STREAM CAPTURE AS A DRIVER OF TRANSIENT INCISION IN THE SOUTHERN BLUE RIDGE ESCARPMENT: A FIELD ASSESSMENT OF THE GREEN RIVER GORGE

Understanding stream capture in the Appalachians is vital to conceptualizing and modeling escarpment evolution and migration. Escarpment evolution has previously been thought of as a slow and uniform retreat along a linear escarpment face. However, new evidence suggests that the Blue Ridge Escarpment (BRE) experiences episodic and irregular retreat. These episodic events are driven by streams being captured away from westward drainages and redirected toward the Atlantic. The waves of incision emanate inward to the heart of the plateau dissecting it, leaving behind relic plateaus. This research examines the Green River in North Carolina as a case study in an attempt to gain a better understanding of how this dissection and retreat is playing out in the southern BRE. From Digital Elevation Models (DEM) we created longitudinal profiles of the Green River and its tributaries. Complimentary field studies examined the structure and lithology of the Green River gorge, focusing specifically on their impacts on the migration of knickpoints caused by the drop in base level. The Green River profile has a major convexity where the river drops off the escarpment. For a river in steady-state equilibrium, the profile should be a smooth, concave upward profile. Hence, the Green River is experiencing an adjustment to a new regional base level that has caused the large convexiety. This zone of incision has created a deep gorge with numerous knickpoints ranging from 2-10 m. The longitudinal profiles reveal a wave of incision on the Green River that is also seen in its tributaries. With these profiles we recreated the section of the escarpment that was eroded away by the incision. The large amount of material carried off from this one event out paced the erosion from competing processes along the BRE. Our findings support the concept of stream capture driving the retreat of the escarpment through episodic jumps. This mechanism potentially could explain not only how the BRE retreats, but how many of the other great escarpments evolved.