The Evolution of the Blue Ridge Parkway

Crossing the Blue Ridge from Charlottesville involves a steep climb up to Rockfish Gap, followed by an equally steep descent to the Shenandoah Valley. 

Along most of its northern segment from Afton to Roanoke, the Blue Ridge is a single, well-defined ridge or group of ridges; high ground surrounded by lowlands.  As the Blue Ridge Parkway sweeps back and forth across the top of the Blue Ridge, magnificent views of the Piedmont to the east alternate with views of the Great Valley of the Appalachians to the west.  There are places where one may stand and look down a thousand feet or more in either direction.

South of Roanoke the picture changes.  The ascent to Floyd County from Woolwine involves a steep, winding, thousand-foot climb up Va 8.  After climbing the Ridge from the Piedmont, however, you are greeted by a landscape very much like that you left behind.  Farms and fields cover rolling hills.  Buffalo Mountain, higher than Peaks of Otter and nearly as high as The Priest, is an obvious but not especially noteworthy, bump on a landscape that slopes gently westward toward the valley of the New River.  There really is no ridge here.  Instead, the Blue Ridge is an escarpment, a step up from one relatively flat region (the Piedmont) to another (the New River Basin).

The change in the Blue Ridge from ridge to escarpment is a reflection of the powerful forces that shape our landscape.  South of Roanoke, through North Carolina, streams do not cut across the ridge.  Instead, the Blue Ridge is a great divide, separating Atlantic drainage streams from those, like the New River, that flow through the Ohio or Tennessee drainages to the Gulf of Mexico.  It is likely that the whole Blue Ridge was once a drainage divide, possibly the ancestral divide dating back to the time of the dinosaurs.

But water likes to seek the fastest way to the sea.  Over the eons, fast moving Atlantic streams have cut back across the ridge, diverting westward draining rivers to the shorter, faster eastern track to the ocean.  From Roanoke north, the ridge is cut by several of these rivers; the Roanoke, the James, and the Potomac.  The fast moving water of these rivers cuts rapidly down into the older stream beds, lowering them nearly to the level of the Piedmont and producing the Great Appalachian Valleys of the Shenandoah, James and Roanoke.  Only where there was little water to do the hard work of erosion, up near the original drainage divide where the streams are small, did the high ground survive.  Thus the northern Blue Ridge is a relic – a fossil marking the old divide.

The work of dismantling mountains continues today.  The Roanoke and James Rivers are cutting back rapidly towards the valley of the New River.  Within a few thousands or tens of thousands of years, one of these (my money is on the Roanoke) will breach the banks of the New River, probably near Blacksburg, divert its waters into its own streambed, and continue the process of transforming a divide into a ridge.

James S. Beard, Curator of Geology, Virginia
Museum of Natural History