What Are Waterfalls, Anyway?

All your urgent waterfall questions, answered.

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In pursuit of a working definition of a waterfall

One afternoon’s walk has supplied a lot of material: I wrote about the mind-blowing geologic history of Silver Falls State Park here, and then I wrote about its weird early twentieth-century history next. Turns out there’s one more installment, and that has to do with exactly what a waterfall even is.

So we’re on this loop called the Trail of Ten Falls, and naturally that means we’re expecting to see ten waterfalls. Signage is minimal, we didn’t bring a map, and we don’t want to spend any time staring at our stupid phones on this beautiful day, so that means we have to figure this out using only our brains.

Some are obvious. You’re not going to miss a 177-foot curtain of water pounding down a rocky cliff.

Some, though, are a little shorter. They’re just sort of gurgling pleasantly over a few short plunges created by boulders or fallen logs. Are those waterfalls?

And some are so skinny, so paltry, as to seem unworthy of the name, even when they fall from a great height.

At one point, we walk under a rocky overhang and a few drops of water trickle down on my hat. “Is this one?” I ask.

So what exactly is a waterfall?

You might be surprised to learn that there isn’t any one official definition. This formula seems to be used a lot: the horizontal distance from the lip to the plunge pool can’t exceed 25 percent of the height.

I know, confusing. I had to make a diagram.

Does this clear it up?

What that means in non-math terms is that steepness matters. If it isn’t terribly steep—if it just lazily drifts down along a gentle diagonal slope—it’s not a waterfall. The water has to actually FALL.

No two waterfalls are alike, but there are ten kinds of waterfalls

Credit belongs to Shari Blaukopf, who taught me how to paint this

Or maybe not ten. Maybe twelve, or thirteen. Or perhaps some should be combined and there’s really only eight. Maybe some are actually subsets of others. We should have consensus on this, but we don’t. I have tried to make sense of it all, and here’s what I came up with:

Cataract waterfall: Five hundred years ago, a cataract meant a window, or a kind of grating over a window. You can see how we’d get from that to an impairment of the lens of the eye.

But what does that have to do with waterfalls? Ask Milton, who, in 1667, wrote, “What if all...this Firmament Of Hell should spout her Cataracts of Fire” prompting other writers around this time to describe an outpouring of something—not necessarily fire, often water—as a cataract.

So. Thanks, I suppose, to Milton, today a “cataract” is a type of waterfall that falls with powerful, even dangerous force, usually from a great height, often from a steep cliff.

A plunge waterfall makes no contact with the rocky wall behind it, and is not necessarily as forceful as a cataract waterfall. Sometimes you can walk behind a plunge waterfall, as I did a few weeks ago, and I do recommend it.

Skogafoss, a massive plunge waterfall in Iceland

A block waterfall you’ve seen before, because Niagara Falls is one. It has an exceptionally wide lip—more of a ledge, really.

Niagara Falls, the largest waterfall in the United States if you’re measuring by flow rate, or the volume of water moving over the falls per second.

A punchbowl waterfall pours into a wide and pleasing pool of the sort you’d probably like to take a swim in…which is probably okay? Waterfalls can be a little intense. It’s not a ride at Disneyland, that’s all I’m saying.

The aptly named Punch Bowl Falls, right here in Oregon

A segmented waterfall comes from a stream that splits in two as it falls, usually reuniting at the base.

Some waterfalls look exactly like their name and don’t require much explanation: a fan waterfall spreads out in a fan shape, a horsetail starts out narrow but spreads out in a loose and misty way, maintaining contact with the rock the way a horse’s tail maintains contact with its behind, a tiered or multi-step waterfall does exactly what you might think it does, and a frozen waterfall is…well, there you go.

Ban Gioc–Detian Falls, between China and Vietnam, a very fine example of a tiered waterfall

There are others, some more dubious, especially if you consider our original definition involving the height and the horizontal distance from lip to plunge pool. A slide waterfall travels along a rocky slope, but never really falls. A cascade waterfall spills over boulders like a tiered waterfall, but never forms a plunge pool. Is that a waterfall or an especially lively babbling brook?

A moulin is a hole in a glacier through with water falls, but if we get into glacier anatomy, we’ll be here all day, so I leave you with…

Undersea waterfalls: Yes! There are waterfalls under the water! How is this possible? It’s because—get ready—cold water is denser than warm water. So when the two meet, the cold water falls! The Denmark Strait Cataract, between Iceland and Greenland, is the world’s largest waterfall, with the dense, cold water plunging over an undersea ridge and falling about TWO MILES to the ocean floor. You will probably never see the Denmark Strait Cataract, but I hope you agree that it is wonderful to know about it.

I made a little cartoon for you about my life. Here I am, telling my husband about underwater waterfalls.

Scott Brown

is a rare book dealer who actually paid attention in school and knows a little bit about a lot of things. It’s kind of scary, the things he either knows or can figure out.

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The Bit at the End

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