© V.L. Leonov1, A.N. Rogozin1,2

1 Institute of Volcanology and Seismology, Far East Division, Russian Academy of Sciences, Petropavlovsk – Kamchatsky, 683006, boulevard Piip 9
2 The Kamchatka State University, Petropavlovsk - Kamchatsky, 683032, Pogranichnaya 4.

The new data about the geologic structure of the caldera Polovinka (Krainyaya) southern board are presented in this paper. Caldera Polovinka is one of the main Quaternary calderas of Kamchatka. We discuss the main rock complexes which outcrop in the valley of the Polovinka river. The special attention is given so-called «wild tuffs» which, as shown, represent a stage volcanism, previous to caldera formation. It is marked, that the volcanism of this stage has paramount value for understanding of the processes occuring in the magmatic center situated in Earth crust and resulting in large catastrophic eruptions from it.