The paper discusses the mechanism of deep magma activity beneath island are volcanoes and similar structures on the basis of data from geophysical investigations in Kamchatka; the analyses of forces that cause the ascent of magma; and related phenomena that are due to hydrostatic forces. It is shown that the ascent of magma through the astnenosphere occurs most likely in magma columns with a diameter of approximately 700–2,000 m and with a velocity of about 0.8–3 m/year. A regular line of such columns spaced in Kamchatka at a distance of about 30 km gives rise to a chain of separate Etrge volcanoes or volcanic centers. Ultrabasic magmas are most likely accumulated near the M discontinuity, whereas the apparent place of andesitic magma accumulation is in the earth’s crust near the boundary between the basement and sediments.