Insituwafer curvature measurements were performed to study mechanical stress in amorphous SiO2during Xe, Ne, and Er ion irradiation at energies in the 0.27–4.0 MeV range. Three phenomena are observed: network compaction, radiation‐induced viscous flow, and a nonsaturating anisotropic deformation phenomenon. The radiation‐inducedviscosityis shown to be inversely proportional to the energy density deposited into atomic displacements. The relation between radiation‐induced flow and diffusion is discussed in the context of the Stokes–Einstein relation. Viscous flow serves to relax stress, yet a continuous nonsaturatinganisotropicdeformationeffect causes the stress in the irradiated layer to saturate at nonzero values: Xe irradiation at an energy below 3.6 MeV results in a tensile saturation stress; for higher energies a compressive stress builds up. These effects are explained in terms of competing bulk and surface deformation processes resulting from local heating of the SiO2around the ion tracks. The macroscopic effect of deformation phenomena is illustrated by showing the surface morphology after 4.9 MeV Er irradiation of silica through a contact implantation mask. Finally, aninsitustress study of an alkali borosilicate glass is presented. In this case a fourth radiation induced effect is observed, namely, the generation and annihilation of volume occupying point defects. These defects are shown to anneal out at room temperature, following a broad spectrum of activation energies. ©1995 American Institute of Physics.