1999 Fiscal Year Final Research Report Summary
Volcano-hydological study in Mt. Usu and Mt. Komagatake
| Project/Area Number |
09640498
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体地球物理学
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| Research Institution | HOKKAIDO UNIVERSITY |
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Principal Investigator |
OSHIMA Hiromitsu Hokkaido Univ., Grad. School of Sci., Inst., 大学院・理学研究科, 助手 (10213703)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUSHIMA Nobuo Geological survey of Japan, Geophysist, 工業技術院・地質調査所, 主任研究員
NISHIDA Yasunori Hokkaido Univ., Grad. School of Sci., Pro., 大学院・理学研究科, 教授 (60000874)
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| Project Period (FY) |
1997 – 1999
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| Keywords | Volcano-Hydrology / Usu volcano / Komagatake volcano / Phreatic explosion / Hydrothermal system / Two-phase flow / AFMT survey |
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| Research Abstract |
We investigate hydrological environment in Usu and Komagatake volcanoes to understand volcanic phenomena caused by the interaction between magma and groundwater such as a phreatic explosion and geothermal activities.
The results are summarized as follows.
1. In and around Usu volcano, Aquifers are divided into three groups: Holocene series, Pleistocene series and Neogene system. The hydraulic conductivity of Holocene series, Pleistocene series and Neogene system are estimated at 900 - 13x10-3 cm/s, 22 - 0.6x10-3 cm/s and 0.5 - 0.0016x10-3 cm/s from pumping tests or the relation between well discharge and drawdown. It reveals that low resistively layer does not always indicate permeable layer to compare resistively of these aquifers and hydraulic parameter of them.
2. Re-examination of geophysical data implies that phreatic explosions in the 1943-45 and the 1977-1982 eruption activities occurred at 60-230m deep below the ground surface. The comparison of this depth with the distributions of aquifers suggests that phreatic explosion took place in the upper Pliocene - Pleistocene series which include permeable layers.
3. A numerical experiment due to one-dimensional two-phase flow in porous medium implies that an impermeable layer provides the environment for a phreatic explosion because the over-pressure caused by contact between magma and water easily diffuses in a permeable layer. A numerical simulation is also carried out to investigate cooling process of intruded magma in aquifer and development of hydrothermal system. The simulation explains the variation of heat discharge rate observed at Usu volcano, but some problems, including distribution of underground temperature, are remained.
4. We carried out AFMT survey to investigate hydrological structure in and around Komagatake volcano. The edifice is characterized by low resistivity, and aquifers could not clearly identified from resistivity structure.
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Research Products
(4 results)
