In many parts of the Piedmont of North Carolina, there is an interesting pattern of streams, lakes and rivers that seems to go against conventional Newtonian wisdom. Many of these drainage features go from the southwest to the northeast, which is 90 degrees away from the fastest path to the ocean. The answer to this paradox is best revealed by looking at a topographic relief map of our state and noting that in the western part of the state the Blue Ridge Mountains and associated landforms are oriented in the southwest to northeast direction as well.
And why is this so? Blame Africa! Starting approximately 450 million years ago there was a series of collisions of two major continental plates, the African Plate from the southeast and the North American Plate from the northwest. The collisions caused buckling, thrust faults, and deep fractures into the older bedrock along a northeast-southwest trend.Because of this continental collision, there is a preferred orientation of strata and rockforms that tends to orient drainage southwest to northeast. This orientation is imprinted in the bedrock, and so it affects groundwater as well as surface drainage. For this reason, it is sometimes possible to find groundwater being transported in a direction quite different from what appears to be downhill.
One of the ways bedrock fractures and flow can be traced is with geophysical surveys, so call us if you ever need such a service!!
Another interesting effect of the orientation of bedrock is seen in the area of Guilford County where levels of radon are seen with a distinct southwest-northeast divide between typically higher readings to the northwest and lower readings to the southeast. Radon is a naturally occurring gas that comes from certain types of bedrock. In the case of Guilford County, this bedrock is located prominently in the northwest half of the county. Thus, you are much more likely to find elevated radon readings in that part of the county versus the southeast.
