Eruptive History of Tokachi-dake Volcano during the Last -,-** Years, Central Hokkaido, Japan

/, (,**1) /,/-,1+ -,-**,**1. +2,**1 2 +* Eruptive History of Tokachi-dake Volcano during the Last -,-** Years, Central Hokkaido, Japan Shinya FUJIWARA, Mitsuhiro NAKAGAWA, Setsuo HASEGAWA and Daisuke KOMATSU Tokachi-dake volcano is one of the most active volcanoes in Japan, and magmatic eruptions occurred three times 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 each source 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 from distinct 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 by pyroclastic 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 the edifice. 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 possibly continued from 2** to -** years ago. Stage IV : Since AD+3,0, magmatic eruptions have repeated near the Central cone. In AD +30,, explosive and voluminous eruption occurred to form new craters at the southern flank of 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 that of each eruption is less than *.*, km - DRE. Thus, magma discharge rate of the volcano is quite small compared with 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 +,* -,**.,. +30* +30- a +31+,,*** -,***,* - +3,0 +30, +322 23 +30-b; Katsui et al., +33* ; +3,1,* +331 +333 +333 -,*** *0* *2+* +* 2 Department of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, N+* W2 Kitaku, Sapporo *0* *2+*, Japan. Corresponding author: Shinya Fujiwara e-mail: shinya@mail.sci.hokudai.ac.jp

254 Fig. +. Topographic map of Tokachi-dake volcano. Symbols A to N indicate the locations of stratigraphic columns in Fig. 0. Symbols A, B, O, and P also show the locations where charcoals for radiometric ages have been gained (Table,). The area surrounded by solid line indicates that of Fig.,. Contour lines are,** m intervals. -,-** -,-**, +/ km +,-**,,*** m +32, ; +32- ; +30-a; +30* Fig.,. Geomorphological map of north-west slope of Tokachi-dake volcano. Nokogiri-dake crater, Ground crater, Suribachi crater, Kitamuki crater, Yakeyama crater, Central crater, 0,-II crater, 0,-III crater, Taisho crater, Showa crater 0,- Fig., +*,* m -,-** Fig., +30-a +32, ; +32- +** NEDO, +33* +30-a +30-a

-,-** 255 +30* +30-a *.++ *.+0 Ma K-Ar NEDO, +33* + -,-** -,-** +3, +2/1 +221 +31+,* - +3,0 +30, +322 23 +30, - - cm + + - cm + Li,B.O 1 + :, XRF MagiX Pro +,,*** SEM-EDS JEOL-JSM-T--* LINK ISIS. -,-** +322 23 Stage. +, - Fig. - Fig.. Fig. / Fig. 0 A-N Fig. + Tk-+ Tk-2. + Stage I Stage +./ m Stage +/ cm / cm - mm Tk-+ +331 To-E1., Stage I Stage 0** m,** m, Fig., Stage Tk-, Gfl-+ -, Sm, Fm-+, -, Gl., + Tk-, : Tk-, Fig. 0 Tk-,-+ Tk-,-, Tk-,-- - Tk-,-+ -, cm, / cm,* cm Tk-,-,,- cm, - cm +* cm / cm / mm Tk-,--,, cm,, - cm / cm G Tk-,-- Tk-,

256 Fig. -. Block diagram showing volcanic history of Tokachi-dake volcano during the last.,.** years. Ages : *, Katsui and Ishikawa (+32+); **, Katsui et al. (+323); ***, Ishikawa et al. (+31+); ****, Ito et al. (+331). PFA: pyroclastic fall deposit, PD: pyroclastic deposits, LF: lava flow, MF : mud flow deposit..,, Sm : A B Sm A *./ + cm, + cm 2* cm + m - cm A - cm., - + Fm-+ : C, m 0* cm.,. Gp : +30-a Gp C G Fig. 1 a Tk-,

-,-** 257 Fig... Geological map of Tokachi-dake volcano, showing deposits ejected during the last -,-** years. Contour lines are,** m intervals. Gfl-+ : + Gfl-, :, Gfl-+ C. m 2* wt. Gfl-, C - m Gfl-+.* wt. C. Gfl-, /* cm, m G Gfl-+ 0* cm +.. m Gp., /, Fm-, : C B Gp C +/* cm 3** m.* cm., 0 Gl: +30-a Gl +,*** +,.** m 02* m Gp / +* m, +/ m

258 Fig. /. Correlative stratigraphic columns for representative sections. Locations of each section are shown in Fig. +. Note that the scales are di#erent between groups of A to C, D to G, and H to N, and that F shows schematic column along Suribachi crater wall.

-,-** 259 Fig. 0. Location and distribution maps for tephra beds distributed to distal area. Numerals show the thickness of tephra in centimeters. Contour lines are,** m intervals.

ª «260 Fig. 1. Outcrop photographs. (a) Ground crater pyroclastic flow deposits (Gfl-+, Gfl-,) at location C. Gfl-, is directly covered by Gfl-+. (b) Kumonodaira pyroclastic deposits (Tk-/) at location E. Tk-/ consist of many layers of pyroclastic fall and their rolling deposits. (c) A close-up photograph of (b) showing clast-supported structure. The scale shows.* cm..ῌ- Stage II ῌ Stage!"#$% &'( )*+,-. /0 + 1 12345 &678!9 1:;&<= 8(- 1:; + ><? - @ ABC<=DE8(-. CF 9 D G. HI Kl-ῌ - JKL 8(Q( R Fig. 2.E AB&<=M NOP AB SR TU AB TV AB WX Y TU AB<= KL HIK&KLM TUH IK Kl-ῌ!"# TVHIK Kl- WX $ % + Z[\ AB ]^ E\(C G. H I Yl CKL.ῌ-ῌ+ Tk-- +331 To-E. Tk-- _ `a E >b L + Stage ῌ Tk-, cd Stage Tk-0 ed GEfEg D +0 cm, +* cm hi&jk+lmn- %o+,- ce pq hig rs tuuv w x+ Stage yz{ 5 } ~g cm + h y. +ῌ, mm Fig. 2. Geological map showing pyroclastic cones and lava flows of Stage II drawn on the base map (+ : +*,***) published by the Geographical Survey Institute. Arrows show directions of lava flow. Abbreviations are same as those in Fig. -. I!"# \- 1 1 ]^ E 2345 } E- Tk-. : +30-a.ῌ-ῌ, wlm d n- 1:; <=t 5L pq + Gp & / -** m <+ c /ῌ,* m w 5L Tk-. C Ln-C

-,-** 261.* m +30-a F. Fig. / +./. m,* -* cm 2* cm /* cm +* cm + m. Fig. 0. - - Tk-/ : Fig. 0 Tk-. Tk-. Fig. 2 E +/ m,* cm - m Fig. 1b - m clast-supported Fig. 1c Tk-/ + m +* cm +333 E Tk-/. -. Tk-0 : +331 To-E- 1** m Fig. 0 Tk-/ Tk-/ F // cm + m +331 Tk-0 +,+** 2* ybp AD 21+ + *,-. - / Kl-I: +30-a - / km / +* m +,-** m,* m Fig. 2. - 0 Kl-II: +30-a KI- 0** m - Kl-,* m. - 1 Kp-II: KI- - /** m +, m. - 2 Ym : 12* m

262 2/* m -* cm cm. - 3 Yl : +30-a +,*** m 12* +,*** m Fig.. KI-I Ym +* m.. Stage III Stage Tk- 1 Cl.. + Tk-1 : +30-a Tk-1 Fig. 0 Tk-0 Kl- Tk-1, m, F, Tk-1-+ /* cm Tk-1-, 2, cm,.., Cl : +30-a 3** m Tk-1 3** +,*** m +* m B / m,2* 3* ybp +31+.. - - Fm-- : C Fm-, C 0* cm.* cm C Fm-, Fm-- +* cm B Fm-, Cl 1 +/ cm Fig. / Cl Stage. / Stage IV Stage +3,0 +3,0 +30, +322 23 - - +30,. / + +3,0 +3,0 +3,1 +31+ /,. +0 +1,* km cm +*,*** m - -,*** m - +3,1. /, +30, Tk-2 +30,. 0,- 0,- +.* m -/ m +30-b +30, 0,- Tk-2 Tk-2 Tk-2-+ Tk-2-,

-,-** 263 Tk-2-- Fig. 0 +30-b +30, 0,3,, + Tk-2-+ Tk-2-, Tk-2-+ -* cm +,0** m *./ + cm Tk-2-, Tk- 2-- +30-b, Tk-2-- 2* cm +30-b. / - +322 23 +322 23 Katsui et al. +33* Miyaji et al. +33* 0,- Katsui et al., +33*, Miyaji et al., +33* 0,- cm,* m 0,- + km +,.** m 2* cm +3,0. 0 Ta-a Ko-c, Ma-b B-Tm ; +331 ; Furuta et al., +320 ; +33, ; +332 ;,**+ Fig. 3 Ta-a +1-3 Fig. 3. SiO,-K,O diagram of volcanic glass of widespread tephras for identification of their source volcanoes. +32+ Ko-c, +03. +323 B-Tm +* +332 ; Horn and Schmincke,,*** Ma-b B-Tm +323 32* +** ybp Katsui et al., +31/ ; +31. +*** Ta-a Ko-c, Tk-1 Tk-2 Fig. / Ta-a Cl B-Tm K Tk-. Tk-0 Fig. / Ma-b +,2/* m Tk-. Tk-/ / / + Stage Fe-Ti -* /* vol. Stage,*./ vol. +- -1 vol.... mm *. vol. *., mm

264 Table +. Representative whole rock chemistry of Tokachi-dake volcanic rocks erupted during the last -,-** years. *./ mm SiO,, +* vol.,.0 mm Fe-Ti * 0 vol.,.2 mm Fe-Ti Fe-Ti *./ - vol. *., mm *.2 mm *.- *.0 mm /, Table + Fig. +* SiO,-FeO* MgO Miyashiro, +31. -,-** SiO, /+ 0* wt. SiO, TiO,, Al,O -, FeO*, MnO, MgO, CaO, P,O / Na,O, K,O Fig. +* Gill +32+ medium-k Stage high-k SiO, FeO* MgO Miyashiro, +31. SiO, MnO P,O / Stage SiO, /- 0* wt. Tk-, Gfl-+ SiO, /- /0 wt. SiO, /1 0* wt. Gfl-, Gl SiO, /- /1 wt. Stage - SiO, /+ /. wt. Stage

-,-** 265 Fig. +*. Whole rock compositions for Tokachi-dake volcanic rocks erupted during the last -,-** years. The lines drawn in SiO,-K,O and SiO,-FeO*/MgO diagrams are from Gill (+32+) and Miyashiro (+31.), respectively.

266 Fig. ++ Stage Tk-1-, SiO, /+.. /+.3 wt. Cl SiO, /,.. /-.- wt. Fig. +, Stage +30, +322 23 SiO, /- /. wt. 0 0 + Gfl-+. / Table, BETA ANARYTIC d +- C Stuiver et al. +332 / d +- C,,33* 0* -,+1* 2* ybp,,,31* -,/1* cal ybp,s Gfl-+ -,-** cal ybp -,-** 0, +33/ +, / km -, L, M Fig. ++. SiO,-MnO variation diagram for whole rock samples of Suribachi and Kitamuki crater. Open and close symbols show proximal and distal deposits, respectively. Fig. +,. SiO,-K,O variation diagram for whole rock samples of Stage II-IV. Table,. Results of +. C dating for charcoals. Locations of each sample are shown in Fig. +.

-,-** 267 Fig. +-. Age-depth diagrams for tephra beds at Loc. L and M. The depth means the cumulative thickness of loam from the surface. Open squares : Loc. L, open diamonds: Loc. M, sold lines: approximate line of each location. Note that ages are normalized by AD,***. Tk-, Gfl-+ -,-** cal ybp Tk-0 +331 AD 21+ + *,- AD 3.1 Fig. +- L +* cm ky M / cm ky +323. +/ cm ky, 1 cm ky AD +3/* Tk-+ L.,-.* ybp, M.,,/* ybp, Tk-- L +,13* ybp, M +,1/* ybp, Tk-1 L 1** ybp, M 13* ybp, +** Tk-+,*,***.*,*** ybp, -,-** + 1 DRE: Dense Rock Equivalent +32+,.1 g cm - Fig. +.. Relation between the area enclosed by isopachs (S) and the thickness (T), for tephras from Tokachi-dake volcano. Dashed lines are isovolume lines assuming V +,., TS (Hayakawa, +32/). Gfl-+ Tk-, Tk-2-+ -, Tk-1-+ Hayakawa +32/ V +,., TS V : T : S : Fig. +. Hayakawa +32/ Hayakawa +32/ +333 Table - Fig. +/ -,-** *.+ km - DRE, *.*- km - DRE ky Stage *.*. km - DRE, Stage *.*-1 km - DRE Stage Stage *.*+3 km - DRE, Stage *.**0 km - DRE

268 Table -. Estimated magmatic volumes, eruptive styles, rock types, and main ejecta types of deposits erupted during the last -,-** years. *: from Katsui et al. (+33*), ** : from Tada and Tsuya (+3,1). Ex: explosive, Ef: e#usive, B: basalt, BA: basaltic andesite, A: andesite. DREs are calculated by setting density of each product as follows; +., g/cm - for scoria and pumice in distal fallouts, +.2 g/cm - for scoria in pyroclastic flows, +.. g/cm - for pumice in pyroclasitic flows, +./ g/cm - for agglutinate,,.. g/cm - for bomb (AD +3,0 and +322 23) and lava flow. Fig. +/. Cumulative magma volume versus time for deposits erupted during the last -,-** ybp. 2 2 + 2 + + Stage I Gfl-+ +31+,,,** +** ybp,,,** -,/** ybp,,,** ybp -,*** ybp d +- C /* ybp Gfl-+ d +- C -,+** ybp, -,-** cal ybp Gfl-+ Gfl-, Stage Tk-, Gfl-+ Gfl-, Tk-, Gfl-+ 2* wt. Sm, Fm-+, Fm-, Sm -,-**

-,-** 269 Gp Gl +30-a Gl Gl Fig. +0 Gl Fig. +0 Gl Stage -,-** m +322 23 -,-** SiO, Stage 2 +, Stage II Stage Tk-- +,1** +,2** ybp Stage +,*** Tk-. -/ -0 Tk-. B-Tm, Ma-b Tk-0 AD 21+ +,*,- +331 +,***,./ km Table + Stage 2 + - Stage III Stage 1** 2** ybp Tk-1-+ -, Stage,** -**,2* 2* ybp Cl Fig. +0. SiO,-MnO variation diagram for whole rock samples of Suribachi and Ground crater ejecta. Tk-1 Cl Fig. +, /** 2 +. Stage IV +3,0 Stage +3,0 +30, +322 23,** -** +30, +322 23 Stage Fig. +, 2,,* Stage Stage Table - Stage Stage Hildreth, +32+ Eichelberger et al., +320 +3,0 Stage

270 +30, Stage Tk-1 Stage,* 2 - -,-** *.*- km - DRE ky -,*** *.-, km - DRE ky +332 +* + +33* *.+ + km - ky 2 + -,-**., - Stage. +3,0 +. C, Eichelberger, J.C., Carrigan, C.R., Westrich, H.R. and Shannon, J.R. (+320) Non-explosive silicic volcanism. Nature, -,-, /32 0*,. +332 B-Tm Laguna no. / // 0,. +331 +03. +1 +2.,,03,13. Furuta, T., Fujioka, K. and Arai, F. (+320) Widespread submarine tephras around Japan petrographic and chemical properties. Marine Geology, 1,, +,/.,. Gill, J.B. (+32+) Orgenic andesites and plate tectonics. Springer-Verlag, -3*p. Hayakawa, Y. (+32/) Pyroclastic geology of Towada Volcano. Bull. Earthq. Res. Inst. Univ. Tokyo, 0*, /*1 /3,. +33/.* +11 +3*. +323,2 + +1. Hildreth, W. (+32+) Gradients in silicic magma chambers : implications for lithospheric magmatism. J. Geophys. Res., 20, +*+/- +*+3,. Horn, S. and Schmincke H.-U. (,***) Volatile emission during the eruption of Baitoushan Volcano (China/ North Korea) ca. 303 AD. Bull. Volcanol., 0+, /-1 ///. +32, 22 // 1*. +32-23 +0- +1,. +31+ +-0p. +333 +333 -. +331 +331.. Katsui, Y., Ando, S. and Inaba, K. (+31/) Formation and magmatic evolution of Mashu volcano, east Hokkaido, Japan. Jour. Fac. Sci., Hokkaido Univ., Ser. IV, +0, /-- //,. +32+ Disaster Map Hazard Map : 3 +-. Katsui, Y., Kawachi, S., Kondo, Y., Ikeda, Y., Nakagawa, M., Gotoh, Y. and Yamagishi, H. (+33*) The+322 +323 explosive eruption of Tokachi-dake, central Hokkaido, its sequence and mode. Bull. Volcanol. Soc. Japan, -/, +++ +,3. +323 2p. +30-a / +.1p.

-,-** 271 +30-b +30,.3,+-,,0. +33,,10p. +333 +320 TB.. // 1*. Miyaji, N., Sumita, M., Yoshida, M, Kondo, Y., Yamazaki, T., Kouyama, K., Sone, T. and Muto, H. (+33*) Tephrastratigraphical study of +322 +323 eruptions of Tokachidake volcano, central Hokkaido. Bull. Volcanol. Soc. Japan, -/, +-+ +./. Miyashiro, A. (+31.) Volcanic rock series in island arcs and active continental margins. Amer. J. Sci.,,1., -,+ -//. NEDO +33* -./0p. +33* -. S,*+ S,*.. +333 +333,. +32+,0 ++1 ++2. +31. +. C +. C 31,2 +*+. Stuiver, M., Reimer, P.J., Bard, E., Beck, J.W., Burr, G.S., Hughen, K.A., Kromer, B., McCormac, G., van der Plicht, J. and Spurk, M. (+332) INTICAL 32 radiocarbon age calibration,,.,*** * cal BP. Radiocarbon,.*, +*.+ +*2-. +3,1,.* 2.. +30* -3 1 +2. +323 +1 -*,1 --. +332 1***.- +.3 +00.,**+ -/ 3 +2. +332 +0.*.+ +-1 +.2.