Source: The 1994-1995 Kamchatka Calendar.
Ostry (Sharp) and Plosky (Flat) Tolbachik are both stratovolcanoes which form to together the Tolbachik massif that is aligned parallel along the east-west border fault in the northern part of this Tolbachik tectonic depression. A 3-km-diameter circular collapse caldera is located on the summit of Plosky Tolbachik. Nested insider this outer caldera is an inner caldera that measures 1.8- 2 km in diameter and 20-150 m deep. Plosky Tolbachik erupted most recently from 1967 to 1970 and again from 1975 to 1976 which resulted in the formation of an inner crater measuring 350-400 m across and 150-200 m deep.
Cinder Cones on the flanks of Tolbachik, Kamchatka, Russia.
The eruption that started July 6th,1975 and continued until December 10, 1976 was correctly predicted by P.I. Tokarev of the Institute of Volcanology of the Far Eastern Scientific Center of the AN SSSR. This prediction was pin-pointed after the most violent earthquake ever recorded in the Kliuchi group of volcanoes occurred in June of 1975. The Kliuchi group consists of the volcanoes; Kliuchevskoi, Udina, Zimina, Bezymianny, Kaman, and the Tolbachiks. The 1975-1976 Tolbachik eruption was the largest basalt eruption in recorded time in the Kuril-Kamchatka belt. This eruption resulted in the formation of four new monogenetic cinder cones (pictured above), an eruption cloud reaching 8 miles (13 km) in height, and 260-foot-thick lava sheets covering over a 15 square mile area (40 square km).
Sources of Information:
Erlich, Edward 1986 Geology of Calderas of Kamchatka and Kurile Islands with Comparison to Calderas of Japan and the Aleutians, Alaska Open-File Report 86-291, US Dept. of the Interior- Geological Survey, p165-170.
Fedotov, S.A.; Ye. K. Markhinin 1983 The Great Tolbachik Fissure Eruption, Cambridge Univ. Press, New York, Preface.
Gushchenko, I.I. 1979 Izverzheniya Vulkanov Mira - Katalog (Eruptions of the Volcanos of the World - Catalog), Nauka, p.23.
Sviatolovsky, A. E. 1959 Atlas of Volcanoes of the Soviet Union, USSR Academy of Sciences, Moscow USSR. p165.