The shape of a plume conduit produced by melting solid paraffin block above a local heat source was studied experimentally as a function of the relative thermal power of the plume Ka = N/N1, where N1 is the power of the plume source and N1 is the power corresponding to the amount of heat transferred by conduction through the plume conduit to the surrounding solid paraffin block. The limiting power of the plume source at which the plume erupts at the Earth’s surface (Nlim1 = (1.35–1.60) × 1010 W) and the power at which the mushroom-shaped plume head formed at the base of the refractory layer (Nlim2 = (1.78–1.90) × 1010 W) with no horizontal mantle flow were determined. The dependence of the diameter of the base of the plume on the Ka number was established. The Ka value and the diameter of the plume base were determined for the Hawaiian and Iceland plumes, for the plume responsible for the formation of the Tunguska syneclise and for the McKenzie and Central Atlantic continental plateau-basalt provinces and for the Ontong Java and Manihiki oceanic lava plateaus.

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