— The dynamics of the volcanic activity, magmatic feeding system, accumulation, movement, and composition of magmas, and structure of the roots of the Northern group of volcanoes (NGV) in Kamchatka are considered. The results of monitoring the field of the ratio of seismic P - and S -wave velocities, the V P / V S parameter in the region of the Klyuchevskaya volcanic group based on the data of the volcanic earthquakes registered by a network of telemetric seismic stations are presented. The parameter changes in space and time during the periods of volcanic activity development. Each segment of the volcanic structure and period of activity is characterized by the own behavior of the field of V P / V S values. In the intermediate magmatic chamber, low V P / V S values are observed beneath the Klyuchevskoi volcano at a depth of 8 to 10 km and beneath Plosky Tolbachik at a depth of 3 to 5 km, which is related to the state of the substance and temperature in these areas, and the entry of a new melt portion of magma and the fluid-gas component from the crust and the mantle. The relation of volcanic earthquakes and earthquakes in the focal zone of Kamchatka, i.e., the ratio of the subduction zone (the sinking Pacific Ocean Plate) and the feeding source of volcanoes, is considered. It is shown that the Klyuchevskoi peripheral chamber is not the only area feeding the NGV. According to the values of the V P / V S parameter, the volcanoes have different magma compositions, which is determined by the physicochemical and temperature features of the medium. In our opinion, the feeding area of volcanoes from the Northern group is a neutral layer that we have identified.