(001) MgO single crystals were implanted with 150 keV krypton ions (Kr+) at a fluence of 5.1016 ions.cm-2 . The implanted surface, observed with an Atomic Force Microscope (AFM) exhibits striking features that can be described as undulations with a wavelength of 0.5 [μm. We correlate these features to the decrease in density and the stresses induced by the implantation damage. As a matter of fact, a model of surface instabilities provides a relationship between the wavelength of the ondulations and internal stresses. Using this model, implantation stresses are calculated to 2.2 GPa. This is in good agreement with the value of 2 GPa obtained with the help of the microindentation technique and the literature data. Some effects of an ionizing post-irradiation on stress and surface roughness are described.