2010 年 116 巻 4 号 p. 229-232
The Futagoyama lava dome, one of the post-caldera central cones of Hakone volcano (Kanagawa, Japan), is though to have formed by a single eruption at 5 ka. However, in this study, we show that the dome formed over the course of at least three eruptions. We discovered a relatively old block-and-ash flow deposit (Hakone-Futagoyama Yamazaki block-and-ash flow deposit [Hk-FtY]) that originated from the Futagoyama lava dome, as indicated by its chemical composition and its age of 20,390 ± 40 yr BP. We also re-examined the source of the Shinanoya pyroclastic flow deposit, which was previously interpreted to be of Komagatake origin and was dated at 17,920 ± 320 yr BP (reference), and concluded that this deposit also originated from the Futagoyama lava dome. The recent eruptive history of Futagoyama suggests that its eruptions may have been synchronous with those of Kamiyama. In addition, the eruptive centers of Futagoyama and Kamiyama are aligned with each other along a linear trace.