著者

渡辺 秀文

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.43, no.5, pp.271-282, 1998-10-30 (Released:2017-03-20)

参考文献数

42

被引用文献数

2

---

An evaluation of the precursors to the 1986 eruption of Izu-Oshima volcano reveals that the long-tenn precursors are clearly divided into two, magma accumulation and ascent, stages. A gradual rise of seismic activity, infiation of the volcano and anomalous decrease in the geomagnetic total intensity, had continued for more than 10 years until around 1980. After 198 1, the volcano showed a small deflation and low seismicity at the caldera area until beginning of the eruption, while we observed anomalous changes in the subsurface resistivity and the magnetic field localized around the summit crater, that indicating a gradual rise of the temperature beneath the crater. By integrating the precursors we propose that the accumulation of magma had continued until 1980, and then the basalt magma started to rise up throuth the well-developed conduit. The magma plumbing system of the summit eruption of Izu-Oshima volcano is characterized by a continuous magma supply and an well-developed conduit connecting the magma reservoir and the summit crater. Since 1987 after the eruption, the EDM and GPS measurements have revealed a re-inflation of the volcano, suggesting a continuous magma supply. Tomographic studies on the subterranean structure also delineated a low velocity zone and a melt batch at the same location (at depths of 5-10 km) beneath the caldera as that of the inflation source. The proposed model for the magma plumbing system might provide a basis for not only the short-term but also mid-term prediction of the future eruption of Izu-Oshima volcano.