Explosive volcanic eruptions triggered by cosmic rays: Volcano as a bubble chamber     

Toshikazu Ebisuzaki  Hiroko Miyahara  Ryuho Kataoka  Tatsuhiko Sato  Yasuhiro Ishimine 《Gondwana Research》2011,19(4):1054-1061

Volcanoes with silica-rich and highly viscous magma tend to produce violent explosive eruptions that result in disasters in local communities and that strongly affect the global environment. We examined the timing of 11 eruptive events that produced silica-rich magma from four volcanoes in Japan (Mt. Fuji, Mt. Usu, Myojin-sho, and Satsuma-Iwo-jima) over the past 306 years (from AD 1700 to AD 2005). Nine of the 11 events occurred during inactive phases of solar magnetic activity (solar minimum), which is well indexed by the group sunspot number. This strong association between eruption timing and the solar minimum is statistically significant to a confidence level of 96.7%. This relationship is not observed for eruptions from volcanoes with relatively silica-poor magma, such as Izu-Ohshima. It is well known that the cosmic-ray flux is negatively correlated with solar magnetic activity, as the strong magnetic field in the solar wind repels charged particles such as galactic cosmic rays that originate from outside of the solar system. The strong negative correlation observed between the timing of silica-rich eruptions and solar activity can be explained by variations in cosmic-ray flux arising from solar modulation. Because silica-rich magma has relatively high surface tension (~ 0.1 Nm^?1), the homogeneous nucleation rate is so low that such magma exists in a highly supersaturated state without considerable exsolution, even when located relatively close to the surface, within the penetration range of cosmic-ray muons (1–10 GeV). These muons can contribute to nucleation in supersaturated magma, as documented by many authors studying a bubble chamber, via ionization loss. This radiation-induced nucleation can lead to the pre-eruptive exsolution of H₂O in the silica-rich magma. We note the possibility that the 1991 Mt. Pinatubo eruption was triggered by the same mechanism: an increase in cosmic-ray flux triggered by Typhoon Yunya, as a decrease in atmospheric pressure results in an increase in cosmic-ray flux. We also speculate that the snowball Earth event was triggered by successive large-scale volcanic eruptions triggered by increased cosmic-ray flux due to nearby supernova explosions.  相似文献   

The Kellwasser events in the Upper Devonian Frasnian to Famennian transition in the Toc Tat Formation,northern Vietnam     

Toshifumi Komatsu  Ryota Urakawa  Toshitaka Inada  Kazuki Yamauchi  Takumi Maekawa  Reishi Takashima  Mark Williams  Phong D. Nguyen  Hung D. Doan  Minh T. Nguyen  Shuji Niko  Gengo Tanaka  Tatsuhiko Yamaguchi 《Island Arc》2019,28(1)

Upper Devonian carbonates of the Toc Tat Formation in the Si Phai Pass area of Dong Van District, northern Vietnam were deposited in carbonate platform, slope, and basin environments. These carbonates yield abundant conodonts indicative of the Palmatolepis nasuta, Pa. linguiformis and Pa. triangularis zones, the Frasnian–Famennian stage boundary being identified by the first occurrence of Pa. triangularis. Two positive carbon isotope excursions are recognized, the lower excursion peaking in the interval of the lower to middle Pa. nasuta Zone, whilst the upper excursion peaks just above the local Frasnian–Famennian boundary. Based on the biostratigraphy, these excursions equate to the Lower and Upper Kellwasser events. Locally, tentaculitoid taxa (Nowakia, Styliolina, Homoctenus, and Metastyliolina?) are abundant in the interval of the Pa. nasuta Zone, but show a drastic decline in abundance before the Lower Kellwasser Event, and only two taxa survived into the Famennian.  相似文献   

Cycladophora davisiana (Radiolaria) in the Okhotsk Sea: A key for reconstructing glacial ocean conditions     

Yusuke Okazaki  Osamu Seki  Takeshi Nakatsuka  Tatsuhiko Sakamoto  Minoru Ikehara  Kozo Takahashi 《Journal of Oceanography》2006,62(5):639-648

Cycladophora davisiana, a radiolarian species dwelling at mesopelagic depths, is known as a representative glacial fauna due to its unique distribution during glacial periods. In the present ocean, abundant production of C. davisiana is only observed in the Okhotsk Sea, indicating an adaptation of C. davisiana for seasonal sea-ice covered conditions. We found pronounced abundant production of C. davisiana during the early to middle Holocene in the Okhotsk Sea, suggesting more favorable conditions for C. davisiana than the present Okhotsk Sea. In order to clarify the reason, oceanographic conditions during the Holocene were reconstructed based on biomarkers, lithogenic grains including ice-rafted debris (IRD), biogenic opal, and total organic carbon (TOC) in two sediment cores from the Okhotsk Sea. These indicators suggest that the pronounced C. davisiana production may be attributed to: 1) a supply to mesopelagic depths under intensified stratification of fine organic particles derived from coccolithophorids, bacteria, and detrital materials; and 2) cold, well-ventilated intermediate water formation.  相似文献   

A new, automatic hydrothermal fluid sampler using a shape-memory alloy   总被引：2，自引：0，他引：2  

Takeshi Naganuma  Masanori Kyo  Tatsuhiko Ueki  Kazuhiko Takeda  Jun-ichiro Ishibashi 《Journal of Oceanography》1998,54(3):241-246

A new hydrothermal fluid sampler has been developed to provide more maneuverability in underwater operation. The sampler characteristically employs a shape-memory alloy, which senses high temperature and actuates the suction mechanism. A shape-memory alloy is also used to switch the intake valve of the sampler, the intention being to avoid missampling when the inlet is in low temperature water. Prototype samplers were designed to collect the fluids hotter than 80°C. Test sampling was performed at hydrothermal vents (1372–1374 m deep) in the submarine volcano, Suiyo Seamount, Izu-Bonin Arc, northwestern Pacific. Observed fluid temperature was between 138 and 298°C, while the ambient seawater temperature was 3.1°C. Each prototype collected about 100 ml fluid as designed. The magnesium concentration in the samples indicated a seawater content of 47.5–90.8%, which indicates the entrainment of ambient seawater. Microscopic observatinn revealed the occurrence of microorganisms in the sample fluids at a population density of 10⁵ to 10⁶ cells ml⁻¹, which is 2–3 orders of magnitude higher than those in seawater at that depth. The use of the newly developed fluid sampler will greatly facilitate the collection of vent-associated microorganisms, which are of potential biological and biotechnological interest.  相似文献   

Short-term variabilities of upper ocean current in the warm pool region during TOGA/COARE IOP     

Iwao Ueki  Kunio Kutsuwada  Hideo Inaba  Arata Kaneko 《Journal of Oceanography》1998,54(3):227-240

Oceanic current data in the warm pool region of the western equatorial Pacific measured by upward-looking moored Acoustic Doppler Current Profilers at two equatorial sites (147°E and 154°E) and two off-equatorial sites (2°N and 2°S, 156°E) during TOGA/COARE Intensive Observing Period (IOP) from November 1992 to February 1993 are used to examine short-term variabilities in the upper layer above 160–240 m. In time series of the zonal and meridional currents in many layers, spectral peaks are found at periods around 2 days and 4 days in addition to high energies in a period range longer than 10 days. The signal with the period of about 2 days has significantly high energies at all sites, and its magnitude is higher for the meridional current than for the zonal one. This signal is especially active in the first half of IOP from November to December in 1992. In this period, the quasi-2-day signal in the current field is coherent between northern (2°N) and southern (2°S) stations, but it has no evident relationship with that in the surface wind field around the stations. The quasi-4-day signal with the period of about 4 days has highest energies in layers above 160 m at the southern station, and is coherent between northern and southern stations. Besides, the signal at the station of 2°S has a significantly high coherence with that in the wind at the southern station, suggesting that it is a local phenomenon.  相似文献   

On the equivalence of two methods for computing partial derivatives of seismic waveforms—II. Laterally homogeneous initial model     

Robert J. Geller  Tatsuhiko Hara  Seiji Tsuboi 《Geophysical Journal International》1990,102(2):499-502

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Synthesis of scalar-wave envelopes in two-dimensional weakly anisotropic random media by using the Markov approximation     

Tatsuhiko Saito 《Geophysical Journal International》2006,165(2):501-515

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Simultaneous waveform inversion for three-dimensional Earth structure and earthquake source parameters considering a wide range of modal coupling     

Tatsuhiko Hara  & Robert J. Geller 《Geophysical Journal International》2000,142(2):539-550

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Determination of the isotropic component of deep focus earthquakes by inversion of normal-mode data     

Tatsuhiko Hara  Keiko Kuge  Hitoshi Kawakatsu 《Geophysical Journal International》1996,127(2):515-528

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Melt inclusion analysis of the Unzen 1991–1995 dacite: implications for crystallization processes of dacite magma     

Koshi Nishimura  Tatsuhiko Kawamoto  Tetsuo Kobayashi  Takeshi Sugimoto  Shigeru Yamashita 《Bulletin of Volcanology》2005,67(7):648-662

Dacitic magma, a mixture of high-temperature (T) aphyric magma and low-T crystal-rich magma, was erupted during the 1991–1995 Mount Unzen eruptive cycle. Here, the crystallization processes of the low-T magma were examined on the basis of melt inclusion analysis and phase relationships. Variation in water content of the melt inclusions (5.1–7.2 wt% H₂O) reflected the degassing history of the low-T magma ascending from deeper levels (250 MPa) to a shallow magma chamber (140 MPa). The ascent rate of the low-T magma decreased markedly towards the emplacement level as crystal content increased. Cooling of magma as well as degassing-induced undercooling drove crystallization. With the decreasing ascent rate, degassing-induced undercooling decreased in importance, and cooling became more instrumental in crystallization, causing local and rapid crystallization along the margin of the magma body. Some crystals contain scores of melt inclusions, whereas there are some crystals without any inclusions. This heterogeneous distribution suggests the variation in the crystallization rate within the magma body; it also suggests that cooling was dominant cause for melt entrapment. Numerical calculations of the cooling magma body suggest that cooling caused rapid crystal growth and enhanced melt entrapment once the magma became a crystal-rich mush with evolved interstitial melt. The rhyolitic composition of melt inclusions is consistent with this model.Editorial responsibility: H Shinohara  相似文献