A two-dimensional model is developed to predict head cut migration rate for the specific case of a relatively erosion-resistant soil layer overlying a deep, relatively erosive base soil. For this geometry, head cut migration can occur as a series of discrete mass failures of the surface layer caused by undercutting in a plunge pool formed immediately downstream. The length scale of one failure episode is modeled as a cantilevered slab failing in bending. The timescale for each failure episode is controlled by the rate and geometry of base layer scour, which is modeled independently of cantilevered slab properties. An integration of the two model components for the case of steady flow and uniform soil properties predicts linear upstream head cut migration with time, occurring in discrete steps bounded by successive mass failure events. The model is calibrated and tested in a series of flume experiments representing ideal conditions of different initial geometries and flow conditions. Head cut migration occurred by the proposed mechanism in a nearly linear rate. Average error between the observed and predicted retreat rate is 40%, most of this error is attributable to prediction of the scour hole shape.