1993 Fiscal Year Final Research Report Summary
Study of formation and collapse of lava dome at Unzen Volcano
| Project/Area Number |
04302020
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| Research Category |
Grant-in-Aid for Co-operative Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体地球物理学
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| Research Institution | KYUSYU UNIVERSITY |
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Principal Investigator |
OHTA Kazuya Kyusyu Univ., Fac.of Sci., Professor, 理学部, 教授 (10037202)
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| Co-Investigator(Kenkyū-buntansha) |
YANAGI Takeru Kyusyu Univ., Fac.of Sci., Professor, 理学部, 教授 (90037234)
HIRABAYASHI Junichi Tokyo Institute Technology, Kusatsu-Shirane Volcano Obs., Associate, 草津白根火山観測所, 助教授 (30114888)
FUJII Toshitsugu Tokyo Univ., Earthq.Res.Inst., Professor, 地震研究所, 教授 (00092320)
HAMAGUCHI Hiroyuki Tohoku Univ., Fac.of Sci., Professor, 理学部, 教授 (20004385)
KAMO Kosuke Kyoto Univ., Disas.Prev.Res.Inst., Professor, 防災研究所, 教授 (70025328)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Unzen / Mt.Fugen / Lava dome / Pyroclastic flow / Prediction of volcanic eruption / Volcanic activity / Volcanic observain |
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| Research Abstract |
A Joint University Research Group investigated the eruptive activity at Unzen Volcano. In particular, lava dome formation and pyroclastic flows were studied in detail. The main results are,
[Seisic observation]Regional seismicity in and around Unzen Volcano remained at a low level after the lava dome extrusion in May 1991. In contrast, summit earthquakes became occasionally intense. No seismic activity was detected beneath Mt.Mayu, where the large collapse took place in the 1792 eruption.
[Tilt observation]Temporal change in daily effusion rate of lava was inferred from tilt oscillation. This method was newly developed for volcanic eruptions.
[Levelling survey]After the eruption, the ground subsided at a maximum value of 66mm around the western shore of the Shimabara Peninsula and at one of 65mm around the Azami Valley, 1km SW from the lava dome.
[Geomagnetic observation]Demagnetization at shallow depths beneath the craters had continued until the summer of 1993.
[Gravity]The gravity increased with a maximum value of 120mugal, corresponding to the accumulation of lava.
[Volcanic gas]SO_2 emission rate was 50-200 tons/day, which were correlated to the volume of lava supply.
SO_2/HCL were 0.7-1.8. No marked change was seen in these data.
[Aerial observation]Twelve lobes have been recognized. Laba dome complex became 1,000m(E-W)x800m(N-S)x200m(height).
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