ῒΐ  .3  (,**.)
 -  +,3ῌ+., ῕ ῔ +3., 






 
    ,**-  +,  +*  ,**.  .  +* The +3., Eruption of Hokkaido-Komagatake Volcano Was Phreatomagmatic
Ryo TAKAHASHI῍, Mitsuhiro NAKAGAWA῍, Kiyoshi NAKANISHI῍῍ and Mitsuhiro YOSHIMOTO῍῍῍During the ,*th century, two major eruptions of Hokkaido-Komagatake volcano occurred in +3,3 and +3.,.
The +3,3 eruption was one of the largest magmatic eruptions in Japan in the last +** years, and has been
investigated in detail. On the other hand, no systematic volcanological research has ever been done on the +3.,
eruption. Since it has not been clariﬁed whether the +3., eruption was magmatic or phreatic, we decided toinvestigate the sequence and eruption mode of this event. At the summit, the +3., eruptives overlie the +3,3
pyroclastic fall deposits and are covered by ash-fall deposits of recent phreatic eruptions. Based on thephotographs, documentary descriptions and sequence of the eruptive deposits, we were able to divide the eruption
into three phases. Phase-+ : Start of the eruption on November +0 at 2 : ** (JST) that formed NW-SE trending
ﬁssure +.0 km in length. This was followed by eruptions at the main crater (+3,3 crater) that produced the
pyroclastic surges (2 : +*). Phase-, : Eruption column had grown up from 2 : +2ῌ2 : ,* and ash-fall started tospread towards the southeast portion of the +3,3 crater. Phase-- : Decrease of the eruption activity at 2 : .* andcontinuous ash emission until the evening.
We newly found fresh pumice and its fragments in the deposits associated with the Phase-+ event. This fresh
pumice exhibits no alteration features and has similar petrological features to other historic pumice since +0.*.
This fresh pumice, however, could be distinguished from other historic pumice by the most silicic nature of its
matrix glasses. Therefore, we concluded that the pumice was derived from the juvenile magma that caused the+3., eruption. Considering the temporal evolution of the component of the eruptive materials, the +3., eruption
began with a phreatomagmatic eruption (Phase-+) followed by phreatic eruptions (Phase-, and --).
Before the two major eruptions in +3,3 and +3.,, small eruptions occurred intermittently from +3+3ῌ+3,.
and +3-.ῌ+3-2, respectively. Based on these observations, the preceding eruptions could be possible precursor
activities of subsequent magmatic eruptions. Since +330, small phreatic eruptions have intermittently occurred in
Hokkaido-Komagatake until ,***. The present state of the volcano, as we would like to emphasize, has beenquite similar to the conditions prior to the two previous magmatic eruptions.
Key words : Hokkaido-Komagatake volcano, phreatomagmatic eruption, juvenile ejecta+ῌ ῐ ῎ ῑ ῏

STU=2VWXABCD YZ[\7=27]^_V

 !"# $% !"#&'( )* +`abcBZ/ de f +331 a ;f ,**+g h,-./01234 +0.* $5 . 6789:;<=2

7ij7kl7m&K&AB ,* no+Cp/ !"#>?@ABCD 4EFGHIJ237 + K4L/

7 , 67qI=27rsVL/g +3,3 +)t=uv(Fig. +). !"#4) +330 MN ,*** O4PQRJ

w *./, km- 7 2xy>&FJz{QRJ89:;<=

 |*0*ῌ*2+* }~ +*  2  {{ 
Department of Earth and Planetary Sciences,
Graduate School of Science, Hokkaido University, N+*W2 Kita-ku, Sapporo *0*ῌ*2+*, Japan.
 |*.3ῌ,-3-   +..ῌ+
Mori Town O$ce, +..ῌ+ Miyuki, Mori, Kayabe,

Hokkaido *.3ῌ,-3-, Japan.
 |++-ῌ**-,  +ῌ+ῌ+{
Earthquake Research Institute, University of Tokyo,+ῌ+ῌ+ Yayoi, Bunkyo-ku, Tokyo ++-ῌ**-,, Japan.
Corresponding author : Ryo Takahashi
e-mail : takaryo@ep.sci.hokudai.ac.jp

I Y ¹ºZ [ »¼130  +-  +3., 

+1 



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 

9wxd"BM+3.- 



:;N> "LM f.N>





+3+3+3,.  +3-.+3-2   

ef. yz+3., C)":;:BNfC !" #  $%&'(&

:;:FGH!") -

 +330,*** %)" ghN$R {| . }<6&#  *&+,-/012-, 

3 4 56&/0 78 +323 9 :;:+3,3 

.^_` -,,*** (Takeuchi and Nakamura, ,**+) 6=/

< 5

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-3 / %T" 

0>-? & !@ +3.,  5   &  = /,/** A)"-:;:BCDE %)"= /,*** Na

+3.- FGH+IE & 

J9KLM

+1 

^_`

%Ne~ >? Vi

/0N

+0.*  +03.  +2/0  alx +3,3  . > -3 ?)  !O"P#Q$R

4N-O@- NbA E &S& Katsui and Komuro, +32. ; 7& 78 +31/ ; +323 ; u  +331 ;  88 +323 T +3,3  +3.,  +332 E"

UN :;: %VW &Hv9 & 78 +31/

' XY,&)ZO)[(
:;:)ZO) %
)*N+X6&T\-]$& ^_`+3  B)"CD3-FG+3,3  ,* & !@

Em@


+3+3 )" +3,. i-FGHNbA6 +3,3 a  )-b& ))?"/  4 alx0,c-- +3., NdM

4)"-b FCG= *./, km- &ef. ):;:5/01 . ") 6&23&gh +3., +X12

Zi" ^_

78 +323

+3-. )" +3-2 iH-FG`:;: %VW)*N+X6&jk3

HNbA6N +3,3 @)& ! l mn  &^_" +-  +3., ` a!"%+X, o

45N>O &p567NK86&jqr^_`N!

 !>? .  lb
E FCG -+*0 t "
+330 

FGH;6&CkG + 

j@, 8 +331 b ;   ,**+
 /* jI-JK mn+330  8 +331 a +332  ,*** FGH





& )

,*** 

 0 N! ab d¡LMFN- ClῌS ;)" :;:i OP6&I¢d£¤¥¦@,3- &!§E   ,**+- +3.,

 +3., yz 

5© (+3..)(+3.-) alx¨pl $RE E" n ^_`ª

Q"«¬R)"v99­S®¯N> , "N yzN Table +iT+3.,   %VW   . T
Fig. +. Location of Hokkaido-Komagatake volcano.
Active volcanoes are also shown.

 ++ ° +, T dUalxdV ±²³²³´ 
OµT" & µW¶·¸`Xµ=¶y· +3., *¸¹¸º»¼
    ++  +0  2  !"# 2  +* $ %&"'  ()


' *+,

'

1# (Fig. , a). ./0$- -

234



5

 67$89: 2  +2;,* 
=' $>?()# 2,*** m @

<

7A# 

*+~O$9 (Katsui and Komuro,+32.). @

()

B'

4

C DE/F

131



, W

++  +2 (

=#: W 4)'' j +3,3
*O

7 1#





e

+,C - (Phase) }:$-7l: e-./

0$

1#

 (Phase-+), $>?()#

X (Phase-,), i&>#?C i&@7 . (Phase--) 7l:

E/FG HI ' 4 ,  $J9
:  2K L$4

MN7 8

72' KO( +** m (A#PQ: 2
 ,*;,- '*+,

4

7<RS$TU. +3., 
+3., *L(mn#' e W /CW [+:)'+' mn ?

 @ 2V 89: 'L#mn#: #C#4ON 012

()W,2 (Fig. , b),  / W

 67' 31#11mn

6XYZ 0 cm

4

44M=[\9] (Fig. , c). L4' 4M' 4+3,3 *O

+3., *4 5' @ON7=:++3., *L=8# (Figs. ., /). 4& 66

 +, km `7' [^ ab$cd

7l:11 +3., *L=8}:

@' e +* fg 2  .* h

72C

^ _74

6[\# OC

$#: 4ONi&' 2  /* >!  jkl:^"@7g2' mn

4 /**;+,*** m`7' [

o9$ , cm (A#(Fig. -). @ 7' >?()#4

6[^= #' -./0 pC' q#$r4ON +3,3 *[\K$ +** m (

o97mn#: s ¡u¢' +31/w  [\Kmn

X( +3,3 *

X.

Q:£7¤¥¦ 4^§$ ,;. cm

LP
o97

 +3., *L 4^§=8¨9$ 4 C89: sKtuv' +3.-w : +3-. *C +3-2 *!" xy%=z{|h7' >ª#:«u¢ (+3-3) +[^¬$­®

 H© +3-1 * ?()#&4&='\#&}:C ;¯9:$' °± <²7e³´}:[ +.0 km\4^=8}:72C  f e+4ON3ῌ
Table +.

Sequence of the +3., eruption of Hokkaido-Komagatake volcano.

132|} ~



Fig. ,. Photographs of the +3., Hokkaido-Komagatake eruption (Mori Meteorological Observatory, +3..). (a)Eruption cloud of about / minutes after beginning of eruption from Shikabe town (about +, km east-southeast
from the vent). The arrow indicates pyroclastic surge. (b) Eruption cloud at +* : ,* from Onuma (about 2
km south from the vent). (c) Eruptives of the +3., eruption at Shikabe town.

 +3-1   +3., !"# +330 $%&'()#*+),-./01 23 4 +3., )/0 5678
. /1 cm 9/0:; <= +>?@78ABC I II III  - DEFGH#IJ 4
(Fig. 0). Fig. . #KLM#?NKEFGH567

8OP1 $Q#KEFGHRSO T. f  *+#D + f U#+VJWOX
YZ[#\] (Fig. 1).
5Q^EFGHῌ+> 2 mm $Q _` +a, f#bcdOeDfgh<=ij:)kC
Fig. -. Isopach map of the +3., volcanic ash (MoriMeteorological Observatory, +3..). Contour
lines are ,** m intervals.

 l/0 +3,3 )mnoCpo#CNq`Jr1. 78 / cm stu` vwh
78ABx (Fig. .). yz;{LMµ¶· +3., 0 *¸¹¸º» *¼rJ

Fig. ..
Maps showing thickness of each unit in centimeters at each locality.
localities of stratigraphic columns in Fig. /. Contour lines are +* m intervals.

133

Symbols A to F indicate the II 9\]^ _ III  II 9K  !"#$ %&`() *+, , I
a II

bcKLM-./Ud*1e34&
f&gh

73

8

+3,3 0*1,52EiPQR (Fig. .). IJ+3,3 0*1=> ?@j FG -2 cm
DEH/ 
+3., 0Fig. /. Correlative stratigraphic columns for representative sections. Locations of each section are
shown in Fig. ..

*


bcn

o

pPqrJ I" kP +f s9 &tkR&<lmuv

wbxy[ z \{P|J }~k4PJ *U

PqrJ s94P

J -P z  \{P
J \{P,J j G8s9 

cm



 II 

!" #$ %&'() *+, - .
/ +3,3 0*12

34" 5

73 8  I 9:;<

6+3,3 0*1=> ?@ABCDE FG ,*cm

H (Fig. .). IJ I 9K KLM k : PqrJ \G 

PW-+.*.  XRF

bx£¤¥ G §¨ EPMA«¬­ k®< ¯ * °m*+./
wbx*+./

±)²³R&< +3., 09K+* cm STx£¤¥ PqrJ

*+ ZY[ II  6 

JEOL22** ¦ZAF ©Pª<J&NOPQR  II I*UVWIXYH - *UV+: , 

J} ¡ ¢P&<J } wk´ \ } wb®¯ °©±²³°©´ µ°¶·¸¹

134

Fig. 0.
Generalized columnar section of the +3.,
tephra.
Fig. 1.
Grain size distribution at representative
section of the +3., ejecta.
0 
0ῌ+   A, 

RTU VRU  Fe-Ti WX "#-./ B   !"#$%fN"#

&' (')*+ ,"#-./ 012

 f LIBm RS)+m U"34567./#-. intersertal N5i  i + 

0ῌ+ῌ+ 

=9:5>? @A

BCD&'EF.GHIJF/ KLM NOHPQ R
S RTU VRU Fe-Ti WX Y KLZ-.[.* vol.ῌ Y\./ ]^_` JZ abM Ycd#'

Ee fgh1iabM%SIjd#'./

Pk"1lmijd#'./(b)  B &'E#krs-tuvYw;'./ Pk"1lmRS RTU VRU) A )z{Y KLZiz|

1JF/ fgh }:~YB^?Ee ]^gh1abM

fM IL ?EF.ijd#'./ CD&'<5GHIJF/(d) 

 KLZI1JB | -1!
?EF./  @ ABCD&'EF.GHIJF/
KLMRS RTU VRU Fe-Ti WX Y\e f 1¡¢Y eutaxitic N5/ B  n:;< :5>? o)pqCD

FeyTi WX./ +

1!  B-GHIJFI Pk"1

89:;<

ix;'./ KLM

1`.)IY

LIB hyalo-ophitic N5i Y\./ (a)  A  A B,%S jd#'-F/(c) 

 KmY:5>? KL RS

(e)

!

£ KLM NOHPQNI¤¥¡¦§-
1 !?<Y ¨)?EM "#-./
0ῌ+ῌ, ,©1 6o"1 ('#I*"Btª&'<)«¬#'.gh  A,  B
)M I­j&'</(a)  A gh

"ºy+,- +3., G H }~}»¼
 A 



   !"#(b)  B  IHb`

135: 3/ wt.ῌ A^ QR

S: 2/ wt.ῌ n"#   A %Ta"  B  $=T`# B 

$% 

&'



()*


!

 HJS Qt:¡_n"#  2* wt.ῌ A^  A II

0* wt.

ῌ  B  ,* wt.ῌ >?a"# i "#(c) 

a"HJ¢  B T"#  +,-. /0"1 Qt£F  A  ) ;

 1 2 312 (4 Fe-Ti 56$

£F B $"#  III "#: 4 )= 0ῌ, 

¤ A T="#. 7 89: ;) <=>?

@ABC D@:EF"# +3., G-* wt.ῌ vn



Qt¥:

 ) ; Z A $" B  $=!#HI JKL M NOPQRS:T7
U VWXYZ +323[ : \]A^"

1

QRS:

1ῌ+ 

+,-J_A7!`:EF"# a`+,-  HbC =):.Uc



+3., G .! &¦x"  dJ:@:+,-J_T`U`A, B §&¡_ ;efgh!# `biaj$U!"dJ:x" ¥©ª$"#  «tklmn  intersertal o !¬1 1 2 312 (4 Fe-Ti

pAq  rsQt? u=dJ: +,-J_
vw :x"efgn"# h@: H

56AO!"# ­
¯ ;

«t

Z¥¥S&A¨)a"§&

n"# §&  @ }°±yL :x"EF"#+,- z{| }~}@ !% $=!# ² S&¥ ©ª S&

.U $` }~}@ ³ª 1}°±´"#efgn"# l@ $=! B

1ῌ,  

 ; efg!#T  

.U  `®

 A (4 B  -..* vol.ῌ

H

z{|

s.

ῌ  

U`efg=!# }~}@n"

H

§&

H

VTable -[# +3., G¤: SiO,=oHµ!

 B /3.20,.. wt.

$=!
o!¶¥

TP8T!  :sUx"

¥·) SiO,¸0*.20+.- wt.ῌ n"# i §&n"# z{| H §&¹oAqx (Fig. 2).

0ῌ- 

  ZQRS: )a; :

+* wt.ῌ >?n"# |s= Table , -, f. 7Aqx#

Table ,. Temporal variations in component of the+3., ejecta.

Table -. Representative whole rock chemical compositions of white pumice of the +3., and historic
eruptions. Total Fe as Fe, O-.

U_ `abcdae faghij

136

Fig. 2.

Harker diagrams for white pumice of the +3., and historic eruptions.

Table .. Representative matrix glass chemical compositions of white pumice of the +3., and historic
eruptions.

4567,-" SiO,, Al, O-, FeO* 8
9 CaO :";<%=9.
1ῌ- ῌ῎῍ῐ῏#$% A #$% B >?@AB67
CDE (Table .).

123?

@AB67 SiO, F1/.*G11.* wt.ῌ  SiO, HI
 Al, O-  FeO*, CaO :"J567K)L,- (Fig. 3). +3., M

1#$% A ?@A

B NOP#$% A @ABQ SiO, F1/.2G2*., wt.ῌ

123?@AB67RS"

T SiO,  Al, O- UJ CaO  FeO*  (Fig.
3). /0 #$% B ?@ABNOP#$% B @ABQ SiO, F1/.1G11.- wt.ῌ 

1?@AB(V67WX<Y,-. #$% B Na, O 



?@AB +2/0 M +3,3 MRZT SiO, 89 Na, O  !" #$% B 

Al, O- :"J [&'() Na, O *+,-.

,-O^E.

/0#$% A 

1#$% B 23

14567\]´µ¶·¸O +3., Q ¹º» ¼d137

Fig. 3.
Harker diagrams of matrix glass chemical compositions of white pumice of the +3., and historic
eruptions.

2 @ῌghij0>/01tu)*2ῌ+ 

῍῎ +[ vw.  /0*
,[ 51678rBx9:(;<1=>/0*      !-[ vw.yz>{|}  ~"῏" #῎ $%&  '

-;<1=>  vw yz>{|} ()*  +,- '.

0-  C/0* /012 3451678)()9:(+[ re ,[;<1=>  1?>/0 @ῌ0A4)8/&%b  

ij08B&8Cb* ;,[B&8C* DE- 9:(FGH" )9:

4)8  

(FGH1$I"1J>/00(* 3C  b  *

KLMNO +33*P+33/ Q  (Nakada et al., +33/ ;3 ,[ 0?+[ /01 2> @ῌ0(* ῐWatanabe et al., +333), =R. ,*** Q  STUVW-(

,**+ ; XYVW ,**, ; TUVUZ ,**,[ \]^ ,***

   - ¡ -+ ¢ .£  ¤37

Q  SX_VW ,**+ ; `aVW ,**+ ; UZVTU

9:(¥¦FGH 3(§῎ $%&8)* /&B,**,[ bcῑ0(def  @ῌghij1k>

FGH  ¨© ª«¬bd

/012>+, ()* ,*** Q=R.

 FGH­®10/¯ =R.°'&Blm1n% 8 opq.  r7

῍ S±²῍[ X³FGH/0 J3  sef(ij1k>/01

B& !FGH"/0 ¦B3 (d ST¶· v¸¹o wºx»¼

138 ,**+ ;  ,**,+  ,, P%Q  !   ; 

          !  " # $ "%&' ()* + -', -."" /0, 12%&'- .

$! ,>'*,"#SuqrR)*%&'v; !8$-M 8?;*C
2ῌ,+3., ΐ῕ῐῌ῎῍῎῔ῑ

+ + >? -

 ,-8 S>5w8 * xy

3456* $ " 7 z +3., 

>?

:#;<

(J |

J  "%&!

,-8"9" !*#Sakuyama, +32- =$%>?$@%A

/ &B* CD>/0E' # /, /08

"/0 F&!

"G( #-8 2HI)*)$*?>):#;< + +333/0 7 %& 

{T

}~Q   A,  B  ?
 U6A A U6  5AV
!"qr

87B

  A }

~Q"W) XY1Z8`?!  u ! QD = $~A1"qr

,8

8[

* SiO,  Al, O- \ FeO* ]

J-8" $/0KLM,#C-N,

(Fig. 3). ~W%-8C0OPQ ! $->?  *" \ - u8 $%N&A1

S F&%&8J-8 R *~A1" FeO*=

 SiO, 8 Al, O- ^_

*8"T; KLM"U."

= " ?>U_\J : +302 ; /V M W KL 0X`a +32+ ;  ,**- --8>? A }Y1Z2 $ *[34\5J36'N)*~Q" ~)*-

$%& "-N *"] r bc 8b;?!

)*7B/0 )* ^  " %
& "_^8`?!a9 8b;?
)*+ - c J 7B/0!q

U_ B }~Q"de!
QD ~A1%N&A1"-] qr

A18Uf

A1 R
1,

:   %& E( #-8

(Figs. 2, 3). = U6A1"A1g 8`¡A

U. 8b;?! --8"1 

1 ¢* h£¤i & *¥¦7Bj R  

HI d< !* dHI#8 *;8" Ruapehu  +33/  3e+* f  " =%&!^)*-89"!

%&-N * (Reagan et al., +321 ; Streck et al., ,**,).
g ,*** §"¢?! (Fig. +*). -8>?  B }~Q"^%Q "

(Nakagawa et al., +333), ,* OA W>? *@ Arenal  B }

8S> #?~A1" SiO,  K, O \ Al, O- ] C h£¤i 8"^A1
R, (Figs. 3, ++). --8>? B }

g~Q" P%Q "8; )*"%N&A1"

 B }7~Q" + + >? -

h8D +311 

8ij, CD>. *kB E( #: ,**, = lCD ,***

3G #

  "mE8F>? 2ῌ- +3.,   8+3., ΐ῕ῐῌῒ῏

 "$%& ^W $ `F -- " +k8bc^¨ 8 +3., l© mk, +3.,   " +3,3 ª>



>

n,

`oG?

:H ,**+ ; pI ,**+ ; JK ,**,

?

,88 noῌpK_«L +.0km ¬!

>  ,***  = L /** OKLM

qª1 !* (Katsui and Komuro, +32.). =8]¬!qª1¤0 b­, ®¯°±r²

 ,***   "qr /** ONs KL-N8 ¯°± II 8 III " +3,3 ª16

M>?mE8F>? -8R !

C¥ r²sv,³«W (Fig. .), -!?

-M (Amma-Miyasaka and Nakagawa, ,**-):Amma-Miyasaka et al., Ot

+3,3 ª´$µt¬!qª>?

--!?HI# A>J 88

8 R * U_¯°±ῌ"0u r²b +3., [\[+139

Fig. +*. Histograms of core compositions of phenocrystic minerals in white pumice of historic eruptions andType-B pumice of the +3., eruption.





 +3,3  !" #$%&'()* + ,-.

/(0123 I 45-6789#$ 0123 I
0123 II ': III

;&(<=> ?
IJ,-K@ABCDEFGH-$

L( +3,3 MN'-?@ABC45-$ +

%& OPQ /RS'-T/45

U ./)(?@ABCDEFGH-45V
W$ 0123 I OPQ /RSXY,-Z  [\[(]^_
123

T`a45 Z/0

#Z

%&'-(+3., 

/gE45-!"

/bcdef-$ h./ij +3., !"/(-$(Fig. .), +3., h /k(/h+ !"-$lmno'p* +qrst
KL(/uvFwx-$ 0123 I ygz{4P|


-Z h

k}s~KL( !"-$ 0123 II  0123 Iyygz{4P|-$ _+./ no#-k(/

>-Z

h

0123 IITk}s~KL(  +$ g0123 III 
ygz{4/P|Fig. ++. Histograms for K,O content of matrix
glass of white pumice from historic eruptions
and Type-B pumice of the +3., eruption.

 ./ no#-k(/ g,- (Figs.
-, .). Z/Z h 0123 III kKL( +$ 0123 III /#/Q45´µ ?^]¶·^¸ ¹^º»¼140
 Phase-+  I  II

  III  Phase-,

Y }~& ,*** (P CDC>6$4>&OUXi 6 8
Xi 9]^_ ,**+; +3,3  +3.,     ( !"O:>6YU6 }~&B   +3.,  !"# $%CDC& '() *+, - ,*** *( q6 +3,3 !#./0 123( , UXi B6UX +330 &$4 5 678 9Phase-+ : ; <r= +3,3 &> ?@AB CDC123

i +3., !#Yi $4qr CDC

6EB 9Phase-+ =; FGHIJ6(Phase-,), >KL&M (Phase--). > N

OP  + QRBSTBOU
+3., ΐ῔ῒ῎ῑ῕2ῌ.

CDC6$BXi!%t()O

$ & PY,***  %'Q,**- (*( `{b

O(Y +3,3  +3.,  

: !(Y+3,3  +3., : p

VW&$UX +3., CDC(YUR QH&  $%&6)8&ui

6ZU < [\ ]^_ (,**+) &$UX*

XQ*(+(Oi BB  wI$%&d8P&t `{b(O0P=pR `abc Table /&$efOg6hUXij&kl

$%& ,* mn&oU , 

CDC <p:&qrO123Is4tHRIPOU

&,BXF- I.%l)(Y =
/01&$IBX 2: :I3It 64(Yz%Xi 6Z (Table /).
,* mn, u vwIx q

QHCDC> >&$UXy)o 8Xi CDC :xOt 6(Yz%

F/ `{b( +330  +332

& + | <BX ,*** & 0 |qrO123

Is4BXi CDC> > (

Table /.

3ῌ ῏ ῍ ῐ+3., 

,5¡¢£

¤6&x

¥¦O78Iu§¨©$ ª«¬9 :cQ; §¨!­¨O78I® ¯° $4P<Bª«¬±Iu 

CDC²(Y=>B ³UX +3., 

Summary of eruptions of Hokkaido-Komagatake from AD +2/0 to ,***.

; *+, +3., T  
+3,3  +3.,  

 , ῌ
       ! "#

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: 2&" ; <=!"#>? $%&'>?  (@!<)*+, A-!<)*+,
2BCDE)*+, 2&" ./01>? 2
234  F56FG "@7
H89IJ K:;<%=L>M N?1@>M 
AOPQRS&T& UBCV D6WE&
-Fῌ ῑ ῐ ῍Amma-Miyasaka, M. and Nakagawa, M. (,**-) Evolutionof deeper basaltic and shallower andesitic magmas during
the AD +.03ῌ+32- eruptions of Miyake-jima volcano,
Izu-Mariana arc : inferences from temporal variations ofmineral compositions in crystal-clots. J. Petrol., .., ,++-ῌ,+-2.
XFGHYZ5I[Y\J]HKYL/^MY_`Nab+331c ; *+,\ +03.  -def;2g +1h+2 3iOjkPf
\ ., ,03ῌ,13.
QF"R Y l5ST b+3.-c #L +1  ++ m +0 U*+,V @A ,3 0/ῌ2* +**ῌ++,.
QWZnYFHo b+333c ; X YZ\[-@Q<\]! @A 3. ,13ῌ,3..
^`p_Yq\ `Ya/1bYrst_ b+31/c *+,f\cdYuY vw2Bexy; exz{ p. +3..
Katsui, Y. and Komuro, H. (+32.) Formation of fracturesin Komagatake volcano, Hokkaido. J. Fac. Sci. Hokkaido
Univ. Ser. ῌ, ,+, +2-ῌ+3/.
^`p_Yfg|RYh}ijYZ~k b+323c ;*+,\cdl cdmKnoM Y p#' b,**,c q! ,*** \r?
5d-s \ .1 ,1ῌ-+.
7tn b+3..c #L +1  ++ m +0 U*+,VmK
X7tnu
Nakada, S., Motomura, Y. and Shimizu, H. (+33/) Mannerof magma ascent at Unzen Volcano (Japan). Geophys.
Res. Lett., ,,, /01ῌ/1*.
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$LY}~?YN?1@Ya` b,**+c 
q! ,*** f\[-f

141

c< ++* +02ῌ+2*.
Nakagawa, M., Wada, K., Thordarson, T., Wood, C. P.
and Gamble, J. A. (+333) Petrologic investigations of the+33/ and +330 eruptions of Ruapehu volcano, New Zealand : formation of discrete and small magma pockets
and their intermittent discharge. Bull. Volcanol., 0+, +/ῌ-+.
FHoY$BMYQWZnYZ5I[Yl Y
Q`aL Y r Y % L Y   Y i"YQ  b,**+c ; *+, ,***  9p : [-\*+2!d)  ! \ .0 ,3/ῌ-*..
FHoYQWZnYZ5I[Ya YtMY
F L Y { Y 5? Y ai Y l
 Y Q`aL Y r Y $¡? Y ῌ¢
 Y L/^M Y `/| b,**,c A ,*** [- : £*-92! \ .1 ,13ῌ,22.
%¤¥HK Y ¦a§_ Y ¨a1R b+3-3c ;*+,0w c ++ +/,ῌ+0*.
¢ b+302c \©`cª 2g@Q2dv
5&" c +1 0/ῌ13.
¢ b,**-c U5«c\[- ¬A$%
¡A- ¢£'­ \ .2 .-ῌ0+.
¢Y¤¥L b+32+c \  ¦ ¡AA- +/ S,,-ῌ,-2.
Reagan, M. K., Gill, J. B., Malavassi, E. and Garcia, M. O.
(+321) Changes in magma composition at Arenal volcano, Costa Rica, +302ῌ+32/ : real-time monitoring of
open-system di#erentiation. Bull. Volcanol., .3, .+/ῌ.-..
Sakuyama, M. (+32-) Petrology of arc volcanic rocks andtheir origin by mantle diapers. J. Volcanol. Geotherm.
Res., +2, ,31ῌ-,*.
Streck, M. J., Dungan, M. A., Malavassi, E., Reagan, M. K.
and Bussy, F. (,**,) The role of basalt replenishment in
the generation of basaltic andesites of the ongoing activity at Arenal volcano, Costa Rica : evidence fromclinopyroxene and spinel. Bull. Volcanol., 0., -+0ῌ-,1.
Takeuchi, S. and Nakamura, M. (,**+) Role of precursory
less-viscous mixed magma in the eruption of phenocrystrich magma : evidence from the Hokkaido-Komagatake+3,3 eruption. Bull. Volcanol., 0-, -0/ῌ-10.
p#'YoM b,**,c A\ ,***  - m -+ U
[-®¯°E \ .1 00-ῌ01..
p#'YoMY§¨aRY\±²³YF©ª~Y¨a~R b,**+c A\ ,***  - m -+ U9
5d- cdmK´­u  /, ,+/ῌ,,3.
_`Na Y Z5I[ Y XFGH Y QWZn Y Z/«¬
RYc­ Y^`p_YiaiRYµ®¶>Y$B
M b+331 ac ; *+, +330  - m \ ., +.+ῌ+/+.
_`Na Y Z5I[ Y ¨a¯L Y l5 · Y % L
b+331 bc ; *+, +330  - m[°jkP \ ., .,3ῌ.-+.
_±nY²³Y¸a±MY¹a¥LY/ ´YF©ª~ Y §¨aR Y \±²³ Y oM Y p#'Y¨a~RYµY¶s[ b,**+c q!\ ,*** B·º»¼f2 m +2 U[-

142

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 SO,   ++* ,/1ῌ,1*.
Watanabe, K., Danhara, T., Watanabe, K., Terai, K. andYamashita, T. (+333) Juvenile volcanic glass erupted
before the appearance of the +33+ lava dome, Unzen

volcano, Kyusyu, Japan. J. Volcanol. Geotherm. Res., 23,++-ῌ+,+.
   +332 !"#$%& +0.* '()*  .- +-1ῌ+.2.
+,-. /0 1