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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 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 possibly
continued 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

V@*fA ^DUV=`a+PYf A+ῌ ῐ ῎ ῑ ῏!" #$%&'()*+,-./01)@]a+\ P]A)z? ,* 78)E+ - 92:

2 !")345+,-./06 ,* 78) - 92:;;:</ +3,0 +30, +322ῌ23  )_5+T>:</=>? @A)BCD6 ,**.  , EFGH .

J]a  ? -i j +30-b ; Katsui et al.,)IJK*LMN</=OP5*Q RSDTB+33* ;   +3,1\ ``*fA ,* 78{2TUVW*/02XYZD[+\ P]^D,-./0)

/02</ ^n]]2</2 < _`a60bcd2efgh +30* -i j +30-

EFG:;:2 s26^ A)@]aa )Fkalm@] n2op

j +31+ )Fka

*\ C  j +331   +333 

qrstuv2wxyfz?A] /0f ,,***ῌ  +333 D6#") ¡5+¢£¤=¥¦`-,*** {)|}W</=}~@a <=&§2<¨=©ª -,*** {«2</¬­)Z®*0*ῌ*2+* ¯°±² +* ³& 2 ´ µµ¶µ·¸¹º·µ»¼Department of Earth and Planetary Sciences, Graduate
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;¶·<B$¸¹B9º=B»¼¤>

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 thatof Fig. ,. Contour lines are ,** m intervals.

   

Fig. ,. Geomorphological map of north-west slopeof Tokachi-dake volcano.  Nokogiri-dake crater, Ground crater,  Suribachi crater,  Kitamuki crater,  Yakeyama crater,  Central
crater,  0,-II crater,
0,-III crater,
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255

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+UN"¤¶x# +322ῌ23 " #  Stage ῌ2῍

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« )XI / cm "@ ] / mm  #^

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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.

.ῌ,ῌ,  Sm : A 

.ῌ,ῌ- B  + Fm-+ :abc C  23456789 !"#$ Sm %7: ;<=> de?@"#X

 A "% *./ῌ+ cm &'()*+ , ,

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cm P$7897: ;<=> ?@$ AB%.ῌ,ῌ.  Gp : C/ 2* cm D E(F GHIJFK+ LMN

+30-a  !"#$O + m PQ LB1 - cm 9-"% HI

Gp %ghijkl-mn7:

234

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Tk-, ?{$ 7:%|}~(·8i¸ ¹º»O -,-** 9#7¼

257

Fig. .. Geological map of Tokachi-dake volcano, showing deposits ejected during the last -,-** years.
Contour lines are ,** m intervals.

   Gfl-+ : Aa$(

 +   Gfl-, : 

rD[ Z+ ,  !"  #$%&#',<8;!Q()*+,-./$012 " Gfl-+ $3456@AVCCC<< B4( 7 C 89:$ . m 8;!"CVCKCC<8;!"< $=>?@A56 BCDEFGHB.ῌ,ῌ/ 

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$O8 2* wt.ῌ (PQ!" RS T U9./VD r Gp (#$+,8;!" %77 C

C
W

2!"

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(l*!" Gfl-, $=( 7 C 89:$RS8 - m 8;!"mno$=>?@A !"#$Gl $(& +,***῍+,.** m 7 < m  d$(  & 02* m '

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Vb8c y7D

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| Gfl-+}0BC1 2(K"~r VO 0* cm =>?@A8.U¯4°56Q! 9: +.. m  Aa~k*!"²³+<$®3r V <C± ´µ8°5)¶7 

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.

258


  -,-**   Fig. 0. Location and distribution maps for tephra beds distributed to distal area.
tephra in centimeters. Contour lines are ,** m intervals.

259

Numerals show the thickness of¡¢£¤¥¦§¨¤©ª¦«¬¤­®¯

260

Fig. 1. Outcrop photographs. (a) Ground crater pyroclastic ﬂow deposits (Gﬂ-+, Gﬂ-,) at location C. Gﬂ-, isdirectly covered by Gﬂ-+. (b) Kumonodaira pyroclastic deposits (Tk-/) at location E. Tk-/ consist of manylayers 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 -῍ JKL8(Q(RFig. 2 .EAB&<=M NOP AB SR

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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+

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Fig. 2. Geological map showing pyroclastic cones
and lava ﬂows of Stage II drawn on the basemap (+ : +*,***) 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- 

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 .* m 







8 -,-** jK  ¼.ῌ-ῌ.

    +30-a  1)23)4 5678 Tk-0 :  +331
 To-E-   F  !"# .  $%&'()*" +,-./

261

0"
9:

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R:tuj"+ 67 567 '(Z)\XYtuj Fig. 0;< Tk-/ R=V F;, Fig. / $%&'()*<=> ?5@,A +./ῌ. m B /B2CD$ EA // cm  ab c !2CD$Rd"/# ! 8 2* cm B F,,*ῌ-* cm

_ Tk-/ "`B  F R eE + m Rf{G$%&'()*-.0/H

U,I J/yBP hijk AD 21+ῌ+ *,-

95678 /* cm0:

M#,

+331 6@ Tk-0 LY $g +,+**2*lmnojk;, $%&'()*"0 KA +* cmpq, // 3f(g3hiji  L!J/ 1)23)4MN

34fg3k5/l B

8

9A + m 9"!#$/

9

.ῌ-ῌ/

:;, F, G KO% PKKQ
RS&TH, U . B$%&'()* VW 8 XY2CD$"  '(Z[)\ Fig. 0 ]^* F" 567 +_ ,`%`"`%`./aU./a b@0cFde;,`)&"12 Kl-I :  +30-a  !" C>Z? ope~ ` >(C $r d - / km CY$$!

C 8[¡¢£¤6@I!RJ st¥¦`§ ¨ uv=©,C

ew[xyB Aª[ /ῌ+* m  z
¡ +,-** m W{|+}~a ,* m// 3f(g3hiji34fg3k5/] «N >Z? opl B

>(¬5@ >Z? op567mn o.ῌ-ῌ-  Tk-/ : p >­e, Fig. 2 F F"mn opR: XY2CD$5 CC ® opR¯ C"z67+ 67" '(qRrd89{, 3f(g3hiji34fg3k5/

s(:

XYtuj

;<B Fig. 0 Tk-. R=V mn op e+12 Tk-. v. >l B.ῌ-ῌ0Z?@ op ww>x@ Ry""#

Kl-II : 



+30-a

 

z{, mn opwwA |w }f C KI-ῌ"`  ([ 0** m CY

RB F,~C7H"z{ !"# -  $$ C ;< Kl-ῌR=V, Fig. 2  E DA +/ m  4A

A ,* m  N©H ,* cmῌ- mEFu)&*GN

Fig. 1b 4H !UI!RJ2CD$!RKH +
H,

N

8LE - m 56M

HOP clast-supported:QRB Fig. 1c U mn op 'R, S Tk-/
/ 
A +* cm 

88A + m

0, + Y

L! 1)23)4T.

UV +333  E WXY

Tk-/ R,- oC" 1)23)4]XY o"12+eRd5@ st != 9! °Dih)a UC Rt<ji±:Q#MN 3f(g3hiji34fg3k5/l B.ῌ-ῌ1

# Kp-II : KI-῍ R= >Z?@



opRe

«R-²³ - $%&'()*, F, !=I! 2CD$@ 8[ ?µ >Z?@ LE +ῌ, m 

ope´ /** m ]H "z{,M\.

M¶}~ d·,a st ¡¢£N ~Z / 3[\],- XY

¤6@I!R7 // 3hi "12N // 3f(g3hij

ji3f(g34fg3k5/l B

i34fg3k5/l B

wwU.ῌ-ῌ2 $%& Ym :

¸{r¹C z¡ 12* m 5 Cº,n»¼nD

262
 





   2/* m -* cm 



 



  cm !"#+30-a&'

)*+ Fig. . KI-I ,-.

( 12*ῌ+,*** m01 22! !" 3

456$78%&'()*++ 9,:-./;!<=>?!0!3A4B3CDED35AB3@*12!3CDED

3A4B35AB3F6! !
qrsn8M
Fm-, /

t_`CC

 0* cm!"#
t +* cm *0~ 
D\ .* cm 

C  Fm-,Fm-- *+1
B ,%t 1ῌ+/ cm 6[<Fm-,Cl 

T6 Fig. / 

῍"MStage III

Stage ῍GEHDI&'J7(,86 ,K&'L@9MN:O  ,K&'&P Tk1 6,K&'! Cl 7(M ;Q!3R<

T6  N:UO*V> 6WX

S2

(3YM!0,fgS ,2*3* yBP hifjkl

 Cl 6hUO*(M6WXY Stage

F6! !
.ῌ.

ke".ῌ.ῌ-   - Fm-- : !"!   +,*** mYm /T@*{|m 3no +31+ *pY8h$%$.ῌ-ῌ3  Yl : # +* mCf_Y8 4\hbcd

.ῌ/Stage IV

Stage ῎ +3,0 k]N:+ Gh(M7& +3,0 k +30, k;8 +322ῌ23 k - TY - 7&,K&',-.;4u *( +30, k7& vM>&PL*@93YM ;YY.ῌ.ῌ+  Tk-1 : +30-a 
Tk-1 ,K&'L@91

aY7&  7&w$7&sh8xh ¡y¢*>3Y8h

Z[E6;=:

;MTT £5o 6?

 ,-.>?>4\@A1 ]Z[E Fig. 0 B

.ῌ/ῌ+C  Tk-0 ,-. Kl-ῌ/ ,K&'L@93Y+3,0 k7&wsh87&z¤¥

MDE&'F Tk-1 &'GH68 ^I_` *;YaY# , m 0bJ12Gcdefg* , KL(8hj!kl93Y+ oF

M{|}¦ +3,1 $ 3no +31+ xh
TY~§- 6 / ¨ ,.  +0 U +1 @*

TYi-8,K&'"*© ;Y8ª* MmNnO8,

**(M ;8*(66 & !

]Z[E6pqrP.

 , stuvgw@

k$& b*h(3Y ;G63Y &]xyz} Tk-1-+ *# /* cm

2*{|+3,0 #$%&'()* *,K&'4uh(3YM A&)m@A8,+ «¬ ­m,K&'# ,*Q~Q& b,-.R

km 

!ST6 & byfZDG3YMxyz2

8h *U"#} Tk-1-, *# 2, cm -m*VMxyz2 l93Y R!STY

 , K]&PWX&'?F8YZ< >4\\8< [UD\3m>!3A4B3CDED

qrs|®

,h8 cm]&P ¯ T> & !k*+*,*** m- &* -,*** m- 6Y8,+ {|}¦ +3,1 0U.ῌ/ῌ,.ῌ.ῌ,  Cl : +30-a+30, k7&-8° . s&'*±YM* ;,K&'   3** m]K22!

+ Tk-1  @A1k*1@<8h7( 0,-ῌ&PL@91^ _h  3**ῌ+,*** m  !

 !`a6 !^*{|3Y!" *+* m 

B / mzD

m9 &PL@91 ³M 0,-ῌ&' +.* m ´@> &'F# -/ m  M

+30, # Tk-2

/² 0,-ῌ&'*D

35AB3F6!

T7&-87(Mexyz2$&!

µ¶o +30-b +30, k7&-8

Z[E6;=: ,-.>4·M]Z[EBC8y Tk-2 6¸¹

Tk-2 "&T61 

Tk-2-+ ; }Q& b Tk-2-, ,-.RT» y.;` -,-** « ¼ Tk-2--263

  Fig. 0  +30-b  +30,  0  ,3  ,,  +   !"#$%&!'

 ()&&* +,-.+ /
!0 &12 Tk-2-+ & Tk-2-, 34 56
7 ) (&89  Tk-2-+ 3:;-* cm +,<)=>?@AB03C.& D.#$E2 !F . !G +,0** m "#H3: *./῍+ cm $EIJK&!'L%HM Tk-2-, 3&,
N+,'(C.+<% &! O) .+ P

3QRQST&89 C

3U(VW XYZ )*&+,  Tk2-- 3-.!0[,N+,<%   

Fig. 3. SiO,-K,O diagram of volcanic glass of widespread tephras for identiﬁcation of their source
volcanoes.

/\0EQRQ ]^!0  +30-b  5 ,  7 1_)&89  B0 
O2`H3 Tk-2-- ;+32+  Ko-c, 3G_ +03.   +323  B-Tm 3

2* cm 3)C+* `¤ IJKH1 a9 bc +332 ;.aBbc1 4 3 )

Horn and Schmincke, ,***  B0 Ma-b 3 R

&4 d*O

dF'K B-Tm ¥d)4& e +323  K

 ( 0.

H1&89   +30-b  /CC#(¦

53efKf5g h56gh5i7#Cj.#H1

'F4& Katsui et al., +31/ ; ©ªj +31.

.ῌ/ῌ-+322ῌ23 al. +33* m!F 4 n' 0,-῍O

3. (  !!op9Eq:qrs
t<;n0 Katsui et al., +33*, Miyaji et al., +33*  4(0.3 uT 0,-῍ONRKvfwO< x'! =:>ycm *

;¨fghi H +*** QIJKH1&89  /OH

+322῍23 k8l]3 Katsui et al. +33*  Miyaji etH32*§+** yBP 

3 Ta-a d Ko-c, 3.kdF' Tk-1 & Tk-2
«U(  Fig. /  Ta-a 3 Cl ¥)*L%HM0 B-Tm 3"# K dF*)(¦T' Tk-. & Tk-0 «U( 0 Fig. /  B0 Ma-b3y.l !G +,2/* m "#dF'
Tk-. & Tk-/ «(¦TU(!0,* m z{*BH?|) =E#$*B>U  /C>?@A@C#A

B}3CD! B~A<E'F*
B} )*3FH1n04&<!'F q:)*3 0,-῍ O

GH + km "#BH

L%HM !G +,.** m 2`6IH

/



/ῌ+



Stage ῌ¬5<­M m' (3g=5 ef

Kf5 6gh5 g h5 Fe-Ti ®¯<a n°

3H 2*

 -*῍/* vol.ῌ efKf5g h56gh5i7#N

cm H +3,0 J:)*<KLMn'F +,C

i7#Cj.#1F3g h5efKf56gh5i<N! /C3-.F=>?@A[,#$7#Ni7#Cj.#H1 Stage ῌ¬53 ±

E B0B@C#A<a /CC#53e

efKf5d5²n°<a n° ,*῍./ vol.ῌ

fKf5g h56gh5i7#Cj.#H1

efKf5aNB03efKf55²aNg h56.ῌ0 

gh5j.#H1

/OH3y. PQ. Ta-a 
R Ko-c,  S. Ma-b dTU
&V. B-Tm <g=53³swZH +-῍-1 vol.ῌ =oAB03
AH=:3;H ... mm H1 ´p´H1(T&)IJK<U(!

2 qI r<µ¶*BF °<·sIt

0 1W3#XY9 KZ<u r<N)*BF :o Fn°3vw

?s [ ; +331 ; Furuta et al., +320 ; \E**U  ·sIx2 3¸ ]  +33, ; ¡/¢ +332 ; ^] ,**+ &¹¸ 1F3°m d{*BHº|)W£!0 Fig. 3  Ta-a 3G_ +1-3  5[ efKf53³swZH *῍. vol.ῌ :3 *., mm

²³´°µ¶·°?¸µ¹º°»¼ 

264

Table +. Representative whole rock chemistry of Tokachi-dake volcanic rocks erupted
during the last -,-** years.



 *./ mm  /2*n5opq/2) TiO,, Al,O-, FeO*, MnO,  

MgO, CaO, P,O/ )rst

!"# $%&%'() *+ SiO, ,-.

PQ gFig. +*h Gill g+32+h .e) _L/012 345.67# 89):;<=>) medium-K .v/ Stage ῌ_Lwx)

 ,῍+* vol.ῌ ?@A0) ?B

high-K .v# A0 SiO, 67.m/2 FeO* ῌ) ,.0 mm  C(D.EFG&HI Fe-Ti

JKL# A0 MNOPQ 9):;<=> *῍0 vol.ῌ ?@A0)?B)

 ,.2 mm  EFG

MgO )yqz{

K

Na,O, K,O )ust_L*n)$|}~|$3 %<2 gMiyashiro, +31.h
_L)H;)]10 SiO,=>Z/ b;$;c)w%&HI Fe-Ti JKL# A<2

0 89I$%&%#]%<2 Stage ῌ

!"# Fe-Ti JKL):;<=> *./῍- vol.ῌ) => gSiO,/-῍0* wt.ῌh 

B) *., mm RS

 *.2 mm 

MnO I P,O/ )H; )_L

Tk-, def Gfl-+ H~)el gSiO, /-῍ ) T.UAQV)

/0 wt.ῌhT)el? gSiO,/1῍0* wt.ῌh =

B *.-῍*.0 mm RS WXYZ#>/k=>.  Gfl-,/ῌ, ῏ῐΐῑ῎ῌ῍ῒῐTable + .[\5]^Gl .)T)yqz{PQ SiO, ) /-῍/1 wt.ῌ 
_L`>

*+Ka=



¡¢:;£|q Stage ῍-῎) SiO,/+῍/. wt.ῌ> Fig. +* .b;$;cdef SiO,-FeO* ῌ MgO c¤¥+¦¤¥+§^+¨©¨ª«/ P

gMiyashiro, +31.h Z/0 ]^ i -,-** jk¬H~def+ _L ­+ SiO, ) /+῍0* wt.ῌ l SiO,  K.m

Stage ῍ ®¯]qp°±^]qb;$;c  -,-**   

265Fig. +*. 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.

°±²%³B´µ³¶·¸¹³º»¼&

266 

WXYZ ! . [\ / ] ^LWX_`^a Fig. ++   Kb)c! ]YZ[\d@ef) Table , 5g!"#$%&'( )*+ , -.

h d@(Nij BETA ANARYTIC k5l ! d /0 1 2343 56789:3 ;35<=>/0)?@A BC/0)D ! Stage ῌ
( "#$%&'1 Tk-1-,  SiO,E/+..῍/+.3 wt.ῌ 5



Cl ( SiO,E/,..῍/-.- wt.ῌ F (GH I Fig. +, G Stage ῍
5J! +30, K +322῍23 Kῌ+-C m)Ijnopqf)r

et al. +332

] d@ef( d +-C rKb ,,33*y0*z-,+1*y
2* yBP, Kb ,,31*z-,/1* cal yBP ,s {! ;3X

( SiO, E/-῍/. wt.

 !LM)N:X5 Stuiver

stuvt$WXKwr)x ! /efWX Gfl-+/Kb( -,-** cal yBP 

|}Z ~{!( -,-** KWX
!;XW5{!0ῌ,  ! "#0    
0ῌ+ 

OP

55 X3R17t )QRSTU/0DV   Gfl-+ #5 Kb R  Kb)N Kb
@5J!{j(  +33/)5

$79&t+ Kb RN;

, A  5

W+/0WX / km

!3!"¡)¢£ - ¤1)¥ jI! #¦§jI"¡(¨©ª«)$!N , +"¡[\ L, M )Ij ¬­῍Kb®)¯ ! ¯5Fig. ++. SiO,-MnO variation diagram for whole rocksamples of Suribachi and Kitamuki crater. Openand close symbols show proximal and distal
deposits, respectively.

Table ,.

Results of +.C dating for charcoals.

Fig. +,. SiO,-K,O variation diagram for whole rocksamples of Stage II-IV.

Locations of each sample are shown in Fig. +.

%¸¹& ºx» c¬§ -,-**

Fig. +-. Age-depth diagrams for tephra beds at
Loc. L and M. The depth means the cumulative thickness of loam from the surface. Opensquares : Loc. L, open diamonds : Loc. M, soldlines : approximate line of each location. Notethat ages are normalized by AD ,***.

 Tk-,  Gfl-+   Tk-0  +331 Fig. +.. Relation between the area enclosed byisopachs (S) and the thickness (T), for tephras
from Tokachi-dake volcano. Dashed lines are isovolume lines assuming V+,., TS (Hayakawa,+32/).

~ !  s }  | Gfl-+  Tk-, !
& Fig. +-  '()*+,%-. L / +* cm ῌ ky -. M / / cm ῌ ky
1 234 +323 567-/8*+,% .ῌ+/ cmῌky, 9 1 cmῌky

0z0;GH  n 1n ! 0 8"# $%ῌ

267-,-** cal yBP AD 21+ῌ+ *,-  AD 3.1



A ¼

 Tk-2-+ -, Tk-1-+ H 5d// jkjn ! B\'(){X *+  Hayakawa +32/ y: 0;! <V+,., TS V : OPQ+ T : B\\f S : AD +3/* =>/?@  Tk-+ -B\5+ ;+! >. L / .,-.* yBP, -. M / .,,/* yBP, Tk-- -. L

B\5HOPQb; Fig. +. B\/ +,13* yBP, -. M / +,1/* yBP, Tk-1 -. L / 1**_+ST?

yBP, -. M / 13* yBP Hayakawa +32/ + B<01 , -.A/

C +**

 IJ 

7

DEF! GH<KLMNOPQ BRST

;! 

 Hayakawa +32/ y/ ¡+G
5/¢0; @£5   +333 G ¤/ ¡-¥&p+U1 _H

U: 0;!
 VW'()*+,% Tk-+ XYZ[@
'()BB\]^@  _`AAa ,*,***ῌ.*,*** yBP,

! GHB\ῌ+

0! GG  -,-**

  cd0e U +DIb;

Ac OPQ*+fgh%iZ0jkj 0 lmH!

¦§ ¨BB\©ªG / ¡H +DVo

!
Table -  +jkjn! ¬§ -,-**

cjkjn<« Fig. +/ ?

Ajkjn ­®/ *.+ km-

DRE, 9n!  *.*- km- DREῌky
1ῌ ῎ ῍ ῏

7n n0!

sO(¯"/p  Stage ῌ5¬U°±#/ *.*. kmDRE : Dense Rock Equivalent DXop+U! qrQst(uv wx4 +32+ ; y z0np{%8 |}% ,.1 gῌcm-

DRE, _² Stage ῍/ *.*-1 km- DRE / Stage ῌ³h%jkj5n  Stage ῎/ *.*+3 km- DRE,
Stage ῏/ *.**0 km- DRE

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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- forbomb (AD +3,0 and +322῍23) and lava ﬂow.

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rc) stuvwKttxyz1w
Fig. +/. Cumulative magma volume versus time fordeposits erupted during the last -,-** yBP.

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#DEB:9 Gl #12F Fig. +0"GH Gl 6BI#4566IJKG Fig. +0" L 
#6G6M  78
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Fig. +0. SiO,-MnO variation diagram for whole rocksamples of Suribachi and Ground crater ejecta.

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270

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kC"OHg1K9 .!hl =m@Z:X   Eichelberger, J.C., Carrigan, C.R., Westrich, H.R. and
Shannon, J.R. (+320) Non-explosive silicic volcanism.

Nature, -,-, /32ῌ0*,.
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4+3318 ^|_( +03. 1 ^|_123 +1V+2 P
( ., ,03ῌ,13.
Furuta, T., Fujioka, K. and Arai, F. (+320) Widespreadsubmarine tephras around Japanpetrographic andchemical properties. Marine Geology, 1,, +,/ῌ.,.
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*, /*1ῌ/3,.
K  4+33/8 1jhX 
 4 ( .* +11ῌ+3*.
K 7 6 4+3238 |(,$% ,2 +ῌ+1.
Hildreth, W. (+32+) Gradients in silicic magma chambers :implications for lithospheric magmatism. J. Geophys.
Res., 20, +*+/-ῌ+*+3,.
Horn, S. and Schmincke H.-U. (,***) Volatile emission
during the eruption of Baitoushan Volcano (China/
North Korea) ca. 303 AD. Bull. Volcanol., 0+, /-1ῌ///.
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tu7(  4+32-8 ^|_ wKAk
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Katsui, Y., Ando, S. and Inaba, K. (+31/) Formation andmagmatic evolution of Mashu volcano, east Hokkaido,
Japan. Jour. Fac. Sci., Hokkaido Univ., Ser. IV, +0, /--ῌ//,.
6 7<K` 4+32+8 ¡¢(, 0F
c2K_ Disaster Map ¢®£¯ ¤'¥°T$%¦§¨¢®/$%$%4±§¨¢®°T:\$%©
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¬8 3ῌ+-.
Katsui, Y., Kawachi, S., Kondo, Y., Ikeda, Y., Nakagawa,
M., Gotoh, Y. and Yamagishi, H. (+33*) The +322ῌ+323
explosive eruption of Tokachi-dake, central Hokkaido,
its sequence and mode. Bull. Volcanol. Soc. Japan, -/,+++ῌ+,3.
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Miyaji, N., Sumita, M., Yoshida, M, Kondo, Y., Yamazaki,T., Kouyama, K., Sone, T. and Muto, H. (+33*) Tephrastratigraphical study of +322ῌ+323 eruptions of Tokachidake volcano, central Hokkaido. Bull. Volcanol. Soc.
Japan, -/, +-+ῌ+./.
Miyashiro, A. (+31.) Volcanic rock series in island arcs
and active continental margins. Amer. J. Sci., ,1., -,+ῌ-//.
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Stuiver, M., Reimer, P. J., Bard, E., Beck, J.W., Burr, G.S.,
Hughen, K.A., Kromer, B., McCormac, G., van derPlicht, J. and Spurk, M. (+332) INTICAL 32 radiocarbon age calibration, ,.,***ῌ* cal BP. Radiocarbon, .*,+*.+ῌ+*2-.
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