North Georgia’s waterfalls make a great destination for a day excursion. There are a lot of truly spectacular ones, Amicalola Falls for example. At 729 feet, it’s more than three times the height of Niagara Falls, New York. Toccoa Falls, in Stephens County, has water going down a vertical drop of 186 feet. That’s just 2 feet short of the Horseshoe portion of Niagara. Visiting Hurricane Falls in Tallulah Gorge requires more of a physical commitment. The descent from the parking lot near the dam takes you from 1,569 feet to 1,150 feet at the bottom of the falls. The return trip up some long stairways can be challenging, but the views are worth it.
Waterfalls commonly form where there’s a change in bedrock geology. Niagara Falls is a textbook example. It’s made from a tilted sandwich-like arrangement of rock layers. They are all sedimentary, developed from particles that settled on an ocean floor about 420 million years ago. Shale forming the bottom of the falls isn’t permeable to water. It gets carved into a hollow shape, like one would use a chisel to turn a tree trunk into a canoe. The chisel doesn’t cut deep, it only chips away. On top of the shale are layers of limestone and dolomite, both water soluble. Water gets into cracks and widens them chemically until a big chunk breaks off and falls to the bottom. This is how the falls remain steep. Every time something comes off the top, the edge of the fall is shifting backward up the river.
Rocks made either from magma deep inside the Earth, or by compression of other rocks, behave differently. At Toccoa Falls, water encounters a hard crystalline rock that doesn’t wear away quickly. So the stream is forced to plunge down and continue its erosion work at the bottom of the falls. Looking Glass Falls near Brevard, North Carolina is another good example. The water runs 60 feet toward the bottom over a curved surface. If it reminds you of Stone Mountain, that’s correct. Erosion of surrounding rock (the Carolina Gneiss) has exposed a chunk of very hard granite that wears away very slowly, so water must plunge down over it. It was once a molten bubble far underground, and preserves its round slope just like nearby Looking Glass Rock does on a grand scale.
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.