ῒΐ  /*  (,**/)
 0  ..+ῌ./. ῕ ῔῍ΐ῎ῑ ῕ῑῌῐῒ῏῔ῌ,**/  1  +  ,**/  +*  + Growth History of Mayuyama, Unzen Volcano, Kyushu, Southwest JapanNobuyuki 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 asTakadake, 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{

./ 01 +31, $23#*456-789-|}$Z?@z- ~  +33/:  (Fig. +): $7;< /* =>?@ABCDE (1*2 m) E   (2+2.1 m) EIU , $JKNOq st u vw

BMB MBltk t t

FG HIJKLMJKNOP$QRESG*TU blockPX!*῍zCD|Z8 )῎*45

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