I am saddened that my dear brother, Steve, is no longer with us and cannot help me with this page. Steve was a geologist, but more important, he was a thinker extraordinaire, the most intelligent person I’ve ever known. While he couldn’t help me directly with this page, he did help me immensely with my general understanding of waterfall geology through many conversations over the years. Much of what I’ve written here comes from those discussions and from writings he had made for me about waterfalls. Also, I’d like to thank my other brother, Laurie Adams, an accomplished amateur geologist and mineralogist, for reviewing this page and offering his guidance.

I’m not a geologist. But for the purposes of this page, that might be a good thing. I’ve studied the writings and speeches of so many geologists that my brain is fried, yet I still have a difficult time understanding the processes and time periods of mountain formation in North Carolina. But, of course, it must be discussed because without it we would not have any waterfalls.

Mercifully, here is a concise, basic, and relatively painless discussion of how the Appalachians formed from Anton DuMars, adjunct professor of geology at College of Charleston.

The Appalachian Mountains have been described as very old mountains with a face-lift. The rocks that make up these mountains come from two main sources, lithified ocean sediments thrust upon each other via tectonic plate convergence, and volcanic/ igneous activity.

During a 200-million-year stretch between (approximately) 450 and 250 million years ago, the Appalachian Mountains took shape. Tectonic plates crashed together in three separate mountain building events, culminating in the formation of supercontinent Pangaea. These events broke and bent sedimentary and igneous rocks into and on top of each other, as evidenced by countless faults and folds throughout the Appalachians.

This entangled mélange of Appalachian Mountain building over-prints onto a similar mountain building/ supercontinent forming event that happened over a billion years ago in roughly the same place. The Grenville mountains and Rodinia were formed then. In geologic terms, the Appalachian Mountains are a gigantic puzzle.

While either (or both) of these events created steep slopes enough for water to cascade from, earth scientists tell us that these ancient mountains most likely eroded flat in 20-30 million years after they formed some odd 250 million years ago. As such, the Appalachians shouldn't be here.

Researchers indicate that the modern Appalachian Mountains, as we know them, exist due to a (geologically) recent tectonic uplift, believed to have started 5 to 15 million years ago. This uplift formed many of the cliffs, coves, and valleys present today—thus the face-lift.

So, established within the modern Appalachian Mountains are slopes and cliffs available for water to cascade over. The region provides a catchment for rainwater. Groundwater infiltration seeps down-dip toward established streams. Episodic microbursts produce boulder-moving floods in these streams. All waterfall-making components are present.

Okay, that wasn’t too hard to grasp. Yay! Now, let’s talk about some specifics regarding waterfall (not mountain) formation and erosion. Not only do our waterfalls look nothing like they did after the mountains formed, they aren’t even in the same place. Millions of years of erosion created the looks and locations for the waterfalls we see today. The erosion occurred predominantly from landslides, freeze-thaw action, and streambed scouring, all of which are initiated by water.

When I first began studying waterfalls, I had a hard time grasping the concept of water wearing down rock, especially on the scale of changing mountains and forming waterfalls. A landslide is easy enough to understand, as are rocks splitting apart from freezing and thawing, but most stream erosion is the result of scouring. How could water really do that? The answer is that it doesn’t. By itself, water is not a very efficient erosional force, although it does serve as a dissolving agent for the rock. Water erodes rock because of the material it carries. Fine rock particles are always present, and during floods, the stream can carry surprisingly large rocks. This material causes erosion by abrasion.

You can probably comprehend that during the flood of 1916 streambeds changed across western North Carolina. Now imagine a flood like that occurring just once every 100 years, but over a period of 5 million years. That’s 50,000 floods! If each flood caused erosion measuring just one-sixteenth inch, it would result in 260 feet of erosion. Imagine what today’s waterfalls and creekbeds would look like if they suddenly eroded 260 feet. And consider that this is based on only 5 million years of erosion, the shortest time span stated above. What if we use the 15-million-year figure instead? Or what if the floods occur more often, or we throw in an occasional flood at the level of Tropical Storm Helene? Helene is said by some to be a thousand-year event. Well, there are five thousand thousands in 5 million years!

So, tectonic plates shifted, forming mountains, and erosion caused the waterfalls we see today. But there’s more to this equation. There must be another element involved or else there would be no significant stream relief to form the waterfalls. It would just be a steep stream until the mountains wore completely down.

One other factor is different rock types and differences in the harness of the rocks. Softer rocks erode faster than harder ones, and when these different rocks exist close together along a stream, this causes variances in the stream profile. This is referred to as differential erosion and explains the existence of many waterfalls in North Carolina.

Most explanations of waterfall formation talk about harder rock overlying softer rock. The softer rock erodes faster and causes undercutting. When the ledge of hard rock loses enough support from the softer rock below, it breaks off. In this manner, the waterfall “migrates” upstream. Waterfalls of this type are often called “caprock waterfalls.”

Caprock falls occur throughout the world, but few waterfalls of this type occur in North Carolina. Our waterfalls are indeed formed by differences in the rock hardness, but the rock layers have been so scrunched and twisted topsy-turvy that most of the falls don’t neatly fit the caprock definition. North Carolina’s waterfalls may not fit the model of caprock falls, but soft rock, whether it be under, beside, or on top of the hard rock, erodes faster, creating differences in the stream profile.

North Carolina’s waterfalls may not fit the model of caprock falls, but variations of the theme are indeed responsible for our waterfalls. Soft rock, whether it be under, beside, or on top of the hard rock, erodes faster, creating differences in the stream profile. Some types of hard rock also erode more easily due to its structure, such as those with layers that allow water to seep in and cause fracturing during freeze/thaw cycles.

Undercut cliff faces are very common at waterfalls, even if the waterfalls themselves don’t perfectly fit the mold of caprock falls. Off to the side of a waterfall, spray settles into cracks in the rock. In winter, the spray freezes, expands, and cuts the rock ever deeper. Above the drop, the rock stays drier, so it doesn’t cut back as fast. The result is an undercut cliff. A good example is the river-left cliff at Looking Glass Falls.

Not all undercut cliff faces can be fully explained by frost wedging from spray. Some smaller streams make very uneven gentler cascades with minimal or no evidence of any undercutting, while some small streams drop over large overhangs. Bridal Veil Falls near Highlands is on a very small stream, yet it is undercut enough that a road was built under it. In contrast, Crabtree Falls, also on a small stream, tumbles intricately down a sloping face with no hint of undercutting. The difference here is the angle of the rock bedding. Waterfalls like Bridal Veil plunge over rock layers that slope outward in overhangs.

It’s common to find waterfalls on smaller tributaries at their junction with larger streams. The larger streams have more erosive power and are able to cut into the rock more rapidly, resulting in the riverbed lying at a lower level than the smaller stream joining it.

Another way that waterfalls can formed has only recently been studied. Joel S. Scheingross and a team of researchers at University of Nevada, Reno, built a sloping bed of artificial bedrock using polyurethane foam, over which they directed a flow of water containing small pebbles. The foam did not erode uniformly and as a result created waterfalls. This study suggests that there doesn’t need to be a difference in rock types (hardness) for waterfalls to form. Scheingross’ published his research in the journal Nature in 2019.¹²¹

I had a bit of an aha moment when I fully digested what Scheingross’ research revealed. Having seen thousands of waterfalls in my journeys, it has always seemed unlikely to me that all of them had to have formed by outside influences such as tectonic activity or differential erosion due to rock type. Why couldn’t the bedrock just erode randomly and occasionally form a waterfall as a result?

As I stated from the outset, it's hard to wrap my head around the geological processes of waterfall formation and I defer to the experts for any sort of matter-of-fact statements. But I have to say, I would not be surprised if the formation of a good number (most?) of North Carolina’s waterfalls could be explained using Scheingross’ model.

Okay, let’s see if we can tidy up everything. Tectonic plates shift, causing mountains to form. Erosion cuts the mountains down, forming waterfalls in the process. The size and shape of the waterfalls are determined by the hardness and configuration of the rock, along with the size of the stream. Bigger stream = more erosion. Some waterfalls form in homogenous rock due to the erosive power of sediment-carrying water.

More about stream size and the largest waterfalls in North Carolina.

Learn more about the geology of North Carolina’s waterfalls.