Hakkōda Mountains

The Hakkodasan complex 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. The craters at Hakkoda-Odake, Ido-dake, and Tsurugi-dake appear morphologically young. Akakuradake has a 1-km-wide explosion crater breached to the north. An active solfatara occurs at Idodake, and hot springs are found at several locations within the caldera. Three minor phreatic events from Jigokunuma on the SW flank of Odake volcano produced tephra radiocarbon dated to the 13th-17th centuries. Three soldiers on a training mission in July 1997 were killed on the lower N flank of Hakkoda when they slipped into a depression containing a high percentage of CO2 gas wiht a magmatic origin.