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Eruptive History of Tokachi-dake Volcano during the Last -,-** Years,Central Hokkaido, JapanShinya FUJIWARA῍, Mitsuhiro NAKAGAWA῍, Setsuo HASEGAWA῍ and Daisuke KOMATSU῍Tokachi-dake volcano is one of the most active volcanoes in Japan, and magmatic eruptions occurred threetimes during the ,*th century. We reinvestigated the recent eruptive history and eruption style of this volcano on
the basis of geological and petrological studies. Distinct whole-rock chemistry of proximal deposits from eachsource crater area allows us to correlate distal tephras with proximal deposits.
The volcanic activity during the last -,-** years can be divided into four stages, which has occurred fromdistinct craters areas. Stage I : Most explosive and voluminous eruptions had occurred after+*,*** years’
repose period to form the Ground crater. The eruption was initiated by scoria and pumice fallout followed bypyroclastic ﬂows (-,-** cal yBP). This stage was terminated by e#usion of lava ﬂow. Stage II : Explosive
eruptions had repeated three times to form a maar and multiple scoria cones at the northwestern ﬂank of theediﬁce. The activities were followed by e#usion of basaltic lava ﬂows. These activities would occur around ca.
+,*** yBP. Stage III : After several hundreds years’ dormancy, magmatic activity started again with explosive
eruption to form the Central cone, which was followed by e#usion of lava ﬂows from the cone. This possiblycontinued from 2** to -** years ago. Stage IV : Since AD+3,0, magmatic eruptions have repeated near theCentral cone. In AD +30,, explosive and voluminous eruption occurred to form new craters at the southern ﬂankof the cone. Considering the similar temporal change of eruption style in each stage, from explosive to lava
e#usion, it could be considered that +30, eruption was the initial explosive eruption of the new stage.
Total amount of e#used magma during -,-** years is about *.+ km- DRE (dense rock equivalent), and thatof each eruption is less than *.*, km- DRE. Thus, magma discharge rate of the volcano is quite small comparedwith other active volcanoes in Japan. However, mud ﬂows had repeatedly occurred during the last -,-** years,
suggesting that serious hazard by mud ﬂows should be considered in the volcano as in the case of +3,0 eruption.
Key words : Tokachi-dake volcano, eruptive history, eruptive style, tephra

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School of Science, Hokkaido University, N+* W2 Kita-ku, Sapporo *0*ῌ*2+*, Japan.
Corresponding author : Shinya Fujiwara
e-mail : shinya@mail.sci.hokudai.ac.jp