Date of this Version
Robert F. Diffendal, Jr. 1988. River potholes: Modern and ancient. The Cleveland Museum of Natural History Explorer 30:3, 33-35.
A river pothole is a cylindrical, bowl-shaped, or irregular hollow that is usually deeper than wide. It is formed in the rocky bed of a stream by either the grinding action of sediment whirled around by stream eddies or the force of fast flowing water. Potholes usually have spirally grooved surfaces. Their widths and depths range from a few inches to many feet. Potholes on the floor of the Susquehanna River near Columbia, Pennsylvania, for example, are large enough to hold objects the size of a small car.
Potholes generally are formed in fairly homogeneous rock by streams that at least periodically have high discharges. Long grooves running parallel or nearly parallel to the stream flow are often carved into the bedrock floor of the channel and may lead from one pothole to another. A wonderful example of these related features occurs on the channel floor of the Niobrara River at Norden Bridge in north-central Nebraska. As the river continues to erode its channel the shapes and sizes of the grooves and potholes change.
Another fantastic example of pothole development occurs at Boiling Pots Park on the southwest outskirts of Hilo, Hawaii. Here a stream has carved a valley through several sheets of hardened lava rock or basalt. The stream plunges over successively exposed layers of this basalt, each of which are up to 20 feet thick. A pothole or series of potholes in each layer of rock crossed by the stream produces a series of circular pools that at times of low water are arranged like a string of beads.