2018 Volume 69 Issue 3 Pages 165-200
Early to Middle Pleistocene volcanic history in the area surrounding Lake Towada was constructed based on stratigraphy, petrology and K–Ar and U–Pb age determinations. The volcanic activity in this area started at 2.5 Ma after the period of inactive volcanic activity during Pliocene. Andesite to dacite magma erupted from several eruptive centers and formed volcanic bodies during 2.5 to 1.6 Ma in the southeastern area. The eruptive style in this period was characterized by formation of lava domes and dome collapse-derived block-and-ash flows. Subsequently, volcanic activity occurred during 1.6 to 0.6 Ma in the northwestern area. In this period, basalt to andesite magma erupted and formed a stratovolcano. Simultaneous dacite magma erupted at the northern and northeastern foot of the stratovolcano and formed several lava domes. Furthermore, andesite magma erupted in the northeastern area and formed an isolated pyroclastic cone just before 0.76 Ma. There was a volcanic repose time of 0.4 million years between 0.6 Ma and 0.22 Ma. The volcanic activity of Towada volcano has started since 0.22 Ma. The long repose time shows that the volcanic activity before 0.6 Ma was different from that of Towada volcano.