[S-VC30] Volcanic and igneous activities, and these long-term forecasting

[SVC30-P06] Reconstruction of the volcanic history of Nakadake volcano in Kirishima volcano group, Kyushu, Japan (1)

*Yasuhisa Tajima¹, Atsushi Yasuda², Mitsuru Okuno³ (1.Research & Development Center, Nippon Koei Co.,LTD., 2.Earthquake Research Institute, University of Tokyo, 3.Faculty of Science Department of Earth System Science, Fukuoka University)

Keywords:Kirishima volcano group, Nakadake volcano, volcanic history

The long-term eruption histories of Ohachi, Shinmoedake, and Ebinokogen-Ioyama volcanoes in Kirishima volcano group were revealed through recent geologic observations (Tsustui et al., 2007; Tajima et al., 2013, 2014). However, detailed eruption histories of the Nakadake and Ohatayama volcanoes, which erupted during the Holocene, remain unknown. It was found that Nd1 and Nd2 lava were covered by the K-Ah tephra, whereas for Nd3 and Nd4 lava, the key tephra relationship has not been investigated. Nd7 lava is likely newer than Nd6 lava, while Nd8–Nd11 lava were the youngest Nakadake lava (Inoue, 1993). Based on ¹⁴C ages and the key tephra layer relationship, the earlier 10 tephra layers of the Nakadake volcano are known to originate from eruptions occurring from 4700 to 2200 cal BP (Tsutsui et al., 2005, 2007). However, the beginning ¹⁴C age of the Nakadake lava above the K-Ah tephra is unknown.

We investigated the lava and tephra layers around Nakadake volcano by using chronology and geochemical techniques. The earlier stage of the Nakadake volcano likely originated from Nd3 lava, as it sits at the bottom layer of the earlier Nakadake tephra layers above the Miike tephra. Additionally, the ¹⁴C ages of 3680±40 BP (JAT-14,003) and 3500±40 BP (JAT-14,002) in the earlier Nakadake tephra layers above the Sm-Sy tephra (4.5 cal BP) were measured for humic soils. The AMS¹⁴C dating was carried out at Tono Geoscience Center of Japan Atomic Energy Agency (JAEA).