Journal of Volcanology and Geothermal Research最新文献

Raung volcano, located within the Ijen UNESCO Global Geopark in East Java, poses a significant risk of volcanic hazard for nearby residents and visitors. Our study provides a framework to understand Raung long-term behavior and potential hazards by examining its stratigraphy, petrology, and temporal magma evolution. The erupted products of Raung vary from lava flow, pyroclastic density current (ignimbrite and block and ash flow), scoria fall, and pumice fall. Radiocarbon dating of charcoal samples within pyroclastic deposits and weathered sediments beneath tephra fall layers yield the age of 840 ± 30 BP to 370 ± 30 BP. It provides an important chronological marker that confirms the past VEI-4 to VEI-5 eruption around 1200 to 1600 CE. Petrological and geochemical data reveal that Raung magma composition ranges from basalt to dacite (48–64 wt% SiO₂) and can be classified into two distinct magma types. Type 1 magma has med-K series, low Rb/Nb, and no Eu anomaly. Type 2 magma has high-K series, high Rb/Nb, and negative Eu anomaly. Evidence of disequilibrium features (e.g., reverse zoning, sieve texture, resorption texture, orthopyroxene mantled by clinopyroxene) and mingling texture, along with geochemical features, indicate magma mixing and many episodes of mafic magma replenishment. While the current volcanic activity is dominated by andesitic Strombolian eruption, the characteristics of Raung eruptive products suggest that past major Plinian eruptions (VEI 4–5) had occurred in both andesitic and dacitic magmatic systems, with greater VEI associated with dacitic composition. The study of Raung temporal evolution documented various eruptive behaviors related to its wide range of magma composition, thus providing an essential database for hazard assessment and mitigation.

Sulfur isotopic ratio in sulfate and sulfide in subvolcanic hydrothermal systems is a valuable tracer to study the magmatic-hydrothermal processes from the magma source through to volcanic eruptions. Zao volcano is among the most active volcanoes in NE Japan, with historical explosive eruptions occurring during the last thousand years and unrest episodes since 2013. This necessitates a detailed assessment of the potential risk of future volcanic hazards. We investigated the magmatic-hydrothermal processes that occurred during the 1895 CE eruption sequence at Zao volcano by conducting mineralogical and sulfur isotope analyses in the exposed well: (i) six volcanic units (Layers 1–6) of the 1895 CE eruption products (clayish ash deposits with andesitic bombs, lapilli of scoria, and minor altered lithic fragments) deposited on the rim of Okama crater lake; and (ii) clay-altered and silicified rocks from the Nigorikawa alteration zone (NGA) surrounding the Goshikidake cone. Mineralogical data show that the samples mainly consist of alunite, pyrite, and gypsum. Alunite and pyrite occur as fine crystal mixtures associated with mineral assemblages of both advanced argillic alteration (i.e., those of cristobalite and kaolinite) and silicification (i.e., those of cristobalite, tridymite and native sulfur). Gypsum typically appears as isolated euhedral crystals of several millimeters in size. Samples of the 1895 CE eruption products have a narrow range of δ³⁴S values from +3 ‰ to +5 ‰ for gypsum, from +9 ‰ to +13 ‰ for alunite, and approximately −10 ‰ for pyrite. For the NGA samples, the δ³⁴S_gypsum, δ³⁴S_{native sulfur}, and δ³⁴S_pyrite values range from −12 ‰ to −9 ‰, whereas for alunite, these range from +8 ‰ to +18 ‰. This indicates that alunite and pyrite in the 1895 CE eruption products were derived from the advanced argillic alteration and silicification zones that developed under Okama crater, which is exposed as the NGA. Estimated alteration temperatures based on the sulfur isotopic equilibrium between alunite and pyrite pairs are 200 °C–300 °C. By contrast, δ³⁴S_gypsum values in the 1895 CE products are significantly higher than those in the NGA (which are derived from oxidation of pyrite or H₂S, or both), ranging between an estimated parental fluid of δ³⁴S_bulk-initial = ca. +1 ‰ and the Quaternary volcanic rocks of the Japan arc. This suggests that gypsum in the 1895 CE eruption products derived from magmatic vapor condensate (anhydrite) formed in the volcanic conduit during the eruption, thus becoming replacement of anhydrite by gypsum after or during the tephra deposition on the Zao summit surface. Our results on sulfur-bearing minerals provide new clues for better understanding (and monitoring) the syn-eruptive processes of volcanic eruptions focused on subvolcanic hydrothermal systems.

It is well known that magmatic plumbing systems change over time, but there is much debate as to why and how. We studied volcanic ejecta continuously deposited in an outcrop at Kagosaka Pass at the eastern base of Mount Fuji to investigate the factors responsible for changes in the magmatic plumbing system. The sample consisted of pyroclastic sediments from explosive eruptions for approximately 3000 y, which sandwiched the time of the Gotemba sector collapse at approximately 2500 BP. Chemical analyses of whole rocks, minerals, and matrix glasses, as well as mode measurements of glass and bubbles, were performed on samples collected from approximately 30 layers; significant changes were observed before and after the collapse. For example, before and after the collapse, matrix glass area increased around 60% to over 80% and anorthite content (Ca / (Ca + Na) * 100) of phenocryst plagioclase decreased from over 80 to below 65. For a period after the collapse, possibly hundreds of years, the plagioclase and olivine phenocrysts exhibited characteristics indicative of crystallization at low temperatures and pressures, and the pyroclast matrix became highly vitreous. Eruptions with ejecta of these characteristics continued more than a dozen times, lasting about 500 years. In addition, the trend in the distribution of the bulk rock chemical composition changed significantly, showing a differentiation trend with only plagioclase and clinopyroxene crystal separation. An investigation using the MELTS software revealed that the phenomenon of direct eruptions from deep magma chambers to the surface, bypassing shallow magma reservoirs, continued for several hundred years after the collapse. This can be interpreted as a decrease in confining pressure associated with the collapse, facilitating the eruption of magma from the depths. Furthermore, based on an examination of the water content in the magma during this period, we posit that the trigger for the rise of magma from the deep magma chamber of Mount Fuji is the acquisition of excess pressure by the injection of magma from a deeper level.

Long lava flows exceeding 50 km in length are usually produced during large-volume flood basalt eruptions (>100 to 10,000 km³) but can also occur from small to moderate-volume (<30 km³) basaltic eruptions in continental intraplate monogenetic volcanic fields. Eruptive volume, therefore, is not an a priori barrier to producing long lava flows. Key factors that promote long lava flows include efficient lava transport systems that minimise heat loss, long-lived and sustained effusion rates to maintain flow advancement, and lava flow across low topographic gradients (<1°-10°) with minimal topographic barriers.

Here, we focus on an anomalously young and poorly studied basaltic monogenetic volcanic field in southeast Queensland, Australia, that formed part of the broader intraplate volcanism in eastern Australia since the Late Cretaceous. The Coalstoun Lakes Volcanic Field (CLVF) comprises three lava fields: the Barambah Basalt Flow Field, the Deep Creek Flow Field and the Hunters Hill Flow Field. Basalt from the Barambah Basalt Flow Field has been redated here by Ar⁴⁰/Ar³⁹ analysis of groundmass material, yielding a weighted mean age of 0.520 ± 0.016 Ma. The Barambah Basalt Flow Field contains most of the eruptive volume and has advanced up to 165 km from the vent. The Hunters Hill and the Deep Creek flow fields are comparatively smaller in volume and have advanced ∼30 and ∼ 20 km from the vent, respectively. Lava tubes are only known from proximal regions and do not appear to be a significant factor in promoting long run-out in the CLVF. Flow confinement and utilisation of existing drainage networks are features of both lava flow fields, and advancement down the sand-based and ephemeral Burnett River significantly promoted long run-out despite low topographic gradients.

New whole-rock geochemical data on our CLVF samples indicates that all lavas are hawaiites, a common feature of other Quaternary long lava flows globally. Overall, there is some compositional variation, but a cryptic zonation is readily apparent in trace element abundances, which helps to further distinguish the flow fields as the products of separate but closely spaced eruptions. The combination of field and geochemical data indicates that the long lava flow of the Barambah Basalt Flow Field resulted from a sustained and relatively low effusion eruption, creating a pāhoehoe flow field that continuously advanced across the landscape, utilising a drainage system that guided lava flow and helped to circumvent any topographic barriers.

The coexistence of monogenetic and polygenetic volcanoes is a common phenomenon in volcanic areas. However, the genetic relationship between monogenetic and polygenetic systems and the factors controlling their distinct eruptive styles are not well understood. In active volcanic areas, analysing the clustering and vent alignment of monogenetic volcanoes, as well as examining the geomorphology and relative ages of scoria cones, offers quantitative insights into magma supply rates, volcano type distribution, and volcanic development trends. Our study presents geomorphological and spatio-temporal analyses of the co-existing monogenetic volcanoes in the Longgang Volcanic Field (LVF) and those associated with a polygenetic volcano (Tianchi) in the Changbaishan Volcanic Area, China. The distance between the two volcanic areas is around 150 km. Monogenetic vents in the LVF exhibit greater density compared to the dispersed system associated with Tianchi. The LVF vents also show better alignment, particularly in the direction of pre-existing basement faults (NE-SW, NW-SE and EW). By using scoria cone morphometric parameters and features, we estimated the relative ages and erupted volumes of monogenetic volcanoes in the LVF and the Tianchi area. We classified the cones of the two volcanic systems into five eruptive periods and found that, despite similar magma sources and output rates over approximately 870 kyr, differing numbers of scoria cones across age classes suggest that Tianchi's magma system influences its associated monogenetic volcanic plumbing. Furthermore, the continuous rise in output rates of monogenetic volcanoes in the Tianchi area highlights the increasing magma supply sustaining Tianchi volcano. Together, these interpretations are consistent with the two systems being controlled by different factors: the Tianchi monogenetic volcanic system is more controlled by magmatism, whereas the LVF is more strongly controlled by local tectonic structures, alongside an increasing magma supply causing the formation of progressively larger individual volcanoes. In volcanic areas, analysing monogenetic volcanoes' spatial-temporal distribution, volumes and recurrence rate provides a framework to evaluate magma supply rates and tectonic associations, which are key to the development of different volcano types.

Volcanism at Mt. Etna (Italy) started with an early tholeiitic stage dating back to 542 ka during which subaqueous to subaerial magmas were emitted chiefly through fissure-type eruptions on widespread areas located on the southern flank of the modern volcano edifice. Volcanic products belonging to the earlier Aci Trezza Synthem (542–496 ka) and those of the later Adrano Synthem (332–320 ka) are basalts within a narrow range of variation. Despite the rather homogeneous geochemical characteristics, zoning patterns and FeMg diffusion chronometry on olivine crystals from lavas of both the Synthemic Units have evidenced different dynamics and kinetics of storage and transfer before eruptions. Specifically, one dominant, normally-zoned, Fo_83–86 olivine population makes peculiar lavas of the Aci Trezza Synthem, whose patterns can be interpreted as due to simple upward migration from deep storage reservoirs directly to the surface with timescales of 109–200 days. Volcanic rocks of the Adrano Synthem have at least three additional olivine populations (i.e., Fo_78-81, Fo_73-74, Fo_64-70) bearing more complex normal and reverse zoning patterns, features revealing that magmas ascended from the deeper storage zones and then intruded and stalled in shallower reservoirs before being erupted. Transfers throughout these magma reservoirs record both short (<46 days) and long timescales (>106 days), suggesting that tectonics could have accelerated or inhibited magma supply during this later stage of volcanic activity. This new dataset points out that the embryonic plumbing system of Mt. Etna developed a more complex architecture throughout the first ~200 ka of volcanism as a consequence of a declining effect of transtensional tectonics over time.

Several powerful explosive eruptions have taken place in the populated lower East Rift Zone of Kīlauea within the past ∼750 years. These have created distinctive landforms, including a tephra rim enclosing Puʻulena Crater immediately south of the Puna Geothermal Venture power station, a tuff cone at Kapoho Crater near the eastern cape of the Island of Hawaiʻi, and a set of littoral cones, the Sand Hill in Nānāwale, where the 1840 lava flow poured into the ocean. Kapoho Crater tuff cone is the largest of these recent pyroclastic features. Mineral, glass, and melt inclusion analyses of tuff cone ash and later fissure-related scoriaceous materials also found within the crater indicate slightly evolved basaltic magmas (1120–1130 °C) that are compositionally similar to parts of the effusive lower East Rift Zone eruptions in 1955 and 2018. Tuff cone magmas were stored at depths of ∼2.5–3.5 km and had pre-eruptive volatile contents (0.5–0.8 wt% H₂O, 280–340 ppm CO₂, 1400–1800 ppm S) similar to other Kīlauea eruptions (e.g., 1959, 1960), suggesting that internal magma properties were unlikely to account for the unusual explosiveness of this eruption. Tephra componentry, grain-size analyses, and field observations confirm that the cone grew during a phreatomagmatic eruption mostly of vitric ash, probably where a fissure opened across the coastline or shallow ocean floor nearby. Supporting this hypothesis is the identification of at least two genera of marine diatoms within tuff cone strata. Sand Hill littoral cone ash is also vitric like that of Kapoho Crater, but distinctly coarser with abundant fluidal ejecta represented. In contrast, the Puʻulena Crater eruption deposited lithic ash and related blocks with minor juvenile magmatic contribution; a phreatomagmatic eruption that was dominantly phreatic. Differences in eruption styles are related to unique mechanics that tephra analyses help us interpret. While powerful explosive eruptions in the lower East Rift Zone are rare, they present a definite future hazard for inhabitants in this part of Hawaii.

Understanding the mechanisms of magma intrusion underpins our ability to interpret geophysical monitoring signals at volcanoes and thus issue reliable forecasts of future activity. The basaltic caldera volcanoes of the western Galápagos Islands, Ecuador, exhibit exceptionally high rates of deformation driven by shallow magma accumulation and migration. However, the nature and evolution of magma storage at these volcanoes is poorly constrained by earthquake hypocentre locations or geodetic inversions. Here we show that transient variations in seismic velocity before, during, and after the 2018 eruption of the Sierra Negra volcano track the accumulation of magma in a shallow sill complex and the emplacement of a lateral flank intrusion. A four-dimensional tomographic technique applied to the P-wave arrivals of local earthquakes provides high spatiotemporal resolution of changes in the physical properties of the shallow volcanic system. In the month before the eruption, the expansion of a low-velocity zone above the sub-caldera sill complex coincides with caldera uplift and near-surface fracturing, driven by persistent shallow magma accumulation. A new low-velocity anomaly appeared progressively in the western flank of the volcano in the days after the onset of the eruption, coinciding with the opening of a curved sill that supplied magma to secondary eruptive fissures. The anomaly disappeared as the curved sill deflated after the initial opening, despite it remaining the conduit for magma from the caldera complex to the flank fissures. Low velocities across the shallow caldera after the end of the eruption likely result from rapid inflation due to recharge with fresh magma from depth. These results indicate a previously unknown complexity to the magmatic plumbing system at Sierra Negra and suggest velocity changes resulting from an interplay of thermal and stress perturbations.

The Paricutin-Tancítaro region (PTR) within the Michoacán-Guanajuato monogenetic Volcanic Field (MGVF) is characterized by a large stratovolcano, Tancítaro enclosed in a dense distribution of monogenetic volcanoes, mainly scoria cones, that includes the well-known Paricutin. The succession of seismic swarms beginning 54 years after the birth of Paricutin in 1943 represents a challenge for apprising the region's volcanic and seismic hazards. In this work, we introduce a novel methodology to assess the spatiotemporal evolution of the monogenetic scoria cones and the distributed volcanic hazards. We first performed a morpho-chronometric analysis of 171 scoria cones to estimate their relative ages, which revealed an increasing trend in the rate of monogenetic eruptions over the last 120 kyr, especially in the last 20 kyr, with a current mean waiting interval between monogenetic eruptions of only 120 yr. In a second step, we estimate the spatiotemporal evolution of monogenetic volcanic activity in PTR using a Voronoi tessellation to represent the spatial density distribution of scoria cone emplacement through time to detect dynamic shifts in volcanic activity locations in the region. This approach thus reveals spatial dynamic patterns in the rates of monogenetic eruptions over time. Subsequently, a Poisson process is assumed to estimate the spatially distributed cone-forming eruption probabilities based on the morpho-chronometrically analyzed cones. Remarkably, a high spatial correlation was found between the areas with the highest probabilities and the location of the recent seismic swarms recorded in the PTR.

The Late Pleistocene-Holocene Laoguipo volcano in the Tengchong Volcanic Field (TVF), southwestern China, displays significant geochemical and geophysical anomalies characteristics. Here we present petrographic observations, mineral chemistry, bulk rock geochemistry, thermobarometry, and thermodynamic simulation to evaluate the crystallization conditions and pre-eruptive magmatic processes occurring within the magma plumbing system. This study reveals the existence of two magma reservoirs beneath the Laoguipo volcano. The deep magma reservoir is composed of basaltic trachyandesite (SiO₂ = 54–57 wt%), which is located at 15–19 km depths with 1087–1160 °C, 1.5–2 wt% H₂O content, oxygen fugacity of ΔNNO+1 (Ni-NiO buffer), melt viscosity of 10^1.7–10^2.6 Pa·s, and density of 2.5–2.6 g/cm³. The formation of the deep magma reservoir is attributed to the 31% mass fractional crystallization of primitive basalt in the TVF. The shallow magma reservoir is composed of trachyte (SiO₂ = 63–64 wt%), which is located at 6–11 km depths with 780–825 °C, 5.9–6.5 wt% H₂O content, oxygen fugacity of ΔNNO+1 (Ni–NiO buffer), melt viscosity of 10^3.9–10^4.8 Pa·s, and density of 2.2–2.3 g/cm³. The shallow magma reservoir formed after the basaltic trachyandesite had assimilated 19% mass of the upper crustal material and fractionated 41% mass of the crystals. This study suggests that the shallow trachyte magma reservoir is being heated by the ascending deep basaltic trachyandesite magma, resulting in crystal dissolution, remobilization of crystal mush, and magma convection, which may be the main factors responsible for the geochemical and geophysical anomalies characteristics. The Laoguipo volcano is forming a mature magma plumbing system, which is of significance for forecasting future volcanic eruptions.