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Salt–alkali stress can lead to a decrease in crop quality and yield, therefore, the ability to alleviate crop salt–alkali stress and elucidate its mechanism of action will be of great significance. This study investigated the effects of applying five different proportions (0%, 5%, 15%, 25%, and 35%) of volcanic ash on thin-skinned melons (Cucumis melo L.) under salt–alkali stress. Physiological test results indicated that the application of volcanic ash had a certain alleviating effect on salt–alkali stress on melons, and the effect of 35% volcanic ash was the best. Metabolome and transcriptome analysis was performed on melons grown in three different soils (rural soil, salt–alkali soil, and 35% volcanic ash treated salt–alkali soil). Notably, a total of 71 differentially expressed genes were predominantly enriched in the amino acid biosynthesis pathway. The metabolites involved in differential metabolism exhibited significant enrichment in phenylpropanoids, flavonoids, amino acids, and arginine. Intriguingly, correlation analysis between metabolomics and transcriptomics revealed significant associations among pathways such as cysteine and methionine metabolism, amino acid biosynthesis, arginine biosynthesis, alanine-aspartate-glutamate metabolism, as well as fructose–mannose metabolism. Our research elucidated the molecular mechanism of salt–alkali tolerance in thin-skinned melons, providing new references for improving salt–alkali tolerance and improving salt–alkali soil in the future.

In the present work, the electrical and dielectric properties of ceramic samples prepared from volcanic ash were investigated. For this purpose, ceramic samples were prepared using milled volcanic ash with a binder material at a sintering temperature of 950 °C for 2 h. The chemical content of the milled volcanic ash was investigated using XRF. Differential thermal analysis and thermogravimetry were performed to determine the firing conditions. The crystalline phases and microstructures of the ceramic samples were investigated using XRD and SEM, respectively. Finally, the electrical and dielectric properties of the obtained samples were evaluated at a frequency ranging from 1 × 102 to 4 × 106 Hz and temperatures ranging from room temperature to 800 °C. The XRD results revealed that the ceramic samples contained three main phases: albite, hematite, and augite. Moreover, the microstructures of the samples exhibited a large crystal size with a dense surface. The conductivities and dielectric constants of the samples remained stable up to 500 °C. The real and imaginary parts of the dielectric constant decreased with an increase in frequency and increased with an increase in temperature. The results indicated that ceramics based on volcanic ash are promising for use in technological applications such as high-voltage power insulators.

The East Asia black cotton soil (BCS) cannot be used as embankment filling directly due to its high clay content, liquid limit, plasticity index, and low CBR strength (CBR < 3%). This study evaluates the effects of treating East Asia BCS with lime, volcanic ash, or a combination of both on its engineering properties. Experiments were conducted to analyze the basic physical properties, swelling characteristics, and mechanical properties of the treated soil. Results indicate that lime addition significantly reduces the free swelling rate, improves limit moisture content, increases optimum moisture content, decreases maximum dry density, and enhances CBR value. Although volcanic ash also improves BCS performance, its effects are less pronounced than those of lime. The combined treatment with lime and volcanic ash exhibits superior performance, greatly reducing expansion potential and significantly increasing soil strength. Specifically, a mixture of 3% lime and 15% volcanic ash optimizes the liquid limit, plasticity index, and CBR value to 49.2%, 23.8, and 24.7%, respectively, meeting the JTG D30-2015 requirements and reducing construction costs. The treatment mechanisms involve hydration exothermic reactions, volcanic ash reactions, and semipermeable membrane effects, which collectively enhance the soil’s properties by producing dense, high-strength compounds.

Agriculture is an important economic sector for Ecuador, sustained by food crops like maize, potatoes, and vegetables cultivated in the highlands while cash crops such as coffee, bananas, cacao, and palm oil are grown on the coastal plains. But, Ecuador is also a country under the influence of several natural hazards due to its geographical location, atmospheric dynamics, and geological characteristics. One of the main risks to food security is the presence of a large number of active volcanoes scattered all over the country with the most representative enemy, the falling volcanic ash. The bibliography in general highlights the potential toxicity of volcanic ash from a human health perspective, but it also negatively influences plant development at the seed’s germination, as well as low crop pollination, damaged fruits, reduced leaf respiration depending on the type of crop, the developmental stage, the ash layer, and the climate. The mineral composition of the volcanic ash can also be beneficial for the soil by increasing fertility but at the same time with contrasting effects on plants due to the influence on soil characteristics such as pH, soil aeration, and biodiversity, which can detrimentally affect some crops.

Background : Sudden volcanic eruptions can lead to volcanic ash entering the eyes, causing severe discomfort and complicating evacuation efforts. The specific effects of volcanic ash on ocular tissues, especially when wearing soft contact lenses (SCLs), are not well documented, prompting this experimental investigation. Methods : White rabbits with normal eyes were randomly divided into three groups: (1) a bare eye group: bare eye + volcanic ash exposure + eye washing, (2) an SCL group: SCL-wearing eye + volcanic ash exposure + eye washing, and (3) a control group: eye washing only. In groups 1 and 2, volcanic ash was applied to one eye under topical anesthesia, followed by immediate saline rinsing. Slit-lamp microscopy and histopathological analysis were conducted after euthanasia. Results : Slit-lamp and histopathological examinations revealed more significant corneal and conjunctival erosion in the bare eye group compared to the SCL group, which showed limited damage. The control group displayed no ocular damage. Conclusions : Guidelines from the "Volcanic Ash Health Effects: A Guide for the Public" by the National Research Institute for Earth Science and Disaster Resilience recommend removing SCLs during ashfall. Our findings suggest that the damage to the corneal and conjunctival epithelium is less severe in SCL-wearing eyes than in bare eyes, recommending that SCL wearers prioritize evacuation over lens removal during sudden ashfall.

Extraordinary efforts should be carried out in Pakistan to prepare green concrete from waste materials. The utilization of Volcanic Ash (VA) in concrete can make sustainable concrete that will produce less carbon dioxide (CO2) emissions and give positive outcomes. Hence, compressive strength was tested on VA concrete with changing concentrations ranging from 0, 10, and 20% with constant W/C, and the result was evaluated by scanning electron microscopy. The analysis of results reveals that the intrusion of VA with 10% replacement gives a significant response, and enhances the strength of the overall matrix.

The inhalation of natural nanoparticles (NPs) emitted from volcanic activity may be a risk to human health. However, the literature rarely reports the fate and response of NPs once in contact with lung fluids. In this work, we studied the particle size distribution of ashfall from Popocatépetl volcano, Mexico. The collected ashes (n = 5) were analyzed with scanning electron microscopy (SEM) to obtain the elemental composition and morphology, and to determine the size of the ash particles using ParticleMetric software (PMS). The PMS reported most of the ash to have submicrometric size (

Today’s agriculture has the challenge of ensuring food supply for a growing population while human activity has already deteriorated about 40% of the world’s soils, reducing productive capacity and increasing reliance on mineral fertilizers. In this context, valorizing and recycling mineral and agricultural waste for use as substrates or soil supplements enhance a sustainable economy, as well as the development of activities focused on finishing the soil nutrients’ cycle. Looking for an effective solution to the massive waste generation and to enhance the agronomic qualities of soils, this study investigates the agronomic impact of contrasting inorganic and organic materials such as green compost (GC), wood biochar (WB), rice husk ash (RA), and volcanic ash (VA) as amendments to an alkaline Luvisol under controlled conditions. In this sense, barley seeds were planted and grown in a greenhouse under controlled conditions for 60 days on a soil amended with the aforementioned materials. The amendments demonstrated appropriate attributes for improving soil agronomic properties, enhancing the soil’s nutritional content with no effect on barley germination. The WB showed high aromaticity and abundance of refractory organic C. Both ash-rich amendments showed high P and K contents, which are important elements for plant development. The GC has high water retention capacity and an adequate C and N balance. Although the application of the amendments had no effect on barley yields, the plants from the ash-amended pots showed an increase of Photosystem II efficiency, indicative of a better physiological status. In terms of toxicological safety, the abundance of trace elements in soils and plants was investigated. All soils met the maximum allowable limits for these persistent pollutants. Nevertheless, longer-term tests on plants are required to determine the risk of Pb accumulation, particularly in soils amended with GC and compost-ash mixtures. The simultaneous combination of organic and inorganic amendments showed adequate agronomic attributes. WB analysis revealed its great recalcitrance and carbon sequestration potential.

The rigorous assessment of volcanic hazards relies on setting contemporary monitoring observations within an accurate, longer-term geological context. Revealing that geological context requires the detailed fieldwork, mapping and laboratory analysis of the erupted materials. However, many of the world’s most dangerous volcanic systems are located on or near coasts (e.g., the Phlegraean Fields and Vesuvius in Italy), islands (e.g., the volcanic archipelagos of the Pacific, south-east Asia, and Eastern Caribbean), or underwater (e.g., the recently erupting Hunga Tonga–Hunga Ha’apai volcano), meaning that much of their erupted material is deposited on the sea bed. The only way to sample this material directly is with seafloor sediment cores. This perspectives paper outlines how marine sediment cores are a vital yet underused resource for assessing volcanic hazards by: (1) outlining the spatio-temporal scope of the marine volcanic record and its main deposit types, (2) providing existing examples where marine sediments have contributed to volcanic hazard assessments; (3) highlighting the Sunda Arc, Indonesia as an example location where marine sediment cores are yet to contribute to hazard assessments, and (4) proposing that marine sediment cores can contribute to our understanding of very large eruptions that have a global impact. Overall, this perspectives paper aims to promote the utility of marine sediment cores in future volcanic hazard assessments, while also providing some basic information to assist researchers who are considering integrating marine sediment cores into their volcanological research.

In the Canary Islands and in other parts of the world where it can be found in its natural state, basaltic tephra, or “Picón” as it is known locally, is commonly used as a soilless substrate for crops. The aim of this study is to learn more about the physical properties of the Canary Islands’ tuff, and to find a simple method to predict the hydraulic behaviour of these substrates due to their heterogeneity. To accomplish this, 32 tuff samples were collected from all the quarries on the island of Tenerife (Canary Islands) that were authorised for the study. The tuffs had hydraulic properties that were highly influenced by the particle size. Coarse tuffs had an aeration capacity greater than 35% v/v and easily available water of less than 5% (v/v), while fine tuffs had aeration capacities below 20% v/v and elevated water retention (20 to 26% v/v). The intermediate tuffs had characteristics that varied between those of the two previous groups. Particle size fractions of less than 1 mm demonstrated the best correlation to common air:water ratios and present the best predictive capacity to relations involving air. By focusing on air:water ratios and the previous assumption, an attempt was made to predict the suitability of new pyroclastic material samples emitted by the La Palma Volcano as growing substrates for vegetables.

With the support of public authorities and research institutions, volcanic ash fallout and its impact on the safety of people, infrastructure and services are addressed with the aim of defining protocols and instruments for the reliable and effective handling of related emergencies. Most of the solutions proposed in the literature on ash fallout monitoring suffer from high cost and are demanding in terms of installation and maintenance. The approach suggested in this work is based on the use of a low-cost vision embedded system and a dedicated algorithm which automatically processes acquired frames of ground-deposited volcanic ash in order to estimate the main geometric properties of each particle identified in the work area. A complete characterization of the system is presented, along with a robustness analysis of particle shapes, their orientation and their position in the inspected frame. An accuracy of ±40.2 µm (with a 3σ limit) and a resolution of 32.9 µm (in the worst case), over a framed area of 130 mm by 100 mm, were estimated; these values would fulfill the objectives of the application.

Volcanic explosive eruptions inject several different types of particles and gasses into the atmosphere, giving rise to the formation and propagation of volcanic clouds. These can pose a serious threat to the health of people living near an active volcano and cause damage to air traffic. Many efforts have been devoted to monitor and characterize volcanic clouds. Satellite infrared (IR) sensors have been shown to be well suitable for volcanic cloud monitoring tasks. Here, a machine learning (ML) approach was developed in Google Earth Engine (GEE) to detect a volcanic cloud and to classify its main components using satellite infrared images. We implemented a supervised support vector machine (SVM) algorithm to segment a combination of thermal infrared (TIR) bands acquired by the geostationary MSG-SEVIRI (Meteosat Second Generation—Spinning Enhanced Visible and Infrared Imager). This ML algorithm was applied to some of the paroxysmal explosive events that occurred at Mt. Etna between 2020 and 2022. We found that the ML approach using a combination of TIR bands from the geostationary satellite is very efficient, achieving an accuracy of 0.86, being able to properly detect, track and map automatically volcanic ash clouds in near real-time.

The use of ensemble models to forecast the dispersion and transport of airborne volcanic ash in operational contexts is increasingly being explored. The ensemble members are usually constructed to represent a priori uncertainty estimates in meteorological fields and volcanic ash source parameters. Satellite data can be used to further filter ensemble members within an analysis time window by rejecting poorly performing members, leading to improved forecasts. In this study, the ensemble filtering technique is used to improve the representation of temporal source variations. Ensemble members are initially created by representing the source time variations as random functions of time that are modulated by crude initial estimates of the variations estimated from satellite imagery. Ensemble filtering is then used to remove members whose fields match poorly with observations within a specified analysis time window that are represented by satellite retrievals of volcanic ash properties such as mass load, effective radius, and cloud top height. The filtering process leads to an ensemble with statistics in closer agreement with the observations. It is shown in the context of the 30 May 2014 Sangeang Api eruption case study that this method leads to significantly enhanced forecasting skill beyond the analysis time window—about 20% improvement on average—when compared to a system that assumes constant emission rates for the duration of the eruption, as is the case in many operational volcanic ash forecasting systems.

This work studies the feasibility to employ a combination of volcanic ash (natural waste) with different raw materials in the production of geopolymers: fly ash and mining tailing (considered hazardous solid waste), natural pozzolan, and metakaolin. This study compares the properties of geopolymers based on volcanic ash with fly ash, pozzolan, metakaolin, and mining tailing in a relation of 1:1 with the addition of NaOH 15M and Na2SiO3 as alkali activators. FTIR and XRD assays and mechanical tests were employed to characterize the geopolymers. The results showed that those materials can be used as raw materials to produce geopolymers. Additionally, the results revealed that prime material composition and their mineralogical characteristics influence the geopolymerization reaction and compression strength, reaching values of 35 MPa for the volcanic ash-pozzolan mixture. The pozzolan is a good source of Al2O3 and SiO2 and is highly reactive to the alkali activators resulting in a better geopolymerization in comparison to the mixtures of volcanic ash with metakaolin, fly ash, or mining tailing.

The aim of this study was to investigate the influence of fineness and heat-treatment on the pozzolanic and engineering properties of volcanic ash. To this end, two different fineness levels of volcanic ash, ultra-fine (VAF) and fine (VA), without and after heat treatment at different temperatures (VA550, VA650, and VA750), were partially substituted for cement. In addition to the control (100% cement), five binary mortar mixes, each containing 20% of the different types of volcanic ash (VAF and VA; heat-treated and not), were prepared. First, X-ray fluorescence (XRF), X-ray powder diffraction (XRD), particle size analysis, and modified Chappelle tests were used to characterize the material. All mortar mixes were then tested for compressive strength development, water absorption, and apparent porosity. Finally, the microstructure of each of the mixes was evaluated by performing XRD, thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) analyses on paste samples at 91 days post-formation. The XRD and Chappelle reactivity results revealed increased pozzolanic reactivity with increasing volcanic ash fineness. In contrast, heat treatment adversely affected the pozzolanic reactivity of the volcanic ash due to the formation of crystalline phases at high temperatures. The mortars containing VAF20 (VAF, no heat, at 20%) showed slightly improved compressive strength (69.6 MPa) than the control (68.1 MPa) and all other binary mixes (66.7, 63.5, 64.2, and 63.9 MPa for VA20, VA20-550, VA20-650, and VA20-750, respectively) at 91 days. The mortar containing VAF20 demonstrated the lowest level of water absorption (9.3%) and apparent porosity (19.1%) of all mixes, including the control. The XRD results for the paste samples show that both VA and VAF showed the least intensity of portlandite phase, as compared to the control and other binary mixes. TGA results also show that binary mixes of VA and VAF have a reduced amount of portlandite, resulting in the densification of the mixes’ microstructures. With the addition of VAF, there is a significant shift in the FTIR band from 980 to 992 cm−1, which causes the formation of additional C–S–H gels that lead to the densification of the paste matrix. These results demonstrate that VAF exhibits high pozzolanic reactivity, making it suitable for use as a natural pozzolan that can partially substitute cement in the production of strong, durable, and environmentally friendly concrete.

For thousands of years, the volcanic activity present along the Andes Mountain range has generated a large amount of pyroclastic material. As a result, around 60 percent of the soils present in Chile have a volcanic origin, of which, we can find soils derived from volcanic ash. These correspond to soils whose origin is the weathering of volcanic ash, which generates minerals such as allophane, imogolite, and halloysite. The presence of these minerals gives these soils unique geotechnical properties, such as high plasticity, low dry unit weight, and a unique internal structure. Subjecting these soils to extreme temperatures like those needed to perform standard laboratory tests produces changes in their structures, and thus in their geotechnical behavior. These changes are important to be aware of with respect to slope stability problems, embankment conformation, surface foundations, etc. In the present study, a type of soil found in Chile originating from the weathering of volcanic ash and locally named Trumao was studied. Due to its age and formation processes, the main minerals found in the soil are allophane and imogolite, and hence it belongs to the allophanic soil type. The material was studied in its natural state (undisturbed) and, after being oven-dried using common geotechnical tests, the behaviors of both samples were compared. The study shows that some properties are affected significantly by the oven-drying process, and thus it is not recommended to expose the material to high temperatures during geotechnical laboratory testing to avoid misleading results.

The Eyjafjallajökull volcanic ash crisis in 2010 temporarily suspended European air traffic operations, as the 39-day eruption caused widely dispersed ashes to enter the lower atmosphere. In this paper, we assessed the effects of this event on the ionosphere layer and, consequently, on GPS positioning. We collected and analysed the data from four IGS stations, nearest to the volcano, for the month of April 2010. We recorded Vertical Total Electron Content (VTEC) time series, analysed their dynamics, and compared them with the GPS positioning errors of a commercial-grade, un-aided, single-frequency GPS receiver (simulating the response of a mass-market GPS receiver). The geomagnetic indices during the time period show little geomagnetic disturbance, especially during the volcanic event. Our results show an enhancement in ionosphere error by up to 15% during the volcanic ash event and an enhanced variance in GPS position components errors. This study reveals the potential impact of the charged volcanic ash on single-frequency, unaided GPS positioning accuracy in the Adriatic Sea region and establishes a foundation for studying similar events in future.

In this research, the influence of natural zeolites obtained from the volcanic ash of the Ubinas volcano has been studied as synergistic agents in a flame-retardant system (composed of ammonium polyphosphate, pentaerythritol, and polypropylene). Four zeolites were synthesized from volcanic ash, including those that had been calcined and those that had not. These were then placed in an alkaline solution at three synthesis temperatures. Zeolites were characterized through X-ray diffraction, specific surface area by nitrogen adsorption analysis (Brunauer–Emmett–Teller) and scanning electron microscopy. Polypropylene matrix composites were prepared with ammonium polyphosphate, pentaerythritol and zeolites at 1, 5 and 9%. Its thermal stability and fire resistance were evaluated by thermogravimetric analysis, limiting oxygen index, vertical burning test and cone calorimeter and its morphological structure by scanning electron microscopy. It was determined that the synthesis temperature and the use of calcined and without calcined volcanic ash have an influence on the characteristics of the zeolites and on its synergistic action.

We describe NASA’s Applied Sciences Disasters Program, which is a collaborative project between the Direct Readout Laboratory (DRL), ozone processing team, Jet Propulsion Laboratory, Geographic Information Network of Alaska (GINA), and Finnish Meteorological Institute (FMI), to expedite the processing and delivery of direct readout (DR) volcanic ash and sulfur dioxide (SO2) satellite data. We developed low-latency quantitative retrievals of SO2 column density from the solar backscattered ultraviolet (UV) measurements using the Ozone Mapping and Profiler Suite (OMPS) spectrometers as well as the thermal infrared (TIR) SO2 and ash indices using Visible Infrared Imaging Radiometer Suite (VIIRS) instruments, all flying aboard US polar-orbiting meteorological satellites. The VIIRS TIR indices were developed to address the critical need for nighttime coverage over northern polar regions. Our UV and TIR SO2 and ash software packages were designed for the DRL’s International Planetary Observation Processing Package (IPOPP); IPOPP runs operationally at GINA and FMI stations in Fairbanks, Alaska, and Sodankylä, Finland. The data are produced within 30 min of satellite overpasses and are distributed to the Alaska Volcano Observatory and Anchorage Volcanic Ash Advisory Center. FMI receives DR data from GINA and posts composite Arctic maps for ozone, volcanic SO2, and UV aerosol index (UVAI, proxy for ash or smoke) on its public website and provides DR data to EUMETCast users. The IPOPP-based software packages are available through DRL to a broad DR user community worldwide.

Volcanic ash fall-out represents a serious hazard for air and road traffic. The forecasting models used to predict its time–space evolution require information about the core characteristics of volcanic particles, such as their granulometry. Typically, such information is gained by the spot direct observation of the ash collected at the ground or by using expensive instrumentation. In this paper, a vision-based methodology aimed at the estimation of ash granulometry is presented. A dedicated image processing paradigm was developed and implemented in LabVIEW™. The methodology was validated experimentally using digital reference images resembling different operating conditions. The outcome of the assessment procedure was very encouraging, showing an accuracy of the image processing algorithm of 1.76%.

Forecasting the compressive strength of concrete is a complex task owing to the interactions among concrete ingredients. In addition, an important characteristic of the concrete failure surface is its six-fold symmetry. In this study, an artificial neural network (ANN) and adaptive neuro fuzzy interface system (ANFIS) were employed to model the compressive strength of natural volcanic ash mortar (VAM) by using the six-fold symmetry of concrete failure. The modeling was correlated with four parameters. To train and test the projected models, data for more than 150 samples were collected from the literature. Furthermore, mortar samples with varying proportions of volcanic ash were prepared in the laboratory and tested, and the results were used to validate the models. The performance of the developed models was assessed using numerous statistical measures. The results show that both the ANN and ANFIS models accurately predict the compressive strength of VAM with R-square above 0.9 and lower error statistics. The permutation feature analysis confirmed that the age of specimens affects the strength of VAM the most, followed by the water-to-cement ratio, curing temperature, and percentage of volcanic ash.

Improved quantitative forecasts of volcanic ash are in great demand by the aviation industry to enable better risk management during disruptive volcanic eruption events. However, poor knowledge of volcanic source parameters and other dispersion and transport modelling uncertainties, such as those due to errors in numerical weather prediction fields, make this problem very challenging. Nonetheless, satellite-based algorithms that retrieve ash properties, such as mass load, effective radius, and cloud top height, combined with inverse modelling techniques, such as ensemble filtering, can significantly ameliorate these problems. The satellite-retrieved data can be used to better constrain the volcanic source parameters, but they can also be used to avoid the description of the volcanic source altogether by direct insertion into the forecasting model. In this study we investigate the utility of the direct insertion approach when employed within an ensemble filtering framework. Ensemble members are formed by initializing dispersion models with data from different timesteps, different values of cloud top height, thickness, and NWP ensemble members. This large ensemble is then filtered with respect to observations to produce a refined forecast. We apply this approach to 14 different eruption case studies in the tropical atmosphere. We demonstrate that the direct insertion of data improves model forecast skill, particularly when it is used in a hybrid ensemble in which some ensemble members are initialized from the volcanic source. Moreover, good forecast skill can be obtained even when detailed satellite retrievals are not available, which is frequently the case for volcanic eruptions in the tropics.

The realistic representation of atmospheric pollutant dispersal over areas of complex topography presents a challenging application for meteorological models. Here, we present results from high–resolution atmospheric modeling in order to gain insight into local processes that can affect ash transport and deposition. The nested Weather Research and Forecasting (WRF) model with the finest resolution of 50 m was used to simulate atmospheric flow over the complex topography of Sakurajima volcano, Japan, for two volcanic eruption cases. The simulated airflow results were shown to compare well against surface observations. As a preliminary application, idealized trajectory modeling for the two cases revealed that accounting for local circulations can significantly impact volcanic ash deposition leading to a total fall velocity up to 2–3 times the particle’s terminal velocity depending on the size. Such a modification of the estimated particle settling velocity over areas with complex topography can be used to parametrize the impact of orographic effects in dispersal models, in order to improve fidelity.

Two polarization-sensitive lidars were operated continuously to monitor the three-dimensional distribution of small volcanic ash particles around Sakurajima volcano, Kagoshima, Japan. Here, we estimated monthly averaged extinction coefficients of particles between the lidar equipment and the vent and compared our results with monthly records of volcanic activity reported by the Japan Meteorological Agency, namely the numbers of eruptions and explosions, the density of ash fall, and the number of days on which ash fall was observed at the Kagoshima observatory. Elevated extinction coefficients were observed when the surface wind direction was toward the lidar. Peaks in extinction coefficient did not always coincide with peaks in ash fall density, and these differences likely indicate differences in particle size.

In this study, a technique facilitating the enhanced detection of airborne volcanic ash (VA) has been developed, which is based on the use of visible (VIS), near-infrared (NIR), and infrared (IR) bands by meteorological satellite systems. Channels with NIR and IR bands centered at ~3.8, 7.3, 8.7, 10.5, and 12.3 μm are utilized, which enhances the accuracy of VA detection. The technique is based on two-band brightness temperature differences (BTDs), two-band brightness temperature ratios (BTRs), and background image BTDs. The physical effects of the observed BTDs and BTRs, which can be used to distinguish VA from meteorological clouds based on absorption differences, depend on the channel and time of day. The Advanced Meteorological Imager onboard the GEOKOMPSAT-2A (GK-2A) satellite has several advantages, including the day- and nighttime detection of land and ocean. Based on the GK-2A data on several volcanic eruptions, multispectral data are more sensitive to volcanic clouds than ice and water clouds, ensuring the detection of VA. They can also be used as an input to provide detailed information about volcanoes, such as the height of the VA layer and VA mass. The GK-2A was optimized, and an improved ash algorithm was established by focusing on the volcanic eruptions that occurred in 2020. In particular, the 3.8 μm band was utilized, the threshold was changed by division between day and night, and efforts were made to reduce the effects of clouds and the discontinuity between land and ocean. The GK-2A imagery was used to study volcanic clouds related to the eruptions of Taal, Philippines, on 12 January and Nishinoshima, Japan, from 30 July–2 August to demonstrate the applicability of this product during volcanic events. The improved VA product of GK-2A provides vital information, helping forecasters to locate VA as well as guidance for the aviation industry in preventing dangerous and expensive interactions between aircrafts and VA.

Ground-based remote sensing equipment have the potential to be used for the nowcasting of the tephra hazard from volcanic eruptions. To do so raw data from the equipment first need to be accurately transformed to tephra-related physical quantities. In order to establish these relations for Sakurajima volcano, Japan, we propose a methodology based on high-resolution simulations. An eruption that occurred at Sakurajima on 16 July 2018 is used as the basis of a pilot study. The westwards dispersal of the tephra cloud was ideal for the observation network that has been installed near the volcano. In total, the plume and subsequent tephra cloud were recorded by 2 XMP radars, 1 lidar and 3 optical disdrometers, providing insight on all phases of the eruption, from plume generation to tephra transport away from the volcano. The Weather Research and Forecasting (WRF) and FALL3D models were used to reconstruct the transport and deposition patterns. Simulated airborne tephra concentration and accumulated load were linked, respectively, to lidar backscatter intensity and radar reflectivity. Overall, results highlight the possibility of using such a high-resolution modelling-based methodology as a reliable complementary strategy to common approaches for retrieving tephra-related quantities from remote sensing data.

Volcanic ash can interact with the earth system on many temporal and spatial scales and is a significant hazard to aircraft. In the event of a volcanic eruption, fast and robust decisions need to be made by aviation authorities about which routes are safe to operate. Such decisions take into account forecasts of ash location issued by Volcanic Ash Advisory Centers (VAACs) which are informed by simulations from Volcanic Ash Transport and Dispersion (VATD) models. The estimation of the time-evolving vertical distribution of ash emissions for use in VATD simulations in real time is difficult which can lead to large uncertainty in these forecasts. This study presents a method for constraining the ash emission estimates by combining an inversion modeling technique with an ensemble of meteorological forecasts, resulting in an ensemble of ash emission estimates. These estimates of ash emissions can be used to produce a robust ash forecast consistent with observations. This new ensemble approach is applied to the 2011 eruption of the Icelandic volcano Grímsvötn. The resulting emission profiles each have a similar temporal evolution but there are differences in the magnitude of ash emitted at different heights. For this eruption, the impact of precipitation uncertainty (and the associated wet deposition of ash) on the estimate of the total amount of ash emitted is larger than the impact of the uncertainty in the wind fields. Despite the differences that are dominated by wet deposition uncertainty, the ensemble inversion provides confidence that the reduction of the unconstrained emissions (a priori), particularly above 4 km, is robust across all members. In this case, the use of posterior emission profiles greatly reduces the magnitude and extent of the forecast ash cloud. The ensemble of posterior emission profiles gives a range of ash column loadings much closer in agreement with a set of independent satellite retrievals in comparison to the a priori emissions. Furthermore, airspace containing volcanic ash concentrations deemed to be associated with the highest risk (likelihood of exceeding a high concentration threshold) to aviation are reduced by over 85%. Such improvements could have large implications in emergency response situations. Future research will focus on quantifying the impact of uncertainty in precipitation forecasts on wet deposition in other eruptions and developing an inversion system that makes use of the state-of-the-art meteorological ensembles which has the potential to be used in an operational setting.

Atmospheric aviation hazards due to turbulence, poor visibility, high-altitude ice crystals and volcanic ash and gases are known problems for aviation and can cause both economic damage to engines and airframes as well as having the potential to cause the engines to stall in flight with possible loss of the aircraft. Current space- and ground-based assets allow observations of some of these hazards and their detection and movement can be forecast using modern computer weather forecasting and dispersion models. These largely strategic resources have proved very valuable but somewhat limited in the tactical sense, where commercial aviation must make rapid decisions in order to avoid an undetected or un-forecast hazardous cloud or atmospheric condition. Here we investigate the use of multi-spectral (two channels or more) infrared imaging from an aircraft perspective, and show that it is possible to use this information to provide tactical awareness tools for use by aviators and other stakeholders. This study has a strong focus on volcanic ash as an aviation hazard but also includes applications to some forms of clear air turbulence (CAT), to high-altitude ice crystals (HAIC) and windblown desert dust. For volcanic ash detection, the research shows that current two-channel satellite-based infrared techniques provide acceptable discrimination and quantification, but two-channel infrared imaging airborne solutions have significant drawbacks. Because of the limitation of two-channel methods, infrared spectroscopic techniques are investigated and it is shown they can significantly reduce the confusion caused by meteorological hydrometeors and potentially provide information on other atmospheric hazards to aviation, such as HAIC and some forms of turbulence. Not only are these findings important for on-going efforts to incorporate IR imaging onto commercial aircraft, but they also have relevance to the increasing use of drones for hazard detection, research and monitoring. Uncooled infrared bolometric imaging cameras with spectroscopic capabilities are available and we describe one such system for use on airborne platforms.

The size distribution of volcanic ash is rarely measured in real time and Volcanic Ash Advisory Centres (VAACs) often rely on a default particle size distribution (PSD) to initialise their dispersion models when forecasting the movement of ash clouds. We conducted a sensitivity study to investigate the impact of PSD on model output and consider how best to apply default PSDs in operational dispersion modelling. Compiled grain size data confirm that, when considering particles likely to be in the distal ash cloud (< 125 µm diameter), magma composition and eruption size are the dominant controls on grain size distribution. Constraining the PSD is challenging but we find that the grain size of deposits from large hydromagmatic eruptions remains relatively constant with distance, suggesting that total (whole-deposit) grain size distributions (TGSDs) for these eruptions could be estimated from a few samples. We investigated the sensitivity of modelled ash mass loadings (in the air and on the ground) to input PSDs based on coarse to fine TGSDs from our dataset. We found clear differences between modelled mass loadings and the extent of the plume. Comparing TGSDs based on ground-only and ground-plus-satellite data for the Eyjafjallajökull 2010 eruption, we found that basing input PSDs on TGSDs from deposits alone (likely missing the finest particles) led to lower modelled peak ash concentrations and a smaller plume.

It has been 10 years since the ash cloud from the eruption of Eyjafjallajökull caused unprecedented disruption to air traffic across Europe. During this event, the London Volcanic Ash Advisory Centre (VAAC) provided advice and guidance on the expected location of volcanic ash in the atmosphere using observations and the atmospheric dispersion model NAME (Numerical Atmospheric-Dispersion Modelling Environment). Rapid changes in regulatory response and procedures during the eruption introduced the requirement to also provide forecasts of ash concentrations, representing a step-change in the level of interrogation of the dispersion model output. Although disruptive, the longevity of the event afforded the scientific community the opportunity to observe and extensively study the transport and dispersion of a volcanic ash cloud. We present the development of the NAME atmospheric dispersion model and modifications to its application in the London VAAC forecasting system since 2010, based on the lessons learned. Our ability to represent both the vertical and horizontal transport of ash in the atmosphere and its removal have been improved through the introduction of new schemes to represent the sedimentation and wet deposition of volcanic ash, and updated schemes to represent deep moist atmospheric convection and parametrizations for plume spread due to unresolved mesoscale motions. A good simulation of the transport and dispersion of a volcanic ash cloud requires an accurate representation of the source and we have introduced more sophisticated approaches to representing the eruption source parameters, and their uncertainties, used to initialize NAME. Finally, upper air wind field data used by the dispersion model is now more accurate than it was in 2010. These developments have resulted in a more robust modelling system at the London VAAC, ready to provide forecasts and guidance during the next volcanic ash event.

Poor knowledge of dispersion model source parameters related to quantities such as the total fine ash mass emission rate, its effective spatial distribution, and particle size distribution makes the provision of quantitative forecasts of volcanic ash a difficult problem. To ameliorate this problem, we make use of satellite-retrieved mass load data from 14 eruption case studies to estimate fine ash mass emission rates and other source parameters by an inverse modelling procedure, which requires multidimensional sampling of several thousand trial simulations with different values of source parameters. We then estimate the dependence of these optimal source parameters on eruption height. We show that using these empirical relationships in a data assimilation procedure leads to substantial improvements to the forecasts of ash mass loads, with the use of empirical relationships between parameters and eruption height having the added advantage of computational efficiency because of dimensional reduction. In addition, the use of empirical relationships, which encode information in satellite retrievals from past case studies, implies that quantitative forecasts can still be issued even when satellite retrievals of mass load are not available in real time due to cloud cover or other reasons, making it especially useful for operations in the tropics where ice and water clouds are ubiquitous.

Shale oil exploration has been a key area of onshore oil and gas exploration in China in recent years. In this study, organic geochemistry and element geochemistry are united to study the shale oil and source rock in the Lucaogou formation of Jimusar sag, in order to reveal the paleoclimate, paleoenvironment, source of organic matter, and factors affecting organic matter accumulation and shale oil generation. The shale oil in the study area is mainly accumulated in two strata with good reservoir properties and oiliness, known as the upper sweet spot and lower sweet spot. Indexes of biomarkers and sensitive elements revealed the warm and semi-arid paleoclimate during Lucaogou formation, and the water column was brackish to salty. Water stratification caused a suboxic to anoxic environment in the deep-water column and coincided with the anoxic photic zone phenomenon. Compared with the lower sweet spot, the more humid climate, deeper and fresher water, and stronger water stratification characterize the upper sweet spot during sedimentation. This made the photic zone with freshwater more suitable for the reproduction of algae in the upper sweet spot. Meanwhile, the organic matter was well-preserved in the anoxic zone. Volcanic ash caused algae bloom, which promoted primary productivity and ensured the supply of organic matter. The composition and distribution pattern of biomarkers prove that phytoplankton is the most important source of organic matter in the study area and the contribution of higher plants is insignificant. The relationship between parameters of paleoproductivity and the redox condition versus total organic carbon (TOC) suggests that compared with the preservation conditions, the input of organic carbon is the most important controlling factor of organic matter accumulation in the study area.

Pyroclastic soils are widespread in the world. In particular, they cover a great part of Campania, a densely populated country of Southern Italy, where some distinct volcanic centers are present. In these soils, precipitations can trigger fast flow-like landslides causing destruction and loss of human lives. The movement style, the high velocity and the long run-out of these landslides are an indication of the occurrence, in the saturated soil mass, of mechanisms of undrained instability due to the inability of soil to sustain the deviator stress related to the slope condition. This paper reports the results of a wide experimental laboratory program carried out on a volcanic ash, which recently has been the seat of a killer landslide, stressing the factors that govern the undrained response of these materials.

Agriculture is an important economic sector for Ecuador, sustained by food crops like maize, potatoes, and vegetables cultivated in the highlands while cash crops such as coffee, bananas, cacao, and palm oil are grown on the coastal plains. But, Ecuador is also a country under the influence of several natural hazards due to its geographical location, atmospheric dynamics, and geological characteristics. One of the main risks to food security is the presence of a large number of active volcanoes scattered all over the country with the most representative enemy, the falling volcanic ash. The bibliography in general highlights the potential toxicity of volcanic ash from a human health perspective, but it also negatively influences plant development at the seed's germination, as well as low crop pollination, damaged fruits, reduced leaf respiration depending on the type of crop, the developmental stage, the ash layer, and the climate. The mineral composition of the volcanic ash can also be beneficial for the soil by increasing fertility but at the same time with contrasting effects on plants due to the influence on soil characteristics such as pH, soil aeration, and biodiversity, which can detrimentally affect some crops.

One of the major concerns of concrete industries is to develop materials that consume less natural virgin resources and energy to make sustainable construction practices. Efforts have been made and even implemented to use the waste/by product materials such as fly ash, slag, silica fume, and natural pozzolana as a partial or complete replacement for Portland cement in concrete mixtures. The deterioration of concrete structures in the existing hot and cold climates of Gulf Cooperation Council countries, along with chloride and sulphate attack, demands the use of pozzolanic materials for concrete construction. Volcanic ash incorporated cement based concretes are known for its better performance in terms of strength and durability in harsh marine environments. Understanding the cement hydration process and characterizing the hydration products in microstructural level is a complex and interdependent process that allows one to design complex mix proportions to produce sustainable concrete materials. In this paper, the early and late age hydration behavior along with micro- and pore structure of cement paste samples prepared with locally available ordinary Portland cement (OPC) and volcanic ash (VA) obtained from Saudi Arabia was monitored using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric (TGA) and N2-Adsorption analysis. The hydration progress of cement paste samples with different combinations of OPC and VA (0%, 15%, 25%, and 35%) at a w/c ratio of 0.45 after 14, 28, and 90 days were discussed. The qualitative XRD and SEM of cement paste samples showed no new phases were formed during the course of hydration. The disappearance of portlandite with increase in VA content was due to both pozzolanic effect and dilution effect. This was further confirmed quantitatively by the TGA observations that the samples with VA contain less Ca(OH)2 compared to the control specimens. N2 adsorption experiments after 90 days of curing showed larger hysteresis as the VA content increases. The studies show that the incorporation of volcanic ash certainly contributes to the generation of C-S-H and hence the cement hydration progress, especially in the later ages through pozzolanic reactions. A 15−25 % volcanic ash blended cement paste samples showed compact and denser morphological features, which will be highly detrimental for the durability performances.

Current Earth Observation (EO) satellites provide excellent spatial, temporal and spectral coverage for passive measurements of atmospheric volcanic emissions. Of particular value for ash detection and quantification are the geostationary satellites that now carry multispectral imagers. These instruments have multiple spectral channels spanning the visible to infrared (IR) wavelengths and provide 1 × 1 km2 to 4 × 4 km2 resolution data every 5–15 min, continuously. For ash detection, two channels situated near 11 and 12 μ m are needed; for ash quantification a third or fourth channel also in the infrared is useful for constraining the height of the ash cloud. This work describes passive EO infrared measurements and techniques to determine volcanic cloud properties and includes examples using current methods with an emphasis on the main difficulties and ways to overcome them. A challenging aspect of using satellite data is to design algorithms that make use of the spectral, temporal (especially for geostationary sensors) and spatial information. The hyperspectral sensor AIRS is used to identify specific molecules from their spectral signatures (e.g., for SO2) and retrievals are demonstrated as global, regional and hemispheric maps of AIRS column SO2. This kind of information is not available on all sensors, but by combining temporal, spatial and broadband multi-spectral information from polar and geo sensors (e.g., MODIS and SEVIRI) useful insights can be made. For example, repeat coverage of a particular area using geostationary data can reveal temporal behaviour of broadband channels indicative of eruptive activity. In many instances, identifying the nature of a pixel (clear, cloud, ash etc.) is the major challenge. Sophisticated cloud detection schemes have been developed that utilise statistical measures, physical models and temporal variation to classify pixels. The state of the art on cloud detection is good, but improvements are always needed. An IR-based multispectral cloud identification scheme is described and some examples shown. The scheme is physically based but has deficiencies that can be improved during the daytime by including information from the visible channels. Physical retrieval schemes applied to ash detected pixels suffer from a lack of knowledge of some basic microphysical and optical parameters needed to run the retrieval models. In particular, there is a lack of accurate spectral refractive index information for ash particles. The size distribution of fine ash (1–63 μ m, diameter) is poorly constrained and more measurements are needed, particularly for ash that is airborne. Height measurements are also lacking and a satellite-based stereoscopic height retrieval is used to illustrate the value of this information for aviation. The importance of water in volcanic clouds is discussed here and the separation of ice-rich and ash-rich portions of volcanic clouds is analysed for the first time. More work is required in trying to identify ice-coated ash particles, and it is suggested that a class of ice-rich volcanic cloud be recognized and termed a ‘volcanic ice’ cloud. Such clouds are frequently observed in tropical eruptions of great vertical extent (e.g., 8 km or higher) and are often not identified correctly by traditional IR methods (e.g., reverse absorption). Finally, the global, hemispheric and regional sampling of EO satellites is demonstrated for a few eruptions where the ash and SO 2 dispersed over large distances (1000s km).

On 22 April 2015, the Calbuco volcano in Chile (Lat: 41.33 ∘ S, Long: 72.62 ∘ W) erupted after 43 years of inactivity followed by a great amount of aerosol injection into the atmosphere. The pyroclastic material dispersed into the atmosphere posed a potential threat to aviation traffic and air quality over affected a large area. The plumes and debris spread from its location to Patagonian and Pampean regions, reaching the Atlantic and Pacific Oceans and neighboring countries, such as Argentina, Brazil and Uruguay, driven by the westerly winds at these latitudes. The presence of volcanic aerosol layers could be identified promptly at the proximities of Calbuco and afterwards by remote sensing using satellites and lidars in the path of the dispersed aerosols. The Cloud-Aerosol Lidar and Pathfinder Satellite Observations (CALIPSO), Moderate Resolution Imaging Spectroradiometer (MODIS) on board of AQUA/TERRA satellites and Ozone Mapping and Profiler Suite (OMPS) on board of Suomi National Polar-orbiting Partnership (Suomi NPP) satellite were the space platforms used to track the injected layers and a multi-channel lidar system from Latin America Lidar Network (LALINET) SPU Lidar station in South America allowed us to get the spatial and temporal distribution of Calbuco ashes after its occurrence. The SPU lidar stations co-located Aerosol Robotic Network (AERONET) sunphotometers to help in the optical characterization. Here, we present the volcanic layer transported over São Paulo area and the detection of aerosol plume between 18 and 20 km. The path traveled by the volcanic aerosol to reach the Metropolitan Area of São Paulo (MASP) was tracked by CALIPSO and the aerosol optical and geometrical properties were retrieved at some points to monitor the plume evolution. Total attenuated backscatter profile at 532 nm obtained by CALIPSO revealed the height range extension of the aerosol plume between 18 and 20 km and are in agreement with SPU lidar range corrected signal at 532 nm. The daily evolution of Aerosol Optical Depth (AOD) at 532 and 355 nm, retrieved from AERONET sunphotometer, showed a substantial increasing on 27 April, the day of the volcanic plume detection at Metropolitan Area of São Paulo (MASP), achieving values of 0 . 33 ± 0 . 16 and 0 . 22 ± 0 . 09 at 355 and 532 nm, respectively. AERONET aerosol size distribution was dominated by fine mode aerosol over coarse mode, especially on 27 and 28 April. The space and time coincident aerosol extinction profiles from SPU lidar station and OMPS LP from the Calbuco eruption conducted on 27 April agreed on the double layer structure. The main objective of this study was the application of the transmittance method, using the Platt formalism, to calculate the optical and physical properties of volcanic plume, i.e., aerosol bottom and top altitude, the aerosol optical depth and lidar ratio. The aerosol plume was detected between 18 and 19.3 km, with AOD value of 0.159 at 532 nm and Ånsgtröm exponent of 0 . 61 ± 0 . 58 . The lidar ratio retrieved was 76 ± 27 sr and 63 ± 21 sr at 532 and 355 nm, respectively. Considering the values of these parameters, the Calbuco volcanic aerosol layers could be classified as sulfates with some ash type.

The inhalation of natural nanoparticles (NPs) emitted from volcanic activity may be a risk to human health. However, the literature rarely reports the fate and response of NPs once in contact with lung fluids. In this work, we studied the particle size distribution of ashfall from Popocatépetl volcano, Mexico. The collected ashes (n = 5) were analyzed with scanning electron microscopy (SEM) to obtain the elemental composition and morphology, and to determine the size of the ash particles using ParticleMetric software (PMS). The PMS reported most of the ash to have submicrometric size (<1 μm) and an average equivalent circle of 2.72 μm. Moreover, to our knowledge, this study investigated for the first time the behavior of ash NPs at different times (0 to 24 h) while in contact with in vitro lung fluid, Gamble Solution (GS) and Artificial Lysosomal Fluid (ALF) using dynamic light scattering (DLS). We found a large variability in the hydrodynamic diameter, with values less than 1 nm and greater than 5 μm. Furthermore, aggregation and disaggregation processes were recognized in GS and ALF, respectively. The results of this study increase the knowledge of the interaction between NPs and lung fluids, particularly within the alveolar macrophage region.

Municipal solid waste incinerator fly ash (MSWI-FA) was used synergistically with volcanic ash (VA) to synthesize Geopolymer cement. The effects of the incorporation of 0%, 30%, and 50% of VA and the alkalinity of activating solution on the structure and properties were studied by using the X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), field emission gun scanning electron microscopy (FEG-SEM), and mechanical testing. The encapsulation efficiency of the cements was carried out by using a toxicity characteristic leaching procedure (TCLP). The geopolymerization of MSWI-FA promoted the formation of new minerals such as Thernadite (Na2SO4), Hydrocalumite (Ca4Al2O6(CO3)0.67(SO3)0.33), C-S-H, and Faujasite-Na(Na2Ca)0.075(Al0.3Si0.7)O2(H2O)0.22. The Geopolymer cement synthesized with the addition of 50% of VA at 6M NaOH concentration, which exhibited the most compact microstructure. This was the highest strength with the best encapsulation ability. The microstructure analysis of the MSWI-FA-VA system revealed the coexistence of C-S-H and N-A-S-H phases as the main cementitious binders. The TCLP results of cement vis a vis raw MSWI-FA showed the leaching of metals reduced to a great extent. This was much lower than the permissible limit fixed by the United States Environmental Protection Agency (USEPA) for the toxicity characteristic. Furthermore, an attempt was made to correlate the microstructure with mechanical properties.

The Agung volcano (Bali; Indonesia) erupted in later November 2017 after several years of quiescence. Because of ash emissions, hundreds of flights were cancelled, causing an important air traffic disruption in Indonesia. We investigate those ash emissions from space by applying the RSTASH algorithm for the first time to Himawari-8 data and using an ad hoc implementation scheme to reduce the time of the elaboration processes. Himawari-8 is a new generation Japanese geostationary meteorological satellite, whose AHI (Advanced Himawari Imager) sensor offers improved features, in terms of spectral, spatial and temporal resolution, in comparison with the previous imagers of the MTSAT (Multi-Functional Transport Satellite) series. Those features should guarantee further improvements in monitoring rapidly evolving weather/environmental phenomena. Results of this work show that RSTASH was capable of successfully detecting and tracking the Agung ash plume, despite some limitations (e.g., underestimation of ash coverage under certain conditions; generation of residual artefacts). Moreover, estimates of ash cloud-top height indicate that the monitored plume extended up to an altitude of about 9.3 km above sea level during the period 25 November at 21:10 UTC–26 November at 00:50 UTC. The study demonstrates that RSTASH may give a useful contribution for the operational monitoring of ash clouds over East Asia and the Western Pacific region, well exploiting the 10 min temporal resolution and the spectral features of the Himawari-8 data.

Volcanic ash produced during explosive eruptions may serve as ice nuclei in the atmosphere, contributing to the occurrence of volcanic lightning due to tribocharging from ice–ice or ice–ash collisions. Here, different ash samples were tested using deposition-mode and immersion-mode ice nucleation experiments. Results show that bulk composition and mineral abundance have no measurable effect on depositional freezing at the temperatures tested, as all samples have similar ice saturation ratios. In the immersion mode, there is a strong positive correlation between K2O content and ice nucleation site density at −25 °C and a strong negative correlation between MnO and TiO2 content at temperatures from −35 to −30 °C. The most efficient sample in the immersion mode has the highest surface area, smallest average grain size, highest K2O content, and lowest MnO content. These results indicate that although ash abundance—which creates more available surface area for nucleation—has a significant effect on immersion-mode freezing, composition may also contribute. Consequently, highly explosive eruptions of compositionally evolved magmas create the necessary parameters to promote ice nucleation on grain surfaces, which permits tribocharging due to ice–ice or ice–ash collisions, and contribute to the frequent occurrence of volcanic lightning within the eruptive column and plume during these events.

Volcanic ash is a volcanic product with a wide distribution that can be used as a geological marker. In volcanic regions such as Indonesia, the identification of the sources of volcanic ash and tuff layers from different volcanoes or eruptive events is a challenging task. In this study, samples of volcanic ash from the 2010 eruption of Bromo—a relatively young and active tuff cone volcano within the Sandsea caldera in the Tengger volcanic complex in East Java, Indonesia—along with two older tuff layers from the same caldera (Widodaren tuff: 1.8 kyr and Segarawedi tuff: 33 kyr) were subjected to magnetic measurements, geochemical analyses, and petrographic analyses. The aim is to attempt to use magnetic characters as a fingerprint for volcanic ash and tuff layers. The results show that the samples had variations in grain size and magnetic domain as indicated by the hysteresis parameters. These magnetic characters correlated with the results of geochemical and petrographic analyses, suggesting that magnetic properties may potentially be used as fingerprints to identify volcanic ashes and tuff layers.