Tyagi P.,Hokkaido University |
Yamamoto S.,Hokkaido University |
Yamamoto S.,Mount Fuji Research Institute |
Kawamura K.,Hokkaido University
Biogeosciences | Year: 2015
Hydroxy fatty acids (FAs) in fresh snow from Sapporo, one of the heaviest snowfall regions in the world, have been studied to ascertain the airborne bacterial endotoxin concentrations and their biomass. The presence of β-hydroxy FAs (C9-C28), constituents of the Gram-negative bacterium (GNB), suggests long-range transport of soil microbes. Likewise, the occurrence of α-and β-hydroxy FAs (C9-C30 and C9-C28, respectively) in snow reveals their contribution from epicuticular waxes and soil microorganisms. Estimated endotoxin and GNB mass can aid in assessing their possible impacts on the diversity and functioning of aquatic and terrestrial ecosystems, as well as lethal effects on pedestrians through dispersal of microbes. Air mass back trajectories together with hydroxy FAs reveal their sources from Siberia, the Russian Far East and northern China by the Asian monsoon. This study highlights the role of fresh snow that reduces the human health risk of GNB and endotoxin by the scavenging from air. © Author(s) 2015.
Mori T.,University of Tokyo |
Hashimoto T.,Hokkaido University |
Terada A.,Tokyo Institute of Technology |
Yoshimoto M.,Mount Fuji Research Institute |
And 3 more authors.
Earth, Planets and Space | Year: 2016
A phreatic eruption of Mt. Ontake, Japan, started abruptly on September 27, 2014, and caused the worst volcanic calamity in recent 70 years in Japan. We conducted volcanic plume surveys using an electric multirotor unmanned aerial vehicle to elucidate the conditions of Mt. Ontake's plume, which is flowing over 3000 m altitude. A plume gas composition, sulfur dioxide flux and thermal image measurements and a particle sampling were carried out using the unmanned aerial vehicle for three field campaigns on November 20 and 21, 2014, and June 2, 2015. Together with the results of manned helicopter and aircraft observations, we revealed that the plume of Mt. Ontake was not directly emitted from the magma but was influenced by hydrothermal system, and observed SO2/H2S molar ratios were decreasing after the eruption. High SO2 flux of >2000 t/d observed at least until 20 h after the onset of the eruption implies significant input of magmatic gas and the flux quickly decreased to about 130 t/d in 2 months. In contrast, H2S fluxes retrieved using SO2/H2S ratio and SO2 flux showed significantly high level of 700-800 t/d, which continued at least between 2 weeks and 2 months after the eruption. This is a peculiar feature of the 2014 Mt. Ontake eruption. Considering the trends of the flux changes of SO2 and H2S, we presume that majority of SO2 and H2S are supplied, respectively, from high-temperature magmatic fluid of a deep origin and from hydrothermal system. From the point of view of SO2/H2S ratios and fumarolic temperatures, the plume degassing trend after the 2014 eruption is following the similar course as that after the 1979 eruptions, and we speculate the 2014 eruptive activity will cease slowly similar to the 1979 eruption. © 2016 Mori et al.
Takeshita Y.,Shinshu University |
Matsushima N.,Nature Association of Ina Valley |
Teradaira H.,Nature Association of Ina Valley |
Uchiyama T.,Mount Fuji Research Institute |
Kumai H.,Osaka City University
Quaternary International | Year: 2015
Tephrochronology is an exceptionally important tool in the precise regional correlation of Early and Middle Pleistocene sedimentary strata in Japan. The present study reveals that the Yukawa tephra 5 (YUT5) derived from the Older Ontake volcano, the Nezumigawa (Nzg) and Mitamitajima (Mtj) tephras of the Ina Bazin, and the Byakubi-E tephra (Byk-E) of the Boso Peninsula are the same tephra on the basis oftheir lithofacies, bulk grain composition, mafic mineral composition, major element composition of hornblende, and stratigraphic relationships with the dated tephras. We propose to call the series of tephras correlated with Byk-E the Ontake-Byakubi Tephra Bed (On-Byk Tephra) following the naming convention in which the tephra name consists of the names of the source volcano and the type location. The Matuyama-Brunhes Chronozone boundary occurs just above Byk-E in the type section of the Kokumoto Formation in the Kazusa Group, which is a candidate Global Boundary Stratotype Section and Point (GSSP) for the lower boundary of the Middle Pleistocene Subseries. Therefore, On-Byk Tephra becomes a critically important marker tephra bed for the Early-Middle Pleistocene boundary in central Japan. The present study indicates that the major element composition of hornblende can be a useful tool for identification and correlation of strongly weathered tephra layers such as Nzg and Mtj in which all the volcanic glass shards have been altered. © 2015 Elsevier Ltd and INQUA.
Tsunematsu K.,University of Geneva |
Tsunematsu K.,Mount Fuji Research Institute |
Bonadonna C.,University of Geneva
Bulletin of Volcanology | Year: 2015
Studies of grain-size distributions of explosive volcanic eruptions provide important insights into fragmentation mechanisms and eruptive conditions and are crucial to the modeling of tephra dispersal. As a result of sedimentation processes and plume dynamics, grain-size features vary significantly both in the downwind and crosswind directions and are difficult to characterize. We have analyzed grain-size features in the downwind and crosswind directions of the two largest eruptions of the last 2000 years of Cotopaxi volcano activity (Ecuador). Crosswind grain-size variations are similar for both eruptions (i.e., layers 3 and 5), while at any given downwind distance from vent, the layer 3 deposit is coarser than the layer 5 one. This suggests that layers 3 and 5 were characterized by similar plume height but that layer 3 was advected by a stronger wind. In addition, both deposits are coarsest along the dispersal axis and become richer in ash in the crosswind direction showing a Gaussian decreasing rate. Deposit thickness also shows a Gaussian crosswind decay, but layer 3 is significantly thicker at all points than is layer 5 due to the former's larger erupted mass. Based on both quantitative analysis of field data and on numerical simulations, we show that tephra deposits associated with large explosive eruptions (i.e., plume height of 30 km) should be sampled out to at least 200 km from the vent (depending on wind speed and tropopause height) in order to derive complete grain-size distributions that are not depleted in fines. Eruptions occurring in a strong wind field at high latitudes (e.g., Iceland) require lesser representative-sampling distances because of the lower tropopause heights. © 2015, Springer-Verlag Berlin Heidelberg.
Miyabuchi Y.,Kumamoto University |
Okuno M.,Fukuoka University |
Torii M.,Kumamoto University |
Yoshimoto M.,Hokkaido University |
And 2 more authors.
Journal of Volcanology and Geothermal Research | Year: 2014
A detailed tephrostratigraphy of Toya Volcano in Hokkaido, northern Japan has been constructed to evaluate the post-caldera eruptive history of the volcano. The tephrostratigraphic sequence preserved above the Toya ignimbrite reaches a total thickness of 8m southeast of the caldera. After the caldera formation (115-112ka), there was a long quiescent period of more than 60kayears. The first post-caldera activity started with Nakajima Osarugawa pumice-fall deposit (Nj-Os) inside the caldera at 48ka. Eruptive activity at Nakajima Volcano resumed at 30ka with Nakajima Sekinai pumice-fall deposit (Nj-Sk), and was followed by continuous emission of fine ash including abundant accretionary lapilli. Soon after the Nakajima pyroclastic eruption Usu Volcano began its activity with discharges of basaltic ash and scoria (forming the Usu prehistoric tephra) and extrusion of homogeneous lavas namely Usu somma lava, resulting in the formation of the initial volcanic edifice. Subsequently, a large sector collapse occurred between 30 and 20ka that emplaced the Zenkoji debris avalanche with little break after the formation of the initial Usu volcanic edifice. After the sector collapse, the volcano remained dormant for about 20-30kayears. Eruptive activity at Usu Volcano resumed in 1663AD with the most explosive plinian eruption in the post-caldera stage of Toya Volcano. Since then, seven eruptions have been recorded in 1769, 1822, 1853, 1910, 1943-1945, 1977-1978 and 2000 at multi-decadal interval. Total tephra volume during the post-caldera stage is estimated at about 0.9km3 (dense rock equivalent: DRE), whereas total lava volume is calculated at about 2.3km3. Therefore, the average magma discharge rate during the post-caldera stage of Toya Volcano is estimated at about 0.03km3/ky, which is one or two order smaller than those of other Quaternary volcanoes in Japan. © 2014 Elsevier B.V.