著者

宮縁 育夫 増田 直朗 渡辺 一徳

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.49, no.5, pp.267-282, 2004

参考文献数

31

被引用文献数

7

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The western part of post-caldera central cones of Aso Volcano, southwestern Japan, is characterized by wide chemical variation of lava flows (SiO₂=49-73 wt.%) and complicated topography. Geologic history of the area was reconstructed by stratigraphic relationships between lava flows and airfall tephra layers. Stratigraphy and chronology of lavas and tephra distributed on the western slope of the central cones are as follows: Ayugaerinotaki lava, Matsuhata pumice (MhP), Tochinoki lava (73±10 ka; K-Ar age), Aso central cone pumice 4 (ACP4), Tateno lava. Aso central cone pumice 3 (ACP3), Takanoobane lava (51±5ka), Eboshidake lava, Karisako lava, Akase lava (30 cal ka ; calibrated ¹⁴C age), Sawatsuno lava (27±6ka), Kusasenrigahama pumice (Kpfa; 31 cal ka), Otogase lava and Aso central cone pumice 1 (ACPI ; 4 cal ka), in ascending order. Between about 70,000 to 50,000 years ago Tochinoki lava, Tateno lava and Takanoobane lava accompanied precursor pumice-fall deposits. A catastrophic eruption occurred in and around the Kusasenrigahama crater at 31 cal ka. The eruption was initiated by the dacite Sawatsuno lava now and produced the largest plinian numice-fall deposit (Kpfa; 1.2 km³ in DRE volume). In the western part of post-caldera central cones of Aso Volcano, total discharge volumes of felsic and mafic magmas from about 70,000 to 30,000 years ago were estimated to be about 2.4 km³ and 0.47km³ respectively.