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 ,  03ῌ11 ῐ ῏,**. 
MM 

A B C D @E F G H ,MM@I J K L

,**0 : ++ ; ,+ <=> ,**2 : , ; ,2 <=?Geochemical Observation on the ,**. Eruption of Asama Volcano
through Analysis of Water-soluble Components on the Ashῌ and Jun-ichi HIRABAYASHIῌ
Kenji NOGAMIῌ, Shin’ya ONIZAWAῌ,ῌ
Monitoring of volcanic gases will provide us with important information on volcanic activity and contributes
towards reduction of volcanic disasters. However, approach to an erupting volcano considerably involves danger.
Analysis of water-leachates of pristine ash is also available for estimating composition of volcanic gases. It is asafe and e#ective method for monitoring of eruptive activity without having to use a particular equipment.
Asama volcano lies about +/* km northwest of Tokyo and it is one of the most violent volcanoes in Japan.
After about ,* years dormancy, the three-months-long eruptive activity commenced on September +, ,**. withvulcanian explosion. Non-explosive strombolian eruptions with ash emission followed the explosion, and newlava e#used at the bottom of the summit crater. After that, vulcanian explosions produced ash fall and bombs atintervals.
We examined change in water-soluble F, Cl and SO. contents of volcanic ash in the sequence of the ,**.
eruption of Asama volcano. The ,**. eruptive activity was divided into three phases according to the mode of
the volcanic activity. The ash in Phase I issued by vulcanian explosions before the e#usion of new lava was anaggregate of rock fragments altered under acidic conditions. The contents of water-soluble Na, K, Ca, Mg, Fe,
Al, F, Cl, and SO. were noticeably high. This is mainly attributed to ﬂuoride, chloride and sulfate alteration
products formed by reaction of rock fragments within the summit crater with HF, HCl and SO, in volcanic gases
before the ,**. eruption. Although molar ratio of Cl to SO. in the ash leachates was not equivalent to HCl/SO,of eruptive gases in this phase, increase in the Cl/SO. in the ash leachates in the late of this phase suggests that
volcanic gases signiﬁcantly became hot.
In Phase II, new lava e#used at the crater bottom and the ash was extremely fresh. The contents of thewater-soluble components of the ash in this phase were signiﬁcantly less than those of the ash in Phase I. The Cl/
SO. in the ash leachates was equivalent to the HCl/SO, ratio in the plume observed by FT-IR. This result indicats
that water vapor in plume did not condense into droplets of water. Owing to reaction of the ash particles withvolcanic gases at high temperature without condensation of water vapor, the contents of the water-solublecomponents of the ash were very low. While, the F/Cl values of the ash leachates were signiﬁcantly higher thanthat of plume, which was due to selective ﬁxation of HF on the ash particles.
In Phase III, the contents of the water-soluble components of the ash were clearly more than those of the ash
in Phase II, which suggests that the lava e#used in Phase II was gradually altered by volcanic gases. Althoughmolar ratio of Cl to SO. in the ash leachates is probably not equivalent to that of the eruptive gases in this phase,
the Cl/SO. in the ash leachates mirrored temperature of the hot region at the crater bottom.
Key words : volcanic ash, ash leachate, volatile components-11ῌ+1++ 0.+ῌ-0#$%&'()*+,-./01()23
Volcanic Fluid Research Center, Tokyo Institute ofTechnology, Kusatsu 0.+ῌ-0, Agatsuma, Gunma, -11ῌ
+1++, Japan.
45 : -*/ῌ2/01 6789# +ῌ+ῌ+ !"Institute of Geology and Geoinformation, National
Institute of Advanced Industrial Science and Technology, Higashi +ῌ+ῌ+, Tsukuba, Ibaraki, -*/ῌ2/01, Japan.
Corresponding author : Kenji Nogami
e-mail : knogami@ksvo.titech.ac.jp2 3 .

70+ῌ ῏ ῍ ῐ ῎

 4 5 %&69/:;<7=$+222 %>&'?

78!"%#)*+@()7 *A/ +BCD,E-. %/0F =$(G1*12) 34/0

G& 5HI

F (+8 /9:

L +0 A(BKCD%MC6 NOPQER";<K:

=$/STD*+ 7 F=>? @
FUGV (67J +322ῌ+323 % 7

R(BKCDWVS) CD+322 % +,+323 % - L / AC%

HXYI%&6 7 Z[ R"R=\DF]JK+@ (Katsui et al., +33*) '.L 7

+%^GG-/MN_' 7 F `+

HXab O?()*O-QR/NDdeS fgT =?U=

+332$iX-YD 7 Z[

H,O  CO,, H,S,

1*:FjZ([<@G%&6 (Ikeda et al., +33*)

SO,, HCl, HF \kl)Z[He, H,, Ar, N,
(+300)

 Iwasaki et al.

abo/7 Z[ cpqrs+*

7 Z[Sl)Z[S ( KtgT1*g)*+ ND
,E l)Z[hKgT/ +** ]T

CO,, H,S %&/ gT/

(Bc%+@ 0 P

  V"ab()

78 ! h W /7 l):Fm]%# )@()7*A^4_G/_`?BCD*+@nH
D*+ 0 P +332 d1* ()
SO.

eu)G

+/

7f7

Z[ HCl ῌ SO, .)+33*) ijJ: ) 0 P +332 R"R 7^kx^V()@ C@ lymz{J'D|E/}-% /0 %n6/~Jop1* K/qWr%+7 f
7 Z[(tru%+@eJwx(Z+@7s 7/D#)@/ +uDG(BKCD%&1@
+v P,**+ 'ab() SO. ? VZ[$y/STD*+-:d)1@/

 =|  (FT-IR) ,*** %D#)@ .  7X ()(f$y%X

+3307) NO +332 % ,*** %  % w :  { 1*}~7 Z[

 Clῌ

?%M\D@ 7[vw (Katsui et al.,*_`D* SO,, HCl, HF /BCDX6

7+7 %Z[() Cl ? zV)@ 

SO. /}1@ 7%

 Clῌ

+332 %C%ab 

6 5HI Love et al., +332 ; Mori et al., +33- ; Mori andD1@ 6"r9(5 _hG=\DNotsu +331 ;   ,**/ ;  P +331 7 Z*+@ 'D[S : /HDX1@

) R"R^4}gZ[/zV)@nHD

$y =,*** %1*7m/\C%DN$pq/ fYD xdeS : (H'*+ +v P ,**+ 'Dpq

G%&/ 6G7 =$!_@) ClῌS 

7

Z[S

ab(

:d(H 7F

(% 'D 7 Z[( Kttr !" #$ %&'()*+

u_d4x6G)*+%&6 FT-IR /6F J

7 Z[=$ 7 F  !".(7 )*D*+ +3++ % Aa%*XGV+x\D

7 =$\/\D "0i

7H1*=\D7 b7 Z[ ¡($¢\1*7 =$£/MC1@) F, Cl, SO. /BCD*+' -D*+  ,**/ +3-- % ¤:Ve/0¥¦\ ¡ 5HI ¢£ §¤ +3-/ +3// % +* L¨4R©)*7 =$\/¥¦§ª\D 3"R 7(K<*+«¨%

49/:;<¬eJ7 ¥¦=$­.`1ab()/xT@1* c\D*+ 5HI  +32, ; ®
© +3/1 +32* ; 0¯ +33. 7 Z[ῌ7 b Z[ªT 7 b«° M¬­ ®±fgTU1*
()

?

:

_/ ()³fxVK+´µ)*+@ ClῌSO.

²¶ HClῌSO, *+ (,**-)  %¯ .* %¯F,*    +3-*

/FD% LA@

7)*+@ NO +3/.+3// % +3/2 % +30+ %
V 7/&1@/+3/* %¯ 0* %¯F °·,-.)*+'/0  (+31/) 1¸)*±¹%&1@ +31- %( (+3-/) *²\D@ º CD~O+fx (% B ¨R"R 7/ +32, % +32- %»¼ +33* %) ClῌSO.
'V- ½CD~³+\- () ClῌSO.

CD~ijJ: )*+'/ Hirabayashi et al. (+32,)
1*\D@ 'D¶)* (BKCDHXgsCD/&1@G +31* %¯3* %¯

G7 F±¹°´&1@,*** % 3 L¨a /0F

ffFD°´%µV)*+@ ,**, % 0 L 3 L .fJL +.** (

,**. 123$"456789 !"#$%:2;%

71&<"'( ,**-  , #= .  . >)*+?!+@

(  ,**-  1 #= +* B +0** >

CD" - ,**.g EF-F12./0#=

&<"'(%," - ,**-c ./

-KL5C6,78 ,**,  0 #=-F21239MN JR :;<O9CGHPQ  R,**-  / S=> 0., ?!"7

8C

-KXDYZ%," - ,**-a, c H +* 7C -** RCI%,-0 +32-  .  2.* km 21231CGH4IJ, ./-* km TU@ V/TU@ A , WBCPQYZ GHTU[\E+]F^%G,  (#= . 1J_ ,`9 * Ja#=bKc.L>

 ,**-b SO,   +32- AG +33/ a

R:R

RC

4I:PQPQ  g_ 3  +.

+**,** COf ,**, #= ,**- ;%h

.**+*** Ri  g_

kNlmnoI%,"    ,**.

A,

GdD] eMCN_GH( #

RC

 SO,  jSRi 3  -+*,*  +-/*  3  2,,**  ,0**,**.  + AG TUV p?

 eZ +31- q +32,ῌ+32- ;%hW%,  . AS6 .,* X

 SO, Y%,,**.

- ,**.a, b, c, d r;%;

1 

S6 /,. XY  1  ,/
 ,0 #a^`_ 3

2 km -uv_wB`bYZ%,"z6W{|C -* cd6}e<=
Z%," }7YZ

3  +/+***  

Z9#=0!"   s][!+@

 ] t\  ,**/ ]*F/$5 
#=0 xya-( H+0J~Z f" m7+ % ,**,  3 A,CD7./C CF%,"e" - ,**.e R  1 g GPS a-7M:XDYZ%," h  ,**/ R  Hi#=1jkN7YZ l:

YZ%," mh  ,**/ n 2 B

#$%&'()*+ %

+1 YZ"oYZ a- 0!"V7YZ S +1

6 /1* RCXY z6W{|C) =

!"7 +2

} e<=Z%,a;%C:%^/ῌ/^/q- ,**.fe]2;%qq; 78D": ,**. 3+`_ 2  , #s( g_- 1~%GHq*t@:0./0 s][YZ  \uC -PQ
GH !"#$%:2;%:a ,%|£!"

3  +2 ,-- ,**.g e

iAGr;%-%,  3

: ,3

:0  +*  +*oW*(0 - ,**.g, h eZ=Cvw@qxy¡@ z{1 ¢./.
./CGHD, ,**. 

iRC-,

GHD] uv_@ACeZPQ : ,2,**.  3  +pqRC-,  g_B0r ,¤ZBd}¥

B./0 +*  +3

oW*t@W

GH^0¦~@quv_@C7YZ -

`_ 2  , #  ( :0 ,**.h ,2oW*t@s§ 12../,/_ kNr;%-,%,  ++  +.

km bKcvw@D" /¨©ª6vw«2/3 # 3  ,3

7BCBe<  sN_#=2oCF"bKc /3 ¬vwz{

vw@9qz{1­GHuv_@ACPQ  g,* A,:0 oW*(- ,**.i t\  (,**/) +": 2

Sx®#=..- km C 1./ cm ¥ ¯v#=°7±  rYqq GH7

CGH B²³% / ¢µCF ##=9¶´#$%GH4IJ, ´A =N g_ 12/>#=.

/>#$%GH4IJ, ./3 km xy¡@.uv_L5CGHPQ  12¸./ km ´

t·@ACGHPQ  e+ %/
/./qGHD #=j ,/¹3qº +.0 ¬»#=xy bKc¼½

km A¯CBGH#$%XN® cm 2G%, #%," t\  ,**/ e_ SO, ,***,3** :,78-%t\

 (,**/) +Z? 2Sx®#= . km ½C+* cm ¥

 12C2A¯RC,

DR]p #- ,**.i +,  3

e:=./0 ()*+, 

72-.

Fig. +. Map showing spatial distribution of the ash sampling sites () in this study. Star () indicates thelocation of the summit crater of Asama volcano. Numbers beside the sampling sites correspond to thesamples listed in Table +.

/ 012 ,**.j 34 5678 49

:;<=>? @A!BC3 DE3

FGHI JK ,**2  + L MGNIOPQRSTU

7/3BXPXUYZ (Table +)X[ QR\ XB] ^ _4PX
A` gh cXi j!k

rst s# $%uv$ (Pwde3 \dei Fig. + |FQR + kg VW?

QR\ `a bcdeIf] 
XB7l"Umn X oDpqIC3
x&y (LOI) 7zIYZ4 FeO

N

Fe,O- {}~'`z XB7(3BXPX D Table , |F- 

D7FB)\*+X 7 , :;<:;<pq -I7

. ,**.  8 .S /~XB

-Barnstead NANOpure ῍+ AW3] Phase  Phase ῌ : 

+X +** ml v''QR\03

'`14NGNI 3 L + 2 +. 2 Phase   2* !"#$%&'

῍ : '`1493BXG 3 L$(I.3FG 4  vv +/ 2 +2 2 Phase ῎ : Phase ῍56 3 L +3 2 /C 5¡I5¢3 IC63] D3

£¤¥t

Na, K 7¦§¨n Ca, Mg, Fe, Al 7

.ῌ+

Phase I  

3 L + 2S +. 2

6R7l©Rª

78P«¬

ICP nD Cl, SO. 7:;<­®¯$° F 7

9§ /¬9§ ±²³k´³Pw :3«IµTsuchiya et al. (+32/) AG$¶·¸¹¶¸~º;U»BX ¼-½ ,**/ 

Phase

6R7½

Table +.

Contents of water-soluble components of the volcanic ash issued by the ,**. eruption of Asama volcano.

,**. 

 !
73

&'() * 

74
Table ,.

+,

Chemical composition of the ash issued by the ,**. eruption of Asama volcano.

 Phase -./01

23 

4  56

SO. 789# (Table + ; Fig. ,) =$ LOI >?@A8 (Table,) FHI6 

:; 3 < + B-CDE HFῌSO,, HClῌSO, F&G$

J0 HF, HCl 8KCD LMN2OPQ RS$TU +31-93WX-. YZ[ +31- \ +32,ῌ+32- ]^  3 < + B- SO, L_`9ab c-. YZ

 +32- def +322ῌ+323 -. YZ[ +332 g hi TU +31- B-jkjFLl$.ῌ,7 VCDKF&G$ !"#$ % 
Phase II 

3 < +/ +2 -.mn9CoDpq

rs

Ft99 E[ ,**/ +32- 7uv/$CoDw mn9CoDxy= ,* UzY{

9!|$"#:}79 F +1 $%B- CoD~y#$ &7FLw$ +0 ' LFt(

S

"Sv

9F$ 3 < +* + ,FL
[ ,**/ ; .[ ,**/ J0

-.m$&G$jkj)-^ *

+*[ ,**/ Phase -.5= 1 23 Phase ῌ- Phase -./ '\0 1$.79 (Table + ; Fig. ,) +31- LFM

-.Fmn9709

XCD/#N22 RS$ 

H$ YZ# -.5=$41 23 ¡ 

3FN24#¢3$1 2G£)-^¥¦  =$

456

-.1 2 F, Cl

7 HF, HClCDFM7L$

J0
°?

 
5%  1

(Table ,)

 (+31/)  +/*2/* 5¤CD 6«77¢39F KF9 ¬ab^
±1

7$  ,** BQ

2 Cl Hab CDE1²­

³´/ µ¶1F·9 ¸:2

3 < +. -. 3 < + -./041

3

 +32- =$ LOI >?

7 8§c ¨© ª 0** B&1 2 F, Cl

56"8KM'8K­F®¯$1 23

2

2 F, Cl  abFºH

(Table + ; Fig. ,) F ῌ Cl ºH9F Cl ῌ

E1²­F³´^

$

 SO, 1¡¹

»F@A8 HCl F1;¼½ »^ $ HClῌSO, 9

(Burton et al., ,**+) F -,**. *+, &-./012  34 5  &,6

75)789 ClῌSO. ):;'<=> 3  +0 ?# FT-IR 

>@ HClῌSO, ) * ,  !A ,**/ BC D
 Phase EFG @H (#+*, #++, #+,)
 ClῌSO. (*.+*.,) IJKLM9N

 DOPQ> D Phase ) @$&,RS$TU)VW9'Q(XY Z(N &,[&,RS\)]^_`9'a:bcD(<=> Dd
_e'Q(fghi 3  +0  ?#@ HF ῌ HCl ) *.*-  FῌCl I)j( !A ,**/ _ 

DCklm:Q( (Table + ; Fig. ,) no(+302) -pn (+31/) ) HF, HCl

q:b U

RS&,r\stQ> F ) Cl Ckru
v;whxyBD >Q9N-C D
>OP) HF HCl

q:b @_&,[\9z{ HF ) HCl |N&,}~h
D 9N Z(N @ FῌCl Ck
 FῌCl _Y) !A (,**/) k

9NH@$ HF _&,  ~

9D<=>Phase ῌF (#+-, #+., #+/, #+0, #+1) )EFG @H (#+*, #++, #+,) |NSO. )e9 F, Cl _9;789N (Table + ;Fig. ,) DOP) \9&,RS HF ῌ
SO,, HClῌSO, _9D

Fig. ,. Temporal change in contents of water-soluble
anions and F/Cl and Cl/SO. molar ratios. Solidcircles, open circles and solid diamonds indicate
the ash samples collected in Phase I, Phase II andPhase III, respectively.

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Phase III 

3  ,- )¡¢"#'O£¤[$%O£¥ h eR¦S¤[q

 1Q>fgh&,RSb 1)b OPLM9N"#$%&'( ++  +. ) Phase&!gOP&Q> D Phase )§¨ 5ῌ|N12© )9; 19N'_9r'(BXY )¤ ¤Bª¢

LOI )«Q)B_789N (Table ,) i +*R¦S¤[¬{kD ,2 

&*e9Nn)o ,**/ +*  ,2 ) Phase ῌ|N

SO.  ­®¯°  ±; (Table+ ; Fig. ,) DQ> D>OP) &!r&¤_s² D 9N DF ClῌSO. ) *.-+*..+  +*  ,2 

-C (Table + ; Fig. ,) &!³9r&_&,RS(N´ |N+9N-C (Table + ; Fig. ,)

¤9µdND

9N
!

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Ck9N_ ¸¹)«QB Dº_ kB &!":b)D & Cl ῌ SO. ) Phase ῌ »# ,**.  ++  +1  ) .0. 9+*  ,2 

|N9;9N (Table + ; Fig. ,) DOP 1Q>fgh&,RSb 1)) &,RS HClῌSO, _ +* E¼9;

b

OPLM9N ¸ + ½+# ,. 

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B-

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sK  E ½?m¶CD.67Z=4s ¨ 7 Zῐ ῕ ῔ ῑBurton, M.R., Oppenheimer, C., Horrocks, L.A. and Francis, P.W. (,**+) Diurnal changes in volcanic plumechemistry observed by lunar and solar occultation
spectrometry. Geophys. Res. Lett., ,2, 2.-ῌ2.0.
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 (+32,) #57/0;<A=/
0G' opqr& ,. B-+ ++ῌ,*.
Hirabayashi, J., Ossaka, J. and Ozawa, T. (+32,) Relationship between volcanic activity and chemical compositionof volcanic gases
A case study on the Sakurajima
volcano. Geochem. J., +0, ++ῌ,+.
yzl 
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` | (,**.) %F0B  SO, 01 (}/0C ,**. &p +3/.
Ikeda, Y., Katsui, Y., Nakagawa, M., Kawachi, S., Watanabe, T., Fujibayashi, N., Shibata, T. and Kagami, H.
(+33*) Petrology of the +322ῌ23 Essential ejecta andassociated glassy rocks of Tokachi-dake Volcano in Central Hokkaido, Japan. Bull. Volcanol. Soc. Japan, -/, +.1ῌ+0,.
Iwasaki, I., Ozawa, T., Yoshida, M., Katsura, T., Iwasaki,
B. and Kamada, M. (+300) Di#erentiation of magmaticemanation of gases. Bull. Tokyo Inst. Tech, 1., +ῌ/1.
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 -, &±A²C +*+ῌ+*/.
¬a (+32*) /0G'³ A-B  ,3ῌ.*.
Katusi, Y., Kawachi, S., Kondo Y., Ikeda, Y., Nakagawa,
M., Gotoh, Y., Yamagishi, T., Yamazaki, T. and Sumita,
M. (+33*) The +322ῌ+323 explosive eruption of Tokachidake, central Hokkaido, its sequence and mode. Bull.
Volcanol. Soc. Japan, -/, +++ῌ+,3.
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Love, S.P., Go#, F., Counce, D., Siebe, C. and Delgado, H.
(+332) Passive infrared spectroscopy of the eruption
plume at Popocatepetl volcano, Mexico. Nature, -30, /0-ῌ/01.
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12 ,2-ῌ.0-.
Mori, T., Notsu, K., Tohjima, Y. and Wakita, H. (+33-)
Remote detection of HCl and SO, in volcanic gas from
Unzen volcano, Japan. Geophys. Res. Lett., ,*, +-//ῌ+-/2.
Mori, T. and Notsu, K. (+331) Remote CO, COS, CO,,SO,, HCl detection and temperature estimation of volcanic gas. Geophys. Res. Lett., ,., ,*.1ῌ,*/*.
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Tsuchiya, K., Imagawa, T., Yamaya, K. and Yoshida, M.
(+32/) Separation of microamounts of ﬂuoride coexisting with large amounts of aluminium and silica by improved trimethylsilylating distillation. Anal. Chim. Acta,+10, +/+ῌ+/3.
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