Rock glaciers in ice-rich permafrost can be discriminated from debris-covered glaciers. The key physical phenomenon relates to the tight mechanical coupling between the moving frozen body at depth and the surface layer of debris in the case of rock glaciers, as opposed to the virtually inexistent coupling in the case of surface ice with a debris cover. Contact zones of surface ice with subsurface ice in permafrost constitute diffuse landforms beyond either–or-type landform classification.