十和田火山東麓における八戸テフラ直下の埋没林への年輪年代学の適用

概要

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Fossil forests (approx. 12, 650yrs BP) buried in Hachinohe tephra from Towada Volcano, Aomori Prefecture, northern Japan, were studied dendrochronologically. In the forests, 22 well-preserved wood discs from erect stumps and lying trunks (14 of Picea, 5 of Larix, 3 of Abies) were obtained, and the tree-ring widths were measured and correlated. Cross-dating of Picea and Abies succeeded both among individuals and between genera, and led to the construction of a floating chronology of the cross-dated individuals, while cross-dating of Larix failed. All of the cross-dated erect stumps (8 of Picea and 3 of Abies) revealed that their terminal rings were formed in the same year. Further observation of the terminal rings showed that their latewood formation had already ceased before death. Thus it could be assumed that Towada Volcano erupted between autumn and the following spring, and that the forests were buried by the Hachinohe tephra and died out in the same season.