Journal of Volcanology and Geothermal Research最新文献

Cotopaxi is a large, ice-capped stratovolcano located in the Ecuadorian Andes. After 72 years of repose, Cotopaxi erupted on August 14, 2015. The precursory activity included long-period (LP) events followed by volcano-tectonic (VT) earthquakes, very-long-period events accompanying LP signals (VLP/LP events), tremor, deformation and SO₂ emissions. VLP/LP events were first observed at Cotopaxi in 2002, and persistently occurred from 2009 to 2014 and during the 2015 eruptions. Previous studies of the VLP/LP seismicity suggested that these events originated by repetitive volume changes in a crack due to degassing of water from magma at a depth of 2–3 km beneath the NE flank. Based on this interpretation, we estimated the magma volumes related to individual VLP/LP events from 2009 to 2015, which were systematically extracted from continuous seismic records of the Cotopaxi broadband seismic network. Based on the accumulated magma volume and the VLP/LP activity, our study is divided into seven periods (phases A − G), during which the magma supply rate significantly fluctuated. In phase E (June 1–July 27, 2015), before the eruptions, the magma supply rate increased. Degassing at the VLP source generated gas flows in the conduit and pre-eruptive tremor, gradually drying out a shallow hydrothermal system. In phase F (July 28–September 15, 2015), we estimated the highest magma supply rate, leading to magma fragmentation at the VLP source and eruptions accompanied by tremor. In phase G (September 16–December 29, 2015), the magma supply rate decreased, and overall eruptive activity, VLP/LP events, and tremor gradually waned. These results indicate that the VLP/LP events were likely generated by degassing from magma supplied to the VLP source through an intruded dike before and during the eruptions. The VLP/LP activity provides critical useful information about the magma supply rates that controlled eruptive and gas emission activity at Cotopaxi during this period and may help to constrain magma volumes during future reactivations.

The volcanic evolution of Szent György Hill in the Miocene-Pleistocene Bakony–Balaton Highland Volcanic Field (BBHVF) is examined. Image analysis of cut rock surfaces was conducted to reveal the ratio of different juvenile and lithic components within the pyroclastic samples collected from different layers of the pyroclastic sequence. Results suggest decreasing phreatomagmatic activity over time, with a shift to magmatic-dominated eruptions represented by decreasing ratio of the sideromelane volcanic glass and increasing ratio of the magmatically-fragmented components (basaltic clasts, tachylite) successively. The changing water supply is inferred to have been played a crucial role in changes of eruption style due to the variations of external water availability from the pre-volcanic porous-media aquifers of Miocene siliciclastic sedimentary rock-dominated substrate. The eruptive history of the Szent György Hill is characterized by distinct phases starting with an initial phreatomagmatic eruption in water-saturated clastic sediments forming a shallow maar crater accompanied with a formation of a protodiatreme. Once the eruption locus reached the local karst water level, the phreatomagmatic explosions became sustained as recorded in the tephra succession by an increased accidental lithic content and the presence of ash aggregates indicating vapor-rich ejecta and ash accretion. The depletion of external water supply generated a subsequent magmatic explosive phase with lava effusion within the newly formed crater, building confined lava accumulation within. During the last phase of the eruptive sequence, phreatomagmatism was renewed, building up an intra-maar tuff ring, and finally followed by a spatter cone after a renewed repeated phreatomagmatic-magmatic transition. This study highlights the polycyclic nature of Szent György Hill's volcanic activity creating a complex volcanic edifice and suggesting a common eruption scenario for small-volume eruptions within combined aquifers that are dominated by the thick topmost porous media over high water yield karstic systems. These findings emphasize the role of eruption dynamics of monogenetic volcanic systems controlled by combined aquifer influence driven not only by the pure external conditions but also the evolving crater's hydrogeology.

In the Southern Volcanic Zone of Chile (SVZ, 33–46°S) the interaction between regional fault systems and volcanic centers forms high enthalpy geothermal systems. This study aims to understand the hydrogeochemical processes (e.g., water mixing and water-rock interaction) that control the sources and distribution of Li, B and Sr in geothermal conditions. We selected two high-enthalpy hydrothermal systems that host diverse geothermal features, including boiling springs, fumaroles and geysers: Alpehue and Puyehue-Cordón Caulle. We used a combination of geochemical and isotopic methods, including stable isotopes of lithium (δ⁷Li), boron (δ¹¹B) and strontium (⁸⁷Sr/⁸⁶Sr) in a set of samples from thermal emissions, river waters and volcanic rocks. We analyze the potential sources of dissolved boron, lithium and strontium, and the hydrogeochemical processes that control their behavior in the systems. At Alpehue, geothermal fluids showed isotopic compositions (δ⁷Li ≈ +0.5‰, δ¹¹B ≈ −3.3‰) similar to those in volcanic rocks (δ⁷Li = +1.39‰, δ¹¹B = −2.2‰), suggesting high-temperature water-rock interaction. At Puyehue-Cordón Caulle, the isotopic signal varies inside the large-scale volcanic system: at the steam-heated zone, composed of high temperature features (fumaroles and mud pools) and affected by argillic alteration, waters have boron isotopic signals similar to altered rocks (δ¹¹B ≈ +15‰), while lithium matched the signal of magmatic fluids (δ⁷Li ≈ −2.0‰). In contrast, peripheral bicarbonate springs (T ∼ 50 °C) indicate equilibrium with a deep neutral geothermal reservoir, showing the signal of fresh volcanic rocks (δ⁷Li ≈ +5.9‰; δ¹¹B ≈ −2.2‰) but with very low Li and B concentrations due to mixing with cold surficial waters. The results support a model where geothermal water acquires the isotopic signal from the host rocks, with a variable contribution of magmatic fluids, which is enhanced in steam-heated water conditions. The multi-isotopic analysis conducted in this study identified three main processes controlling the distribution of Li, B and Sr: (1) heat-fluid-rock interaction, controlled by the isotopic signature of each hosting rock, (2) mixing with magmatic fluids, presumably influenced by regional fault systems, and (3) hydrothermal alteration, influencing rock leaching and imprinting its isotopic signature on thermal water.

Ischia Island is an active volcano representing the emerged sector of an E-W trending volcanic ridge largely extending undersea. Its collapsing behaviour, mainly in the form of fast-moving, terrestrial and submarine debris avalanches, has been recognized during the Holocene, but much less is known about previous gravity-driven processes. Using high-resolution multibeam bathymetric data and seismic reflection profiles, we provide evidence that the Island's southwestern flank has been involved in a slow-moving, deep-seated slope deformation that has displaced large volumes of its apron since the Late Pleistocene and until very recent or contemporary times. A long tongue of deformed seafloor, spreading up to 45 km from the Island over an area of 330 km², between 500 and 1300 m water depths, has been detected along its southwestern slope. Different types of mass movements, genetically associated with each other, characterize this landslide: 1) a basal slump anticline, corresponding to a bulge on the bathymetry detaching at about 400 m sub-bottom depth; 2) an intermediate-mass movement chiefly consisting of debris avalanches and debris/turbiditic flows; 3) an upper mass movement consisting of hundred-metre size slumps detaching at relatively shallow depths. Conservative estimates indicate that at least 50 km³ of volcano-clastic and hemipelagic deposits have been mobilized, most of which comprise the basal slump anticline. This submarine landslide can be explained as a gravity failure of the continental slope unrelated to volcanism or rather as a process related to the dynamics of the volcanic edifice, which would imply volcano-spreading.

Raman spectroscopic determination of sulfur species molalities in hydrothermal fluids requires correct assignment and knowledge of the scattering efficiencies of Raman bands. Therefore, we studied the Raman spectra of NaHSO₄ and H₂SO₄ solutions experimentally to 700 °C, and of Na₂SO₄, NaHSO₄, H₂SO₄, and H₂SO₃ solutions by ab initio molecular dynamics simulation at 727 °C. The results indicate that the scattering efficiencies of the ν_s(SO₃), ν_as(SO₃), and ν(S–OH) Raman bands of HSO₄⁻(aq) depend on the H⁺ activity. The asymmetric shape of the ν_s(SO₃) Raman band of HSO₄⁻(aq) becomes more symmetric with increasing temperature, which correlates with decreasing hydrogen bonding in the molecular environment. Proton activity and ion pairing do not have a large effect on the change in the band asymmetry with temperature, and a resonance effect on the band shape is not observed. Therefore, we attribute the asymmetric shape of the ν_s(SO₃) Raman band of HSO₄⁻(aq) mostly to hydrogen bonding of the proton in the H–OSO₃⁻ molecule with water in its environment. The AIMD simulations clarify assignments of Raman bands of H₂SO₄⁰, specifically to ν_s(SO₂) and ν_as(SO₂) at ∼1140 cm⁻¹ and ∼1370 cm⁻¹, to ν_s(SO₄) and ν_as(SO₄) at ∼970 cm⁻¹ and ∼1220 cm⁻¹, and to ν_s(S–(OH)₂) and ν_as(S–(OH)₂) at ∼750 cm⁻¹ and ∼840 cm⁻¹. In addition, the experiments showed that diamond is not inert to H₂SO₄ at high temperatures as reduction of S(VI) to S(IV) produces SO₂⁰ and oxidation of diamond generates CO₂⁰.

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.

Changes in rhyolite melt viscosity during magma decompression and degassing exert a first order control on ascent through the crust and volcanic eruption style. These changes have as yet unknown hazard implications for geothermal drilling in pursuit of particularly hot fluids close to magma storage regions. Here, we exploit the situation at Krafla volcano in which rhyolite has both erupted at Earth's surface and been sampled at shallow storage depths via drilling of the 2009 IDDP-1 and 2008 KJ-39 boreholes. We use differential scanning calorimetry to constrain that the IDDP-1 magma quenched to glass at ∼ 700 K, at a rate of between 7 and 80 K.min⁻¹. We measure the equilibrium viscosity of the IDDP-1 rhyolite at temperatures close to the glass transition interval and show that the rhyolite viscosity is consistent with generalized viscosity models assuming a dissolved $H_{2}O$ concentration of $2.12$ wt%. We couple these results with micro-penetration and concentric cylinder rheometry over a range of potential magma storage temperatures to constrain the response of surficial Krafla rhyolites to stress. The surficial rhyolites at Krafla match the same viscosity model, assuming a lower dissolved $H_{2}O$ concentration of $0.12$ wt%. Our results show that at a storage temperature of 1123–1193 K, the viscosity of the stored magma is ∼ 3×10⁵ Pa.s. At the same temperature, the viscosity following degassing during ascent to the surface rises to ∼ 2×10⁹ Pa.s. Finally, we use high-stress compression tests on the Hrafntinnuhryggur surface obsidian to determine the onset of unrelaxed behavior and viscoelastic melt rupture or fragmentation pertinent to understanding the melt response to rapid pressure changes that may be associated with further (near-) magma exploration at Krafla. Taken together, we characterize the relaxation and viscosity of these magmas from source-to-surface.

We report sustained uplift throughout Volcan Sangay's most recent period of eruption (2019–22), moderated only by transient excursions during some of its largest explosions. Volcan Sangay (Amazonia, Ecuador), has been erupting since 2019, impacting both local communities and distant cities with ash fall and lahars. We analyzed ascending and descending Sentinel-1 radar imagery, constructing a robust network of interferograms spanning this eruptive period to measure relative ground displacements across the volcano. Our time series reveals a consistent uplift pattern (∼68 mm/yr) on the western and northern flanks of the volcano, which we attribute to volume increases in a body of magma located within the volcano's edifice beneath its western flank. This source appears to be vertically extensive, and is best fit by a quadrangular magma pathway, dipping towards the west and increasing in volume by 1.1 × 10⁶ m³ between 2019 and 2022. We additionally identify non-magmatic deformation, including subsidence of fresh deposits and downslope displacement (∼50 mm/year) in the southeastern sector of the volcano. Co-eruptive uplift at Sangay is a rare observation of endogenous growth during an eruption and indicates that stratovolcano edifice stability is sensitive to both magma flux into the edifice and shallow controls on eruption rate.

Amphibole phenocrysts in post-1 ka lava domes deposits of Taranaki volcano, an andesite arc volcano in New Zealand, provide an opportunity to explore late-stage changes in melt composition and volatiles in the run up to eruption. Amphibole is a subordinate phase (0–7% of modal phenocrysts) and the phenocrysts display three types of growth history. Type 1 are large compositionally and texturally uniform phenocrysts that have low MgO (<13 wt%) and high K₂O (∼1–1.4 wt%) contents. In contrast, Type 2 have similar cores but have been partially resorbed and overgrown by a mafic rim distinguished by high MgO (up to 15 wt%) and low K₂O (<1.0 wt%) contents. Type 3 are the least common, and have either normal zoned or concentrically zoned interiors with respect to MgO and FeO. Overall, elemental substitutions and zonation patterns are related to periods of resorption and regrowth that are best explained by changes in melt composition. Based on calculated equilibrium melt compositions, the amphibole crystallisation is consistent with an incrementally grown andesitic to dacitic (SiO₂ 58–67 wt%) crystal mush that was periodically recharged with more mafic magma (SiO₂ ∼ 55 wt%). The melts span a compositional gap (SiO₂ ∼ 60–65 wt%) that is not represented in eruption products from the last 8 ka. Such melts were likely brief stages during ongoing fractional crystallisation and magma mixing. Each recharge event disrupted an evolving system and mixed crystals from different parts of it. This concept supports triggering of eruptions by recharge of mafic melts, as also inferred from plagioclase zonation for some eruptions from Taranaki. The outermost rims (0–5 μm) of many amphibole phenocrysts are enriched in fluorine (up to 1.9 wt%) and surrounded by a thick opacitic decomposition growths. We interpret this as the result of slow magmatic ascent and extensive crystallisation that produced a late-stage halogen-rich interstitial melt. This likely extended the conditions for amphibole stability to lower pressure. If F enrichment was accompanied by comparable enrichments in other halogens that preferentially partition into an aqueous phase, then extensive degassing would have occurred during the dome extrusions.

Here we use δ¹⁸O and δD values as tools to investigate the paleo-altitude and the origin of large-volume (120 km³, 10 × 12 km) ignimbrites of Verkhneavachinskaya caldera (cf. Verkhne-Avachinskaya) (VC) in eastern Kamchatka, formed the in Late Miocene 5.8 Ma. The basaltic-andesitic intracaldera ignimbrite deposit exhibits low δ¹⁸O values, reaching −5.03‰, and δD values of −182‰ across a 1.2 km depth range in several sampled sections. The results support a massive meteoric-hydrothermal system throughout the cooling history of the thick intracaldera ignimbrite deposit. Using triple oxygen isotope data we estimate that the δ¹⁸O values of altering meteoric water are as low as −19‰ to −23‰, much lower than modern precipitation of −14‰, or − 16‰ estimated for the 2–3 °C warmer Kamchatka climate of the late Miocene. Therefore, the VC meteoric-hydrothermal system depended on high-altitude precipitation and glaciers, and altitudinal isotopic lapse rates suggest a paleo-altitude of 3.5 km at 5.8 Ma during caldera formation. These elevations exceed the modern by 1.5 km and provide a unique snapshot into an evolving landscape and paleo-environment of eastern Kamchatka at 6–5 Ma as the dynamic outcomes of accretion of the Kronotski arc. In particular, the existence of such a high plateau is in line with contemporary accretionary tectonics: accretion of the Shipunsky peninsula of this accreting arc terrain, ∼120 km to the east of the VC, and evidence of contemporaneous exhumation of high-grade Ganal amphibolites to the west. We conclude that the eruption of large-volume mafic ignimbrites that formed VC caldera was syncollisional or intracollisional in nature, likely requiring delamination of thickened crust to account for both uplift and magmatism.