Solid Rock Flow

Rockfall

When continental masses, islands, and the sea floor collided with the margin of ancestral North America, they were subjected to intense pressure and heat deep beneath the ground surface. Where the temperature is high but below the melting point of the rocks, the rocks deform and recrystallize in a solid state to become metamorphic rocks. The components separate into bands, and some flow with a consistency like that of toothpaste. In many places along the Blue Ridge Parkway, there are metamorphic rocks with bands of light- and dark-colored minerals, which in some places look like the folds and swirls in a marble cake.

Original layers are partly retained if metamorphic temperature and pressure are low, as happened with some of the sediments that were deposited in the Ocoee basin. During metamorphism, minerals recrystallized in sheets to form rocks (slate or schist) that split easily into thin, smooth layers. When these rocks are near rivers or creeks, they make excellent skipping stones.

The smooth surfaces are also excellent slip planes. These planes can cause serious problems, especially when the layers are steeply inclined. Rocks overlying smooth, inclined surfaces are very prone to sliding downslope, especially when heavy rainfall increases water pressure at the surfaces.