By: Clint Calhoun
Just recently I started the arduous task of digitizing and electronically archiving all of my old slides. I started getting seriously into photography around 1995 when I got my first Canon EOS Rebel II camera. My buddy Travis introduced me to slide film as an alternative to print film due to the quality of the imaging. From there I was hooked. I started shooting slide film in 1997 and accumulated over 2000 slides in the course of about 6 years. The digital photo era began and my interest in slides more or less went the way of the dodo. Archiving old photos offers me an alternative to winter photography which generally doesn’t interest me unless there’s snow on the ground or birds on the bird feeder. As I started scanning slides, I ran across a batch of slides that I took way back in 2001 of the Bottomless Pools and I suddenly became re-interested in what has always been one of, if not the most popular Rutherford County tourist attraction. From a scientific standpoint, the Bottomless Pools are interesting, not because of their beauty, but rather because they are somewhat of a geological oddity.
When you look at Hickory Nut Gorge from a geological perspective, it is very similar to other escarpment gorges, although probably a little less wild than most of the other gorges in North Carolina. The gorge formed over a very long period of time through a lengthy process of erosion. Without going into a long explanation of how our Blue Ridge Mountains were formed, the rock that is found throughout Hickory Nut Gorge went through multiple periods of uplifting, shifting, heating, and cooling. Through this process, the rock was changed physically into the metamorphic rock we know as Henderson augen gneiss. After each cooling process, shear stresses would create fractures in the rock known as joints. Along these joints, the erosion process takes place faster than in places where there are no joints. Geologically speaking, Hickory Nut Gorge is very young in comparison to the rock associated with it which would indicate that Hickory Nut Gorge itself is a large joint or perhaps a tectonic fault that the Broad River has cut through, eroding rock material and depositing it in the lower floodplains in the Piedmont.
Joints are evident all over Hickory Nut Gorge and are evidenced in the unusual rock features associated with them. Chimney Rock exists because of a significant joint that exists behind the Chimney. Because of the weakness where the joint exists, water is able to infiltrate cracks in the rock and flow parallel to the joint, eroding the rock material, creating the “hoodoo” feature we see today.
Perhaps the finest example of joint erosion is the Bottomless Pools. Some geologists believe that the Bottomless Pools may be less than 100 thousand years old which is very young in terms of geologic time. It is quite interesting, because if you explore the Pool Creek drainage, which is only about 6 square miles, while there are a few potholes and pools along Pool Creek and Wolf Creek, there are none as significant or as deep as those at the Bottomless Pools. Why is that?
First of all, the Bottomless Pools are at the bottom of the drainage where water volume is the highest. Second, the creek reaches a significant joint just upstream of the pools. Because of the elevation change, increased water velocities have worn the streambed down to bedrock, so the only thing left to cut is the rock itself. The result is a whirlpool or scour hole where the joint gets eroded until it reaches the much harder rock not associated with the joint. You can see this on a much smaller scale when you look at potholes on rock faces. In these examples water finds a depression in the rock and pools. Wind will move the water causing it to swirl in the depression. As this happens, grit and other particles begin to wear away the surface of the rock. In the case of the Bottomless Pools you have depressions and cracks, surrounded by resistant rock that a high volume of water and water-borne particles are pouring into, eroding the rock surface away.
Looking at each pool individually, it’s possible to infer some interesting possibilities. The bottom plunge pool that the first walking bridge crosses over will someday be connected with the lower pool as the pool continues to scour out the hole. The middle pool, which is the most interesting to me, has lost some of its cutting action. It is also losing depth. The bottom is clearly visible as sediment from upstream has begun to fill it in due to the reduced hydraulic action of the pool. That doesn’t mean nothing is happening though. A new pool is being created as the waterfall of the middle pool cuts deeper into the joint just upstream of the main pool and this new pool is quite deep. The upper pool is likely the deepest of the three and is the youngest in terms of time. There is very prominent swirling action in the pool that I was able to capture on film which shows that erosion is still occurring. Eventually, the middle pool and upper pool will become one, assuming there is enough velocity to cut the lip between the two pools. There is also the possibility that as the pools widen, assuming joint cutting doesn’t occur fast enough, that the pools will begin to lose their cutting ability because of decreased velocities in each pool. Whatever happens, it will not be in our lifetimes, but rather is only something that we can ponder. Do we really know what’s going on? It’s fun to speculate what the pools may look like in another 100,000 years. Will they look like the plunge pool above the second walking bridge which is very large and is no longer an active whirlpool?
I write this because Bottomless Pools is one of our oft forgotten (maybe not forgotten, just seldom mentioned) gorge attractions. I keep hoping that one day, perhaps in my lifetime that we will see the Bottomless Pools open once again, either in continued private ownership, or under the ownership of NC State Parks. Either way, the Bottomless Pools will still be there, waiting, as time slowly passes.
Clint Calhoun is a naturalist and biologist and has worked in the Hickory Nut Gorge area for almost 20 years. He is currently the Environmental Management Officer for the Town of Lake Lure. Check out Clint’s blog at http://clintcalhounadventures.blogspot.com.