Vent Locations Research Articles

Assessing impending hazards from summit eruptions: the new probabilistic map for lava flow inundation at Mt. Etna

The development of probabilistic maps associated with lava flow inundation is essential to assess hazard in open vent volcanoes, especially those that have highly urbanized flanks. In this study we present the new lava flow hazard map linked to the summit eruptions of Mt. Etna, which has been developed using a probabilistic approach that integrates statistical analyses of the volcanological historical data with numerical simulations of lava flows. The statistical analysis of volcanological data (including vent location, duration and lava volumes) about all summit eruptions occurred since 1998 has allowed us both to estimate the spatiotemporal probability of future vent opening and to extract the effusion rate curves for lava flow modelling. Numerical simulations were run using the GPUFLOW model on a 2022 Digital Surface Model derived from optical satellite images. The probabilistic approach has been validated through a back-analysis by calculating the fit between the expected probabilities of inundation and the lava flows actually emplaced during the 2020-2022 period. The obtained map shows a very high probability of inundation of lava flows emitted at vents linked to the South East Crater, according to the observation of the eruptive dynamics in the last decades.

Highly structured populations of deep-sea copepods associated with hydrothermal vents across the Southwest Pacific, despite contrasting life history traits

Hydrothermal vents are extreme environments, where abundant communities of copepods with contrasting life history traits co-exist along hydrothermal gradients. Here, we discuss how these traits may contribute to the observed differences in molecular diversity and population genetic structure. Samples were collected from vent locations across the globe including active ridges and back-arc basins and compared to existing deep-sea hydrothermal vent and shallow water data, covering a total of 22 vents and 3 non-vent sites. A total of 806 sequences of mtDNA from the Cox1 gene were used to reconstruct the phylogeny, haplotypic relationship and demography within vent endemic copepods (Dirivultidae, Stygiopontius spp.) and non-vent-endemic copepods (Ameiridae, Miraciidae and Laophontidae). A species complex within Stygiopontius lauensis was studied across five pacific back-arc basins at eight hydrothermal vent fields, with cryptic species being restricted to the basins they were sampled from. Copepod populations from the Lau, North Fiji and Woodlark basins are undergoing demographic expansion, possibly linked to an increase in hydrothermal activity in the last 10 kya. Highly structured populations of Amphiascus aff. varians 2 were also observed from the Lau to the Woodlark basins with populations also undergoing expansion. Less abundant harpacticoids exhibit little to no population structure and stable populations. This study suggests that similarities in genetic structure and demography may arise in vent-associated copepods despite having different life history traits. As structured meta-populations may be at risk of local extinction should major anthropogenic impacts, such as deep-sea mining, occur, we highlight the importance of incorporating a trait-based approach to investigate patterns of genetic connectivity and demography, particularly regarding area-based management tools and environmental management plans.

Mapping the microbial diversity associated with different geochemical regimes in the shallow-water hydrothermal vents of the Aeolian archipelago, Italy.

Shallow-water hydrothermal vents are unique marine environments ubiquitous along the coast of volcanically active regions of the planet. In contrast to their deep-sea counterparts, primary production at shallow-water vents relies on both photoautotrophy and chemoautotrophy. Such processes are supported by a range of geochemical regimes driven by different geological settings. The Aeolian archipelago, located in the southern Tyrrhenian sea, is characterized by intense hydrothermal activity and harbors some of the best sampled shallow-water vents of the Mediterranean Sea. Despite this, the correlation between microbial diversity, geochemical regimes and geological settings of the different volcanic islands of the archipelago is largely unknown. Here, we report the microbial diversity associated with six distinct shallow-water hydrothermal vents of the Aeolian Islands using a combination of 16S rRNA amplicon sequencing along with physicochemical and geochemical measurements. Samples were collected from biofilms, fluids and sediments from shallow vents on the islands of Lipari, Panarea, Salina, and Vulcano. Two new shallow vent locations are described here for the first time. Our results show the presence of diverse microbial communities consistent in their composition with the local geochemical regimes. The shallow water vents of the Aeolian Islands harbor highly diverse microbial community and should be included in future conservation efforts.

Validation of Play Fairway Analysis of the geothermal potential of Camas Prairie, south-central Idaho, by an exploration well

Play Fairway Analysis (PFA) methodology was adapted for geothermal exploration at Camas Prairie, Idaho. Geophysical data, structural and geologic mapping, volcanic rock ages and vent locations, and the distribution of thermal springs and wells all indicated a relatively high geothermal potential along the southern margin of the Prairie. An exploration well (USU Camas-1) was drilled to a depth of 618.3 m to validate the PFA. A permeable zone was encountered at ~ 357.5 m with a maximum measured temperature of ~ 80 °C, which was suppressed following the injection of cold water. A moderate transmissivity of ~ 0.25–1 cm2/s estimated from an injection test as well a seasonal artesian flow at ~ 0.7 L/s corroborate the presence of a permeable zone. The existence of a lacustrine clay seal was confirmed near the bottom of the basin-fill sediment occupying the upper 314 m of the well. Geothermometers suggest the USU Camas-1 well water equilibrated at a reservoir temperature of ~ 120 °C. Based on the locations of both thermal and cold wells, geothermal fluids appear to be flowing upward along one or both of two fault systems. The presence of young basalts and elevated helium isotope ratios suggest that the heat source of Camas Prairie is magmatic. However, the faults may be acting as a conduit for geothermal fluids to rise from great depth without a shallow magmatic source being present. Camas Prairie is a promising area for geothermal development, but the relatively low reservoir temperatures indicate this resource may not be suitable for electric generation. Perhaps the best use would be for heating.

Deciphering the sources and processes feeding young monogenetic volcanoes from the Michoacán Guanajuato Volcanic Field (Mexico): A study case of El Astillero and El Pedregal

El Astillero and El Pedregal monogenetic volcanoes formed ∼500–700 CE in the Tancítaro region in the southern part of the Michoacán-Guanajuato volcanic field, only 25 km to the SW of the historic Paricutin volcano. The ∼6-year-long eruption was characterized by a change from explosive to effusive activity, accompanied by a shift in the location of the active vents. Initial activity was Strombolian-explosive and first formed the El Astillero cone before turning effusive with the emission of several lava flows. Then, a new vent located 2 km to the ENE opened and produced the purely effusive (non-explosive) El Pedregal lava flow field. As the eruption progressed, the bulk magma composition (major and trace elements) changed from basaltic andesite to andesite (SiO2 = 52–59 wt%), which is also reflected in a successive change in the petrography of the erupted tephras and lavas. However, the El Pedregal lava sequence shows small Mg# reversals followed by a marked final reversal to more mafic compositions. Likewise, 87Sr/86Sr (0.70388–0.70403), 143Nd/144Nd (0.512836–0.512742), 206Pb/204Pb (18.632–18.671), 207Pb/204Pb (15.583–15.598), 208Pb/204Pb (38.376–38.450), 176Hf/177Hf (0.28301–0.28290), and 187Os/188Os (0.1258–0.1865) isotope ratios changed systematically as the eruption progressed, and record a final shift to a distinct isotopic signature. The spatio-temporal proximity of both vents and the petrographic and geochemical characteristics of their magmas suggest a comagmatic evolution that can be explained by a combination of variable degrees of magma recharge, magma mixing, and fractional crystallization of subduction-modified mantle melts. A similar combination of magmatic processes for the genesis and evolution of these magmas has also been proposed for other young monogenetic volcanoes in the Michoacán-Guanajuato volcanic field (e.g., Paricutin, Jorullo, and the Tacámbaro cluster). Accordingly, primitive magmas in the Trans-Mexican Volcanic Belt are subduction-modified mantle melts that evolve largely by crystal fractionation and pass through the crust without significant assimilation.

Distribution of benzene and formaldehyde in tractor cabin: Effects of components, ventilation conditions, and vent positions

Tractor cabin is a relatively closed microenvironment in which operator is exposed to various pollutants that can adversely affect human health. In this study, the distribution of benzene and formaldehyde inside tractor cabin was investigated using computational fluid dynamics (CFD) method and verifying its effectiveness with field measurements. The effects of pollution source, ventilation, and vent position on the distribution of pollutants were discussed by using the validated CFD model. The results indicated that the areas with high concentration of pollutants are mostly distributed in the corners, and the ceiling contributes the most to its emission. The concentration difference of benzene and formaldehyde in the driver’s breathing area can reach a maximum of 20% by adjusting the air supply angle. It can also be reduced by 3.9% and 4.3% for every 1 m s−1 increase in air supply speed when the airflow angle emitted from the vent was 90°. In the common vent locations, the vent arranged on the front ceiling has the best pollutant reduction effect. This study provided a reliable CFD simulation method for benzene and formaldehyde distribution, offered a theoretical basis for the selection of ventilation conditions and the design of internal layout in tractor cabins for improving air quality. It also suggested that then environment and air quality of non-road mobile machinery cabs should be paid more attention in the future.

Analysis and Minimization of Race Tracking in the Resin-Transfer-Molding Process by Monte Carlo Simulation.

A numerical analysis of the influence of race tracking on dry spots formation and the accuracy of permeability measurement during the resin-transfer-molding process is presented. In the numerical simulation of the mold-filling process, defects are randomly generated, and their effect is assessed by a Monte Carlo simulation method. The effect of race tracking on the unsaturated permeability measurement and dry spots formation is investigated on flat plates. It is observed that the race-tracking defects located near the injection gate increase up to 40% of the value of the measured unsaturated permeability. The race-tracking defects located near the air vents are more likely to generate dry spots, whereas those near the injection gates have a less significant influence on dry spots generation. Depending on vent location, it has for instance been shown that the dry spot area can increase by a factor of 30. Dry spots may be mitigated by placing an air vent at a suitable location based on the numerical analysis results. Moreover, those results may be helpful to determine optimal sensor locations for the on-line control of mold-filling processes. Finally, the approach is successfully applied to a complex geometry.

Vents opening susceptibility map of the Colli Albani long dormant volcano

Despite their protracted periods of inactivity, long-dormant volcanoes may be highly hazardous, as their reactivation can be characterized by violent explosive eruptions. An example of such volcanoes is the Colli Albani caldera, onto which deposits Rome Capital City is built, Italy. Its last volcanic activity was characterized by voluminous maar-forming phreatomagmatic eruptions dated between 36 and 25ka, but the volcano has produced several maar lake overflows during the Holocene till historical times. Presently, Colli Albani is affected by recurrent seismic events, anomalous heat flow, ground uplifts, hydrothermal circulation and gas emissions. For these reasons, the Italian Civil Protection has recently listed Colli Albani among the ten active volcanoes of Italy, but products for the evaluation of its volcanic hazards lacking. This work presents the first study on vent opening susceptibility mapping at Colli Albani. We explore the potential of an available geological dataset for building, through geographic information system analysis, an index that classifies areas at different vents opening susceptibility (low, moderate and high). Such result highlights as a solid geological mapping is a prerequisite for the volcanic hazard assessment, especially in remote or poorly studied long-dormant volcanoes such as caldera systems where the location of new vents could occur in different volcano sectors.

Airflow distribution in hospital isolation rooms with different ventilation and exhaust vent configurations

Negative pressure isolation rooms can accommodate and treat patients with highly infectious diseases (such as COVID-19). Airtight conditions in the isolation room protect against infectious diseases. To control airflow and minimize infection risk within the isolation room, this study proposes three exhaust outlet vents with three air change per hour (ACH) conditions, 12, 24 and 48 ACH, in a single-bed hospital room using a computational fluid dynamics (CFD) approach. Results show that using the same ACH air velocity is relatively unaffected by the type and location of the exhaust air vent. The current case, case 1 and case 2 had average velocities of 0.121, 0.130 and 0.116, respectively. When the ACH was increased to 48, the average velocity was decreased to 0.663 m/s in case 1 and 0.589 m/s in case 2, compared to 0.711 m/s in the current case. In terms of infection probability, the study found that in the scenario of 12 ACH, the infection probability for case 1 and case 2 was increased by 11.85% and 3.96%, respectively, compared to the current case. The exhaust air vent in case 2 could effectively prevent the spread of pollutants when it was set to 48 air changes per hour and had the lowest risk level at 10.11%.

Computational Fluid Dynamics Simulations to Assess Spatial Variability and Optimal Ventilation Scenarios for Biological Laboratory Exposures

Introduction: A significant amount of uncertainty exists regarding potential human exposure to laboratory biomaterials and organisms in Biosafety Level 2 (BSL-2) research laboratories. Computational fluid dynamics (CFD) modeling is proposed as a way to better understand potential impacts of different combinations of biomaterials, laboratory manipulations, and exposure routes on risks to laboratory workers. Methods: In this study, we use CFD models to simulate airborne concentrations of contaminants in an actual BSL-2 laboratory under different configurations. Results: Results show that ventilation configuration, sampling location, and contaminant source location can significantly impact airborne concentrations and exposures. Depending on the source location and airflow patterns, the transient and time-integrated concentrations varied by several orders of magnitude. Contaminant plumes from sources located near a return vent (or exhaust like a fume hood or ventilated biosafety cabinet) are likely to be more contained than sources that are further from the exhaust. Having a direct flow between the source and the exhaust (through-flow condition) may reduce potential exposures to individuals outside the air flow path. Conclusion: Designing a BSL-2 room with ventilation and airflow patterns that maximize through-flow conditions to the return/exhaust vents and minimize dispersion and mixing throughout the room is, therefore, recommended. CFD simulations can also be used to assist in characterizing the impacts of supply and return vent locations, room layout, and source locations on spatial and temporal contaminant concentrations. In addition, proper placement of particle sensors can also be informed by CFD simulations to provide additional characterization and monitoring of potential exposures in BSL-2 facilities.

Experimental analysis of the effects of ship motion on hydrogen dispersion in an enclosed area

This study aims to experimentally quantify the hydrogen diffusion characteristics by ship motion. Hydrogen leakage experiments were conducted under various ship motion conditions, and the corresponding hydrogen concentrations for each sensor were expressed by an equation. The experimental facility was a scale model of the hydrogen fuel storage room of a ship. An experiment was conducted by implementing the roll and pitch motions of the ship as well as motion direction using a ship simulator. In the equation describing the hydrogen concentration, the minimum and maximum root mean square deviations were 0.987 and 0.707, respectively, and the correlations were 0.000109 and 0.0012289. Although the results differed as per the sensor location, the hydrogen concentration was affected by the motion period of the ship. The experimental results and prediction equations can be useful for sensor and vent location selection by predicting the concentration when hydrogen leaks in ships in motion.

Geothermal Explosion at the 2014 Landslide-Covered Area of the Geyser Valley, Kamchatka, Russian Far East

Geyser geothermal fields are scenic volcanic landforms that often contain tens to hundreds of thermal spot vents that erupt boiling water or contain bubbling mud pools. The fields are potentially hazardous sites due to boiling water temperatures and changes in vent locations and eruption dynamics, which are poorly understood. Here we report on the rapid and profound changes that can affect such a geyser field and ultimately lead to a dangerous, unanticipated eruption. We studied the Geyser Valley, Kamchatka Peninsula, which is a field of geysers and other thermal features and boiling pools. Using high-resolution tri-stereo satellite data and unmanned aerial systems (UAS) with optical and thermal infrared cameras in 2018 and 2019, we were able to identify a newly emerging explosion site. Structure-from-motion analysis of data acquired before and after the explosion reveals morphological and thermal details of the new vent. The explosion site produced an aureole zone of more than 150 m3 of explosively redeposited gravel and clay, a slightly elliptical crater with a diameter of 7.5 m and a crater rim 0.30 m high. However, comparison with archives of photogrammetric data suggests that this site was thermally active years earlier and contained a crater that was obscured and covered by landslides and river sediments. The results allow us to develop a conceptual model and highlight the hazard potential of thermal features buried by landslides and clastic deposits. Sudden explosions may occur at similar sites elsewhere, highlighting the need for careful assessment and monitoring of geomorphological and hydrological changes at geyser sites in other regions.

Computational fluid dynamic analysis of corona virus patients breathing in an airplane

Effective ventilation systems are essential to control the transmission of airborne aerosol particles, such as the SARS-CoV-2 virus in aircraft cabins, which is a significant concern for people commuting by airplane. Validated computational fluid dynamic models are frequently and effectively used to investigate air distribution and pollutant transport. In this study, the effectiveness of different ventilation systems with varying outlet vent locations were computationally compared to determine the best ventilation system for minimizing the risk of airborne transmission. The cabin air conditioning system was optimized to determine how design variables (air inlet temperature, outlet valve width and location, and mass flow rate) affect output parameters, including particle residence time, age of air, and thermal comfort conditions. Inlet mass flow rate was observed to be an influential variable impacting all output parameters, especially on age of air, where it was the most influential. In contrast, the least effective variable was width of the outlet valve, which only affected the particle residence time. Also, Predicted Mean Vote and Predicted Percentage Dissatisfied indices were the most affected by air inlet temperature, which had an inverse relation, while the outlet valve location had the greatest effect on particle residence time.

Relación entre vulcanismo dacítico monogenético y poligenético. Caso de estudio del domo Tapias (<95 ka) y volcán Cerro Machín (<50 ka), Colombia

The Tapias lava dome is located ~5 km SE of the explosive, Cerro Machín polygenetic volcano, both located on the Colombian Central Cordillera. The edifices have been interpreted as generated by the same magmatic system; however, the genetic and temporal relations between both edifices have not been established. In this work, the Tapias dome is studied using petrographic characterizations, mineral-, whole-rock- and isotopic chemistry, geothermobarometric calculations, and a K/Ar radiogenic age, and subsequently it is explored the relationship with the Cerro Machín. The rocks from Tapias dome are porphyritic with phenocrysts of plagioclase (An28-48), amphibole (tschermakite and magnesiohastingsite), biotite, quartz, and Fe-Ti oxides, embedded in a glassy groundmass. Petrographically, two types of amphibole crystals were recognized: type I, which is homogeneous, and type II, which displays different rims. The composition of Tapias is dacitic (SiO2: 66.59 wt.%) with calc-alkaline affinity. Our geothermobarometric calculations indicate that type I amphibole crystallized at 871-874°C, between 10.2 and 10.4 km depth. The core of the type II amphibole crystallized at 852-920°C, between 8.5 and 12.3 km depth, while its rim did it at higher temperatures (880-973°C), but at similar depths (9.1-11.8 km). The K/Ar radiogenic age obtained for the groundmass shows an emplacement age not older than 95 ± 0.05 ka. When comparing the results to the Cerro Machín, it is noted that the mineral and compositional characteristics are nearly identical. These results suggest that indeed both volcanoes share the same magmatic system and are fed by magma hosted between ~9 and ~12 km depth. Moreover, it is proposed that the vent location of both edifices, as well as the time gap between the eruption at Tapias and the beginning of the activity at the Cerro Machín (~50 ka), are the result of crustal deformation caused by the interaction between the Otú-Pericos and Ibagué faults.

Mechanical Modeling of Pre‐Eruptive Magma Propagation Scenarios at Calderas

AbstractSimulating magma propagation pathways requires both a well‐calibrated model for the stress state of the volcano and models for dike advance within such a stress field. Here, we establish a framework for calculating computationally efficient and flexible magma propagation scenarios in the presence of caldera structures. We first develop a three‐dimensional (3D) numerical model for the stress state at volcanoes with mild topography, including the stress induced by surface loads and unloading due to the formation of caldera depressions. Then, we introduce a new, simplified 3D model of dike propagation. Such a model captures the complexity of 3D magma trajectories with low running time, and can backtrack dikes from a vent to the magma storage region. We compare the new dike propagation model to a previously published 3D model. Finally, we employ the simplified model to produce shallow dike propagation scenarios for a set of synthetic caldera settings with increasingly complex topographies. The resulting synthetic magma pathways and eruptive vent locations broadly reproduce the variability observed in natural calderas.

Transition from volcano-sagging to volcano-spreading

Many volcanoes exhibit evidence of long-term deformation driven by gravity. This deformation influences the development of magmatic plumbing systems and volcanic vent locations, and it manifests as earthquakes and ground surface motions. Two end-member deformation styles are volcano sagging (flexure) and volcano spreading. Previous modeling studies indicated that the mechanical and geometric properties of basement rocks below the volcano can control whether a volcano spreads or sags, but these works differed on exactly how. Furthermore, evidence in nature that a volcano may progress from sagging to spreading as it grows has not been tested experimentally. Using Digital Image Correlation (DIC) and a revised scaling approach, we here revisit the classic experiments in which a sand–plaster cone is emplaced upon a basement comprising an upper brittle layer and a lower ductile layer. In a first experiment series, we emplaced the cone instantaneously. By normalizing both brittle and ductile layer thicknesses to cone height, we provide new insight into the dimensionless geometric controls on spreading and sagging. In a novel second experiment series, we emplaced the cone incrementally. We show that as a growing cone migrates through the dimensionless geometric parameter space, its deformation style changes successively in time from sagging to spreading. DIC shows that the horizontal velocity of the cone flank increases linearly or non-linearly during cone construction, but it decreases exponentially after construction ceases. Despite their geometric simplification and the omission of several sedimentological, magmatic, and regional-tectonic processes, our models' results are compatible with a range of observations of volcanoes on Earth and Mars. In particular, they help to explain: (i) why lithosphere-scale loading results in sagging rather than spreading, and (ii) why ocean island volcanoes of >2-3 km in height develop stellate forms and rift zones.

Impact of size and location of outflow opening vent on mixed convective heat transfer induced by two aligned heated cylinders immersed in a partially open channel

AbstractThe current work deals with the numerical investigation of mixed convection occurring from two hot cylinders placed inside vented ducts under different sizes of inflow and locations of outflow opening vents. The mathematical formulation is solved based on the finite volume approach. The location of the outflow section is changed to left, center, and right of enclosure. Impacts of inflow section sizes (1 = 0.125 and 1 = 0.25), locations of outflow section ( = ), space between cylinders (), Reynolds number (), and Richardson number () are implemented. Findings display that the average Nusselt number (Nu) is exceeded by 20% for low due to the effect of nonsymmetrical inflow and outflow sections as compared with the case of equal opening vents. For large Ri, a higher Nu is obtained for nonequal opening vents in comparison with the case of equal opening vents by 10%. The difference in the average Nu between left and right cylinders is about 11%. Findings display that the enhancement in Nu due to the large spacing size between cylinders as compared with those of low spacing size is about 35%. The variations of Nu display the opening vents ratio, Re, , and have an extreme action on the characteristics of flow and temperature fields.

Visual Assessment of Factors Affecting Reverse Pressure Gradients in Liners Using a Simulated Milking Device

Highlights In a simulated milking device, liner internal diameter, pulsation setting, and vent location all affect backflow. Junction point internal diameter affects backflow more than other factors. Vent location has no effect on backflow if the liner internal diameter is large. Backflow is strong with simultaneous pulsation, regardless of other factors. Abstract. The backflow of milk resulting from reverse pressure gradients in liners can cause mastitis. In this study, we hypothesized that liner internal diameter, vent location, and pulsation setting can induce backflow. We therefore attempted to clarify the mechanism of backflow using a flow simulated device. We visually analyzed the effects on backflow of the liner junction point (JP) (i.e., the border from the liner to the short milk tube), the liner inlet point (IP) (i.e., a distance of 63 mm from the end of the short milk tube), vent location, and pulsation setting, using high-speed video recordings of water flow in clear silicone liners at seven flow rates (1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 kg min-1/quarter). The actual flow rate was approximately half of the flow meter set value due to the effect of the pulsation closing phase (C+D phase) on quarter level. The results showed that the degree of backflow in liners increased considerably with an increase in flow rate and a decrease in liner internal diameter. The degree of backflow was affected considerably more by JP internal diameter than by IP internal diameter, pulsation setting, or vent location. The degree of backflow was not affected significantly by short milk tube vents and mouthpiece vents when JP internal diameter was larger. However, the degree of backflow was very strong when simultaneous pulsation was used, even at low flow rates. The findings showed that the JP internal diameter should be >13.0 mm, IP internal diameter should be >11.0 mm, the pulsation rate should be 60 pulses/min, and the pulsation ratio should be 60:40 when the alternative pulsation setting is used. This information might be useful for preventing intramammary gland infection. Keywords: Liner internal diameter, Pulsation setting, Reverse pressure gradients, Simulated milking device, Vent location.

Redescription of Bathymodiolus septemdierum Hashimoto and Okutani, 1994 (Bivalvia, Mytilida, Mytilidae), a mussel broadly distributed across hydrothermal vent locations in the western Pacific and Indian Oceans

Mussels of the genus Bathymodiolus Kenk & Wilson belong to the foundation fauna at hydrothermal vents in the global deep sea. In the western Pacific and Indian oceans, the three nominal taxa B. septemdierum Hashimoto and Okutani, B. brevior Cosel, Métivier & Okutani and B. marisindicus Hashimoto are currently recognized as separate species despite morphological and genetic evidence for their conspecificity. All three are listed with the International Union for Conservation of Nature Red List based on highly restricted ranges. We compile and supplement existing morphometric and molecular data to revise the Bathymodiolus septemdierum species group. We redescribe B. septemdierum as a single species with B. brevior and B. marisindicus recognized as junior synonyms. Given the exceptionally broad range of B. septemdierum, we propose removal of these three taxa from the IUCN Red List.

Dynamics of Two Caldera-Forming Eruptions (Banda Besar and Naira) in the Marine Conservation Zone of Banda, Maluku, Indonesia

This is the first study discussing the dynamics of two caldera-forming eruptions in the Banda volcanic complex (BVC) in the marine conservation zone of Banda, Maluku, Indonesia. The first and second caldera episodes are, hereafter, termed as Banda Besar and Naira, respectively. The formation of Banda Besar caldera (ca. 8 × 7 km) ejected homogeneous rhyolitic magmas (bulk-rock, 73.1–73.8 wt.% SiO2) in the following three stages: (1) sub-Plinian (BB-5a), (2) intra-sub-Plinian flow (BB-5b), and (3) caldera collapse (BB-5c and BB-5d). The BB-5a stage produced a reversely graded white pumice fall layer with moderate lithics (2–11%), which originated from a sub-Plinian eruption with an estimated plume height of 22–23 km. Subsequently, intensive erosion of wall rock (13–25%) causes conduit enlargement, leading to the partial collapse of the eruption columns, forming intra-sub-Plinian flow deposits (BB-5b). It is likely that conduit size surpassed the minimum threshold value for a buoyant plume during the final phase of the second stage, causing the complete formation of a pumice-rich pyroclastic density current (PDC) during the early-third stage (BB-5c). Finally, the evacuation of voluminous magma from the reservoir yields the first caldera collapse during the late-third stage, producing a lithic-dominated PDC with minor pumices (BB-5d). The formation of the Naira caldera (ca. 3 × 3 km) ejected homogeneous dacitic magmas (bulk-rock, 66.2–67.2 wt.% SiO2) in the following three stages: (1) early sub-Plinian (N-2a and 2b), (2) late sub-Plinian (N-2c, 2d, 2e), and (3) caldera collapse (N-2f). This research distinguishes the sub-Plinian into two stages on the basis of different vent locations (assumed from the isopach map). In particular, this research suggests that the early sub-Plinian stage (N-2a and 2b) erupted from the northern vent, producing 14 and 8 km eruption plume heights, respectively. Additionally, the late sub-Plinian stage (N-2c, 2d, 2e) was generated from a newly-formed conduit located in the relatively southern position, producing 12–17, 9, and 6 km eruption plume heights, respectively. Conduit enlargement is expected to occur during at both sub-Plinian stages, as lithic portions are considerably high (10–72%) and ultimately generate PDCs during the third stage (caldera collapse; N-2f). Because most of the erupted materials (for both caldera-forming eruptions) are emplaced in the ocean, estimating the erupted volume becomes difficult. However, with the assumption that the caldera dimension represents the erupted volume of magma (Vmagma), and that the total erupted volume (Vtotal) is a summation of Vmagma and the now-vanished pre-caldera island (Vvanished, represented by average lithic fractions), the first and second caldera might produce (at least) 35.2 and 2.4 km3 of erupted materials, scaling them as VEI (volcano explosivity index) 6 and 5, respectively. That VEI is more than enough to initiate a secondary hazard in the form of tsunamis triggered by volcanic activities.