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(Japanese Quaternary Volcanoes database, RIODB, http://riodb02.ibase.aist.go.jp/strata/VOL_JP/EN/index.htm and Geol Surv Japan, AIST, http://www.gsj.jp/)
Izu-Tobu volcanic field is a group of pyroclastic beds, a lava platform, shield volcanoes, stratovolcanoes and lava domes in Japan. Many vents erupted lava and pyroclastic material in this area. This built many small volcanoes instead of one large cone like nearby volcanoes. Izu-Tobu consists of six or seven volcanoes and several partly destroyed craters or vents. All this lies within an area about 5 by 6 miles (8 by 10 km) wide just south of the city of Ito. Sukumo-yama, a separate volcano ~4.5 miles (7 km) northwest of Ito is also included in this group.
South of Ito, flat lying lava and pyroclastic beds form a plateau. Two cones, Omuro-yama and Komuro-yama, rise above this area. North, west, and southwest of the plateau, steep mountains made of Pleistocene volcanic rocks are found. Tertiary rocks which blocked the lava flows of Izu-Tobu are also found here.
Most of the craters or vents of Ito are found on a thin zone running N 20 degrees E. Only one recent eruption has taken place in Izu-Tobu, but many earthquakes have occurred in historic times. In fact, 4880 earthquakes shook the area between February 13, 1930 and the end of April in the same year. Most of the earthquakes originate in the northeast area of the zone described earlier. Izu-Tobu has had five historic eruptions. The last of these eruptions occurred in 1989.
Sources of Information:
Kuno, Hisashi, "Catalogue of the Active Volcanoes of the World Including Solfatara Fields: Part XI, Japan, Taiwan and Marianas," International Association of Volcanology, Rome, Italy, 332 pp., 1962.