The basaltic-to-rhyolitic Hakkodasan volcano includes at least 17 stratovolcanoes and lava domes south of Mutsu Bay at the northern end of Honshu. The NE rim of an 8-km-wide Pleistocene caldera forms an arcuate ridge across a flat caldera-floor moat NE of the Hakkoda group volcanoes, which bury the SE caldera wall. A northern group of volcanoes, constructed within the caldera, appears to be younger than the southern group. Hakkoda-Odake, Ido-dake, and Tsurugi-dake have well-preserved craters. Akakuradake has a 1-km-wide explosion crater breached to the north. No historical eruptions are known, although an active solfatara occurs at Idodake, and hot springs are found at several locations within the caldera. Three minor phreatic eruptions were documented from Jigokunuma on the SW flank of Odake volcano from the 13th-17th centuries. Three soldiers on a training mission in July 1997 were killed by inhalation of volcanic gas.