The Klyuchevskoi group of volcanoes (KGV) in Kamchatka is the most powerful existing island arc and subduction zone volcanic center. The Holocene volcanic activity in the southern part of the KGV is concentrated in a large basaltic volcano, Ploskii Tolbachik (PT), altitude 3085 m and in itsTolbachik zone of cinder cones (TZ), length 70 km, which are similar to Hawaiian-type volcanoes and their rifts. A variety of different basalt types are erupted at a rate of 18 x 106 t/yr. This paper provides information on the PT peripheral magma chamber obtained by several independent methods. We used data on the evolution, eruptions, magma discharge, deformation, and earthquakes in the PT and TZ, as well as calculations that give the size of the PT flow-through magma chamber. The use of seis- mological and geodetic data places the chamber under the PT summit caldera, gives its transverse size as below 6 km, and the top of the chamber at a depth of 2 km. Our calculations give 4.9-5.8 km for the transverse chamber dimension, 3.2-3.9 km for its vertical dimension, 40-70 km' for chamber volume, and about 4 km for the depth of chamber center. The information we provide makes the properties of this source of PT and TZ alumina-rich basalts clear, as well as those of the entire KGV complex plumbing system.

Based on of experimental data obtained during almost 30 years period at the Kamchatka volcanic eruptions, acoustic signals in the range of 1,0-10 Hz are considered, generated immediately during the magma disebaige onto the surface due to its degassing. It is shown that the acoustic signals from this range generated by volcanic eruptions are weak shock airwaves in the nearby zone. They can be divided based on their of its impulse form and statistical parameters in to 6 types associated with different unsteady processes conditioned by magma degassing. The crater dimensions control the characteristic time of pulse of surplus pressure of volcanic shock airwaves. Acoustic signals contain information about eruption dynamics and crater geometry modifications, on the examples of terminal and lateral eruptions of the Kluchevskoi volcano in May-June, 1983. The author made estimations of explosive gas amount for three strombolian type eruptions, using acoustic signals parameters. Basis for a scientific direction – volcanic acoustics – is established.
The book is of special interest for specialists in volcanology, atmosphere acoustics and explosions.