8 /. 9 ,**/#

163ῌ῍ 

    +0  +,  ,!"  +1  +  +-!#Isotope-hydrological Study on Formation Mechanism ofCarbonate Springs at the Southeastern Foothills of
Kuju Volcano, Central Kyushu, Japan
Makoto YAMADA, Kazuhiro AMITA and Shinji OHSAWA
Beppu Geothermal Research Laboratory, Institute for Geothermal Sciences,
Graduate School of Science, Kyoto University

Abstract
Groundwater, which discharge as hot springs, mineral springs, cold springs and wellat the southeastern foothills of Kuju Volcano, Central Kyushu, Japan, were collected for
dD, d+2O, d+-C and concentration of dissolved inorganic carbon (DIC) analyses. dD and d+2O
values of the samples deﬁnitely show that all of the waters are derived from the local
meteoric water. Recharge elevation of the waters is estimated to be about 21*ῌ+,-* m by
dD values. The groundwater recharged at such elevations of the southeastern ﬂank of
the volcanic ediﬁce discharges as mineral springs at relatively high elevations of thesoutheastern foothills of Kuju Volcano and partly discharges as hot springs at relatively
low elevations there (Nagayu area). The characteristics of d+-C values and pCO, show thatmagmatic CO, is mixed into groundwater discharged from hot springs, the mineralsprings and some cold springs. Topographical distribution of concentrations of DIC andthe result of groundwater ﬂow analysis by dD values suggest that highly carbonatedgroundwater is produced by the mixing of magmatic CO, into the recharged groundwater at the southeastern ﬂank of the volcanic ediﬁce and the mixed groundwater ﬂow
from west to east and form the carbonate water zone at the southeastern foothills of Kuju
volcano. These highly carbonated groundwater discharges as the mineral and hot
springs, which are mixed with shallow groundwaters dissolved soil CO, nearby thedischarge areas.
Key words : Hydrogen and oxygen stable isotopic ratio, Stable carbon isotopic ratio,
Dissolved inorganic carbon, Carbonate spring, Nagayu Hot Spring$%&%' : ()ῌ*)+,-./0 1)+,-./0 231* 1*4 5674

¶L

164

+ῌ ῏ ῍ ῐ ῎

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

$%&'( )*+,-./" 01!"#2345 6 7 #89845 6 7 # :;-.<=>?@AB<C* DChiodini et al., ,*** ; Ohsawa et al., ,**, ;Evans et al., ,**,E F*"  GHI-J"  $%&'( )*&'(K

LMNO-.+,PQRST DUVῌ$W" +33. ; XYZA" ,**,E A"
G-.<[\-]AAT@^" GHI _F`*FSTb@^" 

aI-J +,

 =>cd-e?BfQRg

hijkl-'mnop" RJA (qkr +* km -sBt> u
ql-hvῌwx/" @op =>n( Xu]=>!y z(Dhv : -,***{/,*** !|" wx : r +,1** !|E  D}~ῌ" +333E F*" hv kr / km - +33/ !-

4*op/" ] BI@ hv q DFig. +E -RJA1" hiῌd\hBd-1n" ]u]QT

@ F*"  ¡¢y-n-£¤ ¥M¦)b/ DXY" +333E"
§RA@ ¨©*TA< 01

89845?@AB< Dª«ZA" ,***E" ¬ =>b.­HI®¯°±-J?@A-B F*" ²³  ´µ-J +,FSTB ¬+," opq

Fig. + Map showing locations of hot springs (open triangles), cold springs (solid circles), mineralsprings (solid squares) and well (solid rhombus) at the southeastern foothills of Kuju Volcano.

] /. ¼ ;,**/<

 X2Y»3" Z*["

 %&'\165

     

   !"#$



%&'"()*+,-./0, 
12ῌ 
,1 .9: ;Fig. +3  +2  4 .  56+   . 78

Table +< ="  pH  >-0 

;DIC : dissolved inorganic carbon?CO,;aq<@HCO-A@CO-,A< L<

DIC   

;+;+** mL< 3BCD" E-FGH ;IJK!LMNFGH :BAREX῍< "9:-0 OPQ"RST>- 3 U.FGHUU"V# ;/W< "$

-0 U-

  3BXC!YZ[H% ;,* mL< "&' $-0

DIC 3 (" \ CO,;aq< ")] Z^_` ;*a+,!
IM-+B< "-.-/1+b ;*a+,! CE-,-/<  0 c123"d -0
DIC 

 ;+-Cῌ+,C< 3 ;+L< " 1CGe_fgh+,+4

- SrCO- i56j kE"l_7m 89
-0 U- DῌH 

+2

> -0 

CO, n18":'

Oῌ O 3 oEpEq;ar-st3 /1<u3"+0 3=v>n wxyE d? ;z< .@- ;d?{;RsmpῌRstd<A+|}+***<0 kk. Rsmp, Rstd 3oEpE@ 0 =v>n"3 V-PDB ;Peedee AhZG1B<   =v

;SMOW<  -0

d+-C, dD, d+2O  C3oEpE*.+z +z *.+z.

3IX_n2

=v>n

"oEpE ~=v>n
0 kEx



Q ;Rafter Stable Isotope Laboratory,

Institute of Geological and Nuclear Sciences< .>-0 ! Table + "-0--+ 

 4 56 wx9:-D dD ?

d+2O ?nE ;Giggenbach, +33,<  Fig. , "-0 F m 

D'-G7 n DE  F

2I"eJGE   (w .o¡¢ !JxE

 H
;K£¤

w +330<0 w ¥¦9:- 3 \F 2 ;dD?2 d O@+*< "§>¤¨eJGE
+2 D©ª3«xE¢0 ->kEx \ 3F ¬­. d 9 ®EwG.LME- .
m F ¬­.
O.

),xE 0G7 m  =¯!oLM N

k °;6Pῌ± +33.<0 Qx ;,**-< 3  dD ?  m  =¯!A+.-1zῌ+** m«R²d dD ? m <³LM= H ;m<;m LM2<  dD?A*.*+-1HA.+.02

-0 S



 3 ´T. d

9:- 3 \UµVdF ¬­.

),xE . I¶·W.¸ 0 9:

dD ?m

LM2 Fig. - "-0 9:-  dD ?3 + (- = ;S+,< ¹¸A/2./ºA/-.0zE-0 S+, ?3 m LM2"

ῒ῕ΐ῔

166
Table +

Chemical and isotopic data of the water samples at the southeastern foothills of Kuju Volcano

Point
Name

Sampling
Date

Water
Temperature
(ῐ)

pH

d+2O
(ῑ)

dD
(ῑ)

DIC
(mg/L)

d+-CDIC
(ῑ)

Well
Depth
(m)

S*+
S*,
S*S*.
S*/
S*0
S*1
S*2
S*3
S+*
S++
S+,
S+S+.
S+/
S+0
S+1
S+2
M*+
M*,
M*M*.
G*+
H*+
H*,
H*H*.

,**,. ++. +0,**,. ++. +0,**,. ++. +0,**,. ++. +0,**,. ++. +0,**,. ++. ,/,**,. ++. +,,**,. ++. +,,**,. ++. ,/,**,. ++. +,,**,. ++. +,,**,. ++. +,,**,. ++. +,,**,. ++. +,,**,. ++. +,,**,. ++. +,,**,. ++. ,.
,**,. ++. +,,**,. ++. +,,**,. ++. +,,**,. ++. ,/,**,. ++. ,/,**,. ++. +,,**.. *1. ,*,**.. *1. ,*,**.. *1. ,*,**.. *1. ,*

+-42
+-41
+.4.
+/4.
+-43
+-40
+/4+
+*43
++41
+143
+.4,
+,42
+/41
+.4+
+.4*
+.42
+.4+.4,
+34+
++40
++4+
+.42
+.4,
.,4+
..4*
..4*
.,40

/42
04,
04+
043
040
040
14+
14/
14/
040
14*
24/
040
14/
14,
14,
14+
143
04/4/
/4.
/43
042
043
040
041
040

῎24/
῎24.
῎24/
῎24.
῎24῎24/
῎241
῎243
῎24.
῎24,
῎24.
῎14/
῎24,
῎24.
῎24/
῎241
῎34*
῎241
῎241
῎34+
῎34*
῎34*
῎24/
῎242
῎242
῎242
῎242

῎//42
῎/04/
῎/04,
῎/040
῎/04῎/14*
῎/043
῎/24῎/142
῎/-43
῎//42
῎..4.
῎/-41
῎//4῎//42
῎/14+
῎/141
῎//43
῎//4῎//43
῎/143
῎/24/
῎//4῎/24῎/-40
῎/04*
῎//4-

,*3
20
+*1
30+
2.
,+1
+2
-2
-.3
3.
+++
+.3
,+
,.
23
,++
.0
+*.,
3,3
3*+
00+
20
,/1.
,.+,
,/,*
,,20

῎340
῎+-4῎++42
῎+,43
῎+*42
῎+,4,
῎/41
῎04῎+,41
῎24,
῎+.41
῎040
῎+,4῎+04῎+243
῎+14*
῎24*
῎/4*
῎.42
῎.41
῎-41
῎.4+
῎+/4.
῎,4῎,4/
῎-4,
῎,4-

ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
ῌ
-23
,0*
+03
,0*
++*

Fig. , dD-d+2O plots of water samples discharged as hot springs (open triangles), cold springs (solid
circles), mineral springs (solid squares) and well (solid rhombus) from the studied area. The
diagonally shaded box shows the ranges of dD and d+2O values of andesitic magmatic steam(Giggenbach, +33,). Solid line labeled with MWL expresses meteoric water line : dD῏2d+2O῍+*.

» /. ¼ ,**/ ´µA¶·x$¸C[\]+V$_¨¦¹º167

Fig. - Relation between discharge elevation and dD values of waters from hot springs(open triangles), cold springs (solid circles), mineral springs (solid squares) andwell (solid rhombus). Solid line expressed in equation : dD*.*+-1H.+.02 is arecharge-water line in Kuju volcanic area estimated by Yamada et al. (,**-).



  Fig. , 

 !" dD  d+2O #$% &'(+$, -./$' + 012345?@A BCDE)(&*'

678 9: ;$<  =& >&FGHIJ KL&%dD  $MN0OPQRSF$

21*T+,,-* m?@0U ' 21*T+,,-* m VWX YZ[\]^ ;&(&% >

_ `_ ab c_ ,YZ[\]^  21*T+,,-* m 0deU $ If/$% 6 <0
U g/&  hilmn

_=& `_ !jAWX + hi ki

op0cqrst uvw0U c_ +$ 78g/$%-, 
Table + &xy_ `_ ab c_z{& DIC |} 6/~/ +2

T-.3 mgῌL, 00+T+,*., mgῌL, 20 mgῌL, ,,,20T,,/1. mgῌL;

! 6/~/ +2.3T/.* ..2T-.1 +/.. -.,T,.-D8;(&% Ohsawa et al.

,**,'[ F&  |},!' y'F/

6  CO, d+-C,/ ; ῌ[> +33-  &0O d+-CDIC,-T
+3 ; ῌ[> +33-  CO,

d+-C+,T,./ ; Fischer et al, +331 '

$< $% CO, ' /$0OW¡ ¢£¤54¥ D¦§¨¦©ª«¬'If/$%A  CO,  &0O­¬® CO, '¯°V$W¡
B CO, 2&0O

 CO, &0O¡A W¡ 0O DIC |}d+-CDIC  ¢± ²V< ' ³$%'¡V$Wm»¼

168

d+-Cgw

C+
C*d+-C*+***Cmagd+-Cmag+***+***Cgw

DIC 

 gw, *, magῌ CO,    CO,  !" #$ B %& '()*+"
d+-Cgw

+d+-CmagCmagXd+-CsoilCsoil+XCgw

῍

CgwCmagXCsoil+X



X ,-.

 soil῎&/& 0 CO,  1 2345

ῌ ()6 7+"
84&9:!(;<=>?@A*B!+)C DE F1G+&9: &H IJK@LM+)CN 7O  CO, PJ )1Q RS TU
 VWXYZ Z$..1[  \Y +330  0 CO, ]1$PJ)1Q ,*[ +3^,-[ : _ῌU +33- `+)C D+" #$ DIC @
0 CO, ]1$abcde pCO,  *.*+ atm ,-. *.*- atm )1 ῏ (`Qfg1$`+)C D+"
C



l
hpCO,
RT

C

῏

DIC  l

Ostwald :i R!" *, B &@n`Q

VJji Tklm pCO,

abcde CO, o]1$abcde  7+$M pVe abcdo)q1Q`+ pCO, : + atm rj1$" sZ@ tmuG1C&1Qtm)1Qv!+%& ;?>w + ) tm)xmC&
1Qxm)1Qv!+%& ;?>w , Cy Z++/z ` ;?>w ,;?>w +  Ostwald :i@v!+m .*z )1$)D@ +/z @!+m{(YZfg1 m  Ostwald :i`$"84&@9!+9:(YZLM$&9: &H )|}~>? pCO,d+-CDIC
@1$C Fig. .

7+"

Z ,***WX CO,, He PJYZ m{ca  7+) 1Q`+C

Fig. .

m `&H8@s*`"  pVabcdeCm@ Q@s` -h+*. atm

7+$Mv@WXCO PJ x` CO, C@1$ 7+)y Z+" | mv

CO, WXG v1Q,O S`PJ  C  OG+@7+" #$ @n`Q C¡Q,+-

O  &H-O¢£x`PJ  1Q`+)!+ A 7¤G"28]~m),-.¥{caC CO, )0 CO,

& ¦6$) 1Q`+C §&H O@ pD*¨C*`$M A B `&©ª«Q`+Y@n`Q ¬­®@ D*`" 

{cax`

!K"@¯#1Qo$"{ca" Fig. /m°±) p²U$%³&'x 0**^+,*** m ´@ +,*** mgῌL ªxC{µ1 ´¥ ()´ 21*^+,,-* m)\¶S*+"   CO, C()´·* 1Q`+) 1Q,O xca ()´· ¦1Q`+)¸± ¹1Q`+" #$ mºM+) p

u /. v =,**/> :ef&ghVijk-lmnodp,-3JKqrst169

Fig. . Plots of d+-C of dissolved inorganic carbon (DIC) versus pCO, of waters calculated from pH, watertemperature and concentration of DIC. Solid (black and gray) and broken lines show expected mixing
relations between magmatic CO, and soil CO, in groundwaters. For detail, see text.

Fig. / Topographical distribution of concentrations of dissolved inorganic carbon of waters
discharged as hot springs, cold springs, mineral springs and well. The diagonally shaded
area shows main recharge area of groundwater.

 2**+,*** m    -. +!"#$%&'( )*+,-. /  012345673&456)89:; <)=Fig. -> 0123&?@#45A BCBDE CO, FGHIJK/#?

<-)LM-NO <-. #P  &,QR6S 2**+,,** m[ <-.

\ S+*

JK/ T RUVW

X'(Y-?),-Z=Fig. +> ]Y^_`a =S /** m> bc 3d

b^»¼

170

 ῌ

 ,**.   !

"#$%&'()*+,#-.+,/0 1)#23( 4
56 , 789:9;<=>?@ ABCD B EFEGH CO, I#J6
" KLGH CO, #J6" !M3(N3 !OPQRSTU0!
VWABCD B N3 Fig. . XYEFEGH CO, #J6" M3Z3#5(S[\ ]^

_ `ab^

c SdeKLGH CO, #J6" Mf#g\hij.#5 U/S `ab^Sk( b^ lmnoSpWWV/q Fig. + rstugv PCO, wx
Fig. . 0`a|}~o'6

NySgz{[ Fig. -,!SS8(KLGHCO, #J6" Mf# [Z3oj.#5 7\ `ab^

-oU06" .o[itNyo6" !U/SM
f(Sgz:9U0p+,/0  ' SO6+,/0* S+* -W/(^!`ab^ g\pb!i 8p  b : /-.. DIC : ,0-* mgῌL  o" Mf;<=>
8 #5+,/0  [tNyo6" Mf3#p6S S+* -oU06^S7p QR [Sg ¡#¢?£ !¤\ ¥¦QR§¨6-- 





0o+©ª«#pS ¬$ ^:9­®¯°±#²S³6
! Fig. 0 o¤ EFEGH CO, to" SMf #:9 ´KLGH CO, #J6" Mµ\ ¶·tyS¸¹( ]^´% EFEGH CO, JSg\:9U06 º\#'Fig. 0 Schematic representation of formation process of carbonate springs at
the southeastern foothills of Kuju Volcano.

U /. ¼ ,**/ 2G/»75+hijO -*+3,bc|?
 


171

  ῌ  !" #$%&'() *+ ,-.ῌ ῎ ῍ ῏,ῌ.,ῌ/0ῌ,12 3412567
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Chiodini, G., Frondini, F., Cardellini, C., Parello, F. and Peruzzi, L. (,***) : Rate of di#use carbon
dioxide Earth degassing estimated from carbon balance of regional aquifers : The case ofcentral Apennine, Italy, J. Geophys. Res., +*/, 2.,-ῌ2.-..
Evans, W.C., Sorey, M.L., Cook, A.C., Kennedy, B.M., Shuster, D.L., Colvard, E.M., White, L.D.
and Huebner, M.A. (,**,) : Tracing and quantifying magmatic carbon discharge in cold
groundwaters : lessons learned form Mammoth Mountain, USA, J. Volcanol. Geotherm.

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Fischer, T.P., Sturchio, N.C., Stix, J., Arehart, G.B., Counce, D. and Williams, S.N. (+331) : The
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Volcano, Colombia, J. Volcanol. Geotherm. Res., 11, ,,3ῌ,/-.

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Giggenbach, W.F. (+33,) : Isotopic shifts in waters from geothermal and volcanic system along
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Ohsawa, S., Kazahaya, K., Yasuhara, M., Kono, T., Kitaoka, K., Yusa, Y. and Yamaguchi, K.
(,**,) : Escape of volcanic gas into shallow groundwater systems at Unzen Volcano(Japan) : Evidence from chemical and stable carbon isotope compositions of dissolved
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