geothermal flow the flow of heat travelling from the interior of the earth to the surface of the earth, in consequence of the higher temperatures prevailing in the interior arising from the natural decay of radioactive elements in the earth's crust and residual heat in the earth's formation GRM: n. Note: the mean geothermal heat flow at the earth's surface amounts to approximately 0.06 W/m2 References: SEEgeothermal fluid