Multi-phase flow instabilities have always been a great interest in fluid flow in porous media, as they can create fingers and drastically change the travel times of solutes to ground water and/or change the sweep efficiency. Yves Parlange has been at the forefront of this research for the past 40 years, beginning with his classic papers on front stability with Hill. In the last decade, it has become apparent that gravity driven instabilities profiles cannot be described by traditional unsaturated continuum flow models (e.g. the Richards Equation). In this talk, I will detail this connection, and in turn, show how measurements of flow instabilities are key to developing the correct physical extensions of multi-phase flow.