開聞岳火山の海食崖に露出するテフラ層から得られた炭化木片の放射性炭素年代＜特集＞火山噴火史解明のための露頭データベース構築の検討(3))

抄録

Kaimondake volcano, located in southwest Japan, first erupted ca. 4.4 cal kBP and produced 12 eruptive episodes (Km1 to Km12, in ascending order) until AD885. As radiocarbon dating is a useful tool for establishing a chronostratigraphic framework, this study determined five radiocarbon dates of charcoal fragments to check the stratigraphy of tephra layers exposed at sea cliffs surrounding the volcano. Km12 a pyroclastic flow deposits (AD 874) are distributed at the western foot of the volcano (Hanasezaki to Tanosaki). Three dates (1310±40 BP, 1235±40 BP, and 1045±40 BP) obtained from the deposits are nearly consistent with ancient documents pertaining to Km12. The remaining part of the sea cliff (Tanosaki to Kawajiri) consists of tephra layers and lavas of the Km10 (3rd Century) and Km11 (7th Century) eruptions. Two dates (1690±35 BP and 1705±45 BP) obtained from an ash fall deposit distributed from Kurose to Kaimonzaki suggest that this deposit was a product of the Km10 eruption.