The decay of a profile artificially produced on a crystal surface below its roughening transition is studied by means of a qualitative theory. In the case of a bidirectional modulation the height h(t) is a linear function of time t and the lifetime τ is proportional to λ 3h(0), where λ is the wavelength. As suggested by Bonzel et al. the formation of facets is a sensitive information to determine whether a surface is below its roughening temperature. Near the flat part the profile has a (x - x0)3/2 singularity as in a crystal at equilibrium. The case of a unidirectional modulation is still open although some heuristic treatments give a qualitative agreement with experimental results.