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Experimental Studies of Dehydration and Open-System Degassing of Magma
Satoshi OKUMURA+    %&%*Q4%'(578*9$ /K NO$
R.M'S/

K$

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B5

, 123 %&%'( /T!$ UVWFXY

3 EZE'"#.'[\/K$$ -6*%&']'('^_`ab FXY'LM*c'CD*d(e2f$ lNO$)g3B42* h*ij*k+/,"#$ %&%'(')  *+ ,-.* %&%'(578*/0 m'FGH
IJt

 m

E#u5'9`*+/@n ,- :x m'/7y 8, 9M +3 :=EZ{|>} )g'B42'/
NO$ {/B 8 -m  )g'@n-ij'op/?

5* UVWFXY'qr-b( /T!$ &\'s+2f ]1./0$- 123 78*9$

B42''2/NO 3Kvw4565m
*;$ )g'/NO$z<**3 EZ7

8M'~?wcl? @A '%&%l'78'FGHIJ5  %&%'CDE'&

EZEb -*E /$ CDwF*E*w l G2tGJ/M$ CDwH*./0$ . 123 ,ῌ- 1'4565 78*9$ 
':;'*+<*=

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&2f 4-m'CDw"#.b [\3 **wK';5w

E#u'"#./,EZE'L's+3 %&%'(*MDA

$hw[\5  ENO/"#$ %&%'(5M2f

78bS

P**C ^_`ab ,(bQ c(/(Fig. +) "#$%&%3

B m'op%&%*AbM

@U 'A'M3 EZE'L5w(Fig. +) X/?5*-'AMRb¡ ¢S£¤bR¥Tb ,wE*w
5¦(Mason et al., ,**0) 4- EZ*sV2 M-AW§b¨< A©ªY«¬ (­®¯°±X/?X m'­®¯°±X²bM 5 AO'78Mb³Y´2 

5^_`a/Z,  %&%'"#'£¤8µX/

78 $ B52E'L3¶6

>? ?@A

m'-6

(Humphreys et al. ,**2 ; Liu(' 578'·[bEZE'F./\]*

et al. ,**1) B'CD* E'FGHIJ/ K *T!$ 5¦

E'"#./X-**I?$ -6*3 A'Ml (t78'/T!$ &\3$l* ¸¹ E'F.
tE#u/I?$ B533º^)g3(t78' /T!$ &\/$l*$ -6* i/T!$ %&%'(  +43UVWFXY
'('^_`a/ij**vX$ %&bf('^_`a32_M'UVWFXY*; »

j*k+/, -/@n ,-(e.g., Nowak and Behrens, +331 ; Zhang

P23 )gb@n ,-ij*/¼*%&

and Behrens, ,*** ; Zhang et al. +33+) b `'LM 32*ῌ2/12  0ῌ-

 32*ῌ2/12, Japan

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Division of Earth and Planetary Materials Science,
Department of Earth Science, Graduate School of Science, Tohoku University, 0ῌ- Aoba, Sendai, Miyagi

Tel/Fax : *,,ῌ13/ῌ110.
Corresponding author : Satoshi Okumura
e-mail : sokumura@mail.tains.tohoku.ac.jp

AB

208

Fig. +. A schematic view of explosive and e#usive
eruptions with dehydration, bubble formation,
magma fragmentation and permeable ﬂow degassing.

89::;<= Oku-

mura

and Nakashima (,**., ,**0) <H+,-89:

IJKJ8 L . M / +,-NOP
QL0128R L +,-S 01

G

Fig. ,. Summary of water di#usivities at +.* wtῌ
water in natural composition melts and glasses :+. Rhyolite (Zhang and Behrens, ,*** ; Okumura
and Nakashima, ,**.) ; ,. Basalt, Andesite andDacite (Okumura and Nakashima, ,**0) ; -.
Dacite (Liu et al., ,**.) ; .. Andesite and Dacite(Behrens et al., ,**.) ; and /. Basalt (Zhang
and Stolper, +33+).

8WL6 NOP

28TU  V

>01 ?@:< AB (,**0) XY<Z[ CCD \]2^_

< de01fghij kL`abc 
Okumura and Nakashima (,**., ,**0) < >8ElN



(e.g., Chakraborty, +33/ ;OPmno8[L [L pqE>

Lasaga, +32+) d67 \]2^_ 

 :rs>t! 8V L6 dL >t. NBOῌTS NOP"mno>0128R L

y z{h|}~"~ 

6 C DR L6>012

.Z[< ;c  `L6 (Okumura

H,Oand Nakashima, ,**.) Okumura and Nakashima (,**.,

fghij k.}` 67,**0) D!



60128 "#D;cX Fig. ,  >012<E>Zuv89:< 8wx

NBOῌT Z[! _.01D}

  

.=

C

D01

  :rs NOP012<     $ c

 % .F[&}` 67 Fig. , D<E>. + wtῌ 

Okumura and Nakashima (,**0) < C8w

0128L  012<+,-TUD'L #+,-NOPs (3DX + .F  r6QL0128 VD} L6

+,-./

012345./ 67

012<3  ) 
1**( *s+3D<>012.X}` . +.**( s3D<,S  N- ¡012<c0128~£¤¥oi¦§L!6\]2^_(Df) (Ea)  NBOῌ

T : . $ ¯ /0 °-z{h (T) 2Q

Df$Cῌ*.1%exp+*.2,&+*.*%NBOῌT'(+)

Ea$+01***&,****%ln NBOῌT&*.*,+!

(,)

CCD C <E> (wtῌ) DF  Okumura and Nakashima (,**0) D< *.1 wtῌ TU8L¢s Fig. - < + wtῌ ¨©ª«8L6 6
L ¬<+E>.­ ()*+ wtῌ) D! 6®

1 ±²O³U´µ8X L 67 sE>D2¶(NBO) 2' 8 Fig. -  NBO ῌ T   .Z%DF S<·¸ ¹3.45DF  r6 012

[ :rsS ,º +»6 

¼745:X·¸¹3½8DF ,-

¡ \]2^_

&'&()G)*+ HCD

209

IJI KL M! 2ND 0=>"F2;O PP &'&(Q2RS(T
U=>VE0W X. # Y0." CD &'&2Z" )*+[(\2]
^_`>a(Takeuchi et al., ,**/ ; Westrich andEichelberger, +33.)# 0>( bc" &'&(

dKL
volῌ

)*+[;O("  0*:;<=>. # ?  2** .@AeG - wtῌ (f&'&2gh" &'& iG(j T => 0* volῌ ( kl
(m

/** m

)G2p"

. 08 $!no.(qK!# 0>(rs=>" F2;O

&'&()*+,- ./0 1#B ." CD=> EF- .()*+."Ft*+ul(vErs2w#.aqK
# $hc" xy%z{. +33,῍+33- &(| '(.vEFt*+ul (Cl/H,O } S/H,O) " '~ -.3

km :m(M).3j*+(ulB*"0'~ km =>)*+  028
 (Ohba et al., ,**2)#  

 Montserrat◊ Hills Ft.^" Ft*+(vE=> +33/
( Soufriere&:  km (m =>'( Q*++
/a gh> (Edmonds et al., ,**-)# 0
Fig. -. (a) Pre-exponential factor (Df) and (b) the
activation energy (Ea) in the Arrhenius relation
for water di#usivity plotted as a function of
NBO/T. The plotted data are obtained basedon the data in Fig. , : Zhang and Stolper (+33+)(Z&S’3+) ; Zhang and Behrens (,***) (Z&B’**) ;Behrens et al. (,**.) (Behrens’*.) ; Liu et al.
(,**.) (Liu’*.) ; and Okumura and Nakashima(,**0) (O&N’*0). The dashed curves represent
the di#usivities calculated from equations (+)
and (,).

>(vErs" Fm =>[ )*+2/0
345670289#)*+2_34567(, " &'&(- .du(\># RS(dIJ(v=>" &'&(I)*+2 (e.g., Marti et al., +333 ; Polacci
et al., ,**+ ; Rust et al., ,**- ; Stasiuk et al., +330)#g}" 12I .&'&Q(_\ P# :;(b324
h" 5- 

=" &'&.(d/(0 H"&'&(12ICD2<(Okumura et al. ,**0, ,**2, submitted)#

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" Eichelberger

et al. (+320) d /  ; r0.Ild ¡¢£¤2<0Q)*+2=¥(Fig. +)# 0(¦§¨©ª>>" ;O&'&=>()*+([2«" ` " (".  (e.g., Lejeune et al., +333 ; Stein and
Spera, +33, ; Stein and Spera, ,**,)" du}Q # Okumura et al. (,**0,,**2, submitted) &'&(-2¬­(e.g.,`" ?M~.®@2¯°+±²³£´(

Eichelberger et al., +320 ; Klug and Cashman, +330 ; Melnikµ¶12ICD·A2<0 CD2< # d= " u@ ®a¸¹ `" @2B;" C

RS'( "A. D%+ $d(º®.»£.aµ¶IB¼M½E

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*+

210

Fig. .. Three dimensional (--D) image of shearedrhyolite (+* rotations at *./ rpm) obtained bysynchrotron X-ray CT (BL,*B,, SPring-2) (Okumura et al., ,**2). The bubbles without interconnection are colored separately. The graycolored bubble is the largest bubble. The blackarrows represent the direction of rotation.

 (Paterson and Olgaard, ,***) -,

Fig. /. Bubble number density in the samples ofdeformation experiments (A : / rotations at *.rpm, and B : / rotations at *./ rpm) and vesiculation experiments without deformation (Cand D) in terms of the spherical radius of the
bubble with equivalent volume (data from Okumura et al., ,**2). The large bubbles (+/**῍+1** mm) formed via bubble coalescence arefound only in the samples of deformation experiment (A and B).

 ./#$%01 -2
 31/(rpm)

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'()( ,+*0 Pa · s

BCDEF; &FB

(Hess and Dingwell, +330) *.,0/ Nῌm (Bagdassarov et al.,GHIJ HKLM (e.g., Lyu,***)*.*/ s+

NOPQ(    89  '()(-/  -T :07U X V CT

et al., ,**, ; Rust and Manga, ,**,)

  0RSM   (Goto,

01/BWXYZ (Fig. .) (Okumura et al., ,**0,+333 ; Tu#en et al., ,**-) F[\]O^3(_456; `!a b"# `c$

%d&B;e (Rust et al., ,**- ; Rust and Cash-,**2)

f'0aA/ (Okumura et al. submitted)
Bghi0jk(/lDBghiman, ,**1) H@Q  +*, s+ 

NOPQ(1 <(-=>)m ( *.*/ s+) n3*+0 Fig. / oM ,5pqHP ;/6

:   (+) rs9tHB  89jk (/.u;/qBDEvw+1** mm x;z{( (,) <A1 |}Q( Okumura et al. (submitted) +**῍,** mm B0RSM!1P --Q(
c$RSxyGx~1 X V CT -Q(/@Q0Q

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'

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@Hpq rs9tHBGBxCDE

M510 R-0W

;z{(/%0PA1 Fig. . 

D?< 2\G km @Q0M

B {QB34M( .u `

 5&x< 0o/¡¢t£{(1< P*@ (Fig. .) <pq
HB%;zF;e¤ ;p6.ῌ ῏῍ῐ῍ῒῑ῎ΐ῔c$xRSM 5&0o¥1 Okumura et6¦ 7§xaAt/¨ al. (submitted) .u;/qc$¤08©

n1 '(Q0ª9M:«34¬­/® ;-T7U:c$0f'/¯°/ , ± ²³´#$%µ¶1x¨' ·*H.u;x5  ; `c$

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(!) AE $23456"/7.% 897 :;<=> ?.+ @A%B&C# DEBF!

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R/0RO$1

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1 )B^CDE$60&FG7_ `$Ha1

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< rs\Z W] t[o uvwxN

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1 c@Jd7]. ?:;<=>

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jE@.,7 %  7e (,**2)!f%}~b$110@=1 Jj: :

gh%i$1 ]*./ wtῌ #  ``}kl1F  XYZn[o moX#)$  n%1 12*῍2-*

op6NK]q;W< 46N8iW

!X#)!l`# ?OPQhl`

&rsB QsgL,.@%`$N`$8t1  OPQhuv!@ :@,&_10 1  w&x

1  456N7

Qh7 yz1 {|)&7  `Qhuv!

89:;W< }7_;W< ~ iW 7

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1 =Z>$11 b ?1 j"#$K@60&7 1 

E$I1 b PS  PQ@ )!
OPQhl` ¡$¢1 jE$ 
-$.,1 &n!S  `  
` !

Y=£¤¥5¦$S1 jE $Z_ `! jE?$  -$\Z §!0 ?"b%§@LMLP L@$  -§Ln¨^c%i$ A©b
 uPOPQh@LMP:;<=>p+Aq.
!@ Tu#en et al. (,**-)(Goto, +333) ª«

Neuberg et al. (,**0) %

"/NN¬,.`­®+ 

 Lavallée et al. (,**2)

Tu#en

et al. (,**2) @p¯°u±OP

QhIb AE 25²³¤¦´µ¤¶·z $  QhLMP:;<=>
p+!S

P$¸1 1,1 Neuberg etal. (,**0) " Soufriere◊ Hills LM¹w

OPQhl` w@º»¤3S#7 p¯°Ac! LY$JN1) $¼D!0,b,B½

C  uPOPQh  c@ A   }7_;W<:z῎ ῍ ῑ ῌBagdassarov, N., Dorfman, A. and Dingwell, D.B. (,***)
E#ect of alkalis, phosphorus, and water on the surface
tension of haplogranitic melt. Am. Mineral., 2/, --῍.*.
Behrens, H., Zhang, Y. and Xu, Z. (,**.) H,O di#usion in
dacitic and andesitic melts. Geochim. Cosmochim. Acta,
02, /+-3῍/+/*.
Chakraborty, S. (+33/) Di#usion in silicate melts. In Structure, Dynamics and Properties of Silicate Melts (Stebbins,
J.F., McMillan, P.F. and Dingwell, D.B. eds), Mineralogical Society of America, Washington, -,, .++῍/*-.
Eichelberger, J.C., Carrigan, C.R., Westrich, H.R. andPrice, R.H. (+320) Non-explosive silicic volcanism. Nature,-,-, /32῍0*,.
Edmonds, M., Oppenheimer, C., Pyle, D.M., Herd, R.A.
and Thompson, G. (,**-) SO, emissions from Soufriere◊
Hills Volcano and their relationship to conduit permeability, hydrothermal interaction and degassing regime. J.
Volcanol. Geotherm. Res., +,., ,-῍.-.
Gonnermann, H.M. and Manga, M. (,**-) Explosive volcanism may not be an inevitable consequence of magma
fragmentation. Nature, .,0, .-,῍.-/.
Goto, A. (+333) A new model for volcanic earthquake at
Unzen Volcano : melt rupture model. Geophys. Res. Lett.,,0, ,/.+῍,/...

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Hess, K.-U. and Dingwell, D.B. (+330) Viscosities of hydrous leucogranitic melts : a non-Arrhenian model. Am.
Mineral., 2+, +,31ῌ+-**.
Humphreys, M.C.S., Menand, T., Blundy, J.D. and Klimm,
K. (,**2) Magma ascent rates in explosive eruptions :constraints from H,O di#usion in melt inclusions. Earth
Planet. Sci. Lett., ,1*, ,/ῌ.*.
Klug, C. and Cashman, K.V. (+330) Permeability development in vesiculating magmas : implications for fragmentation. Bull. Volcanol., /2, 21ῌ+**.
Lasaga, A.C. (+32+) Transition state theory. In Kinetics ofGeochemical Processes (Lasaga, A.C. and Kirkpatrick, R.
J. eds), Mineralogical Society of America, Washington,
2, +-/ῌ+03.
Lavallée, Y., Meredith, P.G., Dingwell, D.B., Hess, K.-U.,
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