the state of balance, or equilibrium, which sections of the earth's lithosphere (whether continental or oceanic) are thought ultimately to achieve when the vertical forces upon them remain unchanged. The lithosphere floats upon the semifluid asthenosphere below. If a section of lithosphere is loaded, as by ice, it will slowly subside to a new equilibrium position; if a section of lithosphere is reduced in mass, as by erosion, it will slowly rise to a new equilibrium position