Reconstruction of the 2014 eruption sequence of Ontake Volcano from recorded images and interviews

A phreatic eruption at Mount Ontake (3067 m) on September 27, 2014, led to 64 casualties, including missing people. In this paper, we clarify the eruption sequence of the 2014 eruption from recorded images (photographs and videos obtained by climbers) and interviews with mountain guides and workers in mountain huts. The onset of eruption was sudden, without any clear precursory surface phenomena (such as ground rumbling or strong smell of sulfide). Our data indicate that the eruption sequence can be divided into three phases. Phase 1: The eruption started with dry pyroclastic density currents (PDCs) caused by ash column collapse. The PDCs flowed down 2.5 km SW and 2 km NW from the craters. In addition, PDCs moved horizontally by approximately 1.5 km toward N and E beyond summit ridges. The temperature of PDCs at the summit area partially exceeded 100 °C, and an analysis of interview results suggested that the temperature of PDCs was mostly in the range of 30–100 °C. At the summit area, there were violent falling ballistic rocks. Phase 2: When the outflow of PDCs stopped, the altitude of the eruption column increased; tephra with muddy rain started to fall; and ambient air temperature decreased. Falling ballistic rocks were almost absent during this phase. Phase 3: Finally, muddy hot water flowed out from the craters. These models reconstructed from observations are consistent with the phreatic eruption models and typical eruption sequences recorded at similar volcanoes.ArticleEarth, Planets and Space. 68:79 (2016)journal articl

Reconstruction of a phreatic eruption on 27 September 2014 at Ontake volcano, central Japan, based on proximal pyroclastic density current and fallout deposits

The phreatic eruption at Ontake volcano on 27 September 2014, which caused the worst volcanic disaster in the past half-century in Japan, was reconstructed based on observations of the proximal pyroclastic density current (PDC) and fallout deposits. Witness observations were also used to clarify the eruption process. The deposits are divided into three major depositional units (Units A, B, and C) which are characterized by massive, extremely poorly sorted, and multimodal grain-size distribution with 30–50 wt% of fine ash (silt–clay component). The depositional condition was initially dry but eventually changed to wet. Unit A originated from gravity-driven turbulent PDCs in the relatively dry, vent-opening phase. Unit B was then produced mainly by fallout from a vigorous moist plume during vent development. Unit C was derived from wet ash fall in the declining stage. Ballistic ejecta continuously occurred during vent opening and development. As observed in the finest population of the grain-size distribution, aggregate particles were formed throughout the eruption, and the effect of water in the plume on the aggregation increased with time and distance. Based on the deposit thickness, duration, and grain-size data, and by applying a scaling analysis using a depth-averaged model of turbulent gravity currents, the particle concentration and initial flow speed of the PDC at the summit area were estimated as 2 × 10−4–2 × 10−3 and 24–28 m/s, respectively. The tephra thinning trend in the proximal area shows a steeper slope than in similar-sized magmatic eruptions, indicating a large tephra volume deposited over a short distance owing to the wet dispersal conditions. The Ontake eruption provided an opportunity to examine the deposits from a phreatic eruption with a complex eruption sequence that reflects the effect of external water on the eruption dynamics.ArticleEarth, Planets and Space. 68: 82(2016)journal articl

Petrological architecture of a magmatic shear zone: A multidisciplinary investigation of strain localisation during magma ascent at Unzen volcano, Japan

Shearing of magma during ascent can promote strain localisation near the conduit margins. Anymechanical and thermal discontinuities associated with such events may alter the chemical, physicaland rheological stability of the magma and thus its propensity to erupt. Lava spines can record suchprocesses, preserving a range of macroscopic and microscopic deformation textures, attributed toshearing and friction, as magma ascends through the viscous-brittle transition. Here, we use a multi-disciplinary approach combining petrology, microstructures, crystallography, magnetics and experi-mentation to assess the evidence, role and extent of shearing across a marginal shear zone of the1994–1995 lava spine at Unzen volcano, Japan. Our results show that crystals can effectively moni-tor stress conditions during magma ascent, with viscous remobilisation, crystal plasticity and com-minution all systematically increasing towards the spine margin. Accompanying this, we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex-tural variations across the shear zone, from symplectitic to granular rims towards the spine margin.In addition, the compaction of pores, chemical and textural alteration of interstitial glass and mag-netic variations all change systematically with shear intensity. The strong correlation between thedegree of shearing, crystal deformation and disequilibrium features, together with distinct magneticproperties, implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent. This was accompanied by late-stage or post-emplacement fluid- andgas-induced alteration of the gouge, as well as oxidation and glass devitrification. Understandingand recognising evidence for strain localisation during magma ascent may, therefore, be vital whenassessing factors that regulate the style of volcanic eruptions, which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava dome

Mitochonic Acid 5 (MA-5) Facilitates ATP Synthase Oligomerization and Cell Survival in Various Mitochondrial Diseases

Mitochondrial dysfunction increases oxidative stress and depletes ATP in a variety of disorders. Several antioxidant therapies and drugs affecting mitochondrial biogenesis are undergoing investigation, although not all of them have demonstrated favorable effects in the clinic. We recently reported a therapeutic mitochondrial drug mitochonic acid MA-5 (Tohoku J. Exp. Med., 2015). MA-5 increased ATP, rescued mitochondrial disease fibroblasts and prolonged the life span of the disease model “Mitomouse” (JASN, 2016). To investigate the potential of MA-5 on various mitochondrial diseases, we collected 25 cases of fibroblasts from various genetic mutations and cell protective effect of MA-5 and the ATP producing mechanism was examined. 24 out of the 25 patient fibroblasts (96%) were responded to MA-5. Under oxidative stress condition, the GDF-15 was increased and this increase was significantly abrogated by MA-5. The serum GDF-15 elevated in Mitomouse was likewise reduced by MA-5. MA-5 facilitates mitochondrial ATP production and reduces ROS independent of ETC by facilitating ATP synthase oligomerization and supercomplex formation with mitofilin/Mic60. MA-5 reduced mitochondria fragmentation, restores crista shape and dynamics. MA-5 has potential as a drug for the treatment of various mitochondrial diseases. The diagnostic use of GDF-15 will be also useful in a forthcoming MA-5 clinical trial

Seismic exploration at Fuji volcano with active sources : The outline of the experiment and the arrival time data

Fuji volcano (altitude 3,776m) is the largest basaltic stratovolcano in Japan. In late August and early September 2003, seismic exploration was conducted around Fuji volcano by the detonation of 500 kg charges of dynamite to investigate the seismic structure of that area. Seismographs with an eigenfrequency of 2 Hz were used for observation, positioned along a WSW-ENE line passing through the summit of the mountain. A total of 469 seismic stations were installed at intervals of 250-500 m. The data were stored in memory on-site using data loggers. The sampling interval was 4 ms. Charges were detonated at 5 points, one at each end of the observation line and 3 along its length. The first arrival times and the later-phase arrival times at each station for each detonation were recorded as data. P-wave velocities in the surface layer were estimated from the travel time curves near the explosion points, with results of 2.5 km/s obtained for the vicinity of Fuji volcano and 4.0 km5/s elsewhere

外帯S-type珪長質火成岩類中にみられるI-type火成

Two kinds of igneous xenoliths of andesitic composition were found in the granodiorite　porphyry in the Miocene Osuzuyama felsic igneous complex in the Outer Zone of Southwest Japan. Both black-coloured lens and crystal clot were found in the rhyolite to dacite welded tuff of the complex. Phenocrysts of the granodiorite porphyry are plagioclase, orthopyroxene and quartz. One of the xenoliths is the Oseuchi type (OsX) composed of plagioclase, orthopyroxene and (±） quartz, and the other is the Mimikawa type (MiX) composed of orthopyroxene, augite, subcalcic-augite, pigeonite, plagioclase and devitrified glass. Black lens consists of plagioclase phenocryst, pyroxene (?) and plagioclase microphenocrysts, cryptocrystalline matrix and crystal clot. Crystal clot in the welded tuff, as well as in the black lens, shows the texture of plagioclase-orthopyroxene aggregation. Pigeonite geothermometry gives about 1000°C for MiX, while equilibrium temperature of the host magma had been estimated at about 800°C. It may be suggested that MiX is a part of quenched andesite magma which was injected into the felsic magma chamber before the eruption, and that OsX is crystal cumulation transported from the bottom of the magma chamber during the agitation by the injected magma (MiX). Black lens may be a part of the andesite magma with some small pieces of OsX, crystal clot. The granodiorite porphyry of 14 m. y. ago had a 67^Sr/66^Sr ratio of 0. 7099 and belongs to the S-type (CHAPPELL & WHITE, 1974), while OsX and MiX with low 67^Sr/86^Sr ratios to the I-type. In explanation of the above petrographical and geochemical data for the host rock and xenolith, a possible manner of ascent of the felsic magma is partial zone melting. Xenoliths similar to OsX and MiX were also found in other felsic igneous complexes of the S-type in the Outer Zone, Southwest Japan

A sequence of a plinian eruption preceded by dome destruction at Kelud volcano, Indonesia, on February 13, 2014, revealed from tephra fallout and pyroclastic density current deposits

A plinian-style eruption with a radially spreading umbrella cloud occurred on February 13, 2014, at Kelud volcano, Indonesia. We present the sequence of this plinian event based on a geological survey of the eruption products and analysis of satellite images. The eruptive deposits were divided into four major depositional units (Units A, B, C, and D) and used to determine the sequence of events. The plinian phase was preceded by partial destruction of the existing lava dome and generation of high-energy pyroclastic density currents (PDCs) mainly toward the NE that produced a series of depositional subunits (Units A0–2) and blown-down trees (stage 1). In the main phase of the plinian eruption, tephra fallout (Unit B) was widely distributed over East Java (stage 2). The winds above the volcano significantly affected the tephra dispersal process. In stage 3, the plinian column collapsed, generating dense PDCs that flowed down the volcano valleys, producing pumiceous lobate deposits (Unit C). The declining phase of the eruption produced fine-rich fallout tephra layers (Unit D1–2) from low-level eruption plumes and/or ash lofted from PDCs. The eruption sequence constructed from field observations is supported by geophysical observations. The deposit features and componentry suggest that newly ascended magma triggered the destruction of the lava dome and the generation of high-energy PDCs, and during the subsequent climactic phase the dome was completely destroyed. We estimate a total erupted volume of 0.25–0.50 km3 (bulk deposit volume, 0.14–0.28 km3 in dense rock equivalent) and a mass eruption rate of 6.5 ± 2.8 × 107 kg/s, with a volcanic explosivity index of 4. The eruption sequence and physical parameters of the 2014 eruption will help assess future volcanic activity and hazards at Kelud volcano

ガラス円板を使った珪酸塩岩石中微量元素のけい光X線分析

Analytical techniques for X-ray fluorescence analysis for 9 trace elements (Zr, Y, Sr, Rb, Zn, Cu, Ni, V and Ba) in silicate rocks were investigated by using fused rock samples. The method to make glass disks was the same as that developed for major element analysis (NAKADA et al., 1985). The disks were made from 1 g of a powdered rock sample, 5 g of flux (Li_2 B_4 O_7) and about 30 mg of lithium bromide. To make standard samples for the calibration, pure chemical reagents of trace elements were diluted by flux, and, then, mixed with synthetic rock sample which was also made from chemical reagents. X-ray intensity of a trace element is proportional to its concentration and inversely proportional to the mass absorption coefficient of the glass disk. Background intensities at 2θ=17° and 33° of glass disks were found to be a function of the mass absorption coefficients. This relation was used for the estimation of the mass absorption at a wavelength of X-ray radiated from a trace element. This method is effective for the elements with the absorption edges shorter than Fe-Kα. Glass disks of various compositions, but without any interference of spectral lines, were prepared to estimate interference effects of spectral lines (Sr-Kβ on Zr-Kα, Rb-Kβ on Y-Kα, Br-Kβ on Rb-Kα, Ti-Kα on V-Kα, and Ti-Kα on Ba-Lα). Although the intensity of Y-Kα was corrected twice for spectral interference of Br-Kβ and Rb-Kβ, the correlation between the intensity and the concentration is good, as well as for the other trace elements. The detection limits are about 10 ppm for most trace elements. The analytical results of inter-laboratory geochemical standards are in good agree with their recommended values