TERRACES AND INCISION HISTORY OF THE JAMES RIVER NEAR THE BLUE RIDGE OF VIRGINIA

Terrace profiles along the James River between Glasgow and Lynchburg, Virginia could be interpreted to suggest migrating knickpoints have and are eroding through the James River gap in the Blue Ridge. Downstream of the Blue Ridge, mapped terrace profiles are roughly parallel to the river profile. The terraces can be grouped into 3 levels at approximately 27, 43, and 67 meters above the river, plus one remnant at 107 m. The extent of the terrace remnants is not well correlated to terrace elevation; terraces near the current river elevation are narrow, whereas the highest terrace remnant is the most extensive. The gradient of the river increases at a knickpoint in the lower portion of the gap, raising the upstream profile approximately 12 m. Few terraces exist in the Blue Ridge gap, which makes correlation speculative, but the terrace profiles appear to project without a knickpoint through the gap to correlate with upstream terraces and knickpoints.

Physical and chemical properties of soils in the terraces <100 m correlate with the highest soils in terrace remnants in the Valley and Ridge as well as farther downstream on the Piedmont. However, the highest terrace is more weathered than any terrace remnant observed in the James River upstream of Lynchburg. The weathering, extent, and height of the 107 m terrace suggests a remarkable origin and great age, perhaps greater than several million years when compared with terraces at the mouth of the James. Such a terrace might be the product of capture and rearrangement of drainage in the upper portion of the James River.