羅臼岳火山における最近2200年間の噴火史

抄録

Recent eruptive episodes since the last 2200 years of Rausudake volcano, east Hokkaido, are revealed by tephrochronology, geological survey of volcanic edifice and petrology of eruptive products. Eruptive ages of these episodes are estimated by ¹⁴C age dating, presence of wide spread tephras, Ma-b from Mashu volcano (about 1 ka) and Ta-a from Tarumai volcano (AD 1739), and thickness of soil between tephra. We identify three major eruption episodes occurring in ca. 2200, ca. 1400 and 500-700 y. B. P. In each episode, plinian eruption associated with generation of pyroclastic flows and possibly with effusion of lava flows and domes had occurred from the summit area. Volcanic explosive index (VEI) of each eruption is 2-4. Tephra identified as the deposits of ca. 1400 y. B. P, eruption had spread widely and has been found in Kunashiri Island which locates about 60 km east of Rausudake volcano. In Shiretoko Peninsula, east Hokkaido, Mt. Shiretoko-Iouzan has been recognized to be an active volcano. We should note that Mt. Rausudake is also active volcano that repeated its magmatic eruptions at intervals of ca. 800 years.