I shot this photograph upstream from Baby Falls, along the Tellico River in the Cherokee National Forest of eastern Tennessee. As seen on the large boulder in the river, as well as in the second photograph included, river rocks often have hollow carve-outs. On site, there were dozens visible in and under the water, as well as along the shore – some measuring approx. 4-feet in diameter.
This is caused over time when a smaller rock consisting of a harder mineral substance becomes caught in a depression or crevasse. Water from the river continually moves the smaller rock within this space, until it bores a hole into the larger rock.