The evolution of the surface topography of fused silica during low-energy Ar ion beam sputtering was studied by atomic force microscopy. Depending on the incidence angle of the ion beam and the ion energy the topography was dominated by regular ripple structures with an orientation perpendicular or parallel to the ion beam direction and a characteristic wavelength), between 30 and 300 nm. The time evolution of the ripple wavelength follows the power law lambda similar to t while gamma depends on the ion beam parameters. In addition, we found a distinct energy dependence of the ripple wavelength as well as the resulting scaling behaviour of the surface roughness. These results will be discussed within the limits of existing continuum models for surface erosion by ion sputtering.