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腀腆 膴膰臥膮膓膙 膴膰臥臖膄 膄臺臙膏膆膑腼膄腼 臬膶臷 臬膶 腦腙腖 腒腬腠 膱膈腤腞臚腯腛 臦膪臼腜腩 腽腎腢 膨臥腽膪腡腳腷 腽腢 腳腷臲臮膷膖膧臬 腔腦腭 臞腦腜膕腓腋膔臌 腽腎臓腋腖 腕腡膝 腠至臋腓腖臖 腽腜腊腭 臄臥 腳腷膼臥 臒腡腽膞腍腬 膋腡 膸腎膭腦腭 臦臒腜腢 膋腎膀 臘臋腟腞 自腴腟膚臀腎膇膩腒腯腖 腽腜腩腊腙腖 臛腠 臭腓腖膝 腕腡腺膢腜膀臢 腽腎臓腏 臮致腡 腌腫腣臖臅 腽膯 膈腠臄臥腎膲 腝膸膚腓腖 臄臥腎腤腥膸腕腰腙腖腑腰 腡腳腷 腽腠腚腋腛腡膍膹腢 臧膱腡膛 膻腲臉 腍腬 膀臢腜腡臱至腎膘臜腠腟腭 臡臯腩至臋腓臵膁腎 腓腖腩腡腜腊腭 腕腡臐臔臑腲臣膃腠臶腏腗腓腛腋 臋腔腛腋腮 腦腖 腽膝 膴膰臥 腡腹臺膀膊腜腢腴臂 腡腳腷 腽腠腚腋腛腡膍膦腢 腟膠臟腠腧腦腱腯 膾腟腐腝腩 臮腢腾臻腓腟腍腙 腽膯 腠膿膥腠膍膹腒腯腛腋腮腖腨 腑腝腟腞腎膍腒腯腛腋腮 膬膱臕腡 腽腜 膉腓腛腢臖臅 腡腧腲膫 腓腖 臋腔腖 膋臨腡 臹腲膳腓腛腋腮 臖臅 腠腢 腽腠臍 腘膒至臙 腳腷膼臥腠腚腋腛 膂臣腟臙膵膄臣膗膐腲膤膺腠 臆腡至臋腪腵膜臈腡 臩腪膀臈腡 臃腟腞膘臜腟臏臝膚 膟腙腖腡腢膪膞 腜腊腮 腩臖臊 臀腎腊腭 膂臣腟 腽腡 膱膈臏腠腢膪臠腍腬臰腸 腡膗膐 膣腡腟腍腜 腳腷 腽腠腚腋腛膎 腲腓腛腋 腎腊腎腭 腕腡膝腠臫臒膪臼腍腬膕腓腋膔臌 腽腎膭 臌臎 臨腢 腉腂 腉腂 ῒΐ ῐ῎ῑ῏ 腈腎腇腉 腄腆腐腇 腂腍腀腁 腋腎 腄腆腊腎 腃腌腅 OBAYASHI ( ) Department of Earth and Environmental Sciences, Fac- I reconstructed the eruptive sequence of the An-ei eruption ( ) of Sakurajima volcano based on documentary records. The important results are as follows ; first, submarine eruption started earlier than the entrance of terrestrial lava flow into the sea ; second, a larger volume of magma intruded into the sediments at the bottom of the sea, and generated a large submarine cryptodome. When magma was ejected, floated islets consisting of giant pumice were formed for a while, which were subsequently followed by violent phreatomagmatic eruptions, and finally massive lava appeared on the sea. However, when the sandy islets were uplifted, they were not accompanied by any eruptions. All the islets were formed nearly within a year, then followed by submarine explosions that generated tsunami. The explosions were produced by the interaction between seawater and the intruded magma of the An-ei cryptodome. Some tsunamis might be triggered by landslides on the slope of the submarine cryptodome. I found similar explosion vent structure at Yuwandake, an early Pleistocene intrusive body into wet sediments, to the northwest of the Aira caldera. Funnel-shaped vent breccia penetrated the central part of the jointed Yuwandake lava, suggesting that the submarine explosion occurred at the final stage of the consolidation of magma. Similar vent structures may exist in the An-ei submarine cryptodome. : Omori ( ) a, b: Omori ( ) ( a, b) ( a, p. ) ( ) Koto ( ) ( ) ( ) ( ) , Korimoto, Kagoshima , Japan Corresponding author : Tetsuo Kobayashi ulty of Science, Kagoshima University e-mail : [email protected] Tetsuo K Origin of New Islets (An-ei islets) Formed During the An-ei Eruption ( ) of Sakurajima Volcano, Southern Kyushu, Japan Key words /. ,**3 + + +- ,**1 / +. ,**2 +, 3 +113 +32, , +113 ++ 1 + +3+0 +3+2 +3+0 . / + +3+2 +3+2 +3, +30 +3+/ +3+0 - +3-/ +32, +33, 23* **0/ + ,+ -/ + ,+ -/ 23* **0/ +113 +12, +113 +12, +

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OBAYASHI

( )

Department of Earth and Environmental Sciences, Fac-

I reconstructed the eruptive sequence of the An-ei eruption ( ) of Sakurajima volcano based on

documentary records. The important results are as follows ; first, submarine eruption started earlier than the

entrance of terrestrial lava flow into the sea ; second, a larger volume of magma intruded into the sediments at the

bottom of the sea, and generated a large submarine cryptodome. When magma was ejected, floated islets

consisting of giant pumice were formed for a while, which were subsequently followed by violent phreatomagmatic

eruptions, and finally massive lava appeared on the sea. However, when the sandy islets were uplifted, they were

not accompanied by any eruptions. All the islets were formed nearly within a year, then followed by submarine

explosions that generated tsunami. The explosions were produced by the interaction between seawater and the

intruded magma of the An-ei cryptodome. Some tsunamis might be triggered by landslides on the slope of the

submarine cryptodome. I found similar explosion vent structure at Yuwandake, an early Pleistocene intrusive

body into wet sediments, to the northwest of the Aira caldera. Funnel-shaped vent breccia penetrated the central

part of the jointed Yuwandake lava, suggesting that the submarine explosion occurred at the final stage of the

consolidation of magma. Similar vent structures may exist in the An-ei submarine cryptodome.

:

Omori ( ) a, b :

Omori ( )

( a, b)

( a, p. )

( ) Koto ( )

( ) ( ) ( )

, Korimoto, Kagoshima , Japan

Corresponding author : Tetsuo Kobayashi

ulty of Science, Kagoshima University e-mail : [email protected]

Tetsuo K

Origin of New Islets (An-ei islets) Formed During the An-ei Eruption ( )

of Sakurajima Volcano, Southern Kyushu, Japan

Key words

/. ,**3+ + +-

,**1 / +. ,**2 +, 3

+113 +32,

,

+113 ++

1

+

+3+0 +3+2

+3+0 . /

+

+3+2

+3+2 +3, +30

+3+/ +3+0

-

+3-/ +32, +33,

23* **0/ + ,+ -/ + ,+ -/ 23* **0/

+113 +12,

+113 +12,

+

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eruption. : submerged first-islet, : Inokojima, :

2

Fig. . Index map of Sakurajima volcano (solid tri-

angle) and distribution of lava flows and tu ring

in historical time. An-ei eruption in occur- Fig. . Newly-formed topography of the north-eastern

red from fissure vents that opened on the NE and sector of Sakurajima volcano during the An-ei

S sectors of the volcano. NE area enclosed by

broken lines in the sea denotes the lava flow Nakanoshima, : Iojima, : Shinjima, : Doro-

plunging into the sea and submarine cryptodome. jima (now submerged). Submarine craters are re-

presented by hachures. Bathymetric map is from.

Japan Coast Guard ( ).

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( )

Fig. . Formation sequence of Showa-Iojima (Fig.

in Tanakadate, ). a) Dec. , ; b) early( )

January, . They were probably drawn from

the summit of Satsuma-Iodake.

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9

Fig. . Giant pumice erupted in the submarine erup-

tion of Showa-Iojima. a) drifted giant pumice as

large as m on the coast of Iojima (Fig. inFig. . Occurrence of giant pumice on the An-ei

Tanakadate, ) ; b) sunken giant pumice largerislets. a) Nakanoshima, b) Shinjima.

than m on the submerged caldera floor near. a)

Showa-Iojima (Photo in Nakamura , ).b)

face of giant pumices.

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Koto ( , p. )

et al.

et al.,

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I

ern Kyushu, , years ago. ,

jima and Kaimondake volcanoes, southern Kyushu, Japan.

.

unusual bed of giant pumice in Mexico. ,

C dating of historic eruptions of the Kirishima, Sakura-

( )

Shinjima (Moeshima) Island, Kagoshima Bay, SW Japan.

explosive eruption, Milos, Greece. ,

( ) : ,

Kobayashi, T. ( ) Tectonic setting and major pyro-

13

( )

no. .

( )

. ( )

( b) no. .

( )

. .

Aramaki, S. ( ) Formation of the Aira Caldera, south- Matumoto, T. ( ) The four gigantic caldera volcanoes

of Kyushu. , p.

, ( )

( ) .

( )

. .

Clough, B.J., Wright, J.V. and Walker, G.P.L. ( ) An ( )

giant punice

.

( )

. .

( ) Okuno, M., Nakamura, T. and Kobayashi, T. ( ) AMS

.

( )

P. , .

( ) Omori, F. ( ) The Sakurajima eruptions and earth-

quakes. II. ,

. .

( a) no.

p.

( b) no.

p.

( )

. .

( ) ( )

no.

. .

Kano, K., Yamamoto, T., and Ono, K. ( ) Subaqueous ( )

eruption and emplacement of the Shinjima Pumice, no. .

Stewart, A.L. and McPhie, J., , An Upper Pliocene

, . coarse pumice breccia generated by a shallow submarine

( ) .

( )

. .

( ) : ( )

. No. .

Wilson, C.J.N. and Walker, G.P.L., , The Taupo

clastic eruptions in southern Kyushu. A guide book for eruption, New Zealand I. General aspects.

Sakurajima Volcano (Kagoshima International Confer- , .

ence on Volcanoes, ed), Kagoshima Prefectural Govern- ( )

ment, . .

( ) ( )

p.

Koto, B. ( ) The great eruption of Sakura-jima in .

, .

J. Geophys. Res.,

Nature,

Bull. Volcanol.,

Jap. J. Geol. Geogr.,

Radiocarbon,

Bull. Imp. Earthq. Invest. Committee,

J. Volcanol. Geotherm. Res.,

Phil. Trans. R.

Soc. London, A.,

J. Coll. Sci. Imp. Univ. Tokyo,

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