| Project/Area Number |
17340131
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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 |
Solid earth and planetary physics
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| Research Institution | Kyushu University |
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Principal Investigator |
TORAMARU Atsushi Kyushu University, Faculty of sciences, Professor (50202205)
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| Project Period (FY) |
2005 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥12,970,000 (Direct Cost: ¥12,400,000、Indirect Cost: ¥570,000)
Fiscal Year 2007: ¥2,470,000 (Direct Cost: ¥1,900,000、Indirect Cost: ¥570,000)
Fiscal Year 2006: ¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 2005: ¥8,600,000 (Direct Cost: ¥8,600,000)
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| Keywords | vesiculation / crystallization / bubble / microlite / decompression rate meter / water exsolution rate meter / ブルカノ式噴火 / マグマの発泡 / 噴火の強度 / マイクロライト・システマティックス / 桜島ブルカノ式噴火 / 爆発地震 / BL型地震 / 空振強度 / 火山ガラス / 火山灰 / 桜島大正噴火 / 雲仙平成噴火 / 気泡数密度(BND) / マイクロライト数密度(MND) / BND減圧速度計 / MND脱水速度計 / マグマの上昇速度 |
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| Research Abstract |
Developing bubble number density (BND) decompression rate meter and microlite number density (MND) water exsolution rate meter, we have established the method to quantitatively estimate the decompression rate or water exsolution rate from measured values of BND or MND for given the magma temperature, compositions, and initial water content.
Applications of this method to nature have revealed the following things. For explosive eruptions, 1) the decompression rates at bubble nucleation for plinian eruptions are up to 10^6 to 10^8 Pa/s, which must be accompanied by the rapid decompression like due to a rarefaction shock wave. 2) In subplinian eruptions of basaltic andesitic magmas, the water exsolution at the microlite nucleation proceeds the diffusion limited bubble growth during the disequilibrium vesiculation. BND or crystallinity has correlations with the temporal variation of eruptions such as changes of exit velocities. 3)The fact that pyroclasts erupted at the same time have the variation in estimated rates of water exsolution suggests that the flow in the conduit is turbulent For non-explosive eruptions, 4) estimated water exsolution rate is approximately 10^<-5> wt%/s, and 0.01 to 0.1 m/s of ascent velocity and 10^2-10^3 Pa/s of decompression rate. 5)The water exsolution rates are uniform across the conduit 6) The water exsolution might proceeds at deeper level of the conduit though it is still unclear whether the vesiculation is equilibrium or disequilibrium. These facts suggests that the flow in the conduit for non-explosive eruptions is like a plug flow.
Carrying out a combined simulation of vesiculation and crystallization, and making a comparison with the laboratory experiments by Couch, et. al. (2003), we have found that MND is controlled by the amount of decompression through the driving force of diffusive bubble growths under disequilibrium vesiculation.
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