Shape changes in glasses due to surface flow

It has recently been suggested that at the surface of glasses there is a thin layer of material with finite viscosity that can flow even if the hulk is frozen. We address the observable consequences of this phenomenon on the time evolution of a given geometrical profile. The effects of surface flow turn out to be quite different than those expected in the case of bulk flow. We suggest that surface flow of glasses near the glass transition is likely to be observable in ultra-centrifuge experiments. (C) 2000 Elsevier Science B.V. All rights reserved.