Vug waves are a joint deformation/fluid-migration mechanism in which a rock deforms by the movement of a penny-shaped, fluid-filled crack dislocation across a plane of shear, with migration of the crack and fluid driven by the release of elastic shear strain energy. Vug waves (here so named because a vug is a hole in the Earth and wave implies that it moves) may provide an effective means for (1) rapidly migrating and focusing relatively isolated batches of melt to mid-ocean ridge axes, (2) a possible origin for weakness and rheological and seismic anisotropy of Earth's asthenosphere, and (3) the origin of large, weak shear zones within Earth's mantle and crust. The existence of vug waves would also imply that in many geologic environments the strain-energy release from migrating a fluid-filled crack through a stressed solid may play a larger role in shaping fluid migration than the buoyancy of the fluid with respect to its host rock.