ῒΐ  /+  (,**0) -  +/+ῌ+/3 ῕ ῔ ,**.  3     

   ,**/  .  1  ,**0  .  +2 Measurement of Water Dissolved in the Groundmass Glass in the Ejecta of
the September ,**. Eruptions from the Asama Volcano, Central Japan
Kuniaki MAKINO῍, Tatsuro TSUGANE῍῍, Takafumi SONEHARA῍῍ and Yasuyuki MIYAKE῍
Infrared absorption spectra were taken to determine concentration of water dissolved in rhyolitic glass ofpumice, scoria and andesite fragments ejected by the Asama ,**. September eruptions. As the groundmass in the
fragments includes a lot of microlites of plagioclase and pyroxene, thickness of the volcanic glass itself is di$cult
to measure directly. However, an absorption peak, assigned to volcanic glass, is observed at +,2/* cm+, and its
peak intensity obtained by a curve-ﬁtting method gives the net thickness of the glass. This net thickness provides
the intensities of water per glass thickness without microlite contamination. The relationship between water
concentration and two absorption peak-intensity (-,/1*, +,0-* cm+) is derived from infrared analyses of theaphyric Wada obsidian, whose water content was determined by Karl Fischer titrator.
Following the above procedure, the water contents in the glass of the pumice of the September +st eruption,and scoria and andesite fragments of the September ,-rd eruption are estimated to be *.00, *.+, *.+῍*., wtῌ,
respectively. The magma represented by the quenched marginal crust of the pumice preserves considerable
amount of water (*.00 wtῌ) for its shallow location beneath the crater ﬂoor, prior to the September +st eruption.
The tensile strength of the cap rock presumably kept su$cient pressure in the top of the magma column to dissolve
water into the magma, whereas the magma providing the scoria and andesite fragments of the September ,-rd
eruption lost most of water.
Key words : Asama September eruptions, ejecta, Karl Fischer titrator, infrared absorption, water content+ῌ ῐ ῎ ῑ ῏|}+~[-345S<40v$D ,**.  3  +  ! " +, #$%&'()*+&,-. /0)* 12345

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*.+ mm  etp(x +g

0CB $D>E0F*0GHI/0J\9tp 0<4eM>0$+KLM>NO(P0QR$D2 S2T,UVWX

345w 06E+hpM>0$D>.

YZ0 PS[\ <=<]0E0 1^\_

$ q01(6Etp ,>kl 0`-abc0def:;\g> (Stix et al., +331).

 345]0ES345

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$"¢ tpM>qS$$O>qS+£M. q0

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l34506EmnopM>qSe$O>. [m[$  3  ,>j ]034506E

rs008

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+tpM>uv 8 0klw xyjz{xyj ¨-3*῍20,+ ©ª« -῍+῍+¬N­­w®j¯­¯
Department of Geology, Faculty of Science, Shinshu
University, Asahi -῍+῍+, Matsumoto -3*῍20,+, Japan.
 ¨-3*῍20,+ ©ª« -῍+῍+¬N­N­°±­²³´¯®µ¶·¸5¹º¯­»¼

M>.
Division of Environmental System Science, Graduate
School of Science and Technology, Shinshu University, Asahi -῍+῍+, Matsumoto -3*῍20,+, Japan.
Corresponding author : Kuniaki Makino
e-mail : makinox@shinshu-u.ac.jp

I&§& ¹º¡¢&%»¼152,    +  

,,- 3 

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 _H6  fKdf B- AY]K

+

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

$ %& (,**/) '()  (,'dPt3uQeAY]K ~ 4  *+(,- 3

+

 
 

 '$./ ! 012.3 45 +* mm *+6 78$ !

19:'3 ;'<.;
=7>  3<?

 '!:=+ fmd73aQ B'gY]Khi7j 1Q  3aY]K fmdk=^l7CW '($. hiY]K'4W=7{: -` XY
7?s.^=&' H( 3

 

,-

 I)*J -KLM 4'!:<? : +/ wtῌ6  3
= +NCD#  O 3 3

+

=

+NCD#

,-

7P 3OH (+W 

Q^-=Ptfmd1q-A' H, O

f
H, O

OH '(

fmdt +u'B'Q +,0-* cm+ 

H, O '(fmdt7v.^=7''- :^=jCD@A7 =Pt ft7w4xWy7z
 CD@A .WKLIG (Table +) ^   *,'> .%=-'./.Q ! .0R12S31{@A7.mnoqrm=3s

':

'=

Pt fB'' |}5; *.+ mm ~7>  ! 561TU.Q

@A7dnmMPt3uuts 4*+d'4. 3


,-

 

mn =^l fr1B- (Newman et al., +320) s$. -,/1*

:



W
OH 1

H, O

-,/1* cm+ 'A1 opmd

cm+ 

 ! '$G$.> .%Y]K='^O.` (Stolper, +32,)

1wtῌ @"A.    = B-CD# - EF+b  *+'c73a.B'W
,**.  3 

3+(VS- ! '78WKLM 1EF ', ! 9YKZ:'

P.[XW:'; - mm63

3u Janssen MFT-,*** spectrometer6 

FT-IR :;mrc : *.-῍*.+ mm ( &X
3,-+

=33 45

KLM 7\<

"xFp : -, F

ZQB' CD@A5 cdemm (ID-C++,B ; Mitutoyo) B' =^-f -,/1* cm+ '@Amdt

. Y]K^=7_> -` A3,,/1* cm+-,10* cm+ A 7Q7pd

?@A %& (,**/) \<

!]

WmdV7hi

ftO ^=B':CD&a[@A . EFbcde]cf7g

hi^O-IG7 CD@A .HIjJjkKLM 4l HKN6
OIG7 ^=7mnopqrm=3+ H, O '( +,0-* cm

 fmdtdf7mnopo!W
fK

4c6 ':
-` @A~md¡ (JSM-s'Pt3uQCD@A  IG

/,**LVP ; Jeol) #  4r +***῍+/**6 7¢ 

KLRvST *+KLIG (w O.<£a[@A . Long Valley caldera  Lookout Moun-]¦ 4GSR*. : §&tain OIG 4*+ Lookout IG6 3?

+) 3

+

~¤ ')
={¥e!

,**06 ¨?{: (Table}3-``( ,.

volῌ  cde]cf16©. Y]K#- UVxW & XYY]Kb?

ª«m3¬Y]K^=yZ[z\QbPt3uQ (Newman et al., +320 ;Stolper, +32, ; Yamashita et al., +331) {:A.

SEM (JSM-/-+*E ; Jeol)-DX. (EDAX) qK¦6 ''(=¯ X

t°7[.

B

±m

¦7 *.*+, mm ²'³´. yµ +/ kV, X 1**

A0R1| -Y]K B- 

pA B' 4B'¶·= 4]336 KLM 

XY  CD# 7W (Table ,)

EF }~ 4^'_H  cde]cf6*.^=3?¶ (Q7¸%1'c

Y]K`| -? Y]K3

cde¥em­]c®m 4EDX :+ ,**. 7a6 ¶j·¸ ,**. ¹ 3 º »r8
Table +. Modal composition and weight fractions of
the Wada and Lookout obsidians and of the
Asama pumice.

maﬁc : pyroxene² biotite in the Wada obsidian. pyroxene in the Lookout obsidian and the Asama pumice.
For calculation of weight fractions, the following
density values (g/cm-) are assumed ; plagioclase³,.02, opaque (magnetite)³/.,*, pyroxene³-..*, andglass³,.--.
Area (mm,) is measured part for modal composition.

¼5-6 %&153

Table ,. Chemical composition of volcanic glasses in
the Wada obsidian and of the pumice, scoria andandesite fragments from the Asama volcano.

Analyzed values (wtῌ) of NBS0++ by EDS areconsistent with the recommended ones by NITS
within an error. For example, analyzed (error) ; SiO,
³1,.* (-) and Na,O³+..* (+) and recommended ;SiO,³1+.2 and Na,O³+..*.
num : number of analyses. ( ) : standard deviation.
n.d. : not detectable.

-ῌ+ ῑ῏῎ῒῌ῍ῐΐ



 MKC-/+*N ;  !"# $%&'( )*+,-*./012 3 *./ volῌ# 4( 5-678 9:;<=>%:

/5-6:?@A (Table +)' B( )*+,*. CDEFGE$ +.**1 H $IJKLMNOHP' Q( RS TUHVW
XY/Z[\]4( ^ _/ *.*1῍*.+ mm ?`ab(+,*c ?defgh$ ,. ijklmnR( /%&'  %&( +,***c ?mnh?
Fig. +. Infrared absorption spectra of groundmass
in 3.+ pumice, Wada obsidian, which is heated
and dehydrated, and each of plagioclase andpyroxene powder. The groundmass of the pumiceshows complex spectra, which is constituted ofabsorption bands due to (H,O´OH) at -/1*
cmµ+, glass (+,2/*, +,0+* cmµ+), H,O (+,0-*cmµ+) and microlites (plagioclase and pyroxene).
In the Wada obsidian, absorption peaks due toglass are appearant around +,2/* and +,0+*
cmµ+, the latter is close to H,O band (+,0-*cmµ+). There is not any characteristic peak for
powdered plagioclase and pyroxene from +,/**
cmµ+ to ,,,** cmµ+. bg : straight backgroundof glass absorbance peak.

/opR( qrstOHuHviw$xy\]zzT` -* {|#' Hz( }~56?3 /ῌ56/Pmn?T~/qre] H, O 

H,  H, O %&\]' mnxyR(  qr -=>%&xyiw +-<E/ A=> +-<E/PE/ \]' +<E s?T]( r$ *.*, mg {|$]'a$( %&/=u\]^ ?$
HPJLOVW\]Tu¡>eP] (e.g.
Newman et al., +320)' 5-6?¢e] £G/&4]?( ¤¥/¦§$mnr~¨/\©~?@b)ª«¬$%]­®O¯°±$(Newman et al., +320 ; Stolper, +32, ; Yamashita etMN´OµPeQRµ¶·¸¹SµºT»¼

154

Table -. Water concentration and data on Karl Fischer and infrared analyses in the Wada and Lookout obsidians.

Variation of water content in the Wada obsidian is +ῌ as standard deviation.
KF : Karl Fischer titration method. IR : IR spectroscopy based on the equation (.) (see text). err : analyticalerror. n.d. : not detectable. - : not determined. # : estimated by the curve-ﬁtting as described in Fig. ..

al., +331)    E<D j1 H, O  /,,** +,0-*   Newman et al. (+320) 

cmi+ OH  .,/** cmi+ (/ m -,/1* cmi+




#$%&

 !"'  *.+/῍*./ mm (   )  +/** /./ + , -  . ( /      0 1 2 3 4561 7( 8)9):  -/( H, O  OH 7Lkj-m

(Newman et al., +320 ; Stolper, +32,) [%\ (/,,** cmi+ (H, O)  .,/** cmi+ (OH) d }-  ,jk!zm

 j  + mm 8!"

! -9: (Newman et al., +320) d#$%&(; <)=( -;<%d (->?@+ABC(BD  EF9

+ mm  GH IJ=T (%_-D( /,,** cmi+ : .,/** cmi+ 

j1I9D  -KL/ LMNO>? *.+ mm @=

PQR L QSL T .D !

-,/1* cmi+  +,0-* cmi+  jk!7 (Fig. +)

01234561 UVWXY"LP#$[%\ ]^_&'(`La LT

jJ

7J (H, OOH) VWX jk! (-,/1* cmi+) H, O (+,0** cmi+)  jk!AJd Z<L
!Eb9 k)c +,**** (012 d  D71 -9:D +¡(B (Newman et al., +320) =T

34561 Ud 7Lc e(fI  01234561 U)¢!B£J

QBVWX)g*h( -,/1* cmi+ 

jk!

( #$[%\=T C¤D)Ll,J m

E VW jk!  Y! B¥

7LK:

+ -n n.PQo/0c +,** ( ,. +,pqr 01234561 U( .*** s()s¦ C¤)"#$%&zm§3LL  tu7J Evw 01234561

01234561

U(z Ec¨E FT-IR7L H' *.*1῍*.+ mm (  !((F©L)c  7xy (*.*+ῌ) PZ(/ z

GªH Y!L <DC¤) 0**Y!7 =T

 +. 7LE12ds   +,**** )({|31** 1/* 2/** ( + +,I«L . ¬JL

J (Table -) <L}

(Table .) F:NO+(­KL ®­T 

#$[%\d  *.01 (+) ῌ(/ (Table -)-ῌ, VWX k j
4~5 H, O 

H   OH   j6 Y- DD¯° ±d  2 ²8!D ¯°
VWjk!,³X-Lm

(Fig. ,)PQ  -,/1*, +,0-* cmi+ VW jk!F

{| ,**.  3

}k~Z()*bN

155

Table .. Data from stepwise heating experiment on athin plate of Wada obsidian.

KF : Karl Fischer titration method. IR : derived from
infrared absorption intensity by the equation (.) (seetext). err : analytical error. # : estimated by the curveﬁtting as described in Fig. ..

 

Fig. ,. Variation of extracted water content andabsorbance (-,/1* and +,0-* cm0+) in a thinplate of the Wada obsidian during stepwise
heating experiment. Filled circle shows watercontent from grain fraction heated at +***.



 H, O ῔ CH,O OH  H, O

!

῔ COH "#  C$CH,O%COH &'# ()*+,- (cm) './ abs (abs-/ : -,/1* cm0+,0+

abs+0 : +,0-* cm ) 12345'# (Newman et al., +320)
abs-/$6e+ · CH,O%e, · COH7 · rῌ+2.*,(+)

abs+0$e- · CH,O · rῌ+2.*,(,)

88& r 29 (g/cm-) e+, e, ; :;<; -,/1* cm0+ 
H, O  OH  /= e- ; +,0-* cm0+  H, O  /=  C ($CH,O%COH)  abs-/  abs+0 &>?@"
 (+) (,) ῐ + abs %ῌ + 0 e+ ῎abs ῒ· +2.*,
ῑe, -/ ῍e- e,e-῏ +0ΐ r

C$

(-)

4# AB CDEFGHIJKL (Tables -,.)  C M"# abs-/  abs+0 = ((mol ·cm)/cm-) 5N;# OPQRS# (-) 2
C$6*.***306+7 · abs-/%*.***3*607 · abs+07 · +2.*,ῌr(.)

4# 8 (.) T!U;VWXYZ Look-

Fig. -. Comparison between water contents of theobsidians (Wada and Lookout) determined by
Karl Fischer titration and by infrared spectroscopy based on the equation (.) combining-,/1* cm0+ absorbance with +,0-* cm0+.

Beer p ; Stolper, +32,7 8 qr-Ust/+,- (cm) uvwx#8
5&?#  "&yz{|}k~

out XYZ[\]^_`a\S#bN

Z2 ) 6 Z Z7 (2 Fig. - c"de"# 4f ghU;)*4~&'#& ()*

i# /= e(Newman et al., +320) j;# (.)-UTb"#82&?4i  +,2/*

=2 abs-/  abs+0 M:;<; *.**+** (,)cm0+ ()*\"#8&:\*.***2* (2) !kU;lmde"#-ῌ-  

/2-U1no"# 6Lambert- (ABS+2) )i()*-U (d) #85&?#
()*#

4

2 3**῕+,,** cm0+

A2´BµC¶DEµF·¸¹GµºH»¼156bc( 

7a H, O\']^_^YW  deK

>

2?]^_^YW =c fg\'( fg\'  h =i) 3.**j D+***j k +0 Dl.mnh6

D

PUVWXYZopbc= (Fig. +)( H, O
fg\' (+,0-* cm"+) hq i)Dhr=i)

>2?G( N= <=4 )5)
P

>2?tus=OHfg\'( vw P`7a . x!

fg\'

,,,**++,/** cm"+sPyz{|"#}( =\']^V_^YW~ Fig. . ( -,,,**++,/** cm"+\']^_^YW (+,2/*cm"+)  H, O (+,0-* cm"+)
Fig. .. Comparison between observed IR spectrum
and calculated curve by curve-ﬁtting procedure.
The ﬁtting curve gc (x) is described as followed.
gc (x) a+ · g+ (x)³a, · g, (x)³a- · g- (x)³a. · g.
(x)³a/ · x³a0. (x ; wave number (cm"+)), where
ﬁxed curves of g+, g,, g- and g. are from glass,
H,O at +,0-* cm"+, plagioclase and pyroxene
spectra, respectively. Coe$cients of a+ (glass), a,(H,O), a- (plagioclase), a.(pyroxene), and a/
and a0 are parameters to ﬁt the observed IR
spectrum (go) with the curve (gc). The peakheight (absorbance) of glass and H,O correspond
to a+ and a,.

,T 36 (  7.= (ABS+2)

JK (d) # i) d~D d (cm) *.*--- (+) · ABS+2  (Fig. /)(/01024

)5)

s=

UVWXYZT (Fig. +)(  7$% & '()EF8=9
:8( t EFL;=c 4 ) 5)
* 3+ *.*- mm6 . KBr 3S\X6 h.h=>V2i),- w
.. /S= (Fig. 0)( 4) +0 wtῌ 5) 3 wtῌ

%01 KBr &=>V2 3*.*+2 g,  ,./ mm6  ,i)
3JK *.**00 cm  *.**.- cm6 .OHP=(  

    ! +,2** cm"+ #$%+,.**+,,+** cm"+

 &'

( )*,&'

-$%

.

 +,2** cm"+&'

 /0102 34 ) 5)6 78

(Shinoda and Aikawa, +33.)

9:;8 <=4 )5)?+,2/* cm"+

-#

@

A (Fig. +)( BC. +,2/* cm"+Dt e KBr >V2OHP2+** 1/ /*,/ *ῌ 7 KBr >V2MN

%01i)34 '

KBr >V2OH

C=(

>2?¡0¢

5=c£o;6 4 )¤5)01

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8*.**2/ cm

 (+,2/* cm"+) 7I J *.**1- cm D *.**/* cm /S /0102M9

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I JKQRS.M  (,,,**++,/** cm"+

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UVWXYZ

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,**. « 3 lmn`>Fig. /. Relationship between specimen thickness
and absorbance (+,2/* cm3+) of glasses from
Wada obsidian. Lambert-Beer’s law is conﬁrmed
for obsidian glass.

157

Fig. 1. Absorbance variation of water at -,/1* cm3+and glass at +,2/* cm3+ in groundmass of thepumice, scoria and andesite fragments from the
Asama volcano. Each of plots corresponds to ameasured point with varied microlite contents.
The pumice and scoria show that absorption
intensity of water correlates strongly with thatof glass, and their groundmass glasses appear to
be almost constant in concentration of H,O andOH.

AG8J *.00 *.++ *.+* K *.+2 wt ῌ ?
(Table 0)& LMNO P8Q#RSTUMVWXY4Z[7O\]^_`>aT%4 bSQLM%OcABTD
N LMd7 *.0* wtῌ 'eeFig. 0. E#ect of powdered plagioclase and pyroxene
on absorption intensity (+,2/* cm3+) of Wadaobsidian glass. The intensity is a relative
absorbance of the glass covered by a mixture of
KBr, plagioclase and pyroxene to the glass.
Below *.. in the weight fraction, the relative
absorbance is from +.* to +.+.

$#Tfg4hQ (Fig. 2)&
/ 







i_ jklmn(*+),op
qrOT`>stDuvO& wxyz7
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

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S¨/%OC'T©& C Sª2D ,./ gῌDE$^A¦BC^¹º»¼^¨@©ª158

Table /. Representative water content with its infraredabsorbance in volcanic glasses of the pumice,scoria and andesite fragments from the Asama
volcano.

# : estimated by the curve-ﬁtting as described in Fig. ..
residual : ῌ (gc¸go),. go : observed spectrum, gc :ﬁtting curve.
() : analytical error. Number of data is /13 for calculation of curve-ﬁtting.

Fig. 2. Homogeneous distribution of water in theglass of the crust portion of the pumice.

0ῌ ῎ ῍ ῏+) 3fAg8hghij6,kl
Table 0. Average water content with its range involcanic glass of the pumice, scoria and andesite
fragments from the Asama volcano.

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"#$%& '( (Self et al., +313) ) *ΐ+,!-. /+,0 1 ,** m*!B(-2%34 5 6& '7% +,

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 ¡¢£¤-9¥¦ /k: (C) : +1/.*.-/0

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3>

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T 3 U$V*@WXY TZ!!
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*)de% L

c$$./¨@©ª380 !« ¬$%­%ῐ ῕ ῔ ῑ
McBirney, A. R. (+30-) Factor governing the nature ofsubmarine volcanism. Bull. Volcanol., ,0, .//῍.03.
McMillan, P. F. (+33.) Water solubility and speciation.
Rev. Mineral., -*, +-+῍+/0.
¨@©ª^7® ©^A¦BC^DE$^¯EF°^±GH²^I³´µ^,2?3f *. "3J
¶qs (,**/) 2?3f ,**. " 3 >3·>?,**. @ 3 VA)*W!XYZ[\]/* ---ῌ-.0.
 
Newman, S., Stolper, E. M. and Epstein, S. (+320) Measurement of water in rhyolitic glasses : calibration of an
infrared spectroscopic technique. Amer. Mineral., 1+,+/,1ῌ+/.+.
Self, S., Wilson, L. and Nairn, I. A. (+313) Vulcanianeruption mechanism. Nature, ,11, ..*ῌ..-.
Shinoda, K. and Aikawa, N. (+33.) Absorption coe$cientof overtone and combination modes of quartz. Mineral.
Mag., /2, 0*+ῌ0*0
Silver, L. A., Ihinger, P. D. and Stolper, E. (+33*) The
inﬂuence of bulk composition on the speciation of waterin silicate glasses. Contrib. Mineral. Petrol., +*., +.,ῌ+0,
Stix, J., Torres, R. C., Narváez, L. M., Cortés, G. P. J.,
Raigosa, J. A., Gómez, D. M. and Castonguay, R. (+331)

159

A model of vulcanian eruptions at Galeras volcano,
Colombia. Jour. Volcanol. Geotherm. Res., 11, ,2/ῌ-*-.
Stolper E. (+32,) Water in silicate glasses : an infrared
spectroscopic study. Contrib. Mineral. Petrol., 2+, +ῌ+1.
 (,**.)       !"#$%&'()$*+ ,-. ++* +/2ῌ+1..
/01234567389:;3<= : (,**0) >?
 ,**. @AABCDEF%GHGI/+ .3ῌ0,.
JKLM Yamashita, S., Kitamura, T. and Kusakabe, M. (+331)
Infrared spectroscopy of hydrous glasses of arc magmacompositions. Geochem Jour., -+, +03ῌ+1..
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