Journal of Volcanology and Geothermal Research最新文献

{"title":"Investigating the connection between superhydrous melts, magma reservoir nucleation and the scarcity of mafic eruptions in post-collisional settings","authors":"Alissa Näpflin ,&nbsp;Răzvan-Gabriel Popa ,&nbsp;Ioan Seghedi ,&nbsp;Olivier Bachmann","doi":"10.1016/j.jvolgeores.2026.108542","DOIUrl":"10.1016/j.jvolgeores.2026.108542","url":null,"abstract":"<div><div>Magma reservoir emplacement in the brittle upper-crust typically requires prolonged heating to modify host-rock rheology, allowing magma to accumulate rather than erupt. In thermally immature crust, early eruptions are expected to be mafic, yet many volcanic provinces, particularly those with water-rich melts, lack significant initial mafic volcanism, suggesting an alternative trapping mechanism. We investigate this using Caraci volcano (Romania's Apuseni Mountains), a water-rich system that started with relatively differentiated, andesitic eruptions. The first eruptions at Caraci extruded water-rich (5–6 ± 0.35 wt% dissolved H₂O) amphibole-plagioclase andesites (890–920 ± 22 °C) stored at water-saturated conditions in the upper-crust (∼2 ± 0.5 kbar). These magmas were associated with superhydrous primitive melts (&gt;6 wt% H₂O), which evolved in a polybaric system (crystallization pressure varying from 2 to 8 ± 0.5 kbar), evidenced by high-Mg amphibole and delayed plagioclase crystallization. These deeper storage melts likely reached water saturation during ascent towards the upper crust, inducing degassing and crystallization, which increased viscosity and enabled stalling in the cold crust, explaining the lack of initial mafic eruptions and providing the efficient trapping mechanism in a thermally immature crust. Progressive drying of the source and generation of less hydrous magmas initiated the eruptions and construction of the stratovolcano, and ultimately terminated the system. As a result, the final eruption extruded somewhat drier (4–4.5 ± 0.35 wt% H₂O), hotter (930–960 ± 45 °C) pyroxene-bearing andesites erupted from water-undersaturated storage. This trapping mechanism of water-rich magmas may explain the typical scarcity of mafic volcanism in arc and post-collisional settings.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"472 ","pages":"Article 108542"},"PeriodicalIF":2.3,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146081931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modelled versus tracked ballistic trajectories of volcanic bombs at Stromboli (Italy)","authors":"A. Sork ,&nbsp;L. Watson ,&nbsp;B. Kennedy ,&nbsp;R.H. Fitzgerald ,&nbsp;J. Taddeucci ,&nbsp;M. Sellier ,&nbsp;P. Scarlato ,&nbsp;E. Del Bello ,&nbsp;T. Ricci","doi":"10.1016/j.jvolgeores.2026.108543","DOIUrl":"10.1016/j.jvolgeores.2026.108543","url":null,"abstract":"<div><div>Validation for computational modelling of volcanic ballistic projectiles (VBPs) has often been accomplished by replication of field-surveyed VBP distributions. However, a range of ejection parameters can result in the same impact location, with differing impact energies and therefore hazard implications. Ballistic hazard models must accurately represent the whole trajectory to better estimate ballistic energy and interpret eruption dynamics.</div><div>We examine model performance by directly measuring Strombolian VBP ejection parameters and trajectories from high-speed video and comparing with modelled trajectories using the same parameters. We illustrate the effects of velocity and size on drag. We synthesize and investigate different methods by which the Reynolds number (<em>Re</em>) - drag coefficient (C_D) relationship is incorporated into models and how this affects modelling results. Our computational model allows for application of different existing <em>Re</em>-C_D methods and direct comparison to tracked trajectories on the metrics of impact distance and peak height.</div><div>Even with validated ejection parameters and appropriate <em>Re</em>-C_D relationships, the model rarely accurately reproduces both height and distance within a 5% threshold. The most common scenario is model overestimation of both metrics. The gas jet is the largest factor contributing to this discrepancy. Significant slowing of VBPs in excess of gravity is observed while bombs are rising (and within the gas jet radius) but not while falling. Slowing in the gas jet is potentially caused by friction with ash and lapilli, surface temperature effects, or other fluid dynamics effects.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"472 ","pages":"Article 108543"},"PeriodicalIF":2.3,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146081932","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Subsurface mass monitoring at Theistareykir geothermal field, Iceland, using hybrid gravimetry","authors":"B. Giuliante ,&nbsp;U. Riccardi ,&nbsp;J. Hinderer ,&nbsp;P. Jousset ,&nbsp;T. Pivetta ,&nbsp;A.K. Mortensen ,&nbsp;J.D. Bernard ,&nbsp;S. Schröder ,&nbsp;C.M. Krawczyk","doi":"10.1016/j.jvolgeores.2026.108539","DOIUrl":"10.1016/j.jvolgeores.2026.108539","url":null,"abstract":"<div><div>Understanding underground mass redistribution in geothermal fields is fundamental to assess the harnessing in geothermal reservoir. Here we apply the hybrid gravimetry method at Theistareykir geothermal field (Northern Iceland). We collected absolute and discrete microgravity measurements yearly within the geothermal field at fixed locations jointly with continuously recorded gravity time series with two superconducting gravimeters (SGs). Data acquisition started in 2017 at the onset of the anthropogenic perturbation. We present and interpret the discrete and continuous gravity datasets from 2017 until 2024 in an attempt to characterize fluid redistribution within the subsurface. The hybrid gravimetry dataset reveal a gravity decrease nearby the extraction area with rates of about −20 μGal per year for the 2017–2022 period, that reduces to few μGal per year in the last two years (2023–2024). An increase in gravity is observed towards the injection area (around 5 to 10 μGal per year). Time-lapse gravity maps reveal a localized gravity decrease (with a maximum of −60 μGal), not collocated with the zone of largest extraction and furthermore an additional trendline of gravity increase (+15 μGal) is observed towards the North. The first suggests a possible lower permeability subsurface zone within the geothermal field, the latter, is in accordance with the direction of the fault system that crosses Theistareykir field, suggesting potential underground fluid pathways. From 2023, although extraction and injection rates did not change, we evidence a change in the gravity trends outside the western part of the geothermal field possibly associated with the 2023 magmatic intrusion.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"472 ","pages":"Article 108539"},"PeriodicalIF":2.3,"publicationDate":"2026-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146190870","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reconstruction of the plinian phase of the 7.3 ka “Akahoya” caldera-forming eruption at the Kikai caldera, Japan","authors":"Yusuke Haruta ,&nbsp;Fukashi Maeno ,&nbsp;Yujiro J. Suzuki","doi":"10.1016/j.jvolgeores.2026.108541","DOIUrl":"10.1016/j.jvolgeores.2026.108541","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Most caldera-forming eruptions begin as plinian events. These plinian phases cause magma chamber decompression and result in subsequent caldera collapse and climactic phases characterized by large-scale pyroclastic density currents (PDCs). It is thus essential to understand the eruption sequence and parameters of the plinian phases to constrain the mechanisms of caldera-forming eruption. Here we reconstruct the detailed sequence of the plinian phase of the 7.3 ka caldera-forming eruption (Akahoya eruption) at the Kikai caldera, Japan, based on a geological survey and plume modeling. The proximal facies of the plinian phase deposits indicate that the source vent was located in the western part of the caldera. The eruptive deposits can be divided into seven subunits (Units A0, A1, A2, A3, A4a, A4b, and B) based on their lithofacies. These subunits were further classified into three groups, separated by minor erosive features. The first group comprised an ash fall layer (Unit A0) distributed only in the proximal area within 20 km of the source vent. The second group comprised a pumice fall layer (Unit A1) distributed within 80 km-distance from the Kikai caldera, and overlying PDC or co-PDC fall deposits (Unit A2) distributed in the proximal area. The third group in the proximal area comprised multiple pumice fall layers (Units A3 and A4a) and PDC deposits (Unit B); whilst in the distal area it comprised up to six pumice fall layers intercalated with ash fall layers (Units A4a and A4b). The uppermost pumice fall layers of the third group (Unit A4b) exhibited a more widespread distribution. Based on fall deposit data and plume modeling, eruptive volumes and mass discharge rates (MDRs) were estimated for the three groups to be &lt;span&gt;&lt;math&gt;&lt;mn&gt;0.0013&lt;/mn&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;0.020&lt;/mn&gt;&lt;/math&gt;&lt;/span&gt; km&lt;sup&gt;3&lt;/sup&gt; (first group), &lt;span&gt;&lt;math&gt;&lt;mn&gt;0.22&lt;/mn&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;1.0&lt;/mn&gt;&lt;/math&gt;&lt;/span&gt; km&lt;sup&gt;3&lt;/sup&gt; and &lt;span&gt;&lt;math&gt;&lt;mn&gt;3.1&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mn&gt;7&lt;/mn&gt;&lt;/msup&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;1.5&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mn&gt;8&lt;/mn&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; kg/s (second group), and &lt;span&gt;&lt;math&gt;&lt;mn&gt;5.0&lt;/mn&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;14.0&lt;/mn&gt;&lt;/math&gt;&lt;/span&gt; km&lt;sup&gt;3&lt;/sup&gt; and &lt;span&gt;&lt;math&gt;&lt;mn&gt;5.2&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mn&gt;8&lt;/mn&gt;&lt;/msup&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;2.2&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mn&gt;9&lt;/mn&gt;&lt;/msup&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;/math&gt;&lt;/span&gt;kg/s (third group). The results revealed that the plinian phase of the Akahoya eruption consisted of three eruptive events: Event 1, a small-scale explosive eruption; Event 2, a plinian eruption (MDR up to &lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mn&gt;8&lt;/mn&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; kg/s), transitioned into the eruption of small-scale PDCs; Event 3, a large-scale plinian eruption (MDR up to &lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mn&gt;9&lt;/mn&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; kg/s) marked by continuous partial column collapses. This eruption sequence is characterized by a gradual increase in eruptive intensity and scale, similar to plinian phases of many caldera-forming erupti","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"472 ","pages":"Article 108541"},"PeriodicalIF":2.3,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146190951","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrous upper mantle facilitated alkali basalt genesis in the Southeastern Carpathians, Romania","authors":"Levente Patkó ,&nbsp;Ákos Kővágó ,&nbsp;Thomas Pieter Lange ,&nbsp;Alexandru Szakács ,&nbsp;Monika Huraiová ,&nbsp;Márta Berkesi ,&nbsp;László Előd Aradi ,&nbsp;Szilveszter Gergely ,&nbsp;Ábel Szabó ,&nbsp;Károly Németh ,&nbsp;Csaba Szabó ,&nbsp;István János Kovács","doi":"10.1016/j.jvolgeores.2026.108540","DOIUrl":"10.1016/j.jvolgeores.2026.108540","url":null,"abstract":"<div><div>This study investigates the structural hydroxyl content in clinopyroxenes from five cumulate xenoliths hosted by alkali basaltic pyroclastic rocks collected from the Perşani Mountains Volcanic Field (southeastern Transylvania, Romania), revealing structural hydroxyl concentrations ranging from 261 to 436 ppm wt. From these measurements, the ‘water’ content of the equilibrium parental alkali basaltic melt was estimated at 1.2 to 2.5 wt%, consistent with global values for alkali basalts. The mantle source ‘water’ content was also determined and resulted to be a ‘water’-rich mantle volume, ranging from 400 to 840 ppm wt. under batch melting and 310 to 660 ppm wt. for fractional melting models. The hydrous signature appears to be linked to the influence of an earlier subduction event, sustained by continued fluid release from remnants of the sinking slab at asthenospheric depths. The findings highlight the crucial influence of ‘water’ in upwelling mantle material, especially in regions affected by slab rollback and detachment, as is the case in the study area of the East Carpathian bend zone, where ‘water’ governs the extent of partial melting and enhances melt generation.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"472 ","pages":"Article 108540"},"PeriodicalIF":2.3,"publicationDate":"2026-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146057591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The nucleation and growth of mixed H2O–CO2 bubbles in magmas","authors":"Patrick Sullivan ,&nbsp;Edward W. Llewellin ,&nbsp;Fabian B. Wadsworth ,&nbsp;Simone Colucci ,&nbsp;Halim Kusumaatmaja","doi":"10.1016/j.jvolgeores.2026.108538","DOIUrl":"10.1016/j.jvolgeores.2026.108538","url":null,"abstract":"<div><div>Volcanic eruptions are driven by the nucleation and growth of gas bubbles that form when volatile species dissolved in magma become supersaturated. Previous models for bubble growth have focussed on H₂O; however, CO₂ also plays a fundamental role in the nucleation and growth of gas bubbles. Here, we develop a numerical model to explore the nucleation and growth of bubbles containing both H₂O and CO₂ in magma of arbitrary composition. Nucleation is modelled as a Poisson process using classical nucleation theory with composition-appropriate solubility models for the mixed H₂O–CO₂ fluid. We find that CO₂ dramatically increases the depth of bubble nucleation compared with H₂O-only systems; for a case-study rhyolite (Krafla, Iceland) CO₂ increases nucleation depth from 130 m (H₂O-only) to 760 m if CO₂ is included (a factor of 6 increase in nucleation pressure); for a case-study basalt (Fagradalsfjall, Iceland), nucleation occurs at 13 km depth if CO₂ is included, but does not occur at all if H₂O is the only volatile species. Post-nucleation growth of the bubbles is investigated by extending a ‘shell model’ to include CO₂ as well as H₂O. The species are coupled via a mixed equation-of-state for the gas phase, introducing a co-dependence on their solubility that allows H₂O to exsolve at greater depth when CO₂ is present. As a result, exsolution of a small volume of CO₂ can trigger the exsolution of a much larger volume of H₂O, driving rapid, disequilibrium bubble growth. Our findings show that accounting for mixed H₂O–CO₂ volatile compositions is essential for accurate modelling of magma ascent and eruption dynamics.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"472 ","pages":"Article 108538"},"PeriodicalIF":2.3,"publicationDate":"2026-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146190863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Investigating the seismic structure of shallow magmatic conduits: Insights from the Salina Island (southern Italy)","authors":"I. Granados-Chavarría ,&nbsp;F. Di Luccio ,&nbsp;M. Calò ,&nbsp;D. Famiani ,&nbsp;M. Lupi ,&nbsp;M. Palano ,&nbsp;G. Ventura","doi":"10.1016/j.jvolgeores.2026.108536","DOIUrl":"10.1016/j.jvolgeores.2026.108536","url":null,"abstract":"<div><div>The plumbing systems of closely spaced individual volcanoes and volcanic fields may be very complex due to the interaction (or not) of different magma storage zones and magma pathways at variable depths. Ambient noise tomography unveils the shallow seismic structure of Salina Island (Southern Italy), which is characterized by 6 proximal and partly overlapping volcanoes developed between 244 and 15.6 ka. We use two months of continuous data from 40 nodal stations deployed in 2023 at uneven interstation distances. This seismic array yields tomographic maps down to 1.5 km depth in which the geometry of the volcano flank collapses and shallower plumbing systems of eruptive fissures are clearly imaged. Shear wave velocity maps reveal the main structures and deposits of the ‘twin’ stratovolcanoes of Monte dei Porri, to the west, and Monte Fossa delle Felci, to the east. High velocity anomalies beneath these volcanoes become less pronounced at ∼200 m b.s.l. revealing the transition from submarine to subaerial lava flows. 3D images of the eastward dipping subcircular conduits below the main volcanoes suggest that the deep feeding system is located offshore to the east.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"471 ","pages":"Article 108536"},"PeriodicalIF":2.3,"publicationDate":"2026-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146038433","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An analog experiment showing varying shapes of pyroclasts by including crystals and bubbles","authors":"Sayaka Oda,&nbsp;Atsuko Namiki","doi":"10.1016/j.jvolgeores.2026.108534","DOIUrl":"10.1016/j.jvolgeores.2026.108534","url":null,"abstract":"<div><div>Low-viscosity basaltic and basaltic andesitic magmas form pyroclastic materials with various shapes, such as scoria, volcanic ash, and Pele’s hair, through fracturing. Brittle fracture of low-viscosity magma is unlikely. Instead, fluid dynamical deformation during the eruption may cause the magma to tear off. The various morphologies of pyroclast shapes should be determined by their deformation history. High crystallinity in magma increases its effective viscosity, potentially enabling brittle-like fracture. To understand how the shape of pyroclastic material produced by low-viscosity magma is determined, we conducted uniaxial extension experiments using a magma analog mixture of liquid, solid, and gas phases. Our experiments demonstrate that fluids with a high solid particle fraction (<span><math><mo>&gt;</mo></math></span>0.3) tend to tear off at a small strain, thereby generating a rough fracture surface. The solid particles were undeformable, and a high particle fraction reduced the thickness of the deformable liquid region. Thin liquid films are easily disrupted, and thus a small strain can break the entire fluid. In contrast, a particle-free bubbly fluid generates thin threads. Bubbles can coalesce to create a large bubble and deform. Vertically elongated bubbles split the fluid in the longitudinal direction, forming threads. The former mechanism may generate the irregularly shaped scoriae, and the latter forms Pele’s hair. Our experimental results indicate that suspended crystals and bubbles in magma affect not only the physical properties of magma but also the fracture manner, thereby determining the shapes of pyroclasts.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"471 ","pages":"Article 108534"},"PeriodicalIF":2.3,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146038434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hyperspectral imaging, mineralogy, and degassing: Exploring the volcanic hydrothermal system of Red Crater, Tongariro, Aotearoa New Zealand","authors":"Daniel Sturgess ,&nbsp;Gabor Kereszturi ,&nbsp;Agnes Mazot ,&nbsp;Rachelle Sanchez ,&nbsp;Antonio M. Álvarez-Valero ,&nbsp;Vladyslav Zakharovskyi","doi":"10.1016/j.jvolgeores.2026.108535","DOIUrl":"10.1016/j.jvolgeores.2026.108535","url":null,"abstract":"<div><div>Hydrothermal alteration on volcanoes can compromise the strength and permeability of the host rock, contributing to flank collapses (e.g., Te Maari, 2012) and phreatic eruptions (e.g., Whakaari, 2019). Alteration processes occur at volcanoes hosting hydrothermal systems, where hot, acidic fluid flow is driven by a supply of magmatic heat and gas inputs, resulting in the dissolution of primary minerals and the deposition of secondary assemblages. We investigated hydrothermal alteration at Red Crater, Tongariro, Aotearoa New Zealand, using a combination of laboratory and airborne hyperspectral imaging, mineralogical, and geochemical techniques. Two distinct alteration styles were identified: (1) advanced argillic alteration, characterised by amorphous silica, kaolinite, and alunite, primarily focused at the Red Crater scoria cone, and (2) silicification at Oturere and the Emerald Lakes. The distribution of these units was mapped using supervised image classification of airborne hyperspectral data. Textural and isotopic analyses suggest acid-sulphate alteration is primarily driven by the oxidation of rising H₂S in a steam-heated environment. Red Crater hosts four main regions of heightened degassing, coinciding with geothermal surface features and hydrothermal alteration deposits, with 26.2 <span><math><mo>±</mo></math></span>1.5 t/d of CO₂ emissions and an H₂S flux of 131.1 g/m²/d. This study presents a conceptual model of hydrothermal alteration processes at Red Crater. Our mapping of alteration and degassing can indicate areas of potential future hazards, and may support simulations assessing flank instability, improving hazard assessment at this active vent.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"471 ","pages":"Article 108535"},"PeriodicalIF":2.3,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146038344","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Granophyric crystallization within the Gomez Tuff, the world's largest pantelleritic ignimbrite, Davis Mountains, Trans-Pecos Texas","authors":"Don F. Parker ,&nbsp;John C. White ,&nbsp;Kevin Urbanczyk","doi":"10.1016/j.jvolgeores.2025.108527","DOIUrl":"10.1016/j.jvolgeores.2025.108527","url":null,"abstract":"<div><div>The Gomez Tuff was erupted ∼37 Ma as an explosive component of widespread silicic lava (“flood rhyolite”). The Gomez eruption covered an area &gt; 4000 km², with an estimated dense rock equivalent volume of ∼220 km³, making it the largest known pantelleritic ignimbrite. The eruption formed a ∼18 × 24 km-diameter caldera, within which the ignimbrite ponded to thicknesses approaching 500 m. Estimated water content (∼1.9 wt%) of the erupting magma was relatively low, favoring eruption of dense pyroclastic flows over pyroclastic falls. Within thicker sections of the tuff, rheomorphic flow created flow banding, large folds and ramp structures. Granophyric crystallization (af, cpx, aenig, amph, qz) destroyed the fragmental nature of the tuff, except for abundant lithic inclusions.</div><div>Gomez phenocryst assemblages include alkali feldspar (Or₃₆_–₃₉) and quartz ± fayalite, with minor hedenbergite, ilmenite and apatite. Magmatic conditions previously deduced from these assemblages assuming <em>P</em> = 2 kbar, a magmatic temperature of ∼750 °C from phase equilibria and not using fayalite in the calculations indicated a temperature range of ∼870 to 750 °C, with oxygen fugacity (ΔFMQ ∼ −1.92) below the NNO buffer (<span><span>Parker and White, 2008</span></span>). Alternative calculations suggest ranges of 855 to 766 °C, assuming fayalite stable in all samples, and 900 to 700 °C, assuming aenigmatite was stable in lieu of fayalite. The calculations assuming neither fayalite nor aenigmatite was stable as a phenocryst are preferred, as fayalite was only observed in two samples and aenigmatite was not observed as a phenocryst in any sample.</div><div>The original Peralkalinity Index (P·I.) was likely ∼1.3. During granophyric crystallization (at ∼687 °C) in thick sections of the tuff, groundmass feldspar increased its iron content and became more potassic, driving glass and calculated groundmass compositions to ∼1.48. In the final stages of crystallization, groundmass pyroxene approached stoichiometric aegirine and arfvedsonite became less magnesian and more sodic, suggesting that the P·I. of the final crystallizing glass neared 1.8, judging from comparison to the Type 1 Green Tuff of Pantelleria.</div><div>We model the Gomez magma chamber as an extensive sill, in which pantelleritic magma accumulated above a reservoir of trachytic magma. Eruption of the ignimbrite efficiently drained the evolved magma, allowing the eruption of trachyte lava, which subsequently filled the caldera.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"471 ","pages":"Article 108527"},"PeriodicalIF":2.3,"publicationDate":"2026-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145979052","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}