, such as degassing and crystallisation and changes in conduit geometry. Multilobate, irregular dispersal patterns and laterally variable pyroclast assemblage indicate unsteady eruption conditions characterised by weak eruption plumes controlled by prevailing winds. This study testifies the complexity of tephra sequences associated with long-lasting, small-to-moderate eruptions, and describes the key eruption parameters that can be obtained through a detailed characterisation and identifies the main limitations related to the classification of these eruptive styles. [ABSTRACT FROM AUTHOR]

Early detection of volcanic ash clouds is crucial to aviation safety and airspace surveillance. With the increase in air traffic and the frequency of volcanic eruptions, the need for effective warning procedures and improved detection methods has become obvious. The eruption of the Eyjafjallajökull volcano in 2010 showed that air traffic operations were severely disrupted and highlighted the importance of effective communication strategies between stakeholders. To improve monitoring capabilities, satellite techniques have become essential due to their wide coverage and rapid response. This article presents the HOTVOLC 3.0 web-Geographic Information System (GIS) interface, an enhanced version of the French operational monitoring platform developed at the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC) and certified by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS-INSU). By integrating data from the Meteosat Second Generation (MSG) satellites, HOTVOLC 3.0 enables early detection of volcanic activity and monitoring of ash plumes and clouds. The HOTVOLC service is designed to support volcanic observatories, volcano research institutes, Volcanic Ash Advisory Centers (VAAC), and other operational actors who play a crucial role in decision-making and the implementation of effective risk management strategies for aviation safety. After a description of how the system works, we provide details of the updated web interface, which enhances the user experience by offering an interface with an operational mode and an archive mode, enabling easy access to past eruptions for training purposes. In the second part, we look at the various ash-related observation products (detection algorithms and quantitative products) that are disseminated via the new interface. Finally, we explore future developments of the platform, including the use of machine learning for ash detection, the integration of data from other geostationary satellites to improve product quality, and the forthcoming arrival of data from Meteosat Third Generation (MTG) satellites. [ABSTRACT FROM AUTHOR]

In the eruptive event of Tajogaite (2021) in La Palma, Canary Islands, large quantities of volcanic ash were accumulated, affecting the local environment and urban areas. In this study, volcanic ash sampled from urban areas (catalogued as municipal waste (20 03 03) by the European Wastes Catalogue) were converted into zeolites by hydrothermal synthesis at 100 °C with previous alkaline fusion at 550 °C with distilled water. During this process, new phases of zeolite principally type X and sodalite have been identified by XRD at 2 h of incubation. These zeolites, with the course of incubation time, present competitive processes where the transformation into sodalite develops after 24 h as the predominant phase. The synthesized zeolitic material presents a high concentration as impurities in Fe2O3 (13.70 wt%), Na2O (12.70 wt%), CaO (11.65 wt%), and TiO2 (3.89 wt%) coming from the volcanic ash and NaOH introduced in the synthesis methodology. These impurities impart different physicochemical capabilities to the zeolitic material. The application of zeolites obtained in a preliminary fluoride adsorption experiment with volcanic leachate water rich in fluoride has been tested in a novel way. Removal efficiencies of 41.4% at acidic pH (5.77) have been obtained with 2 g L−1 adsorbent zeolitic material doses. A value-added material is obtained and applied in a preliminary way to solve a problem generated by the volcanic ash itself, allowing the End of Waste status and meeting different objectives of the sustainable development goals of the UN Agenda 2030. [ABSTRACT FROM AUTHOR]

Volcanic ash provides unique pieces of information that can help to understand the progress of volcanic activity at the early stages of unrest, and possible transitions towards different eruptive styles. Ash contains different types of particles that are indicative of eruptive styles and magma ascent processes. However, classifying ash particles into its main components is not straightforward. Diagnostic observations vary depending on the magma composition and the style of eruption, which leads to ambiguities in assigning a given particle to a given class. Moreover, there is no standardized methodology for particle classification, and thus different observers may infer different interpretations. To improve this situation, we created the web-based platform Volcanic Ash DataBase (VolcAshDB). The database contains > 6,300 multi-focused high-resolution images of ash particles as seen under the binocular microscope from a wide range of magma compositions and types of volcanic activity. For each particle image, we quantitatively extracted 33 features of shape, texture, and color, and petrographically classified each particle into one of the four main categories: free crystal, altered material, lithic, and juvenile. VolcAshDB (https://volcash.wovodat.org) is publicly available and enables users to browse, obtain visual summaries, and download the images with their corresponding labels. The classified images could be used for comparative studies and to train Machine Learning models to automatically classify particles and minimize observer biases. [ABSTRACT FROM AUTHOR]

Probabilistic forecasting of volcanic ash dispersion involves simulating an ensemble of realistic event scenarios to estimate the probability of a particular hazard threshold being exceeded. Although the number of samples that make up the ensemble, how they are chosen, and the desired threshold all set the uncertainty of (or confidence in) the estimated exceedance probability, current practice does not quantify and communicate the uncertainty in ensemble predictions. In this study, we use standard statistical methods to estimate the variance in probabilistic ensembles and use this measure of uncertainty to assess different sampling strategies for the wind field, using the example of volcanic ash transport from a representative explosive eruption in Iceland. For stochastic (random) sampling of the wind field, we show how the variance is reduced with increasing ensemble size and how the variance depends on the desired hazard threshold and the proximity of a target site to the volcanic source. We demonstrate how estimated variances can be used to compare different ensemble designs, by comparing stochastic forecasts with forecasts obtained from a stratified sampling approach using a set of 29 Northern European weather regimes, known as Grosswetterlagen (GWL). Sampling wind fields from within the GWL regimes reduces the number of samples needed to achieve the same variance as compared to conventional stochastic sampling. Our results show that uncertainty in volcanic ash dispersion forecasts can be straightforwardly calculated and communicated, and highlight the need for the volcanic ash forecasting community and operational end-users to jointly choose acceptable levels of variance for ash forecasts in the future. [ABSTRACT FROM AUTHOR]

The area of seaweed beds along Japanese coasts has decreased by approximately 40% in the last 40 years due to climate change and human activity. In addition, there are similar concerns regarding coastlines worldwide. Thus, it is critical to recover seaweed communities quickly to maintain marine plants and environments. The frequency of eruptions at Mt. Sakurajima in the Kagoshima Prefecture of the Kyushu region peaked in 2011 and was the highest since observations began in 1955. Additionally, large amounts of waste material, such as scrap ceramics and gypsum, are discharged from the ceramics industry in the Saga and Nagasaki Prefectures of Kyushu, Japan. The effective use of volcanic ash and industrial wastes (scrap ceramics and gypsum) represents an important problem that must be solved in the Kyushu region of Japan. The objective of this study is to develop environmentally oriented base materials for seaweed beds with a low environmental load using volcanic ash and several recycled materials from industrial waste. The developed base materials were placed into Kagoshima Bay in May 2013, and monitoring began. A discussion of the results of long-term monitoring over 4 years and 2 months is presented. [ABSTRACT FROM AUTHOR]

Coiled tube field-flow fractionation (CTFFF) is currently applied to environmental and material studies. In the present work, a novel zone elution mode in CTFFF has been proposed and developed. Zone elution mode is based on the separation of particles by stepwise decreasing the flow rate of the carrier fluid and their subsequent elution at a constant flow rate. The fractionation parameters were optimized using a mixture of standard silica submicron particles (150, 390, and 900 nm). Taking samples of volcanic ash as examples, it has been demonstrated that zone elution mode can be successfully used for the fractionation of environmental nano- and submicron particles. For the first time, CTFFF was coupled online with a dynamic light scattering detector for the size characterization of eluted particles. Zone elution in CTFFF can serve for the further development of hyphenated techniques enabling efficient fractionation and size/elemental characterization of environmental particles in nano- and submicrometric size ranges. [ABSTRACT FROM AUTHOR]

Obtained data on the composition and properties of ash nanoparticles from Klyuchevskoy, Tolbachik, Kizimen, and Shiveluch volcanoes (Kamchatka, Russia) are generalized. It has been shown that the concentration of toxic and potentially toxic metals and metalloids (Ni, Cu, As, Se, Ag, Cd, Sn, Te, Hg, Tl, Pb, Bi) in volcanic ash nanoparticles can be 10–535 times higher than their concentration in bulk polydisperse samples. The most volatile elements such as As, Sn, Te, Hg, Tl, and Bi have the highest concentration factors in the range of 100–535. Based on the data on single particle inductively coupled plasma mass spectrometry, it is assumed that the listed metals and metalloids are accumulated in the fraction of volcanic ash nanoparticles mainly through the condensation of these elements or their compounds from the gaseous phase and the formation of individual (single) nanophases with an average size in the range of 12–74 nm. It should be noted that approximately an order of magnitude less nanoparticles have been isolated from the acidic volcanic ashes of the Kizimen and Shiveluch volcanoes as compared to those of basic ashes of the Tolbachik and Klyuchevskoy volcanoes. This fact is inconsistent with published data showing that the fraction of fine ash is usually larger for acidic explosive eruptions compared to basaltic eruptions. The Pearson correlation coefficients between the basicity index of volcanic ash and the concentration of more than 50 elements in the ash and ash nanoparticles have been calculated. Some elements have a correlation coefficient |R| > 0.7, which, according to the Chaddock scale, indicates the high degree of correlation. It is noted that a number of elements have an opposite correlation between the basicity index of ash and the concentration of elements in ash and ash nanoparticles. For example, Hg and Tl content in ash have a negative correlation with basicity index, that is, their concentration decreases with increasing basicity index of the ash, whereas their concentrations in nanoparticles positively correlate with ash basicity index. The concentration of Ca, Ho, and Er in the ash increases with an increase in the ash basicity index, whereas ash nanoparticles show an opposite correlation. The revealed regularities are unexpected and confirm the unique features of nanostructures and raise new questions of nanogeochemistry. [ABSTRACT FROM AUTHOR]

Identifying the microstructural characteristics of volcanic ash particles is key in developing our understanding of their production, transport and impact. Volcanic glass in ash clouds can damage aircraft engines, surfaces and coatings, and if inhaled cause harm to humans and animals on which they depend. We present results of 3D imaging of volcanic glass particles from two Icelandic volcanoes together with two samples of experimentally vesiculated volcanic glass. True colour 3D images were obtained using an Olympus LEXT 3D laser scanning confocal microscope. The images enabled examination of bubble structure, fracture patterns, and shape morphology characteristics of grains. For the two simulated fragments, the bubbles had a median long axis lengths of 13.2 and 37.0 μm. For the material from Grimsvötn and Eyjafjallajökul volcanic eruptions, the median long axis length was 25.2 μm and 23.1 μm, respectively. Laser confocal microscopy-based 3D imaging of volcanic glass fragments provides a rapid, non-destructive way to assess 3D particle geometry and quantify internal artefacts responsible for their formation. [ABSTRACT FROM AUTHOR]

The present work studies gel evolution and microstructure of geopolymers synthesized with volcanic ash (VA) and blast furnace slag (BFS). The synthesis parameters such as BFS proportions on geopolymer formation were investigated. Gel evolution and microstructure of the geopolymers were studied by FTIR, X-ray diffraction (XRD), 29Si NMR spectroscopy and scanning electron microscopy measurements. Silicate gels (N–S–H) were mainly formed in VA-based geopolymers of low compressive strength (14.07 MPa). While with VA and BFS each account for 50%, VA-BFS–based geopolymers possessed a compressive strength of 55.6 MPa, as well as the homogeneous C–(A)–S–H and N–A–S–H gels were formed. The C–(A)–S–H and N–A–S–H gels show synergistic effects on the mechanical property of the geopolymers. This work provides a clue for the synthesis of geopolymers with superior mechanical properties in areas of architecture. Detailed characterization gel evolution and microstructure of geopolymers synthesized with volcanic ash (VA) and blast furnace slag (BFS) were studied. Silicate gels (N–S–H) were mainly formed in VA-based geopolymers of low compressive strength (14.07 MPa). When VA and BFS each account for 50%, VA-BFS–based geopolymers possessed a compressive strength of 55.6 MPa, as well as the homogeneous C–(A)–S–H and N–A–S–H gels formed. Synthesis protocol for VA-BFS–based geopolymers. [ABSTRACT FROM AUTHOR]

We investigated temporal changes in the rock-magnetic properties of volcanic ash ejected from the Aso Nakadake volcano during a sequence of ash eruptions from 2019 to 2020. For 39 volcanic ash samples, magnetic hysteresis parameters, including saturation magnetization (Ms), saturation remanent magnetization (Mrs), coercivity (Bc), and coercivity of remanence (Bcr), were obtained. Curie temperature (Tc) of the samples was also estimated using thermomagnetic analyses. Titanium-rich and -poor titanomagnetites were the dominant magnetic minerals in the volcanic ash, of which the titanium-rich phase was dominant. Systematic magnetic measurements of the volcanic ash ejected during the 1-year eruption event indicate that temporal changes in the hysteresis parameters occurred throughout the event. These temporal changes suggest that the Mrs/Ms and Bc values of the volcanic ash increased considerably during several periods. The clear increases in Mrs/Ms and Bc, associated with the central peak in FORC diagrams, indicate that non-interacting single-domain grains increased. For these high Mrs/Ms and Bc samples, thermal demagnetizations of 3-axis IRM show that the low unblocking-temperature component up to 250–300 °C has apparently higher coercivity, suggesting that the above-mentioned, non-interacting single-domain grains are Ti-rich titanomagnetite. Interestingly, the high Mrs/Ms and Bc values were synchronous with observations of volcanic glow. These results suggest that changes in the magnetic properties of titanomagnetite grains in volcanic ash reflect changes in physical conditions from the vent to the conduit of the volcano. [ABSTRACT FROM AUTHOR]

In this study, four geopolymer sorbents GP0, GP10, GP30 and GP50 were synthesized using volcanic ash (VA) and metakaolin (MK) blends as precursors with 0, 10, 30 and 50% MK content by mass, respectively. The materials were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Raman spectroscopy, and Brunauer–Emmett–Teller (BET) surface area analyses, revealing successful geopolymerization of the precursors and increasing surface area with increasing MK content. The sorption performance of the VA, MK and VA-MK geopolymers was then evaluated for the removal of cationic methylene blue (MB) dye from aqueous media. Sorption capacity was independent of composition, providing flexibility in sorbent synthesis. Sorption rate, on the other hand, was 3–8 times greater for the VA-MK geopolymers than the precursor materials. The equilibrium adsorption data were suitably explained by the Freundlich model, denoting multilayer adsorption onto a heterogeneous adsorption surface with higher Freundlich affinity constant (KF) for geopolymers than VA. The adsorption kinetics obeyed the pseudo-second-order (PSO) kinetic law with an average of 98% removal efficiency in 30 min. MB uptake was pH-dependent and driven by electrostatic chemisorption interactions. These results motivate further studies on the use of locally sourced geopolymers for water purification applications. [ABSTRACT FROM AUTHOR]

The Youngest Toba Tuff eruption, contemplated to be a largest volcanic activity with volcanic explosive index (VEI) 8 on the Earth during the Quaternary period, had disseminated ash throughout Southeast Asian countries including Malaysia. In Malaysia, the ash is principally preserved in the alluvial deposits of several river basins including Padang Terap and Lenggong valley. The glass shards from the same ash have been examined for morphological characteristics in order to better comprehend fragmentation mechanism occurred at the time of eruption as well as to deduce paleoenvironmental conditions in the basin areas. The morphological description, carried out using FE-SEM technique, implies the presence of three distinct sorts of glass masses with various morphotypes in the ash, i.e., (i) platy, (ii) bubble walled, and (iii) pumice. Surfaces of platy shards with angular and upturned plate shape exhibit adhering material and foliations, whereas the bubble walled is distinguished into four different types as (i) two bubble shards constituting a single elongated boundary between two vesicles; (ii) Y-shaped attributing three angular bubbles joined with a tri-radiate boundary. It also reveals depression of bubbles with disturbed foliations, chemical pits, and associated material. (iii) Blocky exhibits equant shape, conchoidal structures, chemical pits, and subspherical to elongated depressions and coalescence of vesicles, and (iv) the shards with elongated vesicles are usually elongated in shape and possess coalesced, short to long vesicles having space between them. Conchoidal structures, depressions of vesicles, and adhering material on the surface are additional features. The pumice shards with a tightly stretched shape demonstrate elongated vesicles and conchoidal structures. Considering varied morphologies and structures of glass shards, it reflects that prior to the eruption, the melt would have different in gas bubble growth, vesiculation rate, composition of exsolution gases, temperature, and pressure and fragmented presumably by both hydromagmatic and magmatic processes. These processes are distinguishable at a time using varied morphologies and structures of the glass shards. The shards with blocky and equant morphologies would have formed during hydromagmatic fragmentation, whereas the two, Y-shaped and shards with elongated vesicles during rupturing of magmatic exsolution melts. The fragmentation of melts during hydromagmatic processes leads in chemical pits, conchoidal structures, depressions, and coalesced of vesicles of the glass shards. Given the angular shapes and preservations of various sorts of the sedimentary structures within the ash (parallel laminations, minute cross beddings and soft sediment deformations), it may be assumed that the tephra would have deposited in a tranquil aquatic environment of the meandering river systems and transported a short distance in the basin areas after falling intermittently from the atmosphere. [ABSTRACT FROM AUTHOR]

The electrification of volcanic plumes has been described intermittently since at least the time of Pliny the Younger and the 79 AD eruption of Vesuvius. Although sometimes disregarded in the past as secondary effects, recent work suggests that the electrical properties of volcanic plumes reveal intrinsic and otherwise inaccessible parameters of explosive eruptions. An increasing number of volcanic lightning studies across the last decade have shown that electrification is ubiquitous in volcanic plumes. Technological advances in engineering and numerical modelling, paired with close observation of recent eruptions and dedicated laboratory studies (shock-tube and current impulse experiments), show that charge generation and electrical activity are related to the physical, chemical, and dynamic processes underpinning the eruption itself. Refining our understanding of volcanic plume electrification will continue advancing the fundamental understanding of eruptive processes to improve volcano monitoring. Realizing this goal, however, requires an interdisciplinary approach at the intersection of volcanology, atmospheric science, atmospheric electricity, and engineering. Our paper summarizes the rapid and steady progress achieved in recent volcanic lightning research and provides a vision for future developments in this growing field. [ABSTRACT FROM AUTHOR]

The results of a multidisciplinary study of two Holocene tephras from lacustrine sediments of the Northern Okhotsk area are presented. A comprehensive characterization of the tephra, including magnetic properties, petrochemical and grain-size composition, magnetic–mineralogical data, and radiocarbon dating, is presented for the first time. The distinctive features of two tephra layers and their possible use as regional chronological markers of the Middle and Late Holocene are shown. [ABSTRACT FROM AUTHOR]

The present study deals with the possibilities of applying the zircon saturation thermometry, which is based on the equilibrium between the zircon crystals and the melt, to strongly altered volcanic ashes—bentonites. It proposes an alternative to a widely used method of calculating magma temperature from Zr content and major component composition (Boehnke in Chem Geol 351:324–333, 2013), that is not suitable for bentonites, as most of the major components have been largely altered in these rocks. For calculating source magma temperatures in strongly altered volcanic ashes, the exponential function from the Zr (ppm)/Al2O3 (%) ratio with compositional corrections from the TiO2/Al2O3 ratio was found applicable. The idea to use the ratios of these elements is based on the low mobility of these elements in the earth's surface conditions. Temperatures of magma, forming in the partial melting process, are assessed from the bulk rock composition. Pre-eruption temperatures were estimated from the composition of fine fractions of bentonites. The accuracy of the new method was established from comparison with the method by Boehnke et al. (Chem Geol 351:324–333, 2013). The difference between the two methods was mostly less than ± 30° to ± 50°. The comparison with the magma temperature, estimated from the sanidine composition, revealed 13° lower values on average. Although the proposed method for estimating the source magma temperatures is less precise than the method of accounting for detailed rock compositions, it can be used in strongly altered rocks, where other methods are not usable. The new method still enables differentiation between felsic source magmas originating at low or high temperatures. Early Palaeozoic bentonites in the Baltic Basin can be divided, according to the source magma temperatures, into two types: (1) Low temperature (650–790 °C), containing potassium-rich sanidine and abundant biotite (S type), (2) high temperature (770–850 °C) with sodium-rich sanidine and scarce biotite (I type). [ABSTRACT FROM AUTHOR]

This study assesses the effects of curing temperatures (28 and 60 °C) and P2O5 / H2O molar ratio percentages (4 to 12 %) on initial setting time, microstructure and mechanical strength of volcanic ash-based phosphate inorganic polymers. The inorganic polymers along with the raw materials were characterized by X Ray Fluorescence (XRF), X Ray Diffraction (XRD), Fourier Transform Infra Red (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). In addition, initial setting time of pastes was determined along with compressive strength and water absorption on specimens aged 28 days. The results showed that initial setting time decreases with the increase of P2O5 / H2O molar ratio percentage in the range of 126 − 20 Min (28 °C) and 20 − 10 Min (60 °C). Conversely, either at 28 or 60 °C curing, compressive strength increases with the increase of P2O5 / H2O molar ratio percentage. FTIR spectra show the presence of Ca-O and Fe-O and Al-O-P-O bonds. Dependent on curing temperature, new crystalline phases including hydroxyl apatite, brushite, sigloite, aluminium phosphate hydrate, potassium magnesium phosphate hydrate and silicon hydrogen phosphate were formed. Hence, initial setting time, microstructure and mechanical strength of volcanic ash-based phosphate inorganic polymers are P2O5 / H2O molar ratio percentage, curing temperature and chemical composition dependent. [ABSTRACT FROM AUTHOR]

This paper investigates the resistance of alkali-activated binder from volcanic ash (VA) + Municipal Solid Waste Incinerator Fly Ash (MSWI-FA) system exposed into sulphuric acid solution and artificial seawater at 56 days. The effect of these aggressive media on the physical, structural, mechanical and microstructural properties of alkali-activated mortars was discussed. The degradation was studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The decrease of compressive strength after 56 days was 9.10%, 22.08%, 32.5% in artificial seawater, 2% H2SO4 and 4% H2SO4, respectively. The loss of strength in both media is primarily due to the fact that the water molecules present in these media penetrated into the pore cavities between binders and aggregates, making them weak. In an acidic medium, it is also due to the decalcification and depolymerization reactions whereas in seawater medium, it is attributed to the movement of content ions and probable formation of Friedel's salt. The results disclose that VA + MSWI-FA based alkali activated materials resist better in seawater than in sulphuric acid solution. Synergistic use of volcanic ash and MSWI-FA for construction materials through alkaline activation looks like the upcoming trend to valorize these wastes. [ABSTRACT FROM AUTHOR]

This study aimed to determine the best composition of ceramic pastes from clays and volcanic ashes mixture. Two samples of clay from Koutaba and one of volcanic ashes from Foumbot (western Cameroon) were collected and physically characterised (granulometry and plasticity). Four formulations were prepared with 60wt% of ball clay; 10, 20, 30 and 40wt% of kaolin; and 30, 20, 10 and 0wt% of volcanic ashes (VAs). Brick samples of 80 × 40 × 15 mm were made and heated at 1050, 1100 and 1150 °C. Physico-mechanical and technological tests were done on fired products. Results showed that ball clays were plastic (Ip = 48.52%) compared to kaolin (Ip = 6.05%). Fired products displayed brown colour, accentuated with temperature and the increase in volcanic ash. Metallic sound was obtained beyond 10wt% VA. With increase in VA, linear shrinkage increased between 1050 and 1100 °C, then decreased between 1100 and 1150 °C. Low shrinkage (< 5%) showed that no correction is needed. With increasing temperature, water absorption decreased while compressive strength increased. Bending strength gave good values (> 36 MPa) beyond 10wt% VA at 1150 °C. Hence, ceramics with 20 and 30wt% VA with heating temperature of 1100 and 1150 °C are suggestible. [ABSTRACT FROM AUTHOR]

Formation of soluble sulfate and halide salts on volcanic ash particles via syn-eruptive interactions between ash surfaces and magmatic gases is a ubiquitous phenomenon in explosive eruptions. Surficial salts may be rapidly mobilized into their depositional environment undermining the quality of drinking water, harming aquatic life, and damaging soil and vegetation. Assessment of the potential for salt formation on ash and related environmental impacts have been based almost exclusively on bulk mineralogical or chemical analyses of ash; similarly, quantification of surficial salts has been made via leachate analysis only. However, it is the ash surface state and salt crystal properties that exert the predominant control on its reactivity, thus in determining their immediate environmental impact. Here, using scanning electron microscope (SEM) images, we present a novel image analysis protocol for the quantitative characterization of surficial salts, together with chemical analyses of resulting leachates. As volcanic ash proxies, we used synthetic rhyolitic glass particles (with systematic variations in FeOT and CaO content) and a crushed obsidian. Using an ash-gas reactor, we artificially surface-loaded samples with CaSO4 and NaCl crystals, the most common crystal phases found on volcanic ash surfaces. Analogous variations were found using both methods: for CaSO4 crystals, higher temperature treatments or increasing FeOT content at the same temperature led to higher concentrations of salt leachate and higher salt volumes; unexpectedly, increasing the CaO content caused only a minor increase in salt formation. In addition to bulk salt formation, morphometric results provided insight into formation processes, nucleation and growth rates, and limiting factors for salt formation. Higher temperatures increased CaSO4 crystal size and surface coverage which we infer to result from higher element mobility in the glasses driving crystal growth. Increasing FeOT content of the glasses yielded increased salt surface coverage and leachate concentrations, but decreased crystal size (i.e., the salt number density increased). This latter effect likely relates to the role of iron as an electron-donor to charge balance salt-forming cation migration to the ash surface, indicating the importance of iron in determining surface reaction site density and, consequently, environmental reactivity. The controlling roles of ash composition and temperature on salt formation observed here can improve estimations for surface salt formation, volatile scavenging, and environmental impact for eruptions producing glass-rich ash. Our characterization protocol can therefore become a useful tool for the investigation of solid–gas reactions for terrestrial and planetary processes, and it also appears to be a powerful complement to research into atmospheric processes mediated by ash surfaces, such as ash aggregation and nucleation of water or ice on ash. [ABSTRACT FROM AUTHOR]

Juvenile pyroclasts, especially in the ash size range, provide important information on primary fragmentation processes, i.e., initial explosive magma fragmentation, and on the state of the magma both prior to and at the point of fragmentation and quenching. There exists an extensive body of literature focusing on the quantification of juvenile particle morphology (shape), internal textures, and surface features spanning several decades; however, a standardized method has yet to emerge for comparative studies. No community-wide consensus currently exists (i) regarding the most representative size fraction(s) to be examined, (ii) on sample preparation procedures (such as whether to use whole-particle silhouettes or 2D cross-sections), (iii) on imaging techniques and image acquisition parameters, or (iv) on the optimal morphometric parameters to measure. Lack of a standardized method precludes robust comparison between different studies and laboratories. We propose here a preliminary "best practices" and workflow for characterization of juvenile pyroclasts, for comparative studies of primary fragmentation. If the community follows such a standardized method, it will become possible to accumulate a large volume of consistent data on juvenile pyroclasts from a range of eruption styles, fragmentation mechanisms, and magma compositions. This will ultimately allow deeper insights into the full panoply of magma-to-pyroclast processes that drive particle-producing volcanic eruptions. One or more "fragmentation diagrams" may eventually be developed to allow different types of magmatic and phreatomagmatic explosive eruptions to be distinguished based on their products. [ABSTRACT FROM AUTHOR]

Popocatépetl volcano produced 625 ash emissions to heights greater than1 km between 1994 and 2008. During this time, ash fall affected mostly populations within a 60 km radius around the volcano, a zone which includes 4.5 million people. We assess the effects of prolonged ash fall on human health in these areas between 1994 and 2008. To do this, we considered 94,000 non-infectious respiratory disease (NIRD) records from five health databases. This included the 98 municipalities where ash fall was frequent, plus two municipalities outside of the ash fall area which served as a control group. NIRD rates (cases/1 k inhabitants) from 1992, 2 years before the beginning of the eruptive period, tol 2008 were compared with mapped ash distributions during the same period. Wind dispersed 29% of these ash emissions to the northeast, 20% to the east, 17% to the southwest, 13% to the northwest, 9% to the southeast, and12% in other directions, producing more ash fall in the northeast and east sectors and higher NIRD rates. Results, tested with an analysis of variance (ANOVA) and covariance statistical analyses, show that changes in NIRD rates correlate with ash dispersion direction and the amount of fine ash deposited. During eruptive crises in 1994–2003 and 2005, NIRD rates increased from < 1 to > 2.6, reaching levels up to > 3 in municipalities where ash was sampled. In 2004 and 2006–2008 when ash plume frequency and ash concentration decreased (e.g., only two minor ash emissions in 2004), the NIRD rates remained unchanged. This was a result of the chronic effect on health of the preceding ash fall. We found that health impacts are principally related to the amount of ash, as well as the percentage of fine particles which in turn is also a function of the prolonged nature of the eruption. The fine ash from Popocatépetl is composed of up to 19.2% of particles smaller than 10 μm and up to 5.7% smaller than 2.5 μm and contains plagioclase crystals, lithic particles, glass, pyroxene crystals, cristobalite, and minor amounts of titanomagnetite and sublimates. [ABSTRACT FROM AUTHOR]

This work aimed to evaluate the role of the addition of blast furnace slag for the formation of reaction products and the strength development of volcanic ash-based phosphate geopolymer. Volcanic ash was replaced by 4 and 6 wt% of ground granulated blast furnace slag to accelerate the reaction kinetics. Then, the influence of boric acid for controlling the setting and kinetics reactions was also evaluated. The results demonstrated that the competition between the dissolution of boric acid and volcanic ash-slag particles is the main process controlling the setting and kinetics reaction. The addition of slag has significantly accelerated the initial and final setting times, whereas the addition of boric acid was beneficial for delaying the setting times. Consequently, it also enhanced the flowability of the paste. The compressive strength increased significantly with the addition of slag, and the optimum replaced rate was 4 wt% which resulted in 28 d strength of 27 MPa. Beyond that percentage, the strength was reduced because of the flash setting of the binder which does not allow a subsequent dissolution of the particles and their precipitation. The binders formed with the addition of slag and/or boric acid are beneficial for the improvement of the water stability of the volcanic ash-based phosphate geopolymer. [ABSTRACT FROM AUTHOR]

We have found out the general patterns in the elemental composition of ash ejected by the Kuril volcanoes Alaid and Ebeko. The ashes show persistent exceedances in the concentrations of K, Bi, U, Cs, Th, Na, and Yb relative to the mean concentrations for the respective types of volcanic rock. The deficient elements (Kk < 1) include Mg, Ag, Sn, Nb, Ta, Ni, and Cr. Inspection of the range of ashes ejected by different volcanoes of Kamchatka (Klyuchevskoi, Tolbachik, Ksudach, Bezymyannyi, Koryaksky, Shiveluch, and Kizimen) showed that the ejecta of Shiveluch and Kizimen are the most similar in elemental composition to the ashes discharged by the volcanoes of the Kuril Islands studied here. The ashes of Alaid and Ebeko volcanoes differ from most Kamchatka ashes in having higher concentrations of radioactive elements (U, Th). We have found a comparatively high potential of biological productivity for the Kuril ashes. The potential fertility index considered here (PFI) when compared with the most productive ash on the Kamchatka Peninsula whose PFI was taken to be unity is 0.72 and 0.66 for Alaid and Ebeko, respectively. The PFI shows a persistent dependence on the concentration of silicon in the ashes: the higher the basicity of an ash, the greater is its potential fertility. It is for the first time that we have discovered fractionation of rare earth elements occurring in all volcanic ashes under study here (both those for the Kuril Islands and for Kamchatka) in the form of a positive europium anomaly with E/Er* varying between 1.2 and 1.8. The estimation of the elemental composition for the surface waters of a brook that flowed on Ebeko Volcano did not reveal any tendency of active transfer of radioactive elements from ashes to naturally occurring solutions. A comparative analysis of the waters of this brook and the streams around the Kamchatka volcanoes studied here showed that the relationship between their compositions is largely controlled by the time factor. Streams near different volcanoes show similarities at the time of an eruption, and their water very actively receives rare earth elements (REE), their concentrations in brooks exceed the mean REE concentrations for fresh waters in continents by two orders of magnitude. When the volcanic event comes to an end, the relationship between the geochemical compositions of water in areas of ashfalls due to different volcanoes becomes weaker. The waters of small streams near volcanoes during eruptions can be regarded as natural liquid REE-bearing fertilizers. [ABSTRACT FROM AUTHOR]

To demonstrate a synergy between radionuclide (RN) and infrasound observations and Atmospheric Transport Modelling (ATM), the volcanic activity of Bogoslof in Alaska, USA, is used as an example. The study period covers 3 months of intense eruptive activity, from 19 December 2016 to 8 March 2017. During that period, the International Monitoring System (IMS) infrasound station located in Alaska, USA, recorded signals from three eruptive sequences. The second sequence was reported in the International Data Centre (IDC) Reviewed Event Bulletin (REB) with 3 infrasound stations: in Alaska, USA, in Kamchatka, Russian Federation and in Hawaii, USA. As reported by The Alaska Volcano Observatory (AVO), during each of these events ash plumes reaching the altitude of more than 10 km were observed for several consecutive days. These observations were used to identify the length of each eruptive episode. To demonstrate the influence of volcanic ash on the berillium-7 (Be-7) activity concentration values measured by two IMS RN stations in Alaska, the ATM was used. To monitor the arrival time of a volcanic ash plume at the IMS stations, a series of 14 days forward simulations released daily from Bogoslof during each of these events, was generated. Comparison of Be-7 daily surface values with the seasonal median for the period of 9 years (2009–2017), revealed that an influx of volcanic ash up to the tropopause (1.5–12 km) tends to locally increase surface Be-7 concentrations in area under the influence of subsiding ash plume. It is also demonstrated that with the arrival of volcanic ash at the surface level, the enrichment in radioactive particulates like uranium, thorium, and potassium was observed. [ABSTRACT FROM AUTHOR]

Exposure to volcanic ash is a long-standing health concern for people living near active volcanoes and in distal urban areas. During transport and deposition, ash is subjected to various physicochemical processes that may change its surface composition and, consequently, bioreactivity. One such process is the interaction with anthropogenic pollutants; however, the potential for adsorbed, deleterious organic compounds to directly impact human health is unknown. We use an in vitro bioanalytical approach to screen for the presence of organic compounds of toxicological concern on ash surfaces and assess their biological potency. These compounds include polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dlPCBs). Analysis of ash collected in or near urbanised areas at five active volcanoes across the world (Etna, Italy; Fuego, Guatemala; Kelud, Indonesia; Sakurajima, Japan; Tungurahua, Ecuador) using the bioassay inferred the presence of such compounds on all samples. A relatively low response to PCDD/Fs and the absence of a dlPCBs response in the bioassay suggest that the measured activity is dominated by PAHs and PAH-like compounds. This study is the first to demonstrate a biological potency of organic pollutants associated with volcanic ash particles. According to our estimations, they are present in quantities below recommended exposure limits and likely pose a low direct concern for human health. [ABSTRACT FROM AUTHOR]

The occurrence of groundmass crystals reveals the shallow conduit process of magmas, which affects the behavior of eruptions. Here, we analyzed groundmass microtextures of ash samples from the 2018 eruption of Shinmoedake volcano, Japan, to evaluate the change of magma ascent conditions during the eruption sequence. The eruptive activity changed from ash venting (Phase 1: March 1–6) to lava effusion with continuous ash-laden plumes (Phase 2: March 6–9) and then shifted to Vulcanian explosions (Phase 3: March 10–April 5). Non-juvenile particles were abundant in Phase 1, whereas juvenile particles were dominant in Phases 2 and 3. Vesicular juvenile particles were more abundant in Phase 2 than Phase 3. The lower microlite crystallinity and groundmass SiO2 concentrations of the vesicular particles indicate that they were sourced from magma that ascended rapidly. Abundant nanolites were observed in the black interstitial glass of juvenile particles under an optical microscope, whereas few nanolites were observed in the transparent ones. The presence of nanolites can be explained by the dehydration of silicate melt, as well as cooling and oxidation between fragmentation and quenching. Temporal changes in the ash componentry show that the eruption activity started from the erosion of the pre-existing vent plug (Phase 1), shifted to the simultaneous eruption of bubble-bearing and outgassed magmas (Phase 2), and concluded with explosions of the stagnant lava (Phase 3), thereby demonstrating the sequence of vent opening and extrusion and stagnation of magma. Therefore, ash microtextures are valuable for monitoring the shallow conduit process of eruptive magma. [ABSTRACT FROM AUTHOR]

A method for retrieving volcanic ash parameters from satellite data is presented. The fundamental difference between the presented methodology and classical algorithms for the retrieval of volcanic ash parameters is the simultaneous use of various optical models of volcanic clouds. The models contain information not only about volcanic rocks (andesite or basalt) but also about their combinations with water drops and the aqueous solution of sulfuric acid. The volcanic ash parameters are determined by the characteristics of solar radiation reflected from a volcanic cloud and the cloud's self-radiation in the infrared atmospheric window. The volcanic ash parameters are retrieved according to the Meteosat-9 SEVIRI satellite radiometer for the case of the Eyjafjallajokull volcano eruption (Iceland, May 2010). The results are compared with data of aircraft lidar measurements and show a good qualitative and quantitative agreement. [ABSTRACT FROM AUTHOR]

State-of-the-art approaches to the study of environmental natural and man-made nano- and microparticles are summarized. Separation methods (sedimentation, membrane filtration, field-flow fractionation), methods for assessing particle size and morphology (electron microscopy, dynamic and static light scattering), and also methods for their elemental analysis (inductively coupled plasma atomic emission and mass spectrometry, atomic absorption spectrometry, energy-dispersive X-ray spectroscopy) are considered. Some particular examples of studies of natural particles of dust, volcanic ash, and natural waters, and also of synthetic nanoparticles of environment samples are presented. A necessity of using a complex of complementary methods of the separation, characterization, and analysis in the study of environmental particles is shown. Special attention is paid to hybrid methods ensuring the online separation, size evaluation, and analysis of particles. The main problems of the characterization and analysis of natural nanoparticles are formulated, and possible methods of their solution are proposed. [ABSTRACT FROM AUTHOR]

The Kangdian Upland, mainly covered by the Emeishan basalt and a small amount of intermediate-felsic rocks (e.g., trachyte and rhyolite), is the primary sediment source area of the coal-bearing basin in southwestern China. Different from the formation of authigenic quartz in other Late Permian coals reported by previous studies, the authigenic quartz identified in the No. 7 coal of Shugentian mine was derived not only from the siliceous solution weathered from the Emeishan basalt in the Kangdian Upland, but also from the silicon-rich hydrothermal fluids that migrated along the fault zones due to multi-phase tectonic movement. Chamosite in this study was mainly considered as the interaction product between kaolinite and Fe-Mg-rich hydrothermal fluids, according to the modes of occurrence of chamosite and its close relationship with kaolinite and quartz. Anatase occurred as either coarse-crystalline or reticular forms filled with authigenic quartz, implying the intrusion of multi-stage hydrothermal fluids. The parting sample, characterized by sharp-edged quartz and angular zircon crystals with eroded holes and cracks, was identified as a layer of pyroclastic tonstein, the high Al2O3/TiO2 ratio of which supported that the parent volcanic ash was felsic in composition. The influence of seawater made not only a contribution to the higher content of total sulfur and pyrite, but also a comfortably alkaline environment for the formation of cell-filling calcite and ankerite. The differences of content and modes of occurrence of calcite and ankerite between the 7L and 7U coal seam in the Shugentian mine indicated that the coal-forming microenvironment has evolved from alkaline to acidic dominant. [ABSTRACT FROM AUTHOR]

Nanoparticles are a potential source and carrier of nutrients and pollutants in aquatic ecosystems, yet the stability of nanoparticles in environmental conditions is poorly known. Here, we studied volcanic ash nanoparticles by simultaneous application of capillary zone electrophoresis and laser diffraction for determination of size, zeta-potential and long-term aggregation stability. Results show that volcanic ash nanoparticles remained stable for at least 28 days. Stability increases from pH 5.5 to 8.5. Zeta-potentials are − 56 mV at pH 7.2 and − 64 mV at pH 8.5. Findings imply that volcanic ash nanoparticles have a high potential for long-range transport of nutrient and toxic elements in surface waters. Moreover, the developed method allows direct conversion of electropherograms into particle size distributions. [ABSTRACT FROM AUTHOR]

In this work, municipal solid waste incinerator fly ash (MSWI-FA) was used as precursor to alter the reactivity of low reactive volcanic ash (VA) for alkali-activated cement synthesised. The effects of various proportions of MSWI-FA (0, 5, 10, 15 and 20%) on the final properties of the inorganic polymer are reported. The increase in MSWI-FA content increases the heat of reaction in MSWI-FA as the result of the reaction between the amorphous alumina-silica and the Ca-rich precursor. Isothermal conduction calorimetry, FTIR, XRD SEM/EDS, and physico-mechanical analyses were used to follow up the different formulations. New crystalline phases, namely Margarite (CaAl2 (Al2Si2)O10(OH)2, PDF#04-013-3004), Mordernite-(Ca) ((Ca, Na2, K2)(Al2 Si10 O24)·7H2O, PDF#00-011-0155) and Thernadite (Na2SO4, PDF#01-074-2036) confirm the good reactivity. The SEM/EDS exhibited the coexistence of C–S(-N-A)–H and N-A-S-H gels in binary system alkali-activated. The compressive strength and bulk density ranged from 9.38 to 21.07 MPa and from 1.56 to 1.77 g/cm3, respectively. These results indicated the possibility to use VA and MSWI-FA to synthesize room temperature alkali-activated matrices applicable in the manufacture of structural and functional materials. MSWI-FA appears energy-efficient and sustainable solution for the improvement of the volcanic ash based alkaline activated materials. [ABSTRACT FROM AUTHOR]

In this work, a silica-based mesoporous oxide (SMO) was directly fabricated via a template-free method using the abundant and inexpensive volcanic ash as raw material. By alkali hydrothermal activation and acid hydrothermal etching of volcanic ash, the SMO with large mesopore size (7.94 nm), high specific surface area (459.5 m2/g), and total pore volume of 1.05 cm3/g was produced. The main ingredient of SMO is amorphous microporous silica. The structural evolutions of the mesoporous materials were revealed by X-ray powder diffraction, scanning electron microscope, Fourier transform infrared spectrometry, N2 adsorption/desorption, and transmission electron microscopy techniques. The as-prepared SMO possessed excellent adsorption of water vapor as high as 616.0 g/m2 at the relative humidity ranging from 33 to 75%. This SMO provides a platform for preparing high performance template-freely humidity self-regulating material. Highlights: The silica-based mesoporous oxide (SMO) was successfully fabricated via a template-free method. The SMO have large mesopore size (7.94 nm), high specific surface area (459.5 m2/g) and total pore volume of 1.05 cm3/g. The as-prepared SMO possessed excellent adsorption of water vapor as high as 616.0 g/m2. [ABSTRACT FROM AUTHOR]

The damage induced by volcanic ash attack in thermal barrier coating (TBC) has been widely reported. This study focuses on actual volcanic ashes that were collected from an active volcano. The fusion properties and penetration characteristics into the TBC are discussed. Volcanic ash collected at Mt. Aso and Mt. Sakurajima was exposed by an electric furnace. It was revealed that the melting temperature of ash varies because of a difference in the chemical composition between different active volcanoes. The TBC sample with pellet-shaped volcanic ash was exposed at a temperature of 1413 K. From the SEM and EDS analysis results, it was clear that the molten volcanic ash is penetrated into the ceramic layer in TBC and a dense microstructure is formed by the penetration. It was also found that volcanic ash deposition leads to vertical and horizontal cracks in the ceramic layer. The finite element analysis results revealed that vertical cracks were initiated by thermal stress during the heating process. Horizontal cracks were initiated and propagated along the interface by a higher concentration of stress around the interface between the penetration area and the original area in the ceramic coating layer. [ABSTRACT FROM AUTHOR]

Satellite data (GOES, VIIRS, MODIS, AVHRR) were used in near real-time during the 2016–2017 eruption of Bogoslof volcano, Alaska, to detect explosive eruptive activity and to characterize the resulting volcanic clouds. This study examines satellite data to estimate volcanic cloud heights and mass eruption rates for 47 of the 70 explosive events. Eighteen of the volcanic clouds reached an altitude in excess of 8.5 km asl, where they posed a potential hazard to aviation. We estimate eruption rates were in the range of 104–107 kg/s. Eruption durations were available for 28 events, and the total mass of these events was 5.7 × 1010 kg. Most of the explosions occurred from submarine vents, producing volcanic clouds with water-rich characteristics in satellite data. We infer that these water-rich (phreatomagmatic) events contained ice-coated ash particles, which changed their visible and multispectral characteristics. Only two of the explosions produced clouds with satellite characteristics that would be considered ash-rich. We conclude that these events were relatively dry eruptions with limited access to ocean water. Although some of the explosive events transitioned from submarine to subaerial vents, we observed no change in the character of the volcanic clouds during these transitions. We speculate that enhanced removal of fine-grained volcanic ash likely occurred due to aggregation, with implications for modeling ash transport and fallout. We conclude that the majority of Bogoslof's water-rich volcanic clouds did contain volcanic ash despite the lack of conventional "ash signature" in satellite data. This has implications for satellite monitoring of future water-rich/shallow submarine eruptions. [ABSTRACT FROM AUTHOR]

The 2016–2017 shallow submarine eruption of Bogoslof volcano in Alaska injected plumes of ash and seawater to maximum heights of ~ 12 km. More than 4550 volcanic lightning strokes were detected by the World Wide Lightning Location Network (WWLLN) and Vaisala's Global Lightning Dataset (GLD360) over 9 months. Lightning assisted monitoring efforts by confirming ash-producing explosions in near-real time, but only 32 out of the 70 explosive events produced detectable lightning. What led to electrical activity within some of the volcanic plumes, but not others? And why did the lightning intensity wax and wane over the lifetime of individual explosions? We address these questions using multiparametric observations from ground-based lightning sensors, satellite imagery, photographs, acoustic signals, and 1D plume modeling. Detailed time-series of monitoring data show that the plumes did not produce detectable lightning until they rose higher than the atmospheric freezing level (approximated by − 20 °C temperatures). For example, on 28 May 2017 (event 40), the delayed onset of lightning coincides with modeled ice formation in upper levels of the plume. Model results suggest that microphysical conditions inside the plume rivaled those of severe thunderstorms, with liquid water contents > 5 g m−3 and vigorous updrafts > 40 m s−1 in the mixed-phase region where liquid water and ice coexist. Based on these findings, we infer that 'thunderstorm-style' collisional ice-charging catalyzed the volcanic lightning. However, charge mechanisms likely operated on a continuum, with silicate collisions dominating electrification in the near-vent region, and ice charging taking over in the upper-level plumes. A key implication of this study is that lightning during the Bogoslof eruption provided a reliable indicator of sustained, ash-rich plumes (and associated hazards) above the atmospheric freezing level. [ABSTRACT FROM AUTHOR]

We here examined the sedimentation process of falling ash particles during a short-lived Vulcanian eruption at Sakurajima volcano, Japan, using high-speed camera imaging of airborne ash particles, as well as grain size analyses of ash samples collected at high temporal resolution. Ashfalls from a sequence of two Vulcanian eruptions at 10:44 and 11:26 JST (Japan Standard Time) on 26 March 2016 were investigated. The field site for imaging and sampling was located approximately 3.5 km from the vent. The ash particles collected exhibit bimodal grain size distributions (GSDs). The median particle size of the main subpopulation decreased throughout the ashfall owing to size-dependent segregation of ash particles from a single source released from a constant height. The volume fraction of the subordinate subpopulation is interpreted to represent a component of ash aggregates and shows an increase in its volume fraction after the eruption onset. High-speed camera imaging reveals that the mean particle density decreased over time as the ashfall continued. These data suggest an increasing contribution of low-density aggregates during the course of the ashfall. The temporal changes in the density of airborne ash particles and in the GSD of ash samples demonstrate that the sedimentation process during a Vulcanian eruption at Sakurajima volcano is characterized by sedimentation of ash particles from transient eruption plumes at constant height, in which ash aggregation increases over time. Moreover, time series analysis of the ash falling rate shows that secondary thickening occurred during these Vulcanian eruptions and that this can be triggered by the settling of ash aggregates. [ABSTRACT FROM AUTHOR]

An advantage of using capillary zone electrophoresis and static light scattering is demonstrated on an example of suspensions containing nano- and submicroparticles of volcanic ash under the condition of simultaneous studies using the same aqueous suspensions. We found the dependences of the electrophoretic mobility and the zeta potential of nano- and submicroparticles on size by comparing electropherograms with diagrams of size distributions. These dependences can be used for the satisfactory estimation of weight-average particles size in the newly prepared suspensions. [ABSTRACT FROM AUTHOR]