AMS radiocarbon dating of wood trunks in the pumiceous deposits of the Kikai-Akahoya eruption in Yakushima Island, SW Japan

Okuno, Mitsuru*; Nakamura, Toshio*; Geshi, Nobuo*; Kimura, Katsuhiko*; Kokubu, Yoko   ; Kobayashi, Tetsuo*

We found numerous wood trunks from pumiceous deposits along Nagata, Isso and Miyanoura rivers on the northern side of Yakushima Island, 60 km south of Kyushu Island, and conducted radiocarbon dating using accelerator mass spectrometry (AMS). The obtained C dates were around 6500 BP, and geological characteristics of the pumiceous deposits indicate that these specimens were buried during the Kikai-Akahoya (K-Ah) eruption from the Kikai caldera. However, they are not charred, suggesting that the origin of these deposits is not of pyroclastic flow but that of tsunami. Fourteen taxa were identified through anatomical characteristics. This is the first discovery on species of the forest of the Yakushima Island before the devastating eruption.