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 /  ,01ῌ,2, ῕ ῔
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,**-  +*  ,  ,**.  2  ,3 Geologic History of the Western Part of Post-caldera Central Cones of Aso Volcano,Southwestern Japan, Based on Stratigraphic Relationships
between Lava Flows and Airfall Tephra Layers
Yasuo MIYABUCHI῍, Naoaki MASUDA῍῍ and Kazunori WATANABE῍῍῍The western part of post-caldera central cones of Aso Volcano, southwestern Japan, is characterized by widechemical variation of lava ﬂows (SiO,.3῍1- wt.ῌ) and complicated topography. Geologic history of the area
was reconstructed by stratigraphic relationships between lava ﬂows and airfall tephra layers. Stratigraphy andchronology of lavas and tephra distributed on the western slope of the central cones are as follows : Ayugaerinotaki
lava, Matsuhata pumice (MhP), Tochinoki lava (1-+* ka ; K-Ar age), Aso central cone pumice . (ACP.),
Tateno lava, Aso central cone pumice - (ACP-), Takanoobane lava (/+/ ka), Eboshidake lava, Karisako lava,
Akase lava (-* cal ka ; calibrated +. C age), Sawatsuno lava (,10 ka), Kusasenrigahama pumice (Kpfa ; -+ calka), Otogase lava and Aso central cone pumice + (ACP+ ; . cal ka), in ascending order. Between about 1*,***
to /*,*** years ago Tochinoki lava, Tateno lava and Takanoobane lava accompanied precursor pumice-falldeposits. A catastrophic eruption occurred in and around the Kusasenrigahama crater at -+ cal ka. The
eruption was initiated by the dacite Sawatsuno lava ﬂow and produced the largest plinian pumice-fall deposit(Kpfa ; +., km- in DRE volume). In the western part of post-caldera central cones of Aso Volcano, total
discharge volumes of felsic and maﬁc magmas from about 1*,*** to -*,*** years ago were estimated to be about,.. km- and *..1 km-, respectively.
Key words : Post-caldera central cones, Aso Volcano, lava ﬂows, tephra, geologic history+ῌ ῐ ῎ ῑ ῏

0vD`P wa x +33+S dyI7zD {|}~

 !"# $%&'()*+ ,-./012.

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(+31,) @deIfgC [Uh QR  (+32/) E

 ~ZU\]^_I^YP:znS [U[U\]^_I<`D+

ab c(+3-2)

ij (,**+) @kCl3ZmnS  !"# $IE`D Tv34fg5vD`P(U=.UAB*%&opqUrs / <U=.I<`D+ K-Ar t@u: Y@OPTZ;CnS TUTZ;m20*῍*20, a ¡ .῍++῍+0¢£¤¥¦§¨©ª«¨Kyushu Research Center, Forestry and Forest
Products Research Institute, Kurokami .῍++῍+0,
Kumamoto 20*῍*20,, Japan.
203῍,,,/ a¬­®¯° ± +,00
"²³
Aso Junior High School, Kurokawa +,00, Asomachi,

Kumamoto 203῍,,,/, Japan.
20*῍2/// a ¡ ,῍.*῍+a¯²´²(
Faculty of Education, Kumamoto University, Kurokami ,῍.*῍+, Kumamoto 20*῍2///, Japan.
Corresponding author : Yasuo Miyabuchi
e-mail : yasuo@a#rc.go.jp

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268

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(Fig. -).

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yrs BP, %

cal ka, K-Ar +.

C

ka &'(#)  * /,***++*,***  '( , K-Ar  -. /01 Fig.

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)*+98 (Fig. +). : ;,-

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H'8I *0 

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' i?(= l/0 &cd>b+32/) 

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KBCD/) 6 LM=23 *00 {| # !"  §¨r©eB

/Q 

0NI

*+BBOEFP"I GH'RST

UI> ' J V K  &56 ,**+ ; Y

1

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1

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+32/)

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^ Z,<,/0 &4'>56 +32/ ; 56 ,**+) : "[1!fCD/ &\ $" ¬S­ ®"I *£B gC¯ -Nhi?(f!j0CD/ \$ kS4CD/) B

*£B3 B¤° &SiO,¥/- wt.ῌ)  §¨" = e] ^_ &i?() = l/0
!m_n1![`l=a0 &M ,**- ;o@>b ,**- b ; cd>b ,**.) / :pef_

g=,-"I h&jq +-) klrm



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 +/ῌ 8
aV]W

R$>S$=T17U+%!= Z¦±/01 S
 AVL.

Z$,-:=§£/01o(Figs. ,, -). *  ¨ +2., m t²8I ©

&p6>qM ,**+) :0`tu#6 .#3S ªP , ³ «S¬­®¯=d01 :8 : Nv GqnrI ,

>A=23j9!C <sgC
Z;wxt=x O:H 8yH1

 uBz{|S"vw: 56 (+31,) =aV]W= , ³ !1  x!6´-ῌ,  1}xN]O NOpe µ¶°w 7U"

yH%~1zB7$ *+!m8I *0

Nh7±*+ / µ¶NO &=>· -/* m) 7 zCD/ {|B}~#1¸7² - km ;w*+23 &4'>5(Figs. +, ,). w1 ,**++,**, 9n6 +32/) :  ¹1aV]WNI,²

Z[S &t ZN) =8>'JVK$8I

!"/01 . 

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 8

;+)_+ &Fig. +

X-X ῍

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³M´i &345 Mº2)C ·µICD/8¶O' &  +3/2 ; 4'>56+32/) = - &56 ,**+)N]O £B5¸¹¸¯ &SiO,¥00 wt.ῌ) 8
= §¨ =º.¯!C &++/ῌ) b »

Fig. +. Geologic map of the western part of post-caldera central cones of Aso Volcano, with the surveyed localities. Distribution of most lava ﬂows
was revised after Ono and Watanabe (+32/). Nakahono lava, Nagano lava, Otogase lava and Otogase debris-avalanche deposit are from
Masuda et al. (,**.).


269

Fig. ,. Stratigraphic relations of lava ﬂows and tephra layers in the western part of Aso caldera.
locations of the sites. +.C age of ACP. is from Miyabuchi et al. (,**. b).

See Fig. + for

270 

-.}de/0/T&  cm   !

 0.Z00 wt.ῌ A[\OPQ ]^_`3aB !b c!

"#$%&'() *+,-./012345

271

d >eVW-.f .gh

ijklm nb *+,-.'( o

6789:;<=> (Figs. ,, -), ?@= /- mp)q'"! AFig. ,  AVL+B CDEFGHI*+

tuvw VWXY)x,-. SiO, J 0, wt.ῌ KL=>$rsoy>z /012345678.{

AMNOP

Q +32/B  RS CDE*, AA*-,- TUB VW

MNOPQ (+32/) $rsCDEFG

|}~3

!  RSi)!   !

XY SiO, J 00 wt.ῌ /012345678

Fig. -.

Geologic cross section of the study area from Tateno to Takanoobane (X-X’ line ; Fig. +).

Fig. .. Stratigraphy and chronology of lava ﬂows and airfall tephra layers distributed in the study area. Solid
tielines show stratigraphic relationships conﬁrmed at outcrops and drilling cores. Broken tieline denotes
estimated relationship. * Calibrated +.C ages from Miyabuchi and Watanabe (+331) and Miyabuchi et al.
(,**- a). ** K-Ar ages (Matsumoto et al., +33+).

º»¼I*)JK*L

272

Table +. Petrography of rocks distributed on the western part of post-caldera central
cones of Aso Volcano.

-ῌ- 

3  Y~QO,+90S

  



0**

>1@9;7>!?;8I1( a

0+* m ; A*-+1    

9N?!(<}>1 (Figs. ,, -).   SiO,1- wt.ῌ 

Cx --.- (AVL+)01.2 m (AVL.)  gh89  !

"#$%&'( )*+ ,**., '"( 9= !$ -. /* +32/ ;  ,**+

:4L<@7>,012$34( 56789:;
, < (=7>!?1@ AB



-ῌ0

-. ,> +./ km 9R?4 @a

;CDEFG9HI!?;?( J;KLM9 ?1ab¡$L¢aqc?/£Ca

NOPOLQR9'S8I

h/c !? )*+ ,**.,}>!?1 /* +32/ ( ¤¥9-ῌ. 

 SiO,02 wt.ῌ 9OI!}>!

TU VWX YTU*-,+ 

0,* m  8¢!M87;A?'(A 1, )*+ (,**.)  Xah$ !Z94"[\]8^7^]_#a ah$4$SiO,.3 wt.ῌ  /* +32/, $`abcdeLf%, gBC 1,-ῌ1h !i?&j'$kl!?1@ mm(88I
1"$ !N  ,**+) +/ῌ *+

-. "#"[\] ¦KJ)[\]$%&  SiO,1, wt.ῌ  8¢!a

, '6,- no./pa§¨ /* +32/ ©ª>!?1,

q90S>'rs +CDEFm

81t 2<uS8I!?;?  ,**+,°c ; -ῌ/ 

 2<u9«¬ ­D®a§¯
/01 m (¡}>!N E3 1a'(781@ «¬$%@1±3 3ab9>v^we4 (  ( 1ua9¢?! -.a  -.

Lx?  ,**+, yz{OQ²³}>1  ,**+, '

"| }79 Y~Q A*-+,   OQ´

|9< !N}( 2*+** m 9L4

$ !N 4 5(6 !?,'

*"

 Y~Q !Zµ !N /* +32/ $9< !? |[FCx.*/* m *+, ±u!Za

(78?[\]"[\]

 //./20.0 m AVL+ NOP . Cx$G4, SiO,02 wt.ῌ , 9""

X>7 ¶H!Z(

$: !N gh89'(·!Zp(¸^?'(}> ¹)

,"# (%µ>!?,¢£u¶·¸<~O/)7)*. (Wdt¼
 








  

      

!"# $ #% 

 

&!'[ZF $SiO,901 wt.ῌ% > $T3 +32/% U
V  !W B
(XGh@Y (B);



ZJ V(Nῌ% [qpjH!J (Tables ,, -) <$ ,**+%

$SiO,901 wt.

  (3RU7V-ῌ2 

S 89 .!L :;<?3RS()*+,-./0 $ +,--1m%273

 12 31!2 !45678 $SiO,9/1

4kV  $T3 +32/% \]3^ (,**.) ?__`  :;<(P3wt.ῌ%  $":# ,*ῌ $%% );<=

R_.Ww

)7> $ ,**+% 7&'&("?@)A

F w*+1,(B); CDEF 3X=c  (Pc< ./0*+7& ()7)

kHr`Ra> b !3:

-GHIJK- ./0)7-ῌ+, 

7&<.!LMN O/01P2Q3RS

(P  +S89 4WV 4  $T3 +32/%

4,5 6 16 //*0** m (PQ $A*,*. (km, U7V>% dV12 31!2 !45e>-ῌ3 

 $\]3^ ,**.%  {!W  tS89 4W $T3 +32/% uv8> DE> (P SiO, 4J<VV (W>:;<X= $A*-+/ (>% +#.! A*-,, (> :;<? $A*-+- (>%   Y

hk:8=V _kV

Z[ZF889 \=12 1!2 6

 SiO, f57 $SiO,9/2 wt.ῌ%   (Figs. +, ,). )7

1- wt.ῌ > S)*

  (PQ+g(("!"

4

4  S h8 :;<? $A*-+-   (+31,) _` AaV  ?

(>% S  (Fig. +). +i 7("]@!<:;<?<^ 2 67῍. bc  < +d]e $T < Lf

3 +32/ ;  ,**+% ?῍.  YZ[ZN jk ¡lV  $\]3^ ,**.%

==`F889fgV ":#

6 ,*ῌ BH 1:":h. 

- . mm $%-G=i  jCDEk89

O/)7)* m-=#N¢£u!

 F<\=`  5l  ":m  + hk¤Hn5 ¥¦Yu@!

GHno?pjH (Table ,) > ./(W>  ¥¦Yu.  k'&C¤V

0_Hq  < ./0Irok §=¢£u    ??tuv8> ":-GVc_(W  N¨_O/)*p .  

wG$%=i \=`DEkJ  S .

_,hp -   (  ©q Tn )7ª «¬/0_K!x .! 4< LC¥­®)7ªO/)*p +  ¯§¢£su ° V :;<±B $A*-*0 (>%M X=yz!N-
-ῌ+*



 _(

W^N¢£ur²UVfw> +(>OP  :;<OP3R{Q|}~" ¥¦Yu@!W-# v³´C µ:#6 ,*ῌ 1!2 12 < 67 $SiO,

i9// wt.ῌ% > $ ,**+% {QR(S  O/)*p .  _¹¨µi<`  VTQ3{Qn>6

!

,.2 km NS 4  (Fig. +).
-ῌ++ 

¶·¸fsG (Fig. ,). ¥¦Yu@!W!

° V §¢£uDEw

VJ  

4":# +*ῌ $%12

 

º»3

^ (,**- a) Hr   `  LM

89  :;<89 $A31+2 (>3R% !


=

1!2

YZ



_(W¢£ur²UV> A*-*0 (>^ !r S hR]e $\]3^·¸!¹= !º»O¼

274

Table ,. Whole rock chemical compositions of lavas distributed on the western part ofpost-caldera central cones of Aso Volcano.

,**. 

    !!"#$%
'( )*+ , - &| K}{| P ~
(k.23&

J 2 ;   <Hno , cm.&/0123+  <1./R-ῌ- ; AR_ 2K&P23 @ABCQRF.ῌ+ ῌΐ῕῍῎ῑ῏῔ . ῐῒ (ACP.)<! ,**- a ; A32-+ \] +  SiO,

456789:; .

_<"= +323 ; > ACP.

? 45@ABCDEF*G2H&.IJK? 01 wt.ῌ P2 (Table -). ACP. [ld? *..- km-¡K¢£.2 <! ,**- a3

L2MNCO-P23 @ABCQRF .?S.ῌ, ῌΐ῕῍῎ῑ῏῔ - ῐῒ (ACP-)TNUVAWXYZ[L2  A*-*0 \]^_G

456789:; -<> ACP- ?~¤¥¦§

\F`?abLNUVAWXYZ?*G^_¨eLMNCP2 <"= +3233 A*-*0 \]c Dde fghij^k.23

? ACP. 

A*-*0 \]

l2 ACP. 

Hno <MP ; p`m? +*1 cm P

l2Hn

stu ? ..- cm P+3- qro6vwxyz?{R+.- m ©ª '(k  ,

MNC«¬­ *®¯ [KL.23 A*-*0\] l2 m?

+, cm P2  n°±²hk³hk.23 ´ µ'k.2?
¶"Q_!34 !¹,Dv2²DEº»KO) `a¼
Table -.

Whole rock chemical compositions of pumice in and around Aso caldera.

 MP  ,., cm  







 SiO,  03 wt.ῌ (Table -).   ACP- ! "#$ %&'( ,**- a)

*.*1 km-275.ῌ-  (Kpfa)@83O9~.L {:];
T< ,.-3 km-!#/F Kpfa  Aso-.  01 D!  %&'( ,**- a)
Kpfa =f.>?X@MA]T!M&* %( +32, ; + Kpfa)  ,' %(B +33* ; vB(C +330) M- ./$#0"12!#$(^) qsW/:;mDWn @6DvsM

34  567!#89/:;89T!MF %A*-,* )*) 7 MX


<=

>?>@6 %SiO, A00 wt.ῌ) 

@$E"

(Table -). BC*DEF GDE'.ῌ.  %HIJ8 ) /:;K8  L!

A*-*0 )*./$# Kpfa wg + m F@.

M"N#ODPQ.#R#$ %

  34 G ,3 cal ka %$ ,**,) H Tn D

( +32, ; S$( +32/) T"NDPQvs %IB( +310 +33, ; + AT) M]

UVW!XWYZ[%<\]T!M&' %

T AT ! Kpfa  ,

(AT)

-

JKL" (^) ./$#<] ,**+)
(^) ./$# Kpfa  / _4`a bcd@.
eTn]T!MO fg:Fbcd@ W+hW/ !ij A*-*0 )*./$# 0fgbcd@ W+ kk

 AT  +*h,* cm
cm N.dM Mo +*Z.]T!".$ W(.

j$m,W (+*YR0/.) <- 014¡ *./ cm

+l#m,W (+*YR1/2) <-] 

4<=M 1O ¢£ ¤`a ¥Dv¦-, cm (MP,.- cm)  bcd@ W, mVW (+*§ / A*,*. )*F  AT <YR//0) n @ % +* cm) F .oM

P$# Dv¦

p/#$ bcd@ W- 0) 0"$bcd

 IB( (+33,) M\]T«U.zV]T!M§!89¨QRSM©ª@F % -0 cm) MP " /., cm !1O$ bcd¬W#$ %XB( ,**.)

@ W. qrsW %/BG) <-] 3 cm tuh2

.ῌ/



u6Dvs 0wgbcd@ W/  ,0(^)./$# )Y ,h. m(K-Ah)

­cm m,W (+*YR1/2) M bcd@ W-

 XWZ[®.¯$@X@!

.3x!kkt4 (MP-.- cm) 56My$ z

#/F G°±2²F. 34 



#$

³´µ¶·Dvs %\](¸I +311 ; IB(%&'( ,**- a) M {|(^) !}7.bcd+312 +33, ; + K-Ah) M^#$ K-Ah  0 _bcd@.eMN¼q%r%+7s276

 +*,* cm   (1./YR0/2)  

 AT  

K-Ah  !"

#$  %& '( )*
 ,% ,**.- ./01+"K-Ah 234

56"#$

7

 809: *./+ m ;< (+*YR-/.) $.ῌ0  +#$ ! 

&C."=>?# + @ ,A +323 ; $% ACP+ K-Ah B&C D'()7EF@"ICJK*LJ ,+ +33, ; MN%+ +331- ACP+ 
OP,Q- A*-*0 -&C #@ F9 (,./Y1/,) @ (MP-., cm)  ;G< (1./R-/-)  ,qJr ,
-C

cm-

AVL+ 1

 6i 3X YWEkFBEk , l. m- 5 l . m :^_^`a ,SiO,b02 wt.ῌ ;Table -- EF@4+"i F@

HCJ

, l 0.2 m-#@ 1)

(ACP+)

 #@"G N1 H

0* cm EF@Z[ S&C$t  AVL.  J`o4XhZ[ @aTU< , l +0 m-*4!"i (Fig. ,).

.ῌ3 

EkFLJTU<5
g#$S l +./..1 m EF@ 4+" (Fig.

80./01R234+" $S.

,), #"YC6\*4!"

567T  A3./2 - (Fig. +) U J#$ #@^_ka ,SiO,b1, wt.ῌ- 

 #- VWR X$8 !"  YC
  #@$#Z[9:\W]

:^_^`a ,SiO,b0- wt.ῌ-  (Table -), c;ad<$>? ,A

2e=fg#$

6hi



 

; 

&CJ (Figs. ,, /A). #@F9 l +,0 cm  

 (Tables ,, -).

6i AVL+ EkqF +* m 

ShPmno`O¦o4§d 1 BEke¨

4

.ῌ+*

!"  !"@AB¬­f ,A*,*. -- 1
Fg@$ ®

+" "=)ppF l -, cm @fg,), ¬­f@ ,$% OtP- $}¯",**.- ® "mno` , l -* cm-  MP) qF ¬­fEk

&C 1 (Fig.

2G< (/YR//0) 

HC

m£¤¥

kwOPX@ABCD ,A*-,- --  CjDEkFE
F@ BEk !`2e=af uS s bcXEk$¡¢© "ª EFTU<«WE+323-
.ῌ1i']

l 1* cm  ,%
HCJ

,.- cm $qXIJK#$ ")B@ ¬­f# + @ ,$L@  qmno` , l 0. cm- % OtP+- FB@¬­f# , @ ,$% OtP,- $l! +, cm 2

ShHCJ$

 °!"

 h±$Xc;ad<$ & '$X JrMsX4+" ,MP,,./cm- @

$N&'fg^_ka ,SiO,b1- wt.ῌ- @"f6"c;ad<N&'$& 'CjD ">?B¬­fEk$¡¢

Ek$t #@ 801uvO

 $S OtP+  LJTU<5g#$

P$wOP i+ xy-z{Q$
6hi|R@ ,$% MhP- $}~#$J|R@Fl +-* cm @

2G< (/YR//0) S¬­fEki]" Ek$7S:) :\iX ,% ,**.-

ICJ

 #"@1)/# $%&'()*+,-./012

j ."=>?²0&CJCjDEk6LJ
4+"

(MhP)% Ek

 i



 

% @

7S:TU<$" Vi) CjDEkFDW
#$ ,+ ,**+- &CJ#$ X!" EkF MhP $!FB7$!"

DW

TU<Z.ῌ2 



@ABF ,A*-+, --  YWEkF l

Ek$OP$ ³´µ (Fig. .) h BX)kS¶801uqBEk^¬­fEk
h AT $234 ·l ,\ m , m n-< "HCJ#$ ]

 ,%

 ,**.- EkF¬­f@ ,OtP+ 1)
OtP,-

9:/0¸@ op¹ º»8* J#$ ¹i῍#;±&'Wg².³´µ¶·¸¹daº#»¼ῌ



 Kpfa 

!



+,

277

ACP-  ACP. "efg!

KWg wxyz ACP- T$7, #(Fig. /B, /C) " ῎#$%&'(! )*+uvg 3 4. ^_` /A*-+/ ab2 +

,-. /01 ,**+23 45 Kpfa .S.T%7#XY"HI+J+, "

#&'

6$7# Kpfa 89:;<"=> /+*?13cm2 @AB #C῏DE
F+! GA"HI+J(Fig. /B). K#K

A*-+. abt"ij!

3 S

g A32,2 abVT A*-,, ab+ #$7VT~OP;B+ Kpfa "efgLMNOP;"QRS TUB.3 Kg#KWg wxyz

VW5 Kpfa "XY.KBZ[ ! 3 \] 

;ij  Kpfa  ACP- VTt(!  ^_`ῌ /A***+ ab2 #ῑc##ῒj\d+ Kpfa #;< ,?- cm #OP;

 wxyz R"ῐ¡"efg ῎h#5W"ijklm"noS.3 Kg#pqWg
#LMrsf !"
#]"$7, klm"t!uv 3
W | .

wxyz ^_`{N} /A32,/ ab2 V!
 Kpfa #%7~VTOP; /8;< .2
cm2 B+ij !

(Figs. ,, /D). K#OP;

K"W-.3 .TU

V Sg;!KWg wxyz\, !!r#LM+, klm"
, 3 W"g ῎#$%&'(! #¢£+*gW

K"+JW-.3~¤¥¦§B¨© ACP- " ~¤¥῍ª+, t«¬S klm"t!K+t} (+323) VT­®¯ (,**- a) "° ! 3 

Fig. /. Photographs showing stratigraphic relationships between lava ﬂows and airfall pumice layers. (A)Tochinoki lava overlying Matsuhata pumice (MhP) at locality A*-,-. Scale is + m. (B) Sawatsuno lava
overlain by Kusasenrigahama pumice (Kpfa) at locality A30+3. Scale is , m. (C) Akase lava overlain by Kpfa
at locality A32,3. Scale is , m. (D) Eboshidake lava occurring below Kpfa at locality A32,/. Scale is , m.

¼rM>?sMR$ct

278

 +32/( L'1YZ,#  ,..1 m  !"+X0* ,N GH-#$%& Fig. , ' AVL+

C< ,S/=+8(+ +, Kpfa

AVL.( )&*-'

.

,

AVL

'

% A*-+1 ( >?M+8 A*-*0 [ ]^=/VW /  ?* +323 ; X'3456,* 345

7

9: ACP- 12'6;"</* ACP-

T'1 ,UFtI"/'12

"/%0 *=,>? @+ AB'

 ACP/ 8, ACP-

,**. ,* W''

:;$%



* S#0  , 0(Y<& p * GH A*-,-  'GH

C+8 #D 0 &('2 ,* A--EFGFHI



,Z

p345<

* K A(Fig. /A). ',5'4f ¡z=/0

AVL+ M- ,N LSRS'u0|'F[

O +P= &( ' ,QRS<9V* %/' ,efg5\Ti+"/%

0J"/%
*-+,  LT  U<9V* W'=/ ACP.
 +X( ' ,* 



9:

VW 0  ?* +323 ; X ACP0 '¢£ M * ,**- a]¤<( )&* efg5 '6YZ* A*-*0  9:345\Ti+¥¦$%& ACP0

6* $/ '[\ ]^* _` !'=/,* _` !'1+b J¤ (Tables ,, -).

abc"#d0( <& * efg5h$i+<=<* Z,P§= + +<=qr+X0'j345+8 ACP.

,* c%'&'+8( )&* 

AVL. + ACP.

-.$%( '

9:GH* $/ ¨^m\ <T© _©FtI()k #$%&*+'lm'&',*(=/aO,&'

i

=

, ACP0 'b5< =/* ªA

+,':;F~<=|"9J( §%* L^` * GH,/*  (ACP.) C n/'c01o<* CY ba2K023< S/

O,23<& p+8( 1

= 0 &('qrNsF4] * FtIc%',* uCv) &w* 56'FC

b * n/c01o<O,23<( $/ u0 

V«C ,* / 'C7&w gxyxzmF,C ' K-Ar BCb¬P% cM * +33+( 

p{8F&| & }$%(' K-Ar BC,* !3 .*Arῌ-0Ar ;}d* [ ]^M[6M9_` !0|'+
?M

,**.

:;$%~<=8,* >G$%( eB

Y p­ b6YZ #d0Jf®+X D¯$%&Td+33/)(Matsumoto

andKobayashi,

b'+8( i 9,* IJ!$%  '@1'  A*-,* ,1°0 ka*  /+°/ ka* GH 1-°+* ka,* KpfaW''   A0'B

CD -, cal ka ; M * ,**- a "/%( )&*p - ' K-Ar BCg/% cM

* +33+(EF0|=/,GH IJ- )&* Vefg5 W'h$i+,* 345

b' }$% >?M * ,**.( <'hi .F:± <* 5J' +.C BCbk.$%P:+,0* F

D²$%X& MR$* +331 ; M * ,**- a ; :; ,6K ab#d,0( W'M * ,**. a( cj+³&345'+,* Kpfa:;L<  * '>?, /%(D -+ cal ka

pBCk´$%&* W%

V2'345 Y<,6YZ l]BCm ,*'L345 'M'

g/%0= &&"* 2=/ ACP- D -.3 eBY*

6YZ,'+qr +X0= &( <ACP. D . eBY=<* 'N Vb2 8 ,M+ P= 9V* )&,EFOP+GH

' ACP. +2¸$%&no_'¹H'ºp

FQ

b'

-.$%  M R$*

pCBC}$%&* ,**- a( <=<* µJ¶· 0  A*-+,

»m6Eq

(AMS)

d

 +.C BCb¬P%*

+KTUV ¥¦<§¨©ª« X7B¬
Table ..

Results of AMS C age determinations for buried soils.

.-,,** +.C yrs BP  .0 cal ka    ,**. b    (,**-

a)  !" #$%&'( )* +
***+

=

&ku

.    ,**- a% Q; ACP- 1+^;?

*..f+./ m $| / /,-. /0123 4 Beta Analyt-y.X-.; ACP-  ACP. ^;? *.,f, m

ic 563. AMS  C 7893% ? ,f,* cm e|

+:<=> B C D@A" 

0   1 2 3  (Fig. ,). C 

+:



,/,0,*E++* C yrs BP (Beta-+.*/+3),; Kitagawa and van der Plicht (+332

F3 C G!HI J K+.

 -* cal ka LM (Table .). N OP

QRSTUV  W X" +

+st

,A"

+ῌACP. ^]^.   +- ACP. Y

+ῌACP- bc"]d / -Olm% ; ACP. :Q7u 8tG!$.0 cal ka  ,**. b K9
3KQe%a :; +<=+ +Z.

; &'WQ>?LTUV}1" Q

YZ.["%
+

 r

/

TUV  r+st +ῌACP- 1,**. b% 0Q; 1,/,2,*E+,* +.C yrs BP (Beta-+.*/,*) ! +.C 

% @A3.% ^_;  +** 56u

B

+.

)*

(Fig.

,) Q 4;3.% a vwx)* +:;<=> / ? +.0 m

a, +332 b)", A

+.



279

+.

+Kpfa ; !\L]^^_`aL bc"]dY#Qe% Qe -+f-* cal ka ; G!$+ K-Ar \LM% :; +;@8 + 1-E+* ka ; ~0 +33+ | a<=+; ¡* +

 , -O | ¢A ,**. 3

,1E0 ka gh%ija .% 3 M. mL   +;n)op +@8 +^- ZY#3.;  (,**- a)

,A" £M.Q CY; 1&k3 -+ cal ka lm.'(L%n)op +q* +; K

-f. -O^u %+r+st +^,A"  --C . -1 

OY3Ku %z¤RS.\ +TUVNYaQ ACP - Y; vwxy.Q

Aso-. z{UV

 -.3 -O



K3. Q;¥¦<§¨©ª« X
7B¬Z.l­" (Fig. .). L- ® +U3

u .  ,**- a% 33 ACP- ;r.; C¯ND°?L? --C>¯ +st +:]^^_`aJ@A3.-|>E6 ,., gῌcm- ± ; ²  +33- ³´3%" +"]dY#Qe }/u % 3
M. 0Q;r +st + K-Ar  ~0 +33+   ACP- Y / -O !

&k3+K>¯ +¶´G (DRE ;,./ g/cm-) 3.F3%·H+:; +; ¸A IQ¹­Q\<"%
W X-.r +st +:;1a {:>¯;  ,**- aµF3+§¨©ª +<QKºKKQe ² Je| u C:@A"; ACP. 2. +32/%  +;  1 -O|;}83u % ACP. Z.;  . -O

Qe|:»G@A"<§¨©ª¼d+>¼tab-uv

280 +33. 





1
km-

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 

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'7

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& 0** m ^ ,**`-**


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ab ,**.

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HI0 1J0=2t¢  S

%?R !6gha£63m%¤῍¥¦

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

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9:;(&2kªi('60\45('
ACP. S,TU 1VW"XY?S«=j¨

G.P¤ 3A

M4NOP Z # 7[\K kL¬­lm"?n]?^8R 33= ( _ +./`, km 

'6 9:+ *.+. km-d;<a6 , b3c

- ="% 2© +323

3

G.0Y+?A£ ¤ ®¯p°±[?¨

H°±[' (&2k G.'9:/ - % (ACP- ; *.*- km-) ?

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SS,H .

e=fg Z # hP

0i8&' P:?^8 5(
j_ / km kl&>hP09:+ ; *.+2 km- P:

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q² SiO,·.3`1-ῌ L¸

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D?=bwhPxE (*.*0 km-)
=e=fg,

y?W='"

-+ cal ka z c3{|XYY} "A FG

 2

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G~.I,#

JS,TKJLM(

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 !6=3R&' S

T (*.-. km-)!"#.$W((P(_ 0km '!

HU !"#.$ Aso-. km<UV\

2 WXm%

!"#.$m% ; Kpfa ; +.+/ km- ?

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6

"

Fig. 0. Alkali versus silica variation diagram forrocks and pumice of Aso Volcano. Data for
Aso pyroclastic-ﬂow deposits (Aso-+, ,, -, .)are from Ono et al. (+311).

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 ,  qr 1p 1 N'%`=s5t8N *.0+ km-  *.+1 km-    -+ cal ka 

! "# Aso-. $\uvwx

%&' +..3 km- ()*)+,  Kpfa- ./01 /2

34  1  5-  .  ,..
km- 67  1/ 8

9

1:

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281

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Kitagawa, H. and van der Plicht, J. (+332 a) A .*,***-year
varve chronology from lake Suigetsu, Japan : extensionof the +.C calibration curve. Radiocarbon, .*, /*/ῌ/+/.
Kitagawa, H. and van der Plicht, J. (+332 b) Atmosphericradiocarbon calibration to ./,*** yr B.P. : Late Glacial
ﬂuctuations and cosmogenic isotope production. Science,,13, ++21ῌ++3*.
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Q)¤¥$
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Matsumoto, A. and Kobayashi, T. (+33/) K-Ar age determination of late Quaternary volcanic rocks using the“mass fractionation correction procedure” : application
to the Younger Ontake Volcano, central Japan. Chemical
Geology, +,/, +,-ῌ+-/.
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