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,**/  1  +  ,**/  +*  + Growth History of Mayuyama, Unzen Volcano, Kyushu, Southwest Japan
Nobuyuki OZEKI῍, Mitsuru OKUNO῍῍ and Tetsuo KOBAYASHI῍῍῍Unzen volcano is a large volcanic complex which started its eruption ca. *./ Ma at the center of Unzen graben,
Shimabara peninsula, northwestern Kyushu, Japan. This volcano consists of many volcanic ediﬁces such as
Takadake, Kusenbudake, Fugendake volcanoes etc. These volcanoes are composed mainly of lava domes andthick lava ﬂows of hornblende andesite and dacite. Volcanic history of Unzen volcano is divided into two stages :the older and younger stages. The younger stage is subdivided into three sub-stages which consist of Nodake
volcano, Myokendake volcano, and Fugendake and Mayuyama volcanoes, respectively. Mayuyama is an isolated
volcano on the eastern foot of Fugendake, and is the youngest among them with an age of ca. . ka.
Mayuyama volcano consists of two adjoining volcanic ediﬁces, Shichimenzan and Tenguyama, which trend
north to south. Geological data indicate that there was once a large lava dome of the same size and at the sameplace of the present Mayuyama. At the beginning of the Mayuyama eruption, uplift occurred around the present
site of Mayuyama, and pre-Mayuyama collapsed. The Shimabara debris avalanche resulted from this movement.
A small area to the west of Mayuyama tilted and formed the Taruki plateau, a ﬂat uplifted surface. After thegrowth of Tenguyama lava dome, Shichimenzan, a volcanic spine, was formed at the northern slope ofTenguyama. Due to the growth of Shichimenzan, the northern part of Tenguyama su#ered intense shear-stresswhich resulted to the formation of many faults and lineaments. During the formation of Mayuyama volcano,Mutsugi block and ash ﬂow was generated mainly to the north of Mayuyama. On the bases of two radiocarbon
dates, we estimate the eruption age of Mayuyama as ca. ..0 cal kyr BP.
Summit lava domes of Fugendake were also generated shortly before the Mayuyama eruption. This meansthat lava domes at the summit and ﬂank of Unzen volcano were almost simultaneously formed during the ..0 cal
kyr BP eruption.
Key words : Unzen volcano, Mayuyama, eruptive history, lava dome, ground deformation+ῌ ῐ ῎ ῑ ῏+333): [$\ ]^_`Kabcdcefghg$7  !"#$%&'%()"*+,-;XijklI-: mnop r#p xypz{

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and ash ﬂow $VWX7;$YZ89- (Hoshizumi et al.,klI-:--+ῌ20-2 FIDB!  ,ῌ,1,ῌcde  ¡¢£h¤¥¦# §¨ ¨©ªO ¨©hO«
Dia Consultant Co., Ltd., ,ῌ,1,ῌ- Yoshino-cho, Kitaku, Saitama --+ῌ20-2, Japan.
2+.ῌ*+2* ¬­®¯ 2ῌ+3ῌ+¬­°±±#.²³´±µ¶Department of Earth System Science, Faculty of Science, Fukuoka University, 2ῌ+3ῌ+ Nanakuma, Jonan-ku, Fukuoka 2+.ῌ*+2*, Japan.
23*ῌ**0/ ·¸%¹º +ῌ,+ῌ-/·¸%°±±#.²»¼´±µ¶Department of Earth and Environmental Sciences,
Faculty of Science, Kagoshima University, +ῌ,+ῌ-/Korimoto, Kagoshima 23*ῌ**0/, Japan.
Corresponding author : Nobuyuki Ozeki
e-mail : N.Ozeki@diaconsult.co.jp

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442

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Fig. +. Map showing the location of Mayuyama ofUnzen Volcano. Mayuyama consists of two
adjoining lava domes, Shichimenzan (S) and
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represent tephra section in Fig. +*. Locality 1 represents outcrop in Fig. ++. Locality 2 represents sampling
point of carbonized wood in Mizunashigawa pyroclastic ﬂow deposit. S : Shichimenzan, T : Tenguyama, Ta :Taruki plateau, Mg : Mutsugi pyroclastic ﬂow deposit.

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Fig. /. Sketch of Tenguyama lava showing thefacies change from massive lava to crumble
breccia.

Fig. -. Map showing the distribution of pre-Mayuyama rocks.

Fig. 0. Distribution of lineaments delineated fromaerial photographs. Solid star represents the
locality in Fig. +-.

Fig. .. Aerial view of Mayuyama taken from thesouth.

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Fig. 1. Aerial view of Taruki plateau taken fromthe northwest.

Fig. 3. Cross section showing the geographicalfeature of Taruiki plateau. A-Aῌ line is shown in
Fig. 2. Arrows indicate the vertical movementof the faulted sectors. Southwest part ischaracterized by predominant step faults, middle
part by small graben along the crest of
deformation, and northeast part by a steep scarp
due to inclined upheaval.

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Fig. +*. Representative tephra sections around Mayuyama. Locations from + to 0 are shown in Fig. ,. AT and
K-Ah are wide-spread co-ignimbrite ash-fall deposits from Aira caldera of ,3 ka, and Kikai caldera of 1.- ka,
respectively. Wood fragments are present at the bottom of the lacustrine deposit.

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(Reimer et al., ,**.) / =<I> Calib Rev/.*.+ (Stuiver and Reimer, +33-) 9*G TT'+ G~=)
,"

o!# ,  #-$h. +320 ;%&$ +33/'  . kyr BP  T6}x)a(,s)  .....2 cal kyr BP E TL a..3*.. ka #/0$ +333' (\^_ Loc. . 2 ,"


?@

 --0*+** BP (NUTA-

0/0* : d+- C-,1.1)  +.C a9(G Ta -..-.2 cal kyr BP }x)1  ' XY}2#9] G"  @,3 ¡a\FG Loc. 2 #Fig. , : /¢£¤4 
' "5¥ .+.*+**BP (NUTA-0//3 : d C¦,/.-)  +.C a9(G +--$6 (+33+) o!#9:|G - a# 
 . kyr BP \ T6}x)a (,s)  ..0..2
Fig. ++. Sketch of exposure at the surface of Taruki
plateau. Although greater part of soil-tephra
layers were washed away during the deformation of the area, some of them are wellpreserved especially along fault scarps due torapid burial.

cal kyr BP E'§¨ TL a((6 Takashima and Watanabe (+33.)  ,.1-.. ka 7$ (,**.)

8© ..+*.2 ka ª -.2*.0
ka 99«  T6 TL a '¬­a( ,"/$: K-Ah ;Da#+. C a 0./ kyr BP }x)a 1.- cal kyr BP ;

 


"

#

 !

$%& +33/' ()

*+,-..-"Kitagawa et al., +33/ ; <= +33/' ` T/9

] 
>¢$ (+33-) /®?@.¯=> FT a9 0
- ka /9«$%& (+33/) "- -/01 2 3456/(/®?@.¯=>¬­AHG°B9±C G

786 K-Ah 9:;<=>?@ 2* cm FG D²)E@.F³@. TL a #7$

A<BA( ( AT CD56E

 ,**.'  p6{6 -.+*.0 ka -..*.0 ka \FG HAIJA(  K<JAL/®?@.¯=>/´G 

MNOPA<BA K-Ah *+QRS
 TUL VWXY(*+Z[\HGT/9])

E2,".¶EP6

H?µ@I)/¢ K-Ar a *.+/*.*, Ma / *.+2

*.*- Ma #J$ +33,' \ K·ba9])/ 



^_`G ,  C a9 bcde General+.

'¬­Z¸ VWLMN ,*-* ka  TL a((6 #7$ ,**.' ´]^ 

 E _`ab

USDP-+  

! ,*"/0 m #$%&449

IJ+ +3* ka  K-Ar -/ 89:; +33/ NOPQ

RSTUVIJ *.+1 K *.*, Ma  K-Ar -/'()#*+ , ,-. C -/0123456

WX:; +33+ ; Watanabe et al., +33- Y +,*K-* ka

7 89:; ,**, <=>?@AB5C D+-*K-* ka  TL -/ (Takashima and Watanabe, +33.)+.

E

FGHIJ ,/K+, ka GLM

Table +.

Table ,.

0Z[45C D

Radiocarbon dates for Mayuyama volcano and its adjacent area.

TL, FT and K-Ar dates for Mayuyama volcano and its adjacent area.

Pﬂ : pyroclastic ﬂow deposit, DA : debris avalanche deposit, \: Kureishibaru pyroclastic ﬂow
deposit in original paper, \\: weighted mean value»U¼, ¥U?

450
0 
0ῌ+



 



  


 

!"#

Fig. 0 Fig. +, $ % !"#&'()*+,-.'/0 %& 12
,34 !56. 7.6&89":';<=2 7,3># ?34=@A B&CD$3E F%=2 %GH,
3E& &I'J&'KL?34F%M.*NO&( /P ,@ *NO
&& QRI'J)%*S&=+6.=2 T,U-. +332 %.63&V
VWX4!56. B&/Y4Z0[\]^ Fig. +,  FG 4_6. %GH\]^ CD$3E@G<WX
1`& F%a %Y2 3bMc4d6QRI'452% $ 
6eM.f7g.4h%d6 hI''&89' ,ij4d6QRI

Fig. +,. Close-up of fractures of Tenguyama lava
exposed at the +13, scarp. a : continuous crack,b : discontinuous crack, FG : fault gouge.

' k6. :`/l5= k; 4mno p2Q
RI' <k5=M. F%q>r&6d&,24 3b4>
0%

? /Ys*t@AB 0CDEuM.vwq>&FG0x%.yz H{I|bJKLM&N 

19i0A j2='d2
 F ,=2 9i,@&?*40A

"+Gx=44kx=2 l m¡ n#/1`%d6 gIh &]_ F _ ¢ =M.

=F%M.OPM.4 7}2,~& £¤3 ¥o¡¦$@G<

PM.=2,dx H{I|bJKLM Q;pK§@wgIh ]_ F¨©& gI& RSY c|YT0h ]_q4N_ª0% $A n`Y24H{I|bJ~& k2

gIh

B ; &U#VW41,**.  h ; |st$  *lW TL bc ,*«-* ka : q U r`=@A H{I|bJ~XY k%/¬u@m­ +.C bc v , wbx : y®Ur ,**,

  Z&|bJKLM@Y[\]&89Bz 7.¯k gIh & //&{[/Z4  ~P ,&^°|2|±4|st$6.,dx 75 H{I|bJ&NF%@k6. %.6%d6 gIh &{°³|0q)dk,24n$0

st$ 0x 4 Nª_}x=~%GH& 12qmn´_ ¢0A %h ¡1$4

=@A 7_>%dH{I|bJ4)

,2&=2 `a&NF%bc d|bc =5 k6.

H{I|bJKLM +.C bc9e (..0 cal kyr BP)²%=2

S]_}x=qlm4WM.

|_}H Sµ,~´& ¶·fd|@2=¸¹0ῌ,  |& ~´@A* ~´@A4

M.=2 · ,*** bd

gIh  K&,x=24 4&& "+ M67º4&QRI'}H»g 2?¼:


 ,**, +311+32, 

451



 

     ! " #$%&'$ ()*+,-./(Katsui et al., +32/)

01  23

456/*7$ 89 :,0, ,** m ;<= >>01 2? -.0@
A/*7$ BCBDE)*
FGH/*4 >I+

MNO (cryptodome) 0P/*4L>0

2FJKL
QMNORKSTU+4  (,**,)VSI W 04IX Y=ZI
0ῌ- 

^! K-Ah $_`=>0

[L\+]

a& *4 "#bc +33/ ; Hoshizumi et al.,+333 /d/ $efῌ%gf K-Ah $/4&

h 2 i F'^/  2
jk()& i

*4+4 l* (+3+0) m)/+ 01 @n,o9=$ >-./pq+r 2?0I! " 0I
9J= s >,oLt [L\+]^!0u+)*7$ > + jk0+$Fig. +-. Distribution of two debris avalanche deposits.
Shaded area shows the probable source for
Shimabara debris avalanche. Ma : Mayuyama
debris avalanche deposit, Sh : Shimabara debris
avalanche deposit. Solid star represents the
locality of lacustrine deposit (Loc. . in Fig. +*).

v+4Fig. +-  [L\+]^!0L\+]^!-1w= 2x-1Ap (+33.) 0;y3 =  zx-1{)& R+ 

z4 2w+4>0d  

A/*[L\+]S/ ,0v

|5 6} +332 ~4*4 [L\+] S+ ( 2?8+ T )* ^!7  2x89:;=  zxL\+]^!03:;<-1/*4 a [L\+]^! iJ L\+]&h/ [L\+]^!-1x_7UV@/ Q7

+]

^!=

^SWO ^!= i, 3:; >FG/ s -1?^ &h)*-./,;y3 = S+ ( .K`@ A ^/ ,0v

0;y3 B&  (Fig. +-) KF+.

)S  >7 -1FCDS>0 ZD d+4

[L\+]^!d E

K-Ar F *.+/

S/ =ZI

Loc. . Fig. +-  +  ¡ ^! [L\ > 

¢X+£¤]/ ^!YZC F¥0[¦/*7$ i6\.K0>0ῌ. 

*.*, Ma 0 *.+2*.*- Ma G +33, =$A&hHI-SJLK L0

A&hHI-SJLK ~4

5§7 ^!]d +$ ¨^R ?$ ,** m ,L  K-Ar  F *.+1  *.*, Ma : " #   +33+ ;©4`@ _© -2* m s`¢a-1/*4 >Watanabe et al., +33-  TL F (+,*-* ka, +-*-*I(ka : Takashima and Watanabe, +33.) 0;yJL/*4d¯Ld Je+4>0d  ,0,0e°+±; i v [L\+] jk .KK/*4 ^R`@K/*4 (Fig. +-) =$ i^LKª«¬­®/ bc R^R^!=) 0m)&  >^! .K²RF+S cWMMNO-/ L)*?& T ]³CD 1 03*4 ,0P& eW F´³ ,0vµFE+4[L\+]^!0Q7^!^LJ ¶§·Lt¸¹ºfL=¹Mº/µ9 »/e:¼)452

  
     ! USDP-+%&'#(  

6

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L j  dz{ =89 41.

 

0 j<2 0 #L-@ 7y JK12  eB CYf-|

5  7$g%,  }Ah/ib

 ~L J A I )  + 5 . 3  2** m h RiP#H5  jRi

4 .

gLk&h5 l. 0c 5 12. 7  , 8.

,** m  6 9:. !    "#$.%&';9:(=>.  0

;9:&?

@) ;4 .** m 
C.DEFGH+ 40 .
4,-@ .

4 !12 0 JKL 41

gLf`:P#H j- R 89 JKL Zc

5c

 A 04 . *, .** m  AB
JKL Zc. )/ ,**,+  0 

12

<2

 5c

 

)*-30 m+     )
+ ,-

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

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,I

)[+ Zc
BP41.,p 0,S

 ..0 cal kyr

[ 4ohP#H  . 0 1! 5q<2  I /

 r

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



4^8.4 0 mn8.ok&k,8.' Y^- s? 5q.

 +h it1@  u 

5qBB.]AJ. k&k.0ῌ/ 

(v,-  &w..0 cal kyr BP 2 NO 3P#HQ4 v41.

>3 

x

45 5  NO67 
R 89  0 , S 
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BP

;T

+.



C <= UV ...W..2 cal kyr

<=4>8. +.C <= (,XY Z[\?@X]A. 8 ^V 6
7

   B_CD_!EB 0 _R .8. 0_4R

 F

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 @aB +* cm bU G-.  aBc ; H

1@ a;I+13, <- Nf NO89  f,:O4 
k&kM F,@ Sl. 0 j NOT

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=

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*

=   W r"B <2 )XY +32.

U+

=  -K«

ª5 *@:) +. C <=^=  ,/,

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]AJ1.  0 /``dE
e@Kf`@ .yz{ "1@ 4 @  (B)(+) J«¬´

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I/ 

L )v¯° :+.-2**-*+  =±( : µ²r+ ,³8 
1

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

..0 cal kyr BP

P#H I _

gL NO 3  T` 5 T`  ab8.1!wx*

   ´z µ/9¶/)/3c (+33-) · [¶·¸¹%/§\·º<=^ ¸»¼/ '2UP+33- 
   /+.
(+33/)     ! -. +-/ῌ+.3.
" (+31.)+13,  #$% &', !!" +1B ,/3ῌ,0..
()* +
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D ,, ,-1ῌ,./.
/0=1>?@34(5 (+33/) / K-Ar
+67 #8"% /9:A +33/ 
  33.
Hoshizumi, H., Uto, K. and Watanabe, K. (+333) Geology
and eruptive history of Unzen Volcano, Shimabara Peninsula, Kyushu, SW Japan. J. Volcanol. Geotherm. Res.,23, 2+ῌ3..
/0=1>?@;<(= >EF ?G
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UV1 (+32*) GF BCD , .-/ῌ..+.
Katsui, Y., Komuro, H. and Uda, T. (+32/) Developmentof fault and growth of Usu-Shinzan cryptodome in +311ῌ
+32, at Usu volcano, north Japan. Jour. Fac. Sci.,
Hokkaido Univ., IV, ,+, --3ῌ-0,.
Kitagawa, H., Fukuzawa, H., Nakamura, T., Okamura,M., Takemura, K., Hayashida, A. and Yasuda, Y.
(+33/) AMS +.C dating of the varved sediments from
Lake Suigetsu, central Japan and atmospheric +.C change
during the late Pleistocene. Radiocarbon, -1, -1+ῌ-12.
[#<1c'\1 (+320) /'2A +320 
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  _` ¡Z]I1 (+33/) c¢Wl (AMS) Xy[ +.C +67 Pxyz$£¤F ! -. +1+ῌ+2-.
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# %8= (+33,) /W # *% K-Ar + +33,   +.
¡{© (+3*2) $u¢Ns W +/
+2+ ..1ῌ./*.
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u !! !"b / 0ῌ-/.
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yzHY¬ £ -. 10ῌ2+.
J(_ (+32.) /'W]W¤­® 32 p.
J(_ (+321) /WVQ]W _`O¯?¥+° ¦ §" -- 1+ῌ2/.
bYVh  [#<1 (,***a) / '2U,*** leP Dc/k Yd  Va-*,/.
bYVh[#<1 (,***b) / ¨Z ©,*** 
ª'  +,2.
Reimer, P. J. et al. (,**.) IntCal*. terrestrial radiocarbon
age calibration, *ῌ,0 cal kyr BP. Radiocarbon, .0, +*,3ῌ+*/2.
±'«¬ (+3+2) u`g   -* -.3
/0ῌ/1.
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+33.   2*.
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3. +*3ῌ++3.
H,· (+311) Hq´XYZ[¸o¹IKºµ»¼ "¹Sp +1* p.
Stuiver, M. and Reimer, P. J. (+33-) Extended +.C database and revised CALIB -.* +.C age calibration program.
Radiocarbon, -/, ,+/ῌ,-*.
Sugiyama, H., Hayashi, M. and Fujino, T. (+320) Fission

454¸C¹º ^»῍¼

track age of the Unzen volcanic rocks in western
Kyushu, Japan. Bull. Volcanol. Soc. Japan, -+, 2/ῌ3..
Takashima, I. and Watanabe, K. (+33.) Thermoluminescence age determination of lava ﬂows/domes and collapsed materials at Unzen Volcano, SW Japan. Bull.
Volcanol. Soc. Japan, -3, +ῌ+,.
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Watanabe, K., Hoshizumi, H. and Itaya, T. (+33-) K-Ar
ages of Unzen Volcano in Kyushu, Japan :with some
aspects of geology of Mayu-yama:. Mem. Fac. Educ.
Kumamoto Univ., Nat. Sci., .,, -/ῌ.+.
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