Mount Usu (有珠山 Usu-zan) is an active stratovolcano in the Shikotsu-Toya National Park, Hokkaidō, Japan. It has erupted four times since 1900: in 1910, 1944–45 (which created Shōwa-shinzan), August 7, 1977, and on March 31, 2000. To the north lies Lake Toya. Mount Usu formed on the southern rim of the caldera containing the lake.
Mount Usu and Shōwa-shinzan are major tourist attractions in the Shikotsu-Toya National Park. A ropeway on Mount Usu takes visitors to viewing platforms overlooking Shōwa-shinzan. The 1977 eruption is mentioned in passing in Alan Booth's travelogue, The Roads to Sata. The 2008 G8 Summit was held near Mount Usu at Lake Toya.
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