Microrelief consisting of mounds or hummocks was examined at selected sites in the discontinuous and continuous permafrost zones of the Canadian north. Observations of the macromorphology and micromorphology of the mounds were used to interpret the dynamics of their formation. There was evidence that pressures were created inside the mounds as the freezing interface migrated towards the permafrost table during early winter. These pressures moved material inwards and upwards within the mounds, causing the plasmic lamellae and flattened quartz grains in the microfabric to rotate into a preferred alignment. Except at the most silty sites, the mounds were fractured at their centres. Subsoil spread over the surface of the sandier mounds, or the surface was severely heaved. This kind of microrelief can easily be damaged by traffic.