Re-evaluation of the history of phreatic eruptions from Atosanupuri Volcano, eastern Hokkaido, Japan:: Inferred from 14 C ages and borehole cores of Japan Meteorological Agency@@@炭素年代および気象庁ボーリングコアからの検討

Atosanupuri Volcano is one of the active volcanoes, located in the Akan–Shiretoko Volcanic Chain, eastern Hokkaido. Tephro-strati-graphic and tephro-chronologic studies were conducted on two drill cores and new outcrops around the volcano to reveal a recent history of the explosive eruptions. Widespread tephra layers, such as the 10 th century B-Tm tephra, and the 2 . 7 cal. ka BP Ta-c 2 tephra were distinguished by the geochemical composition of volcanic glass. In addition, 14 C ages of organic samples underlying the eruption deposits were obtained. Using these data, we identified seven phreatic eruption deposits, At-ph 1 to At-ph 7 , overlying the T-c 2 tephra; these include the previously described At-a and At-b tephras. At-ph 7 yields the oldest 14 C calibrated age ( 2 . 5 – 2 . 7 cal. ka), and the deposition ages of At-ph 6 to At-ph 1 range from cal. AD 554 to 1678 . At-ph 4 (At-b) is the thickest phreatic ejecta, with a volume of ~ 3 × 10 6 m 3 . Five phreatic eruptions occurred from Atosanupuri Volcano between 1 , 500 and 1 , 000 cal. BP. The youngest eruption, At-ph 1 (At-a) occurred at 300 ~ 400 cal. BP, which might be documented in historical records. phreatic