熊本大学学術リポジトリ Kumamoto University Repositor Title 阿蘇火山米塚の噴火年代 Author(s) 宮縁, 育夫 Citation 火山, 55(5): Issue date Type URL Right Journal

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1 熊本大学学術リポジトリ Kumamoto University Repositor Title 阿蘇火山米塚の噴火年代 Author(s) 宮縁育夫 Citation 火山 55(5): Issue date Type URL Right Journal Article 特定非営利活動法人日本火山学会

2 // ( *+*) / +3 / *+* / +- *+* +* / Eruption Age of Komezuka at Aso Volcano Japan Yasuo M IYABUCHI Komezuka Volcano located in the northwestern part of the post-caldera central cones of Aso Volcano SW Japan is a basaltic monogenetic volcano comprising a scoria cone (-1* -2* m in basal diameter ; 2* m in height) 1 - and lava flows ( +*./ km ; / +* m ). We obtained C ages of -*1*.* years BP from a buried soil below silty ash underlying Komezuka lava which corresponds to --1* - +* cal years BP and 10*.* years BP ( 3/* 11* cal years BP) from a soil above silty ash overlying Komezuka lava. The age of soil below the lava suggests that the eruption age of Komezuka Volcano is about --** cal years BP. The eruption age is consistent with the age of Ojodake Volcano (- 0** cal years BP) whose lava underlies Komezuka lava. In the northwestern part of the post-caldera central cones Late Holocene monogenetic volcanic activity commenced with sub-plinian eruptions and lava extrusion from Kishimadake Volcano at approximately.*** cal years BP followed by sub-plinian eruptions and lava extrusion from Ojodake Volcano at -0** cal years BP and ceased with strombolian eruptions and lava extrusion from Komezuka Volcano at --** cal years BP. Key words : Komezuka Volcano scoria cone lava flow eruption age Aso Volcano + **+ +32/ 3/..- m (SiO / wt. ) **+ C +32/ ; ** ; Miyabuchi **3 +-0 m m **+ (Fig. + ) - +32/ 20* 2///.* + Faculty of Education Kumamoto University Kurokami.* + Kumamoto 20* 2/// Japan. Corresponding author: Yasuo Miyabuchi miyabuchi@earth. .ne.jp

. Distribution map of products of Late Holocene monogenetic volcanic activity in the northwestern part of the post-caldera central cones of Aso Volcano ; modified

3 220 Fig. +. Aerial view of Late Holocene scoria cones in the northwestern part of the post-caldera central cones of Aso Volcano from the northwest. +32/ -1* -2* m 2* m 2* m +/ m /1 -/. km +*./ km (Fig. ) / m / +* m 1 - +* m - km +32. Fig.. Distribution map of products of Late Holocene monogenetic volcanic activity in the northwestern part of the post-caldera central cones of Aso Volcano ; modified from + : /**** topographic map Asosan published by Geographical Survey Institute. Solid circles show localities of measured stratigraphic sections. The distribution of lava flows is taken from Ono and Watanabe ( +32/ ). Latitude and longitude are shown by WGS 2..

4 ; Fig ; +331 N+ +* m N+3 +3 (KsS) N0 N C cal ka -. 0 cal ka *3. km +331 ; Miyabuchi **3 +32/ /* +** m / m **+ /.YR-. ; (/ Y / + ) **+ (SiO /+ wt. ) ++* cm A*3+- (Fig. -) (/ Y / + ) m - ( +* YR/) - -. km A ( +* YR /-) Fig. -. Stratigraphic relations of Komezuka lava and tephra layers in and around Komezuka Volcano. See Fig. for locations of the sites. C ages at the A3.+2 section are from Miyabuchi and Watanabe ( +331) and Miyabuchi (**3). ACP + : Aso central cone pumice + KsS: Kishimadake scoria N S: Nakadake N scoria OjS: Ojodake scoria.

5 222 - (Fig. -) * cm ( +* YR /) (. 1/ YR./-) + mm ;. **+ N N S; +331.* +/ 0 cm ( +* YR /-) * cm (/ Y -/ + ) m ; A31+ (Table + ) ( +* YR./.) ( +* YR // 0 )./* C +./ (Yoshida +321 ) + : +* -. cm; +0 cm X / cm ( +* YR /) -*1* N+ Fig.. A cm -. cm SiO /-.. /-. 1 wt. ( +* YR/) - N+ SiO /+. 1 /.- wt. SiO /+. 1 /./ wt. (Fig. -) +** m A 30++ ( +32/ ) ( +323) Table +. Whole-rock chemical compositions of products of Late Holocene monogenetic activity in the northwestern part of the post-caldera central cones of Aso Volcano.

6 223 (Fig. -) Beta Analytic A31+ A30+ b A*3+- (AMS) C Libby //02 d C ( C/ C) Beta Analytic IntCal*. (Reimer et al. **.) Talma and Vogel ( +33-) Fig... K O-SiO variation diagram of whole-rock chemistry for Holocene monogenetic volcanoes A*3+- and Nakadake Volcano. Values are normalized -*1*.* on the basis of total+** wt.. yrs BP (Beta-0*+-*) 10*.* yrs BP (Beta-1+*) C (Table ) --. cal ka 3. cal ka C SiO + ** 0* yrs BP (Beta- ++-/3- ) +. + cal ka / wt. C + 3* 1* yrs BP (Beta- ++-/3. ) / C C +-. cal ka 0 0+ A cm / cm A*3+- **/ (Okuno A 30+ et al. +331) --. cal ka 3. cal ka + Table. Results of C age determinations for buried soils in and around Komezuka Volcano.

7 cal ka --. cal ka 0- C ++. cal ka +*** +32/ +. + cal ka N+ +33/ Paŕıctin Luhr and Simkin cal ka ( -0. cal ka) --. cal ka +33+ ; +331 N cal ka (Fig. -) N. SiO +33/ (Fig..) /-.. /-. 1 wt. 0 SiO SiO /+. 1 /.- wt. **+ SiO /+. 1 /./ wt. C +1 cm +0 cm N+ SiO / wt A30+ A31+ SiO (Fig. -) +1cm +0 cm +-. cal ka ++. cal ka --. cal ka. cal ka

8 cal ka --. cal ka born in a Mexican cornfield. Geoscience Press Inc. Phoenix Arizona.1 p. Miyabuchi Y. (**3) A 3* ***-year tephrostratigraphic framework of Aso Volcano Japan. Sediment. Geol. * ( +331) C..*-.*2. ( +33/ ) no. ++* /. 1 ( +32+ ) no. +* 32 +*0. ( **/) +* *** C /* S*3 S +1. C Okuno M. Nakamura T. Moriwaki H. and Kobayashi -*1*.* yrs BP T. ( +331) AMS radiocarbon dating of the Sakurajima tephra group southern Kyushu Japan. Nucl. Instr. and 10*.* yrs BP C Meth. in Phys. Res. B+-.1* cal ka 3. cal ka ( +323 ) cal ka ( +32/ ) / +.. cal ka ( +33/ ) -0. cal.* +-- +/+. ka Reimer P. J. Baillie M.G.L. Bard E. Bayliss A. Beck J.W. Blackwell P.G. Buck C.E. Burr G.S. Cutler K. --. cal ka B. Damon P.E. Edwards R.L. Fairbanks R.G. Friedrich M. Guilderson T.P. Herring C. Hughen K.A. Kromer B. McCormac F.G. Manning S.W. Ramsey C.B. Reimer R.W. Remmele S. Southon J. R. Stuiver M. Talamo S. Taylor F.W. van der Plicht J. and Weyhenmeyer C.E. (**.) IntCal*. terrestrial radiocarbon age calibration *0 cal kyr BP. Radiocarbon.0 +*3 +*/2. Talma A.S. and Vogel J.C. ( +33-) A simplified approach to calibration C dates. Radiocarbon -/ ( +31. ) no../ 3+*. ( +32. ) X ( +33+ ) no (**+) 1.+ p. Yoshida M. ( +321) Preheating method for the determination of total phosphorus content in Andosols. Soil Science and Plant Nutrition -- /*+ /*/. Luhr J.F. and Simkin T. ( +33-) Paríctin: the volcano

第２６号（ＰＤＦ納品用）／表１・表４・背

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熊本大学学術リポジトリ Kumamoto University Repositor Title 阿蘇火山 米塚の噴火年代 Author(s) 宮縁, 育夫 Citation 火山, 55(5): Issue date Type URL Right Journal

熊本大学学術リポジトリ Kumamoto University Repositor Title 阿蘇火山米塚の噴火年代 Author(s) 宮縁, 育夫 Citation 火山, 55(5): Issue date Type URL Right Journal