What Makes a Waterfall? Maybe It Forms Itself

Perhaps I'm being dense but it seems to that the historic understanding of the formation of falls seems rather silly. The scientists should have observed the natural world around them more closely from the beginning. Something as random as a log that falls in the river can start changes that will alter it's course and character. Long after the log has rotted away those changes will continue to develop. Perhaps a lovely pool will form, perfect for trout. Or a series of rapids. The only difference between rapids and waterfalls is the height of the drop. I certainly hope that the scientific community uses more common sense before they start geo-engineering our world or Crispr-ing our DNA.

Seems geologists were never the brightest bulbs in the lot. Anyone watching water flow for a while in mud would see this phenomenon. Remember the adage: you look, but you do not see!

To equate a river built in a lab with a land-race variety of river built in Nature over ions of time and weather is ridiculous. Somethings are best left to Nature.

I studied what I think was called "calculus of least variations", which in part meant nature tries to do things like reduce change in potential energy, "mgh", as much as possible. That is why many rivers have, roughly speaking, a sinusoidal shape. That shape dissipates potential energy most slowly, which is what nature "wants". If so, a waterfall does the opposite, and would be caused by topological restrictions, not nature's choice.

This article reminds me of readings that show that galaxies were formed in the early universe from tiny quantum fluctuations. The simulated river seized upon slight imperfections/weaknesses in the rock and soil. Over time these minute erosions became small waterfalls. After much more time they became large waterfalls.

I have made models of rivers in sandboxes with fifth graders. We first remove sand then put down a layer of plastic bags or a tarp to simulate bedrock. We then create a landscape with hills and valleys and use gardening watering cans to make it rain. We generally make a drop off at the edge that we imagine was caused by sea erosion. The waterfall happens here which is not as dramatic as the experiment in the article. It’s fascinating to watch rivers form in the same way that is described here. And it’s amazing when the sand is waterlogged enough that the river flows with no rain. I write about this in my teaching memoir, A Gift of Wonder.

Scheingross’ result is reminiscent of the Grand Canyon rapids, ‘waterfalls’ at intervals between sections of placid river.

I don't remember ever being taught that waterfalls were generally of tectonic or glacial origin. Like many fluvial geomorphic features they are geologically short-lived and result from various types of interaction between a stream and the material over which it flows. That falls or rapids could develop along a stream reach of relatively uniform gradient and substrate does not seem at all surprising.

If normal erosion can change the course of rivers over time, why can't that erosion happen near a cliff and then the water spills over? Is there some magic about cliff rocks? Of course not. I guess I'm surprised people thought normal erosion was not a common source of waterfalls. I must be missing something.

Seems that we are dealing with waterfalls of a certain smaller scale here - not the superfalls of Yosemite. An interesting study, but without knowing the literature on waterfalls, it’s hard to know just what specific puzzle/problem it is addressing! Still, this is how scientists work, and that’s fun to see. Personally, the sight of moving water never fails to captivate me.🤓🤗

For those who doubt the validity of this study, I suggest a hike along the dirt trails of the Palos Verde peninsula along the Pacific coast of Southern California. At the beginning of the winter rains the trails were smooth, hard packed dry dirt. Now, months after multiple rain storms most trails with slopes have stream beds of varied depths and widths eroded into them much like those seen in the videos of the laboratory experiment. The deeper ones are up to 12" wide and deep at least. Just look at nature if you want to see how valid the study is.

The idea of self-forming waterfalls caused by reinforcing action is intriguing. It sounds similar to the way potholes can form in roads - a small imperfection causes car tires to hit that part of the road harder, increasing the imperfection, inviting yet harder hits from tires, thus closing the feedback loop. And there will always be a small imperfection somewhere. On roads, it’s often at a joint in the surface. Yes, the model shown in the article is not a replica of a natural watercourse. Nor was it intended to be. It was a “proof of concept” demonstration that a new avenue of thought may prove valuable. Criticism of its realism is a good example of the axiom that the best is the enemy of the good.

We are part of something larger and more intricate than we can understand. Why is it so beautiful? Scientific study is a wonderful tool, and made more wonderful when accompanied by awe, gratitude, and the tingling pleasure of mist on your face.

I don't understand what "self-forming" even means. Water isn't floating in the air by itself; there is always interaction with a surface of some kind. It does seem an odd experiment to use a chute rather than an open surface. A chute can show erosion in an already established channel, but not how the channel gets started. It also seems that the kinds and shapes of the pebbles in the load should be taken into account. Once a slightly larger, heavier pebble with sharp angles punctures the surface, for example, there is the potential beginning of eroding the channel further in a particular direction.

Flawed is an understatement. The course of the "river" is a narrow straight line falling at a specific gradient, something that never happens in nature. For water, the shortest distance between two points is never a straight line, for flowing water always meanders. What we see in this experiment is a vertical rather than a horizontal meander. These forces are in play in nature too, but are conventionally expressed in side to side movement of the channel. Resonance factors come into play too. In nature almost all waterfalls are the result of changes in the durability of the substrate. Travertine falls are an exception to this rule.

Looks like the experiment is flawed. By using foam rocks they made a fundamental mistake, they didn't take the relative density of the materials involved into account. If you wanted the test to be valid you would need a material of the same density and hardness of rock to reach a valid conclusion given that the waters density is a given. If they didn't, time to try again!