  //  (,*+*)
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,*+* , / - +- ./ ,*+* , +* - ,/ ./Eruption Age of Komezuka at Aso Volcano, Japan
Yasuo MIYABUCHI
Komezuka Volcano, located in the northwestern part of the post-caldera central cones of Aso Volcano, SW
Japan, is a basaltic monogenetic volcano comprising a scoria cone (-1*῍-2* m in basal diameter ; 2* m in height)
and lava ﬂows (+*./ km, ; /+*1 m-). We obtained +.C ages of -,*1*.* years BP from a buried soil below silty
ash underlying Komezuka lava, which corresponds to -,-1*῍-,,+* cal years BP, and ,,10*.* years BP (,,3/*῍,,11* cal years BP) from a soil above silty ash overlying Komezuka lava. The age of soil below the lava suggeststhat the eruption age of Komezuka Volcano is about -,-** cal years BP. The eruption age is consistent with theage of Ojodake Volcano (-,0** cal years BP) whose lava underlies Komezuka lava. In the northwestern part ofthe post-caldera central cones, Late Holocene monogenetic volcanic activity commenced with sub-plinian
eruptions and lava extrusion from Kishimadake Volcano at approximately .,*** cal years BP, followed bysub-plinian eruptions and lava extrusion from Ojodake Volcano at -,0** cal years BP, and ceased with strombolian
eruptions and lava extrusion from Komezuka Volcano at -,-** cal years BP.
Key words : Komezuka Volcano, scoria cone, lava ﬂow, eruption age, Aso Volcano+     ,**+

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Faculty of Education, Kumamoto University, Kurokami,῍.*῍+, Kumamoto 20*῍2///, Japan.

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6 78 +32/Corresponding author : Yasuo Miyabuchi
e-mail : miyabuchi@earth.email.ne.jp220 !"#$%&'()*+& ,-./ +32/ ()0123456789' -1*-2* m :'
2* m ;<* =>89 2* m ? +/ m ;<@AB CDAEFGHA$%& I501234J6>K#LMNOAPQ$%& RNOP5STUVWXYZ[%\] /1 ^_`[ 01234K#aabcd -./ km I*e
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 Rsi5 /  +*1 m-

tu& ()01234vwCGxbwJ6>
Fig. +. Aerial view of Late Holocene scoria cones in
the northwestern part of the post-caldera central
cones of Aso Volcano from the northwest.

5: +* y m ;<:If'+f R>g'NO
PQ@ !"#& zd - km vb{| ()NO}5 NO~NOH7 A&'*& ./ +32. I 01234aFig. ,. Distribution map of products of Late Holocene monogenetic volcanic activity in the northwestern part ofthe post-caldera central cones of Aso Volcano ; modiﬁed from + : /*,*** topographic map “Asosan” publishedby Geographical Survey Institute. Solid circles show localities of measured stratigraphic sections. The distribution of lava ﬂows is taken from Ono and Watanabe (+32/). Latitude and longitude are shown by WGS2..

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* *.3 km . ῍ed*nqrs

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eAHI2»µ<z!.^#8
A¢£ (+*YR-/-)_¢£ (+*YR,/-) +¼41®()½J-

067#

Fig. -. Stratigraphic relations of Komezuka lava and tephra layers in and around Komezuka Volcano. See
Fig. , for locations of the sites. +.C ages at the A3.+2 section are from Miyabuchi and Watanabe (+331)
and Miyabuchi (,**3). ACP+ : Aso central cone pumice +, KsS : Kishimadake scoria, N,S : Nakadake N,
scoria, OjS : Ojodake scoria.

*+,

222

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

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'!  @  %cp' 1

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FG u65r!FFMK!2-9#vw(K!;L ,* cm 7x%9y=zTV (/ Y - / +) 8b{{( v9w(8A (| :91

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'

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K!<=> )L!67klb2 ?8N

(Table +) D9EF8G%HIJUV (+*YR./.)UV (+*YR//0) 8KL!M ./* C 8 +./ M (Yoshida, +321) + : +* <=> NZ -., cm ; $O?='!g$\ Af$!BC9  !)9UV!345"#$ S +0 cm 8A

PQ

G K!)L%9S( ,/ cm !TUV (+* YR , / ,) TW

H£¤¥¦§¨36© -*1* 8ª«\ K!:TX N+!E! QR'"#$%&'? 1 p\ )<=>`! A30+,

¡R!¢h X S:TU" V¬­9 Fig. . %®b FG8 B!¯°±@
E% -²Wp p«\³=´3µ%cp'-C?@ %F9 <=>!)9¶UV!345!4.?=' PB@ 'f >

"#$ S +1 cm ?AG K!)L%9S( -. cm 4 9 SiO, cR2? /-../-.1 wt.ῌ !·Xf5!TUV (+*YR,/,) !TWX VY!¸%MG -¹#f8A«\ O  B ' f

%:º' ?='\ K!TWX9 N+!"#$%&' (Fig. -) (% )
<=>`![9 +** m 7x%L"b A 30++ ?@!

>

4 9

SiO, /+.1/,.- wt.ῌ 'f9 SiO, /+.1/,./ wt.
ῌq'E·Xf58A«\ 2'!:TZ9 »\%& (+32/) ¼»\ (+323) %]½('¬­

Table +. Whole-rock chemical compositions of products of Late Holocene monogenetic activity
in the northwestern part of the post-caldera central cones of Aso Volcano.

-./0 1$/

223

23456&789(Fig. -) :;

<*= Beta Analytic >?@9 ABC&D*E

AF&GH9 IJ9 KLEM&NO?P9
 NO A31,+ QR A30+, QR6?S+* b TUV ?W * A*3+- QR , R6X
YZ[:; (AMS)?W*\]9 +. C ^%? Libby _`a /,/02 &P9 d +-C ( +-C/+,C) ?W,bcd:



ef

gD"*+, h? Beta Analytic >ijklmn&

+  jklmnopqrst9* IntCal*.
(Reimer et al., ,**.) &P9
Fig. .. K,O-SiO, variation diagram of whole-rockchemistry for Holocene monogenetic volcanoes
and Nakadake Volcano. Values are normalizedon the basis of total+** wt.ῌ.

A *3+- QR1ygzy1y

yrs BP (Beta-,0*+-*)  ,,10*.* yrs BP (Beta-,1++.*)

1 SiO,  /+., wt.ῌ  ¡¢£[!&'9 (Table ,) &   , -.- cal ka, ,.3 cal ka !, hux9*+,g g?W~?), h,{|t[/0}

  -,*1*.*+~  +.C g9*+,

Talma and Vogel (+33-)?W,Vuvwx&D *+,

 1c
+,,**0* yrs BP (Beta-++-/3-)  +. C  +.+ cal ka ? ¤, ¤? 1c5
 +.C  +,,3*1* yrs BP (Beta-++-/3.) /+.

C 

  +.- cal ka

1/0$/&? , ¥ b/0$%6&789

+.

C N

0

O&\]9 0ῌ+

 

1¦234 A 31,+ QR 1§¨m!©/0$%   $%

&ª~«¬{|t[/0} ­ +0 cm c?

®¯?5g¯9*° !±²³g9 ´,­¤ ,/ cm 23456&78

 , ¥ $%´µ¶g·¥,g

9  h

A*3+- QR?¸+* 1ygz¹+ º ,**/  $%  $,{|t[/0} 4

%g®¯9* 5±²³g9234 56&  ¤?

1¦»

, A 30+, QR 

et al., +331) 1yc¸W¼c5g1&ª~½«¬{|t[/0}

 -.- cal ka  ,.3 cal ka  , b

Table ,.

!"# $%&' ()*+, (Okuno

Results of +.C age determinations for buried soils in and around Komezuka Volcano.

&'(

224

)* +%# , $ -.-,.3 cal ka - !

 ) *. $/0+123"$4

67#8

,5$ / ,+ )* 9:;< , $ -.- cal ka

0ῌ-.=>$
#K +L:MNO+.+ cal ka VWX /Y4)



? @ABC0+9: +.C `7$



*@ABC*

D2EFGHI !,J4

P>"#I,Q$R S%R,+TU,5Z 

[\&]^,'(,5$_9@ABC.*$

+ +*** aLb) +32/ 4#+cd\*+e,

$4 .D-+./,5 /

f[gh/ ijBkgl*0#$ +.+ cal ka

Y

N + 

1 +33/ ? ,+@ABCHm2#3no #4 , $/ +4MNO

*+]VWp^,5qcd\ r6#

@ABC*

K 8<9se/@tuvNBl, 

L:MNO  75  Parı́ctin 

!"# %K:@ABCH;.w

Luhr and Simkin, +33- x /y ?0"#$, zY @ABCH{#+8<9</ >, /+V~/  @ABCH ?

$   @+

) * @ABC ) V;?! 8#VY{(

H{#.

A 4}=>$4

+ -.- cal ka -+9XS%R
B  -.- cal ka(-.0 cal ka)

Y + E`7) *x|

@ABC\dt +6K# ^ L@AB

CHI0p^,5qcd\ 6K#4 / se/@tuvNBl, $D*  +33+ ; &' +331

A#$

,+ N.   -.0,.1 cal ka CD>$ (Fig. -) N.

,$*E-)F# SiO, GH++Rm b)I +33/ / S%R

9~ 6K#$ (Fig. .) 

@ABC*) *J%$Q$R*E+ /-../-.1 wt.ῌ0ῌ,  !

 SiO, GH.G>$  S%R+K:L>$L@ABCHI+Q$R M

SiO,  /+.1  /,.- wt. ῌ %# N ~  + !"#$  ,**+

 %

SiO,/+.1/,./ wt.ῌ

 VWOF# P;9 P#$7,+ %4,,$ S%R -)F#++ L@ABCHI{# 0!>$$  S%R,+ijBkgl J%@Q,+L@ABCH9:cd\.

$R ,+SJ9+J4

>$4
$4

,5Z L*ET9 C  .+.

,5/ L@ABC @ABC+%## +1 cm +0 cm ¡¢V¢V£Utm2# %L:+XYMNO  N+  !"#$m[2#$\©$ 4VY L@ABC.2Yc
d\ A30+, ]^@ABC.2Ycd\

 A31,+ ]^ +0$4

r6#(Fig. -) ^ L@ABCL: +1 cm

@AB ^  @ABCH;;U b
~

) *H 44 + 0

F#,  2N~,+VWW¤@ Z¥¦§¨§ * !"#$
L@ABCH SiO, GH+ /+., wtῌ ,OF#.G$ 1ª«¬,+ L*EL9­®.¯/,5/  E
FGHI !"#I` SiO,
GH

>$ YP #W4

CL: +0 cm :L>$XYMNO°_ +%$ >$  L@ABCHI+2±## +.- cal ka

ab+.+ cal ka , W 4#+`cd\

* L².c"$³´  dµ¶,  4#·/ L@ABCHI+

¹Mº -.- cal ka -,+/ A#$ L@ABCHI+$/# @+ L

9¶ !"$  ·¸xef$/+g/,5 4h 0+12»¼]Q.*E­®.
g/½¯>$ij$ ῍&K&kl>$mn@ABCH/$ 

aL.^ K$  D2E,J4%# >M /eVYO§¨§V$"#+  . cal ka Q$        ! 

-.0 cal ka "    % &'(-.- cal ka   )*+,- 

 #$ )./01 )*+,- ?@'% @A BCDE !F"GA#AH$%9I % $(AKK(LM?@NO%8P'QM$
1ῌ ῎ ῍ ῏ !] ^01012  Z
698F%d %  )   e6-7 +.C 78ZfO%  egg6-789A &QhQ -,*1*.* yrs BP ,,10*.* yrs BP $D9: +.C E;9Q% BQ9

<Z=i:F-.- cal ka, ,.3 cal ka 

M!  )eg@E C!a$qr 

A -.- cal ka sF'%BM ;uv  @wBO%xIy|yC ?A

. cal ka J'      !

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 #

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