Volcanic activity of Kuchinoshima Volcano, Tokara Islands,Kagoshima Prefecture.

Abstract

The eruption history of the Kuchinoshima volcano was reconstructed from the stratigraphical relationship of the volcanic units and tephra. The Kuchinoshima volcano is an andesitic composite volcano on the volcanic front of Ryukyu arc, SW Japan. Kuchinoshima consists of at least 10 hornblende andesitic lava domes on pyroxene andesitic volcanoes older than 0.3 Ma. A series of pumice flow deposits named the Ogachi pyroclastic flow deposit, erupted around 40 ka from the Ueura volcano, which is a composite volcano with some lava domes. After the formation of the Ogochi caldera,at least three lava domes named Yokodake, Minami-Yokodake, Kita-Yokodake were formed. Some pyroclastic flow deposits are associated with the formation of these lava domes, and the pyroclastic flow deposit of Minami-Yokodake was aged ca. 19,000 BP. Iwayaguchi debris avalanche flow deposit was formed around 7.9 ka by a large sector collapse of the Yokodake, Minami-Yokodake and KitaYokodake domes. Maedake lava dome was built inside the sector collapse scarp. The Otoshinodaira and Moetake volcanoes and other minor lava domes were formed after the formation of Maedake. The volume of each lava dome is evaluated as less than 0.3 km³. The effusion rate of the Kuchinoshima volcano in the last ca 40,000 years is evaluated as 8.5×10⁴ m³/yr, and this value is much smaller than the average production rate of a typical volcano on the volcanic front of the NE Japan arc and Ryukyu arc. The Moetake volcano is the youngest lava dome on Kuchinoshima Island. Some explosion craters on the Moetake lava dome indicate that the phreatic explosions were repeated from the Moetake volcano. The last eruption was possibly younger than the 18th century.