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Objective: Long-term administration of dienogest, which is known to have effect on bone mineral density, is frequently done in patients with endometriosis and adenomyosis, but a few studies focused on the bone mineral density changes after finishing the long-term therapy. This study aimed to reveal the factors that adversely affect lumbar bone mineral density. Method: Fifty-seven premenopausal women who visited our hospital were diagnosed as either endometriosis or adenomyosis, and they were treated by dienogest for more than 115 weeks (26.5 months). Based on a previous report, bone mineral density changes less than 2% was categorized as the osteopenic group ( n = 30), and the others were assigned to the unchanged group ( n = 27). Bone mineral density was measured at the lumbar spine using dual-energy X-ray absorptiometry. A representative ovarian reserve marker, endogenous estradiol levels, and follicle-stimulating hormone levels were measured over time and were compared between the osteopenic and unchanged groups. Result: Duration of dienogest intake was 59.5 months (osteopenic group) versus 57.5 months (unchanged group). These patients experienced ovarian surgeries in a similar frequency, but the ovarian reserve in osteopenic group was impaired as suggested by the decline of endogenous estradiol level during intake of dienogest compared to that of unchanged group ( p = 0.0146). Endogenous follicle-stimulating hormone level between osteopenic group and unchanged group did not reach statistically significant difference, although the osteopenic group showed relatively higher level. Conclusion: This study might suggest that decreased ovarian reserve as judged by endogenous estradiol level is a factor that negatively affect bone mineral density, and measurement of endogenous estradiol level during intake of dienogest could have a predictive meaning of future decreased bone mineral density level.

The destruction caused by ballistic ejecta from the phreatic eruptions of Mt. Ontake in 2014 and Mt. Kusatsu-Shirane (Mt. Moto-Shirane) in 2018 in Japan, which resulted in numerous casualties, highlighted the need for better evacuation facilities. In response, some mountain huts were reinforced with aramid fabric to convert them into shelters. However, a number of decisions must be made when working to increase the number of shelters, which depend on the location where they are to be built. In this study, we propose a method of using high-strength steel to reinforce wooden buildings for use as shelters. More specifically, assuming that ballistic ejecta has an impact energy of 9 kJ or more, as in previous studies, we developed a method that utilizes SUS304 and SS400 unprocessed steel plates based on existing impact test data. We found that SUS304 is particularly suitable for use as a reinforcing material because it has excellent impact energy absorption characteristics due to its high ductility as well as excellent corrosion resistance. With the aim of increasing the structural strength of steel shelters, we also conducted an impact test on a shelter fabricated from SS400 deck plates (i.e., steel with improved flexural strength provided by work-hardened trapezoidal corrugated plates). The results show that the shelter could withstand impact with an energy of 13.5 kJ (2.66 kg of simulated ballistic ejecta at 101 m/s on impact). In addition, from the result of the impact test using the roof-simulating structure, it was confirmed the impact absorption energy is further increased when artificial pumice as an additional protective layer installed on this structure. Observations of the shelter after the impact test show that there is still some allowance for deformation caused by projectile impact, which means that the proposed steel shelter holds promise, not only structurally, but also from the aspects of transportation and assembly. Hence, the usefulness of shelters that use steel was shown experimentally. However, shelter construction should be suitable for the target environment.

The GCOM-C (SHIKISAI) satellite was developed to understand the mechanisms of global climate change. The Second-generation Global Imager (SGLI) onboard GCOM-C is an optical sensor observing wavelengths from 380 nm to 12.0 μm in 19 bands. One of the notable features is that the resolution of the 1.63-, 10.8-, and 12.0-µm bands is 250 m, with an observation frequency of 2-3 days. To investigate the effective use and potential of the 250-m resolution of these SGLI bands in the study of eruptive activities, we analyzed four practical cases. As an example of large-scale effusive activity, we studied the 2018 Kilauea eruption. By analyzing the series of 10.8-μm band images using cumulative thermal anomaly maps, we could observe that the lava effused on the lower East Rift Zone, initially flowed down the southern slope to the sea, and then moved eastward. As an example of lava dome growth and generation of associated pyroclastic flows, the activity at Sheveluch between December 2018 and December 2019 was analyzed. The 1.63- and 10.8-µm bands were shown to be suitable for observing growth of the lava dome and occurrence of pyroclastic flows, respectively. We found that the pyroclastic flows occurred during periods of rapid lava dome expansion. For the study of an active crater lake, the activity of Ijen during 2019 was analyzed. The lake temperature was found to rise rapidly in mid-May and reach 38 °C in mid-June. We also analyzed the intermittent activities of small-scale Vulcanian eruptions at Sakurajima in 2019. The 1.63-µm band was useful for detecting activities that are associated with Vulcanian eruptions. Analytical results for these case studies demonstrated that the GCOM-C SGLI images are beneficial for observing various aspects of volcanic activity, and their real-time use may contribute to reducing eruption-related disasters.

The GCOM-C (SHIKISAI) satellite was developed to understand the mechanisms of global climate change. The Second-generation Global Imager (SGLI) onboard GCOM-C is an optical sensor observing wavelengths from 380 nm to 12.0 µm in 19 bands. One of the notable features is that the resolution of the 1.63-, 10.8-, and 12.0-µm bands is 250 m, with an observation frequency of 2–3 days. To investigate the effective use and potential of the 250-m resolution of these SGLI bands in the study of eruptive activities, we analyzed four practical cases. As an example of large-scale effusive activity, we studied the 2018 Kilauea eruption. By analyzing the series of 10.8-µm band images using cumulative thermal anomaly maps, we could observe that the lava effused on the lower East Rift Zone, initially flowed down the southern slope to the sea, and then moved eastward. As an example of lava dome growth and generation of associated pyroclastic flows, the activity at Sheveluch between December 2018 and December 2019 was analyzed. The 1.63- and 10.8-µm bands were shown to be suitable for observing growth of the lava dome and occurrence of pyroclastic flows, respectively. We found that the pyroclastic flows occurred during periods of rapid lava dome expansion. For the study of an active crater lake, the activity of Ijen during 2019 was analyzed. The lake temperature was found to rise rapidly in mid-May and reach 38 °C in mid-June. We also analyzed the intermittent activities of small-scale Vulcanian eruptions at Sakurajima in 2019. The 1.63-µm band was useful for detecting activities that are associated with Vulcanian eruptions. Analytical results for these case studies demonstrated that the GCOM-C SGLI images are beneficial for observing various aspects of volcanic activity, and their real-time use may contribute to reducing eruption-related disasters.

Bursts of gamma ray showers have been observed in coincidence with downward propagating negative leaders in lightning flashes by the Telescope Array Surface Detector (TASD). The TASD is a 700~square kilometer cosmic ray observatory located in southwestern Utah, U.S.A. In data collected between 2014 and 2016, correlated observations showing the structure and temporal development of three shower-producing flashes were obtained with a 3D lightning mapping array, and electric field change measurements were obtained for an additional seven flashes, in both cases co-located with the TASD. National Lightning Detection Network (NLDN) information was also used throughout. The showers arrived in a sequence of 2--5 short-duration ($\le$10~$\mu$s) bursts over time intervals of several hundred microseconds, and originated at an altitude of $\simeq$3--5 kilometers above ground level during the first 1--2 ms of downward negative leader breakdown at the beginning of cloud-to-ground lightning flashes. The shower footprints, associated waveforms and the effect of atmospheric propagation indicate that the showers consist primarily of downward-beamed gamma radiation. This has been supported by GEANT simulation studies, which indicate primary source fluxes of $\simeq$$10^{12}$--$10^{14}$ photons for $16^{\circ}$ half-angle beams. We conclude that the showers are terrestrial gamma-ray flashes (TGFs), similar to those observed by satellites, but that the ground-based observations are more representative of the temporal source activity and are also more sensitive than satellite observations, which detect only the most powerful TGFs.

This discussion concerns the flowage of the 1991 lava lobes at Unzen that were suggested by Goto et al. (2020) to be moving rigidly. Pictorial evidence of flowage of the 1991 lava lobe of Unzen, such as morphological change of the lava lobe, protrusion of the front of lava lobe, crease structure, and wrinkle surface of lava blocks, are presented. Differences in the interpretation of flow mechanisms may reflect slight difference in temperature and glass composition of the lavas. Temperatures used by Goto et al. (2020) were 780–880 °C, whereas those estimated by Venezky and Rutherford (1999) were 900 ± 30 °C. The groundmass glass compositions of 1991 blocks of Unzen dacite used by Goto et al. (2020) are 1–2 wt% higher in SiO2 than those of Nakada and Motomura (1999) and ours, suggesting that the samples used by Goto et al. (2020) represent the cooler rigid parts of the lava lobes. The lava viscosity is delicately influenced by cooling, dewatering, and crystallization during eruption. The direct application of experimental results to understanding the rheological behavior of natural lavas needs much more careful consideration.

The chemical composition of intraplate seamounts is distinct from normal seafloor material, meaning that the subduction of seamounts at a convergent margin can cause a change in the chemistry of the mantle wedge and associated arc magmas. Nishinoshima, a volcanic island in the Izu–Bonin Arc of Japan, has been erupting continuously over the past 2 years, providing an ideal opportunity to examine the effect of seamount subduction on the chemistry of arc magmas. Our research is based on the whole-rock geochemistry and the chemistry of minerals within lavas and air-fall scoria from Nishinoshima that were erupted before 1702, in 1973–1974, and in 2014. The mineral phases within the analyzed samples crystallized under hydrous conditions (H2O = 3–4 wt.%) at temperatures of 970 °C–990 °C in a shallow (3–6 km depth) magma chamber. Trace element data indicate that the recently erupted Nishinoshima volcanics are much less depleted in the high field strength elements (Nb, Ta, Zr, Hf) than other volcanics within the Izu–Bonin Arc. In addition, the level of enrichment in the Nishinoshima magmas has increased in recent years, probably due to the addition of material from HIMU-enriched (i.e., high Nb/Zr and Ta/Hf) seamounts on the Pacific Plate, which is being subducted westwards beneath the Philippine Sea Plate. This suggests that the chemistry of scoria from Nishinoshima volcano records the progressive addition of components derived from subducted seamounts.

The Pierre Auger Collaboration (Auger) recently reported a correlation between the arrival directions of cosmic rays with energies above 39 EeV and the flux pattern of 23 nearby starburst galaxies (SBGs). In this Letter, we tested the same hypothesis using cosmic rays detected by the Telescope Array experiment (TA) in the 9-year period from May 2008 to May 2017. Unlike the Auger analysis, we did not optimize the parameter values but kept them fixed to the best-fit values found by Auger, namely 9.7% for the anisotropic fraction of cosmic rays assumed to originate from the SBGs in the list and 12.9{\deg} for the angular scale of the correlations. The energy threshold we adopted is 43 EeV, corresponding to 39 EeV in Auger when taking into account the energy-scale difference between two experiments. We find that the TA data is compatible with isotropy to within 1.1{\sigma} and with the Auger result to within 1.4{\sigma}, meaning that it is not capable to discriminate between these two hypotheses., Comment: More accurate title, fixed an inconsistency in the declination range used, with a few figures slightly changing as a result, other minor revisions

One of the uncertainties in interpretation of ultra-high energy cosmic ray (UHECR) data comes from the hadronic interaction models used for air shower Monte Carlo (MC) simulations. The number of muons observed at the ground from UHECR-induced air showers is expected to depend upon the hadronic interaction model. One may therefore test the hadronic interaction models by comparing the measured number of muons with the MC prediction. In this paper, we present the results of studies of muon densities in UHE extensive air showers obtained by analyzing the signal of surface detector stations which should have high $\it{muon \, purity}$. The muon purity of a station will depend on both the inclination of the shower and the relative position of the station. In 7 years' data from the Telescope Array experiment, we find that the number of particles observed for signals with an expected muon purity of $\sim$65% at a lateral distance of 2000 m from the shower core is $1.72 \pm 0.10{\rm (stat.)} \pm 0.37 {\rm (syst.)}$ times larger than the MC prediction value using the QGSJET II-03 model for proton-induced showers. A similar effect is also seen in comparisons with other hadronic models such as QGSJET II-04, which shows a $1.67 \pm 0.10 \pm 0.36$ excess. We also studied the dependence of these excesses on lateral distances and found a slower decrease of the lateral distribution of muons in the data as compared to the MC, causing larger discrepancy at larger lateral distances.

The Telescope Array observatory utilizes fluorescence detectors and surface detectors to observe air showers produced by ultra high energy cosmic rays in the Earth's atmosphere. Cosmic ray events observed in this way are termed hybrid data. The depth of air shower maximum is related to the mass of the primary particle that generates the shower. This paper reports on shower maxima data collected over 8.5 years using the Black Rock Mesa and Long Ridge fluorescence detectors in conjunction with the array of surface detectors. We compare the means and standard deviations of the observed $X_{\mathrm{max}}$ distributions with Monte Carlo $X_{\mathrm{max}}$ distributions of unmixed protons, helium, nitrogen, and iron, all generated using the QGSJet~II-04 hadronic model. We also perform an unbinned maximum likelihood test of the observed data, which is subjected to variable systematic shifting of the data $X_{\mathrm{max}}$ distributions to allow us to test the full distributions, and compare them to the Monte Carlo to see which elements are not compatible with the observed data. For all energy bins, QGSJet~II-04 protons are found to be compatible with Telescope Array hybrid data at the 95% confidence level after some systematic $X_{\mathrm{max}}$ shifting of the data. Three other QGSJet~II-04 elements are found to be compatible using the same test procedure in an energy range limited to the highest energies where data statistics are sparse., Comment: 39 pages, 18 figures, 5 tables, published in The Astrophysical Journal. This is a peer-reviewed, un-copyedited version of an article published in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.3847/1538-4357/aabad7

We present the results of the search for ultra-high-energy photons with nine years of data from the Telescope Array surface detector. A multivariate classifier is built upon 16 reconstructed parameters of the extensive air shower. These parameters are related to the curvature and the width of the shower front, the steepness of the lateral distribution function, and the timing parameters of the waveforms sensitive to the shower muon content. A total number of two photon candidates found in the search is fully compatible with the expected background. The $95\%\,$CL limits on the diffuse flux of the photons with energies greater than $10^{18.0}$, $10^{18.5}$, $10^{19.0}$, $10^{19.5}$ and $10^{20.0}$ eV are set at the level of $0.067$, $0.012$, $0.0036$, $0.0013$, $0.0013~\mbox{km}^{-2}\mbox{yr}^{-1}\mbox{sr}^{-1}$ correspondingly., Comment: 7 pages, 2 figures

The results on ultra-high-energy cosmic rays (UHECR) mass composition obtained with the Telescope Array surface detector are presented. The analysis employs the boosted decision tree (BDT) multivariate analysis built upon 14 observables related to both the properties of the shower front and the lateral distribution function. The multivariate classifier is trained with Monte-Carlo sets of events induced by the primary protons and iron. An average atomic mass of UHECR is presented for energies $10^{18.0}-10^{20.0}\ \mbox{eV}$. The average atomic mass of primary particles shows no significant energy dependence and corresponds to $\langle \ln A \rangle = 2.0 \pm 0.1 (stat.) \pm 0.44 (syst.)$. The result is compared to the mass composition obtained by the Telescope Array with $\mbox{X}_{\mbox{max}}$ technique along with the results of other experiments. Possible systematic errors of the method are discussed., Comment: 11 pages, 9 figures

The 2011 Shinmoe-dake eruption started with a phreatomagmatic eruption (Jan 19), followed by climax sub-Plinian events and subsequent explosions (Jan 26–28), lava accumulation in the crater (end of January), and vulcanian eruptions (February–April). We have studied a suite of ejecta to investigate the magmatic system beneath the volcano and remobilization processes in the silicic magma mush. Most of the ejecta, including brown and gray colored pumice clasts (Jan 26–28), ballistically ejected dense lava (Feb 1), and juvenile particles in ash from the phreatomagmatic and vulcanian events are magma mixing products (SiO 2 = 57–58 wt.%; 960–980 °C). Mixing occurred between silicic andesite (SA) and basaltic andesite (BA) magmas at a fixed ratio (40%–30% SA and 60%–70% BA). The SA magma had SiO 2 = 62–63 wt.% and a temperature of 870 °C, and contains 43 vol.% phenocrysts of pyroxene, plagioclase, and Fe–Ti oxide. The BA magma had SiO 2 = 55 wt.% and a temperature of 1030 °C, and contains 9 vol.% phenocrysts of olivine and plagioclase. The SA magma partly erupted without mixing as white parts of pumices and juvenile particles. The two magmatic end-members crystallized at different depths, requiring the presence of two separate magma reservoirs; shallower SA reservoir and deeper BA reservoir. An experimental study reveals that the SA magma had been stored at a pressure of 125 MPa, corresponding to a depth of 5 km. The textures and forms of phenocrysts from the BA magma indicate rapid crystallization directly related to the 2011 eruptive activity. The wide range of H 2 O contents of olivine melt inclusions (5.5–1.6 wt.%) indicates that rapid crystallization was induced by decompression, with olivine crystallization first (≤ 250 MPa), followed by plagioclase addition. The limited occurrence of olivine melt inclusions trapped at depths of Remobilization of mush-like SA magma occurred in two stages before the early sub-Plinian event. Firstly, precursor mixing with BA magma and associated heating occurred (925–871 °C; stage-1 of ≥ 350 h), followed by final mixing with BA magma (stage-2). MgO profiles of magnetite phenocrysts define timescales of 0.7–15.2 h from this final mixing to eruption. The mixed and heated magmas, and stagnant mush that existed in the SA reservoir in the precursor stage, were finally erupted together. Magnetite phenocrysts in the Feb 18 ash reveal the occurrence of continuous erosion of the stagnant mush during the course of the 2011 eruptive activity.

The partition coefficients of hydrogen between plagioclase and basaltic melt were determined by two approaches. For the first part of this study, plagioclase-hosted melt inclusions in mid-ocean ridge basalt (MORB) from the Rodriguez Triple Junction in the Indian Ocean were analyzed. The hydrogen concentration in plagioclase is less than 60 wt ppm water, and the average H 2 O concentration in melt inclusions is 0.3 wt%. Therefore, the apparent partition coefficient of hydrogen between plagioclase and melt is ≈0.01 on a molar basis. For the second part of this study, hydrous melting experiments of arc basaltic magma were performed at 0.35 GPa using an internally-heated pressure vessel at f O 2 ≈NNO+3. The starting material was hydrous basaltic glass with H 2 O ranging from 0.8 to 5.5 wt%. A grain of Ca-rich plagioclase (≈1 mg) and 10 mg of powdered basaltic glass were sealed in a Au 80 Pd 20 alloy capsule, and then kept at near the crystallization temperature of plagioclase as a liquidus phase to attain an equilibrium of hydrogen between plagioclase and melt. Combining the results of these two parts of this study, we formulated two linear equations to correlate the hydrogen concentration in plagioclase and the H 2 O concentration in melt. When H 2 O in melt is ≤1 wt%, hydrogen in plagioclase (wt ppm water)≈80×H 2 O in melt (wt%). When H 2 O in melt is≥4 wt%, hydrogen in plagioclase (wt ppm water)≈40×H 2 O in melt (wt%). Hydrogen concentration in plagioclase lies between two equations when H 2 O in melt ranges from 1 to 4 wt%. In accordance with these formulations, the partition coefficients of hydrogen between plagioclase and basaltic melt switches from 0.01±0.005 under H 2 O-poor conditions (≤100 wt ppm water in plagioclase, ≤1 wt% H 2 O in melt) to 0.005±0.001 under H 2 O-rich conditions (≥150 wt ppm water in plagioclase, ≥4 wt% H 2 O in melt). Such switches of hydrogen partitioning with an increase in H 2 O can be related to change of the atomic site for hydrogen in the crystal structure of plagioclase.

The 2014 Mount Ontake eruption started just before noon on September 27, 2014. It killed 58 people, and five are still missing (as of January 1, 2016). The casualties were mainly caused by the impact of ballistic blocks around the summit area. It is necessary to know the magnitude of the block velocity and energy to construct a hazard map of ballistic projectiles and design effective shelters and mountain huts. The ejection velocities of the ballistic projectiles were estimated by comparing the observed distribution of the ballistic impact craters on the ground with simulated distributions of landing positions under various sets of conditions. A three-dimensional numerical multiparticle ballistic model adapted to account for topographic effect was used to estimate the ejection angles. From these simulations, we have obtained an ejection angle of γ = 20° from vertical to horizontal and α = 20° from north to east. With these ejection angle conditions, the ejection speed was estimated to be between 145 and 185 m/s for a previously obtained range of drag coefficients of 0.62–1.01. The order of magnitude of the mean landing energy obtained using our numerical simulation was 104 J.

Hydrogen in nominally anhydrous minerals (NAMs) in volcanic rocks can be used as a proxy for dissolved H 2 O in melt prior to eruption. Plagioclase is a NAM that accommodates hydrogen in concentrations of up to hundreds of wt. ppm H 2 O. The species of hydrogen in volcanic plagioclase is structural OH. We report the analytical results of OH concentrations in Ca-rich plagioclase from the 1986–1987 summit eruption of Izu-Oshima volcano, a frontal-arc volcano in Izu arc. We demonstrate that the island arc low-K tholeiitic basalt magmas erupting from the frontal-arc volcanoes are H 2 O-saturated and undergo polybaric degassing during the magma ascent. The analyzed OH concentrations in plagioclase range from 20 to 300 wt. ppm H 2 O, and three levels of OH (20–80 wt. ppm H 2 O, 100–180 wt. ppm H 2 O, and 220–300 wt. ppm H 2 O) are found. These variations in OH indicate that crystallized plagioclase is equilibrated with H 2 O-saturated melt at three depths beneath the Izu-Oshima volcano prior to eruption: near the surface level (≈ 1 wt.% H 2 O in melt), at a 4-km-deep magma chamber (≈ 3 wt.% H 2 O in melt), and at a 8–10-km-deep magma chamber (≈ 5 wt.% H 2 O in melt). It is proposed that deep-seated island arc low-K tholeiitic basalt magmas erupting from frontal-arc volcanoes are richer in H 2 O than previously thought, containing approximately 1 wt.% H 2 O based on analyses of “leaked” melt inclusions and phase equilibrium studies at “low-pressure conditions”.

To constrain the timing and conditions of syneruptive magma ascent that are responsible for shifting eruption intensity, we have investigated a basaltic sub-Plinian eruption that produced Yufune-2 scoria in Fuji volcano 2200 years ago. We deduced magmatic decompression conditions from groundmass microlite textures, including decompression path (i.e. evolution in decompression rate) and approximate decompression rate, in order to relate them to eruption intensity. The microlites revealed decompression conditions after water saturation at 700–1100 m depth. The temporal change in scoria size indicates that the magma discharge rate and resultant eruption intensity increased from unit a to unit b, and then declined toward ending units d and e. The overall decompression rate in each eruptive unit has a positive correlation with eruption intensity. The variation in decompression rate was enlarged in the final units, where the maximum remained the same as the peak through the eruption (0.13–0.22 MPa/s for units b and c), while the minimum was 0.025 MPa/s. The large variation here is due to 1) variation in flow velocity across conduit and 2) part of the erupted magma in unit d experienced remarkably slow decompression (0.002–0.003 MPa/s) resulting from decreased overpressure in the reservoir following the major eruption of unit b. Furthermore, crystal size distribution (CSD) of microlites implied that the earliest erupted magma (unit a) had once been decompressed slowly (0.005–0.012 MPa/s), having been arrested by material in the conduit–vent system, which was followed by an increase in decompression rate due to removal of the material at the initiation of the eruption. In addition, the magma that had been ascending slowly before the unit-d eruption may record the increase in decompression rate. This increased rate resulted from being pushed up by the successive magma at the start of that eruption. Two factors had a major impact on eruption intensity. First, magma decompression rate determined the degree of gas-phase separation from ascending magma. Judging from CSD, different decompression rates had been generated at least at the start of microlite crystallization. The second factor is the conduit radius that, in combination with magma ascent rate, controlled the magma discharge rate. Before the major eruption of unit b, the conduit radius likely increased, as evidenced by xenoliths of basaltic lava and lithic fragments with the same petrography as the xenoliths in unit a. In unit e, the conduit radius decreased through inward development of high-density magma from the conduit margin.

A buried, old volcanic body (pre-Komitake Volcano) was discovered during drilling into the northeastern flank of Mount Fuji. The pre-Komitake Volcano is characterized by hornblende-bearing andesite and dacite, in contrast to the porphyritic basaltic rocks of Komitake Volcano and to the olivine-bearing basaltic rocks of Fuji Volcano. K-Ar age determinations and geological analysis of drilling cores suggest that the pre-Komitake Volcano began with effusion of basaltic lava flows around 260 ka and ended with explosive eruptions of basaltic andesite and dacite magma around 160 ka. After deposition of a thin soil layer on the pre-Komitake volcanic rocks, successive effusions of lava flows occurred at Komitake Volcano until 100 ka. Explosive eruptions of Fuji Volcano followed shortly after the activity of Komitake. The long-term eruption rate of about 3 km3/ka or more for Fuji Volcano is much higher than that estimated for pre-Komitake and Komitake. The chemical variation within Fuji Volcano, represented by an increase in incompatible elements at nearly constant SiO2, differs from that within pre-Komitake and other volcanoes in the northern Izu-Bonin arc, where incompatible elements increase with increasing SiO2. These changes in the volcanism in Mount Fuji may have occurred due to a change in regional tectonics around 150 ka, although this remains unproven.

Mt. Fuji consists dominantly of basalt. A study of olivine-hosted melt-inclusions from layers of air-fall scoria, however, shows clear evidence of andesitic liquids. Whole rock compositions show a narrow range of SiO2, but a wide range of FeO*/MgO and incompatible elements. Phenocrystic plagioclase generally shows bi-modal distributions in compositional frequency, while most olivine phenocrysts show uni-modal distribution with reverse zoning and often contain andesitic melt-inclusions. These suggest that magmas erupted from Fuji are generated through mixing between basaltic and more SiO2-rich (often andesitic) end-members. We propose that Fuji's magmatic plumbing system consists of at least two magma chambers: a relatively deep (∼20 km) basaltic one and a relatively shallow (∼ 8–9 km) and more SiO2-rich one. Evolved basalts with wide compositional ranges of incompatible elements are generated in the deep basaltic magma chamber by prevalent fractional crystallization of pyroxenes with olivine and calcic plagioclase at high pressure. Meanwhile basaltic magma left behind by the previous eruption in the conduit accumulates in a shallow magma chamber, and is differentiated to more SiO2-rich composition by fractional crystallization of olivine, less-calcic plagioclase, and clinopyroxene. Shortly before a new eruption, a large amount of evolved basaltic magma containing calcic plagioclase rises from the deeper magma chamber and is mixed with the more SiO2-rich magma in the shallow chamber, to generate the hybrid basaltic magma.

Major and trace element abundances, Sr and Nd isotopic ratios, and 238U-230Th radioactive disequilibria have been analyzed for samples from five volcanoes, Oshima, Miyakejima, Niijima, Teishi Knoll and Fuji, located in the northern Izu arc to investigate across-arc and regional variations of chemical compositions of mantle and fluids expelled from a subducting slab. The abundances and abundance ratios of both fluid mobile and immobile trace elements show across-arc variations. All samples but one have radioactive disequilibria, with (238U/230Th) greater than unity (herein, a ratio in parentheses denotes the activity ratio). The observed disequilibrium is similar to those reported for other arc systems, such as Mariana, Tonga, Kermadec, Chile. It originates from higher mobility of uranium relative to thorium during dewatering of the subducting slab. The degree of radioactive disequilibrium of (238U/230Th) decreases with depth to the Wadati-Benioff zone at each volcano. The radioactivity ratios of (230Th/232Th) of the samples from Miyakejima, however, deviate from an across-arc trend formed by Oshima, Niijima, Teishi Knoll and Fuji. The combined data of (230Th/232Th)-(238U/232Th) of the samples from the Izu and the Mariana arc revealed a well defined array in an isochron diagram with the exceptions of the samples from Miyakejima and Alamagan. This finding requires (230Th/232Th) of the sub-arc mantle beneath the arcs of Izu and Mariana except the magma sources of the two islands of Miyakejima and Alamagan was around 1.1 and relatively homogeneous before the final addition of fluid from slab. The homogeneous (230Th/232Th) necessitates input of Th with homogeneous (230Th/232Th) contributed from sediment melt, which dominates the budget of Th in the sub-arc mantle. It also suggests that influence of fluid addition before the final one had not caused a variation in Th isotopic compositions of the sub-arc mantle.

H2O-undersaturated melting experiments of synthesized basalt (SiO2 = 50.7 wt.%, MgO = 8.3 wt.%, Mg# = 60) were conducted at fO2 corresponding to NNO+1 and NNO−1 to clarify the effects of pressure (2–7 kbar) and H2O on fractional crystallization in island arcs. H2O content was ranged from nominally anhydrous to 4.4 wt.%. Differentiation trends, namely the liquid lines of descent, change sensitively according to pressure-H2O relations. Tholeiitic differentiation trends are reproduced with H2O ≤ ∼2 wt.% in primary magma. With such quantities of H2O, fractional crystallization is controlled by olivine + plagioclase at 2 kbar. Increasing the pressure from 2 to ≥4 kbar induces early crystallization of orthopyroxene instead of olivine and therefore SiO2 enrichment in the residual melts is suppressed. Increasing H2O (≥ ∼2 wt.% in primary magma) stabilizes clinopyroxene relative to orthopyroxene and/or magnetite. Although the phase relations and proportions strongly depend on fO2 and H2O content, differentiation trends are always calc-alkaline.

In order to quantify H2O content and chemical composition of island arc low-K tholeiite magma that crystallized Ca-rich plagioclase, melt inclusions of a typical island arc tholeiite from Izu-Oshima volcano (34°N 44', 139°E 24') were analyzed. Composition of studied plagioclase ranges widely from An83 to An95. Composition of studied melt inclusions also shows wide variation, which suggests that the melt inclusions represent various stages of crystallization differentiation at Izu-Oshima volcano. Ca/Na ratios of plagioclase-hosted melt inclusions are comparable with compositions of aphyric lava, which preclude an exotic origin for the Ca-rich plagioclase. Analyzed H2O content of the melt inclusions ranges from 0.2 to 2.4 wt.% (0.2 to 1.4 wt.% for plagioclase-hosted melt inclusions and 0.8 to 2.4 wt.% for olivine-hosted melt inclusions). Ca/Na partition coefficient between plagioclase and hydrous basaltic melt, KD(Ca-Na)plag-melt, is empirically calibrated based on experimental data as ln KD(Ca-Na)plag-melt = 4100/T(K) -800* P(GPa)/T(K) + 2.2* ln (Al2O3melt(wt.%)/Sio2melt(wt.%)) + 0.33* √ H2Omelt(wt.%). Based on the equilibria between host plagioclase and melt inclusion and taking effect of overgrowth into consideration, 3 to 6 wt.% H2O in melt is required. The lower H2O content of the analyzed melt inclusions is probably due to the leakage of volatiles through the host crystal during decompression, eruption and quench. Variation in estimated H2O content in the melt at the time of crystallization of plagioclase (3 to 6 wt.%) can be due to polybaric crystallization from H2O-saturated melt.

In Japan, 47 among 110 active volcanoes are monitored by the Japan Meteorological Agency on a 24-h basis, and several universities develop volcanological studies with their own volcano observatories at some of the recently active volcanoes. Some other research institutes also study several volcanoes for their own research purposes. The primary mission of the Japanese Coordinating Committee for the Prediction of Volcanic Eruptions is to evaluate the activities of volcanic unrest by integrating various data from various agencies; this system has worked fairly well for most of the recent volcano crises. Especially integration of seismicity and crustal deformation data from various institutions has worked promisingly to predict the onset of vulcanian explosions in some volcanoes recently activated. The reason why this kind of interagency cooperative system has worked so far is because volcanic activity in Japan has been fairly low for almost a hundred years. A new centralized system to monitor, analyze, and issue adequate volcanic information is desired to prepare for the accelerated activity of Japanese volcanoes in the near future.

Precise determination of the partitioning of Mg and Fe2+ between olivine and ultramafic melt has been made at pressures from 5 to 13 GPa using a MA-8 type multi-anvil high-pressure apparatus (PREM) installed at Earthquake Research Institute, University of Tokyo. A very short rhenium capsule (

During the early part of a seismic swarm preceding eruption and caldera formation at Miyakejima Volcano, discoloured sea surfaces were observed ∼1.5 km off the western coast of Miyakejima on 27 June 2000. A later survey of the area using a multi-beam side scan sonar and a remotely operated small submarine revealed four craters of 20–30 m diameter aligned east-west in a 100×10–30 m area on the seafloor, with hot water at ∼140°C being released from one of the centres. Each crater consists of submarine spatter overlain in part by scoria lapilli. Dredged spatter from the craters was fresh, and there was no evidence of activity of marine organisms on the spatter surface, indicating that the discoloured sea surface resulted from magmatic eruption on the seafloor. This eruption occurred when a westward-propagating seismic swarm, initiated beneath Miyakejima’s summit, passed through the area. Finding new magma on the seafloor demonstrates that this seismic swarm was associated with intruding magma, moving outward from beneath Miyakejima. Submarine spatter shows flattened shapes with a brittle crust formed by cooling in water, and its composition is aphyric andesite of ∼54 wt% SiO2. The spatter is similar in whole rock and mineral composition to spatter erupted in 1983. However, the wide range of Cl in melt inclusions in plagioclase of the 27 June submarine spatter shows that it is not simply a remnant of the 1983 magma, which has only high Cl melt inclusions in plagioclase. The mixed character of melt inclusions suggests involvement of a magma with low Cl melt inclusions. The magma erupted explosively on 18 August from Miyakejima’s summit, considered as the second juvenile magma in this eruption, contains low Cl melt inclusions in plagioclase. Based on these observations and the eruption sequence, we present the following model: (1) A shallow magma chamber was filled with a remnant of 1983 magma that had evolved to a composition of 54–55 wt% SiO2. (2) Injection of the 18 August magma into this chamber generated a mixed magma having a wide range of Cl in melt inclusions contained plagioclase. The magma mixing might have occurred shortly before the submarine eruption and could have been a trigger for the initiation of the removal of magma from the chamber as an extensive dyke, which eventually led to caldera subsidence.

Based on the combination of petrologic characteristics of the deposits and carbon-14 dating of charcoal pieces, we determined the burial age of the ancient Roman villa, believed to belong to the first Roman Emperor Augustus, at the northern foot of Mt. Vesuvius. Volcanic deposits covering the site consist of three geological formations related to the eruptive activity of Mt. Vesuvius. Juvenile material of the lowest formation show the same whole-rock chemical composition as that of the AD472 eruption, and carbon-14 ages of charcoal in and below the deposits coincide with AD472, indicating that the villa was first buried by the AD472 eruption. The villa itself is thought to have been already abandoned, judging from the depositional relation of the Plinian-fall and pyroclastic surge deposits to the damaged building frames.

Island arc low-K tholeiites are basaltic magmas erupting from frontal arc volcanoes of juvenile arcs associated with the subduction of old and cold plates. We investigated the origins of geochemical variation in volcanic rocks having multiple phase saturated liquid compositions from the Izu-Oshima volcano in the northern Izu arc. The geochemical variations in the liquids fall between two endmember trends, namely higher- and lower-Al/Si trends. Polybaric differentiation of H2O-saturated melts between a 4-km-deep magma chamber and degassed melts near the surface should be responsible for the observed variation in the liquids.

EARTHQUAKE RESEARCH INSTITUTE, THE UNIVERSITY OF TOKYO, TOKYO 113-0032, JAPAN INSTITUTE FOR GEOTHERMAL SCIENCES, KYOTO UNIVERSITY, NOGUCHIBARU, BEPPU 874-0903, JAPAN PLOT NO. 89, FRIENDS HOUSING SOCIETY LAYOUT-4, DEENDAYALNAGAR, NAGPUR 400 022, INDIA FACULTY OF GEO-ENVIRONMENTAL SCIENCES, RISSHO UNIVERSITY, KUMAGAYA 360-0194, JAPAN DEPARTMENT OF EARTH SCIENCES, NIHON UNIVERSITY, TOKYO 156-0045, JAPAN

The 2000 eruption of Miyakejima volcano started with a submarine eruption of basaltic andesite on the morning of June 27, which occurred following earthquake swarms during the previous night. The main phase of the summit eruption began, being associated by a sudden subsidence of the summit area on July 8. Continuous collapsing of the summit area that had continued until midAugust, resulted in the formation of a caldera with the volume of about 0.6 km3. Phreatic (or phreatomagmatic) eruptions took places during the growth of the caldera, although the total volume of eruptives was about 11 million m3. which is smaller by one magnitude than the caldera volume. Eruptives are enriched with hydrothermally altered materials such as smectite and kaolinite.The manner of the first collapse suggests the existence of a large open space under the summit just before the subsidence. Judging from geophysical observation results, the open space may have ascended in the manner of stoping. Successive formation of open spaces at deeper levels is likely to have caused the continuous collapse of the summit area. These open spaces may have been generated by magma's migration from under Miyakejima to the west. The migration is considered to have continued by August 18.It is likely that an inflow of underground water to the open spaces generated a hydrothermal system, where the open spaces acted as a sort of pressure cooker that built up overpressure of eruptions. The hydrothermal system was broken by the largest eruption on August 18, and the eruption column rose about 15 km above the summit. A boiling-over type of eruption occurred on August 29, whereby sufficient overpressure of steam was not built up, resulting in the generation of low-temperature ash cloud surges moving very slowly.

The water released from descending oceanic lithosphere is thought to have an important role in subduction-zone magmatism, as this water might trigger partial melting of the mantle wedge above the subducting plate1,2,3,4,5,6,7,8. If, however, there is incomplete wetting of mineral grain boundaries in the mantle (that is, the dihedral angle9 at the triple junctions between grains is more than 60°), then the water would not form an interconnected network and might instead be trapped as interstitial fluid in the mantle peridotite. The water would then be transported to deeper parts of the mantle rather than triggering partial melting. Here we use dihedral-angle data to estimate the connectivity of an aqueous fluid phase in a model upper-mantle mineral assemblage (forsterite) at pressures from 3 to 5 GPa (corresponding to depths of ∼80–150 km). By combining these data with previous results10,11, we find that the dihedral angle is greater than 60° at low pressure and temperature (

Large-scale collapse of a dacite dome in the late afternoon of 15 September 1991 generated a series of pyroclastic-flow events at Unzen Volcano. Pyroclastic flows with a volume of 1×106 m3 (as DRE) descended the northeastern slope of the volcano, changing their courses to the southeast due to topographic control. After they exited a narrow gorge, an ash-cloud surge rushed straight ahead, detaching the main body of the flow that turned and followed the topographic lows to the east. The surge swept the Kita-Kamikoba area, which had been devastated by the previous pyroclastic-flow events, and transported a car as far as 120 m. Following detachment, the surge lost its force after it moved several hundred meters, but maintained a high temperature. The deposits consist of a bottom layer of better-sorted ash (unit 1), a thick layer of block and ash (unit 2), and a thin top layer of fall-out ash (unit 3). Unit 2 overlies unit 1 with an erosional contact. The upper part of unit 2 grades into better-sorted ash. At distal block-and-ash flow deposits, the bottom part of unit 2 also consists of better-sorted ash, and the contact with the unit 1 deposits becomes ambiguous. Video footage of cascading pyroclastic flows during the 1991–1995 eruption, traveling over surfaces without any topographic barriers, revealed that lobes of ash cloud protruded intermittently from the moving head and sides, and that these lobes surged ahead on the ground surface. This fact, together with the inspection by helicopter shortly after the events, suggests that the protruded lobes consisted of better-sorted ash, and resulted in the deposits of unit 1. The highest ash-cloud plume at the Oshigadani valley exit, and the thickest deposition of fall-out ash over Kita-Kamikoba and Ohnokoba, indicate that abundant ash was also produced when the flow passed through a narrow gorge. In the model presented here, the ash clouds from the pyroclastic flows were composed of a basal turbulent current of high concentration (main body), an overriding and intermediate fluidization zone, and an overlying dilute cloud. Release of pressurized gas in lava block pores, due to collisions among blocks and the resulting upward current, caused a zone of fluidization just above the main body. The mixture of gas and ash sorted in the fluidization zone moved ahead and to the side of the main body as a gravitational current, where the ash was deposited as surge deposits. The main body, which had high internal friction and shear near its base, then overran the surge deposits, partially eroding them. When the upward current of gas (fluidization) waned, better-sorted ash suspended in the fluidization zone was deposited on block-and-ash deposits. In the distal places of block-and-ash deposits, unit 2 probably was deposited in non-turbulent fashion without any erosion of the underlying layer (unit 1).

Pargasite commonly occurs in the dacitic groundmass of the 1991–1995 eruption products of Unzen volcano. We described the occurrence and chemical compositions of amphibole in the dacite, and also carried out melting experiments to determine the low-pressure stability limit of amphibole in the dacite. The 1991–1995 ejecta of the Unzen volcano show petrographic evidence of magma mixing, such as reverse compositional zoning of plagioclase and amphibole phenocrysts, and we used a groundmass separate as a starting material for the experiments. Reversed experiments show that the maximum temperature for the crystallization of amphibole is 930°C at 196 MPa, 900°C at 98 MPa, and 820°C at 49 MPa. Compared with the experimental results on the Mount St. Helens dacite, present experiments on the Unzen dacitic groundmass show that amphibole is stable to pressures ca. 50 MPa lower at 850°C. Available Fe–Ti oxide thermometry indicates the crystallization temperature of the groundmass of the Unzen dacite to be 880±30°C, suggesting that the groundmass pargasite crystallized at >70 MPa, corresponding to a depth of more than 3 km in the conduit. The chlorine content of the groundmass pargasite is much lower than that of phenocrystic magnesiohornblende in the 1991–1995 dacite of Unzen volcano, indicating that vesiculation/degassing of magma took place before the crystallization of the groundmass pargasite. The present study shows that the magma was water oversaturated and that the degassing of magma along with magma mixing caused crystallization of the groundmass amphibole at depths of more than 3 km in the conduit.

Upward migration of subducted oceanic crust from deep in the upper mantle is discussed based on high-pressure experimental data. Numerical calculation reveals that a subducted oceanic crust, which is negatively buoyant in the present upper mantle, can ascend from the transition zone and be observed as a discrete magma source at the surface only when it has been broken into fragments comparable in dimension with its thickness and involved in a solid diapir of heated peridotite. For example, a solid diapir of heated peridotite with a temperature excess of 200°C can contain up to 15∼20 vol% of fragments of oceanic crust when it passes through the upper mantle, and it may cause extensive basaltic volcanism at the surface.

A composite diapir model for extensive basaltic volcanism is proposed on the basis of the melting phase relations of subducted oceanic crust in the mantle. Ascending peridotitic diapir across 660km discontinuity drags fragments of subducted oceanic crust stagnating there into the diapir and forms a“composite diapir”. Because of the differential melting between peridotite and oceanic crust, ascent of such a composite diapir can produce voluminous basaltic magma by melting of subducted oceanic crust, capsulated in solid peridotite. Release of the voluminous basalt magma would be triggered by partial melting of diapir-forming peridotite in the shallow upper mantle. Physical and chemical properties of the resulting hybrid magma can explain most features of continental flood basalt.

The occurrence of pumice in the Central Indian Basin (CIB) has been a controversy. Some are of the opinion that these pumices are erupted from a volcano along the Ninetyeast ridge while others suggest the Indonesian arc volcanism as their probable source. Recently, it is also suggested that the pumice are the products of in-situ silicic volcanism in the CIB. This study was initiated in order to resolve this controversy about the origin of the fresh pumice from the CIB. The fresh pumice pieces of different sizes and shapes were collected from the surficial sediments of the CIB from an average depth of about 5000 m (12 °S, 76 °E). Glass is the main phase comprising about 95% (volume) and resembles the matrix glass in Krakatau 1883 dacitic pumice which is also very poor (< 5%) in the modal mineral composition. The mineral and glass analyses were carried out with the help of the electron microprobe. The orthopyroxenes, clinopyroxenes, plagioclases and spinels are the mineral phases present in these pumices. The pyroxenes have similar wo, en and fs components to those previously reported from the 1883 Krakatau eruption products. Geochemically, these fresh pumices have a high SiO2 content (71%) and high total alkali content (8%) similar to 1883 eruption products of Krakatau. Thus based on the similarities in mineralogy and glass chemical composition it is inferred that these fresh pumices are the products of the fierce 1883 eruption of the Krakatau volcano in the Sunda Strait of the Indonesian arc.

We have measured the inclusive ${\mathit{D}}^{\mathrm{*}\ifmmode\pm\else\textpm\fi{}}$ production cross secton in a two-photon collision at the KEK ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ collider TRISTAN. The mean \ensuremath{\surd}s of the collider was 57.16 GeV and the integrated luminosity was 150 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$. The differential cross section [d\ensuremath{\sigma}(${\mathit{D}}^{\mathrm{*}\ifmmode\pm\else\textpm\fi{}}$)/${\mathit{dP}}_{\mathit{T}}$] was obtained in the ${\mathit{P}}_{\mathit{T}}$ range between 1.6 and 6.6 GeV and compared with theoretical predictions, such as those involving direct and resolved photon processes.

High pressure melting experiments on an anhydrous abyssal tholeiite collected from the Mid-Atlantic Ridge have been conducted over the pressure interval 3 to 20 GPa to explore the fate of subducted oceanic crust in the mantle. The composition of the mid-ocean ridge basalt (MORB) is almost identical to the average basaltic layer of the oceanic lithosphere. The melting phase relations of the MORB are summarized as follows: (1) the liquidus temperature is about 1425°C at 3 GPa, and it rises almost linearly to above 1900°C at 10 GPa. The slope of the liquidus curve decreases slightly above 10 GPa. Nevertheless, it still has a positive slope with increasing pressure. At 20 GPa, the liquidus temperature is about 2200°C. (2) The liquidus phase changes from clinopyroxene to garnet above 3.5 GPa. (3) The solidus temperature rises almost linearly to 2100 °C at 20 GPa; consequently, the melting interval is slightly narrower at high pressures (

The melting relation of iron-carbon system is studied to see how iron takes in or disgorges carbon at high pressure (up to 12GPa). The understanding on these points is closely related to the problem of the reservoir of carbon in the earth's interior. The results are: (1) Iron-carbon system shows eutectic melting till at least 12GPa. (2) The eutectic composition is about 3 or 4 wt% of carbon, which does not vary very much with pressure. (3) The eutectic temperature slightly goes up as pressure increases at a rate of 7°C/GPa. This gradient is fairly lower than that of the melting temperature of silicates. Based on these results and other facts, the following scenario is inferred on the core formation during the early stage of the earth. Because carbon melts into iron forming eutectic system at low temperature, carbon within the accreted chondritic materials might be absorbed into iron melt near the surface of the magma ocean. The observation that the melting temperature of silicate goes up more rapidly as pressure increases than the eutectic temperature of iron-carbon system, indicates that the temperature within the magma ocean is maintained higher than the melting temperature of iron-carbon system. Therefore, the carbon-bearing iron melt may sink into the deep interior of the earth without solidifying and disgorging carbon. After all, it is strongly suggested that carbon may settle with liquid iron forming core.

To monitor the relative oxidation state, a calcia-stabilized zirconia solid-electrolyte oxygen fugacity sensor was used in high-pressure experiments in a multi-anvil type apparatus. The sensor was tested at high pressures using several combinations of common oxygen buffers, and was shown to work up to at least 7 GPa and 1350°C over a wide range of oxygen fugacities between the iron-wustite (IW) and the magnetite-hematite (MH) oxygen buffers. Rapid responses of the e.m.f. of the sensor to the changes in P-T conditions allow us to carry out in situ oxygen fugacity measurement during high-pressure experiments. The sensor was also used to measure the relative oxygen fugacity prevailing within graphite sample capsules at conditions from 2 to 7 GPa and from 1000 to 1350°C. The redox condition within the graphite capsule is as follows: (1) with increasing temperature, relative to the wustite-magnetite (WM) oxygen buffer, graphite becomes more reducing at constant pressure, and this causes the stable iron oxide phase in the capsule to change from magnetite to wustite; (2) this temperature dependence is, however, affected by pressure—below 3 GPa, graphite becomes more oxidizing relative to WM with increasing pressure at constant temperature, whereas above 3 GPa, it becomes less oxidizing relative to WM with increasing pressure, and this results in an enlargement of the field of graphite-wustite coexistence. Some other applications of the sensor to high-pressure research are briefly discussed, including the in situ detection of phase transformation and pressure calibration at elevated temperature.

We carried out the energy scan between ECM = 58 and 60 GeV at the TRISTAN e+e− collider to search for the possible narrow resonance suggested by the L3 experiment at LEP. The total cross sections are measured for γγ, multihadron, e+e− and μ + μ− production at ten energy points covering this energy range almost uniformly. The results are in good agreement with the Standard Model predictions, and 95% confidence level upper limits are set to Γee × BR of the hypothetical scalar and tensor resonances.