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On 13–15 January 2022, the Hunga Tonga–Hunga Ha'apai underwater volcano erupted. This powerful eruption generated infrasonic waves with amplitudes of thousands of Pascals in the near field. The ground infrasonic stations in China, located approximately 10 000 km from the Hunga volcano, also received waves with frequencies from 0.01 to 0.05 Hz. However, the amplitude reached 17 Pa, which is higher than the predicted amplitude using the absorption model without considering the dispersion effect in the thin thermosphere. At high altitudes, dispersion exists and the sound speed depends on the ratio of the molecular mean collision ratio to sound frequency, which is proportional to the ratio (frequency/pressure). And attenuation coefficients are complex to model. We simulate dispersive sound speeds and attenuation coefficients at different frequencies according to theory and our experimental data. In the thermosphere, the dispersion effect causes noticeable changes of sound speed and then affects wave propagation paths in the far field. The abnormal attenuation coefficient has a smaller impact on thermospheric returns than that of the dispersive sound speed, but it is also not negligible. It explains the large amplitude of thermospheric signals received in our infrasound stations. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'. [ABSTRACT FROM AUTHOR]

On 15 January 2022, a massive underwater eruption occurred at the Hunga Tonga‐Hunga Ha'apai Volcano. The plume reached the mesosphere, and the eruption excited a significant atmospheric Lamb wave, which forced the tsunami. The complicated tsunami waveforms due to ocean‐atmosphere coupling prevented inferring the force history of the excitation. To address this, we analyze ocean surface gravity waves (OSWs) from 15 to 40 mHz, which are decoupled from the Lamb wave due to their slower phase velocities. Modeling these OSWs, we infer that the excitation started at 4:00 UTC with an amplitude of 1010 $1{0}^{10}$ N and lasted for 5 hr, followed by a sub‐event at 8:40 UTC. The observations suggest an initial blowout of seawater above the summit and a subsequent outflow that excited a tsunami below 5 mHz. The 2 hr delayed OSW excitation from 6 to 15 mHz may indicate seawater inflow into the crater. Plain Language Summary: On 15 January 2022, the Hunga Tonga‐Hunga Ha'apai volcano experienced a massive underwater eruption. This eruption sent a plume into the atmosphere and produced a powerful atmospheric wave that caused an early arrival of the tsunami. The complex tsunami propagation coupled with the atmospheric wave prevents us from understanding the excitation processes. To address this, we focussed on ocean surface gravity waves (OSWs) in an oscillatory period from 25 to 67 s, also interpreted as short‐period tsunamis. These OSWs are less affected by these atmospheric waves because of the slow propagation speed. Because the OSWs are less influenced by ocean depth, they are easier to model. The observed OSWs show that the eruption started at 4:00 UTC with a vertical force of approximately 1010 $1{0}^{10}$ N and continued for about 5 hr. Another significant sub‐event occurred around 8:40 UTC. Furthermore, the OSWs in an oscillatory period from 67 to 167 s arrived about 2 hr after the short‐period OSWs. These observations suggest that the eruption blew seawater above the volcano's summit and a subsequent outflow that excited a tsunami. The 2 hr delay in low‐frequency OSW could indicate that seawater flowed into the crater. Key Points: Ocean surface gravity waves at 15–40 mHz were excited at 4:00 UTC when an underwater eruption occurred at Hunga Tonga‐Hunga Ha'apai VolcanoA significant sub‐event at about 8:40 UTC followed the main event, and the ocean surface gravity waves lasted for half a dayThe observations of ocean surface gravity waves suggest a blowout of seawater above the summit and the inflow of seawater into the crater [ABSTRACT FROM AUTHOR]

Seismicity at active volcanoes provides crucial constraints on the dynamics of magma systems and complex fault activation processes preceding and during an eruption. We characterize time‐dependent spectral features of volcanic earthquakes at Axial Seamount with unsupervised machine learning (ML) methods, revealing mixed frequency signals that rapidly increase in number about 15 hr before eruption onset. The events migrate along pre‐existing fissures, suggesting that they represent brittle crack opening driven by influx of magma or volatiles. These results demonstrate the power of unsupervised ML algorithms to characterize subtle changes in magmatic processes associated with eruption preparation, offering new possibilities for forecasting Axial's anticipated next eruption. This analysis is generalizable and can be employed to identify similar precursory signals at other active volcanoes. Plain Language Summary: Our research used observations of small earthquakes to understand the dynamic behaviors of magma and fault systems before and during a volcano eruption. Specifically, we used ML techniques to search for patterns in the waveforms that may inform us of their associated physical processes. At Axial Seamount, an active underwater volcano, we discovered distinct patterns in earthquake signals preceding and during the 2015 eruption. Based on event spectral patterns, we identified signals of mixed‐frequency earthquakes that rapidly increase in number about 15 hr before the eruption starts and migrate along pre‐existing eruptive fissures. The spectral pattern involves a mixture of low frequency energy following the first arrivals, which we interpret to represent opening of cracks and being filled with magma or gases. Our study demonstrates that we can use ML algorithms to detect subtle changes in volcanic signals and help us better understand the processes leading up to an eruption. This may help us in forecasting Axial's upcoming eruption and can be applied to other active volcanoes too. Key Points: Unsupervised learning separated regular earthquakes and precursory mixed frequency earthquakes (MFEs) based on different spectral patternsThe regular earthquakes have strong tidal modulation, corresponding to failures on the caldera ring faults triggered by tidal stress changesThe MFEs intensify 15 hr before eruption and migrate along pre‐existing fissures, likely associated with eruption preparation processes [ABSTRACT FROM AUTHOR]

The Hunga volcano violently erupted on 15 January 2022, producing the largest perturbation of the stratospheric aerosol layer since Pinatubo 1991, despite the initially estimated modest injection of SO2. This study presents novel SO2 and sulfate aerosol (SA) co‐retrievals from the Infrared Atmospheric Sounding Interferometer, and uses them to quantify the initial progression of the Hunga plume. These observations are consistent with rapid conversion of SO2 (e‐folding time: 17.1 ± 4.3 days) to SA, with an injected burden of >1.0 Tg SO2. This points at larger SO2 injections than previously thought. A long‐lasting SA plume was observed, with two separate build‐up phases, and with a meridional dispersion of marked anomalies from the tropics to the higher southern hemispheric latitudes. A limited (∼20%) SA removal was observed after 1‐year dispersion. The total injected SA mass burden was estimated at 1.6 ± 0.5 Tg in the total atmospheric column, with a build‐up e‐folding time of about 2 months. Plain Language Summary: The eruption of the submarine Hunga volcano in January 2022 polluted the global stratosphere with a large amount of water vapor and significantly perturbed the stratospheric aerosol layer. In this paper, we present a 1‐year long aftermath study of the stratospheric sulfur pollution from this volcanic eruption using observations from the Infrared Atmospheric Sounding Interferometer (IASI) satellite‐borne instrument. Gaseous and aerosol sulfur emissions are observed simultaneously using the specific potential of this sensor. These observations provide unique capabilities to characterize the aerosol type in the Hunga plume and the sulfur cycle associated with the volcanic emissions. An extremely rapid conversion of gaseous sulfur emissions to aerosols is observed, leading to larger than expected and persistent anomalies of the stratospheric aerosol layer (compared with a consistent long‐term climatology), still noticeable in the Southern Hemisphere after 1 year. The total mass of the emitted sulfur in gas and aerosol state is also simultaneously estimated, for the first time. Key Points: Novel co‐retrieval of SO2 and sulfate aerosol from Infrared Atmospheric Sounding Interferometer (IASI) used to study the dispersion of the Hunga plume over the entire year 2022Rapid conversion of SO2 (2 weeks e‐folding time) and long‐lasting sulfate aerosol observedLarger SO2 injected mass burden (>1.0 Tg) than previously thought and a large sulfate aerosol total burden (1.6 Tg) estimated [ABSTRACT FROM AUTHOR]

Solar eruptions are sudden release of the magnetic free energy accumulated within a quasi-static evolutionary process of the corona. Interestingly, many solar eruptions are preceded by a short-term slow-rise phase, during which the pre-eruption structure rises at a speed significantly larger than that of the quasi-static evolution. Here we suggest an explanation for the slow-rise phase based on a recent high-accuracy magnetohydrodynamic simulation for initiation of solar eruption. The simulation shows that by continuously shearing a bipolar magnetic arcade, an internal current sheet forms gradually, and an eruption begins once magnetic reconnection is triggered at the current sheet. We find in the simulation that the overlying field presents a slow-rise phase before the reconnection sets in. In addition, the rising speed is significantly larger than that of the core field during this phase. This slow rise is a manifestation of the growing expansion of the arcade in the process of approaching a fully open field state, which is inherent to the formation of a current sheet before the eruption. We also show three flare events with slow-rise phases that are highly consistent with these key characteristics in the simulation: an expansion of the overlying coronal loops with speeds much larger than the quasi-static evolution speed, and for those events with filament eruption, the slow rise of filament is much smaller than that of the overlying loops. In this type of events, the eruption might be initiated through the mechanism as shown in the simulation, and the expansion of overlying coronal loops is a better indicator of the slow-rise phase. [ABSTRACT FROM AUTHOR]

We have obtained the first data on the chemical composition of the eruptive materials from the explosive eruption of Bezymianny volcano on April 7, 2023. Our unique collection includes freshly sampled pumice lapilli from the eruption and juvenile blocks from pyroclastic flows. We have identified interesting patterns in both macro components and specific chalcophile elements, such as copper. The rocks we studied belong to medium-K two-pyroxene basaltic andesite (55.5‒57 wt % SiO2), with mafic enclaves characterized by a slightly more primitive composition (53.7 wt % SiO2). According to mineral geothermometry data, the phenocrysts of basaltic andesite crystallized at temperatures in the range from 940 to 960°C, while the formation of phenocryst rims and microlites occurred at 980°C, which corresponds to conditions immediately before the eruption. The composition of volcanic glass allows us to estimate the pressure at which the magma reached the last equilibrium with crystallizing phases before eruption (0.5‒0.6 kbar). Based on these findings, we have formulated hypotheses about the potential evolution of the shallow magma chamber of Bezymianny volcano during the period from 2017 to 2023. [ABSTRACT FROM AUTHOR]

The paper presents the results of a comparative analysis of sapphire-bearing placers in South Primorye (Shkotovo Plateau, Russia) and in the adjacent Heilongjiang Province (the Muling deposit, China). The placers are confined to intraplate alkali basalts with similar geochemical characteristics and age. It was found that the same minerals from placers in Russia and China are very similar, although with some differences, the most apparent of which being the predominance of fancy-colored gemstones and rubies among Muling corundums and blue-green-yellow sapphires (BGY sapphires) in the Primorye placers. The minerals of the megacryst assemblage, including gem corundum, bear traces of magmatic corrosion and have an affinity with the host alkali basaltic melt. Magma chambers of an alkali basaltic volcano provide the conditions necessary for the growth of large and transparent crystals. It is suggested that the sapphires formed from gaseous aluminum chloride in miarolitic cavities. Megacrysts are rapidly transported to the surface owing to the explosive eruptions of basaltic volcanoes. Further erosion of megacryst-bearing rocks and redeposition of minerals in alluvium lead to the formation of zircon- and sapphire-bearing placers. The publication emphasizes economic importance of placers of gem corundum and zircon in alkali basalts and, hence, the need for their further study. [ABSTRACT FROM AUTHOR]

In a review paper in this same volume, we present the state of the art on modeling of compressible viscous flows ranging from single‐phase to two‐phase systems. It focuses on mathematical properties related to weak stability because they are important for numerical resolution and on the homogenization process that leads from a microscopic description of two separate phases to an averaged two‐phase model. This review serves as the foundation for Parts I and II, which present averaged two‐phase models with phase exchange applicable to magma flow during volcanic eruptions. Part I establishes a two‐phase transient conduit flow model ensuring: (1) mass and volatile species conservation, (2) disequilibrium degassing considering both viscous relaxation and volatile diffusion, and (3) dissipation of total energy. The relaxation limit of this model is then used to obtain a drift‐flux system amenable to simplification. Here, in Part II, we summarize this model and propose a 1.5D simplification of it that alleviates three issues causing difficulties in its numerical implementation. We compare our model outputs to those of another steady‐state, equilibrium degassing, isothermal model under conditions typical of an effusive eruption at an andesitic volcano. Perfect equilibrium degassing is unreachable with a realistic water diffusion coefficient because conduit extremities always contain melt supersaturated with water. Such supersaturation has minor consequences on mass discharge rate. In contrast, releasing the isothermal assumption reduces significantly mass discharge rate by cooling due to gas expansion, which in turn increases liquid viscosity. We propose a simplified system using Darcy's law and omitting several processes such as shear heating and liquid inertia. This minimal system is not dissipative but approximates the steady‐state mass discharge rate of the full system within 10%. A regime diagram valid under a limited set of conditions indicates when this minimal system captures the ascent dynamics of effusive eruptions. Interestingly, the two novel aspects of the full model, diffusive degassing and heat balance, cannot be neglected. In some cases with high diffusion coefficients, a shallow region where porosity and velocities tend toward zero develops initially, possibly blocking an eventual steady state. This local porosity loss also occurs when a steady‐state solution is subjected to a change in shallow permeability. The resulting shallow porosity loss features many characteristics of a plug developing prior to a Vulcanian eruption. [ABSTRACT FROM AUTHOR]

In a review paper in this same volume, we present the state of the art on modeling of compressible viscous flows ranging from single‐phase to two‐phase systems. It focuses on mathematical properties related to weak stability because they are important for numerical resolution and on the homogenization process that leads from a microscopic description of two separate phases to an averaged two‐phase model. This review serves as the foundation for Parts I and II, which present averaged two‐phase models with phase exchange applicable to magma flow during volcanic eruptions. Here, in Part I, after introducing the physical processes occurring in a volcanic conduit, we detail the steps needed at both microscopic and macroscopic scales to obtain a two‐phase transient conduit flow model ensuring: (1) mass and volatile species conservation, (2) disequilibrium degassing considering both viscous relaxation and volatile diffusion, and (3) dissipation of total energy. The resulting compressible/incompressible system has eight transport equations on eight unknowns (gas volume fraction and density, dissolved water content, liquid pressure, and the velocity and temperature of both phases) as well as algebraic closures for gas pressure and bubble radius. We establish valid sets of boundary conditions such as imposing pressures and stress‐free conditions at the conduit outlet and either velocity or pressure at the inlet. This model is then used to obtain a drift‐flux system that isolates the effects of relative velocities, pressures, and temperatures. The dimensional analysis of this drift‐flux system suggests that relative velocities can be captured with a Darcy equation and that gas–liquid pressure differences partly control magma acceleration. Unlike the vanishing small gas–liquid temperature differences, bulk magma temperature is expected to vary because of gas expansion. Mass exchange being a major control of flow dynamics, we propose a limit case of mass exchange by establishing a relaxed system at chemical equilibrium. This single‐velocity, single‐temperature system is a generalization of an existing volcanic conduit flow model. Finally, we compare our full compressible/incompressible system to another existing volcanic conduit flow model where both phases are compressible. This comparison illustrates that different two‐phase systems may be obtained depending on the governing unknowns chosen. Part II presents a 1.5D version of the model established herein that is solved numerically. The numerical outputs are compared to those of another steady‐state, equilibrium degassing, isothermal model under conditions typical of an effusive eruption at an andesitic volcano. [ABSTRACT FROM AUTHOR]

To constrain the timing of magma emplacement and eruption of volcanic rocks at Mt. Halla, Jeju Island, South Korea, a range of dating techniques (U-Pb, U-Th disequilibrium, and (U-Th)/He dating of zircon, and 40Ar/39Ar dating of groundmass) were applied to one trachyandesite sample and one trachyte sample. Trachyandesite sample CS92-7 from north of Mt. Halla yielded a homogeneous population of zircon U-Pb crystallization ages averaging 97 ± 3 ka and U-Th disequilibrium ages averaging 96.2 + 6.2/−10.6 ka. Both groundmass 40Ar/39Ar ages and zircon (U-Th)/He ages corrected for disequilibrium record the time of sample cooling, yielding ages of 105 ± 5 ka and 105.4 ± 4.0 ka, respectively. The nearly concordant crystallization and cooling ages are interpreted to document eruption of the sample shortly after its relatively rapid crystallization in the magma reservoir. The eruption age of this sample, based on the available geo- and thermochronological results, is estimated at 100.4 ± 7.6 ka. Trachyte sample SS35-23 from south of Mt. Halla yielded an overdispersed spectrum of zircon crystallization ages, suggesting protracted crystallization in the magma reservoir over a period of at least 140 ka. Weighted mean ages of 40.0 ± 5.9 ka and 39.4 ± 3.8 ka (determined from U-Pb and U-Th disequilibrium dating of the youngest coherent subpopulation, respectively), provide a maximum limit for the eruption age. The eruption age is directly constrained in this work at 32.4 ± 8.4 ka by (U-Th)/He data. The 40Ar/39Ar age of 54 ± 7 ka is distinctly different from the zircon crystallization and eruption ages, and is considered to be inaccurate due to a possible issue with sample contamination or excess argon. The combined geochronological methods applied in this study constrain the timing of zircon crystallization, magma residence, and eruption of volcanic rocks on Jeju Island, and provide essential information further improving our understanding of the chronological history of volcanic rocks on Jeju Island. [ABSTRACT FROM AUTHOR]

The identification of extreme wave events' deposits is of the main importance in the contexts of global warming and coastal geohazards. Specifically, improving the knowledge of this phenomenon is extremely relevant for high populated volcanic oceanic islands. In this paper, we analyse two extreme wave event deposits located on a coastal platform formed by lavas from the 1730–1736 Timanfaya eruption in Lanzarote Island (Spain). The first one consists of a boulder ridge parallel to the coast of approximately 750 m in length and 7 m asl in elevation. These are accumulations of non‐cemented large boulders and sands that extend about 150 m inland from the intertidal zone. The boulders are of basaltic composition, heterometric, sub‐rounded to angular, and they reach sizes up to 3 m of major axis. They are imbricated both inland and seaward, indicating a strong inundation and backwash. The second deposit is a small outcrop of boulders of equal composition and sizes up to 1 m of major axis, reaching an elevation up to 6 m asl, and has been correlated with the former deposit. Here, the boulders were also deposited on the Timanfaya lavas and later covered by lava flows extruded during the 1824 eruption. Therefore, both deposits could be related with a chronologically well‐contrasted event, between 1736 and 1824. The origin of these deposits could be interpreted as an extreme storm or a tsunami. There are no historical records of extreme storms in the Canary Islands for this period, but there is documentary evidence of the tsunamis of 1761 and 1755. Moreover, for the latter, there is documentation that indicates its impact on coastal infrastructures in the Canary Islands, including the western slope of Lanzarote, and therefore, we propose these deposits as the first sedimentary evidence of the 1755 tsunami in the Canary Islands. [ABSTRACT FROM AUTHOR]

The objective of this study was to clarify the actual physical and chemical properties of volcanic ejecta immediately after the explosive eruption of Shinmoe-dake, Mt. Kirishima, in Japan. The day after the explosive eruption occurred on March 25, 2018, permeability tests using a cylindrical frame were conducted, and samples collected in the test site were subjected to laboratory soil tests. The real infiltration capacity of the volcanic ejecta showed that the final values were lower (38–92 mm/h) in the talus inside the forest than in the plain outside the forest. This was attributed to the small particle size distribution above 1 mm, regardless of the particle size of the silt/clay particle size segment. The rainfall after the explosive eruption was at most 20–22 mm/h, indicating that the real infiltration capacity value at the end of the eruption was higher than the rainfall value. This was consistent with the fact that no debris-flow was observed at the foot of Shinmoe-dake after the recent eruption. On the other hand, examination of the chemical properties of the volcanic ejecta collected revealed high values of Ca and SO4. These compounds form gypsums by reaction with water, could reduce the infiltration capacity of deposit, possibly contributing generation of mudslide. [ABSTRACT FROM AUTHOR]

This study developed a volcanic disaster risk reduction education program that aims to help junior high school students visually understand the risks of volcanic eruptions using map information and acquire independent assessments and actions to protect their own lives from eruption disasters. First, this program analyzed the present state, problems, and educational needs of volcanic disaster risk reduction education in Japan, and thereafter designed the learning content to fuse information and communication technology (ICT) education based on the Global and Innovation Gateway for All (GIGA) School Initiative promoted by Japan with disaster risk reduction education from a geographical viewpoint. We adopted the ADDIE model from instructional design theory to develop the program. An important feature of this program is the realization of geography learning using the "YOU@RISK Volcanic Disaster Edition," a web-based GIS application developed by the National Research Institute for Earth Science and Disaster Resilience (NIED), as an ICT tool. Learners use YOU@RISK on their tablets and perform operations such as visualizing the risk range in the event of a volcanic eruption and searching for appropriate evacuation sites and routes, while acquiring the knowledge and skills necessary for geographical literacy and emergency response actions. The program is able to realize interactive learning, which is a step ahead of education that relies on conventional paper-based hazard maps. Among active volcanoes nationwide, Mt. Nasu was selected as target volcano for this study. In addition, a junior high school located in the area surrounding Mt. Nasu, Nasu Junior High School in Nasu Town, Tochigi Prefecture, was selected as the target school. The program was implemented by teachers using tablets provided for each student at the school. We evaluated the effectiveness of the program by measuring and analyzing the effects of learning through the practice. Consequently, the effectiveness of the volcanic disaster risk reduction education program using ICT was confirmed. [ABSTRACT FROM AUTHOR]

The violent eruption of the Hunga (Tonga) submarine volcano on 15 January 2022 caused a 58 km‐heigh ash plume, catastrophic tsunami, and significant global seismic and infrasound waves. However, the physical mechanism underpinning its multiple‐explosive events remains unclear, and its resolvability relies on the seismic waveform source inversion. The studies of two different point‐source models, the seismic moment tensor (MT) and the single force (SF), have been performed separately for this eruption, which, interestingly, can explain the seismic data adequately. Here, we use a joint inversion of MT and SF to unravel a composite source of an explosion‐like MT and a significant upward force for the first major explosive event. Regarding the direction and magnitude, we propose that the upward force is likely a rebound force in response to the pressure drop on the seafloor because the water body above the volcano was abruptly uplifted by the shallow underwater explosion. Plain Language Summary: The physical process of the violent eruption of the Hunga (Tonga) submarine volcano on 15 January 2022 remains unclear. To date, the common source model for volcano eruptions—a single force (SF) and the common source model for earthquakes and explosions—a moment tensor (MT), have been inferred individually for this eruption. Interestingly, both can explain the recorded seismic signals reasonably well. A question arises whether a combination of sources is a better physical model. Therefore, we combine the MT and SF to represent the eruption process in this study. The source analysis for the first major event of this eruption reveals a possible composite process of a shallow underwater explosion and a significant upward force. The upward force is opposite the common downward‐reaction force to the material jetting. It is likely caused by the abrupt displacement of the water above the volcano resulting from the shallow underwater explosion. When the downward water pressure on the seafloor vanishes, the seafloor responds by an upward‐rebound force. Key Points: We perform probabilistic inversion of seismic waveform data to study the force equivalent system of the 2022 Hunga (Tonga) eruptionThe first major explosive event of the shallow eruption sequences may consist of an explosion‐like moment tensor and a large upward forceA possible mechanism of the accompanying upward force is the rebound force responding to the sudden pressure drop of uplifted water body [ABSTRACT FROM AUTHOR]

Volcanic eruptions and wildfires can impact stratospheric chemistry. We apply tracer‐tracer correlations to satellite data from Atmospheric Chemistry Experiment—Fourier Transform Spectrometer and the Halogen Occultation Experiment at 68 hPa to consistently compare the chemical impact on HCl after multiple wildfires and volcanic eruptions of different magnitudes. The 2020 Australian New Year (ANY) fire displayed an order of magnitude less stratospheric aerosol extinction than the 1991 Pinatubo eruption, but showed similar large changes in mid‐latitude lower stratosphere HCl. While the mid‐latitude aerosol loadings from the 2015 Calbuco and 2022 Hunga volcanic eruptions were similar to the ANY fire, little impact on HCl occurred. The 2009 Australian Black Saturday fire and 2021 smoke remaining from 2020 yield small HCl changes, at the edge of the detection method. These observed contrasts across events highlight greater reactivity for smoke versus volcanic aerosols at warm temperatures. Plain Language Summary: An unprecedented change in HCl was observed in the lower stratosphere after the 2020 Australian New Year (ANY) wildfire using satellite records since 2004. In this study, we conduct a consistent analysis of HCl impacts using an additional satellite product with measurements since 1991 to examine effects of the catastrophic 1991 Pinatubo volcanic eruption and smaller eruptions, and compare them to the 2020 ANY fire (and remaining smoke in 2021), as well as the much smaller 2009 Australian Black Saturday (ABS) bushfire. This allows analysis of different types of particles (smoke vs. volcanic) and the extremes of each observed to date. While the Pinatubo eruption displayed 10 times greater aerosol loading in the stratosphere than the ANY fire, these two events led to similar net chemical changes in HCl. In contrast, no significant changes in HCl were observed in the lower stratosphere following the Hunga and Calbuco volcanic eruptions, which displayed similar levels of extinction to ANY. Small effects were observed from ABS fire and in 2021, allowing identification of the lower limit of the amount of smoke affecting HCl. These contrasts between events indicate that the wildfire smoke aerosols must be more reactive insofar as chlorine chemistry is concerned. Key Points: The tracer‐tracer correlation method reveals chemical perturbations associated with volcanic aerosols or smokeThe 1991 Pinatubo eruption and the 2020 Australian wildfire markedly perturbed HCl in the southern mid‐latitude lower stratosphereThe Pinatubo eruption had 10 times more aerosol loading than the Australian wildfire, but similar decreases in HCl [ABSTRACT FROM AUTHOR]

Here we present a new 850-year long coccolithophore record from core SO130-289KL in the northeastern Arabian Sea that spans the Greenland Interstadial 20–Greenland Stadial 20 transition including the timing of the ∼74 ka Youngest Toba Tuff (YTT) supereruption. During the warm interstadial, the coccolithophore assemblage is characterized by Gephyrocapsa oceanica (41%) and Florisphaera profunda (30%) while the succeeding cold stadial is distinguished by the abundance of small placolith species (Emiliania huxleyi + G. ericsonii) (52%). However, the oldest samples of the study interval seem to show a stadial-like coccolithophore assemblage. Spectral analysis revealed an interdecadal cycle imprinted in the coccolithophore record during the interstadial that was also independently reported in other terrestrial and marine proxies. Immediately after the YTT eruption, small placoliths increased by 42% from 5% right below the YTT layer to 47% ∼1 mm above the YTT layer, while G. oceanica and Helicosphaera carteri increased and F. profunda decreased within the ∼1.15 cm layer representing about 8–19 years. Subsequently, the coccolithophore assemblage returned to a composition similar to the warm interstadial period before abruptly changing to a stadial composition characterized by the abundance of small placoliths about 100–130 years after the YTT eruption. Therefore, the YTT eruption had a significant impact on the overall coccolithophore assemblage but appears to have not caused the climate transition from interstadial to stadial conditions, supporting proxy and modeling data. However, the overall mechanism driving the observed changes and cyclicities remains unknown but might be related to rapid atmospheric teleconnections of North Atlantic climate variability to the low latitudes. [ABSTRACT FROM AUTHOR]

Machine learning (ML) models are commonly used to generate predictions, but these models can also support the discovery of new science. Generating accurate predictions necessitates that a model captures the structure of the underlying data. If the structure is properly extracted, ML could be a useful exploratory and evidential tool. In this paper, we present a case study that demonstrates the use of ML for exploratory data analysis (EDA) in the climate space. We apply the ML explainability method of spatio-temporal zeroed feature importance (stZFI) to understand how climate variable associations evolve over space and time. Our analyses focus on data from ensembles of earth systems models (ESMs), which provide data on different climate states and conditions. We elect to work with ESM ensembles since they allow us to compare feature importance across alternative scenarios not available with observed data. The ensembles also account for natural variability, so we can distinguish between signal and noise due to natural climate variability when computing feature importance. For our analyses, we consider the 1991 volcanic eruption of Mount Pinatubo: a large stratospheric aerosol injection. We explore the climate pathway associated with the eruption from aerosols to radiation to temperature at both the near-surface and stratospheric levels. In addition to applying the method to data generated from two different ESMs, we apply stZFI to reanalysis data to compare the associations identified by stZFI. We show how stZFI tracks the importance of aerosol optical depth over time on forecasting temperatures. This case study illustrates usefulness of an ML tool (stZFI) for EDA on a well studied climate exemplar. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) radiation can damage DNA and kill cells. We use laboratory and observational studies of the harmful effect of UV radiation on marine photosynthesizers to inform the implementation of a UV radiation damage function for phytoplankton photosynthesis in a modified version of the Community Earth System Model version 2 (CESM2-UVphyto). CESM2-UVphyto is capable of simulating UV inhibition of photosynthesis among modelled phytoplankton and ocean column 5 penetration of UV-A and UV-B radiation. We conduct a series of simulations with CESM2-UVphyto using the Marine Biogeochemistry Library (MARBL) ecosystem model to calibrate estimates of the sensitivity of phytoplankton productivity to UV radiation. Results indicate that increased UV radiation shifts the vertical distribution of phytoplankton biomass and productivity deeper into the column, causes a moderate decline in total global productivity, and changes phytoplankton community structure to favor diatoms. Our new CESM2-UVphyto model configuration can be used to quantify the potential ocean biogeochemical 10 and ecosystem impacts resulting from events that disturb the stratospheric ozone layer, such as an asteroid impact, a volcanic eruption, a nuclear war, and stratospheric aerosol injection-based geoengineering. [ABSTRACT FROM AUTHOR]

Following the Hunga Tonga–Hunga Ha'apai (HTHH) eruption in January 2022, significant reductions in stratospheric hydrochloric acid (HCl) were observed in the Southern Hemisphere mid‐latitudes during the latter half of 2022, suggesting potential chlorine activation. The objective of this study is to comprehensively understand the loss of HCl in the aftermath of HTHH. Satellite measurements and a global chemistry‐climate model are employed for the analysis. We find strong agreement of 2022 anomalies between the modeled and the measured data. The observed tracer‐tracer relations between nitrous oxide (N2O) and HCl indicate a significant role of chemical processing in the observed HCl reduction, especially during the austral winter of 2022. Further examining the roles of chlorine gas‐phase and heterogeneous chemistry, we find that heterogeneous chemistry emerges as the primary driver for the chemical loss of HCl, and the reaction between hypobromous acid (HOBr) and HCl on sulfate aerosols is the dominant loss process. Plain Language Summary: After the eruption of the Hunga Tonga–Hunga Ha'apai (HTHH) volcano in January 2022, there was a substantial decrease in stratospheric hydrochloric acid (HCl) in the Southern Hemisphere mid‐latitudes in the latter part of 2022. This decrease suggests that a chemical reaction involving chlorine processing might have happened. This study aims to comprehensively understand the significant loss of HCl following the HTHH eruption, utilizing satellite measurements and a global chemistry‐climate model for analysis. The anomalies in 2022 show remarkable agreement between the modeled and measured data. By comparing the levels of HCl with another gas called nitrous oxide (N2O), we discover that a lot of the HCl loss was due to chemical reactions, especially during the Southern Hemisphere winter. Upon further investigation into the role of chlorine gas‐phase and heterogeneous chemistry, heterogeneous chemistry emerges as a primary driver for the chemical loss of HCl. The reaction between hypobromous acid (HOBr) and HCl on sulfate aerosols is identified as the dominant loss process. Key Points: Analysis using both model and satellites suggest a significant role of chemical processing in the observed HCl reduction at 20 kmAnalysis of gas‐ and heterogeneous‐phase reactions indicates that heterogeneous chemistry is the main driver for the chemical loss of HClThe dominant heterogeneous loss for HCl is via HOBr + HCl, with HCl + OH also significant due to enhanced OH from heterogeneous chemistry [ABSTRACT FROM AUTHOR]

The Tatun Volcano Group (TVG) is located at the northern end of Taiwan, ~ 15 km from the center of Taipei, a metropolitan area of over seven million inhabitants. A volcanic eruption by the TVG of any type or scale could cause catastrophic human and economic impacts. This paper summarizes previous geochemical, geophysical, and geochronological reports and highlights why the widely accepted age model does not comport with the latest observations. This study also reports novel 40Ar/39Ar ages for two andesite samples and one basalt sample from the TVG. A sample collected from Chihsingshan yields a robust 40Ar/39Ar age of 0.081 ± 0.005 Ma. This provides the first direct evidence of TVG volcanic activity after 0.1 Ma. Two samples yield 0.28 ± 0.02 Ma for Tatunshan and 0.159 ± 0.017 Ma for Honglushan. The younger ages refute previously proposed age models for the TVG. Along with new drone photos and LiDAR images, the age data help resolve eruptive history and advance understanding of volcanic hazards and hazard mitigation in Taiwan and surrounding areas. [ABSTRACT FROM AUTHOR]

The Permo-Triassic mass extinction was linked to catastrophic environmental changes and large igneous province (LIP) volcanism. In addition to the widespread marine losses, the Permo–Triassic event was the most severe terrestrial ecological crisis in Earth's history and the only known mass extinction among insects, but the cause of extinction on land remains unclear. In this study, high-resolution Hg concentration records and multiple-archive S-isotope analyses of sediments from the Junggar Basin (China) provide evidence of repeated pulses of volcanic-S (acid rain) and increased Hg loading culminating in a crisis of terrestrial biota in the Junggar Basin coeval with the interval of LIP emplacement. Minor S-isotope analyses are, however, inconsistent with total ozone layer collapse. Our data suggest that LIP volcanism repeatedly stressed end-Permian terrestrial environments in the ~300 kyr preceding the marine extinction locally via S-driven acidification and deposition of Hg, and globally via pulsed addition of CO2. S-isotope and Hg geochemistry across the terrestrial Permian–Triassic mass extinction (252 Ma) provides evidence of repeated volcanic eruptions over ~300 kyr that drove acidification and poisoning of a palaeo-lacustrine ecosystem in northwest China. [ABSTRACT FROM AUTHOR]

The Younger Toba Tuff (YTT) eruption is regarded as one of the largest of its time and possibly responsible for changing past climate and vegetation from C3 to C4 in the Indian subcontinent. A paleosol constituting a Toba pre-tephra horizon at the Jwalapuram locality, exhibits the preservation of biogenic structures identified as Vondrichnus planoglobus and Vondrichnus obovatus. This study investigated their paleoecological and paleoenvironmental significance. These structures are hard and compact, rounded to sub-rounded, spherical to sub-spherical bodies with empty chambers, surrounded by carbonate layers, and preserved in close proximity to termite pipes and nests and rhizolith structures. Their occurrence in the Jwalapuram area is significant, as the locality has been well documented as suitable for reconstruction of past climate and vegetation in light of the impact of the YTT eruption. Based on the present findings, we assume that the investigated locality would likely have an insect population and bush to scrub vegetation, indicating a dry environment immediately before the YTT eruption. [ABSTRACT FROM AUTHOR]

Determining the spatial thickness (z) of in situ and reworked fallout pyroclastic deposits plays a key role in volcanological studies and in shedding light on geomorphological and hydrogeological processes in peri-volcanic areas. However, this is a challenging line of research because (1) field-based measurements are expensive and time-consuming, (2) the ash might have been dispersed in the atmosphere by several volcanic eruptions, and (3) wind characteristics during an eruptive event and soil-forming and/or denudation processes after ash deposition on the ground surface affect the expected spatial distribution of these deposits. This article tries to bridge this knowledge gap by applying statistical techniques for making representative spatial thickness predictions to be used for the analysis of geomorphic processes at the catchment and sub-catchment scales. First, we compiled a field-based thickness measurement dataset (https://doi.org/10.5281/zenodo.8399487 ; Matano et al., 2023) of fallout pyroclastic deposits in the territories of several municipalities in Campania, southern Italy. Second, 18 predictor variables were derived mainly from digital elevation models and satellite images and were assigned to each measurement point. Third, the stepwise regression (STPW) model and random forest (RF) machine learning technique are used for thickness modeling. Fourth, the estimations are compared with those of three models that already exist in the literature. Finally, the statistical combination of different predictions is implemented to develop a less biased model for estimating pyroclastic thickness. The results show that the prediction accuracy of RF (RMSE <82.46 and MAE <48.36) is better than that of existing models in the literature. Moreover, statistical combination of the predictions obtained from the above-mentioned models through a least absolute deviation (LAD) combination approach leads to the most representative thickness estimation (MAE <45.12) in the study area. The maps for the values estimated by RF and LAD (as the best single model and combination approach, respectively) illustrate that the spatial patterns did not change significantly, but the estimations by LAD are smaller. This combined approach can help in estimating the thickness of fallout pyroclastic deposits in other volcanic regions and in managing geohazards in areas covered with loose pyroclastic materials. [ABSTRACT FROM AUTHOR]

The Canadian segment of the Cascade Volcanic Arc (i.e. the Garibaldi Volcanic Belt) comprises more than 100 eruptive centres, spanning the entire Quaternary period (Pleistocene to Holocene in age), and with deposits ranging in composition from alkaline basalt to rhyolite. At least one of the volcanoes is currently active; Mount Meager / Q̓welq̓welústen erupted explosively 2360 years BP and has ongoing fumarolic activity. Long-term forecasting of eruption frequency and style depends on reconstruction of the history and timescales of magmatic processes preceding previous volcanic eruptions. Utilising diffusion chronometry, we investigate the Mount Meager Volcanic Complex focusing on Holocene olivine-phyric basalts (Lillooet Glacier basalts) exposed by the retreat of the Lillooet Glacier. We identify two distinct olivine populations in samples of quenched, glassy basalt lavas that record different magmatic processes and histories. Glomerocrysts of Fo83 olivine phenocrysts, entrained and transported by a hot mafic input, form Population 1. These exhibit resorption and normally zoned outermost rim compositions of Fo76–78; a third of them also show interior reverse compositional zoning. A second population of skeletal microphenocrysts have the same composition as the phenocryst rims (i.e. Fo76–78) and are in equilibrium with the adjacent matrix glass. We estimate the pre-eruptive temperature- f O2 conditions in a shallow reservoir (100 MPa; ~3 km) for a melt with H2O content of 0.5 to 1 wt % as ~1097°C to 1106°C (± 30°C), and NNO + 0.5 (±1.1), respectively. Using these input parameters, we report Fe-Mg diffusion chronometry results for 234 normally zoned profiles from 81 olivine phenocrysts. Diffusion modelling of compositional profiles in oriented crystals indicates pre-eruptive magmatic residence times of 1 to 3 months. These remarkably short residence times in shallow reservoirs prior to eruption suggest very short periods of unrest may precede future eruptions. [ABSTRACT FROM AUTHOR]

The 2050 ± 50 14C yBP caldera-forming eruption of Okmok volcano, Alaska, had a global atmospheric impact with tephra deposits found in distant Arctic ice cores and a sulfate signal found in both Greenland and Antarctic ice cores. The associated global climate cooling was driven by the amount of sulfur injected into the stratosphere during the climactic phase of the eruption. This phase was dominated by pyroclastic density currents, which have complex emplacement dynamics precluding direct estimates of the sulfur stratospheric load. We simulated the dynamics of the climactic phase with the two-phase flow model MFIX-TFM under axisymmetric conditions with several combinations of mass eruption rate, jet water content, vent size, particle size and density, topography, and emission duration. Results suggest that a steady mass eruption rate of 1.2–3.9 × 1011 kg/s is consistent with field observations. Minimal stratospheric injections occur in pulses issued from the central plume initially rising above the caldera center and from successive phoenix ash-clouds caused by the encounter of the pyroclastic density currents with topography. Most of the volcanic gas is injected into the stratosphere by the buoyant liftoff of dilute parts of the currents at the end of the eruption. Overall, 58–64 wt% of the total amount of gas emitted reaches the stratosphere. A fluctuating emission rate or an efficient final liftoff due to seawater interaction is unlikely to have increased this loading. Combined with petrological estimates of the degassed S, our results suggest that the eruption injected 11–20 Tg S into the stratosphere, consistent with the subsequent climate response and Greenland ice sheet deposition. Our results also show that the combination of the source Richardson number and the mass eruption rate is able to characterize the buoyant–collapse transition at Okmok. We extended this result to 141 runs from 10 published numerical studies of eruptive jets and found that this regime diagram is able to capture the first-order layout of the buoyant–collapse transition in all studies except one. An existing multivariate criterion yields the best predictions of this regime transition. [ABSTRACT FROM AUTHOR]

The phreatomagmatic eruption of Taal Volcano in Batangas, Philippines, in January 2020 resulted in a massive ash plume covering a large portion of nearby provinces, including Metro Manila. This event caused damage and disruptions to various sectors, including agriculture, the environment, health, infrastructure, and aviation. The challenge of managing the vast amount of collected tephra environmental waste prompted the initiative of converting it into a useful material. This study characterizes and evaluates the quality of the collected tephra as a potential raw material for the construction industry, based on the Philippine National Standard (PNS) 07:2018, to ensure structural integrity and public safety. Four ashfall samples from strategic locations, identified by the Philippine Institute of Volcanology and Seismology (PHIVOLCS), were obtained and analysed for specific chemical parameters using various analytical techniques. The results suggest that tephra has potential as a raw material for ground-level structures. However, further treatment is necessary to reduce the concentration of certain constituents. The material met the standard specifications for SiO2, MgO, and SO3. However, the levels of Al2O3, Fe2O3, total alkali, loss on ignition, and water-soluble and acid-soluble Cl– exceeded the threshold limits set by PNS 07:2018 and EN 197-1:2000. [ABSTRACT FROM AUTHOR]

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

Coronal mass ejections from the Sun are not always initiated along a radial trajectory; such non-radial eruptions are well known to be caused by the asymmetry of the pre-eruption magnetic configuration, which is primarily determined by the uneven distribution of magnetic flux at the photosphere. Therefore, it is naturally expected that the non-radial eruptions should be rather common, at least as frequent as radial ones, given the typically asymmetrical nature of photospheric magnetic flux. However, statistical studies have shown that only a small fraction of eruptions display non-radial behaviour. Here we aim to shed light on this counterintuitive fact, based on a series of numerical simulations of eruption initiation in bipolar fields with different asymmetric flux distributions. As the asymmetry of the flux distribution increases, the eruption direction tends to deviate further away from the radial path, accompanied by a decrease in eruption intensity. In case of too strong asymmetry, no eruption is triggered, indicating that excessively inclined eruptions cannot occur. Therefore, our simulations suggest that asymmetry plays a negative role in producing eruption, potentially explaining the lesser frequency of non-radial solar eruptions compared to radial ones. With increasing asymmetry, the degree of non-potentiality the field can attain is reduced. Consequently, the intensity of the pre-eruption current sheet decreases, and reconnection becomes less efficient, resulting in weaker eruptions. [ABSTRACT FROM AUTHOR]

Feature Selection (FS) is regarded as an important preprocessing technique with the main aim of discarding irrelevant and redundant features on the premise of improving or retaining classification accuracy. As one of the most popular FS methods, the swarm intelligent (SI) algorithm based FS method faces great challenges in solution quality. Given this, a novel probe mechanism based particle swarm optimization (PPSO) is proposed. The probe mechanism is proposed to test the dataset with different filter methods by employing a part of features to generate high-quality initial population, thus playing a critical role in enhancing the final results of the algorithm. Next, the repeated binarized solution avoid mechanism prevents the same binarized solution from repeating compute the fitness function, which can improve the exploration capability. Additionally, a volcanic eruption mechanism based on the updated information of the global best solution is designed to improve the performance in convergence rate and search precision. In the experiment section, 14 UCI datasets are employed to assess the performance of the PPSO. The outcomes show that the designed strategies can significantly improve the original PSO, and the PPSO is more efficient than the other comparative algorithms for solving the FS problems. In addition, the impact of each strategy is analyzed, and the volcanic eruption mechanism is the most efficient among the three strategies. [ABSTRACT FROM AUTHOR]

Rivers of tropical islands formed by volcanic eruptions experience unpredictable and heavy rainfall and are characterised by irregular topography. During the 2019 and 2020 low-water season, we investigated the responses of benthic macroinvertebrate assemblages to variations in local environmental conditions in four rivers located in areas of different rainfall intensity. We found that changes in local environmental conditions associated with lower rainfall intensity reduced abundance and taxonomic richness and modified taxonomic composition but did not impact the balance of functional feeding groups of macroinvertebrate communities amongst streams, except for piercer herbivores. Heterotrophy associated with substrate instability and autotrophy with a more stable substrate co-occurred in semi-arid climate rivers. In contrast, a change from heterotrophy upstream to autotrophy and substrate stability downstream was apparent in the two humid rivers studied. Surrogates of stream ecosystem function revealed a very low ratio of coarse to fine particulate organic matter related to the quasi-absence of shredders in these streams and suggested a low allochthonous input contribution, which could be the result of the 5% decline in forest cover over the two past decades. [ABSTRACT FROM AUTHOR]

Volcanic eruption is known as multi-hazards to the surrounding environment and society causing the formation of lahar as the frequent hazards that shortly occurred due to airborne tephra after an eruption. Erosion triggered by rainfall on unconsolidated tephra material, such as volcanic ash, is the primary lahar initiation mechanism. The time and scale of lahars vary based on eruptions and watershed conditions. The variability of the erosion process is driven by a set of local factors including the grain size and spatial distribution of volcanic ash thickness, slope, and rainfall intensity. Laboratory simulation experiments were conducted in a 3.00 m long, 0.75 m wide, and 0.50 m deep flume to study the relationship of volcanic ash erosion rate to three driven parameters, namely slope, rainfall intensity, and volcanic ash thickness. Three slope gradients were selected to represent gentle (14.1%), mild (26.8%), and steep (46.6%) slopes. Meanwhile, the rainfall intensity ranged from 0.65 to 1.85 mm.min-1, and the variations of volcanic ash layer thickness were 1.00 cm; 2.50 cm; and 5.00 cm. The erosion rate model was generated from a dimensional analysis accommodating slope, rainfall intensity, flow discharge, and the ratio of critical and applied boundary shear stress as independent variables. The variable coefficients were obtained by parameter optimization of experiment data through nonlinear regression analysis. The erosion rate model performance was tested using the Nash-Sutcliffe model Efficiency (NSE), Index of Agreement (IOA), and Root Mean Square Error (RMSE). The performance of the volcanic ash erosion rate model was proven to be satisfactory with the NSE>0.75, IOA>0.95, and RMSE values ranging from 0.005 to 0.009. This model has proven applicable better for volcanic ash erosion than other erosion models which are sandy soil material-based experiments because of the specific characteristics of volcanic material itself. The volcanic ash erosion model in this study can be implemented to predict the sediment yield of tephra as part of volcanic disaster mitigation. [ABSTRACT FROM AUTHOR]

The early Jurassic syn-rift phase generated a significant set of half-grabens, calderas, and pull-apart basins along the southwestern margin of South America. In particular, the Loncon Complex, located in the western Extra-Andean region of North Patagonia (∼40°S), forms part of such structures. In the present contribution, we characterize and define the Early Jurassic extensional architecture of the Loncon Complex, constituted of a small-scale pull-apart basin associated with polygenetic volcanism, based on outcrop-scale kinematic data from strike-slip faults, and stratigraphic analysis. Lithofacies analysis, texture, componentry, and structural data allow us to distinguish four stages during the evolution of the Complex; the three early stages are followed by a deformational phase, and crowned by a limited felsic monogenetic volcano; stages consist of a) A continental alluvial to fluvial sedimentation related with an early pull-apart basin phase; b) local phreatomagmatic explosions with syn-eruptive sedimentation periods of a medium life cycle (~104-105 years), b) effusive andesitic stage generated by strike-slip transtension, resulting in partial deformation and development of a local unconformity, and c) a final short-term silicic tuff ring volcano construction (days to months' time span). The measured faulting pattern is synchronous with the Loncon Complex's sedimentation and volcanism. Kinematic data allow us to characterize the Loncon Complex evolution under NNE-NNW minimum horizontal stress (SHmin). This local NNE-oriented extension is interpreted as a consequence of a regional process, in a similar way to the report for the Neuquén Basin and the surrounding region in Patagonia. New U-Pb data indicate the onset of volcanism began in the Sinemurian (193.08 ± 1.13 Ma) also supporting an equivalent timing with the vicinity half-grabens areas of the North Patagonia region and the Neuquén Basin (Figure S1a). The process that occurred during the Sinemurian, and probably during the Pliensbachian, affected the entire back-arc basin developed along the southwestern border of Gondwana. [ABSTRACT FROM AUTHOR]

Lacustrine environments from Northern Patagonia are exposed to volcanic events from the Southern Volcanic Zone. Chironomid larvae are an important paleo-proxy because, in addition to their environmental sensitivity, their chitinous cephalic capsules are well preserved in lacustrine sediments, allowing their recovery and identification. We analysed the effects of a recent volcanic eruption (Puyehue-Cordón Caulle Volcanic Complex 2011) on the chironomid community based on their cephalic remains accumulated following the ash deposition process. Two pulses of ash deposition were distinguished: a first stage comprising the immediate coarse ash fall and a delayed finer volcanic deposition. An abrupt decline in chironomid taxa and their densities were noted during the first coarse pulse, followed by an attempt of community recovery through the second finer pulse, characterised by main taxa turnover, observing an alternative community functional structure. Based on these results and comparing with past volcanic depositions, we observed different chironomid responses according to their particular ecological habits, and we noted possible percolation effects, mainly in coarse tephras, and probably a delayed record of very low abundance taxa. Our results suggest caution in analysing chironomid assemblages within and adjacent to tephra deposition as local volcanic eruption could affect chironomid community with possible consequences on paleoreconstructions. [ABSTRACT FROM AUTHOR]

We present 40Ar/39Ar ages of dacite domes and rare volcanic sanidine megacrysts from Taápaca volcano (northern Chile) that record 1.3 m.y. of activity. Our focus is on 20 megacrysts from a single 32.9 ka eruption. We interpret that their surprisingly correlated Ba-rich and Ba-poor growth zones separated by resorption surfaces reflect frequent heat pulses with a uniform thermal history over >300 k.y. of growth. We infer extended storage in small (<400 m), shallow “hot” domains within a larger magma system. Our findings bear on the origin of K-feldspar megacrysts in plutonic rocks, thus linking volcanic and plutonic processes in shallow silicic magma systems, and support protracted residence of hot magma in small batches at upper-crustal levels to produce megacryst-bearing granitoid intrusive complexes. [ABSTRACT FROM AUTHOR]

The impact of geohazards on the mental health of local populations is well recognised but understudied. We used natural language processing (NLP) of Twitter (now known as X) posts (n=10341) to analyse the sentiments expressed in relation to a pre-eruptive seismic unrest and a subsequent volcanic eruption in Iceland in 2019–2021. We show that although these geohazards were of a small size and caused negligible material damage, they were associated with a measurable change in expressed emotions in the local population. The seismic unrest was associated with predominantly negative sentiments (positive-to-negative sentiment ratio of 1:1.3), but the eruption was associated with predominantly positive sentiments (positive-to-negative sentiment ratio of 1.4:1). We demonstrate a cost-effective tool for gauging public discourse that could be used in risk management. [ABSTRACT FROM AUTHOR]

Volcanic eruptions stand as destructive threats to adjacent communities, unleashing multiple hazards such as earthquakes, tsunamis, pyroclastic flows, and toxic gases. The imperative for proactive management of volcanic risks and communities' adaptation cannot be overstated, particularly in densely populated areas where the potential for widespread devastation looms large. Kolumbo, an active submarine volcano located approximately 7 km northeast of Santorini Island in Greece, serves as a pertinent case. Its historical record is characterised by an eruption in 1650 CE that produced a catastrophic tsunami. The aftermath witnessed havoc on neighbouring islands, coupled with casualties stemming from noxious gases in Santorini. Eyewitness accounts mention maximum water run-up heights of 20 m on the southern coast of Ios, inundation of an area of 240 m inland on Sikinos, and a flooding of up to 2 km2 inland on the eastern coast of Santorini. Recent studies suggest that a potential future eruption of Kolumbo poses a substantial hazard to the northern and eastern coasts of Santorini. Unfortunately, the absence of a concrete management protocol leaves these areas vulnerable to an impending threat that demands immediate attention. Therefore, it is recommended that a comprehensive approach be adopted, involving scientific research (active monitoring, hazard maps), community engagement, preparedness planning with government agencies, and the development of timely response strategies to reduce the associated risks, prevent casualties, and mitigate the potential consequences on the region's economy and infrastructure. [ABSTRACT FROM AUTHOR]

Continental intraplate volcano is an ideal probe to unravel the composition and structure of the deep Earth. The intraplate Changbaishan‐Tianchi volcano was one of the most hazardous eruptions on the Earth's planet. The long‐term activity of this volcano from the Pleistocene to 946 CE has erupted materials with a broad compositional range from basalt to rhyolite, which are expected to be associated with the continuous northeastward subduction of the Pacific plate, but the magma source remains controversial. In this paper, we present a comprehensive data set of in situ zircon Hf and O isotope data, combined with whole‐rock element and Sr‐Nd‐Pb isotope compositions, for selected eruptions of the Changbaishan‐Tianchi volcano, aiming to provide new insights into their magma source and the associated geodynamics. Radiogenic isotopic ratios and incompatible trace element compositions indicate that the erupted volcanic rocks at different stages, although with a varied differentiation degree, were derived from a common magma source characterized by a mixture of DM and EM1 end‐members. Zircon Hf and O isotopes are both relatively homogeneous for different lithologies and eruption stages, with the εHf(t) values varying between −5 and +5, and δ18O values between 3.58‰ and 5.97‰. Modeling of source mixing indicates that high‐temperature altered oceanic crust materials are an important component in the source of Changbaishan‐Tianchi volcano, likely derived from an ancient stagnant slab that has been reactivated by the subduction of the Pacific plate. This study demonstrates that the recycling of deeply subducted oceanic crust is potentially an important source and trigger for continental intraplate volcanism. Plain Language Summary: The Millennium Eruption (ME) of the Changbaishan‐Tianchi intraplate volcano at 946 common era (CE) was one of two largest explosive eruptions in the past 2,000 years, but its source is poorly constrained. This paper represents a comprehensive data set of in situ zircon Hf and O isotope data, combined with whole‐rock element and Sr‐Nd‐Pb isotope compositions, for providing a full picture of magma evolution and new insights into the magma source and the associated geodynamics. Our data indicate that high‐temperature altered oceanic crust, likely a former part of the subduction of the Pacific plate, has been an important component in the source of the Changbaishan‐Tianchi volcano. Therefore, the Changbaishan‐Tianchi volcano demonstrates that continental intraplate volcanism can also be impacted by long‐distance subduction of oceanic crusts. Key Points: The long‐term eruptions of the intraplate Changbaishan‐Tianchi volcano from the Pleistocene to 946 CE were derived from a common magma sourceZircon Hf and O isotopes indicate important contributions from subducted oceanic crust [ABSTRACT FROM AUTHOR]

Dating young lava flows is essential for understanding volcano's eruption frequency, yet challenging due to methodological limitations of commonly used dating techniques. Ruapehu (Aotearoa New Zealand) produced many lava flows during the Holocene, but constraints on the timing of these eruptions are scarce. Here, we use paleomagnetic dating to deliver new eruption ages of 18 lava flows with uncertainties ranging between 500 and 2,700 years (at the 95% confidence level). Comparison between lava flows' paleomagnetic directions and a local paleosecular variation record indicates that the large lava flow field located on the Whakapapa area was emplaced during at least three distinct eruptive episodes between 10600 and 7400 BP. Two of these episodes closely followed a large collapse event that affected Ruapehu's northern area and generated large volumes of lava between 10600 and 8800 BP, with the third episode producing less voluminous lava flows between 8100 and 7400 BP. Following a smaller collapse of the southeastern sector of the edifice at ca. 5300 BP, several low‐volume lava flows were emplaced during at least two distinct eruptive episodes prior to ca. 1000 BP, which supplied the Whangaehu valley with lava. The youngest age inferred from our data represents the youngest eruption age provided for a lava flow outside Ruapehu's summit region. This research provides greater detail to the Holocene effusive chronology at Ruapehu, shedding light on partial cone reconstructions after edifice collapses during the Holocene, and the time relationships between trends observed in its effusive and explosive activity. Plain Language Summary: Knowing when volcanoes have erupted is essential for hazard assessments, but the precise timing of geologically young lava flow eruptions is hard to determine with traditional methods. Earth's magnetic field is constantly changing in both direction and strength. Magnetic minerals contained in the lava flows record the direction of the field as the lava cools after eruption. Hence, solidified lavas can be dated by matching their magnetization directions to a reference record. In this study, we analyze the magnetization directions recorded in prehistoric lavas at Mt. Ruapehu (Aotearoa New Zealand) and use them to determine when they erupted. We show that a large flow field in the Whakapapa area (northwest Ruapehu) was formed during at least three distinct eruptive episodes between 10,600 and 7,350 years ago, following a catastrophic volcanic landslide at around 10,600 years ago. We also determine that the lavas present in the Whangaehu valley (east Ruapehu) erupted during at least two episodes between 4,600 and 1,000 years ago, the latter representing the youngest lavas known outside the summit area of Ruapehu. This research helps understand how Ruapehu was rebuilt after slope collapses, and the frequency of lava‐forming eruptions. Key Points: Paleomagnetism was used to date eruptive episodes in lava flow sequences at RuapehuPaleomagnetic dating yields 1300–1050 BP as the youngest eruption age known for a lava flow at the volcanoOur data provide age constraints on the timescales of vent migration and partial edifice rebuilding after collapse events [ABSTRACT FROM AUTHOR]

A large mantle helium anomaly and separate domains of high heat flow are the predominant manifestations of bimodal magmatic activity in the Milford valley. The mantle helium anomaly (1.9–2.6 R/Ra) covers 270 km2 and is subdivided into two separated domains: a cold shallow groundwater regime and high temperature hydrothermal activity. The zone of anomalous heat flow covers >100 km2 and is also subdivided into two adjacent domains, comprising hydrothermal activity at Roosevelt Hot Springs (RHS) (3–7 W/m2) and conductive heat flow (100–180 mW/m2). While the transfer of heat and mantle helium at RHS are coupled, heat and helium transfer are decoupled in the adjacent cold groundwater regime to the west. Both the mantle helium and geothermal anomalies are attributed to recent mafic‐felsic magmatic intrusions of >400 km3, however, the absence of volcanic eruptions <500,000 years indicates magmas stall before rising to shallow crustal level <10 km depth. Deep level magmatism produces a felsic composition melt, which is inferred to be responsible for the widespread and near uniform range of diluted mantle helium values. A thick and impermeable mass of crystalline granitic basement rock at the mid‐crustal level divides the ascent of mantle helium into separate flow paths. It may also impede the rise of buoyant magma trapping thermal energy that facilitates partial melting, slow cooling, and development of a thick thermal aureole. Partitioning of convective and conductive thermal regimes and independent flow paths supplying deeply derived helium characterize the development of a large long‐lived magma‐related geothermal system. Plain Language Summary: Productive high‐grade geothermal resources, a form of renewable energy, are associated with volcanic centers and zones of hydrothermal activity in regions undergoing crustal thinning. The Milford valley in southwest Utah is host to a long dormant volcanic center whose modern expression is mostly limited to hydrothermal activity at Roosevelt Hot Springs, which has produced energy since 1984. The US Department of Energy established the Utah FORGE enhanced geothermal systems (EGS) field laboratory in an adjacent zone of extensive hot dry crystalline rock to advance new methods of energy production. Newly discovered additional natural expression of the geothermal system occurs in the shallow cold groundwaters defined by infiltration of deep‐derived mantle helium. It is the primary indication of undiscovered zones of high heat flow and geothermal resources concealed beneath the surface. The isotopic composition of the helium, plus the high geothermal heat flow, suggest that helium is derived from a large body of magma (>400 km3) that is similar in composition to the volcanic deposits that erupted 500,000 to 800,000 years ago in the nearby Mineral Mountains. A thick mass of impermeable granitic rock forms a barrier to magma ascent, suppressing the recent volcanic activity, and producing geothermal resources instead. Key Points: A large groundwater mantle He anomaly and geothermal resources are shallow manifestations of mafic‐felsic magmatism in the lower crustTwo pathways transect the crust transferring mantle He with or without heat at Roosevelt Hot Springs and the adjacent cold groundwater regimeMid‐crustal granitic basement rock impedes the rise of buoyant magma trapping thermal energy that facilitates partial melting and slow cooling [ABSTRACT FROM AUTHOR]

Deception Island (DI) is an active volcanic caldera in the South Shetland Islands, Antarctica, with an inner bay, Port Foster, formed by an ancient eruption. The bay's seafloor hydrofracture system contains hydrothermal seeps and submarine vents, which are a source of trace metals (TMs) like Fe, Ni, Co, V, and greenhouse gases (GHGs) such as CO2 and CH4. This study presents measurements of TMs and GHGs in Port Foster's surface waters during January-February 2021 to characterize their spatial distribution. TMs concentrations in the northeastern region of the bay, particularly V (74 nM), Fe (361 nM), Co (3.9 nM) and Ni (17.2 nM), were generally higher than in the Southern Ocean, likely due to hydrothermal activity. As some TMs such as Fe are scarce in the SO and limit primary productivity, inputs of these nutrients from DI into surrounding waters may also regionally promote increased primary productivity. Higher surface temperature (ST), elevated partial pressure of CO2 (pCO2), and lower salinity were found near submarine fumaroles, with ST positively correlated with pCO2 and negatively with salinity. Although hydrothermal sites showed localized CO2 outgassing, the bay overall acted as a CO2 sink, with a median flux of -2.78 mol m-2 yr-1 with an interquartile range (IQR) of 3.84 mol m-2 yr-1. CH4 highest concentration levels were found in the southeastern sector. The median concentration was 8.9 nM with an IQR of 1.9 nM, making Port Foster a regional net CH4 source with a median flux of 9.7 μmol m-2 d-1 and an IQR of 3.4 μmol m-2 d-1. Ultimately, the analysis of spatial patterns of the measured variables suggested that fumaroles of DI may be playing a significant role in the alteration of regional seawater biogeochemistry. [ABSTRACT FROM AUTHOR]

Building damage from tephra falls can have a substantial impact on exposed communities around erupting volcanoes. There are limited empirical studies of tephra fall impacts on buildings, with none on tephra falls impacting traditional thatched timber buildings, despite their prevalence across South Pacific island nations and parts of Asia. The 2017/2018 explosive eruption of Manaro Voui, Ambae Island, Vanuatu, resulted in damage to traditional (thatched timber), non-traditional (masonry), and hybrid buildings from tephra falls in March/April and July 2018. Field and photographic surveys were conducted across three separate field studies with building characteristics and damage recorded for a total of 589 buildings. Buildings were classified using a damage state framework customised for this study. Overall, increasing tephra thicknesses were related to increasing severity of building damage, corroborating previous damage surveys and vulnerability estimates. Traditional buildings were found to be less resistant to tephra loading than non-traditional buildings, although there was variation in resistance within each building type. For example, some traditional buildings collapsed under ~40 mm thickness while others sustained no damage when exposed to >200 mm. We attribute this to differences in the pre-eruption condition of the building and the implementation of mitigation strategies. Mitigation strategies included covering thatched roofs with tarpaulins, which helped shed tephra and consequently reduced loading, and providing an internal prop to the main roof beam, which aided structural resistance. As is typical of post-event building damage surveys, we had limited time and access to the exposed communities, and we note the limitations this had for our findings. Our results contribute to the limited empirical data available for tephra fall building damage and can be used to calibrate existing fragility functions, improving our evidence base for forecasting future impacts for similar construction types globally. [ABSTRACT FROM AUTHOR]

The Eldgjá eruption is the largest basalt lava flood of the Common Era. It has been linked to a major ice‐core sulfur (S) spike in 939–940 CE and Northern Hemisphere summer cooling in 940 CE. Despite its magnitude and potential climate impacts, uncertainties remain concerning the eruption timeline, atmospheric dispersal of emitted volatiles, and coincident volcanism in Iceland and elsewhere. Here, we present a comprehensive analysis of Greenland ice‐cores from 936 to 943 CE, revealing a complex volatile record and cryptotephra with numerous geochemical populations. Transitional alkali basalt tephra matching Eldgjá are found in 939–940 CE, while tholeiitic basalt shards present in 936/937 CE and 940/941 CE are compatible with contemporaneous Icelandic eruptions from Grímsvötn and Bárðarbunga‐Veiðivötn systems (including V‐Sv tephra). We also find four silicic tephra populations, one of which we link to the Jala Pumice of Ceboruco (Mexico) at 941 ± 1 CE. Triple S isotopes, Δ33S, spanning 936–940 CE are indicative of upper tropospheric/lower stratospheric transport of aerosol sourced from the Icelandic fissure eruptions. However, anomalous Δ33S (down to −0.4‰) in 940–941 CE evidence stratospheric aerosol transport consistent with summer surface cooling revealed by tree‐ring reconstructions. Tephra associated with the anomalous Δ33S have a variety of compositions, complicating the attribution of climate cooling to Eldgjá alone. Nevertheless, our study confirms a major S emission from Eldgjá in 939–940 CE and implicates Eldgjá and a cluster of eruptions as triggers of summer cooling, severe winters, and privations in ∼940 CE. Plain Language Summary: The eruption of Eldgjá in the tenth century is the largest lava flood in the history of Iceland. Although Eldgjá emitted immense volumes of ash, lava, and gas, the exact timing and duration of this eruption, as well as its environmental and climatic impact remain unclear. Here, we provide a comprehensive chemical analysis of Greenland ice‐core records spanning the period 936–943 CE. We identify volcanic ash from at least three different Icelandic eruptions and confirm that there was a major ash and gas emission from Eldgjá in 939 CE. Using tree ring temperature estimates we find strong evidence for Northern Hemisphere climate cooling in the summer of 940 CE. However, the variety of volcanic ash identified in the ice‐cores shows that several Icelandic and Northern Hemisphere arc volcanoes were also erupting in this period. While Eldgjá remains the prime candidate, these additional eruptions complicate the attribution of reported climate and societal changes to Eldgjá alone. Ultimately, our study sheds new light on a cluster of volcanic eruptions between 936 and 943 CE and highlights the challenges of disentangling the individual contributions of multiple eruptions on the environment and climate. Key Points: New analyses of Greenland ice‐core records of volcanism between 936 and 943 CEIcelandic eruptions from Grímsvötn and Bárðarbunga‐Veiðivötn detected between 936 and 941 CE, and major Eldgjá emission in 939–940 CEVarious silicic eruptions identified, including the Jala Pumice (Mexico), providing new and valuable trans‐continental tephra isochrons [ABSTRACT FROM AUTHOR]

We use measurements of trace gases from the Microwave Limb Sounder and polar stratospheric clouds (PSCs) from the Cloud‐Aerosol Lidar with Orthogonal Polarization to investigate how the extraordinary stratospheric water vapor enhancement from the 2022 Hunga eruption affected polar processing during the 2023 Antarctic winter. Although the dynamical characteristics of the vortex itself were generally unexceptional, the excess moisture initially raised PSC formation threshold temperatures above typical values. Cold conditions, especially in early July, prompted ice PSC formation and unusually severe irreversible dehydration at higher levels (500–700 K), while atypical hydration occurred at lower levels (380–460 K). Heterogeneous chemical processing was more extensive, both vertically (up to 750–800 K) and temporally (earlier in the season), than in prior Antarctic winters. The resultant HCl depletion and ClO enhancement redefined their previously observed ranges at and above 600 K. Albeit unmatched in the satellite record, the early‐winter upper‐level chlorine activation was insufficient to induce substantial ozone loss. Chlorine activation, denitrification, and dehydration processes ran to completion by July/August, with trace gas evolution mostly following the climatological mean thereafter, but with chlorine deactivation starting slightly later than usual. While cumulative ozone losses at 410–550 K were relatively large, probably because of the delayed chlorine deactivation, they were not unprecedented. Thus, ozone depletion was unremarkable throughout the lower stratosphere. Although Hunga enhanced PSC formation and chemical processing in early winter, saturation of lower stratospheric denitrification, dehydration, and chlorine activation (as is typical in the Antarctic) prevented an exceptionally severe ozone hole in 2023. Plain Language Summary: The 2022 eruption of the Hunga volcano produced an increase in stratospheric water vapor unmatched in the satellite record. Excess moisture pervaded the Antarctic stratosphere at the beginning of the 2023 Southern Hemisphere winter. Cold moist conditions prompted formation of ice clouds in the Antarctic stratosphere at higher altitudes than usual. Falling ice particles caused unusually severe permanent removal of water vapor from these levels and deposited it at lower altitudes. Chemical processing on polar stratospheric cloud particles occurred both earlier in the season and over a broader vertical domain than typical, resulting in exceptional early‐winter upper‐level conversion of chlorine from nonreactive into ozone‐destroying forms. Chemical processing ran its course by midwinter (i.e., July/August), with trace gases, including ozone, mostly following average behavior thereafter. Deactivation (reconversion of chlorine into nonreactive forms) started slightly later than in most years. While cumulative seasonal ozone losses were relatively large at some levels, probably because of the delayed chlorine deactivation, they were not unprecedented. Thus, although Hunga accelerated and expanded the vertical extent of chemical processing in early winter, that chemical processing reached completion as usually happens in Antarctic midwinter, preventing an extraordinarily severe ozone hole in 2023. Key Points: Hydration from Hunga led to unusually early and vertically extensive polar stratospheric cloud activity in the 2023 Antarctic vortexAs a result, heterogeneous chlorine activation occurred weeks earlier and at higher altitudes and dehydration removed more H2O than typicalDespite exceptional early‐winter conditions, cumulative ozone losses were unremarkable because stratospheric chemical processing saturated [ABSTRACT FROM AUTHOR]

This study explores the dynamic evolution of the Hunga Volcano in the Kingdom of Tonga and covers two volcanic unrests, focusing on the creation and subsequent disappearance of a new island between Hunga Tonga (HT) and Hunga Ha'apai (HH) between 2013 and 2023. The island expanded in 2015 and vanished in January 2022 due to a massive eruption (VEI = 6), featuring a 57 km high volcanic cloud and generating multiple tsunamis that caused damage across the Pacific Ocean. Utilizing remote sensing techniques, including multispectral imaging from Sentinel 2, Landsat 8-9, and synthetic aperture radar (SAR) imaging from Sentinel 1, the research employs a supervised random forest classification algorithm to individuate the changing subaerial surface area of the volcano. This approach documents size variations in the islands, particularly during weeks surrounding two volcanic unrests. The classifier, trained on nearly cloud-free multispectral images, automatically delineates surface area changes over the years. The temporal resolution of area change, limited to images with less than 5% cloudiness, encompasses about 50% of Landsat and 20% of Sentinel 2 images between 2013 and 2023, selected from 739 available images. The multispectral observations are complemented by 215 Sentinel 1 SAR images, penetrating clouds, though with limited bands. Despite higher noise, the classifier on Sentinel 1 successfully distinguishes land from ocean. Sentinel 1 observations, starting in 2014, cover the volcano unrest of 2014/2015. Earth Engine, a cloud computing data facility, is used for processing. Analysis indicates a slight decrease in the area change post-2015 island formation and identifies the disappearance of the island bridge connecting HT and HH, along with two smaller islands south of HT and HH in 2022. The 2022 explosion is preceded by an increase in island area in the weeks before the eruption. Global satellite coverage could automatically detect changes in oceanic areas and distinguish water from new volcanic islands, offering a means of identifying volcanic unrests and documenting their evolution. [ABSTRACT FROM AUTHOR]

Climatic impacts of historical volcanism are principally tied to the eruption size, while observation versus model discrepancies have been commonly attributed to the uncertainties in paleo‐reconstruction or malpresentation of volcanic aerosols in models. Here we present convergent evidence for significant compensation effect of ocean latent heat (LH) in balancing the tropical volcanic‐induced heat loss, by introducing an effective perturbation ratio which is found to decrease with increasing eruption magnitude. Four LH compensation hot spots overlapping with the trade wind regions are identified, together with three western boundary currents regions with intensified LH loss. Comparison between the 1258 Samalas and 1452 Unidentified eruptions suggests considerable modulation of the concurring El Nino‐Southern Oscillation on LH anomaly, which is further verified by CESM large ensemble sensitivity experiments. This study depicts how the interplay between the ocean and the atmosphere could contribute to the overall resilience of the climate system in the face of volcanic disturbances. Plain Language Summary: Large volcanic eruptions drive significant climate perturbation and the resulting cooling generally decreases with increasing eruption size, especially over the surface and upper ocean. In this study we introduce an effective volcanic perturbation ratio, defined as the ratio between the surface net flux anomaly and the volcanic‐induced shortwave flux anomaly, and analyze its relationship with the eruption magnitude. Our results, based on tree‐ring reconstructions and the CESM‐LME simulations, suggest that the effective ratio gradually decreases with the increasing shortwave perturbation, and the reduction of latent heat (LH) flux from ocean to atmosphere balances a significant portion of the volcanic‐induced net surface heat loss. LH varies with wind speeds and vertical specific humidity gradient. We identify four LH compensation effect hot spots which highly overlap with the trade wind regions, and three western boundary currents regions with intensified ocean latent heat loss. We run sensitivity experiments using the 1815 eruption of Mount Tambora as a test case, and find that the ENSO responses accompanying the eruption could modify the LH compensation effect. Key Points: Volcanic‐induced temperature responses do not scale linearly with the eruption sizes in both reconstruction and model simulations with same aerosol ‐ radiative treatmentOcean latent heat (LH) flux plays an important role in compensating volcanic‐induced radiative heat loss which enhance with growing eruption sizeInternal climate variability such as ENSO inserts significant influence on LH's compensation role through the wind‐evaporation‐SST feedback [ABSTRACT FROM AUTHOR]

Volcanic eruptions carry essential information on the dynamics of volcanic systems. Studies have documented variable eruption styles and eruptive surface deformation. However, co‐eruptive subsurface structural changes remain poorly understood. Here we characterize the seismic velocity changes from July 2019 to July 2023 at Great Sitkin Volcano in the central Aleutian volcanic arc, using single‐station ambient noise interferometry at five three‐component seismic stations. Coincident with the lava effusion since late July 2021, about two months after the explosive eruption on 26 May 2021, we observe a sustained velocity increase, most prominently to the northwest of the caldera. We attribute this velocity increase to the structural changes with magma extrusion, with the spatial variation controlled by the geometry of the magma system or the property of shallow volcaniclastics. Our findings offer insights into understanding co‐eruptive structural modifications at active volcanoes. Plain Language Summary: Volcanic eruptions provide important insights into how volcanoes work and the potential risks they pose. This study looks at the ongoing eruption at Great Sitkin Volcano in the central Aleutian volcanic arc to better understand the changes happening beneath the surface. We measure the changes in the velocity of seismic waves, with data from five seismometers on the island. We collected data from July 2019 to July 2023, covering different eruptive stages and multiple lava effusion episodes during the eruption that started on 26 May 2021. Coincident with the lava effusion since late July 2021, we notice a significant increase in seismic velocities, most prominently at a station northwest of the volcano's central crater. We conclude that this increase reflects the structural change in the shallow subsurface due to magma extrusion, with deflation of the edifice and closure of cracks. The findings in this study help to improve our understanding of how volcanoes behave during eruptions. Key Points: We observe prominent, spatially variable increases in seismic velocity during lava effusions at Great Sitkin Volcano since late July 2021The sustained co‐eruptive increase in seismic velocity reflects structural changes with crack closures as the consequence of magma extrusionThe distinct spatial variation of the velocity increase may be controlled by reservoir geometry or the strength of shallow volcaniclastics [ABSTRACT FROM AUTHOR]

Long-term ground-based lidar observations are important in estimating the contribution of different sources (mostly volcanic eruptions and wildfires) to aerosol loading of the atmosphere and in developing and improving various climate models. In this paper, we carefully analyse aerosol scattering ratio profiles and aerosol layers, observed with 532-nm lidar measurements at the Siberian Lidar Station in Tomsk (56.48°N, 85.05°E) over the period 2018–2022, and identify the layers' potential sources. To compare aerosol loading over Tomsk for the last five years (2018–2022) with that for previous years, we also present and discuss time series of integrated aerosol backscatter coefficient (IABC) for three altitude ranges. The first range (15–30 km) reveals the pure stratospheric aerosol loading provided by volcanic eruptions, the second range (11–15 km) is responsible mainly for aftereffects of wildfire smoke plumes, and the third one (11–30 km) demonstrates aerosol contribution from both sources. In particular, we found for the period 2001–2022 that the annual average IABC reached its maximal values of 2.91 × 10−4 sr−1 (15–30 km) and 8.21 × 10−4 sr−1 (11–30 km) in 2022 due to the Hunga Tonga-Hunga Ha'apai volcanic eruption. The period 2020–2022 exhibited a significant increase in the relative aerosol content at altitudes of 11–15 km in the total aerosol loading at 11–30 km over Tomsk from 54.4% in 2020 to 64.8% in 2022, which indicates a shift of the main part of aerosol loading to altitudes of 11–15 km due to the increased wildfire activity in North America and north-eastern Asia. The Arctic polar vortex is also revealed to distort the real aerosol vertical distribution over Tomsk by replacing it with the aerosol distribution inside the vortex on measurement days when the vortex is over the lidar site. [ABSTRACT FROM AUTHOR]

Aerosol effective radiative forcing (ERF) has persisted as the most uncertain aspect of anthropogenic forcing over the industrial period, limiting our ability to constrain estimates of climate sensitivity and to confidently predict 21st century climate change. Aerosol–cloud interactions are the most uncertain component of aerosol ERF. The 2014–2015 Holuhraun volcanic eruption acted as a large source of sulfur dioxide, providing an opportunistic experiment for studying aerosol–cloud interactions at a climatically relevant scale. We evaluate the observed aerosol-induced perturbation to marine liquid cloud properties inside the volcanic plume in the first month of the eruption and compare the results to those from UKESM1 (UK Earth System Model). In the first 2 weeks, as expected, we find an in-plume shift to smaller and more numerous cloud droplets in both the observations and the simulations. We find an observed increase in liquid water path (LWP) values inside the plume that is not captured in UKESM1. However, in the third week, the in-plume shift to smaller and more numerous cloud droplets is neither observed nor modelled, and there are discrepancies between the observed and modelled response in the fourth week. An analysis of the model simulations and trajectory modelling reveals that air mass history and background meteorological factors can strongly influence aerosol–cloud interactions between the weeks of our analysis. Overall, our study supports the findings of many previous studies: the aerosol impact on cloud effective radius is significant, with differences in the observed and modelled response for in-cloud LWP. [ABSTRACT FROM AUTHOR]