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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]

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]

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]

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]

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]

New 40Sr/39Ar dating revealed that the magnetite phlogopitite at the center of the Araxá complex reached the surface at 98 Ma, and generated volcanoes with mineralized volcanic tuffs and crater lakes. At the bottom of the crater lakes, micro-graywacke deposited. Based on the mineral composition, hydrothermal structures, and δ18O and δD values, a hydrothermal episode occurred between ∼98 and 86 Ma Ma. The δ18O of phlogopites of phlogopities vary between 4.8‰ and 5.7‰, and those of magnetitites are 4.3‰ and 6.8‰. The δ18O of the water in equilibrium with phlogopites of the phlogopitites vary between 2.3‰ and 3.2‰, and those with magnetitite are 4.3‰ and 1.8‰. The δD of phlogopites of phlogopitites vary between −86.5‰ and −95.2‰, and those of magnetitite are −84.9‰, and −85.8‰. The δD of the water in equilibrium with phlogopites of the phlogopitites vary between −26.8‰ and −35.5‰, and with magnetitite are −25.6‰, and −26.26‰. During the hydrothermal event, magnetite phlogopitites were hydrothermally altered into phlogopite magnetitite, magnetite apatitite (epifoskorites), and mineralized with pyrochlore. At 84 Ma, the phlogopitic core was permeated by veins and micro-veins of Sr-rich norsethite carbonatites. At 83.5 Ma, calcitic carbonatites and micro-phlogopitites originating from the same mantle source as the magnetite phlogopitite intruded, which resulted in the formation of a carbonatite ring around the core and the assimilation of part of the phlogopitic core. This magmatism generated a new hydrothermal event of limited coverage that mineralized phlogopitites and carbonatites with monazite and massive pyrite ± chalcopyrite. The magmatism ended at 77 Ma, when phosphorous-saturated calcitic carbonatite surrounded the core. The saturation of phosphorous favored the crystallization of apatite, which generated phosphate deposits. • About 70% of the world's production of niobium is from the Araxá complex (Brazil). • The Araxá's rocks contain magmatic and hydrothermal pyrochlore. • The complex' nucleus is composed mainly by pyrochore-rich phlogopitites with magnetite and apatite. • A P 2 O 5 -rich and Nb-poor carbonatite ring surrounds the complex' nucleus. • Niobium and phosphate ores are regoliths formed by weathering of phlogopitites and carbonatites, respectively. [ABSTRACT FROM AUTHOR]

Azufral (SW Colombia) is a dangerous silicic volcano hosting a crater lake, which serves as an excellent example of an incipient plug disruption through phreatomagmatism. We studied the youngest succession of dilute pyroclastic density currents (PDCs) onlapping the north-eastern crater rim. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy was used to carry out an automated single-particle analysis of fine to extremely fine ash. We were able to obtain fast and accurate chemical analysis and imaging of 15,098 particles within the 250–63-μm and the 63–32-μm size ranges. The 2D form and roughness parameters were determined for 4895 juvenile glassy particles and validated by 3D micro-X ray computer tomography. There are two end members of high (group 1) and low (group 2) roughness juvenile glassy particles. Group 1 comprises high-roughness glass particles with solidity values as low as 0.34 in 2D and 0.33 in 3D, and convexity values as low as 0.33 in 2D and 0.26 in 3D. Group 2 comprises low-roughness glass particles with 2D solidity values > 0.79 and 3D solidity values typically > 0.58. In this group, 2D convexity values are > 0.68 and 3D convexity values are > 0.71. Both end members are mostly discriminated by the 2D Concavity Index (0.14 to 0.77 in group 1 vs. 0.05–0.35 in group 2). The remaining group 3 comprises particles of intermediate roughness values. In this study, we show how an incipient plug developed over a short repose time might be subjected to only a few cycles of vesicle nucleation, collapse and densification, retaining the characteristics of juvenile glass. Each glassy juvenile ash type, defined by a particular morphology, roughness and microtexture can be linked to a density "stratified" conduit model. In Azufral, the capping and conduit lining dense regions and the permeable zones of the incipient plug likely cracked. The newly formed cracks could allow hydraulic forcing caused by external water and induce phreatomagmatic interaction. This interaction favoured the fine fragmentation of the plug while enhancing ongoing magmatic processes. Finally, the variations of bulk componentry provided clues on dilute pyroclastic density current transport and physical fractionation processes by secondary fragmentation, elutriation and interaction with the crater rim. [ABSTRACT FROM AUTHOR]

Topography of a volcano crater can change due to endogenic processes such as deformation or eruption, or surface processes. Erosion and deposition are surface processes that may occur and gradually change the slope of the inner volcano crater. Here, we investigated erosion and deposition processes that occurred in the Kelud crater after the 2014 plinian eruption. We used high-resolution Digital Elevation Models (DEMs) and orthomosaic images derived by drone photogrammetry that acquired between September 2018 and July 2019. We obtained hundreds of aerial images which were reconstructed to obtain 3D models of Kelud’s crater by using Structure from Motion (SfM) technique. Results show erosions at alluvial fans that dominantly located at the east valleys of Kelud crater. The erosion removed the volcanic materials up to -5 m which transported and deposited close to the vicinity of the Kelud crater. The deposition process causes the increase of the Kelud crater lake up to 3 m. Moreover, we also mapped the thermal distribution of the Kelud crater lake by using low cost thermal camera. Our thermal investigation is able to identify some hotspots at the vicinity of the Kelud crater lake with range temperature of 43.7°C – 55.3°C, while the average apparent temperature of the Kelud crater lake is ~ 29°C. This high temperature area may indicate underwater active fractures that continuously release volcanic gasses which leads to convection heat transfer through Kelud’s water lake. [ABSTRACT FROM AUTHOR]

Cameroon is endowed with many freshwater lakes and rivers but, because of increasing anthropogenic activities, most of these water bodies are gradually being degraded. Lake Barombi Kotto is one of the volcanic crater lakes in Cameroon that serves as a prime source of drinking water for the Barombi Kotto community. The overall objective of the study was to determine the water quality of Lake Barombi Kotto making use of some physico-chemical parameters, Carlson's Trophic State Index (TSI), Heavy Metal Pollution index (HPI) and some bacteriological parameters. Water samples were collected over two seasons across a longitudinal transect at two depths and subjected to physico-chemical, bacteriological, nutrient, Chlorophyll a and phytoplankton analyses using standard methods. Descriptions, Analyses of Variance, ordinations and correlations were used to analyse resulting data at α = 0.05. Lake Barombi Kotto had a TSI of 93.67 and 87.92 in the dry and rainy season, respectively, indicating it is eutrophic. Of the six heavy metals studied, only the concentration of Fe was above the WHO (2008) drinking water quality limits. The HPI of the lake was 4.17 and 6.19 for the dry and rainy seasons, respectively, well below the critical index limit of 100. This lake is contaminated with faecal coliforms and pathogenic bacteria, such as Salmonella. This study has not only set baseline conditions for additional monitoring, but has exposed key dynamics and significant socio-economic and public health risks to humans. [ABSTRACT FROM AUTHOR]

The unique case of carbon dioxide accumulation in the bottom layer of the acidic lake formed in the Guadiana open pit (Herrerías mine, SW Spain) led to exceptionally high dissolved gas pressures (ca. 5.0 bar at depths of 50–70 m). This CO2 has formed by carbonate (calcite, dolomite) dissolution during decades of interaction of the acidic water with the rocks of the pit walls and associated mine tunnels. The elevated dissolved gas pressures were only comparable to those found in the volcanic crater lakes of Cameroon like Nyos and Monoun, which erupted in the 1980s and sadly triggered the loss of hundreds of human lives. This gas pressure was not far from the absolute (hydrostatic plus atmospheric) pressure limiting CO2 solubility at depth, thus making this pit lake potentially dangerous for the possibility of a hypothetical limnic eruption. Following detailed field and experimental studies aimed at deciphering the source and accumulation patterns of CO2 in the lake, a degassing project started in 2014, which followed an upscaling strategy with construction and installation of progressively bigger pipelines capable of extracting increasingly higher flow rates of CO2-charged water from the deep part of the lake. As of May 2019, the degassing systems have successfully extracted most of the CO2 originally present in the lake (i.e. ≈ 123,000 m3 CO2), which has been discharged to the atmosphere in a controlled and safe way. The fountains became progressively smaller and finally stopped, due to the decreased gas pressure at depth. The larger pipes will serve as a regulating system in the future. This paper describes the main findings encountered during the degassing project, some relevant technical issues observed during the last 5 years (2014–2019), and lessons learnt from the Guadiana pit lake experience. [ABSTRACT FROM AUTHOR]

Boeri Lake—a small (3.6 ha) but deep (39.6 m) crater lake on Morne Micotrin in Dominica, West Indies—presents a limnological enigma; it exhibits strong morphometric and circumstantial evidence for meromixis, yet it is not stratified. We tested the hypothesis that water seepage from Boeri Lake overcomes morphometric drivers of stratification and prevents the onset of meromixis. We compared water chemistry and plankton community composition in Boeri Lake to perennial streams on Morne Micotrin to assess if water discharging from these springs originates in Boeri Lake. Lacustrine phytoplankton and zooplankton taxa were detected in nearby streams, which also had similar water chemistry to that of Boeri Lake. In contrast, two other streams that drain Morne Micotrin and one neighboring reference stream had little in common with waters from Boeri Lake. This suggests that Boeri Lake's anomalous limnology is explained by hydrologic connectivity to nearby flanking streams, and supports our hypothesis that subsurface water piping, combined with high annual rainfall, stymies the onset of meromixis. We provide an explanation for how holomictic lakes can persist and transport organisms through the ground in tropical mountain ecosystems and discuss implications of consistent water piping for plankton community assembly on island lakes. [ABSTRACT FROM AUTHOR]

Summary: Gonad development of the silver therapon Leiopotherapon plumbeus in two volcanic crater  lake  habitats (Sampaloc Lake, Taal Lake) in south Luzon, Philippines was examined during the annual reproductive cycle. The minimum body size‐at‐maturity of fish in these two lake habitats was also compared. Four gonad development stages were characterized as basis for the classification of ovarian (immature, maturing, mature, spawned) and testicular maturation (immature, maturing, mature) phases. The occurrence of all development stages in individual gonads suggest an asynchronous development whereby advanced stages are recruited continuously from a pool of younger stage germ cells to result in elevated female and male GSI throughout the annual cycle due to active gonadogenesis. Together with the increasing occurrence of advanced stage oocytes and spermatozoa from March until October, the elevated GSI of fish may indicate peak gonadal growth during the onset of the dry season (December–January) for eventual spawning from the beginning (May–June) until the end of the wet season (October–November). In both lake habitats, male fish were smaller than females but, regardless of sex, the minimum size‐at‐maturity of fish in Sampaloc Lake was significantly smaller than fish in Taal Lake. Overall, asynchronous development during oogenesis and spermatogenesis allows for year‐round reproduction of silver therapon, with elevated gonad growth in the dry season in preparation for spawning during the wet season. Compared with fish in Taal Lake, a smaller size‐at‐maturity of fish in Sampaloc Lake may be a response of the wild fishery stock to long‐term high fishing mortality and degradation of the lake habitat. [ABSTRACT FROM AUTHOR]

Abstract The distributions of 137Cs, 237Np, and 239+240Pu activity concentrations in sedimentary soil cores of the volcanic crater-lake have been studied. The 240Pu/239Pu atom ratios measured by MC-ICP-MS and mutual activity ratios were examined. These results were used to evaluate the sedimentation characteristics of the crater-lake (Baengnokdam of Mt. Halla, Korea). The 137Cs, 237Np, and 239+240Pu activity concentrations showed similar distribution patterns and one maximum peak was observed in each sediment core, except at St.10. For all sediment cores, the activity concentrations were in the range 1.03 × 100–1.92 × 102 Bq·kg−1 dw for 137Cs, 7.56 × 10−3 – 7.15 × 100 mBq·kg−1 dw for 237Np, and 5.20 × 10−3 – 5.13 × 100 Bq·kg−1 dw for 239+240Pu, respectively. The averaged 240Pu/239Pu atomic ratio (0.159) was slightly less than the global fallout ratio (0.176). The averaged inventories were estimated to be 9.21 × 103±5.34 × 103 Bq·m−2 for 137Cs, 2.27 × 102±1.58 × 102 Bq·m−2 for 239+240Pu, and 3.22 × 10−1±1.78 × 10−1 Bq·m−2 for 237Np. The averaged 239+240Pu/137Cs and 237Np/239+240Pu activity ratios were 2.21 × 10−2 and 2.21 × 10−3, respectively. The mean sedimentation rates calculated using 239+240Pu activity concentrations at the central area (St.30 – St.45) and at all stations (St.5 – St.75) were estimated to be 0.844 cm yr−1, and 0.767 cm yr−1, respectively. In addition, the sedimentation rates calculated using 210Pb and 226Ra were 0.856 cm yr−1 at depths of 0–35 cm and 0.204 cm yr−1 at depths of 35–55 cm. These results imply that the sedimentation in Baengnokdam was relatively slow (0.204 cm yr−1) until about 44 years ago and then became faster (0.856 cm yr−1) to the present. The excess 210Pb dating is consistent with the sedimentation rate calculated from the vertical 239+240Pu profile. Graphical abstract Image 1 Highlights • This is the first report of radionuclides and sedimentation in the Korean volcanic crater-lake (Baengnokdam of Mt. Halla). • The distributions of 137Cs, 237Np, 239+240Pu and 240Pu/239Pu atom ratios were investigated in sedimentary soil cores. • Sedimentation characteristics were estimated using horizontal and vertical information of the radioactive isotopes. [ABSTRACT FROM AUTHOR]

Lake Rotomahana is a crater lake in the Okataina Volcanic Centre (New Zealand) that was significantly modified by the 1886 Tarawera Rift eruption. The lake is host to numerous sublacustrine hydrothermal vents. Water column studies were conducted in 2011 and 2014 along with sampling of lake shore hot springs and crater lakes in Waimangu Valley to complement magnetic, seismic, bathymetric and heat flux surveys. Helium concentrations below 50 m depth are higher in 2014 compared to 2011 and represent some of the highest concentrations measured, at 6 × 10 − 7 ccSTP/g, with an end-member 3 He/ 4 He value of 7.1 R A . The high concentrations of helium, when coupled with pH anomalies due to high dissolved CO 2 content, suggest the dominant chemical input to the lake is derived from magmatic degassing of an underlying magma. The lake shore hot spring waters show differences in source temperatures using a Na–K geothermometer, with inferred reservoir temperatures ranging between 197 and 232 °C. Water δ 18 O and δD values show isotopic enrichment due to evaporation of a steam heated pool with samples from nearby Waimangu Valley having the greatest enrichment. Results from this study confirm both pre-1886 eruption hydrothermal sites and newly created post-eruption sites are both still active. [ABSTRACT FROM AUTHOR]

El Chichón volcano is one of the most active volcanoes in Mexico. Previous studies have described its poly-extreme conditions and its bacterial composition, although the functional features of the complete microbiome have not been characterized yet. By using metabarcoding analysis, metagenomics, metabolomics and enzymology techniques, the microbiome of the crater lake was characterized in this study. New information is provided on the taxonomic and functional diversity of the representative Archaea phyla, Crenarchaeota and Euryarchaeota, as well as those that are representative of Bacteria, Thermotogales and Aquificae. With culture of microbial consortia and with the genetic information collected from the natural environment sampling, metabolic interactions were identified between prokaryotes, which can withstand multiple extreme conditions. The existence of a close relationship between the biogeochemical cycles of carbon and sulfur in an active volcano has been proposed, while the relationship in the energy metabolism of thermoacidophilic bacteria and archaea in this multi-extreme environment was biochemically revealed for the first time. These findings contribute towards understanding microbial metabolism under extreme conditions, and provide potential knowledge pertaining to "microbial dark matter", which can be applied to biotechnological processes and evolutionary studies. [ABSTRACT FROM AUTHOR]

Cuicocha (4.7 km2) is a volcanic lake located in the province of Imbabura, about 110 km north of Quito, and is one of the two active volcanic lakes of Ecuador. Cuicocha volcano is part of Ecuador's Western Andean volcanic cordillera together with some 16 other active volcanoes as result of interaction of the Nazca oceanic plate with the Caribbean and South American continental plates. Cuicocha represents the fourth most dangerous active volcano in Ecuador with its volcanic activity is represented by the upheating of its waters and a fumarolic activity expressed by gas bubbles and some dead vegetation due to the emission of CO2 through the soils. Monitoring Cuicocha volcanic crater lake has been a priority task due to the presence of a considerable amount of population living within a 20 km radius of Cuicocha caldera rim. We report herein the results of a CO2 efflux survey carried out at this crater lake during October 2018, with the aim of evaluating temporal variations of CO2 efflux and their relationships with volcanic activity since 2006. In the 2018 survey, a total of 113 CO2 efflux measurements were performed on the lake surface by means of a floating accumulation chamber. At each sampling site pH, temperature and conductivity were measured at 15 cm depth from the water surface. To study the possible water stratification and CO2 accumulation in the lake, a dissolved gases were analysed at several depths in a vertical profile was performed reaching 80 m depth. The CO2 efflux values ranged between 4 and 70 g•m−2•d−1 with an average value of 19 g•m−2•d−1. In order to compute the diffuse CO2 emission at the studied area, the CO2 emission spatial distribution map was constructed averaging results of the 100 simulations following the sequential Gaussian simulation algorithm. The highest values of diffuse CO2 efflux and water temperature were observed close to one of the domes located inside the crater lake. The diffuse CO2 output was computed as 76 ± 3 t•d-1, being released through an area of 4.7 km2. Temporal evolution diffuse CO2 output presents a range from 76 to 652 t•d-1, being the 2018 survey the lower value. During March 2012, more than a hundred of earthquakes (M<3) were recorded in the southwestern zone of the Cuicocha volcanic lake, coinciding with the maximum value of diffuse CO2 emission of 652 t•d-1. Periodic diffuse CO2 emission surveys will be tremendously useful to improve the early warning system of future magmatic reactivations. [ABSTRACT FROM AUTHOR]

Taal volcano is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Located on the southwestern part of Luzon Island, Taal consists of a 15-22-km prehistoric caldera, occupied by the Taal Lake, the active vent complex of Volcano Island and the Crater Lake (TCL), 1.9 km in diameter. Six of 24 known eruptions at Taal since 1572 have caused many fatalities, and several million people live within a 20-km radius of Taal's caldera rim, making the volcano the largest threat to the Philippine population. An alarming increase in seismicity, gas emission, deformation and temperature of the TCL from March 2011, was interpreted as the result of a new magma intrusion (Arpa et al., 2013; Hernández et al., 2017). Between 2008 and 2014, ITER/INVOLCAN has collaborated with PHIVOLCS and from 2015 to the present with the University of the Philippines, also counting with the support of the Spanish Agency for International Development Cooperation (AECID), to perform diffuse CO2 efflux surveys at the surface of the TCL. In total, 18 surveys have been undertaken since 2008. Last survey was performed in November 2018, with 75 sites distributed homogenously along the surface of TCL. Together with diffuse CO2 efflux measurements, at each sampling site, water temperature and pH were measured. The CO2 measurements were carried out following the accumulation chamber method by means of a portable LICOR soil CO2 efflux instrument. To estimate the diffuse CO2 output, sequential Gaussian simulations (sGs) were used. The CO2 efflux values ranged from 231 to 20,920 gm-2•d-1. Main CO2 contributions were always observed at those areas where bubbling activity occurs. The estimated diffuse CO2 emission released from the Taal crater lake during 2018 survey was 3,050 ± 107 t•d-1. Observing the time series, the results reveal significant variations from 2008 to 2018 and do not seem to be masked by external variations, showing a temporal correlation with the onsets of high frequency seismic events recorded by PHIVOLCS at Taal. The above observations suggest subsurface magma movement as the cause for the observed changes in the total output of diffuse CO2 emission at the Taal crater lake, and CO2 efflux surveys become an effective volcanic surveillance tool for Taal volcano.Arpa et al., 2013. 2013. BullVolcanol. 75, 1–13.Hernández et al., 2017. J Geol. Soc. Lon. doi.org/10.1144/SP437.1. [ABSTRACT FROM AUTHOR]