A morphodynamic comparison between bedrock and soil-mantled landscapes

Despite the wide occurrence of bedrock landscapes, little is known about the linkages between erosional processes and the characteristic hillslope and river-channel landforms when soil is absent. In this thesis I use high-resolution topographic data derived from airborne laser swath mapping, combined with field measurements, to ask whether the patterns commonly observed in soil-mantled landscapes also occur in a bedrock landscape. My field site is on the east slopes of the Henry Mountains, Utah, where a broad expanse of bare Navajo Sandstone is actively eroding in response to canyon cutting on the Colorado River. I use two measures of curvature, Laplacian and surface-normal, and find that, unlike soil mantled hillslopes, bedrock curvature does not change as gradient increases, however, surface-normal curvature for locations of weathered exfoliation sheets does vary systematically with gradient. These observations are consistent with exfoliation being a dominant process shaping bedrock domes in this landscape. The channel heads, characterized by polygonal fracturing, are shown to have a characteristic surface-normal curvature and drainage area, but not a dependence on slope and area as revealed by the slope-area analysis. Channel longitudinal profiles are composed of alternating low gradient sand reaches and steep bedrock reaches, however only bedrock reaches show the expected decrease in slope with increasing drainage area