Mount Maru (Kamishihoro-Shintoku)
Geology. The western flank of the mountain shows accretionary complex from the late Eocene to the early Miocene. The eastern flank shows non-alkaline mafic volcanic rock from the early to middle Miocene. The mountain is topped with non-alkaline mafic rock from the middle Pleistocene. Eruptive history. Other than fumaroles, the last eruption of Mount Maru, according to historical records, was from approximately December 3, 1898 to December 6. Before that the last eruption was approximately 1700 BC.