TRANSIENT INCISION IN THE UPPER NEW (TEAYS) RIVER BASIN, SOUTHERN APPALACHIANS: EVIDENCE OF THE FAR-REACHING EFFECTS OF GLACIALLY-FORCED DRAINAGE REARRANGEMENT?

The upper New River of Virginia and North Carolina represents the unglaciated headwaters of the ancient Teays River system, which drained much of the southern and central Appalachians to the Gulf of Mexico prior to Pleistocene glaciation. Originally flowing across present-day Ohio, Indiana, and Illinois before turning south, the lower Teays was glacially dammed and diverted near Chillicothe, Ohio to produce the modern New River-Ohio River drainage pattern. Although the upper New and its major tributaries still follow their Teays-era courses, inspection of DEM topography, longitudinal stream profiles, and dated fluvial terraces indicate that the drainage network has experienced numerous episodes of transient incision since the end of the Pliocene. The continued headward migration of these “waves” of incision is indicated by the abundance of high-drainage area knickpoints within the upper New and its tributaries, many of which are developed in weak lithologies. Retreat of these knickpoints has locally dissected the low-relief landscape of the Great Valley and Blue Ridge Plateau physiographic provinces into a series of flat-topped relict surfaces separated by bedrock gorges up to ~150m deep. Regionally, transient incision of this magnitude appears limited to Teays headwaters, suggesting it results from base level drop due to Teays diversion as opposed to broad surface uplift or a climatically-driven increase in stream power. The upper New River landscape may thus provide unique evidence of the potential for glacial drainage rearrangement to force a transient fluvial response hundreds of kilometers beyond the limits of ice sheet advance.