Tolbachik volcano is built by two coalesced late Pleistocene cones: Ostry ("Sharp") Tolbachik and Plosky ("Flat") Tolbachik. Ostry Tolbachik was partly destroyed by a sector collapse, likely in the early Holocene time. Plosky Tolbachik is crowned with a summit caldera, which hosts a small shield volcano, now covered by a glacier. A smaller caldera and a modern crater intermittently filled with a lava lake are located in the western part of the larger caldera.
Tolbachik lava field is formed by numerous cinder cones and their lava flows. Starting from ~3 ka BP the vents formed in a 3-4 km wide axial zone. This zone first stretches for 70 km, from the southern tip of the field NNE towards Plosky Tolbachik volcano, then crosses the latter and extends for another 18-19 km to the northeast. The zone resembles rift zones on some Hawaiian volcanoes (Fedotov, 1984). A fragment of shaded SRTM elevation model released by NASA/JPL/NIMA.

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