an active volcano in southeastern Hokkaido, Japan. Usu has an elevation of 609 m (725 m according to some sources). The crater of the volcano is 2–3 km in diameter and contains two lava domes. Since 1663 there have been six major eruptions, which were accompanied by a considerable vertical displacement of the volcano and the adjacent territory for a short period of time. During the last eruption, between 1943 and 1945, the volcano’s summit was raised 110 m.