1993 Fiscal Year Final Research Report Summary
Research on eruption phenomena of dacite magma
| Project/Area Number |
04452083
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
NAKADA Setsuya Kyushu Univ., Fac. of Sci., Research Assistant, 理学部, 助手 (60128056)
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| Co-Investigator(Kenkyū-buntansha) |
MOTOMURA Yoshinobu Kyushu Univ., Fac. of Sci., Research Assistant, 理学部, 助手 (20037237)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Unzen Volcano / Magma Mixing / Lava dome |
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| Research Abstract |
Unzen Volcano started its eruption in November 1990, and dacite lava has erupted continuously sice May 1991. The head reseacher keeps monitoring of this activity. The eruption style of lava dome at Unzen is unique, and was not recorded at any other volcanoes in the world during historic time. In order to understand the magma supplying system under Unzen Volcano, petrological work was carried out.
Lava remained constant in chemistry and mineral composition during three years, and microphenocrysts of lava were always same in dimension. The mineralogical texture showed several lines of evidence for magma mixing just before eruption for iace lava. The following mechanism was proposed for these facts ; 1) chamber was filled with dacite magma which resulted from mixing of andesite and dacite, 2) degassing of magma during ascent caused crystallization of microphenocrysts and microlites, resulting in the formation of texture showing reaction relation. However, the cause of eruption-rate change can not be explained only by this mechanism. The mechanism which explains the change in eruption rate should be establish by further investigations.
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