著者

安田 裕紀 佐藤 鋭一 和田 恵治 鈴木 桂子

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.60, no.4, pp.447-459, 2015

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Eruption interval between Hb- and Px-types pyroclastic-flows from the Ohachidaira caldera of Taisetsu volcano, central Hokkaido, Japan, was estimated from the paleomagnetic directions. Px-type pyroclastic-flow deposit rests on Hb-type one, and gravel beds are intercalated between them. Oriented 138 samples were collected from 13 sites for paleomagnetic analysis. The paleomagnetic direction of Hb-type pyroclastic-flow deposit shows a normal polarity with a westerly declination(overall mean is N=7, D=-27.1°, I=66.3°, α_<95>=2.7°, k=511.2), while that of Px-type pyroclastic-flow deposit shows a normal polarity with an easterly declination (overall mean is N=6, D=19.8°, I=67.5°, α_<95>=4.6°, k=213.8). The two paleomagnetic directions are significantly different, and the time interval between the two pyroclastic eruptions is estimated to be more than about 100±40 years based on the geomagnetic secular variation in China, Russia, Europe, North America, and Japan.