Tsukasa Ohba
Tohoku University
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Featured researches published by Tsukasa Ohba.
Geophysical Research Letters | 2001
Akio Goto; Hiromitsu Taniguchi; Mario Yoshida; Tsukasa Ohba; Hiromitsu Oshima
We made field explosion experiments as an analogue of volcanic explosion to understand the relationship between the explosion condition and the resultant surface phenomena. The main parameters we employed were explosion depth and explosion energy. Through the experiments we confirmed that scaled depth, which is the depth divided by cube root of energy, is the main parameter determining the properties of explosive volcanism. The energy assigned to blast wave decreased exponentially against the scaled depth. The scaled crater diameter became maximum when the scaled depth was about 4 × 10−3 m/J¹/³. Scaled crater diameters by nuclear, chemical subsurface and some volcanic explosions were almost the same. From the scaling law, the overpressure at crater rim was estimated to be several MPa, which corresponded to typical rock strength. Probably the ground-forming materials were broken inside the area where overpressure exceeded their strength.
Journal of Volcanology and Geothermal Research | 2002
Tsukasa Ohba; Hiromitsu Taniguchi; Hiromitsu Oshima; Mario Yoshida; Akio Goto
Field explosion experiments using dynamite were carried out to investigate the effect of explosion energy and depth on the nature of explosion cloud. The scaling law of explosion was established among the energy, depth, and the nature of explosion cloud; shape, height and duration of flow out. The shape of explosion cloud changed systematically from funnel type via elongated to short types with increasing the scaled depth of explosion. At the shallow scaled depth, both scaled height and scaled duration increased with increasing scaled depth. Both values reached the maximum at 0.003–0.004 m/J1/3 of cube-root scaled depth, and then decreased with increasing scaled depth. If the cube-root scaled depth was over about 0.01 m/J1/3, we could not observe any explosion cloud on the ground surface. These experimental results should be applicable to the understanding of volcanic explosions if the buoyant effect of internal heat in the explosion cloud was negligible and ground medium is identical. We applied these results to the explosion clouds of Usu phreatic explosion at 14:53 h on 17 April 2000, and estimated that the explosion energy and the depth were 4×109 J and 6 m, respectively. Errors caused by uncertainty of scaling factors are less than one order of magnitude for the energy and depth.
Journal of Petrology | 2007
Tsukasa Ohba; Y. Kimura; Hirokazu Fujimaki
Journal of Volcanology and Geothermal Research | 2007
Tsukasa Ohba; Hiromitsu Taniguchi; Tsuyoshi Miyamoto; Shintaro Hayashi; Toshiaki Hasenaka
Journal of Volcanology and Geothermal Research | 2005
Tsukasa Ohba; Y. Kitade
Journal of Petrology | 2009
Tsukasa Ohba; Kazuhide Matsuoka; Yasuyuki Kimura; Hiromasa Ishikawa; Hirokazu Fujimaki
Earth, Planets and Space | 2016
Yusuke Minami; Takumi Imura; Shintaro Hayashi; Tsukasa Ohba
Journal of Volcanology and Geothermal Research | 2008
Akihiko Fujinawa; Masao Ban; Tsukasa Ohba; Kazuo Kontani; Kotaro Miura
Journal of Mineralogy, Petrology and Economic Geology | 1999
Tsukasa Ohba; Koji Umeda
Journal of Mineralogy, Petrology and Economic Geology | 1993
Tsukasa Ohba