BULLETIN OF THE VOLCANOLOGICAL SOCIETY OF JAPAN
Online ISSN : 2189-7182
Print ISSN : 0453-4360
ISSN-L : 0453-4360
Volume 37, Issue 3
Displaying 1-5 of 5 articles from this issue
  • Article type: Photogravure
    1992 Volume 37 Issue 3 Pages App2-
    Published: August 01, 1992
    Released on J-STAGE: March 20, 2017
    JOURNAL FREE ACCESS
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  • Takehiro OHTA, Toshiaki HASENAKA, Masao BAN, Minoru SASAKI
    Article type: Article
    1992 Volume 37 Issue 3 Pages 119-131
    Published: August 01, 1992
    Released on J-STAGE: March 20, 2017
    JOURNAL FREE ACCESS
    Ominomi monogenetic volcano erupted at the Yufu-Tsurumi Graben in central Kyushu, after the deposition of Aira Tn ash (22,000 y.B.P.) and before that of Kikai-Akahoya ash (6,000-6,500 y.B.P.). This volcano consists of a scoria cone and two lava flows. The height of scoria cone is about 30 m, and the diameter is 250-300 m. The crater opens to the west and two lava flows extend about 1 km from the cone. The rocks of Oninomi monogenetic volcano are pargasite bearing clinopyroxene olivine basalt, pargasite clinopyroxene olivine basaltic andesite and orthopyroxene bearing clinopyroxene pargasite olivine andesite. The analyzed samples from this volcano show a SiO2 range of 51.0-54.5 wt.%, and higher K2O, TiO2 and P2O5 contents than the volcanic rocks in central Kyushu. The relation between Fo % in olivine and An % in plagioclase in the volcanic rocks from this volcano is similar to that found in the cumulates from ocean island or MORB settings. Ti, Cr, Ca and Na contents in clinopyroxene of this volcano indicate that the magma is non-orogenic type. Moreover, the feature of bulk chemistry especially shown by Ti-Mn-P diagram and Ti-Zr-Y diagram, reveals that the magma of this volcano is not an island arc type but a within-plate type. These data suggest that Oninomi monogenetic volcano represent a non-arc type volcanism.
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  • Shiro OHMI, Hiroshi SHIMIZU
    Article type: Article
    1992 Volume 37 Issue 3 Pages 133-146
    Published: August 01, 1992
    Released on J-STAGE: March 20, 2017
    JOURNAL FREE ACCESS
    Three dimensional P-wave and S-wave velocity structure in the Unzen volcanic region, southwest Japan was estimated with the arrival time data of local earthquakes. A broad low velocity anomaly crosses the volcanic region from northwest to southeast and dips gradually to southeast. The southeastern deepest portion of the low velocity anomaly coincides with a clear seismicity gap and a prominent low Bouguer gravity anomaly off the Shimabara peninsula. This may suggest the existence of magma activity southeastern portion off the Shimabara peninsula in addition to a magma body under the Chijiwa bay, which has been inferred from previous geological research. The geology of central Kyushu is dominated by the Beppu-Shimabara graben that trends roughly east to west through the center of the studying area. This structure is not apparent in our results, which may mean that the velocity contrasts that define the graben boundaries are too small to be clarified with our data set.
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  • Hiromitsu TANIGUCHI, Keiko KAMATA, Setsuya NAKADA, Kazuyoshi SANGEN, H ...
    Article type: Letter
    1992 Volume 37 Issue 3 Pages 147-151
    Published: August 01, 1992
    Released on J-STAGE: March 20, 2017
    JOURNAL FREE ACCESS
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  • Hans-Ulrich SCHMINCKE
    Article type: Commentary on Photogravure
    1992 Volume 37 Issue 3 Pages 157-158
    Published: August 01, 1992
    Released on J-STAGE: March 20, 2017
    JOURNAL FREE ACCESS
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