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Far from being a recent development of the Earth System, volcanism has accompanied the Earth, terrestrial planets and countless exoplanets since their origins. Volcanism is a material mechanism whereby planets evolve to their differentiated states that are potentially capable of hosting life. Explosive volcanic eruptions are commonly accompanied by volcanic lightning, modulated by charging and discharging mechanisms within the eruption column. As discharges have been proposed as a potential prebiotic synthesis mechanism for forming first organic molecules, the behaviour of volcanic lightning at early Earth conditions could yield further insights into likely environments for the origin of life.Earth´s atmosphere has changed significantly in composition and pressure since its early beginnings. Here, we would like to investigate how volcanic lightning might have operated and was influenced by changes in those environmental conditions. For this purpose, we have developed an experimental device, which consists of a gas-tight modification of a shock-tube apparatus, to investigate experimental discharges in decompressed jets of gas and volcanic ash particles under varying atmospheric conditions. The setup acts as a Faraday cage, capable of measuring discharges close to the vent. The gas inside the particle collector tank is sampled by crimp cap bottles and analysed by gas chromatography. We modified the enveloping atmospheric composition and pressure (200 mbar – 4 bar) and the transporting gas phase (argon and nitrogen).We have tested atmospheres containing carbon dioxide, nitrogen and carbon monoxide to mimic early Earth conditions and obtained discharges with similar magnitude to those achieved in an air atmosphere. We have also varied the atmospheric pressure and observed that decreasing the atmospheric pressure results in less discharges. The results of the experiments demonstrate that it is the coupling between gas and ash particles which largely governs the occurrence and magnitude of discharges close to the jet nozzle. Nitrogen as transporting gas results in fewer discharges compared to argon, emphasizing the importance of the composition of the transporting gas phase in the jet charging and discharging mechanisms. The preliminary results point to active volcanic settings under varying atmospheric conditions as multivariate environment for the emergence of life and thus our experiments continue.

Detection of geophysical signatures associated with a geologic event, such as a volcanic eruption, is key to understanding the underlying physical processes and making an accurate hazard assessment. Magma reservoirs are the main repositories for eruptible magma, and understanding them requires the ability to detect and interpret changes in the magmatic system from surface measurements. Traditionally, monitoring for these changes has been done with seismic and geodetic approaches, both of which require dynamic ‘active’ changes within the magmatic system. Seismic monitoring relies on the number and location of earthquakes, to indicate magma migrating within the magmatic system. In contrast, geodetic efforts rely on identifying ground inflation events which have traditionally been interpreted to represent recharge of magma from a deep parental source into shallower crustal reservoirs. Neither of these techniques is sensitive to the petrology or temperature of the magma though. Thus, additional monitoring techniques able to detect ‘static’ phase changes in the evolving magma and the thermal structure of the magma reservoir are needed. The magnetotelluric method, measures subsurface electrical properties and is sensitive to both ‘magma on the move’ and these petrological changes that occur within the magma reservoir itself. Using Mount St Helens where a detailed magnetotelluric survey was completed during the most recent dome building eruptive phase 2005-06, and is now in a period of quiescence, we compare the original measurements from 2005-06 to repeated measurements in the same locations in 2022 to develop the temporal analysis approaches required for monitoring application. In addition to the repeat campaign we have deployed 4 long-term monitoring stations with continuous data observation and telemetry to local servers. First, qualitative, comparisons of the data from different time periods indicate some significant changes in subsurface conductivity. We will present an overview of the newly acquired data and the monitoring setup and discuss where the most significant changes occur.

Volcanic jet flows in explosive eruptions emit radio frequency signatures, indicative of their fluid dynamic and electrostatic conditions. The emissions originate from sparks supported by an electric field built up by the ejected charged volcanic particles. When shock-defined, low-pressure regions confine the sparks, the signatures may be limited to high-frequency content corresponding to the early components of the avalanche-streamer-leader hierarchy. Here, we image sparks and a standing shock together in a transient supersonic jet of micro-diamonds entrained in argon. Fluid dynamic and kinetic simulations of the experiment demonstrate that the observed sparks originate upstream of the standing shock. The sparks are initiated in the rarefaction region, and cut off at the shock, which would limit their radio frequency emissions to a tell-tale high-frequency regime. We show that sparks transmit an impression of the explosive flow, and open the way for novel instrumentation to diagnose currently inaccessible explosive phenomena., Comment: 9 pages, 6 figures

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.

The eruption of basaltic magmas dominates explosive volcanism on Earth and other planets within the Solar System. The mechanism through which continuous magma fragments into volcanic particles is central in governing eruption dynamics and the ensuing hazards. However, the mechanism of fragmentation of basaltic magmas is still disputed, with both viscous and brittle mechanisms having been proposed. Here we carry out textural analysis of the products of ten eruptions from seven volcanoes by scanning electron microscopy. We find broken crystals surrounded by intact glass that testify to the brittle fragmentation of basaltic magmas during explosive activity worldwide. We then replicated the natural textures of broken crystals in laboratory experiments where variably crystallized basaltic melt was fragmented by rapid deformation. The experiments reveal that crystals are broken by the propagation of a network of fractures through magma, and that afterwards the fractures heal by viscous flow of the melt. Fracturing and healing affect gas mobility, stress distribution, and bubble and crystal size distributions in magma. Our results challenge the idea that the grain size distribution of basaltic eruption products reflects the density of fractures that initially fragmented the magma and ultimately indicate that brittle fracturing and viscous healing of magma may underlie basaltic explosive eruptions globally. In explosive basaltic eruptions, brittle fragmentation and subsequent healing by viscous melt are documented by textural analysis of products from ten disparate eruptions, suggesting that grain size may not reflect the initial fracture density of magma.

Degassing dynamics play a crucial role in controlling the explosivity of magma at erupting volcanoes. Degassing of magmatic water typically involves bubble nucleation and growth, which drive magma ascent. Crystals suspended in magma may influence both nucleation and growth of bubbles. Micron- to centimeter-sized crystals can cause heterogeneous bubble nucleation and facilitate bubble coalescence. Nanometer-scale crystalline phases, so-called “nanolites”, are an underreported phenomenon in erupting magma and could exert a primary control on the eruptive style of silicic volcanoes. Yet the influence of nanolites on degassing processes remains wholly uninvestigated. In order to test the influence of nanolites on bubble nucleation and growth dynamics, we use an experimental approach to document how nanolites can increase the bubble number density and affect growth kinetics in a degassing nanolite-bearing silicic magma. We then examine a compilation of these values from natural volcanic rocks from explosive eruptions leading to the inference that some very high naturally occurring bubble number densities could be associated with the presence of magmatic nanolites. Finally, using a numerical magma ascent model, we show that for reasonable starting conditions for silicic eruptions, an increase in the resulting bubble number density associated with nanolites could push an eruption that would otherwise be effusive into the conditions required for explosive behavior.

Volcanic activity occurring in tropical moist atmospheres can promote deep convection and trigger volcanic thunderstorms. These phenomena, however, are rarely observed to last continuously for more than a day and so insights into the dynamics, microphysics and electrification processes are limited. Here we present a multidisciplinary study on an extreme case, where volcanically-triggered deep convection lasted for six days. We show that this unprecedented event was caused and sustained by phreatomagmatic activity at Anak Krakatau volcano, Indonesia during 22–28 December 2018. Our modelling suggests an ice mass flow rate of ~5 × 106 kg/s for the initial explosive eruption associated with a flank collapse. Following the flank collapse, a deep convective cloud column formed over the volcano and acted as a ‘volcanic freezer’ containing ~3 × 109 kg of ice on average with maxima reaching ~1010 kg. Our satellite analyses reveal that the convective anvil cloud, reaching 16–18 km above sea level, was ice-rich and ash-poor. Cloud-top temperatures hovered around −80 °C and ice particles produced in the anvil were notably small (effective radii ~20 µm). Our analyses indicate that vigorous updrafts (>50 m/s) and prodigious ice production explain the impressive number of lightning flashes (~100,000) recorded near the volcano from 22 to 28 December 2018. Our results, together with the unique dataset we have compiled, show that lightning flash rates were strongly correlated (R = 0.77) with satellite-derived plume heights for this event. We thank Dr. Leonardo Mingari of the Barcelona Supercomputing Center for extracting and processing the ERA5 profiles used in our analysis. We thank Dr. Lieven Clarisse from the Free University of Brussels for providing SO2 columns and heights from IASI-A&B. A.T.P. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement H2020-MSCA-COFUND-2016-754433. A.F. and A.C. have been partially funded by the H2020 Center of Excellence for Exascale in Solid Earth (ChEESE) under the Grant Agreement 823844. A.C. acknowledges the LMU Center of Advanced Studies fellowship “Magma to Tephra: Ash in the Earth System”, the European project EUROVOLC (grant agreement number 731070), and the MIUR project Premiale Ash-RESILIENCE. C.C. acknowledges the support of Deutsche Forschungsgemeinschaft project CI 254/2-1. R.B. acknowledges funding from the VESUVIO project within the Supporting Talent in ReSearch (STARS) grant at Università degli Studi di Padova, IT. This paper contains modified Copernicus Sentinel data [2019] processed by A.T.P.

After 50 years of volcanic quiescence, on 19 September 2021, an eruption started on the western flank of the Cumbre Vieja ridge of La Palma, Canary Islands, Spain. The eruption was characterised by simultaneous effusive and explosive activity from a several hundred-meter-long fissure, which later built up a cone and showed variable eruptive behaviour at different vents, suggesting a spatially complex plumbing system. Explosive eruptive activity ranged from mild ash emissions, Strombolian explosions to fire fountaining episodes.We carried out field measurements to study the variable explosive eruptive activity and associated acoustic signals. A single microphone initially deployed at about 2 km SW of the vents from 6 to 11 October was later replaced by an array of 3 microphones from 6 November to 13 December at about 300 m W of the microphone location in October. The microphones (PCB ½” free field acoustic sensors, 3.15-20 kHz frequency range) were each connected to an OptiMeas SmartPro digitiser continuously sampling at 5000 Hz. The digitisers are GPS synchronised for accurate acoustic array processing. The acoustic array was complemented by a thunderstorm detector continuously recording (since 11 October) lightning and electrical activity generated by the volcanic explosions (Vossen et al., 2022). Additionally, at the beginning of November 2021, thermal videos of the eruptive activity were acquired.Preliminary analysis of the large and unique acoustic dataset shows varying waveforms indicating evolving source conditions: eruption intensity, source mechanism, vent geometry, fragmentation depth and amount of ash ejected. Moreover, we observe a variability of frequency (peak and mean) and amplitude with time. Further analysis includes the characterisation of the acoustic source location within the growing volcanic edifice and the comparison and correlation with lightning and thermal infrared data to detail changes in explosive activity related to the evolving eruption sources. Caron E.J. Vossen et al. (2022), Electrical activity of the 2021 Cumbre Vieja eruption, EGU22-8052.

The eruption of fragmental magma of basaltic composition is the most frequent type of explosive volcanism on Earth and in the Solar System, with eruptions spanning from centuries of persistent, weak explosions, through days to months of lava fountains and ash emissions, to rare, global-scale catastrophic events. The mechanism through which continuous magma fragments into volcanic particles is central in governing eruption dynamics and the ensuing hazards. However, the mechanism of fragmentation of basaltic magmas is still disputed, with both viscous and brittle mechanisms having been proposed for different eruptive styles. Here we carry out textural analysis of the products of ten eruptions from seven volcanoes by Scanning Electron Microscope. We find broken crystals surrounded by intact glass and other features that testify to the brittle fragmentation of basaltic magmas during explosive activity differing in style, intensity and magnitude. We then replicated the natural textures of broken crystals in laboratory experiments where variably crystallised basaltic melt was fragmented by rapid deformation. The experiments reveal that crystals are broken by the propagation of a network of fractures through magma, and that afterwards many of the fractures heal by viscous flow of the melt. Fracturing and healing affect gas mobility, stress distribution, and bubble and crystal size distributions in magma. Our results challenge the idea that the grain size distribution of basaltic eruption products reflects the density of the fractures that initially fragmented the magma. Unrecognised broken crystals and accompanying textures appear in previous literature covering many eruptions spanning Hawaiian lava fountains, catastrophic Plinian events, and more. We conclude that brittle fragmentation and subsequent healing are not specific to some eruption style or pyroclast type, but are ubiquitous factors controlling basaltic explosive volcanism.

Between 19 September and 13 December 2021 (85 days), a flank eruption took place along the Cumbre Vieja ridge (La Palma Island), one of the most active volcanic centers of Canary Islands. The last 7000 years of Cumbre Vieja activity has been characterized by a combination of effusive and explosive eruptions. These generated both cinder cones and lava flows. The previous event occurred between October 26 and November 28, 1971 (eruption of Teneguía). The 2021 eruption was characterized by the alternate (and often simultaneous) emission of lava flows, lava fountains and tephra plumes along a ~1 km-length fissure consisting of about ten vents that built a cinder cone complex. The southern vents were mostly associated with the generation of tephra plumes and lava fountains, while the northern vents were mostly associated with the generation of lava flows. The ~12 km2 lava flow field on the west side of the island reached the sea on September 28, forming a new lava delta and interacting with sea water producing lava haze (i.e. laze). Even though tephra was sedimented all over La Palma and sometimes reached the neighboring islands, the cumulative tephra deposit is mostly elongated towards the southwest and the northeast due to the prevailing wind direction, reaching a maximum thickness southwest of the fissure. Both lava fountains and more explosive tephra plumes contributed to the formation of the tephra deposit. Tephra plumes were associated with variable intensity reaching a few kilometers of altitude (

Volcanic lightning is a common phenomenon observed during explosive eruptions of high magnitude and intensity. Lightning observations in milder explosive eruptions, generally of basaltic composition, are less frequent, arising the question of whether electrification may be a common feature over the whole spectrum of explosive styles and magma compositions.The 2021 eruption of Cumbre Vieja on the island of La Palma (Canary Islands, Spain) started on 19 September 2021, continuously producing lava flows and tephra of average basanite to tephrite composition during 85 consecutive days, eventually generating a >200 m tall scoria cone (about 1220 m a.s.l.) and a vast compound lava flow field. Lightning was frequently observed in the plume during different phases of the explosive activity. This eruption provided the rare opportunity to monitor variations in the electrical activity on various time scales continuously over several weeks. We measured such electrical activity using a lightning detector operating in the extremely low frequency range with a sample rate of 100 Hz (Vossen et al., 2021), installed about 2 km away from the active vents. The detector was deployed on 11 October 2021 and recorded continuously until the end of the eruption on 13 December 2021, thus providing a unique dataset of its kind.Lightning activity varied during the eruption with alternating hours-long periods of high intensity continuous lightning production as well as minutes-long isolated episodes with interposed periods of quiet. Stable fair-weather conditions over La Palma recorded by meteorological stations during the whole eruption (exception made for a thunderstorm episode on 26 November 2021), allow a confident attribution of the changeable lightning activity to the explosive activity of the scoria cone. Here, we present volcanic lightning and electrification timeseries as a function of the varying explosive activity as observed through thermal videography and acoustic recordings (Cigala et al., 2022). Vossen, C. E. J., Cimarelli, C., Bennett, A. J., Geisler, A., Gaudin, D., Miki, D., Iguchi, M., and Dingwell, D. B. (2021). Long-term observation of electrical discharges during persistent Vulcanian activity. Earth Planet. Sci. Lett., 570, 117084. https://doi.org/10.1016/j.epsl.2021.117084.

Stratovolcanoes are often characterized by cyclic eruptive activity marked by effusive-explosive transitions between dome-forming and Plinian eruptions. Guagua Pichincha volcano (Ecuador) has been a location of such cyclicity for the past ~2000 years with recurrent Plinian eruptions in the 1st century, 10th century, and CE 1660 which were separated by dome-forming eruptions such as the recent 1999-2001 eruption. Short time-scale shifts in activity between dome-forming, Vulcanian and Subplinian eruptions also occurred repeatedly in the period September to December 1999. These cycles are therefore a prominent example of effusive-explosive transitions at varying timescales. Here, we investigate the reasons for such shifts in activity, by focusing on degassing and outgassing processes within the conduit, and their roles in pressurization and ensuing eruption dynamics. We have coupled a petrophysical and vesicle textural analysis of dacites from the CE 1660 Plinian eruption and the dome-forming, Vulcanian and Subplinian 1999-2001 eruptions, with percolation models in order to better understand the role of degassing on eruptive style. We demonstrate that the transition from dome-forming to Plinian activity correlates with differences in phenocryst content and consequently in inferred bulk viscosity. A lower initial viscosity is inferred for the Plinian case, consistent with faster ascent, closed-system degassing, explosive fragmentation and eruption. In contrast, dome-forming phases are promoted by a higher magma viscosity, with slower ascent enhancing gas escape and microlite crystallization, yielding effusive activity.

Volcanic lightning—a near ubiquitous feature of explosive volcanic eruptions—possesses great potential for the analysis of volcanic plume dynamics. To date, the lack of quantitative knowledge on the relationships between plume characteristics hinders efficient data analysis and application of the resulting parameterizations. We use a shock-tube apparatus for rapid decompression experiments to produce particle-laden jets. We have systematically and independently varied the water content (0–27 wt%) and the temperature (25–320 °C) of the particle-gas mixture. The addition of a few weight percent of water is sufficient to reduce the observed electrification by an order of magnitude. With increasing temperature, a larger number of smaller discharges are observed, with the overall amount of electrification staying similar. Changes in jet dynamics are proposed as the cause of the temperature-dependence, while multiple factors (including the higher conductivity of wet ash) can be seen responsible for the decreased electrification in wet experiments.

Very low frequency and wide-band lightning detection networks can detect major volcanic plumes via their intense electrical and lightning activity. However, the high number of non-detected explosive episodes confirmed by direct observations, reveals the limits of these systems in the detection of the more frequent smaller ash-rich explosive events. Here, we use a data-efficient thunderstorm detector to observe electrical discharges generated from July 2018 to January 2020 by the persistent Vulcanian activity of Minamidake crater at Sakurajima volcano in Japan. Two thunderstorm detectors recorded the electrical activity produced by explosions at Minamidake crater from a distance of 3 and 4 km from the active vents. The instruments measured the induced current due to the change in electric field with time within the extremely low frequency range (1-45 Hz). Using a volcanic lightning detection algorithm together with the catalogue of volcanic explosions compiled by the Japan Meteorological Agency (JMA) and Tokyo Volcanic Ash Advisory Center (Tokyo VAAC), the number of electrical discharges, the electrical discharge rate and the total amount of measured voltage were determined for each individual explosive event. In addition, the start of the electrical discharges was compared to the explosion onset as provided by the JMA (with a one-minute time resolution). The sensors detected electrical discharges in 71% of the 724 recorded explosions. Our detection algorithm successfully recognises the presence/absence of electrical discharges with an accuracy of 73%. We find a non-linear positive correlation between the number of discharges and the plume height. Moreover, we find that the maximum electrical discharge rate and the maximum amount of measured voltage by a single discharge also increase with plume height. Fracto- and tribo-electrification appear to be the dominant plume electrification mechanisms. Even for the few explosive events that exceeded the −10 °C isotherm, the timescale of electrical activity seems to be too short for ice nucleation to make a significant contribution to the plume electrification. Finally, for 12% of the electrically-active explosive events, discharges were detected by the sensors more than a minute before the JMA explosion onset. Our results show the capability of our detectors in pinpointing the inception of electrified explosive episodes in real-time and in providing an indication of the magnitude of each explosion, demonstrating their effectiveness as a cost- and data-efficient instrumentation for the monitoring of explosive ash emissions at active volcanoes.

Textile production is among the most fundamental and more complex technologies in human prehistory, but is under-investigated due to the perishable nature of fibrous materials. Here we report a discovery of five textile fragments from a prehistoric (fourth-third millennium cal BC) burial deposit located in a small cave at Peñacalera in Sierra Morena hills, near Córdoba, Southern Spain. These textiles accompanied a set of human remains as grave goods, together with other organic elements such as fragments of wood and cork, and some pottery vessels. They were characterized and dated using digital microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Accelerator Mass Spectrometry. Two of the fragments described here are the oldest examples of loom-woven textiles in the Iberian Peninsula, dating from the second half of the fourth millennium cal BC. This correlates chronologically with the first appearance of loom weights in the archaeological record of this region. The more recently dated textile is the earliest preserved cloth intentionally coloured with cinnabar in the western Mediterranean. The Peñacalera finds are a key reference for understanding the development of textile technologies during the Neolithic and Copper Age in western Europe and beyond., The site was discovered by speleologists A. Aljama and R. Bermúdez, who, together with M.J. Martínez-Fernández and G.M. Lara we thank for their cooperation throughout the fieldwork. Dating was carried out thanks to the Spanish Ministry of Science, Innovation and Universities-Universidad de Granada, Juan de la Cierva-Incorporación Agreement IJCI-2016-27812 (2016, by R.M.M.S.), and the funding provided in the framework of the project “Archaeobiology of the Neolithic of the Southern Iberian Peninsula” (NeArqBioSI) A-HUM-460-UGR18 funded by Consejería de Economía, Conocimiento, Empresas y Universidad, FEDER Programme—Junta de Andalucía-Universidad de Granada, Call 2019. M.G.’s work was supported by the European Research Council (Grant Agreement FP/2007-2013-312603).

Volcanic activity occurring in tropical moist atmospheres can promote deep convection and trigger volcanic thunderstorms. These phenomena, however, are rarely observed to last continuously for more than a day and so insights into the dynamics, microphysics and electrification processes are limited. Here we present a multidisciplinary study on an extreme case, where volcanically-triggered deep convection lasted for six days. We show that this unprecedented event was caused and sustained by phreatomagmatic activity at Anak Krakatau volcano, Indonesia during 22-28 December 2018. Our modelling suggests an ice mass flow rate of ~5 × 10

Monitoring and predicting extreme atmospheric events, such as deep convective systems, is very challenging especially when they develop locally in a short time range. Despite the great improvement in model parametrization and the use of satellite measurements, there are still large uncertainties on the knowledge of the dynamical processes of deep convective systems at local scale.We use an innovative approach integrating a dense network of in situ measurements and satellite-based observations/products for the improvement of meteorological nowcasting at airport spatial scale focusing on the Malpensa airport (Italy). We add to the standard atmospheric parameters analysis, the information of integrated water vapour and lightning spatio-temporal behaviour (potential heavy rain precursors) during heavy rain phenomena detected by meteorological radars. The study is based on the anomaly of each atmospheric parameter during a convective event in comparison to its climatology in non-pre-convective environment, so that we are able to detect the variation with respect to the “standard” conditions. The ground based GNSS receivers (allowing the determination of the integrated water vapour trend before and during the storm), together with the lightning detectors, the weather stations (providing the trend of temperature, humidity and wind fields), the radiosondes and the GNSS radio occultations (allowing the estimation of vertical profiles of temperature, pressure and humidity) provide information on the pre-convective and non-pre-convective environment as a 3D picture of the atmospheric conditions.The final goal is the test of a severe weather events nowcasting algorithm with high spatial resolution, and based on neural networks, for improving aviation safety. This is followed by the development of a user-friendly tailored final product, easily understandable by the Air Traffic Management stakeholder.We have collected more than 600 cases suitable to develop the neural network algorithm. We show here the algorithm implementation and the meteorological characterization of deep convection usually developing on the Malpensa airport area.

Volcanoes are increasingly better monitored around the world. Nonetheless, the detection and monitoring of volcanic ash plumes remains difficult, especially in remote areas. Intense electrical activity and lightning in volcanic plumes suggests that electrical monitoring of active volcanoes can aid the detection of ash emissions in near real-time. Current very low frequency and wide-band thunderstorm networks have proven to be able to detect plumes of large magnitude. However, the time delay and the relatively high number of non-detected explosive episodes show that the applicability of these systems to the detection of smaller (and often more frequent) ash-rich explosive events is limited. Here we use a different type of thunderstorm detector to observe electrical discharges generated by the persistent Vulcanian activity of Minamidake crater at Sakurajima volcano in Japan. The sensors consist of two antennas that measure the induced current due to the change in electric field with time. In contrast to the current thunderstorm networks, these sensors measure within the extremely low frequency range (1-45 Hz) and can detect lightning up to 35 kilometres distance.Two detectors were installed at a distance of 3 and 4 kilometres from Minamidake crater and recorded almost continuously since July 2018. Within this period, the ash plumes reached a maximum height of 5.5 kilometres above the crater rim. Using a volcanic lightning detection algorithm and the catalogue of volcanic explosions compiled by the Japan Meteorological Agency (JMA), the number of electrical discharges was determined for each individual explosive event. In addition, the start of electrical discharges was compared to the eruption onset estimated by the JMA.Preliminary results show that the detector closest to the crater had the highest detection efficiency. It detected electrical discharges during 60% of the eruptions listed by the JMA. This is significantly higher than for the World Wide Lightning Location Network, which detected electrical discharges (in the very low frequency range) within 20 kilometres of Sakurajima for less than 0.005% of the eruptions. Furthermore, the results show that for 40% of the detected eruptions, electrical discharges were detected before the estimated JMA timing. Hence, electrical discharges can mark the inception of the explosion with a higher precision and are an indication of ash emission. This demonstrates the value of the cost-effective sensors used here as a monitoring tool at active volcanoes.

Glass-SO₂ reactions occurring at high temperatures in (terrestrial and extraterrestrial) volcanic environments have received increasing attention in the past years (e.g., Renggli and King 2018; Casas et al. 2019; Renggli et al. 2019), based on both natural and experimental observations. Laboratory studies carried out at high temperatures (>200 °C) demonstrate that volcanic glass in the presence of SO₂ reacts to form surficial sulfate-bearing minerals (e.g., Ayris et al. 2013; Delmelle et al. 2018), mostly calcium sulfate salts (CaSO₄). Thus, high temperature glass-SO₂ interaction acts as a sink for the magmatic S released during explosive volcanic activity, potentially impacting the S budget of large explosive eruptions. Here, we present the results of new experiments aimed at assessing the influence of the glass Ca content on SO2 uptake in the temperature range of 600-800 °C. We exposed haplogranitic glasses to SO₂ for diverse time exposures (5-30 minutes). Rhyolitic composition was chosen due to the ubiquity of Si-rich magmas in large explosive eruptions (Cioni et al. 2000).The experimental glasses were synthesized with an initial HPG8 composition (see Holtz et al. 1992), doped with 1 and 2 wt.% CaO. Furthermore, the role of Fe was tested by doping the glasses with 0, 0.1, 1, 1.5, 2 and 2.5 wt.% FeO and equilibrating them at 1500 °C. Leachates of post-treated glasses were analyzed by ion chromatography in order to determine SO2-uptake and the nature of the sulfate-bearing minerals formed by solid-gas reactions. The bulk redox state of iron (Fe³⁺/Fetotal), was obtained by the K₂Cr₂O₇ potentiometric titration method. Our results show a strong correlation between the amount of Ca in the glasses and the formation of CaSO₄ surficial deposits (i.e. SO₂ uptake), i.e. the HPG8 + 2 wt.% CaO treated samples produced up to 40 % more CaSO₄ than the samples containing 1 wt.% CaO. Higher Fe content in the glass also enhanced formation of CaSO₄. In contrast, the absence of Fe oxide resulted in preferential formation of Na₂SO₄ and K₂SO₄, when compared to the Fe-bearing specimens. Our experiments confirm that high temperature SO₂ uptake by glass is strongly dependent on the Ca content and temperature, with the optimal reaction temperatures being ≥600 °C. Increasing the amount of FeO in the glasses seems to enhance SO2 uptake, although this effect appears to be different for Ca than for Na or K, pointing out a more complex influence of redox dynamics on cation diffusion.

The emergence of the first organic molecules as a fundamental step in the prebiotic assembly of life remains enigmatic. Lightning has been considered as a potential energy source for the synthesis for first organic molecules. The iconic abiotic synthesis experiments: the discharge experiments performed in 1953 by Miller and Urey [1] under simulated reducing atmosphere conditions were conducted in the absence of any geomaterial substrate. Further, new views about the composition of the Early Earth’s atmosphere have been developed which require a revisiting of the Miller experiment.Volcanic lightning associated with volcanism provides a possible energy source, a variety of different volcanic gases and possible catalysts to synthesize a variety of primitive organic molecules. Volcanic ash particles are known for their porosity, high surface area and significant surface reactivity. Volcanic plumes themselves provide a high variety of volcanic gases including, but not limited to reducing ones, and therefore may enlarge the spectrum for possibly available gas compositions in the Early Earth atmosphere.Recent laboratory studies have successfully recreated near-vent volcanic lightning under laboratory conditions [2,3]. We will present first insights from volcanic discharge experiments under different atmospheric compositions, varying in CO2, and N2 composition to mimic some first Early Earth conditions. Special focus is given to the role of ash particles as a catalyst and container as well as the influence of gas composition on the yield of organic compounds. [1] Miller, S.L. (1953). A production of amino acids under possible primitive earth conditions. Science, 117, 528-529. [2] Cimarelli, C., Alatorre-Ibargüengoitia, M.A., Kueppers, U., Scheu, B. and Dingwell, D.B. (2014). Experimental generation of volcanic lightening. Geology, 42, 79-82.[3] Gaudin, D. and Cimarelli, C. (2019). The electrification of volcanic jets and controlling parameters: A laboratory study. EPSL, 513, 69-80.

Magma degassing dynamics play an important role controlling the explosivity of volcanic eruptions. Some of the largest explosive eruptions in history have been fed by silica-rich magmas in volcanic systems with complex dynamics of volatiles degassing. Degassing of magmatic water drives bubble nucleation and growth, which in turn increases magma buoyancy and results in magma ascent and an eventual eruption. While micro- to milli-meter sized crystals are known to cause heterogeneous bubble nucleation and to facilitate bubble coalescence, the effects of nanolites remains mostly unexplored. Nanolites have been hypothesized to be a primary control on the eruptive style of silicic volcanoes, however the mechanisms behind this control remains unclear.Here we use an experimental approach to show how nanolites dramatically increase the bubble number density in a degassing silicic magma compared to the same magma without nanolites. The experiments were conducted using both nanolite-free and nanolite-bearing rhyolitic glass with different low initial water content. Using an Optical Dilatometer at 1 bar ambient pressure, cylindrical samples were heated at variable rates (1-30 °C min-1) to final temperatures of 820-1000 °C. This method allowed us to continuously monitor the volume, and hence porosity evolution in time. X-ray computed microtomography (µCT) and Scanning Electron Microscope (SEM) analyses revealed low and high bubble number densities for the nanolite-free and nanolite-bearing samples respectively.Comparing vesicle number densities of natural volcanic rocks from explosive eruptions and our experimental results, we speculate that some very high naturally occurring bubble number densities could be associated with nanolites. We use a magma ascent model with P-T-H2O starting conditions relevant for known silicic eruptions to further underpin that such an increase in bubble number density caused driven by the presence of nanolites can feasibly turn an effusive eruption to an eventually explosive behavior.

Volcanic ash generated by explosive eruptions can act as ice-nucleating particles, promoting freezing of supercooled water droplets in the eruption plume and the ambient atmosphere, and so impacting processes such as plume electrification, ash aggregation, and cloud glaciation. Our initial study of a compositional range of milled ash and glass materials demonstrated that mineralogy is likely a key property influencing ice nucleation by ash.1 However, the surface properties of ash are modified by interaction with magmatic gases in the hot core of the eruption plume, and it is not known how such in-plume interactions might affect the ice-nucleating activity (INA) of ash.Here we investigated the influence of high temperature solid-gas interactions on the INA of three milled ash (Tungurahua, Astroni, Etna) and two milled mineral (K-feldspar, quartz) materials. Sub-samples of these materials were exposed to pure water vapour (H2O) or mixtures of water vapour with HCl(g) (H2O-HCl) or SO2(g) (H2O-SO2) under an 800 °C/400 °C heating sequence in the Advanced Gas-Ash Reactor.2 The INA of the non-treated and treated samples was then assessed using a microlitre Nucleation by Immersed Particle Instrument.3 The H2O treatment decreased the INA relative to that of the non-treated sample for all materials, and the H2O-HCl treatment decreased the INA to the same extent or more. Conversely, the H2O-SO2 treatment increased the INA (Tungurahua ash, Etna ash), or decreased the INA 1) to a lesser extent than the other treatments (Astroni ash), 2) to the same extent as the other treatments (quartz), or 3) to a greater extent than the other treatments (K-feldspar).The depression in INA induced in all cases by the H2O treatment may relate to dehydroxylation of the silicate materials’ surfaces at high temperatures. On the other hand, differing effects on INA of the H2O-HCl and H2O-SO2 treatments is inferred to relate to contrasting reactivities of these materials towards HCl(g) and SO2(g). Water leachates of the samples suggest that chloride and sulphate salts (e.g., NaCl, CaSO4) formed on the H2O-HCl- and H2O-SO2-treated ash surfaces, respectively, but not on the H2O-HCl- and H2O-SO2-treated mineral surfaces. Additional tests suggest that the changes in INA observed for these treated ash samples do not reflect a ‘solute effect’4 imparted by the chloride or sulphate salts in water, implying that the ice-nucleating properties of the ash surfaces themselves are somehow changed by reaction with HCl(g) and SO2(g).Surface-sensitive analyses could be useful to elucidate how sample surfaces have been modified by the different solid-gas interactions at the scale relevant for ice nucleation, and so potentially shed light on the cause of the depression and enhancement in INA observed here. The possibility that in-plume reaction with SO2(g) can increase the INA of volcanic ash in particular merits further investigation, as a previous line of thought has been that exposure of silicate particles to this acidic gas decreases INA. 1Maters et al. (2019) Atmos. Chem. Phys., 19, 5451–5465. doi:10.5194/acp-19-5451-20192Ayris et al. (2015) Bull. Volcanol., 77, 104. doi:10.1007/s00445-015-0990-33Whale et al. (2015) Atmos. Meas. Tech., 8, 2437-2447. doi:10.5194/amt-8-2437-20154Whale et al. (2018) Chem. Sci., 9, 4142-4151. doi:10.1039/C7SC05421A

Many of the grand challenges in volcanic and magmatic research are focused on understanding the dynamics of highly heterogeneous systems and the critical conditions that enable magmas to move or eruptions to initiate. From the formation and development of magma reservoirs, through propagation and arrest of magma, to the conditions in the conduit, gas escape, eruption dynamics, and beyond into the environmental impacts of that eruption, we are trying to define how processes occur, their rates and timings, and their causes and consequences. However, we are usually unable to observe the processes directly. Here we give a short synopsis of the new capabilities and highlight the potential insights that in situ observation can provide. We present the XRheo and Pele furnace experimental apparatus and analytical toolkit for the in situ X-ray tomography-based quantification of magmatic microstructural evolution during rheological testing. We present the first 3D data showing the evolving textural heterogeneity within a shearing magma, highlighting the dynamic changes to microstructure that occur from the initiation of shear, and the variability of the microstructural response to that shear as deformation progresses. The particular shear experiments highlighted here focus on the effect of shear on bubble coalescence with a view to shedding light on both magma transport and fragmentation processes. The XRheo system is intended to help us understand the microstructural controls on the complex and non-Newtonian evolution of magma rheology, and is therefore used to elucidate the many mobilization, transport, and eruption phenomena controlled by the rheological evolution of a multi-phase magmatic flows. The detailed, in situ characterization of sample textures presented here therefore represents the opening of a new field for the accurate parameterization of dynamic microstructural control on rheological behavior.

Observations at numerous volcanoes reveal that eruptions are often accompanied by continual radio frequency (CRF) emissions. The source of this radiation, however, has remained elusive until now. Through experiments and the analysis of field data, we show that CRF originates from proximal discharges driven by the compressible fluid dynamics associated with individual volcanic explosions. Blasts produce flows that expand supersonically, generating regions of weakened dielectric strength in close proximity to the vent. As erupted materialcharged through fragmentation, friction, or other electrification processtransits through such a region, pyroclasts remove charge from their surfaces in the form of small interparticle spark discharges or corona discharge. Discharge is maintained as long as overpressured conditions at the vent remain. Beyond describing the mechanism underlying CRF, we demonstrate that the magnitude of the overpressure at the vent as well as the structure of the supersonic jet can be inferred in real time by detecting and locating CRF sources.

Volcanic lightning studies have revealed that there is a relatively long-lasting source of very high frequency radiation associated with the onset of explosive volcanic eruptions that is distinct from radiation produced by lightning. This very high frequency signal is referred to as continual radio frequency (CRF) due to its long-lasting nature. The discharge mechanism producing this signal was previously hypothesized to be caused by numerous, small (10-100m) leader-forming discharges near the vent of the volcano. To test this hypothesis, a multiparametric data set of electrical and volcanic activity occurring during explosive eruptions of Sakurajima Volcano in Japan was collected from May to June 2015. Our observations show that a single CRF impulse has a duration on the order of 160ns (giving an upper limit on discharge length of 10m) and is distinct from near-vent lightning discharges that were on the order of 30m in length. CRF impulses did not produce discernible electric field changes and occurred in the absence of a net static electric field. Lightning mapping data and infrared video observations of the eruption column showed that CRF impulses originated from the gas thrust region of the column. These observations indicate that CRF impulses are not produced by small, leader-forming discharges but rather are more similar to a streamer discharge, likely on the order of a few meters in length. Plain Language Summary This paper investigates the origin of a radio frequency (RF) signal previously termed continual RF that has been detected from the ash plumes of explosive volcanic eruptions. Continual RF had been hypothesized to be caused by many very small lightning-like discharges on the order of 100m in length occurring at the vent of the volcano. To test this hypothesis, we conducted a multiparametric observational experiment at Sakurajima Volcano in Japan. We measured continual RF during eruptions of Sakurajima in 2015 and found that continual RF is a collection of short duration RF impulses, on the order of 160ns in duration. These RF impulses are distinct from those typically produced by lightning. We also observed small, 30-m lightning discharges occurring near the volcanic vent that were distinct from the source of continual RF. Our observations show that continual RF is caused by an electrical discharge that is more simple than even a very small (approximate to 100m) lightning discharge. We conclude that continual RF is caused by numerous, small, electrical discharges similar to streamer discharges, on the order of a few meters in length.

Volcanic eruptions are associated with a wide range of electrostatic effects. Increasing evidence suggests that high-altitude discharges (lightning) in maturing plumes are driven by electrification processes that require the formation of ice (analogous to processes underpinning meteorological thunderstorms). However, electrical discharges are also common at or near the volcanic vent. A number of “ice-free” electrification mechanisms have been proposed to account for this activity: fractocharging, triboelectric charging, radioactive charging, and charging through induction. Yet, the degree to which each mechanism contributes to a jet's total electrification and how electrification in the gas-thrust region influences electrostatic processes aloft remains poorly constrained. Here, we use a shock-tube to simulate overpressured volcanic jets capable of producing spark discharges in the absence of ice. These discharges may be representative of the continual radio frequency (CRF) emissions observed at a number of eruptions. Using a suite of electrostatic sensors, we demonstrate the presence of size-dependent bipolar charging (SDBC) in a discharge-bearing flow for the first time. SDBC has been readily associated with triboelectric charging in other contexts and provides direct evidence that contact and frictional electrification play significant roles in electrostatic processes in the vent and near-vent regions of an eruption. Additionally, we find that particles leaving the region where discharges occur remain moderately electrified. This degree of electrification may be sufficient to drive near-vent lightning higher in the column. Thus, near-vent discharges may be underpinned by the same electrification mechanisms driving CRF, albeit involving greater degrees of charge separation.

The April to May 2010 eruption of Eyjafjallajokull (Iceland) volcano was characterized by a large compositional variability of erupted products. To contribute to the understanding of the plumbing system dynamics of this volcano, we present new EMPA and LA-ICP-MS data on groundmass glasses of ash particles and minerals erupted between April 15 and 22. The occurrence of disequilibrium textures in minerals, such as resorption and inverse zoning, indicate that open system processes were involved in determining the observed compositional variability. The variation of major and trace element data of glasses corroborates this hypothesis indicating that mixing between magma batches with different compositions interacted throughout the whole duration of the eruption. In particular, the arrival of new basaltic magma into the plumbing system of the volcano destabilized and remobilized magma batches of trachyandesite and rhyolite compositions that, according to geophysical data, might have intruded as sills over the past 20 years beneath the Eyjafjallajokull edifice. Two mixing processes are envisaged to explain the time variation of the compositions recorded by the erupted tephra. The first occurred between basaltic and trachyandesitic end-members. The second occurred between trachyandesite and rhyolites. Least-squares modeling of major elements supports this hypothesis. Furthermore, investigation of compositional histograms of trace elements allows us to estimate the initial proportions of melts that interacted to generate the compositional variability triggered by mixing of trachyandesites and rhyolites.

Shallow‐water coral reef ecosystems, particularly those already impaired by anthropogenic pressures, may be highly sensitive to disturbances from natural catastrophic events, such as volcanic eruptions. Explosive volcanic eruptions expel large quantities of silicate ash particles into the atmosphere, which can disperse across millions of square kilometres and deposit into coral reef ecosystems. Following heavy ash deposition, mass mortality of reef biota is expected, but little is known about the recovery of post‐burial reef ecosystems. Reef regeneration depends partly upon the capacity of the ash deposit to be colonised by waterborne bacterial communities and may be influenced to an unknown extent by the physiochemical properties of the ash substrate itself. To determine the potential for volcanic ash to support pioneer bacterial colonisation, we exposed five well‐characterised volcanic and coral reef substrates to a marine aquarium under low light conditions for 3 months: volcanic ash, synthetic volcanic glass, carbonate reef sand, calcite sand and quartz sand. Multivariate statistical analysis of Automated Ribosomal Intergenic Spacer Analysis (ARISA) fingerprinting data demonstrates clear segregation of volcanic substrates from the quartz and coral reef substrates over 3 months of bacterial colonisation. Overall bacterial diversity showed shared and substrate‐specific bacterial communities; however, the volcanic ash substrate supported the most diverse bacterial community. These data suggest a significant influence of substrate properties (composition, granulometry and colour) on bacterial settlement. Our findings provide first insights into physicochemical controls on pioneer bacterial colonisation of volcanic ash and highlight the potential for volcanic ash deposits to support bacterial diversity in the aftermath of reef burial, on timescales that could permit cascading effects on larval settlement.

Volcanic activity occurring in tropical moist atmospheres can promote deep convection and trigger volcanic thunderstorms. Intense heating at ground surface and entrainment of moist air generates po...

Accurate estimates of the atmospheric impacts of large eruptions on the environment are complicated by a paucity of models for gas-magma or gas-rock interactions that can occur in the subsurface. It is in these environments that high-temperature scavenging of magmatic gases, released during eruptions, may play a major role, resulting in significant time-dependence of the bulk gas budget of the major erupted volatile species. Recent experimental work has identified the principal mechanisms involved in high-temperature scavenging in SO2- and HCl-dominated gas environments, but has neglected the effect of humidity and in-dome gas-magma reactions. Here we present scaled experimental results for the scavenging potential in SO2-H2O mixtures using rhyolitic glass particles above the acid dew point at 200–800 °C. First, we reproduce previous results for anhydrous SO2 scavenging. Such scavenging is accommodated by the growth of CaSO4 crystals on the surface of glass present on ash and limited by the temperature- and particle size-dependent diffusion of Ca2+ to the surface of the glass. Subordinate concentrations of Na2SO4 and potassium-bearing salts also grow on the glass surfaces. Na+ and K+ diffusion appear to be the limiting mechanisms for the formation of these salts, but once the bulk glass network is relaxed and equilibrates oxidation state above ∼600 °C, the diffusion of these cations is inhibited by charge compensation with Fe3+. In SO2-H2O mixed-gas atmospheres, the diffusion of Ca2+ appears unaffected by the activity of H2O on the ash surface. In contrast, the diffusion of Na+ and K+ toward the ash surface is enhanced. We speculate that this occurs by alkali exchange with inward diffusing H+. In hydrous atmospheres, the diffusion of Na+ and K+ is also markedly less at the threshold oxidation temperature. This oxidation temperature is reduced to lower values as the water activity at the surface is increased by increasing the partial pressure of H2O. Taken together, these results enable the exploration of scenarios for in-dome processes where either open-system or batch outgassing prevails through fractures filled with populations of welding volcanic ash. Such scenarios predict that a large fraction of the SO2 flowing through the ash-filled fracture networks may be scavenged in permeable fractured domes, which act as scrubbing filters, potentially explaining some unexpectedly low SO2 emissions from rhyolitic dome-forming eruptions.

Ash aggregation is a common phenomenon in particle-laden environments of volcanic eruption plumes and pyroclastic density currents. Many of these initially fragile aggregates gain sufficient mechanical strength to remain intact after atmospheric transport and deposition. Several processes contribute to ash aggregate stability, including electrostatic and hydrostatic bonding, ice formation, and cementation by salt precipitates. Here, we compare leachate chemistry from aggregates from a variety of eruption and sedimentation conditions, ranging from dry magmatic eruptions with immediate deposition, to eruptions through seawater. The leachate data shows that the broad window of opportunity for aggregation and aggregate break-up may be used to qualitatively constrain suspended ash concentration and its temporal evolution. We show that aggregation rate and aggregate stability largely depend on the availability of external water and salt source. In particular, high humidity and extensive salt precipitation in seawater environments, such as during the Surtseyan eruptions, promote high aggregation rates and aggregate stability, with accordingly accentuated proximal deposition and aggregate concentration in the deposits. On the other hand, low humidity and salt concentrations during dry magmatic eruptions promote less aggregation and more efficient aggregate break-up, explaining the rarity of aggregates in the deposits. These results have strong implications for the ash budget in volcanic plumes and associated models of plume dispersal and related hazards.