Uzon Volcano — Russia

The Uzon and Geysernaya calderas, containing Kamchatka's largest geothermal area, form a 7 x 18 km depression that originated during multiple mid-Pleistocene eruptions. Widespread ignimbrite deposits associated with caldera formation have a volume of 20-25 km3 (exclusive of airfall deposits) and cover an area of 1,700 km2. Post-caldera activity was largely Pleistocene in age and consisted of the extrusion of small silicic lava domes and flows and maar formation in the Geysernaya caldera. The Lake Dal'ny maar in the NE part of the 9 x 12 km western Uzon caldera is early Holocene in age, and several Holocene phreatic eruptions have been documented in the Geysernaya caldera. The extensive high-temperature hydrothermal system includes the many hot springs, mudpots, and geysers of the Valley of Geysers, a 4-km-long canyon on the SE margin of the depression. Hydrothermal explosions took place in the caldera in 1986 and 1989.