浅間火山で頻発した小噴火の噴煙運動の特徴一2004年9月15-18日噴火

全文

(1)῍῎ /* (,**/) 0 ///ῌ/0/ . ῐ ῏.

(2)

(3) ,**. 3 +/῍+2

(4) . . ,**/ . ++ ,**/ +* +3 !". The Kinematic Features of Volcanic Clouds: A Series of Small Eruptions from +/ to +2, September ,**., at Asama Volcano, Japan Akihiko TERADAῌ, Yoshiaki IDAῌῌ, Sei IIJIMAῌῌῌ, Mitsuhiro YOSHIMOTOῌῌῌῌ and Taketo SHIMANOῌῌῌῌῌ Some fundamental features of ascending volcanic clouds have been revealed using images of the clouds that were automatically recorded by video cameras for some eruptions at Asama volcano on +/ to +2 September, ,**.. According to the analysis of +1 volcanic clouds that are nearly isolated and of a symmetrical shape, the radius of a cloud increases linearly with increasing height, meeting self-similarity of ascending motion nearly up to its maximum height. If the height is measured from a suitable virtual origin, the ratio of the radius to the height can be a constant that is identified with the entrainment constant. The entrainment constants determined in this way have a mean value of about *.,. in good agreement with those obtained from previous laboratory experiments, even if the values are greater than *.,/ or less than *.,* for -/ῌ of the analyzed volcanic clouds. During the ascent of a cloud the height squared is nearly proportional to the time and the product of the radius and the ascent velocity is almost constant. These empirical relations are consistent with well-known characters of a thermal that moves in incompressible uniform surroundings. Coupling these kinematic features of the volcanic clouds with the Scorer’s relation and the equation of state, we evaluate the total buoyancy, the total mass, the density and the mean temperature of the clouds that are regarded as thermals. The total buoyancy of most volcanic clouds did not change significantly during their ascent process. The cloud on +1 September has a relatively great density contrast and small total buoyancy, probably reflecting hot ash particles in it supplied by a Strombolian eruption at that time. The volcanic cloud discharged at ++ : /., September +/ contained ash of ,,/**῍-,1** tons or less with the mean temperature of -+*῍-0* K or higher, and the volcanic cloud discharged at 2 : -2, September +2 contained ash less than 2,-**῍3,+** tons with the mean temperature higher than -+* K or higher. Key words : Asama volcano, thermal, volcanic cloud, buoyancy, entrainment. #*0*῍*2+* $%&'()$*$ +* +, 2 -. -23῍*++/, Japan. $%&/0/01!023456789:23;<. #++-῍**-, YZ[\Z*]I +῍+῍+ =>?@ YZ/07823X Institute of Seismology and Volcanology, Graduate Earthquake Research Institute, University of Tokyo, School of Science, Hokkaido University, North +* +῍+῍+ Yayoi, Bunkyo-ku, Tokyo ++-῍**-,, Japan.. #32*῍2/10 ^_Cà)bc*de .+ West 2, Kita-ku, Sapporo *0*῍*2+*, Japan.. #01+῍,,*+ ABCDE)FG ,+01 Y$/0Y$fgf23=>?@ ABCH/0/01IJ!0234 The Center of Northeast Asian Studies, Tohoku Graduate School of Life and Science, University of University, .+ Kawauchi, Aoba-ku, Sendai 32*῍2/01, Hyogo, ,+01 Syosya, Himeji 01+῍,,*+, Japan. Japan.. #-23῍*++/ KC$LMNO

(5) PQRS ++/+῍, TUVO

(6) P<WX Corresponding author : Akihiko Terada Karuizawa Weather Station, Japan Meteorological e-mail : [email protected] Agency, ++/+῍, Oiwake, Karuizawa, Kitasaku, Nagano.

(7) XY¸µhfY¹<h¶· ¸hº`¹»hº»¼¼. 556 +ῌ ῐ ῎ ῑ ῏. a ,**. 6 3 x +. b'( +2 b o.

(8) . wxy ,,*** , rG H.7 .

(9) . Pz ,**.I {S | $ }. . /}i k}/{F l~. !"#$ % &#! '(). n+J* * WF!,. *+, %-./0 !. %-v*$ %B+ `5 . 12+34 / !" %-. /}S {F

(10) . 5# $. < 7( -*#p m/ $.

(11) 6*+ $5%7( &'(8. C%` 3 x +/ b'( +2 b'+. 9):;<= +ῌ. * >?+,?-. -. 78 '( F _tu?. *#@AB11 (Morton et al., +3/0) . 7= ! 9: Scorer (+3/1) . / C DE0F(+G. H.7. PQv*+, $ % NvG . Wilson et al., +312 ; Sparks et al., +320I$ J Woods. :AYZ[A\AY=FE0F ' -. and Kienle (+33.) :AKL=123*+)(. F# '(m d<(' $ (. 3MNO4 PQR5 Redoubt +33*. J Dt>U6*+y. 678. %7 ! 9:-d m- . co-ignimbrite ash cloud !. 9:;< *S6' T= F- >U. $. ?= $ ' %(PQ - -. ] ?g'(_J B?. VWX@6*+ :AYZ[A\AY T= (Morton. ^ %-/ H.7 Pz ,**.I. et al., +3/0) *(+]0 Â B. ` 9(*c0?* $. +:AYZ[A\AY T=/ CDE :A YZ[A\AY=F G6*+ HI,. ,ῌ ΐ ῍ ῒ Fig. + ` , 6 aJ\k . +**$ % &#?_J K ^` L. $ OWK g'(

(12) y 1.1 km . MNO^P aQbc(+]0 Plume. I PzfJ ?. Rise O H.7 Briggs, +303 ; d +312I R eS. \k H TC-2+*I / $ J Pz. 1 HfghK +32-I biT .UG =. Tlh¡¢AK= HI . 1/J0"8+**$ j6 \k. +* PK ' ,ῌ+0 £ + 6. * aJVF."7 lmWn+G. K[¡kB¢£Q¤b

(13) 12+* $ `. +]0 H.7 XYhK ,**-I ZMo. . £ + ¥12 ¦[§ 0.*. p '(F 1[Oq\ %. ¨.2* pixel JPEG ¤¥©

(14) mª+. -pr/ $. $ Table + ©}k\=K$ %%. % &#]s F- XYhK (,**/)

(15) ^_t uX@bv`9:<( '. w a ,**- 6 , x 0 b . OWK o«2+©¬l~N®'m¯. . w 4 / ¦B«+ - 6°± $ %. (² ©¬l~N§q+*. X@- cid efgh-igVW('(. *$ % w ©¨ a>©. y(-+ Thermal ! (Scorer, +3/1). T ª9: «--z %. --z $ Scorer (+3/1) Thermal PQ efg. -?= $ ©³T b`¬ (JST) ). h c j ){)(3MNkl+*. ´+* % ´ ,**. 6 3 x +1 b. b E( ^P-|+m@AB. +2 ®W ¯ JST '(y +- £°+* $ `. F / $ C iN PQ^ }k\=K. ±B ´²*'( `° . n* w aJ~oc(+* !. Ć JJ* $. , pqW&*$ -% XY h K. AVO g'(

(16) y ... km 3. (,**/) 1 i.n %- r. aaJ ³´+* QµK£Q¤. sQ=K t?S'n %-'( u,. \k DV ¶=B

(17) + £y -* . v/n $. +* $ ` ! ¢·=-.

(18) ¹c`hN º ` u»¶·¼¼ ,**. ] 3 ^ +/ῌ+2 > ` ¼¼. 557. OWK

(19) . +

(20). 7s

(21) t uvw abxy

(22) HIe A z6. 0.*.2* pixel JPEG . 78 D z ;Fig. + {< |}$%~N

(23) . !"#$%&'( JST %)

(24) . *.. Pa *~$%ab \&. + *+ ,-%&. +. > - ' -* 3 ^ + >* `

(25) +/. .%-/0123,

(26) 4

(27) 56789:. >y- `\&7P àb). ;Fig. + TTN, WJM 678 HMT< 6=

(28) > 3 '. +0 >

(29) +0 > +/ῌ+0 ' + 'c) 2. a. 678 ,+ '?@$% =&A1BCDED0=. b, +1 >*

(30) àb)

(31) +2. FGHIJK012

(32) LM ;Fig. + KMG< NOP. > ,+ ' - ` `) . Q% =&BDRSTUVW=XYXZJK. .%- u)

(33) h y- +,***ῌ+,/** m \PQ¡. 012[\&. ¢£ -,0**ῌ.,+** m ¤¥*. F$¦ ;HIe

(34). ,**.< - . -ῌ+

(35) . Fig. ,

(36) ,**. ] 3 ^ +.ῌ+2 >6_& àb *ῌ. §c¨©

(37) `ª«t¬-%. 0 '

(38) 0ῌ+, '

(39) +,ῌ+2 '

(40) +2ῌ * ' 0 'cd#\. +/ > `®¯ Fig. -a #\ +.ῌ+/ > `. ;HIefg`h!`hi`hjklm nD21

(41) o. )

(42) °t u±²³\&Py

(43) ´'cN\. p< ..N àb)

(44) OWK qrW ;Fig. + OWK<. &P`hµ ³N¶·¸_-%& °t u). Fig. +. Map of the area around Asama volcano, showing locations of the cameras, infrasonic microphones and upper air observation stations.. Table +.. Parameters of the cameras at OWK and AVO stations..

(45) 558. µs¶tm-s·muv wm¸S¹ºmx»¼. Fig. ,. Time sequences of number of eruptions in each six hours after Seismological and Volcanological Department, Japan Meteorological Agency (pers. comm.). Downward arrows indicate the times at which volcanic clouds analyzed in this study were discharged. Stippled bands represent the periods in which the data are invalid due to cloudy weather..

(46) . t *+ 9> V +1 3. . <7 <R

(47) ? i5@A +0 ). +0 +1

(48) !"# $% & '() *+ ,-

(49) ./ 0123 ( )

(50) 4. ;+ (Fig. -d) +1 B +2 F . C

(51) DQ)<R GQ)#Z +/ . # 56 7

(52) ./8 9 :. E WF+ +2 2 < -1 G +.ῌ+2 . ;+ +/ ,, <=> +0 - <=> ?2@. +NOOH&IZ (Fig.. +0 2 <=> +0 +0 <=>7

(53) ./A#B. -e). # # ( () <

(54) C)DE. -ῌ, ῐῑῌ῎῔῏῍ῒΐ. 4F G&HIJK+)LM NO. JK

(55) 56+<R& Fig. , L. JP 9 GQ #<RRS. Y' ) <RMU3RG?2@. TUV #)V

(56) WJCX. N M#<R ;+ ? N. Plume J& Fig. -b Y'2Z 3. "G #<ROMUPK Q

(57) . 3[J

(58) '\ 5. ?&R6() . +0 - <=> ] !"^_`#a$/ b%'. S ¡¢T ; £W¤#U¥W&. cdef g &G Fig. +h '() 9i*j. [J

(59) ; ¦VW&X§;U Y;. 01V2Z+ g^_`#a$/ klh +. +V

(60) [ ¨Z¤[ # © . !m, (,**/) 23 +0 +* <=>9-.. ª*«\WJ

(61) &XDK (Fig. -) ( 2Z. n +.* m /opqr Ws t V ?U 9-. ]Q +1 $ +7

(62) Q<¬& Fig. , . +0 0/oQ # #)u6. Y' OWK ;cde ® 7R

(63) H7. +0 +/ <=>1vw2 xyz0

(64) 2. # K 7Rf^R2U_` . 3 ) 9i*j 01V g3RG. a?&bc

(65) ¯&XDK (Fig. -c). ,**. 4G0

(66) {56 ,3 |h +0 7 +1. ( [J

(67) de?# °f2. 8 '() 9i*j ,-

(68) ./.

(69) gh i) £W± gj63 Hill, +23.h 2. E95VC :}~;cde<. Z

(70) ":"8²8Zi . f t V (Fig. -c) 'M . i k; ih&=*<Rlm'. = +0 0 ,. <RMU. °nx³ (Scorer, +3/1 ; Woodward, +3/3 ; Turner, +30.a). #)u6. opq ®. +1 7U '() OWK cde. ?U .ῌ, r´ª Thermal. @A01V £W±i 3RG.

(71) wxyz{'|OP}~ ,**. 3 +/ῌ+2 . 559. ,**- , 0

(72) . 1G@ OWK Z[6* J@\]^. ,**/. @C, AVO _K'LMHàC, (Fig.-a). !"#$% &'()*+, -./ +. 01$ 234. . . 56789*: ;<

(73) 7) = +0 0. .ῌ+

(74) . >?$ * OWK @ABC,DDEFG 7. !"#bcC,deR$ fghijk h. OWK 2HI67) J KLM$2NOPQ. lm$jkXno pq r r5sfg. RST

(75) U !"#$VWX'() +/ +, Y>. tûPvk w lm$2NvkXno +,. Fig. -. Sequential photographs of analyzed volcanic clouds that were discharged between +/ and +2 September ,**.. (a) The eruption at ++ : /., September +/, ,**.. The photos were taken at AVO. (b) +2 : ,*, September +0. (c) +3 : +-, September +0. (d) / : ++, September +1. (e) 2 : -2, September +2. The photos were taken at OWK. The times shown in (a) follows JST, while those in other photographs obtained at OWK are of +- seconds’ delay relative to JST..

(76) # µ>$¶ ·?$@A ¸$^$¹º$BC»¼. 560. i

(77)

(78) Fig. - !" pixel

(79) # $ (,**-)

(80)

(81) %&'() q* *+,!"-.) qi /0 i hi

(82) 1234

(83) 56 : hi7ditan8qi9q*:9h*. (+). di %&'*+;<= h* > %&'?@ (Fig. .a) <

(84) ABC D EFG

(85) + HIJK*+L"M NOPQ*+R "S T< U <

(86) A/C "S

(87) V di L

(88) W " (Fig. .b) A JKJ RXY "!Z[ \]"# 8^$$ ,**/: _` KMG 8Fig. + KMG: _abcdefghic'jkl.

(89) mW%n" &o ri Dpqo ,ri Fig. - , $r "sto

(90) pixel 'u S(!

(91) vw)X/0 xM" *+Y y

(92) z+ {| K},, ~) 8- Table +: _`~K uD ONN" ..3ῒ++ m @ (Table +)

(93) ,ῒ- pixel ./. ;Y"M vw_`&o/ X t +*ῒ-* m .@ 0 wi i hi "

(94) SxM" JK1'uXY" 4

(95) 2 + 1./.;Y X5, .ῒ+* 1@S* + "*+xM+Y0 +ῒ- mῌs /. Fig. .. Method for estimating the locations of volcanic clouds from camera recordings. (a) Heights above sea level. (b) Horizontal locations.. @ .ῌ,. Thermal ῌ῍ῐ῏ῑ῎. $|S 3TS4D sDpq Thermal 56

(96) 6S 3 TS D+@ 7Y

(97) D+ Thermal &o rΐSX z 3 rΐ7kz. (,). +. ῌ ra r ῏, rΐῐ ῎ ra ῑ. w7C῍g. (-). w Thermal ¡

(98) AC0 r S ra Thermal 9_`3T¢4 g £. 6¤0@ C v¥xM+Y + ¦§4. S a z r ΐ * S D V R z *. Ÿ©Y Thermal

(99) SS. (Scorer, +3/1) *+5, "X k 4@ rΐ. +Y ª « Thermal [[D 8n. Thermal t&o

(100) .ῒ+ }, ". Scorer, +3/1 ; Saunders, +30+ ; Turner, +30.b: . &o r 8 Thermal 0 EF|*+E a. (Scorer, +3/1) :. "M $ C

(101) + S 56 : C / |¬%n®¯

(102) °; 3T4!D± (-) ²S56<=³

(103) ´"S.

(104) ?@AcX @

(105)

(106) ¼¼ ,**. W 3 ¥ +/ῌ+2 @ ¼¼ z,t. (.a). zt. 561. G*W\ t* *y<Kz2

(107) K+, A *1G 34*. z, t n-ῌ. +ῌ, q +ῌ. / B4m C. + ,. (.b). {

(108) D^Q A t* Zf Fig. /a, b, d q EFF Thermal. (Scorer, +3/1)

(109) .ῌ+ .

(110) G n+ῌ,

(111) 4*vGH.

(112) . qb n+ῌ, ^QW I CFig. /῍

(113) var.D * B}JKL+NU. / . Plume n-ῌ. (Turner, +313) ). /ῌ+ . IM < w Fig. /c

(114). .

(115)

(116) !"

(117) #$. * n+ῌ, I* *.

(118) %& '()

(119)

(120). * Fig. /c 0N?

(121) 2OHPG&. !"

(122) #* KMG (Fig. +) +,. - +1 / +.

(123) , / * #

(124) 01 mῌs 2&. W (/) |

(125) n Q b;

(126) RS

(127) .52&WG w

(128) NU&LM

(129) 5 Fig.. 34*

(130) 56789. /e

(131) ῎ * 0

(132) ;;$ -,2** m ". :0 5;<

(133) =>. F2 =4> 2 MT /[;<. * ?@A@B; C ,,.** mD A ; (,,/02.

(134) k -; -,2** m $S*=4. m) ! E -,*** m "FG

(135) +H

(136) . > 2 MvT (Fig. /eῌ) ; -,2** m "F.

(137) #$;* -,0**ῌ.,+** m G2 CIJ% ,**.D. 00 0\~<

(138) W . 34* K2 &LM

(139) N' ,ῌ-O+ῌ,. 0 -,2** m $+,!x +/* sec S

(140) Q.

(141) 9 (). *TU (,) | (/) |

(142) ¡¢£. M Fig. /e

(143) PQRST* 0NU*+. !J2 i

(144) * V

(145) . V,

(146) T"KM&W NU&L"F

(147) -X*. -=4¤0c (Fig. /eῌ, ῎) 4 n+ῌ,. 52&. *kvGH5 (Fig. /e῍) Fig. /e c. /ῌ,

(148) . NU&L"F

(149)

(150) * ?@A ,**- W ,. Fig. /ῌ Y/Z./[;. ¥ 0 XY-G C¦Z§V ,**/D.

(151) Fig. /῍ +?!;

(152) 0. SN

(153) o62 ?@A

(154) *

(155)

(156) 5'I. \ ]^Q_Q*V,2

(157) 1àbcd. q KB[t EFF. M 2e - pixel 2 ZfZ.gh3. Thermal -

(158) \$t . Fig. /e i5 j

(159) k/[*;<!'. l4mn5 02 o6 +1 p

(160) q7 k

(161) E7* *.,. . 8rs2 9 . 0 . . " 2 ?@A.< ¨©. 7 *.,*ῌ*.,/ Ctu Scorer, +3/1 ; Woodward, +3/3 ;. *

(162) 89bª«(¬¤k. Turner, +30.bD vw: M Fig. /ῌ

(163) /. Scorer. (+3/1) 0| Thermal

(164)

(165) \. [;

(166) = "T; /[0 * a;. 02& * ./. <!xy<Kz z* (Scorer, +3/1)

(167) E7*. @A>®¯MW. ,,.** m @B; ,,.** m vw: Fig. /῎ +?!y<Kz z* 2

(168) ;< z

(169). 0ῌ+ Thermal

(170) m©°`± u / W. , {

(171) 7\ Fig. /e ivj

(172) PQRk=4. k *]¢²³´¢¢²1w: (Turner,. > 0c ?v

(173) NU/. b) ]¢²³´¢¢²1 k * 5I

(174) ]Kµ. (.a) |

(175) 0}@ 0\~< . ¶/|^·\ 1G (Morton. < (.b) |

(176) AW Fig. /῍ Y/+?;<

(177) S=

(178) 1 zACtt*Dn. +30.. et al., +3/0 ; Woods, +322)

(179) w k

(180) 7¸W. _à¹0He'2 Yº

(181) Thermal /G (/). 9»7a 0. 8rs2 :b<. Ctu Scorer, +3/1 ; Woodward, +3/3 ; Turner,.

(182) 562.

(183) . Fig. /. Details of ascent process of volcanic clouds shown in Fig.-. (a) ++ : /., September +/. (b) +2 : ,*, September +0. (c) +3 : +-, September +0. (d) / : ++, September +1. (e) 2 : -2, September +2. ῌ Correlation between top heights and radii. ῍ Heights plotted versus time. Fitted curves for various “n” in the equation (/) are also indicated. Variances are shown for each fitted curves. See chapter / for detail. ῎ Squared heights from the virtual origin plotted versus time. ῏ Time-series of variation of rw, which are proportional to the total buoyancy based on the equation (1)..

(184) 0AR R.»» ,**. Q 3 ¼ +/ΐ+2 »». 563. ^7 Redoubt A +33* QRS. +30.b +/ΐ+2

(185) . > ST UVn +,*** m W co-. k +1. ignimbrite ash cloud 01 !V CR.. k

(186) ! (Fig. 0a).

(187) / (Woods and Kienle, +33.) 7o . "#$%$& ' () k *+ . àXxy+ Y[UZL?. ,- Fig. 0a & k ./

(188) . 0 1 U K g Y / c Y j. 0 &1 23&45/. Woods, +33-. *.,*ΐ*.,/ 678 6 k *.,*. 2 ?81 77 R.Ft&. 9: -/& *.-* 9; +1 <=. 01 [O

(189) 7g. 2 - 7(<

(190) k >? !. \7 k=Nx. @&"-) 4+A # Morton et al.,. L&]^8 U

(191) o. (+3/0) B Woods and Kienle (+33.)

(192) C"DEFGDH. CL_(/ 7(<

(193) U

(194) & `. DE$% k &/IJK'&(L & M). R.$E a

(195) wA -,*** m b c c 0** m b W9b NxLd. $%*+, NO- 0ῌ, . A}Eeu(vAf:/

(196) 8=. PQ -R.& (.) S (3T<7. A}LBXxyL01 . 7/01&23U/7!V. 3& R.$E g()?:h. U (Scorer, +3/1) 6 z WX+ 4YZ. O/-<. 5[\ z* ]6 & ^7 89"_$à. 0ῌ-

(197) . /. 0ῌ-ῌ+ . 7(<

(198) "_$:O 01 8)B3 ! 77& /01 F Fbmr-cradrg. +/ +2 O6 .i. +0ΐ+1 &jLkl¡U ED (0). ¢£Sm¤^¥U `n& 7(<

(199) R.¦ op. &/ (-) S;OeY 77 m & <f. a1 Bn r BCA w CABBn&. gh i

(200) j .pῌ- - k=>?@A6. -? q6wAe§7.

(201) F &23U7/ cYj. ra/ ¨^W7a

(202) wUFt. Morton et al., +3/0 (0) S (-) S&l(< ;. &{©

(203) 27 (,) SB (.b) S&/. OeY :. ªwA -,*** m st ªwA -,*** m & { ./R.W7a

(204) '?f/wA. + -. ῌC,F῏ rwm῍ ῐ ῎mraῑ. (1). u«- +/ +1 +1 v& w A -,*** m w¬ u/xyL 7wU(. Fig. /ῌ ^7UBnCAD rw 0 #. ):h uR.&®z¤

(205) /7¨). ! Fig. /e :O rw &op6$;. - a +0 +3 +. v (Fig. -c, Fig. /c) . 78 (1) Sq= r k B m & 2. & (.) S¯°±²D³ ./"_$NO/. sop6$;7^7!VU/. 9 , & 77 #J

(206) /. a ra & R.$E -,***ΐ.,*** m. Fig. 0b, c ªwAstBn rs -CA ws. FtG /ῒ HA- cTTN, WJM u(v HMT . 0 ! {´? ED¢£Sm¤. wIxJ^7yz U C & { Thermal ./6. +0ΐ+1 +ΐ, µHAf:¶·. $ ; 7 / c Y j Scorer,. . +3/1

(207) 8= rw 6$;|4& /0. 1 F &op23U/7!V/ 6 /01 F &

(208) Kg 7. Fig. 0d rs ws (-) S&/WX. @Ae! 77@Ae& Nx@A, Nx@A¸ (ra-r) ῌ ra - `|. / Yj A}~.L M. & @Ae _

(209) ¶·&1 /0. ;)aNxOPU701 . *.*/ΐ*.+/ HAFt -78 6 +0ΐ. cYj Woods, +322 ; Woods and Bursik ; +33+ 4+. +1 &}/¹Dº~u) MA.

(210) RS²(T³S´)T*µ ¶T· ¸¹Tº%»¼. 564.

(211) . !"#$ %&'(. ) *%+,-+. /0(

(212) +1 ++1* %+,-+.+ &23415

(213) "$ +67 +0ῌ+1 + 89 41:" ;<3 &=>9 ?@A&

(214) +BC5 DE4F G H/3 &I9 J "KLHMNO +/ P +2 + .&Q3 RSTU (,**/) +&V0 * W .&H/XPY1*&Z 93["O \ O] +/ ++ ^ /. +. (Fig. -a, Fig. /a) + 4* -,*** m &J _.+D ,,/**ῌ-,1** ton `> Y1* -+*ῌ-0* K àbc +2 2 ^ -2 + . (Fig. -e, Fig. /e) D 2,-**ῌ3,+** ton `> .Y1* T -+* K àbc 0ῌ-ῌ, Fig. 0e & rs ws +c rs ws + , d&Q3êf". $ (rs ws), (1) g 9 Vh&.+i $ (j !&$ +0ῌ+1 + (rs ws), & %+,-+ke93 -ῌ.ῌ+ῌ. l*mn b .op&q$r

(215) r+KL."o p<)stu=>$ vwxyz{g+| &I9 } *p~"a$ Thermal +4* i F + +ῌ. d&9 (Morton et al., +3/0) F rw + , d&$ (1) g % Fig. 2f & (rsws)+ῌ, " .44* . Ty! " $ (rsws)+ῌ, +f ke"3Yn&Z93 , Fl. *&/ !^k+.4*ke"3 /0(

(216) G +Vh& 4 +.Wa*" $ .4*!"+ .+i$ (j !#r&'¡$$ . ¢ £¤A+%¥r ¦GP a§+¨© &V0.4*¢ \¦G& .W a*" $ .4*+!"+" $kª 1

(217). «e ,**. & 3 ¬ +/ +2 &_3' 9 m+. ®¯+V +1 °"±C. Fig. 0. Time series of parameters associated with ascent processes of the volcanic clouds. (a) Expansion ratio, k (radius/height). (b) Corrected radius rs using the equation (,) at the standard height of -,*** m a.s.l.. (c) Corrected ascent velocity ws using the equation (.b) at the standard height of -,*** m a.s.l.. (d) Density ratio, (ra-r)/ra, obtained from rs and ws using the equation (-). (e) (rsws), that are proportional to the total buoyancy. (f) (rsws)+/, that are proportional to the maximum cloud height. Triangles show the observed maximum heights of volcanic clouds, measured from the vent bottom by Seismological and Volcanological Department, Japan Meteorological Agency (pers. comm.)..

(218) V(89,³.W8

(219) ®¯ ,**. z 3 +/ῌ+2 $8

(220) Scorer (+3/1) Thermal .

(221)

(222) !"#$ %

(223) &# '

(224) ( +ῌ, # . rw . (#)*+,-.

(225) /0, "1#!2"1 "34#

(226) 5# +/ $ ++ /. %67

(227) 89:& ; ,,/**ῌ-,1** ton, '<. = ;( -+*ῌ-0* K )> +* +2 $ 2 -2 %67

(228) 89:"& ; 2,-**ῌ3,+** ton,

(229) '<= ;( -+* K )>?.1 ". +0ῌ+1 $

(230) )>@(+A# +ῌ, , ,- -+ )B%

(231) . +0ῌ+1 $./CD

(232) 012 & 3 EF!=12G4 !2#HF +0ῌ+1 $5678IJ KLMNO98PQ"1:R;, ῏. ῎. S<=TU>?V@W"' S<=AB89C8 9X89YZ[DE\M]^W"' F_` Ga,HIJDEb#K' LM cNOCdefPQR@ gS9hijkTl #b#m' Un oAB_`@V(8 9P?@W9pXq rAP?-FsY6 Z[K) tu\]l#6b!m' ^v_ oò_`wabAB89_`P?\M ]^c9dxq ey?#m zI6 {?K' |fghU}+qO~iq iMK Fjkl-F mn' #op' ῌ ῑ ῐ ῍ Briggs, G. A. (+303) Plume Rise. Critical Review Series, Rep. TID-,/*1/, At. Energy Comm. Washington, D. C., 2+ p. Uiq[7 r[sx (+32-) 89t8u 5#v1w.l# nx oy _`@zE ,0 B-+ 3ῌ,+. Hill, M. J. M. (+23.) On a spherical vortex. Philos. Trans. Roy. Soc. London., A+2/, ,+-ῌ,./. 9{ (+312) 89.SE6^ H, O v1&Plume Rise .| 89 ,- +2-ῌ+31.. 565. S<= (,**.) $F}89 AB[89E y ~ '0 +0 z 3 ,-ῌ-+. Morton, B. R., Taylor, G. and Turner, J. S. (+3/0) Turbulent gravitational convection from maintained and instantaneous source. Proc. Roy. Soc., Ser. a., ,-., +ῌ,-. O+[ [ [C*7[i (,**/) R0 ^¡^ (SAR) P? EV(89 ,**. z88A

(233) 89 /* .*+ῌ.+*. Saunders, P. M. (+30+) An observational study of cumulus. J. Meteor., +2, ./+ῌ.01. Scorer, R. S. (+3/1) Experiments of convection of isolated masses of buoyant fluid. J. Fluid. Mech., ,, /2-ῌ/3.. Sparks, R. S. J., Moore, J. G. and Rice, C. J. (+320) The initial giant umbrella cloud of the May +2th, +32*, explosive eruption of Mount. St. Helens. J. Volcanol. Geotherm. Res., ,2, ,/1ῌ,1.. ¢[U£[ (,**-) Windows PC ¤¥¦J§Ë©89

(234) P ? 89 .2 ../ῌ./3. ¢[Mªq[ [« (,**/)

(235) kT89:1&|V(89 ,**- z , 0 $8

(236) 5# 89 /* +2-ῌ+3.. Turner, J. S. (+30.a) The flow into an expanding spherical vortex. J. Fluid Mech., +2, +3/ῌ,*2. Turner, J. S. (+30.b) The dynamics of spherical masses of buoyant fluid. J. Fluid Mech., +3, .2+ῌ.3*. Turner, J. S. (+313) Buoyancy e#ects in fluids. Cambridge University Press, pp-2.. Wilson. L., Sparks. R. S. J., Huang, T. C. and Watkins, N. D. (+312) The control of volcanic column heights by eruption energetics and dynamics. J. Geophys. Res., 2-, +2,3ῌ+2-0. Woods, A. W. (+322) The fluid dynamics and thermodynamic of eruption columns. Bull. Volcanol. /*, +03ῌ+3-. Woods, A. W. (+33-) Moist convection and the injection of volcanic ash into the atmosphere. J. Geohys. Res., 32, +10,1ῌ+10-0. Woods, A. W. and Bursik, M. I. (+33+) Particle fallout, thermal disequilibrium and volcanic plumes. Bull. Volcanol., /-, //3ῌ/1*. Woods, A. W. and Kienle, J. (+33.) The dynamics and thermodynamics of volcanic clouds : theory and observation from the April +/ and April ,+ +33* eruptions of Redoubt Volcano, Alaska. J. Volcano. Geotherm. Res., 0,, ,1-ῌ,33. Woodward, B. (+3/3) The motion in and around isolated thermals. Quart. J. Roy. Meteor. Soc., 2/, +..ῌ+/+. ¬F[Mªq[[W9pX[ ®[ ¯°[g [±9 °[M¡¢[²° [ £¤³¥ [ 7¦¬® [ ´§¨ [ Mµ© [ ¶>ª [ «¬·¸ [ F µ [ LU¹º (,**/) V(9 ,**. z812®¯»:&?F 8 9 /* /+3ῌ/--. ~°±² W¼.

(237)