The January 2022 eruption of Hunga injected unprecedented volumes of water vapor (150 Tg) and modest sulfur dioxide (SO₂) into the stratosphere, producing accelerated sulfate aerosol formation in the early plume. As the aerosols gradually spread into the global stratosphere, the role of water vapor, among other factors in the spread and residence time of the sulfate aerosols, remained unclear. We used multisatellite observations to better understand the role of water vapor in the spread and lifetime of Hunga volcanic aerosols. Stratospheric circulation transported the plumes to ~26 km within the polar vortices—the Antarctic by August 2022 and the Arctic by January 2023—with the arrival of aerosols lagging behind that of water vapor by months. Even though high injection altitudes (58 km) and strong Brewer–Dobson circulation contributed to prolonging the residence time of aerosols, the water vapor enhanced particle growth and thus accelerated gravitational settling, with the half lifetime of aerosols being 14 months. Our analysis revealed a critical trade-off: after the eruption of the Hunga volcano, an extremely high injection height and strong upward motion slowed the removal of aerosols, but extreme water vapor loading still had a certain impact on the half lifetime of the aerosols. These findings highlight the role of water vapor in the persistence of aerosols from submarine eruptions.

Submarine volcanic eruptions are strong pulse disturbances that can cause abrupt mortality and long-lasting changes in marine communities. In October 2011, a submarine eruption off El Hierro (Canary Islands, Spain) generated a sulphurous plume that affected the Punta de La Restinga-Mar de Las Calmas Marine Reserve and surrounding coastal areas. Using a 25-year time series of fish community data, we assessed post-disturbance trajectories of commercial species across different protection levels within the impacted region. Resilience was analyzed as a sequential process, partitioned into resistance (initial biomass loss), recovery trajectory (temporal trend after the disturbance), and relative recovery compared with pre-eruption conditions. Because all sites were affected by the volcanic plume, our inference is restricted to comparative differences among protection categories rather than to the absolute effectiveness of protection. The no-take zone showed higher relative resistance and faster positive trajectories in total fish biomass than less-protected areas, indicating more favorable post-disturbance dynamics. However, eight years after the eruption, community structure had not fully returned to pre-eruption conditions in any protection level, reflecting contrasting recovery times among species with different life histories. Fast-growing species such as the parrotfish Sparisoma cretense recovered rapidly, whereas long-lived predators such as Epinephelus marginatus remained below their pre-disturbance biomass. Our results provide a long-term, community-level comparison of post-volcanic recovery within a marine reserve and highlight how protection status is associated with differences in recovery dynamics under a rare natural disturbance.

El Hierro, the youngest and smallest island in the Canary archipelago, has active magmatism that poses a potential hazard, evidenced by historical volcanic events such as the 1600 Lomo Negro eruption and the 2011–2012 submarine eruption off its southern coast. Despite extensive geological studies, a detailed geological map of the island was lacking until recent work. This study provides the first detailed geological map of the western sector of El Hierro (approximately 90 km2 ) at a 1:12,500 scale, developed from a geological survey conducted in 2022. Over 100 lava flows were identified and their directions measured, revealing stratigraphic relationships that allowed identifying formations and members and subsequently grouping them in four volcanic stages: Roque del Julan, Morro del Paso, El Jaral, and La Frontera. The study also estimates the minimum erupted volumes of over 70 lava flows. Key findings indicate that El Golfo collapse, a significant event in the island’s volcanic history, led to an increased eruption frequency, but a reduction in individual eruption volumes. Additionally, the study highlights a spatial migration of eruptive fissures toward the island’s outer regions post-collapse, while eruption fissure orientations remained unchanged. These findings are crucial for understanding volcanic hazards and recurrence intervals on El Hierro.

• CaSO 4 and halogens in the Hunga volcanic cloud were mostly derived from seawater. • Sea salts had a strong influence on the stratospheric volcanic cloud at Hunga. • Small- and large-scale submarine eruptions frequently impact the stratosphere. • Non-submarine eruptions can also inject seawater and sea salts in the stratosphere. Submarine volcanic eruptions can form subaerial plumes that reach the stratosphere. Despite this, the impact of submarine eruptions on climate remains unclear due to a lack of clear geological record, with the recent large-scale Hunga eruption on 15 January 2022 being considered as an isolated case. Here, we review the impact of submarine and subaerial volcanoes in island or coastal settings (i.e., near seawater) on volatile/aerosol loading in the stratosphere. Isotopic δ 34 S signatures of the Hunga ash suggest that CaSO 4 salts on the ash surface are dominantly formed by the evaporation of seawater during the eruption. We infer that SO 2 scavenging on volcanic ash did not play a major role in the lower-than-expected SO 2 detected in the volcanic cloud. Chlorine isotopic compositions (δ 37 Cl) also argue in favor of a seawater-derived origin of the chlorides from ash leachates. Combining petrological, leachate, isotopic and thermal analysis data, we demonstrate a near-absence of halogen degassing from the Hunga magma prior to and during the eruption, and conclude that the chlorine and bromine contents of tropospheric and stratospheric volatile species very dominantly derive from seawater/sea salts. We generalize our findings to all submarine eruptions, and large-scale, non-submarine eruptions in island or coastal settings, and propose that these may commonly form volcanic clouds that incorporate seawater thereby leading to the injection of related components (water vapor, sea salts, halogens) into the stratosphere. This makes seawater inputs a serious consideration when evaluating the long-term impact of volcanoes on climate.

Abstract Pumice rafts derived from submarine eruptions can remain afloat for months or even years, traveling thousands of kilometers on ocean currents. These natural phenomena disperse marine organisms and provide important evidence for submarine volcanism yet are not fully understood. Here, we describe pumice clasts from Falkland Islands shorelines and use major‐minor‐trace element analyses to trace their provenance to the 1962 volcanic eruption on Protector Shoal, a large seamount in the South Sandwich Islands, Scotia Sea. Compositional variability between rafted and dredged pumice from Protector Shoal suggests eruptions have varied from explosive to non‐ or mildly explosive (the latter from lava domes and during neptunian events) and the seamount is volcanically diverse. Oceanographic modeling simulations and historical observations show that clasts from the 1962 eruption reached the Falkland Islands via the Antarctic Circumpolar Current, a journey of ∼20,000 km that took approximately three years. Although oceanographic variability strongly affects modeled transport pathways, in all simulations particles consistently reach the Falkland Islands from Protector Shoal seamount, suggesting a persistent long‐distance connection. The results highlight the potential for pumice rafting to disperse non‐native, potentially invasive, marine organisms throughout the Southern Ocean as climate warms.

ABSTRACT Floating pumice rafts from submarine eruptions threaten maritime activities, fisheries, tourism, and coastal populations. Effective tracking is essential to mitigate impacts. While previous approaches have primarily relied on optical satellite data, we investigated the potential of cloud penetrating Synthetic Aperture Radar (SAR) that has not been evaluated for this purpose yet. We analyzed amplitude data from TerraSAR-X (X-band), Sentinel-1 (C-band), and ALOS-2 (L-band). We observed that the co-pol channel proves more suitable for mapping than the cross-pol channel for all investigated SAR bands due to higher contrast between volcanic debris and water and less influence of system noise, which distorts backscatter and makes this channels data unusable for image-based processing. A limiting scenario for SAR were partially or fully submerged pumice rafts after a longer period following the eruption, suggesting that SAR data are not suited for long-term tracking of floating pumice. This finding indicates that SAR data are primarily effective for short-term tracking, as mapping reliability decreases with time once pumice begins to waterlog, submerge or disperse. Nevertheless, SAR imagery captured consolidated pumice rafts well during eruption events and under cloudy conditions, highlighting its value as a complementary data source to optical sensors when visibility is often limited.

Abstract No reliable method can distinguish between subaerial and submarine pumice, but recent work shows that highly vesicular (total porosity, φ > 65%) submarine pumice from the 2012 Havre and 2021 Fukutoku Oka-no-Ba eruptions contains abundant isolated porosity (connectivity, C < 0.6). This differs from textural measurements of subaerial pumice with similarly high vesicularities, where high connectivities ( C > 0.8) are often measured. To investigate the implications of this under-studied texture for bubble nucleation, growth, and coalescence dynamics at submarine eruptions, we analyze the textural characteristics of rafted pumice clasts from the 2019 submarine eruption of Volcano F, located along the Tonga-Kermadec Arc. We examined clasts collected while floating near the vent (50–200 km) and distally on the shores of Fiji (900 km). Using helium pycnometry and X-ray tomography (XRT), we quantified porosity and connectivity in 45 pumice lapilli, classifying them by vesicle macrotexture and edge morphology. Microvesicular clasts, the majority of which have breadcrust and cauliflower textures, exhibit the lowest connectivities ( C = 0.61 ± 0.2), while macrovesicular clasts have high connectivities with C ~ 1. We propose that isolated porosity abundance varies according to clast location in the eruption column post-fragmentation. Microvesicular clasts erupted on the edges of the column and experienced high levels of seawater ingestion and subsequent quenching of the entire clast. Macrovesicular clasts, in contrast, erupted in the center of the eruption column and were thus thermally insulated, allowing magmatic bubbles in the molten pumice to nucleate, grow, and coalesce for longer. Our results and interpretation imply that low connectivity, microvesicular clasts preserve pre and syn-eruptive bubble processes at the 2019 Volcano F eruption.

Abstract The 1650 CE Kolumbo (Greece) submarine eruption resulted in the reported deaths of 50 people and thousands of animals on Santorini (Thera) due to exposure to a cloud of noxious volcanic gases. Lack of ash in the cloud indicates that the gas release was unrelated to a magmatic explosive eruption. Medical evidence from historic accounts suggests lethal exposure to CO 2 and H 2 S, which were likely the main hazardous gases, whereas strongly acidic gases such as SO 2 , HCl, and HF were less relevant due to their high solubility in seawater. Expert elicitation indicates significant uncertainty, with probabilities of gas releases conditional on the occurrence of an eruption in the next 30 years ranging in 15–58–93% (5th–50th–95th percentiles), and a 2–17–48% likelihood of the gas cloud reaching Thera. A transient 3D multiphase fluid dynamics model (ASHEE) is employed to simulate turbulent gas cloud propagation and dilution under scenarios with source and meteorological conditions informed by expert elicitation and ECMWF-ERA5 2005−2016 data. A novel component of this study is the derivation of analytical predictive relationships through a non-dimensional scaling analysis, based on parameters like the Richardson number. Simple models are presented for weak, intermediate, and strong wind regimes, providing a generalized framework for gas transport and hazard assessment in similar volcanic settings. Results indicate about 50% probability of the gas cloud reaching Thera, even with a relatively modest volumetric flow rate of 10 3 m 3 s −1 and a wind speed half of the average. However, hazardous concentrations (above 200 ppm of H 2 S and 10 vol.% of CO 2 ) along the NE coast of Thera are reached if source gas flux exceeds 10 4 m 3 s −1 . By integrating elicitation outcomes, physical modeling, and probabilistic analysis, this study estimates a 16% and 17% likelihood of hazardous gas exposure for CO 2 and H 2 S, respectively, along the NE coast of Thera in case of formation of a gas density current in the next 30 years.

The exact nature of crustal magmatic reservoirs is elusive as they cannot be sampled in situ. The traditional view that magma chambers contain essentially molten material has recently been replaced by the transcrustal magmatic system (TCMS), in which reservoirs are mostly composed of immobile magmatic crystals with a minute fraction of more mobile melt1-3, creating a 'magmatic mush'3. Eruptions are possible if a significant portion of melt segregates into melt-rich lenses within the mush reservoir1-3. The TCMS concept is, however, a default model essentially justified by the absence of clear geophysical signatures of melt-rich magma chambers1,4, and by the rare and tentative estimates of the melt fraction in the crustal storage zones based on geochemical and textural analysis of eruptive products5,6. Here we image a bright electrical conductor at 23 ± 1 km below sea level beneath Mayotte island that we interpret as a magmatic reservoir, based on laboratory measurements of Mayotte's melt conductivity. This large magmatic reservoir (more than 200 km3) contains a high melt fraction (22-42%). Such a crystal-to-liquid ratio matches the reconstructed differentiation paths7-9 producing the melts that recently erupted at Mayotte. This reservoir is possibly connected to the system that fed the large submarine eruption of Fani Maoré in 2018-201910.

Abstract Submarine volcanic eruptions can produce diverse surface phenomena and hazards that differ from those of eruptions on land, such as phreatomagmatic explosions, tsunamis, and pumice rafts. Understanding the causes and processes of these surface phenomena and hazards posed especially by explosive submarine eruptions is essential for disaster prevention and mitigation for volcanoes near or below sea level. I constructed a global database of all known submarine eruptions and extracted their general characteristics. The detailed surface phenomena and processes of noteworthy explosive submarine eruptions in recent years are also summarized. Such data and analyses are useful to elucidate key phenomena and processes during submarine eruptions and to evaluate the types and effects of hazards. I focus on the relationship between water depth and the occurrence of hazardous surface phenomena, including explosivity, subaerial pyroclastic density currents (PDCs), and tsunamis. The number of explosive phenomena on the sea surface and tsunamis produced decreases dramatically where the vent is at depths ≥ 400 m, and eruption detection methods are almost entirely limited to seismoacoustic signals, pumice rafts, discolored water, and direct observation by on-site expeditions. However, because of the difficulty of detecting deep-sea eruptions without surficial manifestations, they are almost certainly under-reported in the database. Eruptions accompanied by PDCs over the sea surface represent less than 11% of the total, although eruptions in shallow water are more likely to be accompanied by PDCs. The database analysis improves our knowledge of hazardous phenomena caused by submarine eruptions, and also contributes to constraining phenomena during past historical eruptions, such as the 1650 CE eruption of Kolumbo Central Volcano, southern Aegean, and assessing future hazards at Kolumbo and other submarine volcanoes.

ABSTRACT Pumice rafts mainly originate from submarine volcanic eruptions, which can be captured by ocean color satellite sensors as shown in several case studies. On a global scale, however, there is a lack of systematic evaluation using consistent algorithms and methods. Here, using daily MODIS (Aqua and Terra) images, we characterize pumice rafts from eight of the nine reported pumice raft events since 2000, representing approximately 15% of all recorded submarine eruptions. For each event, we characterize the duration, daily areal coverage, daily mean pumice areal density, and drift paths of the pumice rafts. Large-scale pumice rafts are found to cover more than 200 km2 of sea surface in a water area exceeding 2,000 km2, which can last for several months before dispersing to the water column and becoming no longer observable from satellites. Surface ocean currents and winds are found to be the major factors affecting the pumice raft drift trajectories and areal coverage.

This paper compares open-source volcanic lava images with official TEPCO videos and reports. The fuel debris formation at Fukushima Dai-Ichi Nuclear Power Station (1F) Unit 1 shows similarities to natural lava flows at various volcanoes, including submarine eruptions and pillow lava. Based on evidence found in 1F debris images, the author suggests the unconventional interaction between molten corium and concrete (MCCI). The MCCI could have started in upper pedestal region due to an RPV failure above the RPV skirt, which is higher than usually considered. Additional volume, which cannot be explained now, was explained in the study as mass of MCCI products created in the upper areas of pedestal where hot corium first reacted with concrete. This unconventional MCCI would have brought enough melt to reach the observed terrace-shaped debris height. The current paper attempts to establish the fact that the natural mechanism of 1F terrace-shaped debris formation is easily identifiable through a multidisciplinary approach, which opens the scientific communities of volcanologists and materials scientists to a collaboration.

The thermal properties of lavas are required for modelling volcanic and hydrothermal processes, yet are scarce for submarine lavas. Laboratory experiments, using the transient hot-strip method, are used to understand the role of porosity, glass content, and pore fluid type on the thermal properties of submarine lavas from Havre volcano. Thermal diffusivity and specific heat capacity do not change systematically with porosity; however, thermal conductivity decreases as porosity increases. The thermal conductivity of the submarine lavas is lower than for subaerial lavas with the same porosity, a consequence of their higher glass contents. We show that, using our data and effective medium models, the thermal properties of any lava can be estimated as long as their porosity, glass content, and void-filling fluid phase is known. This approach can be used to estimate properties for multiphase models for submarine eruption dynamics, hydrothermal system hydrology, cooling timescales, and heat flux calculations.

More than 70% of Earth's magmatic output occurs in the ocean. This volcanism shapes major features of the seafloor, directly impacts the chemical composition of the oceans through water/rock interactions, and drives hydrothermal circulation of seawater. The formation of seafloor mineral deposits and chemosynthetic habitats that encircle the globe along mid-ocean ridges, volcanic arcs, and hotspots is driven by volcanism. The style, magnitude, depth, and frequency of seafloor eruptions create a wide range of physical, chemical, and biological impacts on the seafloor. Research and exploration over the past 30 years have revealed some of the diversity of seafloor eruptions and their impact on the undersea environment. ▪ Submarine eruptions are simultaneously the most common and the least observed form of volcanism on Earth. ▪ Hydrostatic pressure at the vent depth modulates explosive versus effusive eruption and the form of eruptive behavior. ▪ Submarine eruptions have significant impacts on marine biological communities and chemical fluxes to the ocean. ▪ Resilience of fauna to eruption events is also variable, and recovery dynamics can be slow with many years or decades required for communities to reform.

Since the onset of Fani Maore submarine eruption, the volcanism of the Comoros Archipelago has gained renewed interest. Geochronological constraints have been recently obtained for Mohéli, Anjouan and Mayotte islands and nearby seamounts. Here we provide new groundmass K–Ar ages for Grande Comore. Along with major and trace element geochemistry and geomorphological analyses, these ages enable us to propose a three stages reconstruction of the island. The first, or M’Badjini stage, is much older than previously thought, with ages as old as 2.2 Ma. Following a period of quiescence and dismantling, the second phase occurred between 280 and 230 ka, probably on both La Grille and Karthala volcanoes. Then, volcanic activity resumed for a third phase from ca. 130 ka until present time. The Comoros geochronological database, updated with our new results, confirms that the construction history of the archipelago occurred as pulses and follows a northward propagation of volcanism (i.e. a widening of the volcanically active region).

Huge submarine eruptions impact global climate but produce low atmospheric sulfur outputs

The explosive January 2022 Hunga submarine eruption in Tonga injected unprecedented water volumes into the upper atmosphere, generating widespread climatic impacts. However, it ejected anomalously little sulfur compared with other eruptions of similar volume. We explain the missing sulfur with volatile budgets calculated from volcanic ash samples spanning the eruption. We show that magma was stored in a weakly stratified reservoir at 2.1 km to >5.6 km depth. Magma rose within <3 min and fragmented at 400–1,000 m below sea level. This preserves microscale chemical mingling including ~1 wt% contrasts in magmatic water concentrations. The 11-h eruption released a total of 319 Tg of magmatic water, which is <10% of that derived from magmatic seawater interaction. Comparing magmatic and residual glass sulfur concentrations shows a total release of 9.4 TgS, but >93% of this entered the ocean during submarine magma fragmentation. These results raise the concern that satellite SO2 monitoring underestimates the magma output of submarine explosions and they are probably near invisible in ice-core records, despite their climate influence caused by water injection into the upper atmosphere. Little sulfur from the 2022 Hunga submarine eruption reached the atmosphere due to seawater–magma interactions, indicating that the climate impact of this type of eruption may be underestimated, according to analysis of ash collected throughout the event.

The Mayotte seismic-volcanic crisis, initiated in May 2018, represents one of the most significant submarine magmatic events ever monitored in near real-time. This study leverages a nine-year Global Navigation Satellite System (GNSS) time series (2014–2023) from the MAYG station to investigate the temporal evolution and directional changes in ground displacement vectors associated with the event. Using both static and kinematic GNSS processing, including Precise Point Positioning with Ambiguity Resolution (PPP-AR), we identify three distinct phases of deformation: a north-eastward pre-crisis trend, an abrupt eastward shift coinciding with the peak magmatic activity (May 2018 – June 2019), and a post-crisis return to north-eastward motion with diminished but ongoing subsidence. The data reveal a dramatic 20 cm vertical subsidence and significant horizontal movement indicative of deep magma withdrawal and crustal readjustment. High-resolution analyses during the initial five days of the crisis suggest a sequence of discrete magmatic pulses. Our findings provide new insights into the geophysical response of volcanic island settings to deep-seated submarine eruptions and highlight the importance of integrating advanced GNSS techniques in understanding complex crustal deformation processes. Keywords: GNSS deformation monitoring; submarine volcanism; Mayotte seismic-volcanic crisis; displacement vector analysis; PPP-AR geodetic technique

Iron Isotopes reveal volcanogenic input during Oceanic Anoxic Event 2 (OAE 2 ∼ 94 Ma)

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