[S-VC34] Volcanic and igneous activities, and these long-term forecasting

[SVC34-P05] K-Ar age and petrology of Tomaruyama Lava and Isoya Lava, Southwest Hokkaiodo, Japan

*Satoshi Okamura¹, Shunichi Ishizaki², Masataka Aizawa³, Masayuki Ishii⁴, Makoto Sugawara⁵ (1.Hokkaido Soil Research Cooperative Association, 2.Geo-Melange, 3.Sapporo Campus, Hokkaido Education University, 4.Ishii Professional Engineer Office, 5.Earth Science Co., LTD)

Keywords:K-Ar age, Tomaruyama Lava, Isoya Lava, geological disposal, high-level nuclear waste

The literature survey for geological disposal of nuclear waste has been done at Kamoenai and Suttsu areas, Hokkaido for four years since 2020. In the determination of the candidate sites, the Quarternary volcanoes must be avoided and a safe distance at least 15 km should be defined. K-Ar ages of the Late Cenozoic volcanic rocks from the Kamoenai and Suttsu regin are determined to evaluate the requirements of the geological disposal. The samples yielded 4.96±0.15Ma from the Tomaruyama Lava, 2.70±0.6Ma from the Isoya Lava. The Tomaruyama Lave indicates the Early Pliocene volcanic activity, On the other hand, the Isoya Lava indicates Late Pliocene to Eary Pleistocene volcanic activity and suggests low suitability for the repository in the Suttsu area. The andesite to dacite of the Isoya Lava has icelandite-like characterisitics, high FeO*/MgO ratios, which are different those of the nearby Quaternary Niseko-Raiden volcano group.