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,**0  /  3  ,**0  2  ,3 Frequent and Intensive Eruptions in the 3th Century, Izu Islands, Japan : Revision ofVolcano-Stratigraphy Based on Tephras and Historical Document
Masashi TSUKUI῍, Koichiro SAITO῍῍, Kouichiro HAYASHI῍῍,῍῍῍Based on the study of tephra deposits and historical documents concerning with Izu islands, we reexaminedthe volcano-stratigraphy in and around Izu islands. We reconﬁrmed that Kozushima Tenjosan erupted in A.D.
2-2 and Niijima Mukaiyama erupted in A.D.220. Eruptions from both volcanoes were big throughout theireruptive histories. Dispersed tephras from these eruptions covered most of the Izu islands, thus are goodtime-markers.
Our results revealed that the several eruptive events occurred in between the A.D.2-2 and A.D.220 major
volcanic episodes. In Izu-Oshima, the later stage of N -.*, N ,.* and N +.* eruptions took place. In Niijima, aseries of eruptions started with phreatomagmatic eruption of basaltic composition at Kudamaki and ended withthe formation of Atchiyama rhyolite dome. In Miyakejima, lavas were e#used from Oyama central vent which
spilled over Hatchodaira caldera. A lateral ﬁssure extended from the eastern ﬂank to Miike and resulted in aphreatomagmatic eruption around A.D.2/*.
We concluded that the volcanism during the middle of the 3th century in and around Izu islands was
unusually high compared with the eruptions of both the preceding and the following periods.
Key words : Izu Islands, 3th century, historical eruption, historical documents, volcano-stratigraphy+ῌ ῐ ῎ ῑ ῏

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Department of Earth Sciences, Faculty of Science,
Chiba University, Inage-ku, Chiba, Japan ,0-ῌ2/,,
,0-ῌ2/,,  ¡ +ῌ-//¤¥¦£/st£
Graduate School of Science and Technology, Chiba
University, Inage-ku, Chiba, Japan ,0-ῌ2/,,§¨ 2++ῌ+-*,© ©ª ,ῌ,+ῌ-0«!-.¬­o® ¯°±®²³´µ¶·¸¹º»¼
Present address. Kyushu Headquarter, OYO Corporation, ,ῌ,+ῌ-0 Ijiri, Minami-ku, Fukuoka, Japan
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Corresponding author : Masashi Tsukui
e-mail : tsukui@faculty.chiba-u.jp.¶·¸¹'º»­±'D ¼­²

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Table +.

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Records related to eruption and unrest in historical documents.

Promotion of rank in the Imperial list of shrines located on the Izu islands.

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331

Table -. Chemical compositions of A.D.2-2 Kozushima Tenjosan tephra and A.D.220 Niijima
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Sampling localities are indicated in WGS2..

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Fig. .. Map showing thickness of Kudamaki tephra(KdB) and Atchiyama tephra (AtP)(in cm).
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Nakamura, K. (+30*) Stratigraphic study of the pyroclastics of Oshima Volcano, Izu, deposited during the lastﬁfteen centuries. I. Cyclic activity of “Main craters” andthe absolute chronology of the pyroclastic sediments. Sci.
Pap. Coll. Gen. Education, Univ. Tokyo, +*, +,/ῌ+./.
Nakamura, K. (+30.) Volcano-stratigraphic study of Oshima
Volcano, Izu. Bull. Earthq. Res. Inst. Univ. Tokyo, .,,0.3ῌ1,2.

336

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