ῒΐ  /*  (,**/)
 ,  1+ῐ2/ ῕ ῔

,**-  /  +,  ,**/  -  . Eruptive History of Satsuma Iwo-jima Island, Kikai Caldera,
after a 0./ ka Caldera-forming Eruption
Fukashi MAENO῍ and Hiromitsu TANIGUCHI῍῍
Kikai Caldera, +1 km wide and ,* km long, is a Quaternary volcano located, nearly submerged, in the East
China Sea, southern Kyushu. Two volcanoes, Iwo-dake (a rhyolitic volcano) and Inamura-dake (a basaltic
volcano) on Satsuma Iwo-jima Island at the marginal part of this caldera, were formed after the great
caldera-forming eruption of 0./ ka known as the Akahoya Eruption. We made a geological study to understandthe eruptive history of Satsuma Iwo-jima Island after the caldera formation.
The volcanic activity in the island after the Akahoya Eruption is divided into three main stages and ten
sub-stages based on volcanic ediﬁce development and tephra deposits ; the old Iwo-dake stage (stage OIo-ῌ-῍),
the Inamura-dake stage (stage In-ῌ-῏), and the young Iwo-dake stage (stage YIo-ῌ-῏). The old Iwo-dakestage was initiated by phreatomagmatic eruptions and pumice fallout (stage OIo-ῌ), followed by the e#usion ofrhyolitic lava with continuous ejection of ash and lithic fragments, resulting in building up an old volcanic ediﬁce(stage OIo-῍). In the stage OIo-῍, intermittent explosive eruptions also occurred. The Inamura-dake stage ischaracterized by the e#usion of basaltic lava ﬂows and scoria-cone building (stage In-ῌ-῍). After that, at thewestern foot of the cone, phreatomagmatic explosions occurred (stage In-῎) and andesitic lava ﬂow e#used (stageIn-῏). In the young Iwo-dake stage, the explosive eruption occurred at the beginning (stage YIo-ῌ), followed by
the e#usion of multiple rhyolitic lava ﬂows from the summit crater and the formation of hyaloclastite in shallow
sea that made up the marine terrace (stage YIo-῍). During the past +*** years, the volcanic activity changed
to intermittent ones with pumice and bomb fallout (stage YIo-῎-῏). Total phenocryst contents of the Iwo-dakelavas increased up to 2 vol.ῌ through the young stages. The magma of the young Iwo-dake stage is di#erent
from that of the Akahoya Eruption and the old Iwo-dake stage, bordered by the Inamura-dake stage.
Key words : Kikai Caldera, Iwo-dake volcano, rhyolite lava, eruptive history, bimodal volcanism+ῌ ῐ ῎ ῑ ῏efg +* hi+jkIlgm#:nopq+cSr  !"#$%&'() .* km !

st\ 0./ ka + uvwxqyz{ `|(\I }#*+,-. /'(012 34 56 7%89#:pq<~.k  } +312 ; 3 ;<=>?@ABC#!DEFG+,-HIJ+32, ; Kitagawa et al., +33/ ;  ,**,J TUVWAV

KL #:MNOP.QRS TUVWW  VWA A XA89<YZ.Q[G+K\Q]I^_ .Q[O+LHIq < v`aI< b* ,* km, !/ +1 km +Rc>:;

wxpq+sF.k}.]qy`aIJ 3`aI (Matumoto, +3.- ; Figs. +a, b)J d#

 (+32,)   (,***) Kawanabe and Saito (,**,)

 32*῍2/12 ¡¢£b/:¤:¤¥¤¦§¨B¤©ªInstitute of Mineralogy, Petrology, and Economic
Geology, Graduate School of Science, Tohoku University, Aramaki-Aza-Aoba, Aoba-ku, Sendai 32*῍2/12,
Japan.

 32*῍2/10 ¡«¬b/:¤b/v­v¦§®¯°±
Center for Northeast Asian Studies, Tohoku University, Kawauchi, Aoba-ku, Sendai 32*῍2/10, Japan.
Corrsponding author : Fukashi Maeno
E-mail : fmaeno@cneas.tohoku.ac.jp

C ¹Tº»¼

72)C ;{| }~/o9*9j



(0 #.9'9` ;&VW &#+3/ XYZ[ 
?-/ kcL(0, 
,ῌ+

,%XYZ[ -Z[5.
 %-/0 (HJ) %&1%Z[32 (EZ) 

4V&/iP((Figs. +b, c)0 & Fig. ,  56(7e Fig. - xL0 '- XYZ[ :V/  ` Table + '/-0%- 89;:&e;L(<=Z[? ;9 Z[3a?
(0 Z[ Vn/3 -  >?@AOP(0 # @ B%/ ,%;L(@ K-ab ; C 
Fig. +. Maps showing the location (a) and topography (b) of the Kikai Caldera. Figure (c)shows the topography with outcrop distribution
in Satsuma Iwo-jima. For the abbreviations in(c), see the text.

D +32, B % +;L(

@

K-Ns ; CD +32, # ¡ ¢@ K-Kyp, K-Ky ; £¤ +31- ; C  DE+32, 9j(0 .P& @F #P¥P G +.* ka HID ,**+ G 3/ ka(Machida,+333) 0./ ka Kitagawa et al., +33/ ; ¦C ,**,

 

 +.C JKd&P(0 V XYZ[§L ¨©%    /.,ª«%U2 G /2* ka ¬MD ,*** A-ka /iP( I@ K-Sd ; HI­¤!" # $ -.3 ka %&"'() *+ ,., ka , !"-./ &%(0123+33, 3XYZ[P(

4567 89:;<= >?@ A BCDE3/FG >?@/cd&,% B%;V0 '.37- N% G +-®2 ka O-( +.C xLO ¯
° (K-Km) ;L( CD +32, ; ¦C

<=HIJ=KL(MNOP( (Kazahaya+3300 O¯

et al., ,**, ; Shinohara et al., ,**,)0 '- 

 Pt#@-3 /cd&P # ²2

Q R? S (Saito et al., ,**+) @T U2 (Saito et al., ,**,) VW%& 12 XYZ

° +-®2 ka

Z[

³%

G 0*** ±O- (Sz-S)  * 2 L (,Kobayashi and Hayakawa, +32. ; ¦CD +33.0 Z[ \]\7 5^\]\ _T[Q  /)  U

\]\3`abV(/cd&P(2 N;

(Saito et al., ,**, ; Kazahaya et al., ,**,)09@A( (Figs. -, .)0 @\]\7 e fSgh &%iPj( @k lm Vn '- \]\) \]\

 o!"#Vpq MrNOPV0 st#Vu@ +3-.ῌ-/ v$% XYZ[&w123V

#9j(.

/x(0 '&w lmVk y  z(

,ῌ,

/L(

° Z[3

CD (+32,)  Z[3U2L( ` ° _`  5`  ¦CD (,***) ¦C (,**,)  K-IoL, K-In, K-IoU ´µ¶(0 Kawanabe and Saito (,**,)   ·R;L(° (K-Iw) /;S§L¸'

° (K-Sk) /´

°±89G)² O³=XTU RS´

Fig. ,.

73

Geological map of Satsuma Iwo-jima (modiﬁed from Ono et al., +32,).

 



(Inamura-dake stage)

X89& VWX (Young Iwo-

K-Sk-l, K-In, K-Sk-u   ,  , dake stage) YEm ! 2;6 X89&.   2    ! "# $% stage OIo-ῌ, ῍&'(  K-In-+ )*+ ,%& stage In-ῌ῏, , ! -. /0*1 2  34
56 7  89&:;<,  $. 

X89& stage YIo-ῌ῏. Y# (Table +, Figs. -, .)!

FE

VWX L X89& stage

 89GGH IJK L?@A LMB

OIo-ῌ ῍> X89& +a+b, ,a,b (OIo+aC;5 2;7NOPQRSTU+b, OIo,a,b)

VWX;Y# (Table +)!

῎> $%& +, ,, - (In+, In,, In-)

=>

?@A

BCD5E!

L Y Z [\]S^;_` 5abcdefgh" ij 2;.  $%& stage In-ῌ

89& stage YIoῌ῏>

- 

X

X89

& +, ,a,e, -a-c, .a.b (YIo+, YIo,a,e, YIo-a
++ g6 !  _VWXk L"#lm-c, YIo.a.b)

Y#! def nop;qrs2 e

E  Lg # ,a, ,b tguv#2 >wxyz[{RSVW |}*Y#! "# In,  In-  i"#~Xg#2;>!
L?@A LM;7>  VWX
"lm NOPQRS (Akahoya Eruption) X8
9& VWX (Old Iwo-dake stage) $%& VWX* 5afg2g !
,ῌ- ῎ῌ῍

89& O S¡¢ £¤¥
¦"1 §¦¨©ª« ¬¦­ 1** m®¯:Fig. -.

Columnar sections of the outcrops in Satsuma Iwo-jima. Locations of +- sections are shown in Fig. +c.

74ῑΐ ῐῌῒ῍῎῏µS¶CF·¸¹§º» 1¼
Table +.



75

Geological units in Kikai Caldera area      !"# $%!&'

  e rq68  iDU 
^





gf= 78D!D 78 6

 (Fig. /)
()*+,-. /0123! 4 . > (Fig. ,)  IoLAqF5 6789:;<12 684= o SK N @ m (IoL)

12>!?@= 68 12> A!

L NL SK M ; 0ῌ++P  IoL()/012B=CD 12
4 LF

68EF!

G. (Figs. ,, /) 4 HIJK MNLOKP
QR= SKTUJ12VWX! +,Yk.L, D >4=l

L
4=N SK  y=  MO5 +32,PZ[\4 ].



f=pL!

() SK$%!&'CD ^_  ` iD 6rF tu 

abcd ef=  >gh¡ ¢£¤¥¦§¨©£ª (Pichler, +30/) MS

CijH kLlmnop  

 4= SK 

IoLAqF L (Fig. /) rq68sX
(IoLA, B, C) tuvwxN# y z{ sJKwx |}f= H q78
sX

(IoLF) *12z{

! ~tN# $%F!K¢£¤¥¦§¨©£ª ; IoHyP y=«¬ MSKt«¬ ; IoTeP !­)X4 !
.L (Figs. /, 0) ¢£¤¥¦§¨©£ª$%®Ap¡ (IoHy-l) (IoHy-u)op SK +, J ^F
=! ()>¯?pSK  1°  M¢£¤¥¦§¨©£ª±²P ³´ab¦§ ¨©ª3«¬

76

Fig. .. Photograph of the outcrop at Sakamoto (ST). OIo+a>,b, In+>-, and YIo+>.a are derived from the
Old Iwo-dake volcano, the Inamura-dake volcano, and the Young Iwo-dake volcano, respectively.

  ; 1ῌ- 2ῌ+ 


,ῌ.  ! "#$ ,-* m %&'()* +,-./0(123 +45623789 !
:;<= In+>- ?@9 stage In-ῌ>῎ABCDE (InIL) ?@9 stage In-῏ *F GDE (InSL) ,DE (InEL) ! HI stage In-ῌ>῍*F (Table +)
JKLM! NOP<2QRSTU
2VW XYZ/ [\90] ^_   `a7bc9- 
-ῌ+  +a, +b (OIo+a, +b)

d/NOP<ef-ghi (HJ) Tjkl
m (ST) n]MoL 4pqr (OU) *stLun*_ vwx!yzp{>|}~2
Fig. /. Geomorphological map of Iwo-dake volcano.
Shaded area at the western foot of Iwo-dakeshows the distribution of volcanic bombs (YIo.
a, b) ejected from the Kintsuba crater in stageIo-῏.

({ (OIo+a) HRz (OIo+b) LM ,  s0!g /* cm *F OIo+a! 2wx7]j7*n]M  cm  x ¡ ¢£ /v F ¤0 p¥

ºF [» /012^%p*j"1¼
 

77

 "D 2{ <", klmng OIo+b  !"#d  klmn InSL "=Ct /,  $%&'() / cm *+,-  In, [{klmn"2C stage In-῍ -ῌ,  ,a, ,b (OIo,a, ,b). "/012 34

.ῌ.  (InEL), 567.8

"9

,

OIo,a, ,b<>?@AB>CD8, m, :;,< + m *=,-  EF( (+32,) ",*+a
"

 



-A*, z:9 +* m!a

Pa   3,   ""C)

G cm "H CIJ  KHJL ,) -* cm , ),.,klmn"UCt"BMG  BM

B84^

OIo,a =N" InEL klmn"^%A K9 -* cm L  sag structure Q[\ K( +32,L In, =O,PQ  ="RS

῍"1,- T,Q  BM"UVWX
YZQ[\ A,-,]  sag structure

wx0p0 stage In-.ῌ/  - (In-)
Kawanabe and Saito (,**,) " K-In-, "= ,  K"^$_`aN  BMbc  j+klmnL gd  5d  O .6\ G mm

"#By4,"9z: +./ m Pa  z

G cm "&'

+"9d ,- cm "j+klmn "9dG +*efa 

cm

 + m *=" [{z=". 

9d+* cm "j+klmn Y  = +".ῌ+  + (In+)

j+klmn6 E,%&5 ="j+kl

Kawanabe and Saito (,**,) " K-In-+ gd mn ="RSC¡W¢X>?B> hiO 9dG cm "j+klmn Y\ opqr2sCt9u?
v=Q  wx. 6\ !Q[

5-  G mmG cm "7
"£O\, D , cm *+"klmn B> Y O) +* cm "M89 sag\ 9"#By (YW) , 2* cm,  (HJ) , /*structure C^%a  "klmn

cm ,-  klmn "#By,>?B>%&¤|¥£Q

Ci# - $ 



 

!, 

! (ST) , , $C¦] +":?"§B>"# Y  klmn"z:) - cm ,{|%&%  ="j+klmnu?v¨fa u? }?"<"efa  In+ 9dG +* cm "'In-  S{ZQ In,~B> T6 In,.ῌ,   (InSL).ῌ0  (InIL)

( (+32,) ")*+a, ,y"TCiJ©; In- "2pC stage In-῎ 

 

)

1** m 6\ !a -A*, 9d +G m ,-   "), )y., a

9d +* G m "ªBA*,InSL [{ InEL

A«Y  3y¬   )y.,<Q =,>­®¯°X,* (InEL) * (InIL) 6  InSL

, O ?@ -/ m "*6CAa  * "z+Nf S{ZQ*"j klmn"±(C =bc"'+klmnCiJ /, InSL C In+0 stage In-ῌ"1 ~B>²6  qr2C¦| p
klmn^%³ B´CD,-  /,.ῌ-  , (In,)"2C stage In-῏ Kawanabe and Saito (,**,) " K-In-, "+ +  Kj

+klmnL gd  /012 34, , $/ 

"j+klmn hiO >?B>, .

/ῌ+  + (YIo+) !a  9 "#By, , m, , -* cm  qr2sCt9u?v"=,- | "#By, =N"klmnB8E,"#µ,]  ! (ST) =,+ m C

 qr2sz<9 klmn)@) , m Pa+, + cm *+,- =,z: - cm ture C B>Pa   !,,- cm "9d,-  In,>  ¶?"M89

sag struc-[{· Y ,.8 Q EQ 5¸ ¹9 +*-*· ¸v¹º»¼

78

Fig. 0. A marine terrace (a) consists of volcanic conglomerate (IoTe) and hyaloclastite (IoHy-l) at south-coast of
Iwo-dake. A volcanic conglomerate (b) covers a hyaloclastite layer including a block of pseudo-pillow lava(c) with radial cracks due to rapid cooling. Figure d shows a sketch of the pseudo-pillow lava.

cm  



   (HO)  sag structure!"#$%&'()*+,- ./0 1* cm1 
/ῌ,  ,a,e (YIo,a,e)Kawanabe and Saito (,**,)

56789 :; /  <=>?@AB (YIo,a, ,b, ,c, ,d, ,e) CD EFG (HJ) HI(ST)  JK L - m  stage YIo-ῌMN

OPQR STUVLWXY8Z[ XY8
\]^ C_ ` abc@d efghi`]jk' U0l mm,mno pqrs't][ V_ L4l +* cm
uWvQv= (HO)  yzR{| N^}~f
()*+



L4l mm<+ cmuCD#$@]' Q < @fw

_



,mCD

 opq n t %& QR,D (IoLD) f%&$

C YIo,a 234/ῌ- 

 (IoHy-l)QR<

'¡¢£?8}¤¢¥ ,q¦§¨© (0ῌ-)

]'] stage YIo-ῌog῍MN STP ª+[ ^  (IoHy-l)
V«L +/ m ' t  :¬­ ®8}# E¯D°±>?@ w xCD
YIo+pqrs' %&W  #$ QRL4l m 

K-Sk-u-, 234

D (YIo,e)  l mm

%&CD @ EL -* cm l cm

²

D³i,m.l cm< l +* cm 1 ] ´| < ³ .l

mm<l cm 1µB¶"4 tK]»h2n< J!3G¼

79

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

M IoTe J3EFM

    ) !Y  + m !"# $ %&o)/JKY (/ῌ1  (IoTe))/ ( pseudo-pillow (Figs. 0c, d ; Watanabe

/h +* cmi+ m -. Q'() *+,-./,32noG(3/HI32n

and Katsui, +310) 0 ()12

(3,-=>?@-A

>B1L~K0k0(Figs. 0a, b)&4 pseudo-pillow 1$567/ 89. 2nog3s_J 45 W

:;< =>?@-A>B)CD

/ 'M $ r] %]\ ^

67 E +32, ; 8FE +330# )GH IJK (IoTe) L ()M NOPQ )RS 3T0!

"3UVW)XY (3671=>?@-A>h m  (/¢¡>v/Eh cmi£NN¤1d¥/ῌ2  B, C (IoLB, C)

2no7 B, C (IoLB, C) / oyM7B) !
Z3" [#\&

$ %]3%[3^_&1W` [#\& ')a]b.
'M ^_&1W`1$c (W%&1d =>?@-A>B3e 1.:& M

\()If3e

ISD *+# / =>?@

-A>B),g3

h mmih cm -.# M

 /j0k1lm

P)W IN3Q  

2no=>?@-A>BQ

 (IoHy-u) (IoHy-l) 3pq

3"1  e /K31J

_J&/

$ %] [#\&3s6 Ztuv^[#\& '1wca]b. $ 

xg 2noIoLB / ISA*+y3If2no=>?@-A>BQ 
2no7 A (IoLA) 1L

(Figs. 1a, 1b) D -* m !"3457 Q§M/ IoLA )/¨z ©R7

%@/

/ῌ. 

45r]

7O 2no(M)I3¦31m3

/>?   Sh

 e /4.

/ῌ3  D, E (IoLD,E)

2no(ªT 0

T/UV7*1W«

W33 6" /pq¬c xg/Y

2no7 D (IoLD)/ )­X (HO) y®YoG YIo+, YIo,a 1

7 A# y/8&3cMz =I >?@-A>B3e 1m xgM9 ):H"3 YIo, ),3G)RS&$  ;{ '<|m }~

2no7 E(IoLE) / IoLD }zWZ°[ . vol.

/ῌ/  A (IoLA)

ῌ!"\± IoLD )/¨ 70

2no7 A (IoLA) / lY 2no3W 0

(Figs. 1c, d) ¯M 

(Figs. 1a, b)

2no=/ῌ+*  F (IoLF)

sE*B<}ªi]I3^'Dm 7O>?@-A>B"  (IoHy-u) 1  M` e

 IoLAiE <}²³0k1~W´= 0 () >?<}%@ NA0,-.
xg0 ) !D}

()M 8/ IoHy-u 3
786/7_&*B/ C , m  m )

6"

/pq



.:&¬µ _h`3 flow lobe / ¶W /* m 1|S 45·&0/ῌ++  !" (IoTa)

Z1z}~h cmih +* cm 3

2no^MT'Dm ²³0k

'D ( pseudo-pillow 1$5=>?@-A

3 l#  ¸¹}/ -* m !" m>B=

h cm Mh +* cm 345r]

$ r]

1$5 %&/rM

2no(I/ῌ0  (IoSP)(3Q\/ ISC *+3c
-)

(Fig.

 -* cm -. E +* cm !Q3%]<}^3\M

Q=>?@-A>B

(IoHy-l) 3E"0k M IJK (IoTe) W(3),^\$()

Fig. , E

f/ Qº $.3} \ h cm -.# $0

8&&1$c 2no7)abM
()M 73cd4)

efM®Yo!YT/ IoTa 1g)

m g*0k Fig. , 3 k# ¡¢ £¤¥¦

80

Fig. 1. Figures a and b show a photograph and a sketch of the outcrop at south-coast of Iwo-dake (ISA),
respectively. Iwo-dake hyaloclastite (IoHy-l) and Iwo-dake lava A (IoLA), which is a feeder of IoHy-l, arecovered by Iwo-dake lava C (IoLC). Figures c and d show a photograph and a sketch of the outcrop at
Higashi Onsen (HO), respectively. Inamura-dake East lava (InEL), YIo+ and YIo,a are covered by
Iwo-dake lava D (IoLD), talus and fan deposits. Locations of outcrops are shown in Fig. /.

/ῌ+, ῐ῏ῑ῍῎ -aῌ-c (YIo-aῌ-c)
YIo-a-c  



+6728XIkljm Z 0 +* cm y ,!"#$%&

K-z @AB2345{g6728 (YIo-b, -c) FP |m}myM~:-GH672

Sk-u-- (Kawanabe and Saito, ,**,) '() YIo-a

NOPD + cm *+ ,-./0 mm0 cml Zmj;I stage YIo-ῌ

123

456728-9: 8;< 0* cm =>

 @AB 9pkljmBX

/ῌ+- ῐ῏ῑ῍῎ .a, .b (YIo.a, .b) +?@AB8C-DEF ?GHIJK h7ij7Ri IIJK bc

LMNOP QR STUV (HJS)  6

J67 -<X , z* 8ijB

W XBYI Z 6W  [ +F +ym => \]^ -* cm _P`abc-de.

) w YIo.a, .b |m}m sag: fg2672 hR (IOW) 

structure -\]^ 2* cm _P4a67

0 cm, z (YIo.a, .b):F@AB8XIk

`abcijB6W Fkljm

Fkljm 67 #g ?

Z 6W  7nopP`abcijB

2bcg SBmd<a Sag

K-Iw-P+ (Kawanabe and Saito, ,**,) '([m q

structure  2 bc , gr stuvw (IOT)  8 -* cm => x[mIJK S 67

·(¸ '¹0123º»N%e¼81Fig. 2. Microphotographs (cross nicol) of volcanic rocks. Scale bar indicates + mm. Pl : plagioclase, Cpx :augite, Opx : hypersthenes, Ol : olivine. (a) Two pyroxene rhyolite with clear plagioclase (pumice in K-Tk at
HJ), (b) two pyroxene dacite with dusty plagioclase (ballistic bomb in OIo,a at HJ), (c) two pyroxenerhyolite with clear plagioclase (lava ﬂow in IoLE at IOW), (d) two pyroxene andesite with large dusty
plagioclase (banded pumice in K-Tk at TK), (e) olivine two pyroxene basalt with plagioclase aggregates (lava
ﬂow in InSL at INS), (f) two pyroxene andesite with dusty and clear plagioclase (lava ﬂow in InIL at IM).
For the abbreviations of sampling locations, see Fig. +c.



(Fig. /)  
!" YIo.a, .b # $ cm %&

vol. ῌ$! /

j0kl\$$!'()*+,- .

./ 01

\$ ;"23 45$ 6789:$;+<0ῌ, 

=;>" ?@ABC  D@EFG H +*cm

I8JK/L> (K-Iw-P, ; Kawanabe

stage OIo-῍$ ,* vol. ῌI8 (Fig. 3)" fgh)ih V>L#/ stage OIo-῍

OPY;\ OP* (InSL) '()OP * (InEL) $a= ih 
!* (Fig. 2e, Table ,) $ oH +῍- mm roand Saito, ,**,)"

+ ,-" e&j  ro0 

y/G +,-"#:

MN OP QNRSRTU 
 . V>LWX]^+_`" %&Y;Z[N\*abc]^*dbT

OIo+b e& (stage OIo-ῌ) mmy!" I8ro+8fghih

TUb;ro

OP\

 j0kl¤¥¦§\

j0kl\ mnTU+<8" oH +

fghih¡* ; Fig. 2dE}~+#Vro&'" u OIo,a F (stage OIo-῍)  stage OIo-

oH .

;>"

mm 9:pq;roYs$ Fe-Ti t.,

*$

*

 fghih¡*$! (Fig. 2f, Table ,)" pq;ro$¢b£ InSL G InEL

U+]8 (Fig. 2, Table ,)"0ῌ+0ῌ- ,  %¨;>"ῌ mnvwxyz{$! |}~ 

QN©Nª j«¬3­  

|+8ro  - mm +Ys /fgro + mm 9: +8® (1῍3hih2  $! (Figs. 2a, 2b, Table ,)"vol. ῌ) fghih*$!" Q/>\ro j0kl\ stage OIo-ῌ $ /῍1¯° ±'()²7$³´ µ¶/ #Q ºJ<©»¼

82
Table ,.

Model Compositions of Representative Samples from Satsuma Iwo-Jima YIo.a (stage YIo-῎)  
mm   +,῍+- vol. ῌ 
Table ,) +3-.῍-/ -./ +1

vol. ῌ        !"#$ %   &'()*+}$~

", / 01 2345stage OIo-῍%

(Figs. 2, 3,@A ()pqOZ (OIo,a, ,b) *+,

HOIo,a -M )*+  . ` s/ H
0JK +310M OPO12 

 -./



"&34q]60 HI J K6

+32,M BB Aij5 OP - 78+ ]@A=>+ z+ ' )1   

O9:;<6&$) "$mB]1 
9:;<=>?@A 01 B+CD +.C EFG " HIJK+32, ; LJK ,*** ; Kawanabe and Saito, ,**,M %

N OP=>AQ

R



OIo,a, ,b 1pqgy+ JK (,**+)  9 ?  " n> HTiO,, K, O, Zr, Rb QM8+ 

, 9 ῍% s:` CD

ST 01U V+1 W Xs:`  s:`  B]

Y<N Z[ OP = %    9   6"\]6 1
a b*

01!+

CD^A_X`

#cde 01f gh1$

1ῌ+ 

ij

 stage OIo-ῌkAl2`a"$m
%no pq (OIo+a) Bpq  r

srtuv&$'wx`_2`apq

gy+

 z{|  OIo+b "pq{ A" >) 9 

7¢s:` £+ 9 ¤¥rsr85% A /., ka HLJK ,***M" +* vol. ῌ5¡

AG¦gy+ §¨ ©9 ¥¨%2 (IoLAªIoLC)  «¬: 6%  B+  IoLD  CDA]­®¯°±N¶·]

²³´;µ°±$¸¹(»l h3i|09L .;j K¼
IoLD      YIo

 (Figs. 1c, d) +, YIo,a IoLC 

 

!"#

 IoSP$% &' SiO, & 0+῍1+ wt ῌ-.    /0123&()* +,

N: +!D, , @ O+!,D
A3,4  (IoHy-l)

L ,  1*** P 4' 5)Q ,**,: BC
>  R "P   MAST +,  +!, IoLA?IoLC, ,N\' K7OT! z',

 <?U=

4 567 891: ;< =>
IoLA?IoLC  -.  @ A>BC DE

83

M  IoLD?IoLF D, , =4  +!
VW¡ lN (IoHy-l)FGH
I"JK@L 3 vol. ῌ N N, ,+! (IoLA?IoLC)

M N.  OP -.  >QR ST 3῍+* vol. ῌ   \', ,+! ++῍+0

OIo,a, ,bsag structure!3"P,>#$U4D %VWX@ YZ&vol. ῌF^ \'¢£>¤3 IoLA ¢3X¥,

W

 (Table ,, Fig. 3) =4  +!¦>|09

1ῌ, ῍ΐ῏ῌῐ῔Y§=  -.3 ka [\'D]^ YIo-ῌ \'` WD YIo,a?,e  -. ¨©¦>D] ,., ka 5_6( ,*** ; Kawanabe and Saito,, lIa \.3]^b3ª

, ,,**,: 3 )`a . b \'. c L U4 +!32H¨©¦>BC4

stage In-ῌ῍ K@def >@YIo,a?,e >@Z

YZW[C

stage YIo-῎ YIo-a 5$% &«  @*Km,> |09Y§=34jkK@d:* +!, >H\'-g./hi4
stage In-῎ jkef>>l3 01 

2HKmn1o (In-) D3'4=>] kT3IHI¬D"P=>
 +!,

>, stage YIo-῍;j K

p/p4qr56D67,l >89U4 . c \'>BC4 

Kmn1o IU :; = s K7

P$% (K-Iw-P+ ; Kawanabe and Saito, ,**,)

 @ <=3"P,t>?DV stage In-῏ stage YIo-῍+!, IoLF^ @<= =K7uvw+!D, , 

YIo-a 3[CU4 |09Y§=¨©D 3.*­stage In-῎

K7> stage In-῏

K7D

A

l





 @_3".* yBP (Kawanabe and Saito, ,**,) @_ ¨©DF XH@&FD xWa>l stage In-++-*­.* yBP (Kawanabe and Saito, ,**,) @* Km

῎;j 

,D +***­2* yBP 5_6( ,***: F=>\'Ay <=3z{,>BC4

 YIo-a

  

!"# |}~K B

p/p>W^ 56( +320 ; 6( ,**+:
Sr

TCVD + (Notsu et al., +321) =4=> 

P` +*** P>BC4

 = Km,K;j ^b K@dJa 1 KDF l ®b )`W56K=, W\' l,p/p |

stage YIo-῏ ¯)cK@J%WX jk¨©

}~K;j3 |09k3U4-,p/  ./Ni4\'.F W¨© , d (YIo.a, .b) "PD X°l:;QR

p t>?DF1ῌ- ῒῑ῕῎῏ῌῐ῔\'  ,., ka [²X:;³ C´µ®bWKF  = \'5_6( ,*** ; Kawanabe and Saito, ,**,: 3],e /**῍0** P 5_6( ,*** ; Kawanabe and Saito,-. \' 

 <*3±4 (Fig. /) |09Y §=3Q> stage YIo-ῌ E (ST)YIo+ 34H,**,: >U4  YIo.a A   VW¡ +/῍

3 ! 1 56K./hi4 YIo+

+1 vol. ῌ stage YIo-῍ +!, VW¡ ">

4 FlGa <k3IHID6J,

fg3X¥,   +3-.῍-/ P ¶g h=> stage YIo-ῌK.

K, ,,i!+! VW¡ +1 vol. ῌ

3L6W\'>89U4 



stage

·C =

YIo-῍  -.





+!



(IoLA?IoLF), 3^ OP @ ):DL

\'.

W¡-.  ,i!

¸j"P¹k,!"# |}~K>

U4

W/012 ºa^ 56( ,**+:  Srstage YIo-῍ OP^lM3T!K7 5N

TC|}~K ,i!p/p^lVaW»% ¼±²³´µ84Fig. 3. Variations of modal abundance of phenocryst in volcanic rocks for the past 0/** years. The rock of thestage OIo-῍is more crystal-rich (¹,* vol.ῌ) than that of other stages (º,* vol.ῌ). In the Young
Iwo-dake stage, the modal abundance increased gradually with decreasing age.

(Notsu et al., +321)     !"#$%& '



ΐ

ῒ

bcdTeB fghfibcj
klmn opqrstu vwx

(%)*+,

tuy ghbcz{| }~ 2ῌ ῎ ῍ ῏ p \bcp>

~ g p fibcjklm;-./01 !23$vtuy p  

(stage OIo-ῌ4῍)  (stage In-ῌ4῏) p !"pvwx  g (stage YIo-ῌ4῏) 5+,$



678%9:! (stage

OIo-ῌ) ; <=> >! ? @AB

!CD(CEF@GH (stage OIo-῍) I'

'(%JKLMNF

(stage In-ῌ4῍) OC  678%PC''( (stage In-῎4῏) %?QR
 ST +*** <>!%'(BCEF@GH (stage YIo-ῌ4῍) UV +*** < '("+W <=>XY 9:! QZ (stage YIo-῎4῏)   !"#$

%& ' ( [S \]^_`a?

#¡ ¢£¤¥¦¤$_ %§¨©g"ª& By 2«$_¬­+®¯
w'y°ῐ῕῔ῑ'x±²³´µ (+330) ¶·¤'+,(¸!³%)(* !C .+ +1+῍+13.
Kawanabe, Y. and Saito, G. (,**,) Volcanic activity of theSatsuma-Iwojima area during the past 0/** years. Earth
Planets Space, /., ,3/῍-*+.
Kazahaya, K., Shinohara, H. and Saito, G. (,**,) Degassing process of Satsuma-Iwojima volcano, Japan : supplyof volatile components from a deep magma chamber.
Earth Planets Space, /., -,1῍--/.
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