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Usu volcano, Japan
Usu volcano is a small stratovolcano located astride the southern topographic rim of the 110,000-year-old Toya caldera.
The summit of the volcano, seen here above the town of Toyako-Onsen to its NW, consists of dacitic lava domes and a cryptodome that were emplaced in a small summit caldera during historical eruptions, most recently during 1977-82.
Similar historical eruptions have occurred on the flanks.
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.
PHOTO SOURCE: Copyrighted photo by Dick Stoiber, 1981 (Dartmouth College) courtesy of the Global Volcanism Program, Smithsonian National Museum of Natural History, used with permission.
NOTE: The information regarding Volcano on this page is re-published from other sources.
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This page was last modified 23-FEB-10
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