Abstract
The Eniwa-a pumice-fall deposit (En-a), which erupted from Mt. Eniwa in western Hokkaido, is one of the widely distributed tephra layers in the latter half of the Last Glacial.
The new radiocarbon ages for three pieces of wood from the peaty bed intercalated with En-a are 16, 500±270y. B. P. (NUTA-1941) 16, 850±210y. B. P. (NUTA-1946) and 14, 600±100 y. B. P. (Tk-917). Based on these ages and the sedimentation rate of this bed, it is concluded that En-a fell ca. 17, 000 y. B. P.
According to pollen records from Central and Western Hokkaido (Sakaguchi, 1989; Sakaguchi and Katoh, 1990), the paleoclimate became warmer after the coldest period around 19, 000y. B. P., and then became colder again from 15, 000 to 14, 000y. B. P. Judging from the chronological position of En-a in both pollen records, this tephra is considered to have erupted in the interstadial-like time between those two colder or coldest periods.
After the fall of En-a, the paleoclimate became relatively moist from 16, 000 to 14, 000y. B. P. In the Tokachi Plain, this condition may have caused an interruption in the formation of the ancient sand dune which is composed of reworked pumiceous sand of En-a origin.
