Amorphous silica structures which are a few nanometres in width and tens of nanometres in length are seen to become unstable under intense electron irradiation against plastic deformation, necking and failure. Similarly irradiated atomistically sharp tips, which are observed to be stable in crystalline materials, undergo rapid blunting in amorphous structures, caused by evaporation and enhanced viscous flow. The tip extremities separate into spherical bulbs by necking, and local clustering is seen during fluctuations in the microscopic structure. The observations provide information on the nature of microscopic diffusion and flow, during kinetic phenomena such as failure of amorphous structures.