How are potholes formed in the James River?

Potholes in the James River, formed by grinding of rocks and sandHave you ever wondered why there are so many large holes in the huge granite boulders and bedrock along the James River and how they are formed?

Huge boulder, size of a beachball grinding out a hole in another granite boulderJohn Bryan explains this process well in The James River In Richmond: Your Guide to Enjoying America’s Best Urban Waterway:

The water in the river carries small particles of debris which become trapped in the natural fractures in the rock. The force of the running water causes these small particles to move around in the fracture, grinding away part of the rocks like sandpaper. As the hole increases in size, larger debris becomes trapped and these also begin grinding. The result of this grinding away at the rock forms a pothole.

Softball sized rock grinding out a hole in a granite boulderMost of the potholes are shallow, but some that are visible during normal water levels can be as deep as three to four feet. Many are underwater except in drought conditions, below 3.5 feet.

At times, potholes in the most popular areas of the park can be a notorious place to find litter, especially broken glass. Please use caution and help keep the river clean. Also, it is best to leave potholes filled with trapped, stagnant water alone, unless you are conducting a science project.


One response to “How are potholes formed in the James River?

  1. Cool, learn something new every day.

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