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Knickpoints and Disequilibrium in Ancient Orogen: A Study of Central Appalachian Channel Profiles around Crabtree Falls, Virginia
Hoon-Starr, Michelle
Hoon-Starr, Michelle
Abstract
Despite a long period of post-orogenic decay, the southern Appalachians maintain rugged topography with significant relief. Recent work on the origins of this topography has produced seemingly contradictory conclusions: the landscape is in a state of 1) dynamic equilibrium, with high topography maintained by isostatic adjustment to uniform erosion, or 2) disequilibrium driven by uplift by mantle forcing, stream piracy, and/or climate change, producing nonuniform erosion that has increased relief. Here we present river longitudinal profile analyses from the Blue Ridge in west-central Virginia. We have extracted profiles from 10 m NED DEMs in 72 tributaries along ~30 km of the Blue Ridge in the James River drainage basin. Knickpoints, convexities on longitudinal profiles, were located using slope-area plots, from which we determined the elevation, change in elevation, and slope for each identified convexity. Knickpoints’ underlying lithology and proximity to lithological contacts were determined from georeferenced geologic maps. We eliminated from the data set convexities less than 15 m in total height and/or less than 0.03 in slope. Using this criteria, we identified 45 distinct convexities on 41 tributaries. Of these, 31 could not be directly related to lithology, and most cluster around an elevation of 700-900 m. We conclude that within the study area, there is evidence for migratory knickpoints that are increasing valley relief and hillslope angles, producing a rugged, high relief topography.
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2015-01-01
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Geology