Study of the caldera collapse process and magma plumbing system of Miyakejima volcano

三宅岛火山破火山口塌陷过程及岩浆管道系统研究

• 批准号: 13440131
• 负责人: WATANABE Hidefumi
• 金额: $ 9.6万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-13440131/
• 关键词: Miyakejima volcano; caldera; magma; phreatic eruption; volcanic gas; hydrothennal sysytem; seismic exploration; GPS

The manner of the Miyakejima 2000 eruption was largely different from what islanders had experienced these hundred years. Lateral migration of magma outside Miyakejima, which occurred passively due to tectonic reasons, generated the summit subsidence, being associated with explosive eruptions from the summit in the summer of 2000. There are two kinds of juvenile materials in the 2000 eruption; aphyric glassy basaltic andesite erupted in the 27 June spatter and phyric basalt erupted as volcanic bomb of the 18 August eruption. It is likely that juvenile materials was replaced with from basaltic andesite to basalt in the middle August.Very long period seismic pulses (VLP pulses) were observed a few times a day from July 8 to Aug 18, 2000, synchronized with the step-like tilt increase. The pulse width is 40 to 50 sec and is almost constant regardless their amplitude. The occurrence of VLP pulses completely ceased after the summit eruption on Aug 18. Waveform analyzes of these signals show … More that the source mechanism of these pulses is characterized by large volume expansion of 10 m . Several models have been proposed. One is an intermittent subsidence of a piston in the volcanic conduit. Another is an underground vapor expansion model. An analysis of the seismic swarms prior to the VLP pulses also revealed the details of precursors to the piston-like collapse of the summit.We conducted a dense seismic observation during the period of May to September, and could found that the seismic waves were anomalously attenuated when crossing beneath the south part of the island.Based on analyzes of GPS data during the period of active degassing from the summit, we could propose a plausible model that the volume of the magma reservoir decreased corresponding to the amount of the volcanic gas components released from the magma in the reservoir.In order to detect the magma movements and temporal changes of hydrothermal system around the summit conduit, we have conducted electromagnetic and continuous absolute gravity observation, and observed systematic variations possibly caused by a temporal up rise of magma in the conduit in October to November 2001. Less

2000年三宅岛火山爆发的方式与岛上居民这一百年来所经历的大不相同。由于构造原因，三宅岛外岩浆的横向迁移导致了山顶的沉降，并与2000年夏天山顶的爆炸性喷发有关。2000年火山喷发的年轻物质主要有两种：6月27日火山喷发的无定形玻质玄武安山岩和8月18日火山喷发的斑状玄武岩。从2000年7月8日到8月18日，每天都观测到几次极长周期地震脉冲（VLP脉冲），与倾斜的阶梯状增加同步。脉冲宽度为40至50秒，并且几乎恒定，而与其幅度无关。VLP脉冲的出现在8月18日山顶喷发后完全停止。对这些信号的波形分析表明， ...更多信息 这些脉冲的源机制的特征在于10 μ m的大体积膨胀。已经提出了几种模式。一个是火山管道中活塞的间歇性下沉。另一个是地下蒸汽膨胀模型。对VLP脉冲前的震群分析也揭示了山顶活塞式塌陷的前兆细节，我们在5 ~ 9月进行了密集的地震观测，发现地震波在穿过岛南部时有明显的衰减，根据对山顶排气活跃期GPS资料的分析，为了探测顶导管周围的岩浆运动和热液系统的时间变化，我们进行了电磁和连续绝对重力观测，2001年10月至11月，观测到了可能由管道内岩浆上升引起的系统性变化。少

项目成果

Geshi, N., T. Shimano, T. Chiba, S. Nakada: "Caldera collapse during the 2000 eruption of Miyagejima volcano, Japan"Bull. Volcanology. 64. (2002)

Geshi, N.、T. Shimano、T. Chiba、S. Nakada：“2000 年日本宫上岛火山喷发期间火山口崩塌”公牛。

Kaneko, T., N.Sudo, MJ Wooster, N.Geshi, T. Shimano, M.Nagai, S. Nakada: "RADARSAT determination of the outlines of the successively collapsing caldera at the Miyakejima 2000 eruption. Bull. Volcanol. Soc. Japan"火山. 46・4. 205-209 (2001)

Kaneko, T., N.Sudo, MJ Wooster, N.Geshi, T. Shimano, M.Nagai, S. Nakada：“雷达卫星确定了 2000 年三宅岛喷发时连续塌陷的火山口的轮廓。Bull.Volcanol.Soc . 日本“火山. 46・4. 205-209 (2001)

Yasuda, A., S.Nakada, T.Fujii: "Composition of melt inclusions from 2000 Miyakejima eruption and implications for vigorous SO_2 emission"Bull. Earthq. Res. Inst. Univ. Tokyo. 77・1. 43-54 (2002)

安田，S.Nakada，T.Fujii：“2000 年三宅岛喷发的熔融包裹体及其对剧烈 SO_2 排放的影响”，Bull Earthq Univ. 77・1。 ）

中田節也, 長井雅史, 安田 敦, 嶋野岳人: "三宅島2000年噴火の経緯-山頂陥没口と噴出物の特徴-"地学雑誌. 110・2. 168-180 (2001)

中田节也、永井正史、安田敦、岛野武人：“2000年三宅岛喷发的历史 - 山顶洼地和喷射物的特征 -”地质杂志 110・2（2001）。

Furuya, M., S.Okubo, W.Sun, Y.Tanaka, J.Oikawa, H.Watanabe, T.Maekawa: "Spatio-Temporal Gravity Changes at Miyakejima Volcano, Japan : Caldera Collapse, Explosive Eruptions and Magma Movement"J. Geophys. Res.. 108・B4. (2003)

Furuya, M., S.Okubo, W.Sun, Y.Tanaka, J.Oikawa, H.Watanabe, T.Maekawa：“日本三宅岛火山的时空重力变化：破火山口塌陷、喷发和岩浆运动”地球物理学杂志。108・B4。