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Eruptive Style and its Temporal Variation through the +3+.῍+3+/ Eruptionof Sakurajima Volcano, Southern Kyushu, Japan
Maya YASUI῍, Masaki TAKAHASHI῍, Kazuhiro ISHIHARA῍῍ and Daisuke MIKI῍῍
The +3+.῍+3+/ Sakurajima eruption was the largest eruption in Japan in the ,*th century and erupted
andesitic magma was about +./ km- DRE (Dense Rock Equivalent) in volume. Pumice fall and lava ﬂows weregenerated from the ﬁssure vents on the western and the eastern ﬂanks of the volcano and pyroclastic cones wereformed around the vents. Eruptive style changed with time. It is divided into three stages. After the initial,
vigorous, Plinian eruption of about -0 hours (Stage +), extrusion of lava associated with intermittent ash-emitting
eruptions with or without detonations lasted for about ,* days on both sides (Stage ,), followed by an outﬂow oflava for more than +./ years on the eastern side (Stage -). Consequently, the vast lava ﬁelds, which consist of anumber of ﬂow units formed on both sides of the volcano. Some units of lava show evidence of welded
pyroclastic origin, suggesting clastogenic lava. In the western lava ﬁeld, surface blocks characteristically consistof pyroclastic materials which show variable degrees of welding even within a single block. Typical eutaxitic
textures and abundant broken crystals are also recognized under the microscope. Some ﬂow units can be traced
upstream to a pyroclastic cone. These features indicate that many ﬂow units of lava on the western ﬂank areclastogenic, which were generated by the initial, Plinian eruption of Stage +. In the eastern lava ﬁeld, evidenceof pyroclastic origin is rarely discernable. However, the content of broken crystals varies widely from ,*ῌ to
2*ῌ in volume. Most lava ﬂows, which were erupted in Stage , associated with frequent ash-emitting eruptions,contain broken crystals more or less than /*ῌ. This fact indicates that magma in the conduit experienced
repetitive fragmentation and coalescence due to intermittent explosions prior to outﬂow. Lava ﬂows of Stage contain much smaller amounts of broken crystals indicating gentle outﬂow of coherent lava. Relatively
large-scale lava deltas developed toward the sea in the eastern lava ﬁeld. Eyewitness account at that time reportsthat ocean entry of lava from several points started several months after the beginning of Stage -. Althoughsmall-scale breakouts formed at the ﬂow fronts of some lava on both sides, a large volume of the deltas can not be
accounted for by secondary breakouts of ponded lava within the precedent ﬂow lobes. It is considered that lava
tube system fed lava to form the lava deltas.
Key words : Sakurajima Volcano, Taisho eruption, eruptive style, clastogenic lava
+ῌ ῐ ῎ ῑ ῏UVW-XYZ< [$\4  \4 8]9:X!"#$ %" +3+.&+3+/  '()*#+$!8^_!`abCANc;=` %"de 2 fgh,-."/0123 +./ km- $#456768%9:

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+/0῍2//* )?   -῍,/῍.*
>ti
Department of Geosystem Sciences, College of Humanities and Sciences, Nihon University, -῍,/῍.* Sakurajosui, Setagaya-ku, Tokyo +/0῍2//*, Japan.
23+῍+.+3 pq!pq! !#"# ¡

Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, SakurajimaYokoyama, Kagoshima-shi, Kagoshima 23+῍+.+3, Japan.
Corresponding author : Maya Yasui
e-mail : yasui@chs.nihon-u.ac.jp

"·^¸ ¹ _º`»¼

162

Fig. +. Index map of Sakurajima Volcano (a) and distribution of the +3+.ῌ+3+/ eruptive products (b). Area ofsubmerged lava ﬂow on the eastern ﬂank is after Ishihara et al. (+32+). Isopachs of the +3+. pyroclastic fall
deposit by Kobayashi (+320) are slightly modiﬁed. Thickness in cm. The squares on the map show the areasof Figs. ,, -a, 2 and 3a.

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164

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Table +. Summary of ash-emitting eruptions and period of eyewitness of incandescent lava during
the +3+.ῌ+3+/ eruption of Sakurajima Volcano. Data were based on Kagoshima pref. (+3,1),
Omori (+3+0b, +3,*a) and Yamaguchi (+3,1, +302). One month is divided into three in thetable : early represents from + to +*, middle from ++ to ,*, and late after ,+. Phenomena
including rumblings, air disturbances, detonations and eruption clouds were observed at thenorth of Kagoshima city and were recorded in detail in the journal of Kagoshima
Meteorological Observatory (Kagoshima pref., +3,1). Based on the descriptions of thejournal (Kagoshima pref. +3,1), types of ash-emitting eruption are deﬁned as S for eruption
with shock and detonation, R for eruption with rumbling and A for eruption without shockand rumbling. Number of days of individual type of eruptions were distinguished by,  formore than ﬁve days,  for three to four days, and  for one to two days. Asterisks show
the period of tromometer observation at Furusato (Omori, +3,*a). According to Omori(+3,*a), tremor and air disturbances were observed throughout the period of the observationand sometimes detonations were heard.  indicate witnessed incandescent lava.

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166

Fig. ,. Surface features of the +3+. eruptive products on the western ﬂank of Sakurajima Volcano. G+, G, andG- show the localities where samples for sieve analysis were taken. “B” shows the locality of photo b in Fig. /.

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cS:d62: 2:efA ghij

167

Fig. -. (a) Distribution of individual lava ﬂow units, pyroclastic cone and craters C+-C0 on the western ﬂank. W+ and W- : the remnants of pyroclastic cones. Broken thick curves show restored outlines of collapsed cones
W+ and W-, W, : pre-existing domal ediﬁce “Hikinohira” which is thickly covered by the +3+. pyroclastic fall
deposits, W/ and W0 : lavas on the pre-existing slope of Yunohira and Atagoyama, respectively, W., W1 - W+. and W+0 : lava ﬂows, W+/ and W+1 : pyroclastic cones around the explosion craters. (b) Three sections(X-Xῌ, Y-Yῌ and Z-Zῌ) through the +3+. eruptive products on the western ﬂank. Vertical exaggeration is twotimes. Numbers on the sections denote unit numbers in Fig. -a. Gray area shows the +3+. eruptive product.
S+ : shoreline before the eruption, S, : present shoreline.

   

 W. $2:5+;<*=>?

      !"# $ +-@ W/  W0 $ ABC DEF GHI%&'()*JK  +3+. L - M NO PQRSTUVWX +322

(Omori, +3+0b) +, % &(Koto, +3+0) 1-2

YZ -*[

34#)5+ 6!'78 '-9a

+,-./0

$ C D GH\]^_- `()-  W.

bJK , W/

µ¶·w7 ¸x¹76yº7z»;¼

168

 ? :mwi *opx6:NF?;>&yz{(|4  (Figs. /d, /e)G,  G- 6

5 (Fig. ,) OIPK :}O~Q (Md)-..m-.3 RSI (s) ,.*m,.1   W. PK (Fig. 0) + mm O_O ,*ῌ F Y

 +ῌ+0 mm O;v./!ῌ

 TE65 0. mm HFU;
%'|4 ,  0. mm O~ ;;V{OF RSH 4



W+* WXY+

Z[\

|4  Z*opx6vp yz{(
Fig. .. Diagram showing stratigraphic relationships
between units of the +3+. eruptive products on
the western ﬂank. Black tie lines between blocks
are stratigraphic relations based on the aerial
photos. Approximate date is shown on the right.

 ]%  Fqu%4 
W3 ^

W1   
W1 





I 

 W+*       W+*  & W. W1 HF: C, ;' C-W++ _(012F C, ;')`4

W++  W.  W/ S a3-HI  $ % W. W1  C, ;' C- ;'B;'B

W1  W.   W+* 

W2 !"#

W+* "\' W++ W+/  W+0  W+* I W0  W. 

jPK];>&8^ W+*  W. JB  4b*

C, ;' W+* "\', - W++  W+* 79:   &'(  )*+, - W. 

 + 3 +/ c dF;' 5C, ;'8  e /012(AY , (Omori,+3+0b)  Q

.

 + 3 ,0 4 ,  567 +32/8  W2 9%:  
W3 



 C0 ;'!<4"#= $%;>& ?20@A'B C

f

W++ g

W+, _(012F C. ;'`4c0JB W3 +HFb(*$%C() ! m ?

() W3   W. *D012Eh¡F&lL¢

FGBHI W3  W+, JB   *D

\', W3  I  W+,  W!< W+* +

3  W. 79: &  (Fig. -a) W3 ,KLM-

NOJ+,PF ./0 , km

< Q1

W3  + 3 +2 R23- : !

S 4#



TK5 W3  W.    W.  W3  K6UVW C. ;' W. "+,  + 3+4 4#

 Q1



W+-  W+. /i?012 .

W

W3 

 W+- ^e£?+,PF :j~ +* ! m ¤k`i,+ 7? W3  W.  8K£l¥¦=?79:4 , X7Y 

HF¥¦=?  . & :

W+* 

 W+ ;>Z:[;=B\T§¨¤Sªmn W+.  W3  + 3 +2 ©Y

 <=U>]?^@ (Fig. -a) C- _ A;R23oY« :  HI¬ W+-  &'BC`DabEcdFe'!

Kf (Fig. ,) ;'B W+* $%  !

m ghG/(

7U20@A' (Fig. ,)20@A;>& ?F H^20@A

W+/ ] W+*   C- _ A;'B­E

HI HI W+*  + 3 +/ 79   W+/ pq® ¯:iIJj (Fig. /c) G/(20@AfiIkHK%lLf!;'rs;vt&' Mmni *opqrst8u;v  + 3:°

, 3°±45u +3+.8

C-_ A;'B!vE;'!²³´?+,



 

169

Fig. /. Photographs of the +3+. eruptive products on the western ﬂank. (a) Pyroclastic cone seen from
Yunohira. C+ : C+ crater, C- : C- craters, C : ﬂat-topped surface of the pyroclastic cone around the C+
crater, F : fractures develop on the cone, H : Hikinohira, M : Minamidake and K : Kitadake. (b) Coarse
pyroclast contained in the +3+. pumice fall deposit. It locates +.3km NW from C+ crater. Locality B in
Fig. ,. Scale : -- cm. (c) Surface block of W+*. The degree of welding changes from weak to dense
downward within the block. It locates +./km WSW from C+ crater. Scale : -- cm. (d) Moderately
welded part of W+* near C- craters. It locates *.3km WNW from C+ crater. Note that many ﬂattened
pyroclasts are contained. Scale : -- cm. (e) Densely welded part of W+* near C- craters. It locates *.3
km WNW from C+ crater.

~V±²³´µ¶³·¸῍¹³º»M¼

170

 

  + W+/  W+0

4<=>?@ W+1 I! 0* m "#$%&'()*+,-./0 ῌ123

89:; W+0  +9A B + C.  0
W- EF-ῌ, 

4 W+* 56 .0* m 27

W3 J;:

W3 

KLMN<OPQRS,TU

<=>?@8

VW,XRYZ[4\3]^_`a bc

 W+, de GQRS,fgh7ij >klm

W+1 CD W+1

C-  ῌGH +W+* 

no06 +/* m pqrst (Fig. -a)

 C. Z[uv ..-w-+.0/ m&' -+.0/w.*.2 mxy

z{|./0 --.+w--.- m }y~<'y῎A (Fig. 1a) M>dez{&'8 *;. 4 -+.0/ m B.M&' 

4 ..- m B. &'Gyxo

<=q|./-+.,/w-+.0/ mm..-w0., m, ,2.1w,3./ m o῎4* 0.,w++.1 m  ,-w,2.1

῏.%t +,w+2./ mA +2./w,- m

῏33C0t ,3./w-+.,/ m῏.=./ 0?:4v  ,,+**w,,0** kgῌm- ./0 +,w+2./ m 1¡; (Fig. 1b) 19

3¢;:£¤¥=¦t ,+w,/ m  §R
Fig. 0. Cumulative curves of the grain-size distribution of three samples taken from non-weldedpart of the units W. and W+* on the western
ﬂank. Localities of samples are shown in Fig.,.

¨%=3©B ,/./w,2 m  ==ª%]^«¬7­t ®¯°volῌ ./ (Fig. 1c)

Fig. 1. Downhole variations of density (kg/m-), phenocryst content (volῌ), bulk SiO, content(wtῌ), bulk CaO content (wtῌ), FeO*/MgO, and broken plagioclase (BPL) content (volῌ) for selected samples from W3 on the western ﬂank. Bore hole site is shown in Fig. -a.
Lithology is shown on the left column. Sl : soil and sandy part, B : breccia, M : massive
lava, P : porous lava, A : alternation of massive and porous lavas, S : sandy part.

+,w,+

ºG'§ ' 'B&»(¼F·

Fig. 2.

171

Surface features of the +3+.ῌ+3+/ eruptive products on the eastern ﬂank of Sakurajima Volcano.

-ῌ- 



  

 
(Fig. 2)! "#$%&

'

 

()*+

,$- +.%/01234567

3456&z{/.$!
+3+.  + @ +, &DOmori, +3+0b  Fig. 0J 

- C+VC- '?'YZ/]g2 M 
2! O&((v4~'- )*+,M-. - 8)

&8+9:$;<=3456> B /- 0- ,M1$ D

 (Fig. 3a)! ? (+3,1)  +3+.  , @ABC$

- ,**0 2 +J!  3'[4M'?W5B DEF T, GHI T,῍J KLMNO&P$'[\#$jkM8! ;]'?

$M-

'QR

(Figs. +*a, +*b) G9KL(C+) - 6788 .** m g2! C+ 'M3456STU$2! E+VE. ?WX,M

'?WXYZ- '[\=$'[#&0[\¢:;X Fig. 3a Ug! £¤ E+ <¥¦

2! E/- 0- 1- +*- +,- +/- +0- +2- +3 &^ 2M- § '¨R&£¤/2M9¡

Y2! E+ '.$M- E/- E+2 GHI E+3 ]V  ^^§ ' C4©+- 1* m A] - _`M Y2! E,* & E,+ abc

Y2&¢:+2 D=ª« Fig. 3b  Y .J!

ZC$defg2! E2- E+-- E+.- GH
I E+1  h/ijkMY2! +lm=i9no02M-pq =Omori (+3+0b) - >6?¬­@M

Y2®¯A $ DFig. 3a
&:ª! Fig. 3a cJ-  =/ d GHI e <¥9(B! E3  E0 rst u!"#g2$vC$

 =&02! °9'?±C Y2!  YZ- B'[4²³´M '<DRµ E¶

   GHI

w%&3456xyz{|++)! T+ GHI T, }e~> (Fig.

(Fig. 3a) w%MU

g C(/.$- w%M0=3456+&:ª2!

'¨RF·HZ- >

]²³4©+ +,* m ¸¹&¢:+2 DFig.
3b  X .J!

172 

Fig. 3. (a) Distribution of lava ﬂow units, pyroclastic cone and craters C+-C2 on the eastern ﬂank. Units withsimple numbers are T+ lavas, while those with white numbers on a black background belong to T, and T,῍lavas. Areas S+, S, and S- are submarine lavas of which thickness estimated by Ishihara et al. (+32+).
Broken thick curve shows an assumed area of pyroclastic cone E+. Arrows show assumed direction of lava
ﬂows. a : Locality of “Akashi-gongen” at the time of the eruption, b : ﬂat-topped depression which isconsidered to be buried by post-eruptive reworked sediments. c, d and e : slope covered by the +3+.
pyroclastic fall deposits, f : area covered by the +3.0 lava. Seto, Waki and Arimura are villages buried by the+3+. lava. T : Tatsuzaki, S : Shiwofuki-zaki. (b) Three sections through the +3+.ῌ+3+/ eruptive products on
the eastern ﬂank. Vertical exaggeration is two times. The +3+.ῌ+3+/ eruptive products are shown in gray,which is limited to subaerial part for Z-Z῍ section along a pre-eruption o#shoreline. Broken lines in thesections X-X῍ and Y-Y῍ are estimated sea ﬂoor based on the pre-eruption topographic map. S+ : shoreline
before eruption, S, : present shoreline, N : Nabeyama, G : Gongenyama, M : Minamidake

 

173

Fig. +*. Photographs of the +3+.ῌ+3+/ eruptive products on the eastern ﬂank. (a) Panoramic view of the eastern
ﬂank from the top of Sakkabira on October +3+0. N : Nabeyama, A : Akashi-gongen. (b) Photo of the area
shown by square in (a). It was taken on ,, April +3+/. Black, blocky lava (L) can be seen in theforeground and T+ lava and E+ pyroclastic cone in the background. Photos (a) and (b) were taken by theImperial earthquake investigation committee at that time. (c) Occurrence of the surface blocks of E2. A
ﬁeld note in the center is +/ cm long. (d) A block in E2 showing variable degrees of welding. Non-weldedpart can be seen around the hammer with .. cm long. (e) Blocky surface of E,*. A hammer in the upper
center is .. cm long.

´µz¶f·L¸¶=¹oº¶{»2¼

174

Cab=%D'an)op= 3 5qrDsE
F-t +322 G ,-9 ' BG( E/  E0 =
_

uv()

*H (+3+.) 9=-%D

 ()3uv3' Koto (+3+0)  + 6 ,1%D= ()3uv3 w=9=Ix? yJ' () ' <z%D
Fig. + K#?BG(9=(F=2()

L+{+,MN-#?' , m W*OP@)
+5>>f|+,-MN=Q9=}

E/ 

E0 ?



%D'9=

Koto (+3+0) '~.3RS'_
Fig. ++. Diagram showing stratigraphic relationships
between units of the +3+.ῌ+3+/ eruptive productson the eastern ﬂank. Black tie lines between
blocks are stratigraphic relations based on theaerial photos. Approximate month is shown on
the right. See subsection -ῌ- for the periods ofgeneration of individual lava.

9=? T+ 

33

T=. T, %D@)' 9=%D!X)}3 RS'f2UD= ( Va%D=() +3+.  + 6WD'2UDX}
3  Y'Z

%D[YZ\#Jaggar (+3,.)  + 6 -* 1>]0'

^.3a,d'g3' , 6]?4'_.3`.3 Koto (+3+0)  , 6 + 1 ; (+31/)  ,E , 

Omori

6 . 1%D'a[.3uv3 Omori (+3+0b)(+3+0b)  Fig. 2.  E, 

#) +3+/  3 6W{g=X5b'_3     

! "#$%&'()E, * E+ +,-. E+ +,-/012.3'4()+3+0b  Fig. 2. +3+.  . 6789

ῌ

:)+;<= + ?@=!A"#B$
,D' ())  '0='()E. G
Omori (+3+0b)  Fig.
E. ' (

 !' E, 2+ 6 ,+ 1 52R31S4T9 ( E. V) ,+ 1W567.3U'X

 +3+.  . 6( 1 6%DD

U
W*

3'

)]:)@p=¤(Omori, +3+0b)U)(67.3%D)f`i¨.3?Xj1k©.3]].)
E1 V*ª' E+*  E+, !X) +./ km W*X3' ()

+ 6 ,- 1(mE%D'L¬@no1 C0 +;( E1

129
E2  E/ ® E0 p/>f'q

g0 h9=i '_3 9= 5Fig. 3a  a9 %Cj>f +5 (+*- m) #0* m W*f

'..()E/  E0 AYabB#0 /**m kl=V)m)%&.

jabB

+3+.  + 6 ,. 1 +* Y .* ?9=

E1

 n0­. .3_0 (Koto, +3+0b) E1 ?
W4() %D'()

9=

E1 

«Q?@

yJ?Q!X) "0 w=l 1

E.  + 6^1"@)3#A=_

+5:;`<(Fab .3cdeEf, ¥?(0 :). ¦n h§ E, E- "#$ E. YZ89[' \Q]?@(Fig. 3a) g3 E0

uv()3 5; +3029 %DD:;£]1"@)+HIJ, K$3LIMNOE+,2/  +;./)'

e

nKd

.3%C+

E.  C/ +;(F(+;)

' () PQ%C.

E3 ' E0 #0' . af%D)g¡C'*¢.3]

5Omori, +3+0b  Fig. 22 ; Omori, +3,,

. +;)?@* +* m =E0 'd ;. "0 )(0 @)34()> Figs. /0 /19 E- &'E1'(Figs. 2, 3a)5Omori,U)(#0 E0 67 +3+.  , 6*^#A=_kc.3uv()

5Omori, +3+0b  Fig.
E2 #r.st%C.3+HI+,-¯°
(Figs. +*c, +*d) w= E/ & ;E1'4() =
5Fig. 3a  P u9 E2  E/ (v±%D=_

RS'f



E2 ewE²³x%D'y*

º+06)?0 0 » aD¼
 ,  +.  E2     ,**- E2

 ! "#$
E+*  E1  E++  %  E++ & '

*+, -* m " -E+*+** m ! , -** m 61 +3,1

./



 - ,,  C0 012"34



5 , 

 !"#7 E+* "8 

61 (+3,1) 9

AB 
E/ $ E+0 Rxy +P]gzg$!

"3 Rxy E/  E0

   E+*  ) "'

(%

175



$

- :;%<=&'(9 , >?@

y

{-"

VW  +* m

9 aP,  / C :Q"

7(

&

X+b



L

E+0 AB NZ ^ E2  $ E+1  m !L ]_ _  f/
S B

"`0, E+1  +3+. 8 / !Wg$"
Fig. +*a  +*b )ab caHI, @"" J, d yefghi,  - ./' @   E++  E0  E+*

 HI Fig. +*a  +3+0 8 +*  Fig. +*b  +3+/

TU  :Q V- E+0  %  E++  E

8 .  ,, "  +*   Fig. +*a 3j&[



(%



M4!"3 E/ d E0 \]+J, E+0

E++  C1 012-!" :-" +.- km

7( (Fig.

+3,1 L& O<01ap  O7Z

E+1 

!L 33 /Q"4RSM 56(%%[ $ !"8U Fig. 3b

/;OP"01AB '|p }~ Y g$) 618 -!".K L M E+*  , N .

&2) M4! +3+. 8 /  3  C. 01

U:AB .  1C,*  D)E*+ FG2
HI, J, E+*

XYSt@T)A+P]"MAB  E+0 Rx

$9 +3+. 8 . !WAB

 $

 
E+,  C2 01

XY

9&!"3 E+, C2 01:Z-[\;G-+P]

9 C2 01=>3'^<_ E+,

9-- ./,`   E+,  E1   E+/  % 9  DAB  ?5'ab@"
E+* U 

B1




9
+-

 E+2  E+3"AB Fig. 3a

L&j `0!"BF"3 E+3

k, +* m !(%7(3 E+3 \

E+2 @ (% _  3j" 3 :; l3



q

¢

m nc ¡P£,



(Omori, +3+0b) E+0  /  3   3 
$c E+-

E+0  Fig. 3a {3 9  E+2  E+3 HI3

@

C. 012  A  /dd)e E+*_ (Fig. 3a) f/J," Q B

R B

%Q B R 

g$_Bh $iCD  (Fig.2) E$, E+.

 E+-  E+.

:&jEk'F- G) _ o¤ :;P":D E+2 ¥g\ E+3

: ?PMg$"
3jp&  ¦§ E,*  E,+   +** m!: , + km !:

L +, 0* m !: Yq-

 r{ stuv- ¦§)
)w3 E,*  E,+#-xy'tz8¨' (Fig. +*e) ©p {ªA

E+/  C2 01 /** m lmHI3./'«V" 7| g-!¬'U ­_ " :&jEk'`' E,* L_    (,**-)

 E+-  E+. JK3-! (n) +3+. 8 /  ,/

HI J,'  3  J,  9 n-!9 bD:AB 3 ,0 L6

M

Nn

, on

01"apO7T B E,+  U B  

1- ) 8  (Fig. 3a)  ¦§ )wab® 0ῌ- }"tu3
!L"¯~ab°g] M±²

³´ E,CE3  T+ E+*CE+3  T, E,* ¥g\ E

] q P  (Omori, +3+0,+  T,῍µ!,  61 (+31/) g  M46b) !" E++ d E+/

rQs   / @ , L;  o¤  M" 0: E+0 tu  %  E++ abAv'

1 ¡

 wM 3 :;¸ , N¹  M" Ut T,

 C2 01E+/

X , b   T+¶'·´µ¢P¶· ¸.¹QºR»¼

176. 

 (+3,1)  (+320)    (,**+)! (+320) # +*  $ SiO, %"&' ῌ( )*+,-. 0,ῌ /

0 12 /2.130+.2ῌ

 (+31/) 24   , * + *5
66 SiO, 0  , *789:;< =>

 + *?@ , * T+ T, 12A2B;

CC DEFGH0IJ 13 KL M:N SiO, %

7 ..1ῌ 

 /2.-30-ῌ

:O; (Fig. +,) !$0SiO,-MgO #: Fig. +- O; SiO, $PQ"#R   STUVW:X;Y,

Fig. +,. Frequency diagram showing distributions of
SiO, content of the +3+.῍+3+/ lava. For deﬁnitions of T+, T, and T,῎, see text in Chapter ,.
An arrow shows the range of SiO, content of the+3+. pumice fall deposit.

D T+ T, ?@ T,῎
Z5
T+ $ T, :[;$\# 0+./ῌ YR$

SiO, $]^_

T+  D%&` 0+.330-ῌ $ a0 %12 0*.03
0,.1ῌ $bcd (Fig. +,) D% SiO, % e)*+,-.12$fg'(
% T, &` /3..30,..ῌ T,῎ 12
T, $ T,῎&`fg'(/2.-30*.2ῌ

 T,῎)hiE SiO, % T+ $5$ 0*.030,./ῌ j;(Fig. +,)

SiO, %;

T+ lhiE,m;

0

%

&`'*

+k T, &`$'*

D% (T+)  SiO, %Fig. +-.

SiO, vs MgO diagram of the +3+.῍+3+/ lava.

nopT

qrF2  W3 stuVvwxL?l y- ".  (Figs. 1e, 1f) %  E0 E1 E++ E+, E+/3+1  0+..ῌ /0(Fig. +.)

E+* $ E+. 1z{|EFr$ T,$}~F2  /L:GH0:2

 ?<:.65%] (Figs. +/a, +/CC ?B-{hFi 0 l?Cb)

2<F2 I ?<$;Del EF. ?<F.D%&Y, BPL $( :)G HI0 +) J 2; 34

K;< 40¡¢:L£;  ,) ¤M¥, ¦/   

*./ mm YR?<F.D:20 ¡¢§:¨  -) ©ªVT«¬VTG ?<F.$?< .5.6  (+31/)
7 (+312)    (,**+)




! "



8t9$IJ 31 :

;<:N =.~ .> 6?<$%:Y,Z5

@A0

F.:HI;  .) ­ ?<F.D
%&NOῌ( :®<

BPL¯+**°&BPL*±&BPL*²NPL((CC  BPL* ?<F.«¬VT³ NPL ?<  F.«¬VT³

ºW~ ]~]~¦8»¼T `yG

177o8_& (Fig. +/d)





 BPL H ++2.ῌ $

0*ῌ 23 BPL (Fig. +1)=>?@ABCDE&F

'

!

s +6'`,& .*0*ῌ I!=>?@ABCDE&F
(Fig. +1)W3 d>eSfghi71j

k&l 0*ῌ J:&(Fig. 1f) K!=

D' BPL H$bc$ (Fig. +0a) sXs W. W3 8 W+* LM^ W+, LM

N^ BPL 

W+0 _ BPL N&*

+./0 &bc$ I Fig. +0a  Q 
Os

PsXs i7

$ - 0῍+ F)
Fig. +.. Map showing spatial distribution of SiO,
content of the +3+.῍+3+/ lava on the eastern
ﬂank. Units with simple numbers are T+ lavas,
while those with white numbers on a black
background belong to T, and T,῎ lavas.

/ῌ,

   LM+6! ", mm, 1/./ mm ./0*+,  j+67$,% =>?@A
BCDEyGu ,G'()H+ **H+ RSTS+ *+IJK+,G'$ RS BPL  Fig. +0  
Fig. +1 

TS+./0 *., mm J: ![P&Q "#&/ῌ+ 

RSTS+2+-.()"# >p + 8 + -.

      

2jsX3^&"# >p , $     !

 "#$ % "#&

!9'!($   )*+RSTS+Xz\,'ss3^!*+./0",!- +.1 mm, 1- mm $ *+./0", mm 231

0 mm # +67$,%$

*+45%"#8 %

T+ >p , &T, >p + 8 , T,῎>p + u$

T, 8 T,῎R

4a,G'&i7+6'`,
& 



  BPL  H  +-  2+ῌ  $ (Fig. +1) +*-/ῌ 51' (& .*0*ῌ 

& ./ῌ 23i7=>?@ABCDE&F"#!9 :;<%=>?@ABCDE&F"#S$ T+  BPL TH /*ῌ J(Fig. +/a) ,G'()H+ **H+ *+:ww& T, 8 T,῎ 1 Y23 +*-/ῌ 8N&

IJK+,G'$ LMNO /, -.

BPL (Fig.+1)

PQ /0RSTS+4U'VWX + -$O, Y.1Z[RSTS+4U*+80  

H+\,]23^ _.'456

0ῌ+  !"#  `,45 4a,G'&.U V W XYW Z_ ~+6'`,4&bc$ W3 d>eS

I&l~¡z ¢S[£¤ ~¥\~¡'fghi7 1j k&l<%=>?@A}jBCDE&F

W+*  G, 89 (Fig. ,)  

mi7n +, mm o. :;

]~¦(&l§^¤l& S¨ Sumner, +332 ; _ ` © ª « ¥ ,**+ ; Yasui andKoyaguchi, ,**.

=>?@ABCDE&Fab¤pgeh o< =qars `¬­<%"#k8 !~¡z 

>tTp'u (Fig. +/c) =>?@ABCD

8~¥X®csdecM 2j )¯  8°

E&F

v?O ow456@x!yz± ²fg³& }j{+h´'4aAB`,'3^ !* Fig. ,  C 89 AB`,45^ µe >¦]~JP{+C|DP}j~E 0῍. F:  <%~¡]~`,'¶·¤¸8¹i¤µ [¶·N¸¹º»¼178

Fig. +/. Photomicrographs of the +3+. eruptive products on the western ﬂank. (a) Eutaxitic texture in thesurface lava block of W+*. Lines denote broken surfaces of crystals. Many broken phenocrysts and crystal
debris are observed. Open nicols. (b) Broken plagioclase contained in the bore hole core sample of W3 (,+meter in depth). Inner zonal structure is clearly cut o#. Crossed nicols. (c) Vesicular, pyroclastic grainsfrom non-welded part of W+*. Sample was taken at G, (Fig. ,). Grain-size of particles is + ῍ , mm indiameter. Note that some glass shards are remarkably elongated. Open nicols. (d) Grains from an ash fall
deposit which overlies the +3+. pumice fall deposit. Subangular, massive, lava fragments are dominant.
Sample was taken at the locality of C in Fig. ,. Grain-size of particles is +῍, mm in diameter. Open nicols.

 

,**-

  ,**0yz{ |./0&  }N~lmnopqrstuv  *+  !"#$%&'() *+ ! EK E 0}./!,-./0&1(23 4

0&!~lsG'L=L

5 6 !"#$%./0&*+

7389:;<'= > ?4
@& ABA.CDE.FGHIJ1KLMEK NO/G

Gf%!kst
0:<y!3 n + (gE
=L

G

#stEK{ ?4./0&PQGRST O/U1V%!Kst@E¡¢G^_£1( ¤E.

*+!,-XYZ!./0/0&!"k (BPL : 2*ῌ ¥ ) N~1lmnop

W&1[\]G^_`aS bT!cde f

qrstuvG¦_£1( n ,  §E(

fghijE ./0&!"klmno¨0stE ©ªZ«¬­®¯Z°±

pqrstuvG^_1w<xK>1^3

8²9³M ./0&1´'<|

 

179

Fig. +0. Broken plagioclase content of the +3+.ῌ+3+/ eruptive products of Sakurajima Volcano. (a) and (b)show spatial distributions of BPL content of lavas on the western and eastern ﬂanks. Asterisks are samples
with well developed eutaxitic texture. Numbers with ‘Q’ are samples taken from squeezed out lava. Opensquare in (a) shows the locality of bore hole.

³´µi¶x·N¸¶¹º¶j»&¼

180&H'(12 +3+. ) - c ,, *+, C0 ;\-L4d.W8DA+ #/ +* m e0
2123fbgAF Nh\ +31/P ij4 W++ W+, W+0 E++ E+0
56>kH W+, !

8W

DlDlm m nopq

7r[D 89$W342 W:;HG< =>s ?@A*Bt2F
TU42 W+, 7r[DW BPL/*ῌ CK (Fig. +0a) ugA W+, !vwH
BPL x+ 

;\].yz

2FBCQR i2

W+, {|C0 ;\!] W- ;<=?B5iD W+, }~)AKEF
G>HH
W3 p>)F W3

 "%;<W;<6WTU42 W3}~ GHIJ42$ W.  W+*  + iL4 G

HIA;<6QRx i24
Fig. +1. Frequency of BPL contents in the lavas
from the western and eastern ﬂanks. Opencircles : samples with a distinct eutaxitic texture,
T+ : lava ﬂows generated mostly in January +3+.
on the western and eastern ﬂanks, T, : lava
ﬂows generated after February +3+. on theeastern ﬂank, T,῍ : lava ﬂows, which form lavadeltas near Arimura coast, probably generated
after the summer of +3+..

[7)A KD.LH
M,&N ; ["! NW+* !OPP QA J"W!DF;<Z3 NO +320P RS
TD JLgAaH W+* B5
U

%DF;<JWV>@FFFZTUW>r DL
D KLH,Z W+* ! W+ ;<="&X$$5B5*YHi

W+* ;<=:;;<6Wi>.kH ;< (BPL : +*0*ῌ) W.  W+* +   W+* !

"#$

% &'  (Figs. /c, /d, /e) W3 ( E1 E2 + ) *W++ W+, W+0

E/ E0 E+* E+- E+/ E+3 E,* +,- E,+ .

,   E+3 E,* E,+ ! 

7

+

+

/$

012$

+ 34256+) 89:;<=>*?1@AB

CDAEDF ,) GHIA;<6-) J!KL4DF;<>M@A

EDF NO +320P  - )QRSBCQR)ATU VW8


)A

+ c +/ *KD @ Z[>7DFZ ¡\ Nh\ +301P Jaggar

XYW,Z [\!]L4"

W#^. _`$a%Jb(+3+.), c"¢ £[¤12F¥>j¦D§] ¨©VH,TUF i24;<
{|

^[

L4 C, ( C. ;\!]

TU42A (Omori, +3+0b) ;< _mªD
F B `DA>¤HX $LgF
TU42 W(R/a>¤DF;<$ U$ M,hb!
">«.cZX;< wD$TU42
0ῌ, 



Head and Wilson (+323) ( Sumner (+332)

W d,;\]e¬­FR>kDd®

f( ;¯©g DFL>°gF ii ±M,hb W.  W+* ¬­(B5U²hDA;<6W[7>TU»L 
-ῌ+ 



,_3¼ R:gq

181



u1  g13i (Fig. -a)  

6 %E (Later collapse generated lobe) 2*

C-







 ,*  +,+/* m 

345 W+*  W.

!" 

KL jY3c4b'T )2"& W+*(Omori, +3+0b)

#$%&'( C+ )* C-./0

#12

 W. ( W+



 

39



6345*:( W. ( + km ;< =Fig. -b

Y "#> ?@ABC +32-D20 $

%E &

)I

345*

 67683)* W+

+,-

!Pu’u ‘O’o,' F(( GH#$J"KLM %ENOP+`"83( | +%8W#k8

W#( C-`4wxyzlg J+j)TKl)q6 (Fig. ,)


C-

+

%(0

<% e# ,)T-."345* ; % <"  g13i%%E+J"34583V

W+*

W+* (m %XEn""- 8,'-." g%X" o

*(LCQ3*R ! S&%E+3TK+J6,I

7ApqCr"p2 3

U* (Heliker et al., ,**-) 8(  -./

45* %XEn( N]^O_ 12)I XY3+3

V&0WJZV2 < W. ([\ N]^O_

$J<TR+`"345*a,'-."K

L8 Wolfe et al. (+322) ( +32. $ R9

%-2 3st

1"%X

Pu’ui" 8(+J8jk

5En3"K W+* ,(e#t=>;" J8j)TK"nq621AIJ W+* 35c6 f[\N]

( 2"& $J<T^O_

6l<&=m>;" +J6nKEopq6r4 s62  V&t=(26% =m

E



n&K(wx& E,e#)*f - km -:;6 !Sgh& ”spatter-fed flow”

JE tuvKLM+J4b Pu’u ‘O’o 35c"K&d67<
‘O’o



s

21gq)*#( +** mC+s h&-.<83sa 3*

3c 8(ue# ?@A-.6 ,  (E+) 1345* E, (y+3"K !Sg+JBC D&%E+3T2

3

< W+ vE(&FG1

t=>;6 8

E( W+*

eAf

+EL

H" (Fig. ,) J+j)TKwxyzq6 8 2
1AIJ( L +320 $ B/

Pu’u ‘O’o

spatter-fed flow { |K# =RS}~  ,**+>

2h( C+ T" C-#f 1* m 3
, +, C;J< C-

#(V +/ C< =Fig. -b#> C+#W++3"~¡| spatter-fed
}2¢~%E{

0ῌ-

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 W#XAY< ( % n  ' C-

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 %E r4 h"  +,0** m  %E & 3R+J"
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184

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185

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¦ x 9 x Yx 8x "(+3.0)  ,+ J - )%, § XXIV,+.-῍+/3.
Head, J.W. and Wilson, L. (+323) Basaltic pyroclastic
eruptions : inﬂuence of gas release patterns and volume
ﬂuxes on fountain structure, and the formation of cindercones, spatter cones, rootless ﬂows, lava ponds and lava
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