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UNLABELLED: On 15 January 2022, Hunga volcano erupted, creating an extensive and high-reaching umbrella cloud over the open ocean, hindering traditional isopach mapping and fallout volume estimation. In MODIS satellite imagery, ocean surface water was discolored around Hunga following the eruption, which we attribute to ash fallout from the umbrella cloud. By relating intensity of ocean discoloration to fall deposit thicknesses in the Kingdom of Tonga, we develop a methodology for estimating airfall volume over the open ocean. Ash thickness measurements from 41 locations are used to fit a linear relationship between ash thickness and ocean reflectance. This produces a minimum airfall volume estimate of 1.8-0.4+0.3 km3. The whole eruption produced > 6.3 km3 of uncompacted pyroclastic material on the seafloor and a caldera volume change of 6 km3 DRE. Our fall estimates are consistent with the interpretation that most of the seafloor deposits were emplaced by gravity currents rather than fall deposits. Our proposed method does not account for the largest grain sizes, so is thus a minimum estimate. However, this new ocean-discoloration method provides an airfall volume estimate consistent with other independent measures of the plume and is thus effective for rapidly estimating fallout volumes in future volcanic eruptions over oceans. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00445-024-01744-6.

Pumice cones are volcanic landforms that exist worldwide, but whose eruption has never been observed. Interpretations of these eruptions vary significantly in style, intensity, and magnitude, pertinent for volcanic hazard assessment. Aluto volcano (Ethiopia) provides an unprecedented insight into the hazardous nature of these enigmatic eruptions. We investigate nine such pumice cones, and find that they are the product of moderate-intensity explosive eruptions that develop a sustained but unsteady eruption column, deposit lapilli- to block-sized tephra close to the vent forming pumice cones, can deposit distal tephra from an umbrella cloud, produce pyroclastic density currents by repeated partial column-collapse, and end with the emplacement of silicic lava. Like basaltic pyroclastic cones, pumice cones can also undergo collapse by lava flow emplacement. Alongside recent evaluation of distal tephras, we suggest that these eruptions, at least at Aluto, vary in intensity and magnitude from violent-Strombolian to sub-Plinian, and each follow a remarkably similar sequence of eruptive processes.

New data on the composition of the pyroclastic deposits of the Krasheninnikov caldera allowed us to correlate it to the previously studied tephra horizon Geys30, which until recently was erroneously attributed to an eruption within the Geysernaya caldera. Pyroclastic flow deposits from the eruption that led to the formation of the Krasheninnikov caldera were found on the southern shore of Kronotsky Lake, and its distal tephra was found in the sediments of the Central Kamchatka Depression (CKD) at a distance of up to 200 km from the source (from Milkovo to Kliuchi villages). The age of this tephra was previously estimated at ~30 ka, which now allows us to accept this estimate for the Krasheninnikov caldera. The identification of the tephra of the caldera-forming eruption in distal sections allows a minimum estimate of the erupted pyroclastic volume of ~13 km3 and the eruption magnitude of 6.1.

This paper provides data on the April 11, 2023 eruption of Sheveluch Volcano. The impact of the eruption has been assessed. The directed explosion destroyed the lava dome which took over 42 years to grow. According to the data acquired just before the eruption, the lava dome had a volume of about 0.53 km3. The eruption produced a field of explosive ejecta ∼70 km2 in area and 0.49 km3 in volume. The directed explosion was accompanied by pyroclastic flows which traveled for distances of 25–30 km from the volcano. The associated ashfall had a length of over 200 km. The weight of an ash sample varied between 1.2 and 43.9 kg/2, depending on the distance to the volcano. The area of ash deposits (with the weight of ash samples over 50 g/m2) was about 17 thousand m2, the volume of the ash deposits was 0.09 km3. Considered in relation to the total volume of ejecta (over 0.60 km3), the April 11, 2023 eruption of Sheveluch should be termed a great catastrophic eruption of this century. [ABSTRACT FROM AUTHOR]

Rapid and simple estimation of the mass eruption rate (MER) from column height is essential for real‐time volcanic hazard management and reconstruction of past explosive eruptions. Using 134 eruptive events from the new Independent Volcanic Eruption Source Parameter Archive (IVESPA, v1.0), we explore empirical MER‐height relationships for four measures of column height: spreading level, sulfur dioxide height, and top height from direct observations and as reconstructed from deposits. These relationships show significant differences and highlight limitations of empirical models currently used in operational and research applications. The roles of atmospheric stratification, wind, and humidity remain challenging to detect across the wide range of eruptive conditions spanned in IVESPA, ultimately resulting in empirical relationships outperforming analytical models that account for atmospheric conditions. This finding highlights challenges in constraining the MER‐height relation using heterogeneous observations and empirical models, which reinforces the need for improved eruption source parameter data sets and physics‐based models. Plain Language Summary: Explosive volcanic eruptions expel gas and tephra in the form of a volcanic column (or plume) that rises into the atmosphere. Two important metrics characterizing these eruptions are the maximum rise height and the eruptive intensity, that is, the rate at which material is emitted from the eruptive vent. Understanding the relationship between these parameters is critical for reconstructing past volcanic events and managing hazards during volcanic crises. In this study, we use a new database of well‐characterized eruptions to constrain simple relationships between column height and eruptive intensity. We distinguish four different measurements of column height: the maximum height reached by tephra from observations and from analysis of deposits, the height at which ash spreads in the atmosphere, and the height reached by volcanic sulfur gases. We show that each height category has a distinct relationship with the eruption intensity, enabling volcanologists and risk managers to use the relationship most appropriate to the measurements available to them. Despite the improved level of detail, our data set cannot resolve any systematic influence of atmospheric conditions such as wind and humidity on eruption column height, highlighting difficulties in measuring volcanic eruption characteristics and understanding their dynamics. Key Points: We provide empirical scaling relationships between mass eruption rate (MER) and column height using a new database with 134 volcanic eventsWe constrain bespoke relationships and their uncertainties for four height metrics to support ash dispersion forecasters and researchersWe detect no clear atmospheric influence on scaling relationships, highlighting required improvements of scaling models and the database [ABSTRACT FROM AUTHOR]

San Miguel (or Chaparrastique) volcano, El Salvador, erupted on the 29th December 2013, after almost 40 years of quiescence. Initial vent-clearing explosions ejected ballistic blocks and produced a pyroclastic density current (PDC) that flowed down the upper flanks. Plume rise speeds peaked at 50–70 m s-1 and declined over time. The main phase of the VEI 2 eruption produced a Subplinian plume that dispersed 106 m3 ash >20 000 km2 across El Salvador in to Honduras. Plume structure was complex due to strong wind shear and to contributions from co-PDC ash. Tephra fall deposits dispersed westwards include a basal white ash layer of ash-coated clasts and ash aggregates, a grey fine ash co-PDC layer, and a layer of coarse ash to fine lapilli-grade scoria. The eruption provides a useful case study to understand the range of volcanic activity at the volcano and to refine hazard maps.

Abstract Rapid and simple estimation of the mass eruption rate (MER) from column height is essential for real‐time volcanic hazard management and reconstruction of past explosive eruptions. Using 134 eruptive events from the new Independent Volcanic Eruption Source Parameter Archive (IVESPA, v1.0), we explore empirical MER‐height relationships for four measures of column height: spreading level, sulfur dioxide height, and top height from direct observations and as reconstructed from deposits. These relationships show significant differences and highlight limitations of empirical models currently used in operational and research applications. The roles of atmospheric stratification, wind, and humidity remain challenging to detect across the wide range of eruptive conditions spanned in IVESPA, ultimately resulting in empirical relationships outperforming analytical models that account for atmospheric conditions. This finding highlights challenges in constraining the MER‐height relation using heterogeneous observations and empirical models, which reinforces the need for improved eruption source parameter data sets and physics‐based models.

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. • A deep explosive submarine eruption from water depths exceeding 700 m was revealed at Sofu Seamount in the Izu-Bonin Arc. • Repeat bathymetric surveys combined with other observations constrained the timing of the eruption on October 9, 2023. • The young volcanism at Sofu Seamount is controlled by back-arc rifting in the Izu-Bonin Arc. [ABSTRACT FROM AUTHOR]

• Magma in Etna's fall stratified eruption was extremely volatile-rich (9600 ppm CO 2). • Magma ascended from storage at the Moho to the surface in <1–5 days. • High volatiles and fast ascent likely caused explosive intensity of this picritic magma. The 3930 BP Fall Stratified (FS) eruption at Mt. Etna is a rare example of a highly explosive eruption of primitive (picritic) magma directly from the mantle. The eruption produced ash plumes up to an estimated 20 km height, leading to a volcanic explosivity index (VEI) 4 (subplinian). Given its volatile-rich and primitive nature, the FS magma may have ascended rapidly from great depths to avoid fractionation and mixing within the extensive plumbing system beneath Etna. To determine the pressures from which the FS magma derived, we perform rehomogenization experiments on melt inclusions hosted in Fo 90–91 olivines to resorb shrinkage bubbles and determine the initial H 2 O and CO 2 in the melt. With measured CO 2 concentrations of up to 9600 ppm, volatile solubility models yield magma storage pressures of 630–800 MPa. These correspond to depths of 24–30 km, which are comparable to the seismologically estimated Moho. Therefore, the magma's high CO 2 concentration must come from carbon in the mantle (likely from subducted carbonates), as opposed to assimilation of shallow (<10 km) crustal carbonates. Diffusion modeling of H 2 O and forsterite zonation profiles in clear, euhedral, and crystallographically oriented olivines indicates rapid ascent of magma directly from its source region to the surface. Forsterite profiles exhibit a narrow rim of growth zoning but no detectable diffusional zoning, reflecting maximum ascent times of 1–5 days. Eighteen measured H 2 O profiles result in remarkably uniform decompression rates of 0.47 MPa/s (95% confidence interval of 0.16–1.28 MPa/s), which is among the fastest measured for basaltic-intermediate magmas. These decompression rates indicate that the final stage of magma ascent over the region in which H 2 O degasses (between the surface and ∼ 15 km) occurred extremely fast at ∼ 17.5 m/s. This eruption may provide a link between primary magma composition and eruption intensity: we propose that the unusually explosive nature of this picritic eruption was driven by high H 2 O and CO 2 concentrations, which led to continuously rapid ascent without stalling, all the way from the Moho. [ABSTRACT FROM AUTHOR]

Las calderas volcánicas, abundantes tanto en la Tierra como en la Luna, son de gran interés para los vulcanólogos, principalmente por sus grandes dimensiones y por los grandes volúmenes que emiten. En el presente trabajo se considera la dinámica de la formación de calderas por erupciones de muy alta explosividad por medio del análisis de como se produce el fracturamiento de la superficie terrestre por causa de actividad ígnea violenta. Esto lleva a la definición de la “típica caldera de explosión”, que es un prototipo de varias calderas formadas recientemente, en la escala histórica de tiempo. Existen tres ejemplos de ese tipo de calderas: Tambora (Sumbawa), Krakatau (Estrecho de Sunda) y Novarupta (Alaska). La caldera de Tambora es el mejor ejemplo bien documentado del origen de una típica caldera de explosión y que no ha producido erupciones importantes subsecuentes a su formación. La estructura subyacente a la caldera Tambora se discute y se compara con la de la caldera de Krakatau formada en 1883, la segunda erupción más grande en el tiempo histórico. De allí, en contraste con las calderas típicamente basálticas del “tipo colapso”, se define el “tipo Tambora” de caldera como una del “tipo explosión” de gran tamaño, que puede alcanzar diámetros de hasta 10 km. Este concepto de caldera tipo Tambora resulta útil para comprender y caracterizar la estructura y las componentes de otras grandes calderas del mundo. Grandes calderas de explosión completamente desarrolladas, tales como las calderas Aso y Aira en Kyushu, Japón se discuten y se interpretan a partir de datos geofísicos como calderas compuestas: En esas calderas se han producido grandes erupciones adyacentes produciendo emisiones masivas de productos piroclásticos y causando que sus estructuras originales alcanzaran anchuras en exceso de 10 km. doi: https://doi.org/10.22201/igeof.00167169p.2022.61.1.2204

The impact of hazardous pyroclastic density currents (PDCs) increases with runout distance, which is strongly influenced by the mass flux. This article shows that the mass flux of a PDC may derive not only from vent discharge during the eruption, but also from partly hot, temporary stores (accumulations) of aerated pyroclastic material perched high on the volcano. The unforeseen PDC at Fuego volcano (Guatemala) on 3 June 2018 happened c.1.5 hr after the eruption climax. It overran the village of San Miguel Los Lotes causing an estimated 400+ fatalities. Analysis of the facies architecture of the deposit combined with video footage shows that a pulsatory block‐and‐ash flow flowed down the Las Lajas valley and rapidly waxed, the runout briefly increasing to 12.2 km as it filled and then spilled out of river channels, entered a second valley where it devastated the village and became increasingly erosive, prior to waning. Paleomagnetic analysis shows that the PDC contained only 6% very hot (>590°C) clasts, 39% moderately hot (∼200°C–500°C) clasts, and 51% cool (<200°C) clasts. This reveals that the block‐and‐ash flow mostly derived from collapse of loose and partly hot pyroclastic deposits, stored high on the volcano, gradually accumulated during the last 2–3 years. Progressive collapse of unstable deposits supplied the block‐and‐ash flow, causing a bulk‐up process, waxing flow, channel overspill and unexpected runout. The study demonstrates that deposit‐derived pyroclastic currents from perched temporary tephra stores pose a particular hazard that is easy to overlook and requires a new, different approach to hazard assessment and monitoring. Plain Language Summary: Pyroclastic density currents (PDCs) are one of the most dangerous things to happen at a volcano: hot mixtures of ash, gas, and rocks travel at high speed across the ground as far as tens of kilometers from the volcano. Shortly after a small eruption of El Fuego volcano (Guatemala) on 3 June 2018, an unexpected pyroclastic current flowed 12 km down a valley, destroying the village of San Miguel de Los Lotes and killing hundreds of people. To understand the cause of this catastrophe, we combined information from satellite photos, the deposits and magnetic data that record the temperature of the rock fragments. Results show that a pulsatory, waxing PDC was generated by the collapse of a perched, unstable accumulation of warm, loose tephra that had built up during the previous few years high on the volcano, from previous small eruptions. The tephra accumulation was rapidly and unexpectedly mobilized late during the 3 June eruption. We propose that this phenomenon represents a new, common type of volcanic hazard that can threaten populations near steep, frequently active volcanoes across the world, and that a different approach to assessment and monitoring is needed to help mitigate this new type of hazard. Key Points: Unexpected fatal pyroclastic density currents occurred at El Fuego volcano (Guatemala) on 3 June 2018Deposit field relations, facies, and thermoremanent magnetization indicate that the block‐and‐ash flows were deposit‐derivedCollapse of partly hot, perched, unstable tephra accumulations can cause hazardous "deposit‐derived PDCs" requiring a new approach to monitoring [ABSTRACT FROM AUTHOR]

Mocho-Choshuenco volcano has produced several highly explosive eruptions during its history, which make it one of the most hazardous volcanoes in the southern volcanic zone of Chile, although it is still relatively little studied to date. We present a geochemical study of the products of the sub-Plinian, andesitic, Enco eruption that occurred about 1600 years ago. We determined the major and trace elements compositions, as well as the volatile (H2O, CO2, Cl, and S) contents of melt inclusions trapped in minerals (olivine, plagioclase, and pyroxene) using electron microprobe, ion microprobe (SIMS), and 3D confocal Raman mapping. Though the whole-rock composition of the Enco magma is andesitic (60.2 ± 1.1 wt.% SiO2), the melt inclusions have SiO2 contents ranging from 50.3 to 67.3 wt.%, following the magmatic series of Mocho-Choshuenco, and the compositions of the most mafic melt inclusions are close to those of the most mafic erupted magmas. Geochemical modeling indicates that mixing occurred between a mafic magma and an andesitic-to-dacitic magma. Glass analysis revealed typical parental arc magma values for H2O (2.6–3.8 wt.%), S (116–1936 ppm), and Cl (620–1439 ppm). However, CO2 contents are very high in some melt inclusions with concentrations above 4000 ppm (measured in the glass), suggesting trapping depths > ~ 17–22 km. Presence of solid carbonates inside inclusion-hosted bubbles clearly indicates that the CO2 contents measured in the glass phase were minimum values. We conclude that a CO2-rich basaltic magma ascended and mixed with a shallower andesitic magma. The magma cooled and exsolved high amounts of CO2, which may have dramatically increased the pressure and triggered the highly explosive Enco eruption. [ABSTRACT FROM AUTHOR]

Explosive volcanic eruptions can inject sulfur dioxide (SO2) into the stratosphere to form aerosol particles that modify Earth’s radiation balance and drive surface cooling. Eruptions involving interactions with shallow layers (≤500 m) of surface water and ice modify the eruption dynamics that govern the delivery of SO2 to the stratosphere. External surface water controls the evolution of explosive eruptions in two ways that are poorly understood: 1) by modulating the hydrostatic pressure within the conduit and at the vent, and 2) through the ingestion and mixing of external water, which governs fine ash production and eruption column buoyancy flux. To make progress, we couple one-dimensional models of conduit flow and atmospheric column rise through a novel “magma-water interaction” model that simulates the occurrence, extent and consequences of water entrainment depending on the depth of a surface water layer. We explore the effects of hydrostatic pressure on magma ascent in the conduit and gas decompression at the vent, and the conditions for which water entrainment drives fine ash production by quench fragmentation, eruption column collapse, or outright failure of the jet to breach the water surface. We show that the efficiency of water entrainment into the jet is the predominant control on jet behavior. For an increase in water depth of 50–100 m, the critical magma mass eruption rate required for eruption columns to reach the tropopause increases by an order of magnitude. Finally, we estimate that enhanced emission of fine ash leads to up to a 2-fold increase in the mass flux of particles < 125 μm to spreading umbrella clouds, together with up to a 10-fold increase in water mass flux, conditions that can enhance the removal of SO2 via chemical scavenging and ash sedimentation. On average, compared to purely magmatic eruptions, we suggest that hydrovolcanic eruptions will be characterized by reduced climate forcing. Our results suggest one possible mechanism for volcano-climate feedback: temporal changes with climate in surface distributions of water and ice may modify the relative global frequency or dominance of hydrovolcanic eruption processes, modulating, in turn, global patterns in volcano-climate forcing.

Weizhou island, located in the north margin of the South China Sea (SCS), is characterized by multi-stage volcanism, several eruption styles and eruption craters, and is also the youngest Quaternary volcanic island in China. An eruption on this island may pose high risk to life and property. However, the eruptive history of Weizhou island, the craters number and location, and their eruptive sequence and characteristics are still being debated, which are important for potential volcanic hazard assessment. In the present study, field surveys, 40Ar/39Ar and 14C geochronological studies and whole rock composition analysis of volcanic rock are used to investigate the eruption sequences associated with Weizhou island and the characteristics of each period. Four volcanoes were discovered at Henglushan, Hengling, Nanwan and Daling. The Henglushan and Hengling volcanoes were produced by early weak explosive and late effusive eruptions, and lavas from these volcanoes represent the foundation of island. Conversely, the Nanwan and Daling volcanoes are linked to multiple explosive eruption phases, with hydromagmatic eruptions in the first and last phase and a magmatic explosive eruption in the second phase. The pyroclastic density currents (PDCs) deposits of the Nanwan and Daling volcanoes virtually cover the entire island. Volcanic activity in Weizhou island started in Early Pleistocene and ended in Late Pleistocene. This can be divided into the following distinct periods: 1,420–1,260, 870–740, 600–480, 283–222 ka, and 33.7–13 ka. The first four periods were dominated by effusive eruptions associated with the Henglushan and Hengling volcanoes, which peaked between 870 and 740 ka. After this period, explosive eruptions began at around 33.7 ka because of magma–water interactions. These explosive eruptions then created the Nanwan and Daling volcanoes. Early effusive lava flows in Weizhou island are characterized by basaltic compositions and are linked with a small amount of fractional crystallization. Magmas in later eruptions contained slightly lower SiO2 and involved some basanite. Fractional crystallization was also less pronounced in these lavas because of their rapid ascent.

Taupō volcano (New Zealand) is distinguished as the source of Earth's youngest supereruption (∼25.5 ka), with Lake Taupō occupying the resulting caldera. Taupō has also produced eruptions of a wide variety of sizes, styles and associated landscape responses over a ∼350 kyr period. Early Taupō (>54 ka) is poorly demarcated, merging with Maroa to the north, and is represented by widely scattered, geochemically distinct, effusive domes and explosive eruption products from vents all around the modern lake. Taupō had two independent magmatic systems from 54–25.5 ka, one that led to the Oruanui event focussed beneath the area of the modern lake and a second, northeast of the lake that has remained active to the present. Following the Oruanui supereruption, the rebuilt modern hyperactive Taupō magmatic system is primarily focussed beneath the lake and has generated 25 rhyolitic eruptions since ∼12 ka. The young rhyolite magmas come from an evolving silicic magma reservoir, but vary widely in their eruptive sizes and destructive potential. In the modern era Taupō experiences unrest every decade or so, but uncertainties remain over the nature of the magma reservoir and the processes that drive unrest or eruptive activity that require new geophysical data and interpretations. [ABSTRACT FROM AUTHOR]

The 1991 explosive eruption of Hudson volcano in Chile ejected about 2.7 km3 (DRE) of basalt and trachyandesite magma as tephra fall. A majority of the fallout occurred from an eruption during the period August 12-15, 1991, producing an extensive deposit to the east of the volcano in Chile and Argentina. Dacitic, glassy tephra from this phase of the eruption exhibit a remarkable variety in particle morphology and color, ranging from dark, poorly-vesicular shards to light-colored, pipe-vesicular micropumice. Fractal analysis of glassy particle outlines shows that at least four distinct types can be discriminated: blocky, poorly-vesicular, highly vesicular with spherical vesicles, and pipe vesicular. A quantitative comparison of particle morphologies using principal component analysis of fractal spectrums of the Hudson tephra with other tephra produced by eruptions with known fragmentation mechanisms, together with SEM imaging of particle surfaces, indicates that production of the Hudson tephra involved both interaction with external water and exsolution of dissolved volatiles. Blocky particles likely represent magma that was fragmented by magma-water interactions before exsolution of all dissolved volatiles could occur. The great diversity of particle types in the August 12-15, 1991 Hudson tephra fall can be attributed to eruption of volatile-rich trachyandesite magma through an ice-filled caldera where subglacial melting led to a supply of external water that interacted intermittently with the discharge of magma driven primarily by volatile exsolution.

Assessing the potential and likelihood of explosive eruptions is vital for almost 800 million people living near active volcanoes. Magma reservoirs are not directly accessible, limiting our capability to understand the prerequisites for an explosive eruption and our ability to perform experiments that simulate magmatic processes at depth. Therefore, deciphering volcanic precursors is key to forecasting volcanic eruptions. In this study, we used synchrotron‐based X‐ray tomographic microscopy to observe felsic magma vesiculation at high temperature (1,100°C) to establish the pre‐eruptive conditions that favor explosive activity. Specifically, we studied the increase of seismic attenuation with increasing gas content during magma vesiculation. These results are applied to the natural range of volcanic tremors (0.2–5 Hz) to detect the proximity of gas‐charged magma to the surface prior to volcanic eruption: gas‐rich, crystal‐free felsic magmas are detected at larger depth (40 MPa) than gas‐rich, crystal‐bearing systems (10 MPa). Plain Language Summary: Forecasting the likelihood of explosive eruptions is vital for almost 800 million people living near active volcanoes. To this goal, volcano monitoring that uses seismic waves to image magmas at depth is crucial for deciphering the causes driving an explosive eruption. As we have no direct access to magmatic processes at depth, here we use very high‐resolution 3D imaging techniques to observe the formation of gas bubbles in a lab‐scale magma to establish the conditions that favor explosive activity. In particular, we correlate how the presence of excess gas in magmas can modulate the seismic imaging of magmas prior to their eruption. These results offer the opportunity to better illuminate the causes of explosive eruptions and how to apply seismic imaging for detecting the proximity of gas‐rich magma to the surface prior to a volcanic eruption. Key Points: Seismic wave attenuation can be used to determine gas‐charged magma ascent prior to eruption3D imaging of vesiculation and wave attenuation modeling show crystal‐poor magmas are detected at larger depth than crystal‐rich onesLow‐frequency seismic attenuation can be used to pinpoint the gas accumulation in shallow magma reservoirs prior to eruption [ABSTRACT FROM AUTHOR]

Dense, vitric, dacitic pyroclasts (dacite lithics) from the 1991 preclimactic explosions of Mt. Pinatubo were analyzed for their vesicular and crystal textures and dissolved H2O and CO2 contents. Micron-scale heterogeneities in groundmass glass volatile contents (0.9 wt% differences in H2O within 500 μm) are observed and argue that parts of the dacite lithics equilibrated at different depths before finally being constructed. Greater vesicularities and larger and greater number densities of vesicles are observed in groundmass glass around phenocrysts compared to groundmass glass away from phenocrysts, similar to textures produced in experiments that sintered bimodal distributions of particles. Furthermore, increasingly greater proportions of stretched and distorted vesicles are observed in lithics from the later explosions, which parallels the increasingly shorter reposes between explosions. Finally, micron-sized crystal fragments are ubiquitous in groundmass glass of all dacite lithics. The textures, together with the variable volatile contents, lead us to propose a model that the dacite lithics formed by rapid and repetitive sintering of ash particles derived from a variety of depths on the conduit walls above the fragmentation level. We speculate that sintering of conduit material produced impermeable layers that retarded gas flow through the conduit, causing pressure to build until the cap failed and the next explosion occurred. [ABSTRACT FROM AUTHOR]

This paper describes the geology and eruptive history of a Quaternary silicic volcanic complex at Shiribetsu, Hokkaido, Japan, with a focus on volcanic landforms produced by silicic explosive eruptions that were not associated with caldera collapse. The Shiribetsu volcanic complex comprises a dacitic pyroclastic plateau and an overlying dacitic central dome complex. The pyroclastic plateau is 22 × 25 km in size, < 200 m high, and consists of two ignimbrite units (the Km-1 and Km-2 deposits; SiO2 = 67–68 wt%; total volume ~ 10 km3). The central dome complex is 4–5 km wide, rises to 650 m above the pyroclastic plateau, and comprises two adjoining edifices, which are East and West Shiribetsu (SiO2 = 62–64 wt%; total volume = 1.6 km3). East Shiribetsu has a conical morphology, whereas West Shiribetsu comprises lava flows and a dome, and has a large amphitheater. A debris avalanche deposit (volume = 1 km3) extends from the amphitheater to the western foot of West Shiribetsu. A dacitic lava dome (volume = 0.2 km3) occurs within the amphitheater. According to the stratigraphic relationships and new fission-track dating, the Shiribetsu volcanic complex evolved as follows: (1) dacitic explosive eruptions at ca. 130 ka (Km-2) and 70 ka (Km-1) produced the pyroclastic plateau; (2) effusive dacitic eruptions at 70 ka (East Shiribetsu) and 60 ka (West Shiribetsu) produced the central dome complex; (3) sector collapse occurred at West Shiribetsu at 50–60 ka; and (4) lava dome formation within the amphitheater at 50 ka. The evolution of the Shiribetsu volcanic complex resembles that of ignimbrite shield volcanoes in the central Andes. Shiribetsu may be the first identified example of ignimbrite shield volcanoes in an island arc setting. We suggest that these are an independent class of explosive silicic volcanoes, distinct from calderas, and form above small magma chambers. [ABSTRACT FROM AUTHOR]

Bezymianny Volcano is one of the most active volcanoes in Kamchatka and in the world. This paper describes the preparation, behavior, products, dynamics, and the geological effect of the March 15, 2019 explosive eruption of the volcano, which was predicted 6.5 h before it began. The sequence of eruptive events was analyzed using data provided by video and satellite-based monitoring of the volcano; the quantitative characteristics for the distribution of pyroclastic deposits were obtained in the information system "Remote Monitoring of Activity of Volcanoes in Kamchatka and the Kurile Islands". The explosions lifted ash to heights of 15 km above sea level (up to 12 km above the volcano), the eruptive cloud was moving northeastward and east from the volcano, the main ashfall area was 210 400 km2, including 15 000 km2 on land. Apart from tephra, the eruption produced pyroclastic flows and pyroclastic surges covering an area of 30 km2. The total volume of explosive products is estimated as 0.1–0.2 km3. The eruptive rocks are calc-alkaline moderate-K basaltic andesites (SiO2 = 54.84–56.29 wt %), they are the most mafic among all rocks of the current Bezymianny eruption cycle. [ABSTRACT FROM AUTHOR]

Explosive volcanic eruptions produce pumice including bubbles (mainly H2O gas) which form by the vesiculation process under decompression during the magma ascent in the volcanic conduit. Shape of bubbles varies from spherical to tubular or irregular depending on the eruption style, intensity and magnitude. Interestingly, huge eruptions such as caldera-forming eruptions characteristically include elongated bubbles. We conduct the bread baking experiments to examine what controls the shape of bubbles by using the vesiculation process due to the fermentation of yeast. We use two experimental setups, baking within and without a glass conduit, to evaluate the effect of 1 dimensional expansion flow on the bubble shape. Results show that breads baked within the glass conduit typically include the elongated bubbles. We make the textural analysis for the cross section of bread after fermentation and baking with a time interval of 5 min to understand the evolution of bubble texture and with variable concentrations of yeast to evaluate the effect of amount of yeast on fermentation, consequent expansion of dough and bubble texture. By experiments with the variable concentration of yeast, it is found that the maximum expansion occurs at the certain concentration of yeast approximately 0.5 g per 50 g dough, and that the number of bubbles monotonically decreases with increasing the concentration of yeast. Time series experiments show that the number of bubbles decreases and average size of bubble increases with time for both within and without conduit. Aspect ratios of bubbles within a glass conduit are larger in smaller size of bubbles and smaller (i.e., elongated) in larger size. Numerical model simulating the evolution of bubble shape under 1 D expansion demonstrates that smaller bubbles relax to the spherical shape by surface tension effect and larger bubbles maintain the elongated shape formed by 1 D expansion. [ABSTRACT FROM AUTHOR]

The 2016–2017 shallow submarine eruption of Bogoslof volcano produced numerous infrasound signals over 9 months that were recorded on six Alaska Volcano Observatory (AVO) arrays at ranges of 59 to over 800 km from the volcano. The lack of geophysical monitoring near Bogoslof and the repeated production of volcanic clouds to flight levels made monitoring by remote infrasound critical during the eruption; for the first time, AVO relied extensively on automated infrasound detections from regional arrays to dispatch timely notifications of the ongoing activity. Most of the 70 eruptive events were detected on at least one array, but no array detected all of the events mainly because atmospheric conditions were highly variable during the eruption. Acoustic propagation modeling helps explain some of the variation in array detections but also highlights limitations in regional propagation models. To our knowledge, this is the first example of well-recorded infrasound from an explosive eruption occurring in shallow seawater, providing extensive insights into eruption dynamics in this unique environment. The dominance of low-frequency infrasound (0.1–1 Hz) is attributed to eruptions occurring beneath tens of meters of seawater. Higher-frequency infrasound signals were mostly limited to eruptions where the vent was isolated from major interaction with seawater or in several cases where a lava dome grew above sea level. [ABSTRACT FROM AUTHOR]

Extensive deep (>1500 m) non-hydrothermal ash-rich plumes were present in the water column surrounding West Mata submarine volcano (NE Lau basin) during eruptive phases, but were absent when West Mata was quiescent. Deep ash plumes were chemically distinct from hydrothermal plumes originating at West Mata and other hydrothermal sources in the region, and were dominated by very fine shards compositionally similar to the lava erupting at the ∼1200 m summit with morphologies indicative of magma degassing and shattering. Deep ash plume layers occurred at variable water depths (and distances above the seafloor) and were transported by local currents to 10s of km from West Mata. We interpret these deep ash plumes to be syn-eruptively generated ash transported downslope via sediment gravity flows of varying magnitudes, runout distances, and liftoff densities. Final deposition of individual particles will be by settling from suspension (i.e., fallout deposits). The mechanism for initiating gravity flows is uncertain, but their spatial and temporal distribution suggests that eruption column collapse and/or mobilization of unstable volcaniclasts accumulating on steep slopes during the eruption are likely sources. Turbidity within the deep ash plumes decreased by 80% over a 3 week period in 2017, suggesting the eruption that created a new deposit, constrained between March 2016 and November 2017, was likely active as recently as a few weeks to months prior to the FK171110 expedition. Similar deep ash plumes have been observed surrounding other erupting submarine volcanoes. This pattern of syn-eruptive dispersal suggests that fine ash does not have to be lofted high into the water column in event plumes, or enter the ocean from subaerial sources, to be dispersed by local currents and contribute to fallout deposits in regional and distal sediments, which may appear as cryptotephra or thin ash layers if the ash supply exceeds pelagic sedimentation rates; deposits that are often attributed to subaerial eruptions alone. These results also suggest that the presence of deep ash plumes surrounding a submarine volcanic edifice, along with a magmatic-hydrothermal plume above the summit, may be a valuable diagnostic exploration tool for identifying active, or very recently active, submarine eruptions.

It is well known that explosive volcanic eruptions pose serious hazards to local communities and may have worldwide impacts. However, the products of explosive eruptions on volcanic ocean islands are almost inevitably incompletely preserved as a significant portion of the erupted material is deposited into the ocean, thereby impeding our ability to accurately reconstruct past events, determine eruptive source parameters and ultimately assess the associated hazards. Sete Cidades is the westernmost central volcano of São Miguel Island, Azores. Although currently dormant, it has been the most active volcano on the island in the last 5 ky, with at least 17 trachytic explosive eruptions, some of which sub-Plinian, that took place inside the summit caldera. The last paroxysmal explosive eruption took place at ∼16 ka, enlarging the caldera to its present dimensions, and is recorded by the Santa Bárbara Formation. We here present evidence of a mid-distal deposit (>25 km from the vent) that can be correlated with the proximal (on Sete Cidades volcanic edifice) pumice fall deposit of the Santa Bárbara Formation based on deposit characteristics, textural features and geochemistry. This is the first evidence of a decimeter-thick deposit of Sete Cidades volcano in the central part of São Miguel Island, which allows to constrain eruptive source parameters and wind conditions. Given the predominant winds blowing from westerly directions, Sete Cidades is considered the most hazardous volcano for the entire island of São Miguel with its current population of >137,000 inhabitants. Most critically, the main harbor, only airport and hospital are located in the capital city of Ponta Delgada, ∼12 km SE from Sete Cidades caldera. In case of a future explosive eruption, under westerly blowing wind conditions, the impact on São Miguel could be catastrophic, with long-term economic consequences.

Dynamics of explosive eruptions is often strongly controlled by temporal changes in conduit geometry. Quantitative constraints to this problem are difficult to define, but basic information on the lithic fraction in pyroclastic deposits can be used as an input of numerical models to infer conduit and crater evolution in terms of shape and dimension. Field data on the 79 CE Pompeii eruption (Vesuvius, Italy) are used here to constrain depth‐dependent variations in conduit geometry. The different lithology of the accidental components, resulting from the erosion of a conduit/crater system crosscutting a well‐known subsurface stratigraphy, helps in defining the provenance depth of the eroded fragments. We reproduced the eruption evolution by considering three periods of the Plinian phase, associated with the white phonolitic pumice clasts (EU2a) and the tephro‐phonolitic gray pumice clasts (EU3a and EU3b). Results constrain the evolution of key eruptive parameters and are consistent with the estimates of mass discharge rate (MDR) and volume of eroded lithic fragments, which require the involvement of conduit geometries with depth‐dependent diameters rather than a constant‐radius shape. The onset of the Plinian phase (EU2a) was characterized by intense crater excavation processes. The MDR increase during the transition from EU2 to EU3 coincided with a significant increase of conduit diameter at bottom. After the peak of MDR (EU3b), a significant deeping of the fragmentation level and an abrupt inlet pressure drop probably occurred. Exit pressure and velocity would have decreased during all the Plinian phase, consistent with a shift to a collapsing column dynamics. Key Points: Lithic component data can be used to study conduit geometry evolution during explosive eruptions and constrain eruptive parametersThe onset of the Plinian phase of the 79 CE Vesuvius eruption was characterized by intense crater excavation processesExit pressure and velocity decreased during all the Plinian phase of this event, consistent with a shift to a collapsing column dynamics [ABSTRACT FROM AUTHOR]

Early warnings of the timing, style, and size of volcanic eruptions, made on the basis of seismic monitoring, are important for mitigation of the hazards associated with volcanic eruptions. We calculated the rates of seismic energy release at Kelud volcano, Indonesia, preceding both the 2007 effusive lava-dome eruption and the 2014 Plinian eruption. For the 2007 eruption, there was first a step-wise increase in the rate of release of seismic energy, followed by a gradual decrease until the eruption. For the 2014 eruption, the rate of energy release was almost constant until 10 days before the eruption, then gradually increased until there was a dramatic acceleration during the last day before the eruption. The total seismic energy released by the 2007 and 2014 eruptions were 3 × 108 J and 2.2 × 109 J, respectively. The relative difference between the ejected volumes of the 2007 and 2014 eruptions is roughly equivalent to that of the total seismic energy released preceding the eruptions. We conducted several trials of the material failure forecast method (FFM), applying it to the square root of the rate of seismic energy released, to assess its usefulness for predicting the timing of eruptions. The predicted onset of the 2007 eruption was one day earlier than the actual eruption and the seismic energy release preceding the actual eruption did not increase dramatically as suggested by the FFM model. Several trials of FFM for the 2014 eruption predicted the onset of the eruption to be three days to two weeks later than the actual eruption. Even as the end time of the FFM time window approaches several hours to 10 min before the actual eruption onset, the predicted eruption onset is still 3 h later than the actual onset. Thus, the results of our FFM modeling did not show the method to be useful for predicting eruption times for Kelud volcano. The differences of the FFM modeling results for the 2007 and 2014 eruptions likely reflect the differences in the rate of energy release immediately before the two eruptions: a deceleration before the 2007 eruption and an acceleration before the 2014 eruption. These differences may reflect differences in precursory processes for effusive lava-dome and Plinian eruptions. • Material failure forecast method tested as means to predict volcanic eruption time • Applied to precursory seismic energy for 2007 and 2014 eruptions of Kelud volcano • Failed to provide useful predictions of eruption times for 2007 and 2014 eruptions • Revealed differences in precursory energy release of effusive and Plinian eruptions • Differences may reflect different processes before effusive and Plinian eruptions. [ABSTRACT FROM AUTHOR]

Explosive volcanic eruptions are one of the most important driver of climate variability. Yet, we still lack a fundamental understanding of how climate change may affect future eruptions. Here, we use an ensemble of simulations by 1‐D and 3‐D volcanic plume models spanning a large range of eruption source and atmospheric conditions to assess changes in the dynamics of future eruptive columns. Our results shed new light on differences between the predictions of 1‐D and 3‐D plume models. Furthermore, both models suggest that as a result of ongoing climate change, for tropical eruptions, (i) higher eruption intensities will be required for plumes to reach the upper troposphere/lower stratosphere and (ii) the height of plumes currently reaching the upper troposphere/lower stratosphere or above will increase. We discuss the implications of these results for the climatic impacts of future eruptions. Our simulations can directly inform climate model experiments on climate‐volcano feedback. Key Points: We compare the impacts of climate change on the dynamics of eruptive columns, as predicted by 1‐D and 3‐D plume modelsBoth models agree that higher eruption intensities will be required to inject sulfur into the tropical stratosphereEruptive column‐climate interactions are key to understand the climatic impacts of future eruptions [ABSTRACT FROM AUTHOR]

Detailed mineralogical and melt and fluid inclusion constraints on magma storage, and the evolution of melts, are presented for the large-volume caldera eruption on the Vetrovoy Isthmus on Itutrup Island (Kuril Islands, Russia). The shallow magma reservoir beneath the Vetrovoy Isthmus is composed of a mush of plagio-rhyolitic melt, phenocrysts and the products of peritectic reaction(s). The melt appears to have formed as a result of partial melting of previously erupted rocks, which probably had andesitic to basaltic compositions and were metamorphosed into amphibole-bearing assemblages. The breakdown of amphibole in the partially melted precursor rocks led to the formation of early Mg-rich clino- and orthopyroxene, along with plagioclase and Fe–Ti oxides, and the release of aqueous fluids. Variations in fluid pressure are recorded by a strong increase of An contents in plagioclase. Crystallization took place at around 850°C with pressure ranging from 0·9 to 3 kbar. This study demonstrates that dacitic magmas erupted during the course of a 20 kyr voluminous eruption were the result of mixing between plagio-rhyolitic partial melts and the breakdown reaction minerals (i.e. pyroxenes, plagioclase and Fe–Ti oxides). Plagioclase and quartz were the last minerals to crystallize from these melts prior to eruption. [ABSTRACT FROM AUTHOR]

Numerous tephra layers occur within the late Pleistocene Wilson Creek Formation, where they are interbedded with lacustrine deposits of Lake Russell, the ancestor of present-day Mono Lake. Most of the tephra layers are rhyolitic in composition, and were produced from the Mono Craters. We present detailed stratigraphy and sedimentology of the tephra layers, sampled at twelve outcrops near the shoreline of Mono Lake and the Mono Craters, and implement grain size, componentry, and surface morphology analysis to characterize their physical properties. Sub-unit correlation is proposed for certain tephra units. Noticeable features of the tephras, such as the occurrence of low-density rounded or highly vesicular pumice within certain sub-units, are highlighted. The abundant obsidian, lithics, and ostracods within many sub-units suggest that the associated eruption pulses involved water-magma interaction. Eruptions from the Mono Craters during the late Pleistocene were consistent neither in frequency nor volume. The Mono Craters were most active during the eruption of tephras in Sequences C (∼42.5–39.4 ka) and A (∼14.1–12.9 ka), and Pleistocene volcanic activity reached its peak during the eruption of tephra layer C11. Detailed interpretation of tephra layer B7 and tephras in Sequence A is given, which includes the number of eruption pulses, vent location, dispersal direction, occurrence of pyroclastic flow and surge, and other features and processes. Tephras in Sequence B (∼26.2–23.1 ka) may have had their vents located in the southern half of the Mono Craters, or are smaller in volume (except for B7), compared to the other tephras in the Wilson Creek Formation. Vents for tephra layers A4, A3, and A1 are located near the northern end of the Mono Craters. The stratigraphy of tephra layers B7 and A1 suggests an unstable depositional environment, which can be used to help constrain the water-level history of Lake Russell during the late Pleistocene. • Tephra stratigraphy • Wilson Creek Formation • Mono Craters • Lake Russell • Late Pleistocene [ABSTRACT FROM AUTHOR]

Explosive volcanic eruptions can eject large amounts of ash into the atmosphere, posing a serious threat to populations living near the volcano. The abrupt occurrence of such events requires a rapid response and proper volcanic hazard evaluation. Current monitoring procedures still require human intervention, which often results in significant delays between the occurrence of an eruption and notifications being dispatched. We show how dedicated infrasound array processing can be used to detect and notify the authorities, automatically and in real time, of the onset of explosive eruptions. Conceptually, our method relies on the strong coupling between infrasound and the explosive process, and it is not based on probabilistic considerations but on the ability infrasound has to detect the early stage of the explosive phase. This procedure has been tested for the last 8 years, and it is currently applied to issue early warnings for explosive eruptions at Etna Volcano. We show that the system is able to provide a prealert ~1 hr before the eruption, and it has a 96.6% success rate, with only 1.7% false positive alerts and no false negative alerts. This is, to our knowledge, the first example of an operational early warning system totally based on an unsupervised algorithm that provides automatic notifications of eruptions to a government agency. We show that the same early warning concept might be applicable to arrays at large distances (>500 km), suggesting that infrasound could be successfully used to issue automatic notifications of ongoing eruptions at regional to global scales. Plain Language Summary: Most of the volcanic eruptions are rapidly evolving phenomena, strongly limiting the possibility to prompt activate emergency plans. We still lack the possibility to notify volcanic eruptions automatically, making our society highly exposed to the effects of large explosive eruptions. We present the first early‐warning system based on the acoustic waves generated by volcanic eruptions. Our approach relies on the strong coupling between sound and explosive process, and, as for the earthquake, it is not based on probabilistic consideration but on a quasi‐deterministic approach. In the last 8 years, the system was providing a prealert notification ~1 hr before the eruptive onset with 96.6% rate of success, 1.7% positive false alerts, and no negative false alerts. This is, in our knowledge, the first example of an operational early‐warning system totally based on automatic and unmanned algorithm that provides automatic notification of eruption to government agency automatically and without man supervision. Early warnings can be applied even at regional distances (˃500 km), and notification of ongoing volcanic eruptions would be of valuable importance for aviation safety especially for the many active volcanoes worldwide that are still lacking of geophysical monitoring systems. Key Points: We present the first example of operational early warning for volcanic eruptions based on automatic and unsupervised algorithmThe infrasound array processing detects in real‐time explosive eruptions with a 96.6% of success and no false negative alertsThe early‐warning algorithm automatically delivers prealert notification ~1 hr before the occurrence of the eruptive onset [ABSTRACT FROM AUTHOR]

An inversion methodology, named maximum-likelihood (ML) volcanic ash light detection and ranging (Lidar) retrieval (VALR-ML), has been developed and applied to estimate volcanic ash particle size and ash mass concentration within volcanic plumes. Both estimations are based on the ML approach, trained by a polarimetric backscattering forward model coupled with a Monte Carlo ash microphysical model. The VALR-ML approach is applied to Lidar backscattering and depolarization profiles, measured at visible wavelength during two eruptions of Mt. Etna, Catania, Italy, in 2010 and 2011. The results are compared with those of ash products derived from other parametric retrieval algorithms. A detailed comparison among these different retrieval techniques highlights the potential of VALR-ML to determine, on the basis of a physically consistent approach, the ash cloud area that must be interdicted to flight operations. Moreover, the results confirm the usefulness of operating scanning Lidars near active volcanic vents. [ABSTRACT FROM AUTHOR]