1999 Volume 6 Issue 2 Pages 39-47
A vegetational reconstruction and a dendrochronological application were carried out on a subfossil forest (approx.13,000yrs BP) buried by the Hachinohe tephra from the Towada Volcano at Ikenai, Ohdate city, Akita Prefecture, northern Japan. The subfossil forest is located at the southwest of the Towada Volcano and is covered with the pyroclastic flow deposits of the Towada-Hachinohe tephra (To- H) without the pyroclastic fall deposits (To- HP). Subfossil woods show establishment of a Picea forest accompanied with Abies in the Last Glacial Age. The forest trees were studied dendrochronologically to clarify the burial process. In the forest, five well preserved discs were obtained from lying trunks of Picea, and their tree-ring widths were measured and correlated. Cross-dating succeeded among the individuals, and three trees were found to die in the same year. In the previous work at the east slopes of the Towada Volcano, we made a standard tree-ring index (STD) of Picea in subfossil forests under the Towada-Hachinohe tephra. Cross-dating succeeded between three individuals of this study and STD which revealed that the terminal rings were formed in the same year. Further observation on the terminal rings showed that their latewood formation had already ceased before death, agreeing with the result of the previous work. Thus Towada Volcano erupted in winter and the eastern and the southwestern forests were buried by the Hachinohe tephra and died out in the same season.
