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Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc
Isoji MIYAGI῍
The volcanic activity of Hijiori volcano (N-2-0῎-/, E+.*3῎,* ; WGS2.) is reported in detail as a casestudy to understand how a new felsic volcano commences the activity. Hijiori volcano, a small caldera withapproximately , km in diameter, is an active volcano of Japan, which started a series of eruptions +,,*** years ago(in Calendar age), where no volcanic body had existed before.
The eruptive history of Hijiori volcano was divided into four major stages (Stage +, ,, -, .) and thesubdivisions (Stage +, Stage ,῍+, ,῍,, Stage -῍+, -῍,, -῍- [a, b], Stage .῍+ [a, b, c, d, e], .῍,, .῍-). Time spanof each hiatus among the four major stages is shorter enough to produce no black soils, and no signiﬁcantdi#erence in the +.C age have been recognized between the stage + and stage -. The major eruptive product of
Hijiori volcano turns out to be valley ﬁlling non-welded (Stage +, -῍- [a, b]) and partly welded (Stage ,῍,) pumice
ﬂow deposits with total maximum thickness of about +/* m and with a range / km to the southward and 3 km to
the northward. The accompanying pumice fall (Stage +, ,῍,, -῍- [a, b]) and ash fall (Stage .῍,) are dispersed
0* km to the eastward. All the essential pumice from the eruptions were hypersthene-hornblende-quartz dacite.
There are phreatic (or phreatomagmatic) eruptions at the beginning of Stage ,, -, and . which deposited lapilli
falls and ﬂows (Stage ,῍+, -῍+, .῍+ [a῍e]) in the proximity. The volume of the valley ﬁlling pyroclastic ﬂow
deposit and the air fall deposit are +.. and *.0 km-, respectively, and the caldera ﬁlling deposit is estimated to be*.- km-. Therefore, total eruptive volume of Hijiori volcano is estimated to be about ,.- km-.
Key words : Hijiori, caldera, new volcano, pyroclastic ﬂow+ῌ ῐ ῎ ῑ ῏|}C\~IQRS'   $I 'HBD;( H-/I

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+3/3 ; Katsui et al., +313 ; Takahashi, +32*

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qr st +32/op

 ¥¦L- ( V)§¨L ©ª«;:¬*­;(G-uvw xyik +30. ; kz +323 ?@ G&{ ®-*/ῌ2/01 ¯a)° +  +  + £±²³´µ¶·F¡¢ῌQ¸¹º·F»¼4
Geological Survey of Japan, AIST, Tsukuba Central
1, Tsukuba, Ibaraki -*/ῌ2/01, Japan.

Corresponding author : Isoji Miyagi
e-mail : miyagi.iso+.***@aist.go.jp

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Fig. +. Location. Hijiori volcano is located at the northeastern Japan arc. It is just on the edge of a mantle
hot ﬁnger (gray ﬁlled regions) proposed by Tamura
et al. (,**,).

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Fig. ,. Distribution of Hijiori pyroclastic ﬂow deposits. Modiﬁed after Kawaguchi and Murakami (+33.).
The ﬁlled circles with identiﬁer represent locations of outcrops referred in the text. Filled stars represent
the locations of boreholes by NEDO.

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wCc­T'UV=xy2 Fig. /Table + YZ"-ῌ++ 

T'UV +  4~52M (+33.)  £KM T'U
V + *z45%&<4¤ ^_Z ®{¯ :°±°1|[ 23²W875%&<Ccv[ GH"=[  }!³~´Ccµ¶³~´=vG@E·  ¸=?|=<Fig. .. Comparison of the stratigraphy of Hijiori volcano
determined by previous works and this study.

=¹ · .|< %" T'UV + =5%&<-o):=z4v5:

45/ : µ¶Q·`/¸¹º»Fig. /.

317

Schematic columnar section of Hijiori volcano.

  -ῌ- wx< . yz{|Z}$c

 !"#$%&'()S +33.O* _6789:;< -m/ km ?@

A0~#*  + +,-& ./01& D23) * 456789:;<==> ,.3 km{|Z\- LSz?@ + ABC -2 D -/ $ 1.2+ E FG +.* D 2 $ -1.00

 + P\z{|Z$

E ; Fig. , :HIJ + K LMNO P ==F)#<c& i\ */., km ?@ , ABC -2 D -- $ /1.22 E FG +.* D/ A456789:;<F ,* kmOm+* $ .+.+, EO & QR / m LSTQU#: AM ¡ .* kmO <n& 4+ VWXY7Z[\]^ *5¢£¤+aY7Z[Sj &Y_`+ab& Rc + cm dDef

7Z[¢£¥¦§:¨ ©ª 23) * 

Q gh i` j * h+,n i©ª«c A¬­D ®¯°«O &-<kSl +m, m <n eopq Arc /m+*  ,ῌ, ±&²<  -cmO stu v*  + & 

P . ±&«* i³´ sh _f©ª

¹º»¼

318
Table +.



Characteristics of Hijiori eruptive stages.

 +    

!"#"$ % ( + )  + /*012 + 45&'+,-.
Fig. 0A #3678 ,.2῍..* mm

1) 9:;<=>?/

z{G



km) 

(1h

 ,῍+ 45_)(I"'! (Fig. /)*45 ! * |z'/ 
66 R.($[" - ,῍+  /*ῌ 5788! 00ῌ @AB ; CD EFGHI)/JK('!K('"'/L! 1ῌ

RSUVWXx2)yR.(|3$}~I"'  %

M@C D/* D ) *.,/ mm . 97

8 ,.2῍..* mm 1) /

LGNOPKQLRS"T/L! ,1ῌ! *ῌ  +῍+  @Fig. 1  stage +D

/L! ,/ῌ Kz0/!:OT/L!

 + ) UVWXYZ

km  [ " - @! \ -2 # -1  +/..0 $ .3./3 $D 
'^($

!

0.0

] +.* # +-% ./ km 6(&% +* km  (Fig. 2A) )*5_`cm C3a  + 

1;< @012D R}~  4
5Y)//!($ "'{1;K {1) U¡¢ ta:5) *.**,

 Q£!z¤¥. "_¢ !¦o

!|z'/ ) w §{1

km C?5 ! %  

&6 ,῍+ 4 §

R.(0/<j1v!45K

 ,ῌ+UVWXYZ

1/ῌ . @Fig. 1  ,῍+D 9:;<&R*./--ῌ,  , !z0/K

#¨3


!

0.0 km [" - &'( + 45

3 ,῍, +  +b_` / mm c#deO

45©)  + ª«¬fVg h ,-/45 @.e­=45q>_!®¥ @¯°±² +33.D 

ij!kF)/

lD    7+b0/Kmn/T/L +  ,῍+ ©³'©

©´!µ¶K K +  ,῍+ tu  ,῍+ ,῍+ ©©´ ,῍+  ,῍,

1v_`) [" - &'( + cm c#! w©©´ ·¸o_` + cm pQq

rs?K !n';Ia  : 





319

Fig. 0. Backscattered Electron Images of typical essential materials from Hijiori volcano (data from Miyagi ,**0).
A : stage +, B : stage ,ῌ,, C : stage -ῌ-a.

¹º»¼

320

/&f$" &fr0  ,῍, 9:!,( 120123$!s  -* m O

u v? 

D ( a!st345w  3* m OD
PQUg" ^_D( +33. x6( 7&f ,῍, 9:!,( 0123$ 0 5 -2  -/  .2.2, (,.. km 

6 +.*  +*  ...,+ ( y89z{$&|a:<=>?
";b}$~<bb=d( >?U@A$PQUg"
 ,῍, 9:,( B;bUCDE
F8/"
Fig. 1. Constituent of pyroclastic particles (,.2 to ..*mm in size) from Hijiori volcano. For the eruptive product of stage -῍+, discrimination among
the essential, accessory, and reworked particles
was not possible.

b=8y&k(  ,῍, 9:!789:

( 12 I L"#,J/K
UK" CDE LMN Fig. 0B ML 0123O 

0.0 km  -   2.,

km  . U,(  ,῍+  B% -*cm U@AP78

PQ% "  ,῍,

9: D/* 0123O ,῍+  +   BGHK'Qj"

( ,..km  0  ,./, mm, 0.0 km  -  -.+-

 ,     - 

mm, 3.+ km  0.01 mm UKG( 6ERR

  + cm  ,῍+  !"#SL"IJK"  - U% & ,῍, 7$ ,῍,  %% &# '(89:BCT ,.2῍..* mm RUV,( CD ,῍+  ,῍, )**+, -.'EWb  2+ῌ( XYZg%,Wb" /&( 0123 ' 4 2., km  . 5-2  -0  /..-0 (

6 +.*  +.  /0.,0  "CD[k'= 2ῌ( ;b&k\]9z{$&9a=FG"b= ++ῌ U

,(  + 789: ,῍, 789

Kq& Fig. 1  ,῍, # ^$(  0 !":*;' " + <=>? "@A ,῍, 9:!BCT , ODR

BCDEB8FGH IJK

,( XYZg%,Wb "_G( #D ,῍+ L"-.' "

_UCD$ Yb=( CDE`%

/G + @A$&

&^$8U +* a/& 9:!

 ,῍+  $&#MN% " ODPQ '(O, b=b % "#K" c ,῍+ RST9, +  U.¡d¢9:! ; D4( ,**1 (  0 ;', (

VWX*YZ[C @UK"῎῏ῌ῍ ,ῌ,9:!  0 *UR8JZ

 ,῍, ,^_D (+33.)  `KM  ,_a b9:!c L"  +'d" ,῍, 9:!,( efUl[$&£GU b=b $&(,  789:  -\]!&

B"a#D( 0123$$% ,.2 km  / 5 -2  -/  1.2/ (

6 +.*  2  /-..3g¤q&¥¦,( 789:U,§¨UK"&kR©gOhZij$q&^$( 9:!OU,R*ª«kZg lm/`j$&¬>? " n$( '­'­ (  + 9:!D\( e&® '% &9:U( PQL"R

f$&9:!PQUg" #  ,῍,

=8

¡

9:!hi  + 9:!'(D4( ,**+ &k( ¯)U,°o ±p,Ug "#K" c.¡d¢9:! ; ,῍, ( jL" -῍- 9:!

 CDEBGH²'q$8)*$"&k( +l ,-m,n.U&#³(  ,῍, 789:,,( 012

K"

3 ' +, km 6/U´i#rs$& (Fig. 2B) ,῍, 9:!,( opFq( Wµ¶U,tuv,]w$·?¸"B/0 z : - » z ¼9    *  +* cm  .3.1 km

 / cm, ,+*  -* cm  -*.* km,  ,* cm   -* cm +..3 km,  .* cm     *.*+. km-  !"( )*-  +1.0 km

1 ./ -2  -," FG C 4   +o7^G K, +, F +CDDE<E ^DG F
GB C44 U 2#]" @DaGF^G FG- #$%&' ,῍+  ,῍,

+,

321

+1.//  0 +.*  ,*C

# FG3K

RS CD

#

T+J

 $

2.3+

%&' -῍,a .]"D1| H1 -῍,b .]"D1| ¡1 2 $%&' + #+3 ,῍, 456789

1 -῍,c .]"D1| H1 IJ $%&'

 .:;<=>?@ABBA>?@
1 DE FG HI+J $%&' ,῍,

C

-῍,b

 KK

2 # $%&' -῍,a AZ], =1|AZ@DH- 2AZ ]"LD MNOPQDE,RS"#2EJ

2E -A AZ¢L<MNo-ῌ-  - 

 $%&' -῍,  l& (1 km£/* km) # !]" zBij" a, b, c  -ῌ+¤O¥k%2E F F- # $%&' ,῍,





T

B CD

2 ¦G

# FP3K Q§Q2 89UV2 A WVXYAZ< 2E, NOPQR¨RSS

A [ ! - \ ]"^G

© $%&' -῍,a, b, c ª« TU_`a F$%&' -῍+ 

 $%&' -῍+  - # / cm

ED F+Jb?cdefg2T (Fig. 2C)  *£+* cm 2 /-2 km,
 / cm   +*£,* cm 2 ,// km, +/ cm   -* cm 2 ,0.2 km,  -* cm 

#+Jh$"ijDk%2E l& (m1km) 2< nijoD pq'()D $%&' -῍,a, b, c -  *.*1 km- horsDE *t$%&' ,῍+ fu+ ho

,vw-

 

.xyRS FG F^G /0 zNOP{1| M}2,vw-.E~~,vw- 1 28RS- #$%&' -῍+ ,.2῍..* mm

42 2¬­"$%&' -῍,b{3 ,.2῍..* mm

{356 1| 72$%&' +56 AVG]"D 0,ῌ 9 :";;D!ZD 0ῌ YAZD --ῌ 2E, .Fig.
1



4

#

-῍,1 $%&' -῍,a, b, c -A ]" !

1 \ < D®2EJ $%&' + #+3 ,῍,

2W"]"Y< 2E .X !

8A]"D /,ῌ 9 :";]"

- \ <¡@¯x1  $%&' -῍,;D !ZD +*ῌ YAZD@ *.*1 km-  * /0 

-1ῌ 2E, $%&' -῍+   < !

@ *.*+0£*.*,0 km- +J<H .$%&' -῍+  *.**£

2D *.*+ km- :o*.*+ km- °U1 +J $%&' -῍, 

`67 F+M}2-1| 7]"D8AA^*

89A (Houghton andSmith, +33-) ^=>F ;]"D -ῌ,a, b, c
T89U

?@D b?cdA^G ..+ km
2 ./ -2  -0 -ῌ-a, b$%&' -῍-  -῍,$%&' .

-2EJ -῍+ 1|}2D:o8A !]"8AX=>.,.-*  0 +.*  +,

1 #  / 

3.,044  +  B44 U

T89U-2EJ Y±²Z (+33.)

-fuk%2E$%&' -῍,  -῍+- !-

#Dij(+300)/0#´ E[³]¶^]"´

ª

³KM
²µ\

_` (Fig. .)

FG -8AAw! ·3 !]"¦ ¸5 eo2

#

¹&'

 l&2 ]"VG b?cdA^G ,.. kmabº

0 2$%&' ,῍,#  $%&' -῍- -

322

῍῏ῌ῎

Fig. 2. Isopachs in centimeters for fallout deposits of Hijiori volcano. The locations of outcrops are shown by crossmarks. Thickness of fallout at a location is shown by a ﬁgure on the right of each cross mark, or expressed as “nd”
if no data available. The origin of these plot corresponds to the center of Hijiori caldera. Valley-ﬁlling pyroclastic
ﬂow deposits are not included. A : stage +, B : stage ,ῌ,, C : stage -ῌ,, D : stage -ῌ-a, E : stage -ῌ-b, F : stage .ῌ+,G : stage .ῌ,, H (solid curves) : Hj-O from Machida and Arai (+33,), H (dotted curves) : Hj-O from Yonechi and
Kikuchi (+300).

 : 

Fig. 2.

Continued



323

324

¹º»¼

 -* cm    2 m     )n6" B +* km Co D&m 0* km

 (Fig. 2D) 1)E5" ,- -῍-b TD'pqR*)r5 (Fig. 2E) * )+.FGWD2" ,- -῍-a .HsI,- -῍- .    /*tJR uvK wHsI78x 4( ZK yz

0&1 2"   3L" +300[ )E+K   !"  # $%&'()"  * # ,- -῍-a,456 ,- -῍-a 78

,- -῍-b9: Fig. 0C );&/* cm<=>?@2) ..+ km   2
." ,- -῍, ,- -῍-



)" 

+/* cm    5  1 

A78 B"  2* cm   3 ,- -῍-a ) &cm CD & ,- -῍-a

*

 1*

#6,- -῍-b )-῍-b

EF" !"# "$G  !" 78 0)'H
2

 4% /

IJK6L& D/* " ,- -῍-a, -῍-b MN *.+3 mm
" 'O - f,- -῍-a TM*.,. mm(:P )QR*S" <=>?@* 0.0 km 
 -῍, T78-" ,-

)"  ,.* cm 5,- -῍-    1  U,- -῍-ao -+./ km,  1/ cm&~" *.,+ km ,* cm.* cm

5"  /* cm}

3 Y0" ,- -῍-b ToN| ,+. km, 5"  -*{/* cm

5"  /* cm

5"  +* cm

5"  -*{

5"  +* cmM "  +*{-* cmo -0 km, o -2.+ km,  0* cm

}& " *.*2 km-

K

6
<=>?@2O) +1.0 km   1- -῍-b qnP" , Z =

 =[ W"  )'B
uvK6 6" *) 0.0 km  - )+-῍-b EF!"#  &,- .  :( 11 2" Q
RS&\d 3" <eP
56 j-ῌ.  . ,- -῍-a   D/*  *.,. mm

"'O ,.2῍..* mm (:-." 78 2.ῌ" / ++ῌ"  .ῌ

 Y0,- -῍-b   12)MN *.-, mm, .-ῌ" ZFig. 1  -῍-a,- -῍- -῍-b[ 1'()"" 

)3# -῍-b \(78)3# -῍-a )+V'4(6" ]0 \('4( <=>?@2) 3.* km   3 Z*^ -2  -/ /0.23 5" _ +.*  +/  ,2.-0 5[

" ,-



 

 * # )+VWWCB,X+.ῌ" .-ῌo +/3 km  .* cm,

" ,- -῍-b q nP " $%





"  +*{-* cmoN| /3+ km,  ,* cm .ῌ+a, b, c, d, e<=>?@2m +* km Co)" ,- -῍-b :(" )

23TT

uvK  31 2" 1k j ,- .῍+ ." A78 3 .DyU(+33.)  wKM ,- /x3"  )'H¡W¢K6 VT )B£¤0¥X+'XYD¦Z5)'
 Z(O *./{ Q cm 

[\C§D)YD,῍, T78 )" +`67* a&¨©" >?ªu& 4(f()+3 ,* cm T78 " M896):(

VWWC*ij[" a3*   ,/ cm T78$; 6 n M'" .῍+a Z¬­]®["

 bc,- -῍-a, $c,- -῍-b .῍+b Z¬­]®[" .῍+c Z­]®[" .῍+d Z­]®["

.)
"

& ,- -῍-a

-῍-b 

EF

 - 3d<e<=>?R= !"# "

 3 W]0>?)+"#)3 M@.῍+e Z­]®["

6"U / «¦ZK¯° 1/±5²³5)4%´^  6" µ%S¶_32H6 " ­]¬²³

" ]0\df((:gA&6)" 78 U!£· f((:)hK!7*ij6kl(6,- .῍+ T(¸'O ,.2῍..* mm ,- -῍-a TK)]0" <=>?

 <=>?* 2.1 km

IJK(:-." 78 *ῌ" /  +,ῌ" 

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

" #$%&' -῍-b ( " #

)"

*+

325

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BC.p0\,N", #-./0"1 3^ +῍, cm oA0pBC<

 $%&' -῍-b 2/0-34

MN-/! $%&' .῍+ OP-/! .* cm JK

(%&

,$%&' .῍+ -256701$I;? +, - 0$%&' .῍,   " 8,9:7 $%&' -῍-b !?s3^ ,.2῍..* mm ;"< 8()" ./0=

ND <  0,ῌ ^!L0=

>?

BC,NN  +-ῌ  =$%&' .῍+c @! A

B"C"

D

D:] BC.p ,0ῌ  Fig. 1  .῍,

EFG#8H$I - m JKLL%&MNOP-/`9PQX "$%&' .῍,  ! >$N, '(QRST)U* ,.2 km +, +* EFOR -z "  qr

-V -2 . -0 / +/.0- 0 *W +.* . ++ / ++.2/ 0 ;"< pBCoA0N" pBC< 3^

XNYZ" [* -., km +, ++ -V -2

 QRST2"H¡0[ `9!

. -0 / +-.0. 0 *W +.* . ++ / ,3.** 0  .῍+a,b, c, d, e \]1 / m $I .῍+

,N" Fig. 3F[* 3.* km 2+, 3  3^ +cm 4.B"C"

DEFG#FH5_6%¢UH[" Fig. 3E  .῍,
9 `

_`H a!b£4XN$%&' .῍, @!

-zBC7NOP<$;? c+t¤d (+300) C, $%&' -῍-a &7N . 8OP-/! \]1 /* cm $I

"a!be'(OP-/!?s Kf +/h-* cm

,N" 0`9$Iab, YZ f/ $%&' .῍, @!g50"N (Fig. 2F) ) QRST:c $Kd$%&< BC.J8 $%&' .῍,  !'(!;?efg

-z*+h@!  "EFFH $%&'

' .῍+$%&' .῍+a, b, c, d, e @!< $I +*h-* cm i)"=j +2./ km $I ,* cm,

I -*h/* cm i)" +,.1 km,  .* cm
h1* cm i)" 0.3 km,  0* cmi)" 2.2 km,  2* cm;7 *.*, km-, $, $I /*

, $I 1* cm , $I +* cm JP>kl"4.`9)q, $%&' + ,῍, -῍-a !ef '(QRSTM EF%&M[ `9 DEF%&7NOP<!

m  ¥6i¦ #g,$%&'.῍, @! M8`98

EF" (Fig.

/) $%&' .῍, $I/L,8 $%&' + ,῍,῎῏ῌ῍ .ῌ,-῍-a @!  " ;~s *CN§¨

QRST)U?*m -.0 km +, +, -V -2 .
-/ / 0.12 0 *W +.* . +* / /0.*0 0.῍,

8©ji/L;" N?EF"8

XN $

 k7$%&' -῍-a $IlP¨ª«%&' - XC6$%&' .῍+ 5n@ ! , m JK¬­g®mnb¯;"g, $%&' .῍, $I

$I;? 3^ / cm 4.oA0pBC<

°+2"±Nmnb¯¦ +/ km.*

qr;"-/ !Bl, # ! $km e²oFH (Fig. 2G) 0 $%&' .῍,;" D@!EF?sBC.pN

³$I´8pµ" '(QRST¶2< ()", G3tHK (+33.)  uKM $%&1 ,* km )+jXN?*¨[ 1 ,* km%&' .῍,' / vwIOP-/ !x \J;" -y1 -/ km +j-*¨ 0`95K[`9)@!/L;" N?,L OP

6?*¨[ ·q1 / km  rs1 .* km 4-z{ OP< |$} ,N, \~N

" $%&' .῍, l"#EF '(QRSTMX "$%&' .῍,  >$N%&

QRST*91 .* km +jg,c+ t ¤d

MNO  EF0<  !(+300) ¸ ¥t.pNPQnN¹" (Fig. 3D) PQRKYZ0"D-/!)

0a!b<

$I/L Fig. 2H ,uC<  6.SN TN # EF[ºJ;" a!b< G ;"$%&' -῍, -῍- oA.pN #EF ID.῍, ?s $%&' -῍, XC6 -῍- $Imn

326

῎ῐ῍῏

Fig. 3. Typical occurrences of Hijiori eruptive products. A : Stage -ῌ-a pyroclastic ﬂow deposit at “Warabi-no”,
bearing 0+ degrees and /.* km from the caldera center. B : Close up of photo A. C : Flat ﬂoor of the Hijioricaldera covered with lake deposit and circular pit with ,/* m in diameter and ῌ.* m of relative height (centerof this photo) at “Kan-kane-no”. D : Proximal faces of the stage .ῌ, pumice ﬂow deposit at the eastward of“Mogami-tai”, bearing +-3 degrees and -./ km from the caldera center. E : Distal faces of the stage -ῌ-afallout and .ῌ, pumice ﬂow deposit at “Yakurai-san”, bearing 3/ degrees and .1., km from the caldera center.
F : Unconformity between the stage -ῌ-b pyroclastic ﬂow deposit and stage .ῌ+ lapilli fall at “Yuno-tai”, +*,degrees and -., km from the center.

Df : 7l { Dfe b¼
 .ῌ,    .ῌ,!" #   
(")*+,

$.ῌ- %&' -.%/01

23, 452#  %67
)89: 
 !H! ;)FG(I/* km) J!",

 #2L,MN * O=HHK$% m.ῌ, 2; <,"B!%C! DE"

=>?@A: ?? w2iJ.ῌ-,# H #2=>q7DV U  




327

P&'Q%RG 2()

SN%G 7l 2 UWM O,%J,
1= {:pXG (+33.),1= AKM / YT7DE , 1 +-ZK -1* m 1 ++2 [\]G^  _H,^O /*ῌ+** cmT%`![\]aY", # a^1 +- 89)&SJYDf

bc!

 x; 2.ῌ-

HY 

89 {H

C!",,# H #2DE"2&

%

T7DE UG J VWH.ῌ+ .ῌ,2?3.ῌ- IJ2?3HY*XY"+,Z-: 2& ./[0452 %C! \ 1=]2H^>?@A B!%C:23HY Df2DE%dl:F

VWH*3_ [0%C:T7DE 4!"2 `abcdaeDf.ῌ- %IDE%?:#e%6GG w

+32* 5 / g +2 67D

T7DE (Carey and Sigurdsson, +32,) h.  #2]22ijk2i !")*VW +&T7.ῌ+ 

! UG", .ῌ, 7l=89

45 f2 g Df; h,uiD! UG - J mnm7Dfl :¡¢` £#Df<,"7l 2o* .ῌ, 7l2:;]2¤x¥¦ e%?: 

2i<& VW +&=]2DET7p

+!", # 2mnm=>q7D UG

" [\ ${/jH ,.2 km H .,.. km H07l)&? $4Gr @A +32- ; Self"

and Sparks, +312' !Y".ῌ, 2mnm=©! !H!DfW 7l2?3HY.ῌ, 7l ;2  +*s-* cm tJ%dl:mU&mnm7D)Y" no«JYBu /-. km,

% ,* cm

tJ +-/ km, % .* cmJ /*.- km, % 0* cm
km, % 3* cmkm-,/ 1' <," +

P7%kªl&¨ # # H Df e2DE" T7

>q7DY1 O,


T7DE§DE" >E^¨©x:!  -*s/* cm!  /*s1* cm t!  1* cm tJ +2.+!  +* cm 67%C*v"  *.,+

F # 7lD2mnm=>q7D 4!"203,)wG x03,=

 UG
.ῌ,  {2 ¬pD 7lD267­())&q: r­(7l ®sT7^,";%¯: O *.0 km-!

F {°t:DE"

{a| }~Df<," =E b;2O +.. km- $uX +3/- ; Ui, +31+' #YF {7D mnm=>q7D)YH Df7l ®O - ±2T7DE !"" yz"]2Df % 3* km- DRE (dense rock equivalent) 6G; =! ¤* O 1 ±2DE" !"x4= $Self, +32-

{+v!#  7l FH0²

<

member + , - /'.ῌ, { H%IJ2?3HY+3/-' .ῌ{ K ,.3 km

1 +- $L -2 M -0  ,-.-2.ῌ,PQI ?B%;:o?R%>?@A&, $)&SJY'T b?Df %UF! # %

8³& +.+. $uX´! qW%,B ²% ,.0/ $µ¶·¸ }) ./ ¹w xº'N K +.* M ++  +3.1- N' <," 
%O +./ m% T7DE=DE":  7l;

dense rock equivalent 2 *.2- km-»lx { ¬p;2 ¬py PxzY ´:rO *.2 km- $uX +3/-' H )&q:

ApXG (+33.) 2 KM -ῌ-'

. $45 eVY"{ ¬p3

¹º»¼

328

  $t  .῍, snon7lm$t T0@u   AA  T0'NBB7]^vpL+  -  

T0PQRS2!5Cw!

 



- &



! "#$% ! $% '() *+, !-!. + / , $.ῌ- 3CV4G (+33.)

 KM  , s

 - $% '0  ,῍, 'D<t $%Zx:  Eyz{#F1 *+ 2, 3 GH'1JIJ1|$% !+ ,῍, -῍-a, -῍-b $%  4<f./$d ab}~d=Jd,U

1"#$% '56 ! 7' Fig. 1

KL! I -( ./d M%

'8!9 ,.2῍. mm $%:;

 ! <"#$'=%>&'(! ? ?#$)  .῍, -῍-a, -῍-b'@!00ῌ 

AB/*ῌ 6* .῍, $%

! $CDE,!+F! AG-.  : HI
 Fig. +* =J'K 5  - 

3' ./PQRSM'  N +** m
9N /** m 

OEyP sFig. ,  Komatsu-

buchi lava domet , 3

Y Eyz{,`J$d/ =J$dG
H!r',`J

Q1.  OEyP   ,῍, ? '=pRST"U"REy:  + L=M , NO,'3

L+ V)5W, s3CV4G +33. ; -! 33-.  ./PQRSW# - T0'1U2! 3

 3CV4G (+33.)

3CV4G (+33.) 5WX,5 'Z[?\ 63 - 'LYPQRSZ  ./[Rt 2f'(, ]^'=p(-X,  OEyP + YOEyP_`PQR

$T0'\=J]^ 6_`J- ab

S'=Uab. =J'*3-. ./PQRS c73 8d3 93I:'e;!

 - sKM  .t AA'2!  PQRS2

c d4 (+3/-)<f=Z abgJ) 7 >1/5hi ?Uj0 

OEyP

8d3<"

 vent intrusion L=M vent agglomerates _)!J. - A"'  PQRS'7>k 3I3'=U 7lm$/non7lm$#2

C_

OEyP

 -῍-a $!/5p_`J qr'  .῍+ s7lm

Ui, +31+ )5WXt  - (-῍-a) $%

 s¡e +31. ; }¢£Q¤¥f +32- ;]'  ¦' , g§hi#F!9 -*cm¨jkb5 3j   - AA'kb! OEyPl, ),  ,῍, EXl©ª0?,/  - T0«'$m2! ),+ af:¬n3 . ­o53 2,
 OEyP2f - ,`J
 AA,`J 3%

GH  ,῍, $®¯53 2_`J pqEyz{GH_Y   ,῍, $% ])5?#$)q<"°±c sPQRS. +, km Mct k"#! J²qX2
_-.,3   ,῍, $@u  )
q³r-.IJ1|$%<""#
Fig. +*. Estimated amount of eruptive product from the
Hijiori stage +, ,῍,, -῍,, -῍-a, -῍-b, .῍+ and .῍,.

$C'LY$% s)tY ³r´umµ+¶·v¸w'+ xyz. 3'A : " A» 8¼
 

Suzuki et al., ,**/ 

 ,῍, 

329

I4jQR/&^ S}" H2

 , 4=~HI TE +3/-  #  "    !" # 

STUV|/?7U#' Fig. -$%& '()*+'I??STUV/?7',#-./ 0$12',

2 "

"FCVWD/]XY3 -45 6 78 (Fig. 2B)9:;:<=>

I , " &"XY?[ !?  ,῍, 0$ + @\(I*$"]\2I'& ST

 -῍-a < ,3 -45

UV7L1""^_"'n ?*$/6I#ZH

.ῌ. M 

A&"!"#BCD$#m Gijk4 4= +.  KLM DiNy

A"4="`b?7@Bf ,/*%E (Fig. +*, ++)  &BCD$-'<#, 4=9&L #& Fig. , 4= +. / FG'()D*HI

6^`" SKG-- 4=- 4= +. 

,J+-K9#&L ,- ,**,  M#

KLM DiNy"C .** m ,PI2& A9.N%/-  O6

"#I2 , 4=^  SKG-- &IBCD$P0?Q3R

aHIbDC(" AcMI,῍/ &1<STUV2WMX3

SKG---de3 HK, '#'

4CY567Z[\ FBCD

SKG-- &HIA4DCM($?2HI(-89\" A ,῍/ f -6\ ' ?"]:-9\;<^&BCD$ghVD&^Ii +,1** mA"4=" - K3 2I _K>"

(&)D*L89&L j. %C

STUV2 `b?7@ 4= +. 6d -2  -0k lDD$'2i +,1**+,,** m ¡Am

 .0.+, A 7e +.*  3  ...*. A ^Bf ,/* m,a,c 

$C:gh .* m ijk4&^ (Fig. 3C) #I"Alm"n32I DlDD$'2i /**3** m nopq lD'2i 0**+,*** m norso

%Ck¢ADD$'2ioE +33. ; FEpGqrst +31. ; HuvT

 +,1**+,,** m ¡AmwxI +32-  JK>"KLM DiNy&^ z

0**-** m no¢ADD$'2i

K>"4={O" STUV|,27 *./῍+ km P

'2i +,1**+,,** m ¡Am%CktCD
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'2 MI"&4ei|HI
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Fig. ++. Estimated amount of accidental material andessential (ºaccessory) material from the Hijioristage +, ,῍,, -῍,, -῍-a, -῍-b, .῍+ and .῍,.

' ' °±²o³´²µ¶·-¸9/ STUV·'+¯4ei7#" j¹1·'bD7#1'

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&w(
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 QZQ [  D()* .ῌ, BCD JDK\JL9]*^_`M\NaOG Pb cdFeQf_ghRSTGiU j VRWXi;kVYZXa[LlQ [  \]mno^_G  `GaC[b pcdq
jQrs@ [  "atec4ῐ ῕ ῔ ῑufgv (+32-) wx_:.yA'Lhi !
12 z{ | / ++0ῌ+,+.
jg (+32-) }k :  ! z{ | / 0.ῌ1,.
Carey, S. and Sigurdsson, H. (+32,) Inﬂuence of particle
aggregation on deposition of distal tephra from the May+2, +32*, eruption of Mount St. Helens volcano. J. Geophys. Res., 32, 1*0+ῌ1*1,.
f~1l (+3/3) / m + .no bpi kqkr .BCs 0+ p.
t~^b _ (+31+)  '
u*  +/ +++ῌ++3.

vib w (+30.) / m + .no  i;kqkr x yBCs
ziT (+32-) {Q|R}  ,2 ,/ῌ.*.
Houghton, B.F. and Smith, R.T. (+33-) Recycling ofmagmatic clasts during explosive eruptions : estimating
the true juvenile content of phreatomagmatic volcanic
deposits. Bull. Volcanol., //, .+.ῌ.,*.
I~ (+32/) i;km c4/%4$5.5/ Q ')* K,O   `5  5 2*-/,ῌ-0,.
Katsui, Y., Yamamoto, M., Nemoto, S. and Niida, K.
(+313) Genesis of calc-alkalic andesite from Oshimaoshima and Ichinomegata volcanoes, north Japan. J. Fac.
Sci. Hokkaido Univ., Ser. IV, +3, +/1ῌ+02.
iS!bZ (+33.) Om c4%#$1 RVW" +/ 2+ῌ22.
i1b Tbi (,**,) 5
()R NEDO  ¡*¢` 
-3 ,-ῌ-1.
8 (,**/) #$ + - 0 8R  (+31.) / m + .no z i;kkr O£%£¤ -2 p.
& ¡bL¥¢T (,**-) hi !,12
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WR 'b ¥(T (+33,) ¦`!(#)
% §V'¨
© *b+ lbS , (+33-)  !ª-£.«¤5K-Ar u*.y«/0¬¥ y­® , -3ῌ.1.
X Fb RLbI~bT (,**,) #m c4 +** ka P 'HI)Y!i;k% '¯¦  .1 1++ῌ1,/.
Miyagi, I. (+33/) Abundance and solubility of H,O inisland arc magmas. PhD Thesis, Tokyo Institute of Technology.
Miyagi, I. (,**.) On the eruption age of the Hijiori caldera, based on more accurate and reliable radiocarbon
data. Bull. Volcanol. Soc. Japan, .3, ,*+ῌ,*/.
Miyagi, I., Yurimoto, H., Kita, N.T., Morishita, Y., Takahashi, E. and Matsubaya, O. (,**1) The initiation offelsic phreatomagmatic explosions. J. Volcanol. Geotherm.
Res. (submitted).
o§°¨ (,**0) /©ª«¬.BC
f_gWy1] no. .-0.
ZbiS! (+33.) O !E±_²³_´­$®µ RV
W" /3 +ῌ,-.
Nakajima, J., T. Matsuzawa, et al. (,**+) Seismic imaging
of arc magma and ﬂuids under the central part of northeastern Japan. Tectonophysics, -.+, +ῌ+1.
¯°±b ¶p2F b ·f¸l b ²p¹_ b ³´3¡(+33/) 3 g;4O -µº¶·12»¸ ¹C .2 -.0ῌ-//.
4º5bVX°b»¼¼ (+330) z .

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(+31.)   + 
 ,ῌ//.
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Self, S. (+32-) Large-scale phreatomagmatic silicic volcanism : a case study from New Zealand. J. Volcanol. Geotherm. Res., +1, .--ῌ.03.
Self, S. and Sparks, R.S. J. (+312) Characteristics of widespread pyroclastic deposits formed by interaction of silicic
magma and water. Bull. Volcanol., .+, +30ῌ,+,.
 (+32-)  /0 
 !No. , "#$ %&'  (+3/-) (" )*  +,-.
/3 23ῌ3+.
Suzuki, Y. J., Koyaguchi, T., Ogawa, M. and Hachisu, I.
(,**/) A numerical study of turbulent mixing in eruption clouds using a three-dimensional ﬂuid dynamics
model. J. Geophys. Res., ++*, B*2,*+, +ῌ+2.
Takahashi, E. (+32*) Thermal history of Iherzolite xenoliths-+. Petrology of Iherzolite xenoliths from the Ichinomegata crater, Oga Peninsula, Northeast Japan. Geochim. Cosmochim. Acta, .., +0.-ῌ+0/2.
/ 012341Sucipta, E. (,**-) 5678
9:;<=>?@ABC56789DE
BFG HC I", ,**- JKLMNO A+1.
Tamura, Y., Tatsumi, Y., Zhao, D., Kido, Y. and Shukuno,
H. (,**,) Hot ﬁngers in the mantle wedge : new insights
into magma genesis in subduction zones. Earth Planet.
Sci. Lett., +31, +*/ῌ++0.
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X % +DEY +78Z

333&'() (+30+) *[+ \ ,]^-_`ab ./)cdefg0C 1,23OC ehi j ,1ῌ-2.
k456 (,**+) I"l7mno 81p9:qBF
rs;tIu <vwx I" .0 ,/1ῌ,02.
k456 (,**1) ;tIu<v=_>yFzA*+
?@OA BC^owx 31{D ., +,3ῌ+.1.
Ui (+31+) Genesis of magma and structure of magma
chamber of several pyroclastic ﬂows in Japan. J. Fac.
Sci., Univ. Tokyo, Sec. II, +2, /-ῌ+,1.
|}E~1' 1 (+31-) *[Iu<v= +.C  I" +2 +1+ῌ+1,.
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