Search

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

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

The problem of hyperbasites origin is one of the widely discussed topics in geology. This is because they often appear when no expected. Their development does not correspond to the general regularities of the geological complexes’ development. Therefore, when problematic instances of hyperbasites appear, discussion is inevitable. This is due to the imperfections of existing concepts, which are not without flaws. The essence of this concept lies in the fact that during the rotation of the Earth around its axis, geodynamic forces are formed. The hyperbasites complex by its nature belongs to deep igneous formations formed at the initial stage of development of volcano-plutonic processes, where the composition of magmatic products was not subject to decomposition. In general, the origin of igneous rocks is associated with deep anomalous processes, which were formed under the influence of geodynamic forces, where decompression of mantle matter occurs, causing a catastrophic increase in the volume of mantle matter, as well as the associated development of volcanoplutonic processes. Hyperbasites are formed both in divergent and convergent zones of the Earth’s crust. The main factor for their formation is high pressure – deep thermodynamic conditions, where there are no favorable thermodynamic conditions for the complete separation of magmatic melts by composition. The emergence of hypermafic rocks on the surface is associated with geotectonic or denudation processes. Denudation processes can expose only those hypermafic formations that are located at the site of formation. These zones include ancient platforms, sheets, terranes, etc., which were cut by deep erosion processes. As for those hyperbasic formations that are classified as alpinotype hyperbasites, they were moved to the structure of the Alps-Himalayan folded zone from the basement with a collision with subsequent geotectonic processes, where they formed in the bed of the Paleotethys Ocean, both in the process of divergence and convergence. The noted pattern of formation and the mechanism of formation of alpine-type hyperbasites clearly corresponds to the patterns of development of geodynamic forces in the face of the Earth, also with natural laws, which are the main factors in the evolution of the Earth’s crust. From the standpoint of KDEZK, the origin, mechanism of formation, as well as the form of distribution of alpinotype hypermafic rocks of the Lesser Caucasus occurred in the Paleotethys bed, under different thermodynamic conditions and at depths. Further, as a result of the collision, it participated in the formation of folded zones of the Lesser Caucasus. Within the Lesser Caucasus, two genetic types of hypermafic rocks are exposed. Some of them correspond to the convergent zone of the Tethys paleocean, while others correspond to divergent zones. In terms of ore content, the most promising are those hypermafic rocks that are genetically related to convergent zones.

The problem of hyperbasites origin is one of the widely discussed topics in geology. This is because they often appear when no expected. Their development does not correspond to the general regularities of the geological complexes' development. Therefore, when problematic instances of hyperbasites appear, discussion is inevitable. This is due to the imperfections of existing concepts, which are not without flaws. The essence of this concept lies in the fact that during the rotation of the Earth around its axis, geodynamic forces are formed. The hyperbasites complex by its nature belongs to deep igneous formations formed at the initial stage of development of volcano-plutonic processes, where the composition of magmatic products was not subject to decomposition. In general, the origin of igneous rocks is associated with deep anomalous processes, which were formed under the influence of geodynamic forces, where decompression of mantle matter occurs, causing a catastrophic increase in the volume of mantle matter, as well as the associated development of volcanoplutonic processes. Hyperbasites are formed both in divergent and convergent zones of the Earth's crust. The main factor for their formation is high pressure - deep thermodynamic conditions, where there are no favorable thermodynamic conditions for the complete separation of magmatic melts by composition. The emergence of hypermafic rocks on the surface is associated with geotectonic or denudation processes. Denudation processes can expose only those hypermafic formations that are located at the site of formation. These zones include ancient platforms, sheets, terranes, etc., which were cut by deep erosion processes. As for those hyperbasic formations that are classified as alpinotype hyperbasites, they were moved to the structure of the Alps-Himalayan folded zone from the basement with a collision with subsequent geotectonic processes, where they formed in the bed of the Paleotethys Ocean, both in the process of divergence and convergence. The noted pattern of formation and the mechanism of formation of alpine-type hyperbasites clearly corresponds to the patterns of development of geodynamic forces in the face of the Earth, also with natural laws, which are the main factors in the evolution of the Earth's crust. From the standpoint of KDEZK, the origin, mechanism of formation, as well as the form of distribution of alpinotype hypermafic rocks of the Lesser Caucasus occurred in the Paleotethys bed, under different thermodynamic conditions and at depths. Further, as a result of the collision, it participated in the formation of folded zones of the Lesser Caucasus. Within the Lesser Caucasus, two genetic types of hypermafic rocks are exposed. Some of them correspond to the convergent zone of the Tethys paleocean, while others correspond to divergent zones. In terms of ore content, the most promising are those hypermafic rocks that are genetically related to convergent zones. [ABSTRACT FROM AUTHOR]

Cabo de Gata-Níjar geopark is an exceptional volcanic zone in the western Mediterranean because of the submarine effusive volcanism and the large volume of subaerial pyroclastic deposits; volcanism developed between land and sea. Its extensive outcrops attract students and researchers from all over Europe to have a better and more precise understanding of the processes behind this volcanism. The compositional range of the outcrops and climatic conditions have generated amazingly well exposed areas, where a wide range of volcanic deposits can be observed and studied. Its current position makes the whole complex an outstanding area for research and education in geology and volcanology. All this led to the designation of the area as a UNESCO Global Geopark in 2015 and the development of a strategy to highlight the value of the geological heritage of the area, developing diverse tools in the form of brochures, maps, a geosite inventory and a legal framework to make conservation and research main objectives of the management team.

The mid-ocean rift in the Red Sea is one of the youngest rifting systems on Earth. Only recently, state-of-the-art methods and modern deep-sea instruments have been used to explore this young and unique volcanic system. During the first autonomous underwater vehicle surveys of the Red Sea Rift in Spring 2022, we collected multibeam bathymetry, backscatter, sub-bottom profiler data, and water column data over a 9 km long ridge segment in the Hadarba Deep between 22.49°N and 22.56°N to investigate the volcano-tectonic processes of this ultra-slow spreading segment (12 mm/year spreading rate). The high-resolution hydroacoustic data was used to (1) delineate and quantify the geometry of tectonic structures and individual lava flows, (2) define lava flow morphology and eruption style, (3) estimate relative ages of flows and features, and (4) retrace the evolution of the volcanic activity. In addition, the geochemistry of several young lava flows provides information on the relation between the different magma that supply these eruptions. About 90 eruptive units with variable sedimentary cover have been identified within the 43 km2 mapped region. The oldest lava flows are buried under 3 to 4.2 m of sediment, indicating ages of up to ~30 ka based on average sedimentation rate estimates (~14 cm/ka), while the youngest eruptions are covered by

Cabo de Gata-Níjar geopark is an exceptional volcanic zone in the western Mediterranean because of the submarine effusive volcanism and the large volume of subaerial pyroclastic deposits; volcanism developed between land and sea. Its extensive outcrops attract students and researchers from all over Europe to have a better and more precise understanding of the processes behind this volcanism. The compositional range of the outcrops and climatic conditions have generated amazingly well exposed areas, where a wide range of volcanic deposits can be observed and studied. Its current position makes the whole complex an outstanding area for research and education in geology and volcanology. All this led to the designation of the area as a UNESCO Global Geopark in 2015 and the development of a strategy to highlight the value of the geological heritage of the area, developing diverse tools in the form of brochures, maps, a geosite inventory and a legal framework to make conservation and research main objectives of the management team. [ABSTRACT FROM AUTHOR]

From 10 May 2018 to 1 November 2022 (time of writing), an unprecedented seismic activity is observed east of Mayotte Island (France), related to the largest submarine eruption ever recorded with offshore geophysical studies. Using signals from regional and local seismic stations, we build a comprehensive catalog of the local seismicity for the first ten months of the sequence. This catalog includes a total of 2874 events of magnitude (Mlv) ranging from 2.4 to 6.0, with 77% of them relocated using a double difference location procedure. The hypocentral locations over this period are highly dependent on the small seismic network available. Therefore we compare the locations of later events using a similar network and those estimated from a local ocean bottom seismometer (OBS) network installed since March 2019. Based on the time space evolution and characteristics of the seismicity, five distinct phases can be identified, corresponding to the successive activation of two deep seismic swarms, related to the lithospheric-scale magma ascent up to the seafloor, along with progressive deepening of the seismicity interpreted as decompression of a 40 km deep reservoir.

Unlike subaerial volcanic activity, deep submarine eruptions are difficult to detect, observe and monitor. The objective of this paper is to describe a large and complex volcanic region, named the Horseshoe area, recently discovered at ${\sim }$1500 m below sea level on the eastern upper submarine slope of Mayotte Island. The area is crucial because, since 2018, it has experienced an exceptionally deep seismic activity associated with the ongoing submarine eruption that formed a new volcanic edifice, Fani Maoré, about 40 km to the east. We present the results of a multiscale study, based on high-resolution bathymetry and in-situ seafloor observations carried out with autonomous underwater vehicles (AUVs) and deep-towed camera systems. In-situ imagery provides ground-truth for the geological interpretation of seafloor textures mapped with the bathymetry. The combination of both datasets allows us to discuss the nature of the volcanic structures and to propose a relative chronology of previous eruptive events in the Horseshoe area. Based on our analyses, we propose the following chronology: (a) the emplacement of a large explosive volcanic cone, the Horseshoe edifice, (b) the later collapse of this edifice that resulted in the formation of an elongated, 2 km wide horseshoe-shaped depression, crosscutting older hummocky lava flows, (c) the development of an E–W eruptive fissure associated with numerous explosive craters, east of the Horseshoe edifice, and (d) late volcanism emanating from the rim of the horseshoe-shaped depression that fed elongated thin lava flows both towards and away from the depression. While all volcanic features mapped at the Horseshoe area were emplaced prior to the 2018 eruption, our study shows that this region has still been volcanically active in the recent past. Our results thus document a complex geological history at small spatial scales involved in the construction of major submarine edifices, and that are controlled by volcano-tectonic processes at larger scales.

Fissures and faults provide insight into how plate separation is accommodated by magmatism and brittle deformation during crustal accretion. Although fissure and fault geometry can be used to quantify the spreading process at mid‐ocean ridges, accurate measurements are rare due to insufficiently detailed mapping data. Here, fissures and faults at the fast‐spreading 9°50′N segment of the East Pacific Rise were mapped using bathymetric data collected at 1‐m horizontal resolution by autonomous underwater vehicle Sentry. Fault dip estimates from the bathymetric data were calibrated using co‐registered near‐bottom imagery and depth transects acquired by remotely operated vehicle Jason. Fissures are classified as either eruptive or non‐eruptive (i.e., cracks). Tectonic strain estimated from corrected fault heaves suggests that faulting plays a negligible role in the plate separation on crust younger than 72 kyr (<4 km from the ridge axis). Pre‐ and post‐eruption surveys show that most fissures were reactivated during the eruptions in 2005–2006. Variable eruptive fissure geometry could be explained by the frequency with which each fissure is reactivated and partially infilled. Fissure swarms and lava plateaus in low‐relief areas >2 km from the ridge are spatially associated with off‐axis lower‐crustal magma lenses identified in multichannel seismic data. Deep, closely spaced fissures overlie a relatively shallow portion of the axial magma lens. The width of on‐axis fissures and inferred subsurface dike geometry imply a ∼9‐year long diking recurrence interval to fully accommodate plate spreading, which is broadly consistent with cycle intervals obtained from estimates of melt extraction rates, eruption volumes, and spreading rate. Plain Language Summary: New oceanic crust is created by seafloor spreading at mid‐ocean ridges, where lava erupts as the tectonic plates spread apart. Plate separation is accommodated by a combination of slip along dipping faults and the opening of magma‐filled cracks, called dikes. We present bathymetric and profile mapping data collected from near the seafloor on a volcanically active portion of the East Pacific Rise near 9°50′N. The data show faults and fissures (i.e., open cracks) in remarkable detail, with meter‐scale resolution. A total of 707 fissures and 42 faults were identified and measured, suggesting that the amount of plate separation accommodated by faulting is minimal compared to that by dike intrusion causing open cracks. About one‐third of the fissures mapped are located within the region covered by the most recent eruptions in 2005–2006, and most of these fissures seem to have been reactivated from previous eruptions. Based on measurements of fissure width, we estimate that the interval between diking events is ∼9 years, which agrees with previous independent estimates. The analysis in this study reveals the relative importance of faults and fissures in seafloor spreading, and in the magmatic cycles that continuously re‐pave the ocean floor. Key Points: >700 fissures mapped at 1‐m bathymetric resolution at 9°50′N East Pacific Rise, most of which were active during the 2005–2006 eruptionsFault slip and crack opening accommodate <0.3% of plate separation, indicating the dominant role of diking at fast‐spreading ridgesFissures and lava flow located >2 km from the ridge axis are spatially associated with off‐axis lower crustal off‐axis magma lens [ABSTRACT FROM AUTHOR]

Pumice rafting events are a common result of volcanic eruptions occurring near or beneath bodies of water. Such events are frequently associated with hazards such as tsunamis, and drift pumice is known to cause local economic disruptions, damage ships, impede naval traffic, devastate marine populations, and distribute potentially invasive species over long distances. However, our current understanding of the mechanisms that drive the formation and dispersal of drift pumice are extremely limited. This article reviews historical and characteristic pumice raft-forming eruptions, how interactions with water factor into macro-and micro- scale controls on pumice clast formation and dispersal, and current methods for detection and analysis to better track and mitigate hazards associated with explosive volcanic eruptions and pumice rafts. [ABSTRACT FROM AUTHOR]

Meter-scale vesicular blocks, termed “giant pumice,” are characteristic primary products of many subaqueous silicic eruptions. The size of giant pumices allows us to describe meter-scale variations in textures and geochemistry with implications for shearing processes, ascent dynamics, and thermal histories within submarine conduits prior to eruption. The submarine eruption of Havre volcano, Kermadec Arc, in 2012, produced at least 0.1 km3 of rhyolitic giant pumice from a single 900-m-deep vent, with blocks up to 10 m in size transported to at least 6 km from source. We sampled and analyzed 29 giant pumices from the 2012 Havre eruption. Geochemical analyses of whole rock and matrix glass show no evidence for geochemical heterogeneities in parental magma; any textural variations can be attributed to crystallization of phenocrysts and microlites, and degassing. Extensive growth of microlites occurred near conduit walls where magma was then mingled with ascending microlite-poor, low viscosity rhyolite. Meter- to micron-scale textural analyses of giant pumices identify diversity throughout an individual block and between the exteriors of individual blocks. We identify evidence for post-disruption vesicle growth during pumice ascent in the water column above the submarine vent. A 2D cumulative strain model with a flared, shallow conduit may explain observed vesicularity contrasts (elongate tube vesicles vs spherical vesicles). Low vesicle number densities in these pumices from this high-intensity silicic eruption demonstrate the effect of hydrostatic pressure above a deep submarine vent in suppressing rapid late-stage bubble nucleation and inhibiting explosive fragmentation in the shallow conduit.

Abstract Fissures and faults provide insight into how plate separation is accommodated by magmatism and brittle deformation during crustal accretion. Although fissure and fault geometry can be used to quantify the spreading process at mid‐ocean ridges, accurate measurements are rare due to insufficiently detailed mapping data. Here, fissures and faults at the fast‐spreading 9°50′N segment of the East Pacific Rise were mapped using bathymetric data collected at 1‐m horizontal resolution by autonomous underwater vehicle Sentry. Fault dip estimates from the bathymetric data were calibrated using co‐registered near‐bottom imagery and depth transects acquired by remotely operated vehicle Jason. Fissures are classified as either eruptive or non‐eruptive (i.e., cracks). Tectonic strain estimated from corrected fault heaves suggests that faulting plays a negligible role in the plate separation on crust younger than 72 kyr (2 km from the ridge are spatially associated with off‐axis lower‐crustal magma lenses identified in multichannel seismic data. Deep, closely spaced fissures overlie a relatively shallow portion of the axial magma lens. The width of on‐axis fissures and inferred subsurface dike geometry imply a ∼9‐year long diking recurrence interval to fully accommodate plate spreading, which is broadly consistent with cycle intervals obtained from estimates of melt extraction rates, eruption volumes, and spreading rate.

Most Neoproterozoic iron formations (NIF) are closely associated with global or near‐global "Snowball Earth" glaciations. Increasingly, however, studies indicate that some NIFs show no robust evidence of glacial association. Many aspects of non‐glacial NIF genesis, including the paleo‐environmental setting, Fe(II) source, and oxidation mechanisms, are poorly understood. Here, we present a detailed case study of the Jiapigou NIF, a major non‐glacial NIF within a Neoproterozoic volcano‐sedimentary sequence in North Qilian, northwestern China. New U–Pb geochronological data place the depositional age of the Jiapigou NIF at ~600 Ma. Petrographic and geochemical evidence supports its identification as a primary chemical sediment with significant detrital input. Major and trace element concentrations, REE + Y systematics, and εNd(t) values indicate that iron was sourced from mixed seawater and hydrothermal fluids. Iron isotopic values (δ56Fe = −0.04‰–1.43‰) are indicative of partial oxidation of an Fe(II) reservoir. We infer that the Jiapigou NIF was deposited in a redox stratified water column, where hydrothermally sourced Fe(II)‐rich fluids underwent oxidation under suboxic conditions. Lastly, the Jiapigou NIF has strong phosphorous enrichments, which in other iron formations are typically interpreted as signals for high marine phosphate concentrations. This suggests that oceanic phosphorus concentrations could have been enriched throughout the Neoproterozoic, as opposed to simply during glacial intervals. [ABSTRACT FROM AUTHOR]

Low volcanic explosivity index (VEI) eruptions are common occurrences in the Southwest Pacific but, as demonstrated by the 2021/2022 eruption of Hunga Volcano, submerged calderas in the region are also capable of producing much larger and more hazardous eruptions. As such, characterising smaller events from potentially hazardous systems is essential. The 2019 eruption of Volcano-F, a submerged caldera, would likely have gone totally undetected had it not produced a pumice raft that inundated beaches in Fiji and eventually washed up in Australia. New data, acquired 5 months after the eruption, reveal the development of a new vent and the accumulation of at least 3.1*107 m3 bulk volume (dense rock equivalent of 5.6*106 m3) of material on the seafloor. Between 30 and 70% of erupted material entered the raft, while the rest remained near to or was dispersed down-current of the vent. This previously unaccounted for material increases the volume estimate for the eruption, confirming it as a VEI 3 event and highlights the importance of considering not just the floating component of a pumice raft forming eruption for VEI estimation. Geochemical analysis reveals the eruption comprised a homogenous batch of dacitic magma, with compositional characteristics similar to that erupted from the same volcano in 2001, and an until-now-unidentified pumice raft in the Coral Sea in 1964. Volcano-F therefore appears to have had at least three explosive eruptions in the last 60 years, indicating it is significantly at unrest. Repeated eruptions of similar composition and low crystal content magma over decadal to centennial scales indicate the existence of a melt-dominant magma body beneath the volcano. Submerged calderas, like Volcano-F, are common in the wider Southwest Pacific region, with many such calderas producing regular eruptions, implicating active magmatic recharge. Our findings motivate a need to carefully monitor and characterise even apparently small eruptions at this volcano, and others along the Tonga-Kermadec Arc. This is because such eruptions have the potential to subsequently prime or trigger more explosive eruptions and provide critical geochemical evidence about the plumbing system and evolution of the volcano, essential for understanding the diverse hazards they pose. • The 2019 eruption of Volcano-F was VEI 3, sub-Plinian, dacitic, and likely lasted less than a day. • Products are geochemically similar to 2001 and to a previously unattributed pumice raft in 1964. • Volcano-F has therefore had 3 explosive eruptions in 60 years and is significantly at unrest. • Volcano-F is one of several potentially hazardous calderas likely in the caldera recharge phase. • These calderas need monitoring and further study to understand the risk posed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Alteration stages are mainly influenced by host-rock lithofacies. • Propylitic alteration superimpose the diagenetic mineralogy. • Hydrothermal activity can be linked to peperite formation. • Chlorite geothermometer yields values between 125 °C and 225 °C. International Ocean Discovery Program (IODP) Expedition 350 drilled Site U1437 in a submarine volcano-bounded basin situated in the modern Izu-Bonin rear-arc, NW Pacific Ocean. Subaqueous volcaniclastic sediments and rocks with a maximum deposition age of 15.4 ± 0.8 Ma were recovered from 0 to 1,806.5 m below seafloor (mbsf). In order to document post-depositional processes in such geological setting, we describe variations in bulk and clay mineralogy over the entire volcaniclastic succession. Four alteration stages (1, 2, 3 and 4) were identified through the occurrence and development of diagenetic background mineral assemblages (smectite ± Na-Ca zeolites ± illite) that were further superimposed by hydrothermal alteration. Stages 1 and 2 are characterized by diagenetic reactions linked with low fluid/rock interactions that enabled glass devitrification and subsequent lithification under burial conditions. Stages 3 and 4 are characterized by moderate to pervasive alteration processes that are well developed in coarser-grained rocks, and that may be induced by thermal pulses associated with fluid inputs. Below 1,460 mbsf, infilling and replacement textures overprinted the background alteration and can be directly linked with the development of two hydrothermal mineral assemblages: (i) ordered C/S (chlorite-smectite mixed-layers) ± chlorite ± albite, and (ii) calcite ± chalcedony ± anhydrite ± laumontite. Both assemblages evidence relatively low-temperature (up to 225 °C) hydrothermal activity that affected subaqueous volcaniclastic rocks at Site U1437. These assemblages are comparable with propylitc alteration facies present in ore-bearing hydrothermal systems. The preferential development of alteration mineral assemblages in high-permeability, coarse-grained lithofacies, reflects the significant influence of the physical properties of volcaniclastic rocks with depth on chemical kinetics, in comparison with those imposed by the local geothermal gradient. [ABSTRACT FROM AUTHOR]

Large quantities of Cretaceous Fe-oxidising bacteria (FeOB) are documented here for the first time in carbonate injection dykes. These injection dykes occur in fissures of a Palaeozoic metamorphic complex in the Geresd Hills, Hungary, and are made up of microlaminated haematitic carbonate that contain very well preserved helical FeOB stalk fossils similar to recent iron-oxidising Gallionella and Mariprofundus. The presence of filament clusters with semi-parallel textures suggests aerotactic bacterial cell movements. Fractal analysis of the filament clusters showed higher fractal dimension values (D f ∼ 1.9) compared to the typical fractal dimension values of the texturally similar, but inorganic Diffusion-Limited Aggregation (DLA) structures (D f ∼ 1.7). This finding is interpreted to suggest that the observed filamentous texture is of microbial origin. Cretaceous basaltic intrusions that penetrated the gold-bearing pyritic metamorphic basement launched a low-temperature flow of reductive iron-rich fluids. Well‑oxygenated bottom waters percolated through thin pelagic sediments and picked up ferrous iron from the pyritic metamorphic bedrock and made it available for the Fe-oxidising microbes. Reactivation of a major fault zone (Mecsekalja Zone) resulted in the development of extensional faults in the metamorphic basement beneath the seafloor. Pelagic carbonate sediments with FeOB mats were drawn into these fissures, forming a network of injection dykes. This study shows that fractal dimension analysis and directional analysis may be a helpful method to differentiate FeOB textures from inorganic textures in ancient rocks. The presented results are expected to provide useful analogues to aid the reconstruction of similar palaeoenvironments worldwide. • First globally: Cretaceous iron bacteria in injection dykes. • FeOB's stalks suggest aerotactic motion. • Fractal dimensions distinguish FeOB from inorganic structures. • Submarine pyritic rocks served as electron donors for Fe-bacteria. • Pelagic sediment drawn into seismic shock induced fractures to form injection dykes. [ABSTRACT FROM AUTHOR]

In the submarine setting pyroclast cooling and saturation, by controlling the buoyancy of individual clasts and surrounding fluid, exert fundamental controls on the dispersal and fate of volcanic material. In this study we use laboratory experiments to understand and quantify how hot and air-filled pyroclasts cool and saturate in liquid water. By measuring internal temperature and clast submerged weight in over thirty experiments, we find that pumice cools and saturates in two stages. We observe that the first stage is marked by much higher rates of cooling and saturation than the second stage and that the transition between stages is sharp. We propose conceptual and quantitative models for each stage of pyroclast cooling and saturation. Specifically we argue that the first stage is defined by the presence of internal steam. That is, hot pyroclasts ingest liquid water and generate steam. Once a clast's internal pore space is filled with steam, heat loss to the surroundings causes condensation of internal vapor and clast saturation. Stage 1 ends when all internal steam has condensed. We test this idea with a Stefan Model with advection and conclude that heat loss, rather than permeability, controls the saturation of pyroclasts above the boiling temperature. We find that permeability matters for air-filled clasts with initial temperatures below the boiling point. Stage 2 begins after all internal vapor has condensed and we propose that stage 2 cooling and saturation are controlled by heat conduction and thermal contraction of trapped gas, respectively. From our understanding of the processes that govern the stage 1 to 2 transition, we derive an empirical average pyroclast cooling rate of q = 7.5 ± 0.5 W cm−2. Finally, we develop quantitative models for cooling-controlled porous clast saturation and for buoyant clast rise to the ocean surface. We find that meter size clasts stay buoyant for more than 10 min - long enough to reach the surface from a depth of 1000 m. The models developed here test our understanding of clast-scale processes and demonstrate that - in hot and porous clasts - the details of internal texture do not matter because clast saturation, and thus buoyancy and fate in the water column, are governed by heat transfer.

In the submarine setting pyroclast cooling and saturation, by controlling the buoyancy of individual clasts and surrounding fluid, exert fundamental controls on the dispersal and fate of volcanic material. In this study we use laboratory experiments to understand and quantify how hot and air-filled pyroclasts cool and saturate in liquid water. By measuring internal temperature and clast submerged weight in over thirty experiments, we find that pumice cools and saturates in two stages. We observe that the first stage is marked by much higher rates of cooling and saturation than the second stage and that the transition between stages is sharp. We propose conceptual and quantitative models for each stage of pyroclast cooling and saturation. Specifically we argue that the first stage is defined by the presence of internal steam. That is, hot pyroclasts ingest liquid water and generate steam. Once a clast's internal pore space is filled with steam, heat loss to the surroundings causes condensation of internal vapor and clast saturation. Stage 1 ends when all internal steam has condensed. We test this idea with a Stefan Model with advection and conclude that heat loss, rather than permeability, controls the saturation of pyroclasts above the boiling temperature. We find that permeability matters for air-filled clasts with initial temperatures below the boiling point. Stage 2 begins after all internal vapor has condensed and we propose that stage 2 cooling and saturation are controlled by heat conduction and thermal contraction of trapped gas, respectively. From our understanding of the processes that govern the stage 1 to 2 transition, we derive an empirical average pyroclast cooling rate of q = 7.5 ± 0.5 W cm−2. Finally, we develop quantitative models for cooling-controlled porous clast saturation and for buoyant clast rise to the ocean surface. We find that meter size clasts stay buoyant for more than 10 min - long enough to reach the surface from a depth of 1000 m. The models developed here test our understanding of clast-scale processes and demonstrate that - in hot and porous clasts - the details of internal texture do not matter because clast saturation, and thus buoyancy and fate in the water column, are governed by heat transfer.

The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten‐month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone‐shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp‐anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyze the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW‐NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocenters and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore‐pressure perturbations and the re‐distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable. Key Points: Seismicity is clustered in a cone‐shaped volume beneath Kolumbo; the cone's tip coincides with a melt reservoir at 2–4 km depthSeismicity swarms occupy nearby, yet different portions of the crust, ruling out an origin on a single faultSwarms were likely triggered by a combination of fluid pressure perturbations and redistribution of elastic stresses [ABSTRACT FROM AUTHOR]

Addressing questions of magma ascent, volcanic eruption dynamics, and volatile fluxes requires accurate measurement of magmatic water concentrations in volcanic glass. Glass in volcanic rocks in the deep-sea environment can experience rehydration (addition of external water) across a range of temperatures, and from different sources (e.g., seawater and hydrothermal fluids), which can lead to overestimation of magmatic-H 2 O. This study used H and O isotopes (δD and δ18O) to identify sources of rehydration in pumice and lava from the deep-sea 2012 volcanic eruption of Havre volcano, Kermadec Arc, and from a variety of older (tens to thousands of years) silicic submarine deposits across the Izu-Bonin Arc and Lau Basin. We find that old seafloor pumices were rehydrated up to 6 wt.% H 2 O by the diffusion of cold seawater over 100s to 1000s of years, and thus, enriched in δD, bulk-δ18O, and water-in-glass (wig) δ18O up to −30‰, +9‰ and −5‰ respectively. By contrast, the young Havre deposits exhibit a much wider range of both isotopic enrichment and depletion with δD = −50 to −120‰, δ18O bulk = +5.7 to +6.2‰, and δ18O wig = −10 to +4‰, depending on the eruptive units. Using magmatic degassing and vapor δD-H 2 O modeling, a volatile-melt δ18O-geothermometer, and previous textural studies of Havre 2012 deposits, we identify multiple high-temperature rehydration sources, timescales, and mechanisms. δD-depleted pumices were likely rehydrated by vapor co-existing in bubbles and vesicles at temperatures around and below the glass transition (320–670 °C) over timescales of a few minutes during clast cooling above the eruptive vent. Conversely, δD-enriched Havre pumice and lava from different deposits were most likely rehydrated by heated, δD-enriched seawater at glass temperatures > 100 °C. These results provide a natural confirmation of recent experimental findings, which tackle the fundamentals of H and O diffusion and isotope exchange in silicate materials at temperatures of 100–400 °C. Addressing the effects of rehydration, and thus accuracy of H 2 O measurements, in volcanic glasses and crystals is important for improving our understanding of conduit processes during volcanic eruptions, and the kinetics of glass hydration and alteration. [ABSTRACT FROM AUTHOR]

Pumice can float on water for months to years – long enough for pumice to travel across oceans and facilitate the spread of species. Long-lived pumice floatation is unexpected, however, because pumice pores are highly connected and water wets volcanic glass. As a result, observations of long floating times have not been reconciled with predictions of rapid sinking. We propose a mechanism to resolve this paradox – the trapping of gas bubbles by water within the pumice. Gas trapping refers to the isolation of gas by water within pore throats such that the gas becomes disconnected from the atmosphere and unable to escape. We use X-ray microtomography to image partially saturated pumice and demonstrate that non-condensable gas trapping occurs in both ambient temperature and hot (500 °C) pumice. Furthermore, we show that the size distribution of trapped gas clusters matches predictions of percolation theory. Finally, we propose that diffusion of trapped gas determines pumice floatation time. Experimental measurements of pumice floatation support a diffusion control on pumice buoyancy and we find that floatation time τ scales as τ∝L2Dθ2 where L is the characteristic length of pumice, D is the gas–water diffusion coefficient, and θ is pumice water saturation. A mechanistic understanding of pumice floatation is a step towards understanding how pumice is partitioned into floating and sinking components and provides an estimate for the lifetime of pumice rafts in the ocean.

Pumice can float on water for months to years – long enough for pumice to travel across oceans and facilitate the spread of species. Long-lived pumice floatation is unexpected, however, because pumice pores are highly connected and water wets volcanic glass. As a result, observations of long floating times have not been reconciled with predictions of rapid sinking. We propose a mechanism to resolve this paradox – the trapping of gas bubbles by water within the pumice. Gas trapping refers to the isolation of gas by water within pore throats such that the gas becomes disconnected from the atmosphere and unable to escape. We use X-ray microtomography to image partially saturated pumice and demonstrate that non-condensable gas trapping occurs in both ambient temperature and hot (500 °C) pumice. Furthermore, we show that the size distribution of trapped gas clusters matches predictions of percolation theory. Finally, we propose that diffusion of trapped gas determines pumice floatation time. Experimental measurements of pumice floatation support a diffusion control on pumice buoyancy and we find that floatation time τ scales as τ∝L2Dθ2 where L is the characteristic length of pumice, D is the gas–water diffusion coefficient, and θ is pumice water saturation. A mechanistic understanding of pumice floatation is a step towards understanding how pumice is partitioned into floating and sinking components and provides an estimate for the lifetime of pumice rafts in the ocean.

Abstract The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten‐month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone‐shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp‐anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyze the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW‐NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocenters and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore‐pressure perturbations and the re‐distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable.

Offshore geological hazards can occur in any marine domain or environment and represent a serious threat to society, the economy, and the environment. Seismicity, slope sedimentary instabilities, submarine volcanism, fluid flow processes, and bottom currents are considered here because they are the most common hazardous processes; tsunamis are also examined because they are a secondary hazard generated mostly by earthquakes, slope instabilities, or volcanic eruptions. The hazards can co-occur and interact, inducing a cascading sequence of events, especially in certain contexts, such as tectonic indentations, volcanic islands, and canyon heads close to the coast. We analyze the key characteristics and main shortcomings of offshore geological hazards to identify their present and future directions for marine geoscience investigations of their identification and characterization. This review establishes that future research will rely on studies including a high level of multidisciplinarity. This approach, which also involves scientific and technological challenges, will require effective integration and interplay between multiscale analysis, mapping, direct deep-sea observations and testing, modelling, and linking offshore observations with onshore observations.

The origin and role of volcanism in continental rifts remains poorly understood in comparison to other volcano-tectonic settings. The Sicilian Channel (central Mediterranean Sea) is largely floored by continental crust and represents an area affected by pronounced crustal extension and strike-slip tectonism. It hosts a variety of volcanic landforms closely associated with faults, which can be used to better understand the nature and distribution of rift-related volcanism. A paucity of appropriate seafloor data in the Sicilian Channel has led to uncertainties regarding the location, volume, sources and timing of submarine volcanism. To improve on this situation, we use newly acquired geophysical data (multibeam echosounder and magnetic data, sub-bottom profiles) and dredged seafloor samples to: (i) re-assess the evidence for submarine volcanism in the Sicilian Channel and define its spatial pattern, (ii) infer the relative age and style of magmatism, and (iii) relate this to the dominant tectonic structures in the region. Quaternary rift-related volcanism has been focused at Pantelleria and Linosa, at the northwest boundaries of their respective NW-SE trending grabens. Subsidiary and older volcanic sites potentially occur at the Linosa III and Pantelleria SE seamounts, collectively representing the only sites of recent volcanism that can be directly related to the main rift process. These long-lived polygenetic volcanic landforms have been shaped by magmatism that is directly correlated with extensional faulting and buried igneous bodies. Older volcanic landforms, sharing a similar scale and alignment, occur to the north at Nameless Bank and Adventure Bank. These deeply eroded volcanoes have likely been inactive since the Pliocene and are probably related to earlier stages of crustal thinning and underlying feeder structures in the northern region of the Sicilian Channel. Along a similar alignment, Pinne Bank, SE Pinne Bank and Cimotoe in the northern Sicilian Channel lack a surface volcanic signature but are associated with intrusive bodies or deeply buried volcanic rock masses. Terrible Bank, in the same region, also shows evidence of ancient, polygenetic magmatism, but was subject to significant erosion and lacks a prominent alignment. The much younger volcanism at Graham Volcanic Field and along the northern Capo-Granitola-Sciacca Fault Zone differs markedly from that observed in the other study areas. Here, the low-volume and scattered volcanic activity is driven by shallow-water mafic magma eruptions, which gave rise to small individual cones. These sites are associated with large fault structures away from the main rift axis and may have a distinct magmatic origin. Dispersed active fluid venting occurs across both ancient and young volcanic sites in the region and is directly associated with shallow magmatic bodies within tectonically-controlled basins. Our study provides the foundation for an updated tectonic and magmatic framework for the Sicilian Channel, and for future detailed chronological and geochemical assessment of the sources and evolution of magmatic processes in the region. • New geophysical data and samples redefine submarine volcanism in Sicilian Channel. • Three dominant bands of volcanism are distinguished. • Ancient, eroded structures aligned at 120° are tied to faulted banks in the north. • Younger band of similarly aligned volcanism in the south is linked to grabens. • Youngest structures comprise small, dispersed volcanoes with distinct orientation. [ABSTRACT FROM AUTHOR]

Abstract Seafloor volcanic eruptions are difficult to directly observe due to lengthy eruption cycles and the remote location of mid‐ocean ridges. Volcanic eruptions in 2005–2006 at 9°50′N on the East Pacific Rise have been well documented, but the lava volume and flow extent remain uncertain because of the limited near‐bottom bathymetric data. We present near‐bottom data collected during 19 autonomous underwater vehicle (AUV) Sentry dives at 9°50′N in 2018, 2019, and 2021. The resulting 1 m‐resolution bathymetric grid and 20 cm‐resolution sidescan sonar images cover 115 km2, and span the entire area of the 2005–2006 eruptions, including an 8 km2 pre‐eruption survey collected with AUV ABE in 2001. Pre‐ and post‐eruption surveys, combined with sidescan sonar images and seismo‐acoustic impulsive events recorded during the eruptions, are used to quantify the lava flow extent and to estimate changes in seafloor depth caused by lava emplacement. During the 2005–2006 eruptions, lava flowed up to ∼3 km away from the axial summit trough, covering an area of ∼20.8 km2; ∼50% larger than previously thought. Where pre‐ and post‐eruption surveys overlap, individual flow lobes can be resolved, confirming that lava thickness varies from ∼1 to 10 m, and increases with distance from eruptive fissures. The resulting lava volume estimate indicates that ∼57% of the melt extracted from the axial melt lens probably remained in the subsurface as dikes. These observations provide insights into recharge cycles in the subsurface magma system, and are a baseline for studying future eruptions at the 9°50′N area.

From 10 May 2018 to 1 November 2022 (time of writing), an unprecedented seismic activity is observed east of Mayotte Island (France), related to the largest submarine eruption ever recorded with offshore geophysical studies. Using signals from regional and local seismic stations, we build a comprehensive catalog of the local seismicity for the first ten months of the sequence. This catalog includes a total of 2874 events of magnitude (Mlv) ranging from 2.4 to 6.0, with 77% of them relocated using a double difference location procedure. The hypocentral locations over this period are highly dependent on the small seismic network available. Therefore we compare the locations of later events using a similar network and those estimated from a local ocean bottom seismometer (OBS) network installed since March 2019. Based on the time space evolution and characteristics of the seismicity, five distinct phases can be identified, corresponding to the successive activation of two deep seismic swarms, related to the lithospheric-scale magma ascent up to the seafloor, along with progressive deepening of the seismicity interpreted as decompression of a 40 km deep reservoir. [ABSTRACT FROM AUTHOR]

Geophysical survey techniques including electrical resistivity imaging and magnetics were utilized to study the late-Cretaceous submarine volcanic mound of St. Elmo railroad cut located in south Austin, TX. The St. Elmo site cut exposes a sequence of late Cretaceous volcaniclastic rocks in contact with carbonate rocks. Resistivity imaging results provided subsurface evidence that the St. Elmo submarine mound has high resistivity limestone blocks scattered randomly within the resistivity sections. These limestone blocks are interpreted to be erratic blocks of Austin Chalk, which were probably torn from the walls of the volcanic conduits (vents) and ejected. Magnetic anomalies correlate well with the resistivity anomalies, strengthening the interpretation of the resistivity data. Resistivity results from the residential site, not far from the St. Elmo volcanic mound, are interpreted as a conduit which is similar to the conduit anomalies observed on the St. Elmo railroad cut site.

Silicic submarine volcanic eruptions can produce large volumes of pumices that may rise buoyantly to the ocean surface and/or sink to the seafloor. For eruptions that release significant volumes of pumice into rafts, the proximal to medial submarine geologic record is thus depleted in large volumes of pumice that would have sedimented closer to source in any subaerial eruption. The 2012 eruption of Havre volcano, a submarine volcano in the Kermadec Arc, presents a unique opportunity to study the partitioning of well-constrained rafted and seafloor pumice. Macro- and microtextural analysis was performed on clasts from the Havre pumice raft and from coeval pumiceous seafloor units around the Havre caldera. The raft and seafloor clasts have indistinguishable macrotextures, componentry, and vesicularity ranges. Microtextural differences are apparent as raft pumices have higher vesicle number densities (109 cm−3 vs. 108 cm−3) and significantly lower pore space connectivity (0.3–0.95 vs. 0.9–1.0) than seafloor pumices. Porosity analysis shows that high vesicularity raft pumices required trapping of gas in the connected porosity to remain afloat, whereas lower vesicularity raft pumices could float just from gas within isolated porosity. Measurements of minimum vesicle throat openings further show that raft pumices have a larger proportion of small vesicle throats than seafloor pumices. Narrow throats increase gas trapping as a result of higher capillary pressures acting over gas–water interfaces between vesicles and lower capillary number inhibiting gas bubble escape. Differences in isolated porosity and pore throat distribution ultimately control whether pumices sink or float and thus whether pumice deposits are preserved or not on the seafloor. [ABSTRACT FROM AUTHOR]

The transition from subduction to transform motion along horizontal terminations of trenches is associated with tearing of the subducting slab and strike-slip tectonics in the overriding plate. One prominent example is the northern Tonga subduction zone, where abundant strike-slip faulting in the NE Lau back-arc basin is associated with transform motion along the northern plate boundary and asymmetric slab rollback. Here, we address the fundamental question: how does this subduction-transform motion influence the structural and magmatic evolution of the back-arc region? To answer this, we undertake the first comprehensive study of the geology and geodynamics of this region through analyses of morphotectonics (remote-predictive geologic mapping) and fault kinematics interpreted from ship-based multibeam bathymetry and Centroid-Moment Tensor data. Our results highlight two notable features of the NE Lau Basin: 1) the occurrence of widely distributed off-axis volcanism, in contrast to typical ridge-centered back-arc volcanism, and 2) fault kinematics dominated by shallow-crustal strike slip-faulting (rather than normal faulting) extending over ∼120 km from the transform boundary. The orientations of these strike-slip faults are consistent with reactivation of earlier-formed normal faults in a sinistral megashear zone. Notably, two distinct sets of Riedel megashears are identified, indicating a recent counter-clockwise rotation of part of the stress field in the back-arc region closest to the arc. Importantly, the Riedel structures identified in this study directly control the development of complex volcanic-compositional provinces, which are characterized by variably-oriented spreading centers, off-axis volcanic ridges, extensive lava flows, and point-source rear-arc volcanoes. This study adds to our understanding of the geologic and structural evolution of modern backarc systems, including the association between subduction-transform motions and the siting and style of seafloor volcanism.

The emergence and growth of Surtsey during volcanic activity in 1963–1967, from an oceanic depth of 130 m off the south coast of Iceland, remains one of the best-documented island-forming eruptions to date. By extracting information from seismic bulletins and analyzing archived analog seismic data, principally from SID, the most sensitive station in the seismic network existing at the time (131 km from Surtsey), we address key questions on precursors, timing of eruption onset, and duration of the submarine phase. We estimate the magnitude of completeness for earthquakes at Surtsey to have been ML = 2.5. Several seismic events of magnitude ML < 3 in November 3–10, 1963, with epicentral distance fitting with Surtsey are considered to be precursory earthquakes. Continuous tremor of dominant frequency 1–2 Hz, starting in the early afternoon of November 12, is considered to mark the onset of the submarine eruption, about 40 h before the start of subaerial eruption at 06:30 on November 14. The number of earthquakes larger than the threshold magnitude of 2.5 detected in 1963–1966 was 123, with the largest being of magnitude 4.5. Six earthquakes ranging in magnitude between 3.7 and 4.5 were felt in Heimaey, 22 km to the NE of Surtsey. Changes in vent location occurred five times in 1964–1966. Significant earthquake activity after the eruption start occurred in swarms considerably stronger than observed at the start. These swarms preceded vent migration and lasted days to weeks, apparently caused by intrusive activity prior to eruption at the new vents. [ABSTRACT FROM AUTHOR]

Massive CO 2 and SO 2 degassed from large igneous provinces (LIPs) are thought to cause ocean acidification and calcification crisis with a significant loss of calcified marine biota. The ocean acidification caused by the Emeishan LIP event has been proposed as one of the important factors that triggered the end-Guadalupian (Middle Permian) crisis, although the driving mechanism remains unclear. Here we represent a detailed field investigation combined with LA-ICP-MS, SIMS and CA-ID-TIMS zircon geochronology of tuffs from four volcanic sections in the eastern part of the Emeishan LIP. Our new data combined with previous results from this LIP confirm that: (i) the submarine volcanism occurred between ~260.7 Ma and ~ 257.9 Ma, with most basaltic eruptions at ~260.1 Ma to 259.5 Ma; and (ii) explosive tuff eruptions occurred during ~257.9 Ma to ~256.9 Ma in the subaerial environment. We propose a model involving SO 2 release from the submarine basaltic eruptions in the Emeishan LIP as the trigger of the end-Guadalupian ocean acidification, due to the high solubility of SO 2 in seawater that could produce strongly acidic conditions. The late explosive silicic volcanism in the subaerial setting during Early to Middle Wuchiapingian (Late Permian) might have been a potential strong driver of the global Wuchiapingian cooling event. Unlabelled Image • Durations of submarine and subaerial eruptions in the Emeishan LIP are constrained. • Submarine volcanism occurred during the Guadalupian-Lopingian transition. • Subaerial tuff eruptions extended to the Early-Middle Wuchiapingian. [ABSTRACT FROM AUTHOR]

In explosive submarine eruptions, volcanic jets transport fragmented tephra and exsolved gases from the conduit into the water column. Upon eruption the volcanic jet mixes with seawater and rapidly cools. This mixing and associated heat transfer ultimately determines whether steam present in the jet will completely condense or rise to breach the sea surface and become a subaerial hazard. We develop a multiphase model with subgrid calculations for in situ steam condensation to explore the relationship between eruption conditions (e.g., water depth, mass eruption rate, and eruption temperature) and the produced steam jet height and breach potential. We find that mass eruption rate is the predominant control of jet height, more so than vent width. We present a series of parameter maps predicting the limits of eruption breach for water depths of 200, 500, and 1,000 m. We demonstrate the relationship between subsurface jets and sea surface temperature anomalies, and sea surface displacement. Lastly, we evaluate the role of dispersed ash on volcanic jet development by comparing jets with particles of different size and density, as well as differing eruption conditions with particles. Plain Language Summary: In explosive underwater volcanic eruptions, gas jets carry volcanic ash and rocks into the ocean water column and potentially the atmosphere. During the eruption, the jet mixes with seawater which cools the jet and can cause steam present in the jet to condense to liquid water. This condensation controls whether the eruption jet will make it to the surface and become a hazard for nearby populations, ships, and airplanes, or will it condense completely below the surface. We present results from computer models we have developed that demonstrate the conditions necessary for an eruption to make it to the sea surface. We also show other effects the eruptive jet can have that can be measured at the surface, such as increasing the sea surface temperature or generating large waves. Lastly, we examine how including ash and rock in the gas jet can change the height of the gas jet. Key Points: 2D multiphase models evaluate gas jet thrust in subaqueous explosive eruptions from vents at 200, 500, and 1,000 m water depthsMass eruption rate and water depth are the primary controls of jet height, eruption temperature and vent diameter are lesser soSurface breaching eruptions are possible from vents at 500 m water depth, but not 1,000 m depth [ABSTRACT FROM AUTHOR]

• Shikebutai iron formations was chemical sediments of authigenic origin. • This Late Carboniferous-aged IFs intimate association with submarine volcanic activity. • Enhanced hydrothermal activity can shape the marine redox landscape and of the development ferruginous conditions. Iron formations (IFs) are iron-rich chemical sediments that were widespread throughout the Precambrian. The deposition of IFs has provided key evidence about the prevalence of anoxic and ferruginous marine conditions throughout Earth's history. Here, we describe the Shikebutai IF, hosted in a Late Carboniferous volcano-sedimentary sequence in the Western Tianshan region of northwest China. The IF is largely composed of hematite, jasper, and siderite. The chemical composition of the Shikebutai IF is dominated by Fe 2 O 3 and SiO 2 , and very low concentrations of Al 2 O 3 , TiO 2 , Th, Nb, and Sc were observed, indicative of an authigenic origin. High Fe/Ti, Fe/Al, Co/Zn, and Ni/Zn ratios, along with positive Eu anomalies and ε Nd (t) values point to a significant submarine volcanic and hydrothermal contribution. The absence of negative Ce anomalies and heterogeneous δ56Fe values suggest progressive oxidation of hydrothermally sourced Fe(II) and deposition in an anoxic to low oxygen basin. Low P/Fe ratios in the Shikebutai IF, comparable to those found in the Precambrian, are consistent with Si inhibition of P sorption and P drawdown with high hydrothermal inputs. The intimate association of this Late Carboniferous IF with submarine volcanic activity suggests an origin that is analogous to Precambrian Algoma-type IFs. Further, the Shikebutai IF provides evidence for an episode of basin-scale anoxic, ferruginous conditions coinciding with the generally well-oxygenated deep oceans of the Phanerozoic, with deposition driven by enhanced submarine volcanic and hydrothermal activity in the Western Tianshan region during the Late Carboniferous. This demonstrates how, even with near modern surface oxygen levels, enhanced hydrothermal activity can shape the marine redox landscape and cause the development of ferruginous conditions without quantitative sulfate drawdown. [ABSTRACT FROM AUTHOR]

Volcaniclastic deposits, pillow lavas, dikes and sills of the intraplate Waiareka-Deborah Volcanic Field in North Otago were emplaced into and onto the Zealandia Eocene-Early Oligocene continental shelf. The on-land extent is ∼890 km2 but offshore volcanic rocks occurring over an additional ∼3500 km2 may be related. Examination of the on-land volcaniclastic deposits indicates volcanism was dominated by short-lived clustered surtseyan-style eruptions. Pyroclast glass and sill and lava bulk rock chemistries show that the magmas were mainly sub-alkaline basalt to basaltic andesite. Minor alkaline centres are best represented by basanitic-melanephelinitic volcaniclastic deposits at Kakanui, which also contain an array of megacrysts plus mantle and crustal xenoliths. The sub-alkaline and alkaline source reservoirs had similar Sr and Nd isotope ratios (87Sr/86Sr34 Ma = 0.70346 ± 40, 143Nd/144Nd34 Ma = 0.51282 ± 4) but the sub-alkaline rocks tend to be slightly less radiogenic in 206Pb/204Pb or 208Pb/204Pb versus 207Pb/204Pb space. The dominant sub-alkaline nature and the isotopic compositions distinguish this volcanic field from the nearby Dunedin Volcanic Group and Alpine Dike Swarm. As the Waiareka-Deborah isotopic compositions are poorly represented in the Otago mantle lithosphere, the magmas may have been derived from the asthenosphere. There were multiple modes of Cenozoic intraplate volcanism in Otago. [ABSTRACT FROM AUTHOR]

Volcaniclastic and coherent volcanic rocks of the Permian island arc Brook Street Terrane crop out along the Southland coast, New Zealand, near Riverton. Extensive along-strike exposures reveal lateral variations in these submarine deposits and provide a rare opportunity to examine deposits of an arc environment within a thin slice of time. We describe pillow lavas, dikes, hydroclastic breccias, tuffs, lapilli tuffs and argillites, all hydrothermally altered and metamorphosed to prehnite-pumpellyite facies. Trace element geochemical data indicate multiple primitive island arc to MORB-like magma sources. Two separate volcanic centres apparently tapped different mantle domains in a source region transitional between the arc and back-arc. The centres' proximity and inferred small sizes suggest they were satellite vents of a larger arc volcano. Tuff and lapilli tuff were formed as hyaloclastite during eruption of pillow lava, and redeposited by subaqueous mass flows. Peperitic contacts indicate that the lavas intruded unconsolidated volcaniclastic deposits. We infer that hydroclastic fragmentation associated with pillow emplacement produced debris that was then intruded by later pillows, with local peperite formation, as eruption persisted. The hydroclastic debris from these satellite vents was resedimented in turbidite fans with channels, and periodic turbidity currents delivered fine-grained material from the volcano's main vent. [ABSTRACT FROM AUTHOR]

High-resolution swath-bathymetry has been acquired during recent surveys in Saronikos Gulf, near the densely populated city of Athens. This paper presents the first detailed bathymetric map, at a scale of 1:12,000, of the active Submarine Pausanias Volcanic Field located offshore NW Methana Peninsula in Saronikos Gulf, Aegean Sea (Main Map). Rugged morphology characterizes the volcanic field that includes mainly cone-shaped features. Six volcanic outcrops, covering an area of about 12 km2, have been morpho-bathymetrically outlined, and their sub-bottom character has been described by the integration of 2D seismic reflection profiles. Two groups of outcrops have been distinguished. An older group comprising more complex, erosional-shaped outcrops, and a younger group consisting of sub-conical outcrops. Both groups have been morphologically correlated to their onshore equivalents in the adjacent peninsula of Methana. Despite the active tectonic regime of the region, no evidence of mass transport-related features have been observed.

Abstract To investigate the initial phases of magmatism at the leading edge of the upwelling mantle plume, we mapped, photographed, and collected samples from two long, deep‐water lava flows located at the western base of the Galápagos Platform using the remotely operated vehicle Hercules. Lavas were recovered from four areas on the seafloor west of Fernandina volcano, including the western flow fronts of two deep‐water flows, heavily sedimented terrain between the two flows, and the eastern, shallower end of one flow. The sediment cover and morphologies are distinct between the western flow fronts and the eastern region based on seafloor imagery, suggesting that the long lava flows are not a single eruptive unit. Major and trace element concentrations reveal both tholeiitic and alkalic compositions and support the interpretation that multiple eruptive units comprise the deep‐water flows. Alkalic lavas have higher [La/Sm]N ratios (2.05–2.12) and total alkali contents (5.18–5.40) compared to tholeiitic lavas, which have [La/Sm]N ratios ranging from 1.64 to 1.68 and total alkali contents ranging from 3.07 to 4.08 wt%. Radiogenic isotope ratios are relatively homogeneous, suggesting a similar mantle source. We use petrologic models to assess three alternative mechanisms for the formation of the alkalic magmas: (1) high‐pressure crystallization of clinopyroxene, (2) mixing of high silica and mafic magmas, and (3) variable extents of melting of the same mantle source. Our modeling indicates that the alkalic samples form from lower extents of melting compared to the tholeiitic lavas and suggests that the deep‐water alkalic lavas are analogous to the initial, preshield building phase observed south of Hawaii and at the base of Loihi Seamount.

Volcanism is the most widespread expression of cyclic processes of formation and/or destruction that shape the Earth’s surface. Calderas are morphological depressions resulting from the collapse of a magma chamber following large eruptions and are commonly found in subduction-related tectono-magmatic regimes, such as arc and back-arc settings. Some of the most impressive examples of seafloor hydrothermal venting occur within submarine calderas. Here, we show the results of magnetic investigations at two hydrothermally active submarine calderas, i.e., Palinuro Seamount in the Southern Tyrrhenian Sea, Italy, and Brothers volcano of the Kermadec arc, New Zealand. These volcanoes occur in different geodynamic settings but show similarities in the development of their hydrothermal systems, both of which are hosted within calderas. We present a new integrated model based on morphological, geological and magnetic data for the Palinuro caldera, and we compare this with the well-established model of Brothers caldera, highlighting the differences and common features in the geophysical expressions of both hydrothermal systems. For consistency with the results at Brothers volcano, we build a model of demagnetised areas associated with hydrothermal alteration derived from 3D inversion of magnetic data. Both these models for Brothers and Palinuro show that hydrothermal up-flow zones are strongly controlled by caldera structures which provide large-scale permeability pathways, favouring circulation of the hydrothermal fluids at depth.

Submarine volcanism in the western Arctic Ocean, known as Amerasia Basin, is attributed to a mantle plume based on geophysics and meager geochemical evidence. Basaltic samples dredged from Chukchi Borderland within the basin have produced minimum 40Ar/39Ar ages for eruption at circa 118–112, circa 105–100, and circa 90–70 Ma, which we use to constrain tectonic models for basin opening. Major oxide and trace element concentrations and Sr, Nd, and Hf isotopic ratios of the lavas show that the circa 118–112 Ma samples from Northwind Ridge are tholeiites (low‐Ti tholeiite I) with low degrees of rare‐earth element (REE) fractionation, high overall heavy rare‐earth element (HREE), and Mg# (Mg‐number), which suggests magma derivation from a garnet‐free source followed by minor crystal fractionation. Strontium, Nd, and Hf isotope systematics for these lavas and ratios of highly incompatible trace elements point toward a lithospheric source. Eruptions at circa 105–100 and circa 90–70 Ma, both at Healy Spur, produced two types of lavas: low‐Ti tholeiite II—which are generally older than high‐Ti tholeiite—both common in continental flood basalt (CFB) provinces and both with trace element abundance patterns typifying a garnet‐free source and significant crystal fractionation for the high‐Ti tholeiite. The isotope characteristics for both groups are common features of asthenospheric sources. Composition‐time relationships for the lavas suggest inception of melting in the subcontinental lithospheric mantle (SCLM)—probably due to introduction of a heat source by a plume—followed later (at ca. 105–100 and ca. 90–70 Ma) by asthenospheric melting possibly triggered by plume rise. Plain Language Summary: Using U.S. Coast Guard research icebreaker Healy, we dredged basaltic lava flows from the bathymetrically high Chukchi Borderland on the floor of the western Arctic Ocean—an area known as Amerasia Basin—to determine eruption history using radioactivity thereby providing time constraints on the plate tectonic evolution of the region. We also measured the major oxide and trace element compositions as well as the lead, strontium, neodymium, and hafnium isotopic ratios of the lavas to decipher the geochemical character of the source materials deep inside the Earth. This work is part of the push for data collection in the last decade for Extended Continental Shelf (ECS) purposes under the U.N. Convention for Law of the Sea (UNCLOS), Article 76. Submarine eruptions along Chukchi Borderland occurred at circa 118–112, circa 105–100, and circa 90–70 Ma, producing three geochemically distinct rock types akin to lavas in continental flood basalt (CFB) in other magmatic provinces on Earth. These lava compositions are in stark contrast to the compositions of submarine lavas in the eastern Arctic where oceanic crust of significant width developed and separated previously joined continental landmasses and their continental shelves. Key Points: Submarine volcanism in Amerasia Basin of the western Arctic Ocean produced flows dated by 40Ar/39Ar geochronology at circa 118–112 Ma (low‐Ti tholeiite I of the Northwind Ridge) and circa 105–100 Ma (low‐Ti tholeiite II) and circa 90–70 Ma (high‐Ti tholeiite)—both from Healy SpurThe low‐Ti tholeiites I at Northwind Ridge that erupted at circa 118–112 Ma resulted from melting of a subcontinental lithospheric mantle (SCLM) source within the spinel stability field and were precursory to melting and eruption of magmas from isotopically more depleted sources, including the asthenosphereMelting events that produced the circa 105–100 Ma low‐Ti tholeiites II and circa 90–70 Ma high‐Ti tholeiites may be related to ascent of a plume head and the concomitant melting that yielded bimodal distribution of basaltic compositions, typical of plume‐related continental flood basalts (CFB) provinces elsewhere on Earth [ABSTRACT FROM AUTHOR]

On the 7 August 2019, a 195 km2 raft of andesitic pumice was produced at 200 m below sea level at an unnamed submarine volcano in the Tonga Islands (Southwest Pacific Ocean). Drifting chiefly westward, the raft reached the Fiji Islands on the 19 September. Yachts that crossed the raft as early as 2 days post‐eruption provided an outstanding data set of raft characteristics and pristine samples. Further, exceptional tracking of raft dispersal by satellite images allows us to contrast virtual particle tracking methods with ocean model currents to explore the relative influence of surface currents, wind, and wave action on pumice flotsam dispersal over up to 2 years. Attenuation of ocean waves by large and compact pumice rafts appears to reduce the effect of Stokes drift. The coupling of real‐time satellite observations with oceanographic Lagrangian simulations allows near‐real time forecasting for global maritime hazard mitigation. Plain Language Summary: Although 70% of volcanism occurs underwater, submarine eruptions are seldom witnessed owing to their remoteness and absence of technologies enabling their detection. On the 7 August 2019, a submarine volcanic eruption 200 m below sea level in the Tonga Islands formed a 195 km2 pumice raft. The raft was first encountered and sampled by yacht crews, and is visible on satellite images. Pumice rafts are dispersed by ocean currents, wind, and waves, and can cross entire oceans or get stranded on coasts. After 7 weeks of dispersal, the pumice raft reached the Fiji Islands, and a fraction continued its westward route toward Vanuatu and eastern Australia. Excellent imaging of the raft by satellites permitted reconstruction of daily raft dispersal for the first 8 weeks. Here we show that drift calculations, including components of ocean current, wind, and wave action, can usefully forecast raft dispersal. We tested and tuned these drift calculations by comparing the simulated drift with daily satellite images of the raft. Further, a combination of satellite images and drift calculations based on oceanographic models were used for maritime hazard mitigation in near‐real time. Key Points: A >30 million m3 pumice raft formed at an unnamed volcano in Tonga midday on the 7 August 2019 and was dispersed by ocean currents and windForecasts of pumice raft dispersal, based on particle drift with model currents, winds, and waves, are evaluated with daily satellite imagesStokes drift does not improve short‐term predictions on large and compact pumice rafts because these rafts attenuate ocean waves [ABSTRACT FROM AUTHOR]

The lack of visual observations and difficulty recreating ambient conditions in the laboratory mean deep subaqueous volcanic eruptions (>500 m water depth) remain enigmatic. However, the pressure and temperature dependency of water speciation and solubility in volcanic melts and glasses, and water's high diffusion rate, offers a potential window into the processes and conditions during deep subaqueous volcanism. The 2012 submarine eruption of Havre Volcano is the ideal laboratory in which to use water species distributions to understand submarine eruption processes. Post-eruption AUV mapping, and ROV observation and sampling generated an unprecedented amount of contextual information for a deep submarine eruption including on the magma ascent conditions, eruption sequence, and magma fragmentation. Here we present high spatial resolution synchrotron-FTIR measurements of water speciation in glassy ash (125–500 μm) from several subunits (1, 2 and 3) of a widespread ash with lapilli deposit produced in the 2012 eruption. Measurements record OH depletion profiles around vesicles, along with H 2 O mol enrichment profiles. In several thick vesicle walls far-field regions unaffected by processes at the bubble margins have also been identified. By focusing on OH concentrations, which is effectively non-diffusing below the glass transition, we can remove the effects of secondary rehydration and calculate the pressure and water depth at which ash grain quenched. Far-field regions record quench depths within the 650–900 m water depth range for pre- and post- eruption vent depth, suggesting ash grains equilibrated at vent depth. OH depletion profiles produce quench pressures on vesicle margins typically corresponding to 200–400 m water depth shallower, suggesting a 2–4 MPa decompression before ash quench. Diffusion modelling suggests that at eruption temperature the observed OH depletion profiles formed through exsolution in <2 s. The difference in quench pressure within the ash is not reflective of a difference in the depth of quenching. Rather it is reflective of the rapidity of the quench process relative to the diffusion rate. The results imply transient low-pressure conditions formed during ash generation in the 2012 Havre eruption. We discuss several physical processes in the context of submarine volcanism that may explain the formation of transient low-pressure regions. The results have implications for how we understand submarine eruption processes and highlight the potential of high resolution FTIR for studying submarine volcanism. • High spatial resolution measurement of volatile concentration in fine ash. • A 2–4 MPa decompression event was identified during the eruption of Havre Volcano. • A temporal record of conditions and processes in a deep submarine eruption. • Submarine volcanism may generate transient lower than ambient pressure conditions. [ABSTRACT FROM AUTHOR]

The understanding of submarine monogenetic volcanic fields, especially if located near to coastal areas, is fundamental for volcanic risk assessment. Using high-resolution bathymetric data and ROV images, the submarine Graham volcanic field, located 40–50 km offshore southwestern Sicily (Italy), has been described in detail. The field comprises a ten of monogenetic volcanic seamounts aligned along a N-S trending belt at 150–250 m water depths and includes the relict of the short-lived “Ferdinandea Island” produced during the well-documented 1831 “Surtseyan-type” eruption. The present-day morphology of the cones is the result of the interplay between volcanic activity, wave and current erosion, mass-wasting and depositional processes, in relationship with sea-level change, acting in both subaerial and submarine environments. The analysis of the morphometric parameters allowed a detailed morphological classification of the cones. The seamounts are composed of poorly consolidated tephra and show steep slopes and pointy or flat tops, often characterized by sub-vertical knolls. Taking into account analogies with other volcanic seamounts worldwide, the analysis of some morphological characteristics, such as presence and depth of terraces on top and along the slope of the cones in relationship with sea-level fluctuations, allowed us to hypothesize a Late Pleistocene-Holocene age for the volcanism forming the field. The probably older Terribile volcanic field was also identified on the adjacent Terribile Bank and analyzed. Numerous mass-transport deposits and pockmarks were identified in the surroundings of the volcanic fields, suggesting the occurrence of diffuse slope failures and fluid releases, respectively. The distribution and shape of the cones within the volcanic fields provided important insights into the interaction between volcanism and tectonics. The alignment of the cones and the main axis of the clusters in which they are grouped revealed two preferred directions, N-S and NW-SE, respectively, which are consistent with those of the main tectonic structures of the Sicily Channel. The detailed bathy-morphological analysis of the cones proved the monogenetic nature of this volcanism, which represents a peculiarity since it took place outside the typical geodynamic settings of other volcanic fields worldwide such as subduction or oceanic rift zones, and far from long-lived volcanic systems.

Abstract Kick-'em-Jenny and Kick-'em-Jack are two submarine volcanoes located in the southern Lesser Antilles arc. We present data on the temporal and spatial compositional variations in lavas and melt inclusions from Kick-'em-Jenny and four lavas from Kick-'em-Jack. Analyses of crater samples from Kick-'em-Jenny show an evolution in magma compositions between 1972 and 2013/14. Rock types have progressed from predominantly basalts in 1972 to basaltic andesites in 2013/14, while melt inclusions have also become more silicic over time, ranging basaltic to andesitic in 1972 and basaltic andesite to dacitic in 2013/14. Hornblende-phyric basalts are unusually rich in MgO (≤13 wt%) and Ni (≤230 ppm) and contain rare olivine phenocryst cores of Fo 90–92 , suggestive of a primitive character. Other phenocryst phases include spinel, clinopyroxene and plagioclase. Conversely, 2013/14 landslide deposit samples contain orthopyroxene as an additional phenocryst phase and are distinct from crater deposits in terms of phenocryst and bulk rock chemistry. We propose that 1972 and 2013/14 crater deposits sample Kick-'em-Jenny's current edifice, whereas 2013/14 landslide deposits likely represent "proto Kick-'em-Jenny" (an edifice existing pre 43.5 kyr BP). Geochemical data for Kick-'em-Jack support the notion that it is part of the same volcanic complex as Kick-'em-Jenny and probably represents part of the now collapsed proto Kick-'em-Jenny. Low eruption temperatures (~1000 °C), estimated from geothermometry, coupled with whole-rock magma chemistry suggest an origin of the most mafic lavas of Kick-'em-Jenny by dehydration melting of hornblende-peridotite just below the Moho. Subsequent injection of these cool, oxidised, wet primitive basalts into the deep crust was accompanied early fractionation of hornblende-dominated assemblages. Large, zoned hornblende phenocrysts track rapid ascent of magmas through the crust along a trajectory sub-parallel to the hornblende liquidus curve. Melt inclusion data provide clear evidence of volatile-rich (≤5 wt% H 2 O and <3200 ppm CO 2) pre-eruptive magma storage 7–12 km below Kick-'em-Jenny. This new understanding of the architecture of Kick-'em-Jenny's sub-volcanic system will be useful for interpreting future seismic signals and mitigating volcanic hazards. Highlights • New petrological data document magma evolution over >40 years • High concentrations of dissolved volatiles at depth (≤5 wt% H 2 O and <3200 ppm CO 2) • Hydrous, cool, mantle-derived basalt magmas • Preferred pre-eruptive magma storage reservoir ~7–12 km [ABSTRACT FROM AUTHOR]