Years ago, I bought a poster in Brevard, North Carolina showing Looking Glass Falls. It’s a picturesque waterfall alongside U.S. 276, just north of the trailhead that leads to the top of Looking Glass Rock. I compared a more recent photo I had shot of the falls and discovered that a piece was missing. A large boulder, perched on top of the waterfall, had been swept across the cliff and was now resting at the bottom. The two images served as a good demonstration of how river erosion progresses upstream. Water flows downhill, but whenever a chunk of rock is removed, the valley, or in this case the waterfall, has moved farther up the slope.
Waterfalls occur where a river is carving out a valley in the upstream direction and encounters a harder layer of rock. The rounded outline of 60-foot tall Looking Glass Falls is produced by the same granite that also forms whaleback-shaped Looking Glass Rock. Because the granite is so hard, it works like a big curb stone, standing up against surrounding softer Carolina gneiss. The waterfall therefore slowly migrates upstream.
It’s more complex at Niagara Falls, New York. The Niagara River flows over a sandwiched arrangement of soft shale at the bottom and hard limestone at the top. As the shale erodes in the plunging water, chunks of limestone break off the top from time to time, making the waterfall recede upstream. It’s a natural process. Nevertheless, the State of New York decided in 1969 to “stabilize” the American Falls through engineering. All river water was diverted to the Canadian side, and massive projects spent millions of dollars trying to remove rock debris from the base and hold unstable parts in place with screws. Eventually, though, it was decided that complete re-engineering of the waterfall would be too costly and produce questionable results. Given the fact that tourists visit there to see a natural wonder, it makes the most sense to leave the falls in their natural condition.
Currently, plans are on the table to “turn the American Falls off” again in order to replace two crumbling bridges. Lack of state funds makes it unlikely that it will happen this year. But if the project continues, visitors will once again have an opportunity to see an unnaturally dry river and empty waterfall cliff on the American side.
Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.