Possible Age Models for Lake Onuma Lacustrine Sediments Based on Tuffs Recovered in Three Cores

Lake Onuma, Hokkaido, Japan, is located south of Hokkaido-Komagatake volcano. The present Lake Onuma was formed by an intensive eruption and partial collapse of the volcanic cone in 1640 AD, which caused a debris flow that dammed the drainage. Three cores (ON12A, C, and D) were recovered from Lake Onuma to examine the environmental change in the region. These three cores are correlated based on lithological descriptions and water content fluctuation. Volcanic deposits Ko-a (1929 AD), Ko-c1 (1856 AD), Ko-d (1640 AD), and possibly Ko-c2 (1694 AD) were successfully identified with the help of radiocarbon age dating, 137Cs radioactivity measurement, and chemical analyses, to construct an age model of these cores.