A simple model, describing a network of springs moving against friction, is used to study the evolution of surface patterns on a gel undergoing uniaxial expansion. The nonlinear growth equation obtained adequately describes the key experimental observations, such as the scaling of the typical size of patterns and the formation of cusps. The dynamics is carried on a computer, and the patterns obtained are in qualitative agreement with experiments.

• Received 14 March 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.106