| Project/Area Number |
16340166
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | The University of Tokyo |
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Principal Investigator |
NAKADA Setsuya University of Tokyo, Earthquake Research Institute, Professor, 地震研究所, 教授 (60128056)
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| Co-Investigator(Kenkyū-buntansha) |
YASUDA Atsushi University of Tokyo, Earthquake Research Institute, Associate professor, 地震研究所, 助教授 (70222354)
吉本 充宏 東京大学, 地震研究所, 助手 (20334287)
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| Project Period (FY) |
2004 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥13,100,000 (Direct Cost: ¥13,100,000)
Fiscal Year 2006: ¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 2005: ¥4,600,000 (Direct Cost: ¥4,600,000)
Fiscal Year 2004: ¥6,400,000 (Direct Cost: ¥6,400,000)
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| Keywords | Miyakejima / Phreatomagmatic explosion / volcanic ash / groundwater / Anatahan / Academy Nauk / 2000年噴火 / 噴出速度 / 噴煙高度 / プリニー式噴火 |
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| Research Abstract |
The mechanisms of phreatomagmatic explosions that occurred during the eruption at Miyakejima in 2000 were investigated based on geological inspection of the products together with the geophysical monitoring data and video footage. Comparative study was also carried out for the eruptions in Anatahan (Northern Mariana Islands) during 2003-2005 and in the Akademy Nauk lake (Kamchatka) in 1996. In Miyakejima, tephra of every explosion events were identified in many places and the depositional times were determined using stratigraphical makers. Eruption volume of tephra of each explosion event gave the precise eruption rates. The fragmentation extents of magma and whole products of each event were estimated by grain analysis. Component analysis gave the proportion of contribution of magma to each explosion event. These data are very valuable parameters to model the explosions of hydrovolcanic eruptions, which nobody could have presented by this study.
There is positive correlation between th
… More
e magma eruption rate and the height of ashy eruption column, and negative correlation between the extent of fragmentation and magma eruption rate. The latter means the highest extent of fragmentation in non-magmatic explosions. Such the high fragmentation may result from (1) repeated fragmentation of coarse grains within the crater, which failed to rise due to the lack of thermal energy and (2) the effect of supercritical water that breaks silicate into pieces immediately. The lines of evidence showing the most effective energy conversion from heat to fragmentation at the mgama-water ration of 0.3, proposed by Wahletz was not confirmed in the present eruption.
Large contribution of groundwater into the Miyakejima eruption in 2000 is also verfied by the appearance of erupted products and the isotopic ratios of materials attached to the products. Further investigation including textural comparison of products from the Anatahan and Akadamy Nauk is needed to clarify the circumstance of phreatomagmatic explosions. Less
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