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On 8 October 2023 (UTC), unique earthquakes occurred in the Izu‐Ogasawara Arc, Japan, in which the P‐ and S‐phases were barely visible and only the T‐phases were evident, followed by tsunamis that reached islands in the Izu‐Ogasawara Arc and a wide area of the Pacific coast of southwest Japan. Our estimated T‐phase source area coincides with the Sofu Seamount, which was previously unrecognized as an active submarine volcano. A bathymetric survey of the seamount conducted 1 month after the event revealed characteristics of the seamount with a caldera and a central cone. Compared to the bathymetry in 1987, the topography in the caldera had changed significantly such as a crater forming in the central cone. This seamount is likely to be an active volcano. The topographic changes on the caldera‐sized scale that occurred at the caldera can be explained as a source of the October tsunami. Plain Language Summary: On 8 October 2023 (UTC), earthquakes were followed by tsunamis in the Izu‐Ogasawara Arc of Japan that were higher than that estimated from the magnitude of the earthquake. The tsunamis were observed on islands in the Izu‐Ogasawara Arc and a wide area of the Pacific coast of southwest Japanese islands. Strong T‐phases that are underwater acoustic waves were observed accompanying that event. We estimated that the T‐phases originated from the area around the Sofu Seamount, which has not been recognized as an active submarine volcano until now. One month after the event, we conducted a bathymetric survey of the seamount and revealed the characteristics of a caldera and a central cone within the caldera. Compared to the bathymetric data obtained in 1987, the caldera and central cone topography have changed significantly, such as a crater forming in the central cone, indicating that this seamount is likely to have been an active submarine volcano. The topographic changes that occurred at the depth of the caldera (∼1,000 m) and its scale (diameter ∼5 km) can be associated with the source of the tsunami on 8 October 2023. Key Points: A bathymetric survey of the Sofu Seamount was conducted after the unique T‐phase dominant earthquakes and tsunamis on 8 October 2023Compared to data in 1987, the caldera and central cone topography have changed, indicating that this seamount is an active submarine volcanoThe observed seafloor displacement at the caldera scale may have contributed to the source of the tsunami on 8 October 2023 [ABSTRACT FROM AUTHOR]

Absract: Rawa Danau Volcanic Complex (RDVC) in the western part of Banten—Western part of Java Island, Indonesia, holds records and histories of past violent volcanic eruption. These past volcanic activities manifested as huge Rawa Danau caldera and massive Banten Tuff pyroclastic deposits that are distributed for more than ten kilometres away from the source and have played an important role in shaping the morphology of Banten. Previous studies suggest that Banten Tuff is composed of various pumiceous pyroclastic deposits presumably formed in Early Pleistocene. The deposits cover vast area of Banten, and their thickness exceeds 200 m. Despite their significance, there are no detailed studies that discuss the stratigraphic and eruption dynamics of the deposits. This paper provides new insight on the eruption dynamics based on fieldwork observation, volcanic stratigraphy, and petrologic interpretation. The study focuses on the eastern flank of RDVC, where the well-preserved stratified outcrops are located. Aligned with previous studies, the deposit can be divided into two major eruption sequences: 1) Lower Banten Tuff (LBT) and 2) Upper Banten Tuff (UBT). LBT is interpreted as lithic-bearing ignimbrite with accompanying surge deposit and considered as a single-phase eruption. Lithic-rich characteristics in this unit suggest that LBT might be related to the caldera-forming mechanism. On the other hand, UBT shows a more dynamic sequence. It is composed of two fallout units followed by an ignimbrite formed by the eruption column collapse. The appearance of banded pumice in UBT with contrasting andesitic and rhyolitic compositions suggests a mafic injection as the eruption trigger. Pumice and ash compositions are mostly in dacitic to rhyolitic range, with several samples in andesitic range. Componentry analysis suggests that all eruptions were magmatic in origin. [ABSTRACT FROM AUTHOR]

Caldera-forming eruptions represent extremely hazardous events. The Loch Bà Caldera on the Isle of Mull, NW Scotland, preserves an ~120 m thick sequence of Palaeogene silicic pyroclastic rocks and collapse breccias. Here we present the first detailed account of the lithostratigraphy and architecture of the caldera-fill. A silicic explosive eruption generated pyroclastic density currents that deposited a range of rhyolitic ignimbrite lithofacies as the caldera collapsed. Abrupt changes in ignimbrite lithofacies and lateral thickness changes are attributed to volcano-tectonic faults and incremental collapse of the caldera. Five eruption phases have been recognised that record rapid switching between sustained high-fountaining and low-fountaining “boil-over” eruptions. The ignimbrites are unconformably overlain by mesobreccias and inward rotated megablocks of basalt lava country rock, which record catastrophic inward collapse of the caldera walls and margins. Our results provide new insights into caldera collapse and intra-caldera-fill that can be applied to other volcanoes worldwide.

Abstract Understanding carbon dioxide emissions variability in volcanic regions is vital for detecting instabilities in the subvolcanic plumbing system, crucial for managing both volcanic and environmental risks. While changes in magmatic sources drive these variations, non-magmatic processes can complicate signal interpretation, especially in caldera environments. Here, geothermal systems can sequester CO2 within the bedrock through hydrothermal calcite precipitation, significantly impacting surface-level CO2 emissions. Unfortunately, few studies have explored this phenomenon, examining hydrothermal calcite origins and their effects on carbon balances and temporal gaseous patterns in active volcanic settings. Our study developed a specialized methodology for quantifying CO2 sequestered in hydrothermal calcites within alkaline caldera systems. We focused on analyzing hydrothermal calcite in lithics from volcanic deposits of eruptions of varying ages, Volcanic Explosivity Index (VEI), and eruptive vent locations to enhance the representativeness of the entire caldera bedrock. Unlike core samples from geothermal wells, which are infrequent and limited to specific depths, lithics can be easily collected, offering a comprehensive understanding of CO2 sequestration. Through extensive 3D textural characterization and isotopic investigations on hydrothermal calcite within lithic fragments from selected alkaline volcanic deposits in the Campi Flegrei caldera, our findings emphasized the significant influence of calcite sinks on the overall CO2 budget released by volcanoes throughout their evolution.

Understanding carbon dioxide emissions variability in volcanic regions is vital for detecting instabilities in the subvolcanic plumbing system, crucial for managing both volcanic and environmental risks. While changes in magmatic sources drive these variations, non-magmatic processes can complicate signal interpretation, especially in caldera environments. Here, geothermal systems can sequester CO2 within the bedrock through hydrothermal calcite precipitation, significantly impacting surface-level CO2 emissions. Unfortunately, few studies have explored this phenomenon, examining hydrothermal calcite origins and their effects on carbon balances and temporal gaseous patterns in active volcanic settings. Our study developed a specialized methodology for quantifying CO2 sequestered in hydrothermal calcites within alkaline caldera systems. We focused on analyzing hydrothermal calcite in lithics from volcanic deposits of eruptions of varying ages, Volcanic Explosivity Index (VEI), and eruptive vent locations to enhance the representativeness of the entire caldera bedrock. Unlike core samples from geothermal wells, which are infrequent and limited to specific depths, lithics can be easily collected, offering a comprehensive understanding of CO2 sequestration. Through extensive 3D textural characterization and isotopic investigations on hydrothermal calcite within lithic fragments from selected alkaline volcanic deposits in the Campi Flegrei caldera, our findings emphasized the significant influence of calcite sinks on the overall CO2 budget released by volcanoes throughout their evolution. [ABSTRACT FROM AUTHOR]

Abstract On 8 October 2023 (UTC), unique earthquakes occurred in the Izu‐Ogasawara Arc, Japan, in which the P‐ and S‐phases were barely visible and only the T‐phases were evident, followed by tsunamis that reached islands in the Izu‐Ogasawara Arc and a wide area of the Pacific coast of southwest Japan. Our estimated T‐phase source area coincides with the Sofu Seamount, which was previously unrecognized as an active submarine volcano. A bathymetric survey of the seamount conducted 1 month after the event revealed characteristics of the seamount with a caldera and a central cone. Compared to the bathymetry in 1987, the topography in the caldera had changed significantly such as a crater forming in the central cone. This seamount is likely to be an active volcano. The topographic changes on the caldera‐sized scale that occurred at the caldera can be explained as a source of the October tsunami.

This paper examines the Karymsky Volcanic Center to estimate how much volcanic and hydrothermal activity affects the chemical composition of river water. We evaluate the volumes of major and trace elements coming to the Pacific Ocean via the Karymsky River. We assess the quality of river water in compliance with the regulations for potable water, water used for household work, and in fisheries. It is shown that the formation of ion load of the river water mostly occurs by inflow of thermal waters, as well as due to water-soluble complexes of ashes discharged by Karymsky Volcano and coming to the catchment area of the river. The annual volume of dissolved material transported by the river to the Kronotsky Bay of the Pacific Ocean amounts to more than 90 kilotons. [ABSTRACT FROM AUTHOR]

The Eastern Caucasus Mountains in Georgia include products from extensive Miocene volcanic activity that are being unraveled by geological mapping supported by geochronology and geochemistry. This article presents new zircon U–Pb geochronology and whole rock geochemistry of the volcanic ash layers of the intermountain Neogene basin of the Eastern Caucasus. Our investigation in the region demonstrates that these ash layers, whose eruption center(s) have not been identified yet, has age and geochemical characteristics of the Mtkvari (Kura) ignimbrite of the Samtskhe-Javakheti volcanic highland. This study shows that zircons from both formations crystallized at the same time ~ 7.50 Ma ago and have geochemical and morphological similarity. Taken together with the geography of the region (200–300 km from the volcanic source to the sedimentary basins), it is likely that the source of the ash layers was the Upper Miocene volcanic eruptions on the Samtskhe-Javakheti volcanic highlands. Based on the distribution, thickness, and age of the volcanic ash layers and the analysis of the structure and scale of the Mtkvari ignimbrite, the widely distributed ash likely resulted from a Plinian-type eruption in the Samtskhe-Javakheti volcanic highland. These eruptions led to the formation of the large-scale caldera structure (Niala caldera) and the Mtkvari ignimbrite. The inferred caldera extends to the northeastern territory of Türkiye (Turkey), i.e., NE of the Kars Plateau. Ideally, this western portion of the caldera and volcanic highlands can be characterized in the future, and a unified structure model of this volcanic center can be established. [ABSTRACT FROM AUTHOR]

The Campi Flegrei caldera is characterized by the phenomenon of bradyseism, as evidenced by stratigraphic records of alternate oceanic and continental sediments dating back over a thousand years. Since 2005, the caldera has been in a phase of unrest, which is increasing volcanic deformations and associated seismicity around the region, resulting in a growing concern over the dense population in the inhabitation. Recent studies have highlighted that the caldera dynamics are driven by a combination of endogenous processes and modulation phenomena induced by exogenous processes, e.g., rainfall, atmospheric pressure, and tidal loading. Although the complex feedback mechanisms of both endogenous and exogenous processes are still under debate, the present study is focused on the increased potential of modulation due to exogenous processes with the increase or evolution in the degree of inflation of the magma chamber. Specifically, Campi Flegrei volcanic system shows sensitivity to seasonal hydrological cycles during slower rates of inflation and to short-period tidal modulations during higher rates of inflation. The observed seasonal modulations of seismic activity are explained in terms of water infiltration into the shallow aquifers, basins, and vent depression system of the caldera. The rainfall-induced pore pressure build-up also favours the instability of the brittle cap rock, promoting seismicity. In addition, this study suggests that the tidal loadings provide horizontal NS extensions to the mostly NW–SE, NE–SW, and EW-oriented scattered fractures and further contribute towards fracture propagation. During this process, a cyclic opening and sealing of fractures by volatile outgassing and silicate settling may, respectively, produce the episodic behaviour of the seismicity. The seismicity in relation to exogenous processes imposed by seasonal rainfall and tidal loadings shows that the degree of correlation depends on the different rates of inflation. The long-period seasonal modulations and short-period tidal modulations during the evolution of the degree of inflation are finally interpreted in the framework of the fault resonance destabilization model, under rate-and-state dependant frictional formalism. [ABSTRACT FROM AUTHOR]

Silicic magma reservoirs are responsible for producing the largest explosive eruptions in the geologic record. Petrologic and geochronological data provide evidence for these systems spending substantial periods of time (104–105 yrs) within the upper crust prior to eruption; however, the long-term thermochemical evolution of these systems is not fully understood, as existing petrologic data make it challenging to quantify the time interval a magmatic system has spent at certain temperatures, or its "thermal history". Here, we investigate the 74 ka Youngest Toba Tuff (YTT), one of the largest explosive eruptions in the geologic record, to better constrain the long-term thermal evolution of its magmatic system. We combine forward models of Sr diffusion in plagioclase and hornblende, mineral thermometry, and pre-existing trace-element evolution models to quantify the thermochemical evolution of the YTT magmatic system. We find that plagioclase crystals record decades to centuries of storage at temperatures > ∼ 750 ∘ C, while hornblende records up to 6200 years at the same temperatures. Hornblende crystallizes at temperatures around 820 ∘ C and adjusting our diffusion modeling to this temperature results in no more than 900 years at initial crystallization conditions. Combined with previous trace-element modeling work, these results indicate that although there was chemical diversity for long durations in the YTT magma system sufficient to produce unique composition eruptive products, the entire system was experiencing a relatively similar thermal history that did not allow for large bodies of eruptible magma to be present for long periods ( > > 102–103 years). Rather, we suggest that magmas within the YTT magmatic system were stored for long durations at thermal conditions where they were uneruptible and only remobilized within a few centuries prior to eruption. [ABSTRACT FROM AUTHOR]

Submarine volcano monitoring is vital for assessing volcanic hazards but challenging in remote and inaccessible environments. In the vicinity of Kita‐Ioto Island, south of Japan, unusual M ∼ 5 non‐double‐couple volcanic earthquakes exhibited quasi‐regular recurrence near a submarine caldera. Following the earthquakes in 2008 and 2015, a distant ocean bottom pressure sensor recorded distinct tsunami signals. In this study, we aim to find a source model of the tsunami‐generating earthquake and quantify the pre‐seismic magma overpressure within the caldera's magma reservoir. Based on the earthquake's characteristic focal mechanism and efficient tsunami generation, we hypothesize that submarine trapdoor faulting occurred due to highly pressurized magma. To investigate this hypothesis, we establish mechanical earthquake models that link pre‐seismic magma overpressure to the size of the resulting trapdoor faulting, by considering stress interaction between a ring‐fault system and a reservoir of the caldera. The trapdoor faulting with large fault slip due to magma‐induced shear stress in the submarine caldera reproduces well the observed tsunami waveform. Due to limited data, uncertainties in the fault geometry persist, leading to variations of magma overpressure estimation: the pre‐seismic magma overpressure ranging approximately from 5 to 20 MPa, and the co‐seismic pressure drop ratio from 10% to 40%. Although better constraints on the fault geometry are required for robust magma pressure quantification, this study shows that magmatic systems beneath calderas are influenced significantly by intra‐caldera fault systems and that tsunamigenic trapdoor faulting provides rare opportunities to obtain quantitative insights into remote submarine volcanism hidden under the ocean. Plain Language Summary: Monitoring submarine volcanoes is essential to understand and prepare for potential volcanic hazards in/around oceans, but it's challenging because these volcanoes are located in inaccessible environments. In a submarine volcano with a caldera structure in the south of Japan, unusual volcanic earthquakes took place every several years. After one of these earthquakes in 2008, a pressure sensor deployed on the sea bottom recorded a clear signal of tsunami waves. By utilizing the tsunami signal from the earthquake, we attempt to measure how much magma pressure was building up beneath the volcano before the earthquake. Assuming that the earthquake happened with sudden rupture on an intra‐caldera fault system due to highly pressurized magma beneath the volcano, we develop a method to assess the built‐up magma pressure through quantification of the earthquake and tsunami sizes. By applying the method, we estimate that the volcanic edifice was under a highly stressed condition before the earthquake, suggesting the active magma accumulation process that has continued beneath the volcano. Signals emitted from volcanic earthquakes under oceans shed light on the activity of poorly monitored submarine volcanoes. Key Points: Non‐double‐couple earthquakes with seismic magnitudes of 5.2–5.3 recurred in the vicinity of a submarine caldera near Kita‐Ioto IslandA mechanical model of trapdoor faulting based on tsunami data of the 2008 earthquake infers pre‐seismic overpressure in a magma reservoirUncertainty in fault geometry varies our estimate of pre‐seismic overpressure (5–20 MPa) and co‐seismic pressure drop ratio (10%–40%) [ABSTRACT FROM AUTHOR]

Lake Taupō (Taupō-nui-a-Tia) infills the composite caldera above an active rhyolitic magmatic system in the central Taupō Volcanic Zone (TVZ). Ground deformation is a key unrest indicator at Taupō volcano. We present a spreadsheet tool, TaupōInflate, to calculate and plot ground deformation from magmatic inflation at depth beneath Taupō caldera. Examples show detection limits for inflating magma bodies and their ascent through the crust beneath Lake Taupō. Source locations where it is challenging to detect even substantial volumes of inflating magma bodies are as large as 20 km3, with volume changes up to 0.01 km3, owing to the restricted station placement around the lake, although a dike propagating from shallow crustal depths towards the surface is likely to be detectable. For a magma overpressure of 10 MPa, the sizes of detectable inflating bodies at depths of 5–8 km using the present monitoring system are larger than the volumes of many past eruptions, illustrating the importance of future improvements to the geodetic network. We discuss the potential for future equipment installation, including lakebed instrumentation that would require approval of local iwi Ngāti Tūwharetoa through the Tūwharetoa Māori Trust Board who oversee the health and wellbeing of Lake Taupō. [ABSTRACT FROM AUTHOR]

The Bora-Baricha-Tullu Moye (BBTM) volcanic complex is located at a transitional zone in the Main Ethiopian Rift where tectonic and volcanic features show complex interplays. We mapped and characterised volcanic and tectonic features using high-resolution digital elevation models and performed morphometric and vent spatial distribution analyses. Structural analysis reveals NNE–SSW, NE–SW, and NW–SE trending faults in the region. The dominant post-caldera volcanic landforms are lava domes, pumice cones, scoria cones, maars, obsidian coulees and lava flows, which have distinct morphological characteristics. Vent elongation and alignment highlight close association between these landforms and the caldera(s) as well as with tectonic structures, suggesting these structures acted as the main magma pathways during the BBTM recent eruptions. We estimate that during the entire BBTM post-caldera phase a total bulk volume of 10.9 km3 of material was erupted. This would represent a time-averaged magma flux of 0.05 km3 ky-1 in the BBTM.

Understanding the complex dynamics of volcanic systems demands a multidimensional approach that combines geophysics, geology, and geodetics. In this study, we examine observed spatiotemporal gravity changes within the Santorini volcanic complex from 1975 to 2014. The historical data indicates that gravity has been increasing continuously since at least 1966 until our latest measurements in 2014, albeit with a decreasing rate of increase over time. Utilizing gravity inversion of various gravity datasets and evidence from other studies, we explore different scenarios to shed light on the underlying processes. Our preferred interpretation involves both a magmatic episode and continuous evolution of the shallow structure. We find that the 2011-12 unrest period resulted from the intrusion of ∼3.3x1011 kg of basaltic magma at 3 km depth near the previously identified Mogi source. We attribute the continuous gravity increase beneath Nea Kameni to a density increases at about 1350 m depth. We infer these are a result of hydrothermal fluctuations, degassing, and/or vesicle collapse within the stored magma. Units: 1mGal = 10-5 m/s2 (SI)

The fossil record of the southeastern Pacific Ocean has been scarcely studied compared to other regions. We present the detailed description of two pelagic shark species, Alopias vulpinus (common thresher) and Lamna nasus (porbeagle) (Elasmobranchii: Lamniformes), from the Neogene of South America. The fossil teeth described here were recovered from the Bahia Inglesa Formation in Caldera, northern Chile. Our study provides the first comprehensive descriptions of fossil remains of A. vulpinus from Chile and L. nasus from the Americas. The occurrence of the common thresher shark represents the first published record and description of a representative from the family Alopiidae in northern Chile, whereas the fossil remains of the porbeagle shark are recorded for the first time in Chile. This study contributes to the understanding of the past distribution of shark species in the Eastern Pacific of South America during the Neogene period. It further confirms the particular abundance of lamniform sharks in the Neogene of Chile. [ABSTRACT FROM AUTHOR]

This paper presents the results of a detailed petrological study of a continuous section of the Golygin ignimbrite, related to the Pauzhetka caldera-forming eruption (443 ± 8 ka BP). The continuous zoning of the studied sequence suggests that a large magmatic chamber, partially emptied during the eruption, was also zoned and had significant vertical dimensions. Our research included determining the bulk composition of rocks, studying samples of the Golygin ignimbrites in thin sections, and detailed studying of quartz and melt inclusions in it. The roof of the magmatic chamber was at a depth of about 5 km; amphibole and plagioclase crystalloclasts in rocks at the base of the sequence show evidence of formation in a more basic melt at a depth of 24 to 25 km. The composition of the magmatic melt reconstructed from melt inclusions in quartz from this sequence corresponds to medium-K rhyolites (wt %): SiO2 78.1–77.9, Al2O3 12.7–12, FeOt 0.8–0.1, MgO 0.1–0.0, CaO 1.0–0.2, K2O 4.3–3.8, Na2O 4.9–3.3, Cl2 0.1–0.2. Crystallization temperatures calculated for various minerals and their assemblages vary in the range 1009–784°С, which, together with estimates of formation depths of 25 km to 5 km, may reflect different stages of a crystallization of the magmatic melt, magma ascent and evolution in a relatively shallow chamber where it was slowly cooled and crystallized. The maximum water content of the magmatic melt during quartz crystallization was estimated in the range from 4.1 to 7.5 wt % H2O. [ABSTRACT FROM AUTHOR]

Mt. Paektu is the highest one among the famous mountains on the Korean Peninsula. Since Mt. Paektu has abundant geological evidence of volcanic activity from the Pliocene to comparatively modern times about 1000 years ago, it is also of value in the development of geoheritage and geotourist products related to volcanic activity and its ejecta. As a volcanic geoheritage, the most distinctive feature of Mt. Paektu is its very beautiful and unique caldera lake—the Lake Chon, which is located at the highest place in the world. The purpose of this study is to clarify the touristic value of Mt. Paektu as a volcanic geoheritage by comparing it with other caldera volcanoes in the world. This study explains the five stages of the eruptions of Mt. Paektu, and analyzes the geological state. The research results revealed that Mt. Paektu, as a composite volcano that has experienced multiple types of volcanic eruptions, is an important academic research object with high touristic value. [ABSTRACT FROM AUTHOR]

Caldera-forming eruptions are amongst the most hazardous events in the Earth’s history, and understanding their formation is essential to forecasting activity at active calderas worldwide. In this study we present new field and geochronological evidence for a Paleocene-Eocene caldera from Skye, NW Scotland. Magma exploited a regional thrust fault as a conduit, and then ponded against intrusive igneous rocks emplaced against a regional extensional fault. Replenishment of silicic magma reservoirs with basaltic magma triggered eruptions. The eruptions typically deposited extremely coarse ignimbrites, demonstrating catastrophic collapse of the caldera, which occurred via an inner ring fault and a complexly faulted marginal zone. Collapse was followed by remobilisation of silicic magma and caldera resurgence. The magma consumed dolostone country rocks, causing significant release of CO2 and contributed to the Paleocene-Eocene Thermal Maximum. Our results demonstrate how tectonics localise magma and caldera development, and how this can cause cataclysmic volcanic and climatic hazards.

Electric Vehicles (EV) present a unique challenge to electric power system (EPS) operations because of the potential magnitude and timing of load increases due to EV charging. Time-of-Use (TOU) electricity pricing is an established way to reduce peak system loads. It is effective at shifting the timing of some customer-activated residential loads – such as dishwashers, washing machines, or HVAC systems – to off-peak periods. EV charging, though, can be larger than typical residential loads (up to 19.2 kW) and may have on-board controls that automatically begin charging according to a pre-set schedule, such as when off-peak periods begin. To understand and quantify the potential impact of EV charging’s response to TOU pricing, this paper simulates 10 distribution feeders with predicted 2030 EV adoption levels. The simulation results show that distribution EPS experience an increase in peak demand as high as 20% when a majority of the charging begins immediately after on-peak times end, as might occur if EV charging is automatically scheduled. However, if charging start times are randomized within the off-peak period, EV charging is spread out and the simulations showed a decrease in the peak load to be 5% lower than results from simulations that did not implement TOU rates.

Taupō, New Zealand, is an active caldera volcano that in recent times has erupted on average every ~500 years, with the latest explosive eruption in 232±10 CE. Monitoring at Taupō is challenging as there has been no eruptive activity in documented history; however, Taupō does undergo periods of unrest on roughly a decadal timescale, such as in 2019. Key to identifying these unrest periods is understanding what represents 'normal' inter-unrest activity. In this study, we generate an earthquake catalogue for Taupō for 2010–2019 inclusive, consisting of 46,481 earthquakes. This shows that the Taupō region has background earthquake rates of 50–200 earthquakes per month and the 2019 unrest episode was preceded by an exponential increase in earthquake rate. We also show that when attenuation is accounted for there is no evidence for low-frequency earthquakes at Taupō, and that this is an important consideration for volcano monitoring and determining the presence of significant magma movement.

Two submarine earthquakes (Mw 5.8) occurred near volcanic islands, Curtis and Cheeseman, in the Kermadec Arc in 2009 and 2017. Following both earthquakes, similar tsunamis with wave heights of about a meter, larger than expected from their moderate seismic magnitudes, were observed by coastal tide gauges. We investigate the source mechanism for both earthquakes by analyzing tsunami and seismic data of the 2017 event. Tsunami waveform analysis indicates that the earthquake uplifted a submerged caldera around the islands. Combined analysis of tsunami and seismic data suggests that trapdoor faulting, or sudden intra‐caldera fault slip interacted with magma reservoir deformation, occurred due to magma overpressure, possibly in association with caldera resurgence. The earthquake scaling relationship for trapdoor faulting events at three calderas deviates from that for regular earthquakes, possibly due to the fault‐reservoir interaction in calderas. Plain Language Summary: Most tsunamis are generated by large earthquakes with seismic magnitudes M > ∼7, but two moderate‐sized earthquakes with only M 5.8 near volcanic islands, north of New Zealand, caused unusual tsunamis with a maximum wave height of about a meter. In this study, we examine the unusual source mechanism of the volcanic earthquakes that excited unexpected tsunamis. By analyzing the records of tsunamis and seismic waves from the earthquakes, we suggest that the inside of a curved fault system beneath a submerged volcano with a caldera structure suddenly moved upward, together with a large intra‐caldera fault slip and a volume increase of a shallow magma reservoir. Overpressure created by magma accumulation beneath the submarine caldera recurrently induces meter‐scale tsunamis without significant ground motions, calling for attention to tsunami hazards from submarine calderas. Key Points: Unusual tsunamis were caused by two Mw 5.8 volcanic earthquakes in 2009 and 2017 near Curtis and Cheeseman Islands in the Kermadec ArcBy using tsunami and seismic data of the 2017 event, we suggest that a trapdoor faulting event occurred at a submerged resurgent calderaTrapdoor faulting events at calderas had abnormally large slips, possibly due to the fault‐reservoir interaction in calderas [ABSTRACT FROM AUTHOR]

This paper presents the chemical composition (including H2O and CO2) of matrix glass, melt inclusions in phenocrysts, and their host minerals in eruptive products from Aso caldera. We found a group of melt inclusions with clearly lower potassium (0.6–2 wt % K2O at 50–70 wt % SiO2) than previously reported high-K2O whole-rock compositions (3–5 wt % K2O at 55–70 wt % SiO2). While most of the high-K2O intermediate to felsic melt inclusions are vapor undersaturated and show the features of H2O, CO2, and K2O accumulation, the low-K2O basaltic melt already has higher H2O and CO2. We reconcile this discrepancy with a model in which (1) the volatile-rich basalt magmas degas near the surface, (2) migrate back to depths of |$\ge$| 12 km in the crust, and (3) crystallize feldspar and quartz to produce high-K2O felsic melt, (4) magma mixing among the undegassed, degassed, and evolved magmas. By crystallization, about five times as much low-K2O basaltic magma is required to produce high-K2O felsic magma. The quantity of felsic magma ejected from 270 ka (Aso-1) to 90 ka (Aso-4) requires a basalt magma supply rate of 18 to 31 km3/ka. This magma supply rate is comparable to or less than the present-day production rate of degassed magma (73 km3/ka) at an active center of Aso, Nakadake. These findings suggest volcanic gas flux monitoring has the potential to be a 'basalt usage meter' during the dormant period of caldera volcanoes. [ABSTRACT FROM AUTHOR]

Giant volcanic eruptions have the potential to overturn civilizations. Yet, the driving mechanism and timescale over which batholithic magma reservoirs transition from non‐eruptible crystal mush to mobile melt‐dominated stages and our capacity to detect a pending super‐eruption remain obscure. Here we show, using Sr isotope zonation in plagioclase crystals from three Andean large‐magnitude eruptions (Atana, Toconao, and Tara ignimbrites), that eruptible magma forms by amalgamation of isotopically diverse crystal populations and silicic melt without large‐scale reheating. In each case, crystals record large isotopic diversity in crystal cores, converging toward a common value in crystal rims that coincides with the composition of the rhyolitic carrier melt. Using diffusion chronometry, we show that the assembled magma resided pre‐eruptively in the crust for timescales of no more than decades to centuries for Atana and Tara, but up to several millennia for Toconao. These timescales and isotopic observations are consistent with the accumulation and destabilization of melt‐rich layers in crystal mush. While the prospect of capturing such melt lenses with most geophysical monitoring techniques is pessimistic, gravity modeling indicates that such structures are potentially resolvable. Our findings provoke a new assessment of the origin and hazards associated with large magnitude explosive eruptions. Plain Language Summary: Super‐eruptions are the largest manifestation of explosive volcanism on Earth. If such an event would occur today, it could deeply impact human civilization on a global scale. Yet, signals that may emerge prior to such eruptions are difficult to constrain. To gain greater understanding of the mechanisms and timescales over which giant, eruptible, reservoirs form, and to evaluate our capacity of capturing the evolution toward large eruptions, we studied plagioclase crystals, a mineral that is an excellent recorder of magmatic processes. For three large eruptions in the Central Andes, we analyzed strontium isotopes in traverses from crystal cores to rims to provide a temporal record of melt composition. Our results show that, in each case, the eruptible magma amalgamated from distinct pre‐existing magma pockets that merged prior to eruption. This merged state of the magma did not exist for longer than a few hundred to thousands of years based on the preservation of the crystal strontium‐isotope traverses at high temperatures. These results are consistent with the destabilization of melt‐rich layers on timescales comparable to human lifespans. Although most geophysical imaging methods are unlikely to capture this process, our calculations indicate that gravity monitoring of super‐volcanoes can potentially resolve such structures. Key Points: Sr‐isotopes in plagioclase record the emergence of eruptible magma through amalgamation of pre‐existing mush in the Central AndesThe amalgamated magma did not reside at depth for longer than centuries to millennia based on diffusion chronometryForward modeling indicates that high‐precision gravity monitoring has large potential to resolve eruptible magma amalgamation [ABSTRACT FROM AUTHOR]

Abstract Two submarine earthquakes (Mw 5.8) occurred near volcanic islands, Curtis and Cheeseman, in the Kermadec Arc in 2009 and 2017. Following both earthquakes, similar tsunamis with wave heights of about a meter, larger than expected from their moderate seismic magnitudes, were observed by coastal tide gauges. We investigate the source mechanism for both earthquakes by analyzing tsunami and seismic data of the 2017 event. Tsunami waveform analysis indicates that the earthquake uplifted a submerged caldera around the islands. Combined analysis of tsunami and seismic data suggests that trapdoor faulting, or sudden intra‐caldera fault slip interacted with magma reservoir deformation, occurred due to magma overpressure, possibly in association with caldera resurgence. The earthquake scaling relationship for trapdoor faulting events at three calderas deviates from that for regular earthquakes, possibly due to the fault‐reservoir interaction in calderas.

Abstract Giant volcanic eruptions have the potential to overturn civilizations. Yet, the driving mechanism and timescale over which batholithic magma reservoirs transition from non‐eruptible crystal mush to mobile melt‐dominated stages and our capacity to detect a pending super‐eruption remain obscure. Here we show, using Sr isotope zonation in plagioclase crystals from three Andean large‐magnitude eruptions (Atana, Toconao, and Tara ignimbrites), that eruptible magma forms by amalgamation of isotopically diverse crystal populations and silicic melt without large‐scale reheating. In each case, crystals record large isotopic diversity in crystal cores, converging toward a common value in crystal rims that coincides with the composition of the rhyolitic carrier melt. Using diffusion chronometry, we show that the assembled magma resided pre‐eruptively in the crust for timescales of no more than decades to centuries for Atana and Tara, but up to several millennia for Toconao. These timescales and isotopic observations are consistent with the accumulation and destabilization of melt‐rich layers in crystal mush. While the prospect of capturing such melt lenses with most geophysical monitoring techniques is pessimistic, gravity modeling indicates that such structures are potentially resolvable. Our findings provoke a new assessment of the origin and hazards associated with large magnitude explosive eruptions.

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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]

Felsic rocks of the Piskahegan Group and coeval plutons form a major part of a Late Paleozoic epicontinental caldera in southwestern New Brunswick, Canada. The caldera forms an elliptical structure with a length of ∼34 km and a width of ∼13 km. It hosts a significant polymetallic deposit of tin, molybdenum, indium and bismuth associated with mid-sequence granitic intrusions. The caldera formed in the aftermath of the late Early to Middle Devonian Acadian Orogeny during the opening of the late Paleozoic Maritimes Basin in the Northern Appalachian Belt. Its surrounding successions are largely composed of bimodal igneous rocks that were derived from two distinct sources: upper mantle-derived mafic magma and lower crust-derived felsic magma. The rocks that marked the beginning of volcanic activity in the caldera are no younger than 374.2 ± 2 Ma, whereas the uppermost dated volcanic unit in the complex yielded an age of 364.6 ± 0.7 Ma. The latter is conformably overlain by a succession of red beds and undated basalts that also overlie penecontemporaneous felsic volcanic rocks adjacent to the caldera. The post-orogenic felsic rocks are fractionated, peraluminous A-2 type rocks with silica contents ranging from ∼70 to ∼79 wt% along with high K 2 O contents and ɛ Nd (t) ranging from −0.10 to +1.05. They were generated by the melting of lower crustal basement rocks linked to a lithospheric plate that was metasomatized during the Neoproterozoic. Based on available geochemical, geophysical and structural data on Late Paleozoic rocks of southeastern Canada, the melting may have been triggered by the injection of profuse mafic magma that eventually formed a thick underplating at the base of the crust in association with heat derived from an underlying mantle plume and conveyed by transtensional structures. Basal rocks of the Piskahegan Group (the Intracaldera Sequence) and penecontemporaneous volcanic rocks in Nova Scotia are interpreted as small erosional remnants of a Large Igneous Province (LIP) based on the extensive exposure of large coeval plutons throughout southeastern Canada. The new geochronological data suggests that profuse late Frasnian magmatism in this LIP could have contributed to the environmental deterioration that led to a significant extinction at the Frasnian-Famennian boundary (the Kellwasser Event). • The Mount Pleasant caldera complex is associated with a large Late Devonian igneous province in southeastern Canada. • Mafic underplating and profuse felsic magma produced as the Canadian Appalachian Belt was overriding a mantle plume. • Neodymium isotopes are compatible with a Ganderian crustal source. • New U-Pb zircon dates suggest that Frasnian volcanism was voluminous and may have contributed to the Kellwasser event. [ABSTRACT FROM AUTHOR]

Ignimbrites within calderas host intrusions with hazardous and/or economically significant hydrothermal systems. The Hvítserkur ignimbrite at Breiðuvík caldera, north-eastern Iceland, is intruded by basaltic dykes. Our data show that the ignimbrite immediately adjacent to the dyke is hard, dark-coloured, recrystallised quartz, plagioclase, and alkali feldspar with a low permeability and porosity and frequent macrofractures. At 1-2 m from the dyke, the ignimbrite is hard, dominantly glassy with pervasive perlitic microfractures, has high permeability, but low porosity and frequent macrofractures. A narrow zone of pervasive unlithified clay exists 2 m from the dyke. Beyond this, the ignimbrite is soft and zeolite-rich, has low permeability, high porosity and fewer macrofractures. The dyke intrusion promoted a narrow zone of welding, fracturing and perlitisation in the ignimbrite resulting in high permeability and focussed alteration. Our study shows how intrusions and their thermal aureoles create vertical pathways for, and horizontal barriers to, geothermal fluid flow.

Abstract Oxygen isotopes are useful for tracing interactions between magmas, crustal rocks and surface‐derived waters. We use them here to consider links between voluminous silicic magmatism and large‐scale hydrothermal circulation in New Zealand's central Taupō Volcanic Zone (TVZ). We present >350 measurements of plagioclase, quartz, hornblende and groundmass glass δ18O values from 40 eruptions from three discrete magmatic systems: Ōkataina and Taupō calderas, and the smaller Northeast Dome system. For each mineral, mean δ18O values vary by ∼1‰ (δ18Oplag = +6.7–7.8‰, δ18Oqtz = +7.7–+8.7‰, δ18Ohbl = +5.4–+6.4‰, δ18Oglass = +7.1–+8.0‰), and inter‐mineral fractionations mostly reflect high‐temperature equilibria. Outliers (e.g., ∼+6‰ or >+10‰ plagioclase) represent contaminants incorporated on short‐enough timescales to preserve disequilibrium (∼102 yrs for plagioclase). Melt δ18O values calculated from phenocrysts are ∼+7.3–+8.0‰. Where multiple magmas were involved in the same eruption their δ18Omelt values are indistinguishable, implying that their parental mushes were isotopically well‐mixed. However, small (≤0.5‰) but consistent δ18Omelt value gradients occur over millennial timescales at Ōkataina and Taupō, with short‐term ∼0.4–0.5‰ decreases in δ18Omelt values over successive post‐caldera eruptions correlating with increases in 87Sr/86Sr. These changes reflect tens of percent assimilation of a mixture of hydrothermally altered silicic plutonic material and higher‐87Sr/86Sr greywacke. These examples represent the first evidence for assimilation of altered crust into TVZ magmas. The subtle and short‐lived isotopic signals of these interactions are only recognized through the high temporal resolution of the TVZ eruptive record and complementary radiogenic isotope data. Similar interactions may have been obscured in other nominally high‐ or normal‐δ18O magmatic systems.

A volcanological map merging continental and marine areas of the Phlegrean Fields and Procida Island (Southern Italy) is presented at the 1:25,000 scale. The map is based on 1:5,000 field mapping, and marine geology survey carried out during the Italian CAR.G (Geological CARtography, Servizio Geologico d’Italia) project and on bathymetric and seismic data. Geological data are represented on a digital terrain model of the volcano. This allows better visualization of the main morphological, volcanic, and geological features. The legend is organized in seven activity phases identified based on updated absolute ages of eruptions defining periods of high volcanicity and stasis. The geological map highlights the evolutive history of the Phlegrean Fields volcanic field both in the marine and continental portions, and the reconstructed structural framework and evolution of the caldera formed 39.3 Ky ago in its continental and submerged portions.

The phenomenon of dynamic matching was proposed by Carpenter nearly four decades ago. In this work, we perform detailed dynamical studies of the original model studied by Carpenter. Existence of competing mechanisms that influence the extent of dynamic matching with varying depth of the caldera well, as noted by Carpenter, is confirmed. A phase space dynamical viewpoint is provided for the origin of the competing mechanisms. Our results show that the extent of dynamic matching is significantly influenced by the amount of excess energy above the transition state that controls the entrance into the caldera region. Moreover, we find that dynamic matching can persist for fairly deep caldera wells. Quantum dynamical studies are performed to assess the extent of classical‐quantum correspondence in the system and the robustness of the dynamic matching mechanism. [ABSTRACT FROM AUTHOR]

The Taupō Volcanic Zone (TVZ) is the southern extent of the Tonga‐Kermadec volcanic arc and encompasses the Taupō Rift, with the two structures accommodating extension through the central North Island of New Zealand via magmatic and tectonic processes, respectively. Interplay between components of the TVZ and Taupō Rift are evident at Taupō volcano, which exhibits periods of increased seismicity on a decadal scale. One period of increased seismicity occurred in 2001 outside the caldera in the adjacent Taupō Fault Belt. We use seismological analysis to detect and characterize the Taupō Fault Belt seismicity, which aligns in clusters close to active faults, and was preceded by a large cluster of earthquakes beneath Lake Taupō's Western Bay. This cluster and a temporal change in the local stress field imply that a magmatic intrusion beneath the Western Bay initiated the unrest in the fault belt. Our analysis suggests this intrusion may have occurred outside the silicic reservoir at Taupō and that it represents an example of interaction between the regional tectonic and deep mafic magmatic systems at Taupō. Plain Language Summary: The Taupō Volcanic Zone (TVZ) is a large area of volcanism that spans the central North Island of New Zealand. Active volcanism coincides with continental extension, named the Taupō Rift and both are the result of the interaction between the Australian and Pacific plates occurring offshore. At the center of the TVZ is Taupō volcano, a large caldera which undergoes regular phases of seismic unrest involving large numbers of earthquakes and ground shaking. A period of unrest in 2001 contrasts with the other unrest episodes in that most of the seismicity was concentrated in the Taupō Fault Belt rather than within the adjacent caldera, and we hypothesize that its occurrence may provide insight into the interaction between magmatic and tectonic processes around Taupō volcano. Our analysis suggests that the earthquakes in 2001 first occurred beneath Taupō volcano, initiating subsequent seismic activity in the Taupō Fault Belt and temporarily altering the surrounding stress state. We infer that the initial group of earthquakes beneath Taupō volcano coincided with and were triggered by a magmatic intrusion. Therefore, the seismicity in 2001 highlights an example of interaction between the tectonic and deep magmatic systems at Taupō volcano. Key Points: Matched‐filter detection identified 3,782 earthquakes of ML 0.0–2.6 beneath and north of Lake Taupō between January and June 2001Seismicity beneath Lake Taupō suggests an intrusion, possibly mafic, occurred prior to the seismicity within the Taupō Fault BeltThis implies direct interaction between the regional fault network and deep mafic feeder system at Taupō, which may occur elsewhere too [ABSTRACT FROM AUTHOR]

The chemical composition of gases emitted by active volcanoes reflects both magma degassing and shallower processes, such as fluid-rock hydrothermal interaction and mixing with atmospheric-derived fluids. Untangling the magmatic fluid endmember within surface gas emission is therefore challenging, even with the use of well-known magma degassing tracers such as noble gases. Here, we investigate the deep magmatic fluid composition at the Nisyros caldera (Aegean Arc, Greece) by measuring nitrogen and noble gas abundances and isotopes in naturally degassing fumaroles. Gas samples were collected from 32 fumarolic vents at water-boiling temperature between 2018 and 2021. These fumaroles are admixtures of magmatic fluids typical of subduction zones, groundwater (or air saturated water, ASW), and air. The N 2 , He, and Ar composition of the magmatic endmember is calculated by reverse mixing modeling and shows N 2 /He = 31.8 ± 4.5, N 2 /Ar = 281.6, δ 15N = +7 ± 3 ‰, 3He/4He = 6.2 Ra (where Ra is air 3He/4He), and 40Ar/36Ar = 551.6 ± 19.8. Although N 2 /He is significantly low with respect to typical values for arc volcanoes (1,000–10,000), the contribution of subducted sediments to the Aegean Arc magma generation is reflected by the positive δ 15N values of Nisyros fumaroles. The low N 2 /He ratio indicates N 2 -depletion due to solubility-controlled differential degassing of an upper-crustal silicic (dacitic/rhyodacitic) melt in a high-crystallinity reservoir. We compare our 2018–2021 data with N 2 , He, and Ar values collected from the same fumaroles during a hydrothermal unrest following the seismic crisis in 1996–1997. Results show additions of both magmatic fluid and ASW during this unrest. In the same period, fumarolic vents display an increase in magmatic species relative to hydrothermal gas, such as CO 2 /CH 4 and He/CH 4 ratios, an increase of ∼50 °C in the equilibrium temperature of the hydrothermal system (up to 325 °C), and greater amounts of vapor separation. These variations reflect an episode of magmatic fluid expulsion during the seismic crisis. The excess of heat and mass supplied by the magmatic fluid injection is then dissipated through boiling of deeper and peripheral parts of the hydrothermal system. Reverse mixing modeling of fumarolic N 2 -He-Ar has therefore important ramifications not only to disentangle the magmatic signature from gases emitted during periods of dormancy, but also to trace episodes of magmatic outgassing and better understand the state of the upper crustal reservoir. [ABSTRACT FROM AUTHOR]

Mason Spur is a deeply eroded Middle Miocene to Pleistocene (c. 13 to 0.37 Ma) volcanic complex in southern Victoria Land, within the West Antarctic Rift System (WARS). The oldest rocks include a large volume of trachyte ignimbrites that provided abundant volcanic detritus recovered in McMurdo Sound drill cores. The ignimbrites together with early-formed intrusions were strongly deformed during a substantial caldera collapse at c. 13 Ma. Intense erosion modified the volcanic landscape, creating a paleo-relief of several hundred metres. Deep ravines were cut and filled by deposits of multiple lahars probably linked to gravitational collapses of trachyte dome(s). Small-volume trachytic magmas were also erupted, forming lavas and at least one tuff cone. The youngest trachytic activity comprises a lava dome and related block-and-ash-flow deposits, erupted at 6 Ma. Basanite erupted throughout the history of the complex and eruptions younger than 12 Ma are almost exclusively basanite, forming scoria cones, water-cooled lavas, and tuff cones. Three peripheral outcrops are composed of basanitic 'a'ā lava-fed deltas, probably erupted from vents on neighbouring volcanoes at Mount Discovery and Mount Morning. Abundant ignimbrite deposits at Mason Spur differentiate this volcanic complex from others in the WARS. Eruptions were triggered by rift extension initially, yielding the voluminous trachytes sourced from a magma chamber on the margin of the WARS. Later mafic eruptions were associated with deep crustal faults related to residual intraplate deformation. These results add important details to the eruptive history of the intracontinental WARS. [ABSTRACT FROM AUTHOR]

This paper considers geochemical features of the Au-Ag epithermal mineralization at the Kayenmyvaam volcanic uplift (KVU) situated in the middle of the Chukchi segment which is part of the inner zone of the Okhotsk–Chukchi volcanogenic belt (OChVB). New evidence is presented concerning the composition and concentrations of trace elements, including REEs, in the ores of Au-Ag deposits (Arykevaam, Kyaenmyvaam, and Televeem). The ores were found to be enriched in a wide range of trace elements (Li, Se, Mo, Au, Ag, As, Sb, Cu, Pb, In, Cd, Tl, Zn, Bi, Te, and W). The enrichment ratios vary between a few times (Li, Se, Bi, Zn, Tl, In) to tens (Mo, Te, Pb, Cd), hundreds (As, Cu), thousands and tens of thousand times (Au, Ag, Sb). Comparative analysis of the distribution patterns of trace elements shows synchronous enrichment of the ores in similar sets of trace elements. The ores were found to be dominated by light "hydrophile" lanthanoids of the "cerium" group, slightly inclined near-chondrite patterns, without obvious europium maxima and minima, which have configurations similar to the REE patterns of volcanic rock sequences of the andesite–diorite series. The ore-forming fluids belonged to an NaCl–H2O hydrothermal system enriched in Cl relative to F; the Y/Ho ratios in the ores correspond with the range of ratios characteristic for present-day hydrothermal fluids in the backarc basins. The low Co/Ni ratios in the ores probably reflect a large involvement of meteoric near-surface fluids in the mineralization. The Ce/Ce* and Eu/Eu* ratios vary between slightly negative to moderately positive values (Ce/Ce* between 0.71 and 1.07) and (Eu/Eu* between 0.63 and 1.14). This combination of Ce/Ce* and Eu/Eu* corresponds to oxidizing conditions that were existent during the mineralization. The geochemical data indicate andesitic magmas and meteoric waters as the most likely sources of the fluids. The results classify the mineralization under study as belonging to the high sulfidation epithermal class. [ABSTRACT FROM AUTHOR]

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The transport and degassing pathways of volatiles through large silicic magmatic systems are central to understanding geothermal fluid compositions, ore deposit genesis, and volcanic eruption dynamics and impacts. Here, we document sulfur (S), chlorine (Cl), and fluorine (F) concentrations in a range of host materials in eruptive deposits from Taupō volcano (New Zealand). Materials analysed are groundmass glass, silicic melt inclusions, and microphenocrystic apatite that equilibrated in shallow melt-dominant magma bodies; silicic melt and apatite inclusions within crystal cores inferred to be sourced from deeper crystal mush; and olivine-hosted basaltic melt inclusions from mafic enclaves that represent the most primitive feedstock magmas. Sulfur and halogen concentrations each follow distinct concentration pathways during magma differentiation in response to changing pressures, temperatures, oxygen fugacities, crystallising mineral phases, the effects of volatile saturation, and the presence of an aqueous fluid phase. Sulfur contents in the basaltic melt inclusions (~ 2000 ppm) are typical for arc-type magmas, but drop to near detection limits by dacitic compositions, reflecting pyrrhotite crystallisation at ~ 60 wt. % SiO2 during the onset of magnetite crystallisation. In contrast, Cl increases from ~ 500 ppm in basalts to ~ 2500 ppm in dacitic compositions, due to incompatibility in the crystallising phases. Fluorine contents are similar between mafic and silicic compositions (< 1200 ppm) and are primarily controlled by the onset of apatite and/or amphibole crystallisation and then destabilisation. Sulfur and Cl partition strongly into an aqueous fluid and/or vapour phase in the shallow silicic system. Sulfur contents in the rhyolite melts are low, yet the Oruanui supereruption is associated with a major sulfate peak in ice core records in Antarctica and Greenland, implying that excess S was derived from a pre-eruptive gas phase, mafic magma recharge, and/or disintegration of a hydrothermal system. We estimate that the 25.5 ka Oruanui eruption ejected > 130 Tg of S (390 Tg sulfate) and up to ~ 1800 Tg of Cl, with potentially global impacts on climate and stratospheric ozone. [ABSTRACT FROM AUTHOR]

The main cause of tsunamis is large subduction zone earthquakes with seismic magnitudes Mw > 7, but submarine volcanic processes can also generate tsunamis. At the submarine Sumisu caldera in the Izu–Bonin arc, moderate‐sized earthquakes with Mw < 6 occur almost once a decade and cause meter‐scale tsunamis. The source mechanism of the volcanic earthquakes is poorly understood. Here we use tsunami and seismic data from the recent 2015 event to show that abrupt uplift of the submarine caldera, with a large brittle rupture of the ring fault system due to overpressure in its magma reservoir, caused the earthquake and tsunami. This submarine trapdoor faulting mechanism can efficiently generate tsunamis due to large vertical seafloor displacements, but it inefficiently radiates long‐period seismic waves. Similar seismic radiation patterns and tsunami waveforms due to repeated earthquakes indicate that continuous magma supply into the caldera induces quasi‐regular trapdoor faulting. This mechanism of tsunami generation by submarine trapdoor faulting underscores the need to monitor submarine calderas for robust assessment of tsunami hazards. Plain Language Summary: Tsunamis are mainly caused by large submarine earthquakes, but submarine volcanic processes can also trigger tsunamis. Disproportionately large tsunami waves have been generated every decade by moderate‐sized volcanic earthquakes at a submarine volcano with a caldera structure, called Sumisu caldera, in the Izu–Bonin arc, south of Japan. Despite the moderate earthquake size, the maximum wave heights of the tsunamis were about a meter, and their source mechanism has been controversial. In this study, we used tsunami and seismic data from a recent earthquake to show that the submarine caldera abruptly uplifts due to brittle rupture of its intra‐caldera fault system driven by overpressure of magma accumulating in its underlying magma reservoir and generates large tsunamis almost once a decade. The atypical source mechanism for tsunami generation suggests that it is important to monitor active submarine calderas for assessing tsunami hazards. Key Points: Large tsunamis are generated by moderate‐sized volcanic earthquakes at a submarine calderaTsunami and seismic data indicate that abrupt uplift of the submarine caldera by trapdoor faulting causes large tsunamisContinuous magma supply into the submarine caldera induces submarine trapdoor faulting on a decadal timescale [ABSTRACT FROM AUTHOR]

Abstract The Taupō Volcanic Zone (TVZ) is the southern extent of the Tonga‐Kermadec volcanic arc and encompasses the Taupō Rift, with the two structures accommodating extension through the central North Island of New Zealand via magmatic and tectonic processes, respectively. Interplay between components of the TVZ and Taupō Rift are evident at Taupō volcano, which exhibits periods of increased seismicity on a decadal scale. One period of increased seismicity occurred in 2001 outside the caldera in the adjacent Taupō Fault Belt. We use seismological analysis to detect and characterize the Taupō Fault Belt seismicity, which aligns in clusters close to active faults, and was preceded by a large cluster of earthquakes beneath Lake Taupō's Western Bay. This cluster and a temporal change in the local stress field imply that a magmatic intrusion beneath the Western Bay initiated the unrest in the fault belt. Our analysis suggests this intrusion may have occurred outside the silicic reservoir at Taupō and that it represents an example of interaction between the regional tectonic and deep mafic magmatic systems at Taupō.