A climate threshold for ocean deoxygenation during the Early Cretaceous.

Oceanic anoxic events (OAEs) are historical intervals of global-scale ocean deoxygenation associated with hyperthermal climate states and biological crises1,2. Massive volcanic carbon dioxide (CO2) emissions frequently associated with these events are thought to be a common driver of ocean deoxygenation through several climate-warming-related mechanisms1,3,4. The Early Cretaceous OAE1a is one of the most intense ocean deoxygenation events, persisting for more than 1 Myr (refs. 5,6). However, existing records of marine chemistry and climate across OAE1a are insufficient to fully resolve the timing and dynamics of the underlying processes, thus obscuring cause-and-effect relationships between climate forcing and ocean oxygenation states. Here we show that rapid ocean deoxygenation during OAE1a is linked to volcanic CO2 emissions and the crossing of an associated climate threshold, after which the sluggish pace of the silicate-weathering feedback and climate recovery delayed reoxygenation for >1 Myr. At the end of OAE1a, recrossing this threshold allowed for ocean reoxygenation. Following OAE1a, however, the Earth system remained sufficiently warm such that orbitally forced climate dynamics led to continued cyclic ocean deoxygenation on approximately 100-kyr timescales for another 1 Myr. Our results thus imply a tight coupling between volcanism, weathering and ocean oxygen content that is characterized by a climate threshold.

Effects on local atmospheric environment of volcanic ash from Sakurajima volcano, inferred from atmospheric deposition of Potassium-40 at Kagoshima City, Japan.

In this study, we statistically demonstrated that an anomalous high of 40K fallout in the atmospheric fallout in Kagoshima City is caused by heavy ashfall associated with eruptions of Sakurajima volcano. Sakurajima is one of the most active volcanoes in Japan, and its repeated explosive eruptions cause large amounts of ash to fall on Kagoshima City. The fallout of crust-derived natural radionuclides, 40K, 212Pb, and 214Bi, from the atmosphere in Kagoshima City showed a significant correlation with the number of eruptions of Sakurajima volcano and the amount of ashfall in Kagoshima City. In contrast, no significant correlation was found between 40K and 7Be fallout. The 40K fallout indicates that almost all of the atmospheric fallout in Kagoshima City is composed of volcanic ash particles. The contribution from mineral and sea salt particles other than volcanic ash is minimal. The mass balance of the observed 40K fallout, ashfall, and atmospheric fallout yield indicates that there is a significant amount of volcanic ash deposition that is not accounted for as ashfall. In most cases, the ash deposition observed as ashfall is only 30-70 wt% of the total deposition collected as atmospheric fallout samples, and the remaining portion is fine-grained and behaves as suspended volcanic ash particles, which significantly impact the atmospheric environment.

Confocal microscopy 3D imaging and bioreactivity of La Palma volcanic ash particles.

In September 2021 an eruption began of Cumbre Vieja, La Palma (Spain) that lasted 3 months. Previous studies have shown that volcanic ash particles can be associated with adverse effects on human health however, the reasons for this are unclear. Particle shape has been shown to contribute to cellular uptake in prostate cancer cells. Hence we aimed to study 3D structure, elemental composition and effects on cultured lung cells of particles collected from the La Palma volcanic eruption. 3D imaging of PM10 sized and below particles was performed using a LEXT OLS4100 confocal microscope (Olympus Corporation, Japan). A Zeiss EVO 50 (Carl Zeiss AG, Germany) Scanning Electron Microscope (SEM) was used to assess elemental composition. In addition, volcanic particle concentration dose response for pneumococcal adhesion to A549 human alveolar epithelial cells was investigated. Confocal microscopy showed that some PM10 and below sized particles had sharp or angular 3D appearance. SEM x-ray analysis indicated silicate particles with calcium, aluminium and iron. We observed increased colony forming units indicating increased Pneumococcal adhesion due to exposure of cells to volcanic particles. Thus in addition to the toxic nature of some volcanic particles, we suggest that the observed sharp surface particle features may help to explain adverse health effects associated with volcanic eruptions.

The Early Microbial Colonizers of a Short-Lived Volcanic Island in the Kingdom of Tonga.

The island of Hunga Tonga Hunga Ha'apai (HTHH) in the Kingdom of Tonga was formed by Surtseyan eruptions and persisted for 7 years before being obliterated by a massive volcanic eruption on 15 January 2022. Before it was destroyed, HTHH was an unparalleled natural laboratory to study primary succession on a newly formed landmass. We characterized the microbial communities found on the surface sediments of HTHH using a combination of quantitative PCR, marker gene sequencing, and shotgun metagenomic analyses. Contrary to expectations, photosynthetic cyanobacteria were not detected in these sediments, even though they are typically dominant in the earliest stages of primary succession in other terrestrial environments. Instead, our results suggest that the early sediment communities were composed of a diverse array of bacterial taxa, including trace gas oxidizers, anoxygenic photosynthesizers, and chemolithotrophs capable of metabolizing inorganic sulfur, with these bacteria likely sourced from nearby active geothermal environments. While the destruction of HTHH makes it impossible to revisit the site to conduct in situ metabolic measurements or observe how the microbial communities might have continued to change over time, our results do suggest that the early microbial colonizers have unique origins and metabolic capabilities. IMPORTANCE The volcanic island of Hunga Tonga Hunga Ha'apai in the Kingdom of Tonga represents a very rare example of new island formation and thus a unique opportunity to study how organisms colonize a new landmass. We found that the island was colonized by diverse microbial communities shortly after its formation in 2015, with these microbes likely originating from nearby geothermal environments. Primary succession in this system was distinct from that typically observed in other terrestrial environments, with the early microbial colonizers relying on unique metabolic strategies to survive on the surface of this newly formed island, including the capacity to generate energy via sulfur and trace gas metabolism.

Urinary concentrations of metals before and after volcanic eruption: a natural experiment surrounding the eruption of Volcán de Fuego, 2018.

Volcanic eruptions increase environmental heavy metal concentrations, yet little research has been performed on their extrapulmonary human health effects. We fortuitously collected biological samples in a cohort of Guatemalan sugarcane cutters in the area surrounding Volcán de Fuego before and after the June 2018 eruption. We sought to determine whether stratovolcanic activity was associated with changes in urinary concentrations of heavy metals in a cohort of sugarcane workers. In this exploratory analysis, we found significant increases in urinary arsenic, (ß = 1.46, P < 0.0001), cadmium (ß = 1.03, P < 0.0001), and lead (ß = 0.87, P = 0.003) in participants with residential proximity to Volcán de Fuego as compared to participants farther away, suggesting that volcanic activity could be associated with acute heavy metal exposures. This natural experiment is, to our knowledge, the first of its kind and suggests a need for more research into heavy metal exposure-related health impacts of volcanic eruptions.

A millimeter-scale insight into formation mechanism of lacustrine black shale in tephra deposition background.

To reveal the role of tephra in the deposition of black shale during periods of volcanic activity, we performed lithostratigraphic and geochemical analyses on 14 horizontally sliced samples drilled from a 2-cm-thick black shale interval in the lower Ch7 Member of the Upper Triassic Yanchang Formation, southern Ordos Basin. Results indicate that fewer plankton is preserved during tephra deposition than during periods of volcanic quiescence. With the decrease of volcanic activities and tephra deposition, the abundance of redox-sensitive trace elements (RSTEs) and biolimiting elements increases, while terrigenous elements gradually decrease, resulting in the improvement of organic matter (OM) preservation. Paleoenvironmental proxies suggest that the climate during the Late Triassic was generally warm and humid. However, subsequent intense volcanic eruptions may have caused climatic cooling that affected the water column, resulting in enhanced salinity, primary production, water stratification, and bottom water anoxia, leading to enhanced organic carbon production and preservation. Primary productivity and redox conditions controlled the accumulation of organic carbon. Although physical and chemical reactions relating to the deposition of tephra into water are short-lived, climate change induced by volcanic eruptions is the critical cause of black shale formation.

Medication use in populations exposed to the 2010 Eyjafjallajökull eruption: an interrupted time series analysis.

OBJECTIVES: To assess the trends in medication use indicative of physical and psychological morbidity following the 2010 volcanic eruption in Eyjafjallajökull immediately after and during a 3-year period following the eruption. DESIGN: Population-based register study. SETTING: Eyjafjallajökull eruption in Iceland, 2007-2013. PARTICIPANTS: All residents in Iceland who received at least one medication dispensing were identified. Residents of exposed areas were classified into exposure groups (individual-level data) and residents in other parts of Iceland were included as a non-exposed group (aggregated data). INTERVENTION/EXPOSURE: Eyjafjallajökull erupted on 14 April 2010 and continued for 39 days, producing heavy ash fall in South Iceland. MAIN OUTCOME MEASURES: Using interrupted time series analysis, we examined annual and quarterly changes in medicine use, measured as number of dispensed defined daily dose (DDD) per 1000 individuals. We calculated the level shift (immediate change) and change in slope from pre-eruption to post-eruption (long-term change) in medication dispensing. RESULTS: Among exposed residents, there was a 6% decrease (95% CI -7% to -4%) in the annual number of dispensed DDDs 1-year post-eruption in the overall medication class, including analgesics (-5%, 95% CI -6% to -3%), hypnotics and sedatives (-9%, 95% CI -11% to -7%) and respiratory medications (-7%, 95% CI -9% to -5%; -8%, 95% CI -11% to -4%). Simultaneously, there was a 9% decrease (95% CI -14% to -4%) in the overall medication class among non-exposed residents. Moreover, among exposed residents, we observed change in slope of -4% (95% CI -7% to -1%) in the overall medication class, including for analgesics (-6%, 95% CI -8% to -3%) and other respiratory drugs (-10%, 95% CI -16% to -4%). CONCLUSION: Our findings indicate that the eruption did not lead to increases in medication dispensing among residents of exposed areas, rather decreases for some medicine classes. The results should be interpreted with caution since the content of each eruption differs.

Hidden mechanical weaknesses within lava domes provided by buried high-porosity hydrothermal alteration zones.

Catastrophic lava dome collapse is considered an unpredictable volcanic hazard because the physical properties, stress conditions, and internal structure of lava domes are not well understood and can change rapidly through time. To explain the locations of dome instabilities at Merapi volcano, Indonesia, we combined geochemical and mineralogical analyses, rock physical property measurements, drone-based photogrammetry, and geoinformatics. We show that a horseshoe-shaped alteration zone that formed in 2014 was subsequently buried by renewed lava extrusion in 2018. Drone data, as well as geomechanical, mineralogical, and oxygen isotope data suggest that this zone is characterized by high-porosity hydrothermally altered materials that are mechanically weak. We additionally show that the new lava dome is currently collapsing along this now-hidden weak alteration zone, highlighting that a detailed understanding of dome architecture, made possible using the monitoring techniques employed here, is essential for assessing hazards associated with dome and edifice failure at volcanoes worldwide.

Iron and total organic carbon shape the spatial distribution pattern of sediment Fe(III) reducing bacteria in a volcanic lake, NE China.

Fe(III) reducing bacteria (FeRB) play a vital role in the biogeochemical cycle of Fe, C and N in nature. The volcanic lake can be considered as an ideal habitat for FeRB. Here, we investigated the diversity and spatial distribution of FeRB in sediments of Wenbo lake in Wudalianchi volcano based on culture-dependent and independent methods. A total of 28 isolates affiliated with the genera of Enterobacter, Bacillus, Pseudomonas and Clostridium were obtained from 18 sediment samples. We detected 783 operational taxonomic units (OTUs) belonged to FeRB using high high-throughput sequencing, and the dominant phyla were Proteobacteria (3.65%), Acidobacteria (0.29%), Firmicutes (10.78%). The representative FeRB genera such as Geobacter, Pseudomonas, Thiobacillus and Acinetobacter distributed widely in Wenbo lake. Results showed that the diversity and abundance of FeRB declined along the water-flow direction from Libo to Jingbo. In contrast, the FeRB diversity decreased and the FeRB abundance increased along with depth transect of sediments. It was found that the dominant phylum changed from Firmicutes to Proteobacteria along the water-flow direction, while changed from Proteobacteria to Firmicutes along with the depth of sediments. RDA indicated that the FeRB distribution were driven by soluble total iron, total organic carbon, Fe(II) and Fe(III). These will provide information for understanding the role of FeRB in the elements geochemical cycles in the volcanic environment.

Naturaleza y estructura geológica del borde costero del noroeste de Costa Rica / Geological background and structure of the northwestern coastline of Costa Rica

Introducción: El noroeste de Costa Rica representa un área con una alta riqueza geológica que evidencia rocas generadas en diferentes ambientes, como plano abisal, talud continental, plataforma continental, volcánicos continentales efusivos y explosivos, volcánicos submarinos, costeros, erosivos fluviales, erosivos gravitatorios, de intrusión y el manto terrestre. Objetivo: Describir el contexto geológico actual del noroeste de Costa Rica, mediante el análisis y recopilación de datos de campo, geoquímicos, petrológicos, estructurales, paleontológicos y radiométricos con el fin de reconstruir los eventos y etapas de deformación desde el Jurásico a la actualidad. Métodos: Se hizo una recopilación bibliográfica de estudios en diversas ramas geológicas para establecer un estado del arte del extremo noroeste de Costa Rica. Resultados: La historia geológica representa el registro en rocas desde el Jurásico al Holoceno - actualidad con once etapas definidas a partir de interpretaciones petrológicas, estructurales, geocronológicas, estratigráficas y paleontológicas agrupadas en tres etapas de depositación y afectadas por cuatro fases tectónicas compresivas. Conclusiones: Las etapas de depositación corresponden con una primera etapa magmática con afinidad oceánica entre el Jurásico y el Cretácico Superior, una segunda etapa predominantemente sedimentaria con un rango de edad entre el Cretácico Superior y el Oligoceno, y por último una etapa volcánica efusiva - explosiva ubicada desde el Plioceno hasta la actualidad. Las fases tectónicas se asocian con diferentes eventos entre placas. La primera se dio en el Cretácico Inferior y su principal resultado visible fue la emersión de la Ofiolita de Santa Elena; la segunda sucedió del Cretácico Superior temprano al Campaniano y su reconocimiento está ligado a la posición actual de la Ofiolita de Santa Elena y sus estructuras circundantes; la tercera fase aconteció desde el Eoceno Superior hasta el Mioceno y su principal producto fue la generación del tren de pliegues sedimentarios del Golfo de Santa Elena a bahía de Salinas; y por último se presenta una fase Cuaternaria que originó el eje de basculamiento de los productos piroclásticos frente a la cordillera volcánica de Guanacaste.

Introduction: The Costa Rican northwestern coastline has a wide geological uniqueness that exhibits rocks from different environments such as abyssal plane, continental slope, continental platform, volcanic eruptions (effusive, explosive, and submarine), coastal, erosional (fluvial and gravitatory), intrusions, and upper mantle rocks. Objective: To present the geologic state of the art of the northwestern coastline of Costa Rica through the bibliographic review of geochemical, petrologic, structural, paleontological and geochronological data. Methods: A bibliographic revision was done to propose a state of the art of northwestern coastline of Costa Rica. Results: The geologic record shows eleven stages from the Jurassic to the Holocene. These stages were regrouped from petrologic, structural, geochronologic, stratigraphic and paleontological interpretations in three depositional stages and four compressive tectonic phases. Conclusions: The first depositional stage is volcanic with oceanic affinity between the Jurassic and Upper Cretaceous. The second has a sedimentary predominance with an age range between the Upper Cretaceous and the Miocene. The last depositional stage is a volcanic (effusive and explosive) from the Pliocene until the present. The tectonic phases are associate with different interactions between tectonic plates. The first phase triggered the Santa Elena Ophiolite obduction during the Early Cretaceous. The second phase occurred in the Early Upper Cretaceous - Campanian and is recognized by its current position and surrounding structures. The third phase lasted from the Upper Eocene until the Miocene and its main result was the folding of the Bahía de Salinas sedimentary rocks. Finally, the Quaternary phase created a tilt axis and the aperture for the deposition of pyroclastic density currents in front of the Guanacaste volcanic ridge.

Severe volcanic SO2 exposure and respiratory morbidity in the Icelandic population - a register study.

BACKGROUND: The Holuhraun volcanic eruption September 2014 to February 2015 emitted large amounts of sulfur dioxide (SO2). The aim of this study was to determine the association between volcanic SO2 gases on general population respiratory health some 250 km from the eruption site, in the Icelandic capital area. METHODS: Respiratory health outcomes were: asthma medication dispensing (AMD) from the Icelandic Medicines Register, medical doctor consultations in primary care (PCMD) and hospital emergency department visits (HED) in Reykjavík (population: 215000) for respiratory disease from 1 January 2010 to 31 December 2014. The associations between daily counts of health events and daily mean SO2 concentration and high SO2 levels (24-h mean SO2 > 125 µg/m3) were analysed using generalized additive models. RESULTS: After the eruption began, AMD was higher than before (129.4 vs. 158.4 individuals per day, p < 0.05). For PCMD and HED, there were no significant differences between the number of daily events before and after the eruption (142.2 vs 144.8 and 18.3 vs 17.5, respectively). In regression analysis adjusted for other pollutants, SO2 was associated with estimated increases in AMD by 0.99% (95% CI 0.39-1.58%) per 10 µg/m3 at lag 0-2, in PCMD for respiratory causes 1.26% (95% CI 0.72-1.80%) per 10 µg/m3 SO2 at lag 0-2, and in HED by 1.02% (95% CI 0.02-2.03%) per 10 µg/m3 SO2 at lag 0-2. For days over the health limit, the estimated increases were 10.9% (95% CI 2.1-19.6%), 17.2% (95% CI 10.0-24.4%) for AMD and PCMD. Dispensing of short-acting medication increased significantly by 1.09% (95% CI 0.49-1.70%), and PCMD for respiratory infections and asthma and COPD diagnoses and increased significantly by 1.12% (95% CI 0.54-1.71%) and 2.08% (1.13-3.04%). CONCLUSION: High levels of volcanic SO2 are associated with increases in dispensing of AMD, and health care utilization in primary and tertiary care. Individuals with prevalent respiratory disease may be particularly susceptible.

A revised AMS and tephra chronology for the Late Middle to Early Upper Paleolithic occupations of Ortvale Klde, Republic of Georgia.

The nature and timing of the shift from the Late Middle Paleolithic (LMP) to the Early Upper Paleolithic (EUP) varied geographically, temporally, and substantively across the Near East and Eurasia; however, the result of this process was the archaeological disappearance of Middle Paleolithic technologies across the length and breadth of their geographic distribution. Ortvale Klde rockshelter (Republic of Georgia) contains the most detailed LMP-EUP archaeological sequence in the Caucasus, an environmentally and topographically diverse region situated between southwest Asia and Europe. Tephrochronological investigations at the site reveal volcanic ash (tephra) from various volcanic sources and provide a tephrostratigraphy for the site that will facilitate future correlations in the region. We correlate one of the cryptotephra layers to the large, caldera-forming Nemrut Formation eruption (30,000 years ago) from Nemrut volcano in Turkey. We integrate this tephrochronological constraint with new radiocarbon dates and published ages in an OxCal Bayesian age model to produce a revised chronology for the site. This model increases the ages for the end of the LMP (∼47.5-44.2 ka cal BP) and appearance of the EUP (∼46.7-43.6 ka cal BP) at Ortvale Klde, which are earlier than those currently reported for other sites in the Caucasus but similar to estimates for specific sites in southwest Asia and eastern Europe. These data, coupled with archaeological, stratigraphic, and taphonomic observations, suggest that at Ortvale Klde, (1) the appearance of EUP technologies of bone and stone has no technological roots in the preceding LMP, (2) a LMP population vacuum likely preceded the appearance of these EUP technologies, and (3) the systematic combination of tephra correlations and absolute dating chronologies promises to substantially improve our inter-regional understanding of this critical time interval of human evolution and the potential interconnectedness of hominins at different sites.

Metagenomic analysis reveals rapid development of soil biota on fresh volcanic ash.

Little is known of the earliest stages of soil biota development of volcanic ash, and how rapidly it can proceed. We investigated the potential for soil biota development during the first 3 years, using outdoor mesocosms of sterile, freshly fallen volcanic ash from the Sakurajima volcano, Japan. Mesocosms were positioned in a range of climates across Japan and compared over 3 years, against the developed soils of surrounding natural ecosystems. DNA was extracted from mesocosms and community composition assessed using 16S rRNA gene sequences. Metagenome sequences were obtained using shotgun metagenome sequencing. While at 12 months there was insufficient DNA for sequencing, by 24 months and 36 months, the ash-soil metagenomes already showed a similar diversity of functional genes to the developed soils, with a similar range of functions. In a surprising contrast with our hypotheses, we found that the developing ash-soil community already showed a similar gene function diversity, phylum diversity and overall relative abundances of kingdoms of life when compared to developed forest soils. The ash mesocosms also did not show any increased relative abundance of genes associated with autotrophy (rbc, coxL), nor increased relative abundance of genes that are associated with acquisition of nutrients from abiotic sources (nifH). Although gene identities and taxonomic affinities in the developing ash-soils are to some extent distinct from the natural vegetation soils, it is surprising that so many of the key components of a soil community develop already by the 24-month stage. In this system, however, rapid development may be facilitated by the relatively moderate pH of the Sakurajima ash, proximity of our mesocosms to propagule sources, and the rapid establishment of a productive bryophyte and lichen layer on the surface. Ash from other volcanoes richer in acids or more distant from propagule sources could show a different pattern and slower soil biota development.

Nanoscale trace metal imprinting of biocalcification of planktic foraminifers by Toba's super-eruption.

Bioactive metal releases in ocean surface water, such as those by ash falls during volcanic super-eruptions, might have a potentially toxic impact on biocalcifier planktic microorganisms. Nano-XRF imaging with the cutting-edge synchrotron hard X-ray nano-analysis ID16B beamline (ESRF) revealed for the first time a specific Zn- and Mn-rich banding pattern in the test walls of Globorotalia menardii planktic foraminifers extracted from the Young Toba Tuff layer, and thus contemporaneous with Toba's super-eruption, 74,000 years ago. The intra-test correlation of Zn and Mn patterns at the nanoscale with the layered calcareous microarchitecture, indicates that the incorporation of these metals is syngenetic to the wall growth. The preferential Mn and Zn sequestration within the incipient stages of chamber formation suggests a selective incorporation mechanism providing a resilience strategy to metal pollution in the test building of planktic foraminifers.

Evaluation of possible impact on human health of atmospheric mercury emanations from the Popocatépetl volcano.

The contribution of Hg from volcanic emanations is decisive for assessing global mercury emissions given the impact of this highly toxic contaminant on human health and ecosystems. Atmospheric Hg emissions from Popocatépetl volcano and their dispersion were evaluated carrying out two gaseous elemental mercury (GEM) surveys during a period of intense volcanic activity. Continuous GEM measurements were taken for 24 h using a portable mercury vapor analyzer (Lumex RA-915M) at the Altzomoni Atmospheric Observatory (AAO), 11 km from the crater. In addition, a long-distance survey to measure GEM was conducted during an automobile transect around the volcano, covering a distance of 129 km. The evaluation of the GEM data registered in the fixed location showed that heightened volcanic activity clearly intensifies the concentration of atmospheric Hg, extreme values around 5 ng m-3. Highest concentrations of GEM recorded during the mobile survey were about 10 ng m-3. In both surveys, the recorded concentrations during most of the measurement time were below 2 ng m-3, but measurements were taken at a considerable distance from the crater, and GEM is subject to dilution processes. During both surveys, recorded GEM did not exceed the 200 ng m-3 concentration recommended by the WHO (Air quality guidelines for Europe, 2000) as the regulatory limits for Hg in the atmospheric environment for long-term inhalation. Because this study was carried out in inhabited areas around the volcano during a period of intense volcanic activity, it can be concluded that the Popocatépetl does not represent a risk to human health in terms of Hg.

Two distinct mechanisms of fluoride enrichment and associated health risk in springs' water near an inactive volcano, southeast Iran.

Groundwater fluoride contamination is a major issue of water pollution in the world with health hazards such as dental and skeletal fluorosis. This research focused on exposure to the high concentration of fluoride in the springs water in the Bazman volcanic area, southeast Iran. The combination of chemical/isotopic analysis, geochemical modeling, health risk assessment and multivariate statistical methods were applied to investigate the contamination and sources of fluoride in the samples. Groundwater samples were collected from cold and thermal springs. Major ions, fluoride, trace elements and stable isotopes δ18O and δD were measured in the samples using standard methods, ICP-MS and OA-ICOS, respectively. Fluoride content in springs varied from 0.5 to 3.75 mg/L with an average value of 1.66 mg/L. The highest fluoride concentrations were observed in the eastern cold springs while thermal springs showed the minimum fluoride contents. The majority of samples showed F contents higher than the calculated optimal concentration of fluoride (0.75 mg/L). Reaction of fluorite mineral with HCO3 and replacement of F in clay minerals and metal oxy-hydroxides with OH- in water were likely cause fluoride enrichment in the eastern springs. Whereas, in the western springs and thermal springs, origin of fluoride was related to weathering of muscovite, cryolite, apatite and fluoroapatite minerals. The δ18O and δ2H of the water samples displayed the impact on evaporation on fluoride enrichment in all spring water samples. The average value of contamination index (Cd) in the water samples was 1.94 categorizing medium risk level while springs S7, S8, S9 and S4 were above the threshold value of Cd index. The fluoride hazard quotient (HQ) showed that 25%, 44%, 56% and 0% of springs' water resources had high risk level for age group of adults, teenager, children and infants, respectively. Therefore, health risk of fluoride in drinking water resources were in the following order: children > teenager > adults > infants.

Characterization of volcanic structures associated to the silicic magmatism of the Paraná-Etendeka Province, in the Aparados da Serra region, southern Brazil.

The Paraná-Etendeka Magmatic Province is associated with the distensive tectonics that caused the rupture of the Gondwana continent during the Lower Cretaceous and generated an intense volcanism that covers South America and the NW portion of Namibia in Africa. In Brazil, this volcanic sequence is named Serra Geral Group and predominantly consists of basalts and subordinated silicic rocks. The goal of this study is to characterize the geomorphological features observed in the Aparados da Serra region, southern Brazil, and to evaluate the relationship between these structures and the primary silicic volcanic structures. The geomorphological features were first identified using remote sensing and then correlated with flow structures observed in the field, as well as petrographic and geochemical data. AMS data were used to determine magnetic patterns and the direction of magmatic flow of the rocks. Despite the low degree of anisotropy, clear patterns of lineation and foliation were identified in the studied rocks. Our data shows that Units I and II correspond to silicic lava flows linked to effusive fissure eruptions, presenting a dome morphology caused by differential erosion. Unit III rocks may correspond to true volcanic domes, whereas the Unit IV corresponds to the effusive feeder structures.