Explosive Events Research Articles

Artificial Intelligence and Machine Learning Tools for Improving Early Warning Systems of Volcanic Eruptions: The Case of Stromboli.

Explosive volcanic blasts can occur suddenly and without any clear precursors. Many volcanoes have erupted in the last years with no evident change in the eruptive parameters and with dramatic consequences for the population living nearby the volcano and the tourists visiting the active areas. In recent years, a big effort has been made to develop Early Warning systems to issue timely alerts to the population. At Stromboli volcano, the development of sensitive instruments to measure the deformation (tilt) of the ground has revealed that the volcano edifice is inflating tens of minutes before the explosion following a recurrent exponential ramp-like pattern. This scale-invariant of ground deformation has allowed the development of a quasi-deterministic Early Warning system which is operative since 2019. In this article we show how Artificial Intelligence and Machine Learning can be successfully applied to improve the efficiency and the sensitivity of Early Warning systems, provided the availability of a comprehensive experimental data set on past explosive events. The approach presented here for the Stromboli case demonstrates promising results also in forecasting the intensity of explosive events, offering valuable insights and new perspectives into the potential risks associated with volcanic activities.

Three-dimensional peridynamic modeling of damage and penetration in composite plates exposed to localized explosive blasts

Localized failures in composites can lead to catastrophic consequences in some vehicles and systems, such as airplanes and submarines. The paper presents a new three-dimensional (3D) peridynamic model to explore the localized explosive effects on composite plates. The study utilizes the peridynamic method to simulate fractures and deformations in composite plates when exposed to localized explosive blasts. Accurate prediction of composites' performance during explosive blast events is crucial in the design process to avoid the deadly effects of their failures. This study highlights the following novelties: (1) We present, for the first time, a novel 3D mesh-free model to simulate the fracture and damage behavior of composite plates when exposed to explosive blasts; (2) The adopted numerical modeling technique enables highly efficient simulations of fractures and failures in composites when compared with other mesh-based numerical models; (3) We introduce a new mathematical framework to reflect the explosive pressure loads through different composite layers; (4) The study provides an accessible and efficient tool for engineers and researchers to enhance the design of composites in several industries instead relying on limited-access commercial software packages. In addition to the previous novelties, the paper presents a new parametric study that investigates the performance of several composite plates, such as titanium-aramid and aluminum-aramid composites, in explosive blast scenarios. Moreover, the roles of explosive mass and plate thickness in the failure mechanisms of composites are examined.

Experimental Measurements of Explosion Effects Propagating in the Real Geological Environment—Correlation with Small-Scale Model

This research focuses on comparing small-scale and full-scale measurements of wave propagation from explosions by using scaling relationships to find significant correlations between the two. The study investigates how seismic waves generated by explosions behave in the geological environment. The research covers various aspects such as the development of the model, the explosive materials used, measurement methods, evaluation techniques, and relevant software. A scientific approach based on the principle of backward Fourier transform was used to process and evaluate the data, which helps to filter the frequencies. One of the important calculations discussed is the determination of the attenuation coefficient, which helps to describe how waves attenuate as they pass through a material. The research also deals with dynamic scaling, using the dynamic exponent as a scaling factor to provide a better understanding of the behavior of waves at different scales. By comparing real in situ data with results from small-scale models, the study provides a robust framework for predicting the effects of explosions in complex geological environments. The research results show a high correlation coherence of the statistical data files of up to 4.1%. For dynamic tasks and model scaling, an important result can be pointed out, namely the approximately fourfold decrease in the exponents of the dependence on the distance from the excitation source and the amplitudes between P-waves (0.4316) and R-waves (0.1219). Conclusions are targeted at the possibility of correlating three types of results: small-scale simulations, numerical simulations, and a real full-scale experiment.

Recent Experimental Advances in Solid–Liquid Composites for Impact and Blast Mitigation

The development of high-performance composites for mechanical energy dissipation during impact or explosive events is of vital importance for the safety of personnel and infrastructures. Solid–liquid composites are an emerging class of energy absorbers where a liquid-phase filler is seamlessly integrated into a solid matrix to enhance the impact resistance of the protection target. This innovative approach leverages the distinct properties of both phases and the unique interactions between them to achieve superior performance under high-impact conditions. This paper aims to review the liquid-phase materials used in solid–liquid composites, ranging from neat liquids to complex fluids, including liquid nanofoam and shear-thickening fluids, to provide an in-depth analysis of the fundamental physics underpinning the resulting solid–liquid composites, and to explore how their unique properties contribute to enhanced impact resistance and energy absorption. Furthermore, this paper evaluates the advantages and limitations of these solid–liquid composites and offers insights into future directions for the development of solid–liquid composites in various fields, including personal protective equipment, automotive safety systems, and structural protection.

Research on combined damage characteristics of underwater armor-piercing and explosion based on supercavitating projectile

Recent studies of supercavitating projectiles primarily focus on the formation and evolution of the cavity, as well as its underwater ballistic characteristics, while neglecting the terminal damage effects. Little attention has been given to exploring the combined damage effects of armor-piercing-explosion supercavitating projectiles (APESP). Therefore, this study comparatively analyzes the response processes and failure modes of an underwater aluminum alloy cylindrical shell target under the action of three different types of loads: armor piercing, explosion, and combined armor-piercing and explosion. This study investigates the underwater combined damage mechanisms of the APESP, clarifies each damage phase under the combined effect, discusses the advantages of damage resulting from the combined armor-piercing and explosion effect based on the target responses and damage modes, and explores the reasons for dissipation of explosion energy. The results show that: the APESP combines localized point damage characteristics of armor piercing with overall surface damage features of underwater explosion. Depending on load stages and target responses, the target response process under the action of the APESP can be divided into the hydrodynamic ram phase, penetration phase, shock wave phase, stable vibration phase, and bubble pulsation phase. The entire physical system can be abstracted as a low-frequency series spring system (equivalent to bubble pulsation frequency) with high-frequency external energy input, based on the energy relationship of the medium and the structure. The concept of the 'blower effect' is proposed based on target behavior during the stable vibration phase. Following the application of different loads, the plastic deformation of the target in a stable state is ranked as: underwater explosion > combined armor-piercing and explosion > underwater armor piercing. Supercavity, shell casing and penetration hole will cause the dissipation of explosion energy.

Single-cell proteomics delineates murine systemic immune response to blast lung injury

Victims of explosive events frequently suffer from blast lung injuries. Immune system has been implicated in the pathogenesis of this disease. However, systemic immune responses underlying the progression and recovery of injury repair remain poorly understood. Here, we depict the systemic landscape of immune dysregulation during blast lung injury and uncover immune recovery patterns. Single-cell analyses reveal dramatic changes in neutrophils, macrophages, monocytes, dendritic cells, and eosinophils after a gas explosion, along with early involvement of CD4 T, CD8 T, and Th17 cells. We demonstrate that myeloid cells primarily exert functions during the acute phase, while the spleen serves as an alternative source of granulocytes. Granulopoiesis is initiated in the bone marrow at a later stage during blast lung injury recovery, rather than at the acute stage. These findings contribute to a better understanding of the pathogenesis and provide valuable insights for potential immune interventions in blast lung injury.

Candidate detection of GRB221009A by Yangbajing muon telescope

Long gamma-ray bursts (GRBs) can be generated by the collapse of a rapidly rotating massive star into a black hole and are the brightest known explosive events in the Universe. GRB221009A is the most energetic gamma-ray burst ever recorded, providing delayed detection of very high energy photons that challenge the standard propagation mechanisms, possibly suggesting exotic physics phenomena. An excess, synchronous with the ignition of GRB221009A, is detected in the rate of the Yangbajing muon telescope. A preliminary assessment of the significance of this excess limits the probability of a chance coincidence to less than 10−3. The hypothetical mechanisms for producing a muon excess induced by the GRB are exotic/puzzling. If confirmed by further investigations, this excess would add another feature to the many anomalies observed in this extreme astrophysical event.

Emergency Capability Evaluation of Port-Adjacent Oil Storage and Transportation Bases: An Improved Analytic Hierarchy Process Approach

The large-scale storage and stable supply of oil products are essential for national energy security and economic development. As the economy expands and energy demands rise, centralized storage and supply systems become increasingly vital for ensuring the efficiency and reliability of oil product distribution. However, large oil storage depots present substantial safety risks. In the event of fires, explosions, or other accidents, emergency response efforts face stringent demands and challenges. To enhance the emergency response capabilities of oil storage and transportation bases (OSTBs), this paper proposes an innovative approach that integrates the improved analytic hierarchy process (IAHP) with the Entropy Weight Method (EMW) to determine the combined weights of various indices. This approach reduces the subjective bias associated with the traditional analytic hierarchy process (AHP). The emergency response capabilities of OSTBs are subsequently evaluated through fuzzy comprehensive analysis. An empirical study conducted on an OSTB in the Zhoushan archipelago quantitatively assesses its emergency preparedness. The results show that the base excels in pre-incident prevention, demonstrates robust preparedness and response capabilities, and exhibits moderate recovery abilities after incidents. These findings provide a theoretical foundation for reducing the likelihood of accidents, enhancing emergency response efficiency, and mitigating the severity of consequences. Practical recommendations are also offered based on the results.

Explosive eruption processes inferred from high-frequency seismic waveforms of eruption tremor and explosion events

Summary We investigated the relation between high-frequency seismic signals and eruption size and duration using seismic data of eruption tremor and explosion events generated during sub-Plinian and Vulcanian eruptions, respectively, at various volcanoes. We estimated source amplitude functions from seismic envelope seismograms in the 5−10 Hz band, in which S-waves are assumed to radiate isotropically. Because seismic data associated with explosive eruptions can be contaminated by infrasound signals, we confirmed that contamination did not significantly affect the source amplitude functions quantified from our analysed waveforms. We approximated the source amplitude functions of eruption tremor and explosion events by quadrilateral and triangular shapes. For eruption tremor, the durations of the source amplitude functions increased with decreasing slope of the initial phase, i.e. between onset and maximum amplitude. For explosion events, both the maximum and cumulative amplitudes of the source amplitude functions increased with increasing slope of the initial phase, but the overall durations clustered around a typical value. Moreover, the initial phase durations of eruption tremor were longer than those of explosion events. Based on eruption models proposed by previous studies, Vulcanian and sub-Plinian eruptions have been thought to be triggered by accumulation of magma at a shallow part in a conduit and mixing of cool mushy magma with hot fresh magma in a reservoir, respectively. The above differences between the source amplitude functions of eruption tremor and explosion events can be explained by the distinct eruption triggering processes of sub-Plinian and Vulcanian eruptions. Our results suggest that source amplitude functions are useful for investigating eruption processes and estimating eruption sizes and durations for seismic eruption monitoring.

The characteristics and mechanism of NaHCO3 compound fly ash in suppressing gas explosions in pipeline networks

Gas has been widely concerned due to its importance in the industrial and energy fields. In order to improve the inhibition effect of gas explosion, under the self-constructed pipe network system, the inhibition of gas explosion by composite inhibitor of fly ash and NaHCO3 with different ratios was investigated, and the microscopic inhibition mechanism of the two kinds of powders on the explosion of gas was investigated based on the method of density functional theory and transition state theory from the perspective of molecular dynamics. The results show that: the composite powder explosion suppression is better than a single powder, explosion suppression effect with the increase in the proportion of the mass of NaHCO3 significantly improve the 5 groups of conditions NaHCO3 loading of 40% (by mass) is the best, this time, the explosion of the peak overpressure, the peak flame propagation velocity, the peak flame temperature compared to the maximum reduction in the percentage of the measures taken for the maximum of 74.42%, 81.93%, 68.71%. In addition, NaHCO3, fly ash effectively inhibit the key primitive reaction of gas explosion. When the temperature reaches a certain point, the two and O*, O2, OH* and H* reaction rate higher than the rate of CH4 oxidation chain reaction, the dominant reaction, the maximum difference in rate constants of 70.95, 58.81, 60.06, 44.94. The study of the transition from the macro-scale to the molecular level of the study, in-depth understanding of the mechanism of explosion suppression, to reduce the risk of explosion from the ground up, and enriches the Gas explosion prevention and control of the theoretical system, for the operators to provide a strong technical guarantee for safe production.

Blast wave ingress into a room through an opening – Review of past research and US DoD UFC 3-340-02

Blast wave ingress into a room through a facade opening results in complex pressure-time loadings on interior surfaces due to shock diffraction and interior reflections. The U.S. DoD UFC 3-340-02 Structures to Resist the Effects of Accidental Explosions includes a method to predict internal loading for such cases. Parameters such as the opening size, room dimensions and the external pressure wave characteristics influence the interior loading. Recent work suggests that the UFC methodology might overpredict the interior loading by some 600%. Such conservatism can result in over-engineered or prohibitively expensive protective solutions. In this paper we critically review the methodology of the UFC, that of Kaplan’s preceding work (on which the UFC relies), and the experimental data that informed both these works. Through a series of 45 case-studies we compare the UFC and Kaplan’s predictions with those of a computational fluid dynamics (CFD) model. The UFC consistently overpredicts the CFD area-averaged peak pressure of the back wall by up to 290% and the side-wall by up to 425%. Similarly, the UFC overpredicted the CFD side wall positive phase impulse by up to 565%. By contrast, the UFC predicted back wall positive phase impulse was similar to the CFD results. As our CFD results for side and back walls are area averaged, and not solely for the wall centre-point, as in other recent work, our paper gives support for the use of CFD prediction over the UFC for cost-effective design of structures to resist blast ingress.

Visualization of integrated failure consequences of hazardous chemical leakage and explosion

Dangerous chemicals are widely present in various aspects of people's lives, but they often pose risks of leakage and explosion during transportation and storage, resulting in severe casualties and property damage. Firstly, this paper proposes a visualization method applicable to comprehensive failure consequences of hazardous chemical storage tanks. This method considers the toxic hazard range of chemical leaks and the blast overpressure injury range of leak clouds and visualizes the comprehensive failure consequences. Secondly, FLACS is employed to simulate a major leakage and explosion accident at Jinyu Petrochemical Co., Ltd. in Linyi City. The simulation reproduces the leakage and explosion processes and verifies the reliability of the simulation results. Finally, the proposed method is used to visualize the comprehensive failure consequences of this accident, providing comprehensive visual results. The method presented in this paper can serve as a theoretical reference for predicting the development of accidents and clarifying their consequences.

Structural response of steel-concrete composite panels to near field simultaneous blast and fragmentation loading

Steel-concrete composite sandwich panels are used in blast doors or blast walls to protect personnel and equipment in explosive environments due to their superior performance against blast effects. In the design of such panels, most design methods treat blast and fragment loading independently for far-field explosions. However, the synergistic effects of combined blast and fragments loading should be accounted for in close-in explosion scenarios. In this study, a field test program was conducted to assess the damage of the steel-concrete composite panels subjected to close-in explosion of cased charges at various scaled distance between 0.39 and 0.78 m/kg1/3. Characterization test of cased charge detonation was performed to explore the combined loading effect. The analysis includes the pressure-time history from the cased charge detonation, distribution of the fragment masses and velocities over the test panels. The structural damage and response of the composite panels against the combined loading effects was measured. The results indicated that in addition to the damage from the blast wave, the panel was remarkably damaged by the fragment impact. Despite the significant structural damage, the panels maintained its structural integrity after the tests. Additionally, quasi-static load tests were conducted on the panels to quantify their load resistant differences in pristine condition and various damaged conditions due to the explosive effects.

Magma recharge at Manam volcano, Papua New Guinea, identified through thermal and SO2 satellite remote sensing of open-vent emissions

Manam is one of the most frequently active volcanoes in Papua New Guinea and is a top contributor to global volcanic volatile emissions due to its persistent open-vent degassing. Here, we present a multi-year time series (2018–2021) of thermal and SO2 emissions for Manam from satellite remote sensing, which we interpret in the context of open-vent feedback between magma supply, reservoir pressure, and outgassing. We classify the time series into four phases based on the varying SO2 flux and observe a transient, yet substantial, increase in time-averaged SO2 flux from background levels of ~ 0.6 to ~ 4.72 kt day−1 between March and July 2019. We also identify a transition from temporally coupled to decoupled gas and thermal emissions during this period which we explain in the context of a magma recharge event that supplied new, volatile-rich magma to the shallow plumbing system beneath Manam. We infer that the arrival of this recharge magma triggered the series of eruptions between August 2018 and March 2019. These explosive events collectively removed 0.18 km3 of degassed residual magma and signalled the onset of a renewed period of unrest that ultimately culminated in a major eruption on 28 June 2019. We quantify the magnitude of “excess” degassing at Manam after the removal of the inferred residual magma. SO2 emissions reveal that ~ 0.18 km3 of magma was supplied, but only ~ 0.08 km3 was erupted between April 2019 and December 2021. We highlight how multi-parameter remote sensing observations over months to years enable the interpretation of open-vent processes that may be missed by short-duration campaign measurements.

Analysis of fuel storage tanks under internal deflagrations with different venting technologies: an experimental and numerical study

This study investigates small-scale fuel storage tanks subjected to internal methane-air explosions, focusing on three depressurization technologies using roof ventilation to mitigate overpressure and damage. Tests with low methane-air concentrations were conducted to generate a pseudo-static internal pressure. This approach minimized scale effects and aligned internal pressure frequency with real-scale tank behavior during deflagrations. The first prototype features a tank with a frangible roof activated by localized brittle failure of stitch welds around the roof-to-shell junction. This confirms that stitched weld patterns ensure controlled brittle failure with activation pressure estimated by a simplified equation. The second technology employs a sequential ventilation strategy, starting with a small hinged panel followed by stitch weld failure, managing low to medium-intensity explosions with the small vent alone, and allowing rapid operational recovery. In severe explosions, the hinged door facilitates earlier activation of the frangible roof, reducing the initial pressure rise rate and controlling the roof opening direction. Lastly, the study explores tanks with commercial explosion vent panels as an alternative to traditional frangible roofs, offering a practical solution for retrofitting existing tanks. Each technology enhances safety in fuel storage facilities by effectively managing internal pressures during explosive events.

Investigation on the inhibition effect and mechanism of hydrogen explosion by 2-bromo-3,3,3-trifluoropropene

This study investigated the effect of 2-bromo-3,3,3-trifluoropropene (2-BTP, C3H2BrF3) on hydrogen explosion behavior through a combination of experiments and simulations. The maximum explosion pressure (pmax), maximum pressure rise rate ((dp/dt)max), and critical inhibition concentration (CIC), across different equivalence ratios (Φ) and inhibitor concentrations (V), were obtained via experiments. The changes in adiabatic flame temperature, mole fraction of active radicals and sensitivity coefficient throughout the reaction were analyzed using CHEMKIN. The fuel-like properties of 2-BTP and the carbon monoxide (CO) produced by decomposition led to a promoting effect on the lean hydrogen explosion, primarily due to the elementary reactions R31, R806 and R882. When Φ≥1.0, the capture of active radicals via elementary reactions such as R908, R1507, and R88 was enhanced, resulting in the dominance of inhibition and a corresponding inhibitory effect. Notably, 2-BTP exhibited an inhibitory effect for (dp/dt)max at any equivalence ratio. The CIC decreased from 10% to 4% when increasing equivalence ratios from 0.6 to 2.0. This work provides crucial data and a theoretical foundation for the prevention and control of hydrogen explosions.

DDAH1 deficiency exacerbates cerebral vascular endothelial dysfunction by aggravating BBB disruption and oxidative stress in thoracic blast-induced brain injury

As terrorist incidents and underground explosion events have become more frequent around the world, brain injury caused by thoracic blast exposure has been more highlighted due to its injured organ, subsequent social and economic burden. It has been reported dimethylarginine dimethylaminohydrolase 1 (DDAH1) plays important roles in regulating vascular endothelial injury repair and angiogenesis, but its role in thoracic blast-induced brain injury remains to be explained. This study seeks to investigate the mechanism of DDAH1 on thoracic blast-induced brain injury. 40 C57BL/6 wild type mice and 40 DDAH1 knockout mice were randomly and equally divided into control group and blast group, respectively. The integrity of blood-brain barrier (BBB) was detected by Evans blue test. The serum inflammatory factors, nitric oxide (NO) contents, and asymmetric dimethylarginine (ADMA) levels were determined through ELISA. HE staining and reactive oxygen species (ROS) detection were performed for histopathological changes. Western blot was used to detect the proteins related to oxidative stress, tight junction, focal adhesion, vascular endothelial injury, and the DDAH1/ADMA/eNOS signaling pathway. DDAH1 deficiency aggravated thoracic blast-induced BBB leakage, inflammatory response, and the increased levels of inflammatory-related factors. Additionally, DDAH1 deficiency also increased ROS generation, MDA and IRE-α expression. Regarding cerebral vascular endothelial dysfunction, DDAH1 deficiency increased the expression of MCAM, FN1, LIMK1, VEGF, MMP9, Vimentin and N-cadherin, while lowering the expression of FMR1, Occludin, claudin-3, claudin-5, Lyn, LIMA1, Glrb, Sez6, Dystrophin, and phosphorylation of VASP. Also, DDAH1 deficiency exacerbated explosion-induced increase of ADMA and decrease of eNOS activity and NO contents. Thus, we conclude that DDAH1 could prevent cerebral vascular endothelial dysfunction and related injury by inhibiting ADMA signaling and increasing eNOS activity in thoracic blast induced brain injury.

Morphological evidence of an explosive eruption event in October 2023 at Sofu Seamount in the Izu-Bonin Arc

Sofu Seamount is one of the poorly studied submarine edifices in the Izu-Bonin Arc. There is no known historical record of volcanic activity, thus its eruptive history and volcanic features are completely unknown. However, on October 9, 2023, at least 14 T-phases originating near Sofu Seamount were observed. An 80 km-long raft of floating pumice was observed off Sofu Seamount on October 20. These spatially and temporally coherent observations indicate that an eruption occurred from a deep seafloor vent somewhere near Sofu Seamount. In order to investigate the origin of this submarine eruption, we collected new bathymetric data in 2024 and compared it with older bathymetric data collected in 2022, 2007 and 1987. The bathymetric comparison revealed evidence for explosive eruptions at Sofu Seamount between 2022 and 2024. During this time, a crater, 1.6 km wide and 400 m deep, was formed at the pre-existing central cone on the western part of Sofu Seamount, whose pre-eruption summit depth was 737 m. The maximum negative depth change was 451 m and a volume of 430 × 106 m3 was removed due to the crater formation. A dome-like structure, 1 km wide and 100 m high was constructed northeast of the crater, part of which collapsed as a result of the crater formation. The volcanic products were transported over 6 km downslope and emplaced on the adjacent seafloor where positive depth changes up to 75 m were observed. Landslides also occurred around the crater. The largest slide on the northern flank formed a slide scar that is 3.8 km long and 1 km wide. Here, the maximum negative depth change was 148 m and 140 × 106 m3 of material was removed. The slide materials were deposited downslope where positive depth changes up to 61 m were observed. Considering the occurrence of the earthquake swarm on October 2–8, 2023 and T-phase swarm on October 9, the timing of the eruption can be constrained within October 2023.An analysis of volcanic and tectonic morphology reveals a distinct tectonic influence on volcanism at Sofu Seamount. Sofu Seamount is located in a back-arc rift zone where the N–S trending Torishima and Sofu Rifts have formed. The new bathymetric data showed that the rifts have an asymmetric structure and can be divided into two segments, which are identified here as inner and outer rifts. The inner rifts are bounded by steeper fault scarps that have experienced more subsidence than the outer rifts. The western part of Sofu Seamount, where the eruption occurred, is located within the inner rifts, and is heavily dissected by rifting-related normal faults, while the eastern part is located outward of the inner rifts and is not dissected by faults. The October earthquake swarm was more concentrated in the area of the inner rifts and some large earthquakes showed normal fault focal mechanisms with a tension axis approximately in E–W direction. Our morphological observations combined with recent seismic events show that the inner rifts are the currently active tectonic structures and young volcanism at Sofu Seamount is controlled by the back-arc rifting of the Izu-Bonin Arc.

Direct Imaging of a Prolonged Plasma/Current Sheet and Quasiperiodic Magnetic Reconnection on the Sun

Magnetic reconnection is widely believed to be the fundamental process in the solar atmosphere that underlies magnetic energy release and particle acceleration. This process is responsible for the onset of solar flares, coronal mass ejections, and other explosive events (e.g., jets). Here, we report direct imaging of a prolonged plasma/current sheet along with quasiperiodic magnetic reconnection in the solar corona using ultra-high-resolution observations from the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory and the Solar Dynamics Observatory/Atmospheric Imaging Assembly. The current sheet appeared near a null point in the fan–spine topology and persisted over an extended period (≈20 hr). The length and apparent width of the current sheet were about 6″ and 2″, respectively, and the plasma temperature was ≈10–20 MK. We observed quasiperiodic plasma inflows and outflows (bidirectional jets with plasmoids) at the reconnection site/current sheet. Furthermore, quasiperiodic reconnection at the long-lasting current sheet produced recurrent eruptions (small flares and jets) and contributed significantly to the recurrent impulsive heating of the active region. Direct imaging of a plasma/current sheet and recurrent null-point reconnection for such an extended period has not been reported previously. These unprecedented observations provide compelling evidence that supports the universal model for solar eruptions (i.e., the breakout model) and have implications for impulsive heating of active regions by recurrent reconnection near null points. The prolonged and sustained reconnection for about 20 hr at the breakout current sheet provides new insights into the dynamics and energy release processes in the solar corona.

Probabilistic hazard analyses for a small island: methods for quantifying tephra fall hazard and appraising possible impacts on Ascension Island

Proximal to the source, tephra fall can cause severe disruption, and populations of small volcanically active islands can be particularly susceptible. Volcanic hazard assessments draw on data from past events generated from historical observations and the geological record. However, on small volcanic islands, many eruptive deposits are under-represented or missing due to the bulk of tephra being deposited offshore and high erosion rates from weather and landslides. Ascension Island is such an island located in the South Atlantic, with geological evidence of mafic and felsic explosive volcanism. Limited tephra preservation makes it difficult to correlate explosive eruption deposits and constrains the frequency or magnitude of past eruptions. We therefore combined knowledge from the geological record together with eruptions from the analogous São Miguel island, Azores, to probabilistically model a range of possible future explosive eruption scenarios. We simulated felsic events from a single vent in the east of the island, and, as mafic volcanism has largely occurred from monogenetic vents, we accounted for uncertainty in future vent location by using a grid of equally probable source locations within the areas of most recent eruptive activity. We investigated the hazards and some potential impacts of short-lived explosive events where tephra fall deposits could cause significant damage and our results provide probabilities of tephra fall loads from modelled events exceeding threshold values for potential damage. For basaltic events with 6–10 km plume heights, we found a 50% probability that tephra fallout across the west side of the island would impact roads and the airport during a single explosive event, and if roofs cannot be cleared, three modelled explosive phases produced tephra loads that may be sufficient to cause roof collapse (≥ 100 kg m−2). For trachytic events, our results show a 50% probability of loads of 2–12 kg m−2 for a plume height of 6 km increasing to 898–3167 kg m−2 for a plume height of 19 km. Our results can assist in raising awareness of the potential impacts of tephra fall from short-lived explosive events on small islands.