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Country: | Japan | |
| Subregion Name: | Hokkaido (Japan) | ||
| Volcano Number: | 0805-03= | ||
| Volcano Type: | Stratovolcano | ||
| Volcano Status: | Historical | ||
| Last Known Eruption: | 2001 | ||
| Summit Elevation: | 737 m | 2,418 feet | |
| Latitude: | 42.541°N | 42°32'29"N | |
| Longitude: | 140.843°E | 140°50'34"E | |
| Usu, one of Hokkaido's most well-known volcanoes, is a small stratovolcano located astride the southern topographic rim of the 110,000-year-old Toya caldera. The center of the 10-km-wide, lake-filled caldera contains Naka-jima, a group of forested andesitic lava domes. The summit of the basaltic-to-andesitic edifice of Usu is cut by a somma formed about 7-8,000 years ago when collapse of the volcano produced a debris avalanche that reached the sea. Dacitic domes erupted along two NW-SE-trending lines fill and flank the summit caldera. Three of these domes, O-Usu, Ko-Usu and Showa-Shinzan, along with seven crypto-domes, were erupted during historical time. The 1663 eruption of Usu was one of the largest in Hokkaido during historical time. The war-time growth of Showa-Shinzan from 1943-45 was painstakingly documented by the local postmaster, who created the first detailed record of growth of a lava dome. | |||
