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Changes in volcanic activity are frequently correlated with geochemical changes in crater lake waters. Volcanologists employ periodic surveys of the volcano crater lake which include pH and temperature monitoring. Due to the exposure of volcanologists to volcanic hazards, a robotic remote monitoring system was implemented in this study. A ground robot with a tethered sensing device, launcher, and retrieval system is investigated for pH and temperature real-time data sensing considering the challenging conditions of Taal Crater Lake in the Philippines. The sensing device has a tethering system attached to two mechanisms: the launcher and the retrieval systems. From the test experiments, it was found that the system can project the sensing device for a horizontal distance of 3 meters and retrieve it smoothly. The pH and temperature sensors in the device were calibrated and demonstrated acceptable levels of error and reliability. An actual test on a lake environment was implemented. The remote-controlled ground robot can navigate the sensing device to the required default position near the lake shore and effectively launch the sensing device into the water. Moreover, the tethered sensing device successfully performed real-time pH and temperature data sensing of the water and was securely retrieved from the water back to the ground robot. After the real-time data were assessed and validated, the average errors for the temperature and pH data were only 0.44% and 1.8%, respectively. [ABSTRACT FROM AUTHOR]

One of the most intriguing questions of modern volcanology is the inception of an eruption. Despite efforts to detect premonitory signals, numerous unpredicted eruptions have occurred recently. It has been suggested that these unpredicted eruptions might be explained by viscosity variations in elemental sulfur accumulated within the hydrothermal systems present in several volcanic settings under the influence of organics, hydrocarbons, hydrogen sulfide, halogens, and ammonia. Changes in impure sulfur viscosity are more complex than those in pure S, invoked decades ago to trigger eruptions by system sealing in volcanoes hosting a crater lake. Growing evidence suggests that sulfur accumulation is a common process, not restricted to crater lakes. Moreover, both types and amounts of gas species released at the surface, critical for volcano monitoring, would be altered, following chemical reactions involving impure S, invalidating signals used to issue alerts. Impure sulfur behavior may explain puzzling degassing and contrasting signals reported at volcanoes and restless calderas worldwide, with implications for hazard assessment and volcanic-risk-mitigation strategies. [ABSTRACT FROM AUTHOR]

The Tsiolkovsky crater is located on the farside of the Moon. It formed in the late Imbrian epoch and was filled with a large area of mare basalts. Multisource remote sensing data are used to interpret the geological features of the Tsiolkovsky area. Compared with previous studies, new remote sensing data and a chronological model based on crater size–frequency distribution are used to further refine the stratigraphic units and determine the absolute ages of the mare basalt units. The evolution of volcanic activity in this crater is discussed. The results are as follows: Abundances of major elements, Th, and silicate minerals suggest that the mare basalt in the crater floor is not a uniform unit but rather nine units with different compositions. The nine basalt units are divided into two episodes of volcanic activity: The first occurred at 3.5–3.7 Ga, when highly evolved lava erupted at the crater floor at a large scale; the second occurred at ~3.4 Ga, when a small area of more primitive lava extended to the northern portion of the crater floor. [ABSTRACT FROM AUTHOR]

Big Soda Lake, Nevada, is a multi‐extreme meromictic lake, whose hypersaline hyperalkaline bottom waters feature permanent anoxia and high concentrations of arsenic, sulphide and ammonia. These properties make Big Soda Lake—and the adjacent Little Soda Lake—a fascinating system for exploring life's boundaries, discovering novel microbial taxa and identifying biotechnologically useful strains. To date, the taxonomic diversity and metabolic capabilities of microorganisms in this system remain largely unknown. Here, we fill this gap using microbiome surveys across the Big and Little Soda Lake water columns, including 16S rRNA sequencing, fungal ITS2 sequencing and gene‐ and genome‐resolved metagenomics. We accompany these surveys with measurements of salinity, pH, temperature, oxygen, ammonium and ammonia concentrations. Our analyses reveal rich bacterial communities, taxonomically and functionally differentiated along Big Soda Lake's oxycline and, to lesser extent, between lakes. Fungal communities were dominated by a small number of families, while nearly no archaea were detected. Pathways related to perchlorate reduction, anoxygenic phototrophy, fermentation, dissimilatory metabolism of arsenite/arsenate, sulphur compounds, nitrogen compounds and hydrogen, were particularly prevalent. A total of 129 high‐quality bacterial and archaeal metagenome‐assembled genomes (completeness ≥ 80%, contamination ≤ 5%) were recovered, yielding insight into the taxonomic distribution of microbial metabolic pathways. [ABSTRACT FROM AUTHOR]

The varve chronological approach has been applied to older ages (pre-Quaternary) in the Shanwang Basin for the first time. This study focuses on the analysis of diatom shale from the Shanwang Basin, which was formed in Maar Lake (a volcanic crater basin, often filled by a lake). The lacustrine sediments of the basin encapsulate comprehensive geological information. By identifying species and providing systematic paleontological descriptions of diatoms in the profile, two genera and seven species were recognized. A microscopic examination of the thin sections revealed five types of laminae and couplets. On this basis, the study adopted the artificial semi-automatic counting method of the laminae. The calculation results show that the age of the diatom shale section in the Shanwang Basin is 18.524–17.985 Myr B.P, the deposition time is 0.54 Myr, and the deposition rate is 4.06 cm/Kyr. Finally, through the comparative discussion of various dating methods, it can be concluded that the varve chronology is a more accurate and reliable dating method than other dating methods. The research findings contribute to our understanding of the geological history of the region. [ABSTRACT FROM AUTHOR]

Active volcanoes often discharge hot (T ≫ 100 °C) magmatic gases whose original composition has been modified through partial interaction with an externally fed hydrothermal system. The study of methane (CH 4) in these volcanic discharges may provide useful information on the interplay between deep magmatic gases and shallow circulation of hydrothermal fluids. However, the origin of CH 4 in high-temperature volcanic gases and the factors exerting control on its abundance and stable isotope composition are still largely unknown. Here, we present the abundances and stable isotopic composition of CH 4 in hot (99–387 °C) volcanic gases from the La Fossa volcanic crater of Vulcano Island (Southern Italy). Our investigation revealed low (<1.5 μmol/mol) CH 4 concentrations and an extraordinarily large variability in CH 4 stable isotopic composition, with δ13C and δ2H values being positively correlated and varying from −35 to −9.2 ‰ and −670 to −102 ‰, respectively. Notably, CH 4 isotopes measured at Vulcano almost encompasses the global-scale variability observed in natural fluids, with δ2H values ≤ −500 ‰ being the first ever reported in nature. Gases showing extremely negative δ13C-CH 4 and δ2H-CH 4 values systematically display higher CH 4 abundances. We propose two possible scenarios in order to explain the observed huge variation in δ13C and δ2H: (1) mixing of 13C- and 2H-depleted CH 4 with 13C- and 2H-enriched CH 4 of thermogenic origin formed under hydrothermal conditions; (2) post-genetic removal and isotopic alteration of 13C- and 2H-depleted CH 4 occurring during the ascent of volcanic gases. Comparing our dataset with available isotopic data from naturally occurring and artificially produced CH 4 , a thermogenic origin for the isotopically light CH 4 seems unlikely. We postulate that the 13C- and 2H-depleted CH 4 may have formed via kinetically-controlled abiotic synthesis through CO (or CO 2) hydrogenation reactions in the hot ascending gas phase, possibly at temperatures intermediate between those typical of magmatic and hydrothermal conditions. Further investigations of methane in high-temperature volcanic gases are necessary to test this hypothesis. [ABSTRACT FROM AUTHOR]

The Sheveluch volcano is the most active volcano in Kamchatka. The paroxysmal explosive eruption of the volcano that destroyed the lava dome in the volcanic crater continued on April 10–13, 2023. According to various satellite data, the height of the separate eruptive clouds probably exceeded 15 km above sea level. A powerful cyclone, which dominated the entire Kamchatka Peninsula, pulled the eruptive cloud to the west, turned it to the south, stretched it to the north, and directed it to the east from the volcano. The dynamics of the development of ash and aerosol clouds of this eruption is reflected in the animations made from a series of Himawari-9 satellite images in the VolSatView IS from 08:00 UTC on April 10 to 07:00 UTC on April 14 (http://d33.infospace.ru/jr%5fd33/materials/2023v20n2/283-291/1683110898.webm) and of the Arctica-M1 satellite from 16:00 to 21:30 UTC on April 10 (http://d33.infospace.ru/jr%5fd33/materials/2023v20n2/283-291/1683821166.webm). It was noted that the eruptive column was not vertical: for example, at the initial moment of the eruption on April 10 at 13:20 UTC, it deviated to the north–northeast; on April 11, at 12:00 UTC to the northwest; and, on April 12, at 7:00 UTC to the southwest. During the paroxysmal eruption, sulfur dioxide continuously entered the atmosphere, the maximum amount of which was released on April 10–11, as a result of the explosive destruction of the lava dome of the Sheveluch volcano. Ash clouds along with aerosol clouds on April 10–13 were stretched into a strip more than 3500 km long from west to northeast. On April 21–22, the Sheveluch aerosol cloud was observed in the region of the Scandinavian Peninsula. The total area of the territory of Kamchatka and the Pacific Ocean where ash and aerosol plumes and clouds were observed during the April 10–13 eruption was about 3 280 000 km2. The paroxysmal eruption of Sheveluch volcano belongs to the sub-Plinian type because it is characterized by a large height of the eruptive cloud and a long event duration. For this eruption, the Volcanic Explosivity Index is estimated to be 3–4. A detailed description of the paroxysmal explosive eruption of the Sheveluch volcano and the spread of the eruptive cloud was performed based on data from various satellite systems (Himawari-9, NOAA-18/19, GOES-18, Terra, Aqua, JPSS-1, Suomi NPP, Arctica-M1, etc.) in the information system "Remote Monitoring of Kamchatka and Kuril Islands Volcanic Activity" (VolSatView, http://kamchatka.volcanoes.smislab.ru). [ABSTRACT FROM AUTHOR]

This work reports on data on a moderate effusive-explosive eruption of a summit crater of Alaid volcano (Atlasova Island, Northern Kuril Islands) observed from September 10 to December 1, 2022. Based on satellite and visual data, it was determined that the strombolian-vulcanian activity resulted in two lava flows, 2.6- and 1-km long, that outflowed onto the southern slope of the volcano and at least 16 emissions occurred to heights of 2.5 to 6 km a.s.l. The ash plumes spread out mainly in the southeast and east-southeast directions with their maximum length reaching 300–530 km. The eruption posed a danger to local airlines. The lava outflow provoked the formation of lahars that descended along the southern slope of the volcano and reached the island coast. The alluvial fan formed from mudflow masses partially deposited beyond the coastline, causing accretion of the island land. [ABSTRACT FROM AUTHOR]

The Experiment to Study Thunderstorm High-Energy Radiation (ESTHER) is a small project of the Italian National Institute for Astrophysics (INAF), devoted to the study of high-energy emissions from thunderstorms, such as Terrestrial Gamma-ray Flashes and gamma-ray glows, which will start in 2024. In order to reduce the absorption typically undergone by gamma-ray radiation in the lower layers of the atmosphere and make these events detectable on the ground, the ESTHER set-up will be installed at high altitudes on Mt. Etna (Italy). We carried out a detailed analysis of lightning occurrence in this geographic region in order to test how suitable such a location is for the installation of a detection system to investigate thunderstorms and related emissions. The analysis pointed out a strong clustering of lightning in the proximity of the mountain peak and over the main volcano craters, where the frequent presence of volcanic ashes could increase, under the conditions of humid air typical of thunderstorms, electrical conductivity. An estimate of the gamma-ray absorption in the air undergone by typical TGF radiation allowed us to evaluate the suitability of two possible installation sites suggested for the project. This study represents a preliminary work for ESTHER and serves as a launching pad for future analyses. [ABSTRACT FROM AUTHOR]

Rincon de Parangueo (RP) is a Quaternary maar crater located in the Michoacan‐Guanajuato Volcanic Field in central Mexico. Like other volcanic craters in the region, the central part was occupied by an endorheic lacustrine system. As a consequence of extensive groundwater extraction, the perennial lake started a gradual desiccation process and now the remnant ponds host a highly saline–alkaline ecosystem. The stratigraphic record indicates an exceptional and long‐term sedimentation of carbonate microbialites. Previous studies based on the 16S rRNA gene have shown that microbial communities have a widespread presence in the crater at the microbialites, the remaining saline ponds, superficial soils and below the surface. To understand the possible role of the microbial communities that generate these biogeological structures, novel analytical methods to resolve the amplicon datasets and their microbial metabolic potential were used.We describe in detail the relationship between the microbial communities, the evolution of physicochemical parameters, and carbonate morphology, in four micro‐environments. A 16S rRNA gene sequencing dataset from previous publications was re‐analysed using an ASV‐based bioinformatic pipeline to identify new insights into the microbial assemblage. Finally, a taxon‐based metabolic profile was used to predict the potential metabolic contribution of the prokaryotic community.Results indicated a refinement in terms of community composition using the ASV‐based bioinformatic methods. Functional profiling through 16S rRNA gene‐based analysis suggested metabolisms associated with carbonate precipitation, indicating a broad potential for microbially mediated carbonate precipitation (e.g., carbon fixation and photosynthesis). The possibility of biogenic methane gas production by methanogenic microorganisms was recognised, supporting the estimated flow of methane on the surface soils.The lacustrine evolution over the last years and the extreme physicochemical characteristics of RP have an impact on the microbial community structure. Prokaryotic community and metabolic potential results from RP coincide with the diversity and abundance of microbial communities and functional metabolisms reported from other microbialite‐forming lakes along the Trans Mexican Volcanic Belt. The identification of important possible phylotypes involved in carbonate precipitation might be an important factor in considering RP microbialites as active calcifying entities.These findings provide novel insights into the potential key role of metabolic pathways driving the process of carbonate precipitation inside RP and evidence of its importance as a microbial biodiversity hotspot in Mexico. [ABSTRACT FROM AUTHOR]

Stromboli is an open-conduit active volcano located in the southern Tyrrhenian Sea and is the easternmost island of the Aeolian Archipelago. It is known as "the lighthouse of the Mediterranean" for its continuous and mild Strombolian-type explosive activity, occurring at the summit craters. Sometimes the volcano undergoes more intense explosions, called "major explosions" if they affect just the summit above 500 m a.s.l. or "paroxysms" if the whole island is threatened. Effusive eruptions are less frequent, normally occurring every 3–5 years, and may be accompanied or preceded by landslides, crater collapses and tsunamis. Given the small size of the island (maximum diameter of 5 km, NE–SW) and the consequent proximity of the inhabited areas to the active craters (maximum distance 2.5 km), it is of paramount importance to use all available information to forecast the volcano's eruptive activity. The availability of a detailed record of the volcano's eruptive activity spanning some centuries has prompted evaluations on its possible short-term evolution. The aim of this paper is to present some statistical insights on the eruptive activity at Stromboli using a catalogue dating back to 1879 and reviewed for the events during the last two decades. Our results confirm the recent trend of a significant increase in major explosions, small lava flows and summit crater collapses at the volcano, and might help monitoring research institutions and stakeholders to evaluate volcanic hazards from eruptive activity at this and possibly other open-vent active basaltic volcanoes. [ABSTRACT FROM AUTHOR]

Volcano crater lakes, while picturesque, can sometimes mask the occurrence of small eruptions or hydrothermal fluid release events. However, these seemingly hidden events hold a wealth of valuable information about the underlying volcanic conduit and may pose risks to those near the volcano's summit. This study presents a novel method for identifying these hard‐to‐detect fluid release events by examining seismic data from Ruapehu volcano in New Zealand. We undertake a multi‐timescale template‐matching analysis that uses a newly discovered seismic eruption precursor, to identify patterns related to the rapid consolidation of hydrothermal seals, pressurization processes, and the subsequent release of hydrothermal fluids. As a result, we identified a potential instance of sudden fluid‐release events that were previously unnoticed due to the presence of the crater lake. Our findings support a conceptual model of cyclic pressure variation within the conduit beneath an active crater lake. This model involves the formation and disruption of seals, followed by depressurization through hydrothermal fluid release events. Fluid discharge recession recorded as seismic amplitude decay, provides information about the properties of the reservoir, conduit, and the fluid being discharged. We also applied this technique to Kawah‐Ijen (Indonesia) and Copahue (Chile‐Argentina), identifying multiple potential events at these volcanoes. These findings enhance our understanding of the conditions leading to explosive eruptions, including those that could breach the crater lake. Plain Language Summary: We analyzed seismic data from Ruapehu volcano (New Zealand) to improve volcanic event catalogs by locating signatures of rapid hydrothermal seal formation and failure. Events are detected temporally within the seismic record using an empirical model of sealing/pressurization/eruption proposed for Whakaari volcano in New Zealand. The approach allows us to identify fluid release events that might have been obscured by Ruapehu's crater lake or have been too small to be noticed by standard monitoring techniques. Our analysis has revealed several fluid release episodes, including reported eruptions, where a peak in displacement seismic amplitude ratio is followed by a sharp increase in real‐time seismic amplitude measurement and an exponential decay in the hours and days following the events. We model this decay using a linear dependence on the degassing rate, and exponential relaxation from a discharging linear reservoir. These findings can help us conceptualize the conditions leading to explosive, potentially lake breaching eruptions. Key Points: Volcano crater lakes can obscure volcanic fluid release eventsThrough volcano seismic data in a template‐matching approach, we identified short‐term sealing, pressurization, and fluid‐release pulsesWe identified several fluid‐released events at Ruapehu (New Zealand), Copahue (Chile/Argentina), and Kawah Ijen (Indonesia) volcanoes [ABSTRACT FROM AUTHOR]

Volcanic glow, which is often observed at active craters during nighttime, contains information on high-temperature zones deep in the crater that are hidden from view. We analyzed 90 eruption videos capturing volcanic glow before the onset of Vulcanian eruptions at the Showa crater of Sakurajima volcano (Japan), and found that they show clear temporal changes. The red (R)-value and the green-to-red ratio (GR ratio) are used to track glow intensity and temperature change, respectively. We found two types of temporal change in glow intensity: a short-term change approximately 1 s before the onset of explosions, and a long-term change 3 to 330 s before an explosion. Short-term changes were observed for 28 of 90 eruptions, and coincided with an increase in the GR ratio and with a modest precursory infrasound pressure increase. Since an increasing GR ratio means a temperature increase, we consider that the change was associated with the opening of tensile cracks on the crater floor before an explosion. However, the other 62 eruptions did not show short-term changes, suggesting that the opening of cracks is sporadic. Long-term changes were observed for 73 of 90 eruptions, the GR ratio did not exhibit a significant increase. We suggest that long-term changes are caused by gradual gas leakage, which precedes initiation of Vulcanian eruptions. We hypothesize that the long-term gas leakage causes gradual decompression of the conduit, which induces supersaturation of volatile-rich magma beneath the lava plug causing explosive expansion, thereby triggering an eruption. [ABSTRACT FROM AUTHOR]

From April to July 2021, West Crater at Iwo-Yama, Kirishima Volcanic Complex, Japan, was repeatedly filled with hydrothermal water and subsequently evacuated. The overall cycle lasted 14–70 h, and the course of a single cycle followed this sequence of phases: (i) steam effusion disappeared 20–40 min before hydrothermal water discharge; (ii) hydrothermal water discharge occurred, generating a hydrothermal water pool; (iii) steam effusion resumed and gradually increased; and (iv) drain-back (evacuation) of the hydrothermal water occurred 1–1.5 h before the onset of the next hydrothermal water discharge. We used multi-parametric observations (optical camera, thermometer, electric self-potential (SP) electrodes, seismometer, acoustic sensor, and tiltmeter) to investigate the cause of the cyclic hydrothermal water discharge. A change in SP data occurred approximately 2 h before the onset of hydrothermal water discharge. However, the change in SP was small when hydrothermal water discharge did not occur. The temporal change in SP is inferred to have been caused by groundwater flow through the region below West Crater, implying that groundwater flow was occurring 2 h before hydrothermal water discharge. The polarity of SP change suggests that groundwater flowed toward the region underlying the vents. Seismic signals in the frequency range of < 20 Hz decreased 15–45 min after the onset of change in SP. This seismic signal pattern is inferred to have been caused by bubble activity in boiling fluid. We interpret that the inflow of cold groundwater inhibited boiling activity in the conduit, which in turn caused the cessation of both steam effusion and seismic activity. SP data suggest that the inflow of cold groundwater gradually decreased before hydrothermal water discharge. Pressurization sufficient to force the water in the upper part of the conduit to ascend could have built up in the lower part of the conduit owing to a decrease in the input of groundwater into the upper part of the conduit and the continuing supply of steam bubbles and hot water. This increase in pressure finally led to hydrothermal water discharge at the surface. We suggest that the inflow of cold groundwater into the geyser conduit was the key control on the occurrence and cyclicity of hydrothermal water discharge in West Crater at Iwo-Yama. [ABSTRACT FROM AUTHOR]

During a volcanic crisis, high‐rate, localized deformation can indicate magma close to the surface, with important implications for eruption forecasting. However, only a few such examples have been reported, because frequent, dense monitoring is needed. High‐resolution Synthetic Aperture Radar (SAR) is capable of achieving <1 m spatial resolution and sub‐weekly revisit times, but is under‐used. Here we use high‐resolution satellite SAR imagery from COSMO‐SkyMed, TerraSAR‐X, and Sentinel‐1 to detect intra‐crater uplift preceding the November 2017 onset of eruptive activity at Agung, Indonesia. Processing the SAR imagery with an up‐to‐date, accurate, high‐resolution digital elevation model was crucial for preventing aliasing of the deformation signal and for accurate georeferencing. We show that >15 cm of line‐of‐sight shortening occurred over a 400‐by‐400 m area on the crater floor in September‐October 2017, accompanying a deep seismic swarm and flank dyke intrusion. We attribute the deformation to the pressurization of a shallow (<200 m deep) hydrothermal system by the injection of magmatic gases and fluids. We also observe a second pulse of intra‐crater deformation of 3–5 cm within 4 days to 11 hr prior to the first phreatomagmatic eruption, which is consistent with interaction between the hydrothermal system and the ascending magma. This phreatomagmatic eruption created the central pathway used during the final stages of magma ascent. Our observations have important implications for understanding unrest and eruption forecasting, and demonstrate the potential of monitoring with high‐resolution SAR. Plain Language Summary: At volcanoes, the ground surface can move due to the activity of magma and associated fluids underground. This deformation is a warning sign that can be useful when forecasting volcanic eruptions, especially when the deformation area is small (less than 1–2 km2), indicating that magma or magmatic fluids are close to the surface (less than 1 km deep). High‐resolution satellites such as COSMO‐SkyMed can measure ground deformation several times per week with better than 1 m resolution and are thereby able to detect and monitor rapid small‐area deformation. We use high‐resolution elevation and radar satellite data to detect deformation on the crater floor of Mount Agung, Indonesia, occurring before the November 2017 eruption. We show that the crater floor moved toward the satellites by more than 15 cm in September‐October 2017, accompanying an earthquake swarm, caused by magma intruding into the flank of the volcano. In the 4 days leading up to the eruption, we see another 3–5 cm of deformation. A shallow body of magmatic fluids less than 200 m below the crater floor was probably responsible for this ground deformation. Our research shows the potential of monitoring volcanoes with high‐resolution radar satellites. Key Points: We analyze high‐resolution Interferometric Synthetic Aperture Radar data from before the November 2017 eruption of Agung, Indonesia, and find localized deformation∼15 cm of intra‐crater deformation occurred in September‐October, with another 3–5 cm in the 4–0.5 days before the first phreatomagmatic explosionMagmatic fluids emitted by a flank dyke pressurized the shallow (<200 m) hydrothermal system, causing precursory deformation [ABSTRACT FROM AUTHOR]

At active volcanoes, the surface temperature and its spatial distribution can indicate changes in the underlying magmatic and hydrothermal system. Surface temperature monitoring has been widely performed using thermal remote sensing with thermal infrared (TIR) cameras. One of the drawbacks of this method is that the unknown viewing orientation of TIR images inhibits quantitative evaluations of the spatial extent and distributions of thermal anomalies. Therefore, many studies have performed 3D temperature-field reconstructions by processing TIR images photogrammetrically. However, these studies have not included the correction of TIR wave atmospheric attenuation and viewing-angle variation in emissivity in the reconstruction procedure, which can result in significant temperature misestimation. We propose a simple method that incorporates the correction into the reconstruction process, which can improve the estimation of surface temperature, especially in rugged terrains. We demonstrate our method for the active crater of Aso volcano in Japan. We create digital elevation models by applying the Structure from Motion–Multi-view Stereo algorithm to aerial visible images taken at the same time as the TIR images and then project the TIR images onto the DEM with the direct georeferencing method. The correction is carried out using the geometric parameters acquired in the process. We create 1-m resolution orthorectified thermal images of the crater on two separate dates (18 August 2020 and 16 March 2022) and calculate the heat discharge rates from steaming grounds and a volcanic lake. We find that the heat discharge rate from the fumarolic field on the south crater wall showed a sevenfold increase after the phreatic explosions that occurred on 14 and 20 October 2021. [ABSTRACT FROM AUTHOR]

The present work aims to characterize the ephemeral mineral assemblage related to the fumarolic fields of the Tajogaite volcano, formed in 2021 in La Palma Island (Canary Islands, Spain). A set of 73 samples was obtained after two sampling campaigns in different fumarole sectors of the studied area. Mineralization related to these fumaroles formed efflorescent patches located at variable distance from the main volcanic craters. Distal patches are predominantly whitish, while in the vicinities they typically show yellowish to orange colours. Field observations also revealed that fumaroles usually occur in elevated topographic areas as well as over fractured and porous volcanic pyroclastic materials. The mineralogical and textural characterisation of the Tajogaite fumaroles unfolds a complex mineral assemblage, comprising cryptocrystalline phases related to low (< 200 °C) and medium temperature (200–400 °C) conditions. In Tajogaite, we propose a classification of three different fumarolic mineralization types: (1) fluorides and chlorides located in proximal fumarolic areas (~ 300–180 °C); (2) native sulphur associated with gypsum, mascagnite and salammoniac (~ 120–100 °C) and (3) sulphates and alkaline carbonates typically occurred in distal fumarolic areas (< 100 °C). Finally, we present a schematic model of the formation of Tajogaite fumarolic mineralization and their compositional evolution developed during the cooling of the volcanic system. [ABSTRACT FROM AUTHOR]

Interactions between volcanoes and glaciers provide insight to the evolution of a volcanic edifice and may be an indicator for renewed volcanic activity. At Mount St. Helens, Crater Glacier, which has formed in the volcanic crater after the eruption in 1980, is one of the world's last expanding glaciers and provides a unique opportunity to characterize the evolution of a glacier expanding onto an area of significant thermal flux. We combine photographic documentation and glaciovolcanic cave surveys with remote sensing data from Google Earth, UAS, and LiDAR to analyze the present state of Crater Glacier and reconstruct its development since the emplacement of the 2004–2008 lava dome. Our results show that snow accumulation has caused Crater Glacier to grow from 2009 to 2019 by approximately 13.8 × 106 m3, during which time the glacier toe advanced by several hundred meters. The glacier-dome interface shift toward higher elevations against the 2004–2008 lava dome and subsequent encroachment onto thermally active areas led to glacier modification via extensive subglacial cave system formation. Analysis of subglacial tephra layers revealed the existence of juvenile material from the 2004–2008 eruption cycle, providing insights about glacier subsidence of ~ 40 m since 2004/2005 in spite of net growth. Although the lava dome is cooling, the glacier-dome interface seems to have become increasingly stable in the past few years. Our results suggest that glacier development in the accumulation area adjacent to the dome is now being affected by the thermal characteristics of the lava dome itself, making monitoring internal glacier development via tracking glaciovolcanic cave expansion a potentially important volcano monitoring tool. [ABSTRACT FROM AUTHOR]

The topographic fabric of the rift valley floor has been analyzed using the multibeam echosounder data obtained by the autonomous underwater vehicle (AUV) Abyss at two locations over a short segment of the slow-spreading Central Indian Ridge between 10°18′ and 10°57′S. The region is influenced by hydrothermal venting in the near vicinity. Two AUV dives D51 and D52 were performed over this segment at two locations that are 30 km apart and covered 5 km2 and 8 km2 seafloor area, respectively. The dive D51 covered the off-axis part of the rift valley floor in the middle part of the segment, and the dive D52 is located near to the non-transform discontinuity that covered the terminal part of an oceanic core complex (OCC). High-resolution seafloor topography as revealed by the AUV-mounted multibeam echosounder system brought out several micro-bathymetric fabric features such as a lava lake, a cratered volcano, an OCC, and the foot wall volcanic complex at the distal part of the OCC. The valley floor imaged in the D51 is marked by a lava flow encompassing an area of 1 km2 and a volcano in the NE corner. The volcano has a diameter of about 800 m with an elevation of about 200 m from the adjacent seafloor, and the partially mapped volcano crater has a relief of about 60 m. A prominent linear fissure running parallel to the ridge axis has been identified; this feature joins with the volcano. Analysis of AUV-mounted CTD data indicated three distinct temperature spikes ranging 0.009 to 0.013 °C in the region of dive D51. The observed temperature spikes appear to be related to the linear fissure on the seafloor and probably represent leaky venting of fluids from the fissure. With respect to the dive D52, the foot wall volcanic features associated with the OCC are prominent. The volcanic seafloor feature covered an area of 3.45 km2 and is conspicuous with rugged topographic fabric at the base of the OCC. These inferences and the morphotectonics of the rift valley floor as revealed by the AUV data suggest moderate hydrothermal venting in this segment of the slow-spreading Central Indian Ridge. [ABSTRACT FROM AUTHOR]

The Jabal Hadb Ad Dayheen granitic complex in central Saudi Arabia is an alkaline granitic ring complex associated with a collapsed caldera. It mainly consists of monzogranite in the center, biotite-hornblende porphyritic granite, and biotite-aegirine-riebeckite granite, intruded by some felsic and mafic dikes. The petrological and geochemical characteristics show that the granitic suites consist of metalminous-peralkaline A-type granites. The secondary ion mass spectrometry (SIMS) zircon U-Pb analysis yielded 206Pb/238U ages of 613.3 ± 8.1–603.8 ± 3.8, 602.4 ± 3.8, 596 ± 5.6 Ma for biotitehornblende porphyritic granite, microgranite, and biotite-aegirine-riebeckite granite, respectively. The trace element characteristics and positive εHf(t) values (3.2–12.2) indicate that the granitic rocks of the Dayheen Ring Complex are mainly derived from the juvenile crust with the involvement of mantle-derived materials. Combined with the regional tectonic evolution, the formation of the Dayheen Ring Complex mainly covered four periods: (1) subduction initiation and formation of arc terranes (870–620 Ma)—volcanic craters formed during this period provided the channel for alkaline complex intrusion; (2) collision between East and West Gondwana continents and formation of the north East African Orogen (640−613 Ma)—monzogranite stock at the center of the ring complex emplaced during this period; (3) post-collision extension and collapse (613−602 Ma)—red metaluminous biotite-hornblende porphyritic granite and microgranite sheets in the rim of the Dayheen Ring Complex emplaced during this period; (4) within-plate extension (602 − 545 Ma)—white peralkaline biotite-aegirine-riebeckite granite and plenty of felsic and mafic dikes in the rim mainly formed during this period. The granitic rocks of the Dayheen Ring Complex mainly formed during the transitional stage of post-collison to within-plate extension after the collision between East and West Gondwana continents, and part of them formed during the early stage of the within-plate extension. U, Th, Zr, Nb, and rare earth element mineralization mainly formed during the early stage of the last period, having a close relationship with the intrusion of white peralkaline biotite-aegirine-riebeckite granite. [ABSTRACT FROM AUTHOR]

The Dotsero maar volcanic crater formed through phreatomagmatic (interactions of lava with wet, unconsolidated sediment) and magmatic processes around 4,150 ± 300 years before present (B.P.) which erupted through sections of Pennsylvanian age sedimentary deposits. The field observations of the eruptive material showed various xenolith structures, or foreign rock fragments within the cooled magmatic material, which can be categorized into four specific groups based on the mineral grain size of the sediments and subtle color variation. The fieldwork focused on three sites located downslope from the southern crater rim of the Dotsero maar, accounting for all xenoliths = 1 cm in size in selected agglutinate clasts and gathering samples of the localized surface sediments and xenolith structures. The surficial sediment samples and two groups of xenolith structures were examined through X-ray powder diffraction laboratory analyses. The results of this analysis demonstrate that field classifications of xenolith structures continue to be the most accurate form of identification and present grounds for further analyses through scanning electron microscopy (SEM) and thin section observations for differentiation and determination of thermal alterations created by the lava and sediment interactions. [ABSTRACT FROM AUTHOR]

Complex crystal cargo in basaltic eruptions has the potential to yield diverse insights on pre- and syn-eruptive timescales of magma storage and transport. Research on eruption products from the 1959 eruption from Kīlauea Iki Crater at Kīlauea volcano (Hawai'i) demonstrates that time-series samples collected during an eruption can yield a wealth of information not accessible by studying the fall deposit alone. Major element zoning in olivine crystals illustrates four environments of magma storage that were variably mixed and progressively involved in the eruption. Diffusion timescales retrieved from crystals < 1 mm in size are typically much shorter than those from crystals > 1 mm, illustrating the additional complexity of information recorded by different grain sizes and olivine populations. The timescales can be divided into two groups: (1) t > 100 days reflect longer-term magma recharge into Kīlauea's deep (8–10 km) reservoir system and (2) t < 100 days broadly correspond to a period of unrest and inflation beginning ~ 3 months prior to eruption. Some timescales reflect syn-eruptive processes, where diffusion began after the eruption onset. Progressive changes in zoning populations in the time-series scoriae samples illustrate how quickly diffusive re-equilibration can erase older magmatic histories and information and underscores that studies on fall deposits can lead to an incomplete record of magmatic processes. Thus, diffusion timescales from fall deposits alone should be cautiously interpreted with the caveat that they may be missing a substantial part of the total eruptive event and, therefore, the record of magmatic histories inferred from crystal cargo. [ABSTRACT FROM AUTHOR]

Spatial approaches, based on the deformation measurement of volcanic domes and crater rims, is key in evaluating the activity of a volcano, such as Merapi Volcano, where associated disaster risk regularly takes lives. Within this framework, this study aims to detect localized topographic change in the summit area that has occurred concomitantly with the dome growth and explosion reported. The methodology was focused on two sets of data, one LiDAR-based dataset from 2012 and one UAV dataset from 2014. The results show that during the period 2012–2014, the crater walls were 100–120 m above the crater floor at its maximum (from the north to the east–southeast sector), while the west and north sectors present a topographic range of 40–80 m. During the period 2012–2014, the evolution of the crater rim around the dome was generally stable (no large collapse). The opening of a new vent on the surface of the dome has displaced an equivalent volume of 2.04 × 104 m3, corresponding to a maximum −9 m (+/−0.9 m) vertically. The exploded material has partly fallen within the crater, increasing the accumulated loose material while leaving "hollows" where the vents are located, although the potential presence of debris inside these vents made it difficult to determine the exact size of these openings. Despite a measure of the error from the two DEMs, adding a previously published dataset shows further discrepancies, suggesting that there is also a technical need to develop point-cloud technologies for active volcanic craters. [ABSTRACT FROM AUTHOR]

Jeju Island comprises numerous tuff rings and tuff cones and their reworked deposits in the subsurface, which formed on the ca. 120-m-deep Yellow Sea continental shelf under the fluctuating Quaternary sea levels. Tens of meter-thick and massive deposits were found by chance during groundwater drilling at three sites. These deposits are interpreted as either syn-eruptive diatreme-filling deposits or post-eruptive crater-filling deposits, both of hydromagmatic volcanoes. The diatremes were cut into shelf sediment, 70 to 250 m thick, and developed generally within it below the Quaternary sea levels. Abundant external water was therefore available for explosive magma-water interactions at shallow levels. The diatreme deposit in one core shows some features attributable to extreme wetness or water saturation of the diatreme fill, such as the matrix support of larger clasts, meager vertical changes in matrix content, and an absence of features related to particle adhesion. Fluidally shaped clasts with delicate reentrant margins in the core suggest minimal particle abrasion and breakage in a water-saturated and highly fluid slurry of tephra and water that was probably filling a shallow bowl-like diatreme, which is distinguished from both phreatomagmatic and kimberlite diatremes. The diatreme deposits in other cores comprise blocky and angular clasts in a sideromelane ash matrix, suggesting phreatomagmatic explosions at a deeper level. One of the cores contains collapsed deposits of thinly stratified tuff emplaced by pyroclastic surges, indicating that the diatreme is associated with an emergent tuff ring. Both Surtseyan and phreatomagmatic eruptions are therefore interpreted to have occurred on the shelf under the controls of fluctuating Quaternary sea levels. The subsurface diatremes suggest that there can be a variety of diatremes with different sizes, shapes, and material characteristics beneath the craters of hydromagmatic volcanoes, including not only maars but also tuff rings and tuff cones. [ABSTRACT FROM AUTHOR]

The present study utilized earth observation Sentinel5P TROPOMI (TROPOspheric Monitoring Instrument) data for monitoring submarine volcanic activities. The world has seen a sequence of abrupt volcanic eruptions within one-month duration i.e., on 20th December 2021, 13th January 2022 and 15th January 2022. This caused the emissions of natural gaseous pollutants such as Sulphur Dioxide (SO2), Hydrogen Sulphide (H2S) and ash particles. Atmospheric SO2, AAI (Absorbing Aerosol Index) and Cloud fraction data are retrieved from the TROPOMI onboard the Copernicus Sentinel5P European Space Agency satellite. Results confirmed the increased concentration of SO2 column density after 20th December, and it was observed to be 0.002 mol/m2, the highest concentration during the period of study. Generally, SO2 concentration stays within 0.001 mol/m2 or less. Concentration was seen increasing after the first eruption and reached maximum after 15th January 2022 eruption to a level up to 0.002 mol/m2. Similar outcomes were observed for AAI for the chosen site. AAI values increased to 25,000 fold (AAI values of 1.25) during the first eruption and increased to 29,000 fold on 15th January 2022 after eruptions (AAI values of 1.45) as compared AAI values of 0.005 or negative AAI values before eruptions. A cloud fraction of value 1 is observed during this time, along with the top most cloud height at 14,233.16 m (14.23 kms) above the crater of the volcano (maximum estimation limit by S5P). These values are higher as compared to isolated islands, as there are no other sources of emissions at surrounding environment. The outcomes support the role of Earth Observation datasets for disaster monitoring and management plans for mitigation. Demonstrating the capabilities of Sentinel5P TROPOMI for SO2 column density, AAI and Cloud fraction monitoring for submarine volcanic eruption. Unique landform variation- appearance and submergence for the submarine volcano due to eruptions. Formation and erosion of landform of the active submarine volcano during 2009 -2022. [ABSTRACT FROM AUTHOR]

Understanding the stress evolution of extinct volcanoes can improve efforts to forecast flank eruptions on active systems. Field, petrographic, and seismic data are combined with numerical modeling to investigate the paleo‐stress field of New Zealand's Akaroa Volcano, or Akaroa Volcanic Complex. Field mapping identifies 86 radially oriented dikes and seven lava domes found only within a narrow elevation range along Akaroa's erosional crater rim. These observations suggest that crater rim dike emplacement resulted from lateral deflection of vertically ascending intrusions from a centralized magma source, which in turn may have facilitated formation of the lava domes, as well as two scoria cones. We postulate that dike deflection occurred along a stress barrier, as neither a compositional change nor structural boundary are present. We use a finite element model (FEM) simulating Akaroa to test how different factors may have influenced the system's stress state and dike geometry. Elastic, non‐flexural ("roller") model configurations containing a large, oblate, and shallow magma chamber produce stress barriers most conducive to radial dike emplacement along Akaroa's crater rim. These configurations also simulate rapid edifice construction above a preexisting lithospheric "bulge." Conversely, simulating flexural stresses exerted on the lithosphere by Akaroa's large mass hinder rather than promote radial dike emplacement. Temperature‐dependent viscoelastic relaxation promotes gradual increases in stress barrier elevation, though this effect is strongly dependent on magma chamber parameters. These results suggest that Akaroa was constructed rapidly (within ∼100 kyr) prior to crater rim dike emplacement, which occurred throughout the volcano's remaining active lifespan. Plain Language Summary: Fully understanding how magma moves within active volcanoes requires scientists to study solidified remnants of once‐molten magma "plumbing systems" that have been unearthed by the erosion of extinct (i.e., no longer active) volcanoes. Here we present new observations of New Zealand's Akaroa Volcano, an extinct volcanic mountain or "edifice" built from lava eruptions and underground magma movement that occurred in multiple regions rather than one central summit vent. Observations include on‐the‐ground measurements of rock formations, microscope analysis of rock samples, satellite‐derived elevation data, and underground properties inferred from earthquake‐generated seismic waves. We incorporate these observations into a computer model of the once‐active volcano to understand why magma followed the paths it did, erupting on Akaroa's sides, or flanks, rather than its central summit region. Based on the results of our computer model, these eruptions occurred throughout Akaroa's one‐million‐year lifespan, after the volcano itself was constructed in the geologically "brief" period of roughly 100,000 years. Our computer simulations also provide a framework for improving scientists' assessments of future eruption risks on the slopes of active volcanoes with a similar shape and chemical composition to Akaroa, such as Sicily's Mt. Etna or the Galapagos' Fernandina volcano. Key Points: Field, petrographic, and seismic observations constrain the formation of dikes, lava domes and scoria cones on Akaroa Volcano's crater rimTwo‐dimensional axisymmetric finite element model (FEM) indicates a stress barrier may have promoted radial dike emplacement along Akaroa's crater rimOptimal stress barriers occur in elastic, non‐flexural FEMs with large, shallow, oblate chamber and edifice rapidly built on inclined bulge [ABSTRACT FROM AUTHOR]

Blasting experiments were performed that investigate multiple explosions that occur in quick succession in unconsolidated ground and their effects on host material and atmosphere. Such processes are known to occur during phreatomagmatic eruptions at various depths, lateral locations, and energies. The experiments follow a multi‐instrument approach in order to observe phenomena in the atmosphere and in the ground, and measure the respective energy partitioning. The experiments show significant coupling of atmospheric (acoustic)‐ and ground (seismic) signal over a large range of (scaled) distances (30–330 m, 1–10 m J−1/3). The distribution of ejected material strongly depends on the sequence of how the explosions occur. The overall crater sizes are in the expected range of a maximum size for many explosions and a minimum for one explosion at a given lateral location. As previous research showed before, peak atmospheric over‐pressure decays exponentially with scaled depth. An exponential decay rate of d¯0=6.47×10−4mJ−1/3 ${\bar{d}}_{0}=6.47\times 1{0}^{-4}\,\mathrm{m}\,{\mathrm{J}}^{-1/3}$ was measured. At a scaled explosion depth of 4 × 10−3 m J−1/3 ca. 1% of the blast energy is responsible for the formation of the atmospheric pressure pulse; at a more shallow scaled depth of 2.75 × 10−3 m J−1/3 this ratio lies at ca. 5.5%–7.5%. A first order consideration of seismic energy estimates the sum of radiated airborne and seismic energy to be up to 20% of blast energy. Finally, the transient cavity formation during a blast leads to an effectively reduced explosion depth that was determined. Depth reductions of up to 65% were measured. Plain Language Summary: Blasting experiments using six successive explosions were performed. Explosives were detonated in unconsolidated ground material in four different geometric setups (linear and triangular). We monitored the experiments using geophysical instruments. The instruments measured explosive energy, and how much of that energy escapes the crater. The experiments help to understand volcanic (phreatomagmatic) and other subsurface explosive processes. Exact measurements of the resulting craters, together with known explosive energies allow the interpretation of real volcanic craters. The experimental results show initial time developments of crater sizes, which occurs on the order of 1 s for crater sizes of the order of 1 m. Up to 8% of an explosion's energy was detected as airborne signal. Up to 20% of the explosion's energy was detected as seismic (elastic) energy in the ground. Key Points: Airborne energy of an underground blast decays exponentially with scaled depth and is in agreement with previous measurementsTransient crater unloading leads to eruption at the surface from depths that were thought to be deep enough to be contained in the groundCrater sizes correlate with measured seismo‐acoustic and high‐frequency atmospheric signals [ABSTRACT FROM AUTHOR]

We report on the ash cloud related to the gravitational collapse of a portion of the Stromboli volcano crater rim that occurred on 19 May 2021. The collapse produced a pyroclastic density current (PDC) that spread along the northwest flank of the volcano and propagated in the sea for about 1 km. The PDC was associated with a convective ash cloud that rapidly dispersed eastward and deposited a thin layer (< 1 mm) of very fine pinkish ash over the village of Stromboli. The deposit was sampled shortly after the emplacement (within a few hours) and prior to any significant reworking or re-sedimentation. We present a comprehensive description of the deposit including dispersal, sedimentological characteristics and textural and geochemical features. We also compare the 19 May 2021 deposit with fine-ash deposits connected to other PDCs and landslides previously occurring at Stromboli and with the distal ash of a paroxysmal explosive eruption of Mt. Etna volcano. Results indicate that the distributions of the mass on the ground and of the grain size are not correlated with the distance from the source. Also, the componentry reflects a preponderance of remobilized material ingested by the PDC. Therefore, the great amount of fine ash can be ascribed to clasts comminution processes, although the prevalence of dense crystalline components records an overall equiaxial shape, revealing a paucity of elongated clast with complex morphology. Furthermore, the outcomes of this work aim to create a collection of data of a co-PDC ash cloud that may prove useful for comparison with other deposits worldwide. [ABSTRACT FROM AUTHOR]

We report on the ash cloud related to the gravitational collapse of a portion of the Stromboli volcano crater rim that occurred on 19 May 2021. The collapse produced a pyroclastic density current (PDC) that spread along the northwest flank of the volcano and propagated in the sea for about 1 km. The PDC was associated with a convective ash cloud that rapidly dispersed eastward and deposited a thin layer (< 1 mm) of very fine pinkish ash over the village of Stromboli. The deposit was sampled shortly after the emplacement (within a few hours) and prior to any significant reworking or re-sedimentation. We present a comprehensive description of the deposit including dispersal, sedimentological characteristics and textural and geochemical features. We also compare the 19 May 2021 deposit with fine-ash deposits connected to other PDCs and landslides previously occurring at Stromboli and with the distal ash of a paroxysmal explosive eruption of Mt. Etna volcano. Results indicate that the distributions of the mass on the ground and of the grain size are not correlated with the distance from the source. Also, the componentry reflects a preponderance of remobilized material ingested by the PDC. Therefore, the great amount of fine ash can be ascribed to clasts comminution processes, although the prevalence of dense crystalline components records an overall equiaxial shape, revealing a paucity of elongated clast with complex morphology. Furthermore, the outcomes of this work aim to create a collection of data of a co-PDC ash cloud that may prove useful for comparison with other deposits worldwide. [ABSTRACT FROM AUTHOR]

Mount St. Helens, one of the highest-risk volcanoes in the Cascade Volcanic Arc, hosts a novel system of glaciovolcanic caves that has formed around the 2004-2008 lava dome. From 2014 to 2021 a multidisciplinary research team systematically explored and mapped these new caves to ascertain their characteristics. Air and fumarole temperatures, volume flow rates, and wind regimes were also monitored. More than 3.0 km of cave passages have formed in a semicircular pattern in the volcanic crater and provide an opportunity to (1) observe cave development over time, (2) identify low temperature fumaroles as the main driving force for cave formation, (3) verify the impact of seasonal snow accumulation on cave climate, and (4) assess heat distribution in subglacial and subaerial portions of the new lava dome. Glaciovolcanic cave systems on Mount St. Helens are comparatively young (<10 years) and the most dynamic in the Pacific Northwest. Observed cave expansion during the study suggests ongoing genesis and future formation of interconnected systems. However, further expansion may also be limited by increasing fumarole temperatures towards the upper parts of the lava dome, cave instability due to snow overload, or variable subglacial volcanic heat output. New glaciovolcanic cave system development provides a unique barometer of volcanic activity on glacier-mantled volcanoes and to study the subglacial environment. We present the results of eight years of initial study within this dynamic cave system, and discuss a pathway towards future longitudinal analyses. [ABSTRACT FROM AUTHOR]

Global warming enhances atmospheric moisture loading and will likely affect the East-Asian monsoon system across Vietnam. The absence of a long written climate history from Vietnam creates a reliance on geological archives of past monsoon history and regional paleoenvironmental changes to provide a framework for evaluating current climatic trends. Biển Hồ lake (14°03′ N, 108°00′ E) is a volcanic crater (i.e. maar) in Vietnam's Central Highlands that has been accumulating sediment since the Pleistocene. Field campaigns between 2016 and 2018 recovered an abundance of gravity and piston sediment cores extending to a depth of ~15 m, covering approximately the last 30 ka BP. The paleoenvironmental interpretation of Pleistocene and Holocene sediment requires knowledge of modern lacustrine and sedimentary conditions, as well as the origin and transport pathways of the catchment material. Here, we focus on a high-resolution sedimentological and geochemical reconstruction of the recent environmental history - from 1950 AD to the present - based on sediment cores from Biển Hồ maar, in direct comparison with local and regional weather and historic records. The uppermost sedimentary record reflects a substantial anthropogenic influence such as deforestation, military use, crater breaching, dam and sill construction, and reforestation that strongly modified the maar's morphology and hydrology. A strong increase in sedimentation rate during the 1960–70s in Biển Hồ cores coincided with U.S. military activities and water withdrawal. A breach in the maar's rim and the connection to a new external reservoir in 1983-1984 AD increased Biển Hồ water level. Reforestation around most of Biển Hồ's rim in the 1990s curbed erosion and sedimentation rate. Nutrient availability in Biển Hồ declined in the past ~10 years after the installation of a concrete sill between Biển Hồ and the reservoir to limit water exchange with the more nutrient-rich reservoir. This paper is a calibration study on modern sediment to provide an empirical basis for the interpretation of Biển Hồ's deeper Holocene and pre-Holocene sedimentary record. [Display omitted] [ABSTRACT FROM AUTHOR]

Studies on microbial communities, and their associated organic biomarkers, that are found thriving in the aphotic euxinic waters in modern stratified ecosystems are scarce compared to those undertaken in euxinic photic zones. The Dziani Dzaha (Mayotte, Indian Ocean) is a tropical, saline, alkaline crater lake that has recently been presented as a modern analog of Proterozoic Oceans due to its thalassohaline classification (having water of marine origin) and specific biogeochemical characteristics. Continuous intense photosynthetic production and microbial mineralization keep most of the water column permanently aphotic and anoxic preventing the development of a euxinic (sulfidic and anoxic) photic zone despite a high sulfide/sulfate ratio and the presence of permanent or seasonal haloclines. In this study, the molecular composition of the organic matter in Lake Dziani Dzaha was investigated and compared to the microbial diversity evaluated through 16S rRNA gene amplicon sequencing, over two contrasting seasons (rainy vs. dry) that influence water column stratification. Depth profiles of organic biomarker concentrations (chlorophyll‐a and lipid biomarkers) and bacterial and archaeal OTU abundances appeared to be strongly dependent on the presence of aphotic haloclines and euxinia. OTU abundances revealed the importance of specific haloalkaliphilic bacterial and archaeal assemblages in phytoplanktonic biomass recycling and the biogeochemical functioning of the lake, suggesting new haloalkaline non‐phototrophic anaerobic microbial precursors for some of the lipid biomarkers. Uncultured Firmicutes from the family Syntrophomonadaceae (Clostridiales), and Bacteroidetes from the ML635J‐40 aquatic group, emerged as abundant chemotrophic bacterial members in the anoxic or euxinic waters and were probably responsible for the production of short‐chain n‐alkenes, wax esters, diplopterol, and tetrahymanol. Halocline‐dependent euxinia also had a strong impact on the archaeal community which was dominated by Woesearchaeota in the sulfide‐free waters. In the euxinic waters, methanogenic Euryarchaeota from the Methanomicrobia, Thermoplasmata, and WSA2 classes dominated and were likely at the origin of common hydrocarbon biomarkers of methanogens (phytane, pentamethyl‐eicosenes, and partially hydrogenated squalene). [ABSTRACT FROM AUTHOR]

• The J110 Sequence developed during the "biogenic bloom" period, ∼7.8–3.5 Ma. • The ∼ 3.5 Ma compression event created diapir structures along the axes of anticlines. • Cold seepage winnowing as the mechanism for the high quality grainstone reservoirs. The Mid-Pliocene grainstones (MPG) constitute the first type of reservoir to produce oil in Indonesia. So far, most of the MPG wells have been abandoned due to the small scale reservoiring but industry still has expectations for this today. However, its formation mechanism and distribution are still debated. Using seismic data interpretation, the J110 Sequence of the Early Pliocene is widely developed throughout the East Java Island, the Madura Sub-Basin, the Madura Island and the southern volcanic arc area in a bathyal environment as a highly condensed layer during the "biogenic bloom" period, from ∼ 7.8–3.5 Ma. There was a big environment change due to the ∼ 3.5 Ma tectonic compression event. Diapirism caused by the compression event eventually led to formation of pockmarks (or mud volcano craters) developed along the crest of anticlines from onshore East Java east-ward to the offshore Mudura Sub-Basin. Globigerina tests accumulated in the pockmark by cold seepage winnowing mechanism finally as high-quality petroleum reservoirs. [ABSTRACT FROM AUTHOR]

Glass/melt inclusions are repositories of polybaric magma physiochemical interactions. They are fundamental to retrieve the conditions of fluid saturation and magma oxidation state. The latter is usually reported as oxygen fugacity, which is a key thermodynamic variable: involved in such polybaric physiochemical interactions, fO2 affectsmelt saturation properties and fixes the speciation of fluids discharged by magmatic systems either up to volcanic craters or feeding hydrothermal systems. Several oxybarometers have been proposed, based on iron and sulfur oxidation states. In this study I summarize their main features and show their performances for 1-bar and fluid-saturated andesitic and basaltic melts. I then show that any assessment of magma redox behavior that does not account for the melt reactivity, driven by melt polymerization and the so-called oxygen electrode in associationwith iron or sulfur redox couples, may fail in determining the actual contribution of the composition to the observed variations of iron and sulfur oxidation states, resulting in potentially biased fO2 estimates. In the case of Etna volcano, by using a well-established ionic-polymeric approach we showthat a major control is the dehydration taking place during magmatic differentiation and magma ascent. Dehydration determines a slight iron oxidation down to around 2.5 wt% in dissolvedwater, but further dehydration taking place up to the surface results in iron reduction. This dual behavior, related to a change of trivalent iron speciation, is reproduced by reactive ionic-polymeric approaches and for the Etna basalt it is predicted also for constant fO2. Such amodulation of the redox state due to water dissolution cannot be reproduced by empirical formulations. [ABSTRACT FROM AUTHOR]

Ocean acidification, due to the increase of carbon dioxide (CO2) concentration in the atmosphere and its absorption by the oceans, affects many aspects of marine calcifying organisms' biology, including reproduction. Most of the available studies on low pH effects on coral reproduction have been conducted on tropical species under controlled conditions, while little information is reported for either tropical or temperate species in the field. This study describes the influence of decreasing pH on sexual reproduction of the temperate non‐zooxanthellate colonial scleractinian Astroides calycularis, transplanted in four sites along a natural pH gradient at the underwater volcanic crater of Panarea Island (Tyrrhenian Sea, Italy). The average pH values of each site (range: pHTS 8.07–7.40) match different scenarios of the Intergovernmental Panel on Climate Change (IPCC) for the end of the century. After 3 months under experimental conditions, the reproductive parameters of both oocytes and spermaries (abundance, gonadal index, and diameters) seem to be unaffected by low pH. However, a delay in spermary development in the pre‐fertilization period and a persistence of mature oocytes in the fertilization period were observed in the most acidic site. Furthermore, no embryos were found in colonies from the two most acidic sites, suggesting a delay or an interruption of the fertilization process due to acidified conditions. These findings suggest a negative effect of low pH on A. calycularis sexual reproduction. However, long‐term experiments, including the synergistic impact of pH and temperature, are needed to predict if this species will be able to adapt to climate change over the next century. [ABSTRACT FROM AUTHOR]

We propose a new array covariance matrix analysis method, named 'maximum covariance direction method' (MCD method), to detect and locate unconventional seismic sources of weak signals without clear onsets. The MCD method builds a normalized-covariance matrix of time-shifted seismic waveforms recorded in a seismic array and determines the existence of source based on the consistency of the maximum covariance direction with the theoretical prediction. Synthetic tests demonstrate effectiveness of the MCD method in detecting one and multiple isolated sources with low signal-to-noise ratios. As a data application, we study 1-hr long-period tremors (LPTs) around Aso Volcano of Japan in 2014 November 24. A total of 26 LPTs are detected near the Naka-dake first crater of Aso Volcano, with the uncertainties of source location of about 7 km. Using the recorded background noise at the seismic stations, we show that the MCD method can detect LPTs even when the LPT signals are buried in the background noise and become indiscernible in the seismic data. Unlike traditional methods that employ the coherent features of seismic signals for source detection, the MCD method places emphases on both the coherence of seismic signals and consistency of the direction of the coherent signals from a potential source location. The synthetic tests and data application indicate that the MCD method provides a good alternative to other traditional methods for detecting and locating unconventional seismic sources, with a major improvement of avoiding source misidentification in the presence of strong incoherent signals. [ABSTRACT FROM AUTHOR]

Active Haleakala volcano on the island of Maui is the second largest volcano in the Hawaiian Island chain. Prominently incised in Haleakala's slopes are four large (great) valleys. Haleakala Crater, a prominent summit depression, formed by coalescence of two of the great valleys. The great valleys and summit crater have long been attributed solely to fluvial erosion, but two significant enigmas exist in the theory. First, the great valleys of upper Keanae/Koolau Gap, Haleakala Crater, and Kaupo Gap are located in areas of relatively low annual rainfall. Second, the axes of some valley segments are oblique for long distances across the volcanic slopes. This study tested the prevailing erosional theory by reconstructing the volcano's topography just prior to valley incision. The reconstruction produces a belt along the volcano's east rift zone with a morphology that is inconsistent with volcanic aggradation alone, but it is readily explained if it is assumed the surface was displaced along scarps formed by a giant landslide on Haleakala's northeastern flank. Although the landslide head location is well defined, topographic evidence is lacking for the toe and lateral margins. Consequently, the slope failure is interpreted as a sackung-style landslide with a zone of deep-seated distributed shear and broad surface warping downslope of the failure head. Maximum downslope displacement was likely in the range of 400-800 m. Capture of runoff at the headscarps formed atypically large streams that carved Haleakala's great valleys and explains their existence in low-rainfall areas and their slopeoblique orientations. Sackung-style landslides may be more prevalent on Hawaiian volcanoes than previously recognized. [ABSTRACT FROM AUTHOR]

In this study, the paint layer was removed on the surface of 5083 aluminum alloy using laser cleaning and mechanical grinding. The microstructure and performance of experimental samples were carefully investigated using scanning electron microscope, energy disperse spectroscopy and other methodologies. The results showed that compared with mechanical grinding, laser cleaning can improve the surface paint coating of aluminum alloy more effectively. The surface of the matrix formed uniformly distributed volcanic craters and small holes emerged at the spot junction after laser cleaning. The carbon and oxygen content on the substrate surface after laser cleaning was much lower than that after mechanical grinding. In addition, the corrosion resistance and coating adhesion of the substrate were obviously improved using laser cleaning. It was closely associated with refinement of the grains and reduction in surface roughness. We concluded that laser cleaning can be widely used to replace mechanical grinding in manufacturing on the premise of meeting industrial needs. [ABSTRACT FROM AUTHOR]

Extending nanostructures into the third dimension has become a major research avenue in modern magnetism, superconductivity, and spintronics, because of geometry-, curvature-, and topology-induced phenomena. Here, we introduce Co–Fe nanovolcanoes—nanodisks overlaid by nanorings—as purpose-engineered 3D architectures for nanomagnonics, fabricated by focused electron beam-induced deposition. We use both perpendicular spin-wave resonance measurements and micromagnetic simulations to demonstrate that the rings encircling the volcano craters harbor the highest-frequency eigenmodes, while the lower-frequency eigenmodes are concentrated within the volcano crater, due to the non-uniformity of the internal magnetic field. By varying the crater diameter, we demonstrate the deliberate tuning of higher-frequency eigenmodes without affecting the lowest-frequency mode. Thereby, the extension of 2D nanodisks into the third dimension allows one to engineer their lowest eigenfrequency by using 3D nanovolcanoes with 30% smaller footprints. The presented nanovolcanoes can be viewed as multi-mode microwave resonators and 3D building blocks for nanomagnonics. [ABSTRACT FROM AUTHOR]

Ash deposits from short-lived vulcanian eruptions are ubiquitous at active volcanoes and are important for understanding the development of a volcanic edifice. In this study, we investigated the sedimentary system of ash deposits produced by long-term vulcanian activity from Showa crater of Sakurajima volcano, Japan, based on the grain size characteristics of ash from individual eruptions. We collected falling ash samples from 20 individual vulcanian eruptions between March 3 and 11, 2010. The grain size distributions of the ash samples were unimodal, bimodal, and trimodal, depending on the event. The median particle size of the main subpopulation decreases with distance from vent. The low standard deviation of the grain size of the main subpopulation implies deposition from transient volcanic plumes. For the finest subpopulation in the polymodal samples, the median grain size is very fine ash (<30 μm), indicating that this subpopulation was derived from ash aggregates. Overall, the sedimentary system of the long-term vulcanian activity at Sakurajima volcano is explained by accumulation of ash particles from repeated transient plumes and ash aggregation, and the latter controlled the behavior of the very fine ash. [ABSTRACT FROM AUTHOR]