Processes dominating macro-fabric generation in periglacial colluvium

Mass wasting processes in a periglacial environment are considered to result from a combination of frost creep and gelifluction. The relative importance of these processes is often difficult to determine, but appears to be related to factors such as slope angle, soil moisture content, soil texture, and vegetation cover. Further, the importance of any one of these factors can vary from year to year, thereby making long term predictions of slope stability or reconstructions of behaviour history difficult. This study uses two-dimensional macro-fabric analysis as a recorder of the dominant mode of mass-wasting on a slope. Clast trend and plunge data were collected from 68 sites at Eagle Summit, Alaska, and examined in two separate dimensions: the plane of the slope to represent the stress-field driven by gravity; and in a vertical plane trending down the slope to represent the stress-field created by frost heaving pressures. Circular correlation tests indicate the importance of the downslope stress-field on clast position in the plane of the slope. In the vertical plane clast plunge varies according to slope. On gentle slopes, clasts tend to be steeply dipping, on moderate slopes they are parallel to the plane of the slope, and on steep slopes they are imbricated. These observations correspond to modeled experiments of slope deformation under periglacial conditions, and suggest that at the scale of the slope, mass-wasting processes are influenced by varying intensities of frost heave and gravity transfer that are conditioned by slope angle.