National Park Scouts

Ice, Fire and the Waterfalls of Yosemite Valley

Host: Jenni · Park: Yosemite National Park · Topic: waterfalls, glaciers, Horsetail Fall

Intro

It's a February evening in Yosemite Valley, and something strange is happening. A crowd of people is lined up along the road, phones held up, every single one of them staring at the exact same spot on the tallest cliff in the whole park. Because right there, pouring down from a tall cliff, is fire. A stream of glowing orange red dripping down the rock like lava sliding off a volcano. Except, hang on. There's no volcano in Yosemite. There's no lava either. That's water.

For about 10 minutes on a handful of evenings every February, one waterfall in this park turns into fire. Today, we're finding out exactly how a waterfall pulls off a trick like that. And it's going to lead us to every waterfall in this entire valley, and the giant, slow moving ice machines that carved the whole thing out in the first place. Let's go!

Welcome to National Park Scouts, the show where curious kids discover America's wildest places. I'm Jenni. Today we are kicking off a brand new series in one of the most famous national parks on Earth: Yosemite, in California. Over the next four episodes, we're climbing its cliffs, exploring its granite domes, and meeting one of the most mysterious birds. But today we're starting with water, because Yosemite Valley packs more waterfalls into one place than almost anywhere else in North America.

So welcome to Yosemite Valley. We'll meet some famous waterfalls today, plus a waterfall that turns to fire. Let's find out how that actually works.

The mystery of firefall

Here's what's surprising. Most years when people show up hoping to see it turn to fire, nothing happens, because it turns out this might be one of the hardest tricks in the entire natural world to catch. Not because it's rare, like a shooting star; it's hard because it needs three completely different things to go right at the exact same time.

Ingredient one: there actually has to be water. Horsetail Fall only flows for a few weeks a year. The water comes from melting snow. Miss that window, and there's no waterfall there at all; nothing to light up.

Got water? Good. Now you need ingredient two: a totally clear sky right where the sun sets. One thin cloud and the whole thing just doesn't happen. No warning, no do-over. You wait a whole year for your next shot.

And even with water and a clear sky, you still need ingredient three: the sun has to sit at one exact angle in the sky. That only happens for about 10 minutes on a handful of evenings in February.

Water, clear sky, one precise angle of light, all three at the same time for 10 minutes. Scouts, that's not "sometimes it happens." That's very rare.

So here's a question for you: if this is such an incredibly hard trick to catch, how do you think anyone even figured out it was possible in the first place?

Turn back the clock to February 1973. A photographer named Galen Rowell is driving through the valley. Nothing special, just driving. When out of the corner of his eye, he sees it: that impossible orange glow pouring down the cliff. He doesn't even know what he's looking at yet. He just knows he has to get closer right now, before the light disappears. So he steps on the gas, speeding through Yosemite Valley, way over the limit.

And guess who's sitting next to him in the car? A National Park Service ranger. Speeding, with a ranger right there in the car; that's not how it usually goes. The ranger has never seen this either, so instead of writing Rowell a ticket, he watches him skid to a stop, jump a fence with his camera, and start snapping photos of the cliff.

That's it. That's the whole story of how the world found out Horsetail Fall's secret. Not an ancient legend, not something explorers wrote down a hundred years earlier. One regular evening, one guy glancing out a car window at exactly the right second.

But that leaves us with a much bigger question. Horsetail is just one little waterfall on one side of one cliff. So where do all of Yosemite's waterfalls come from? And why does this one valley have so many more of them than almost anywhere else on Earth?

How ice carved the valley

Okay, here's a question to really chew on: how do you carve out a valley that's a mile wide, with granite walls rising thousands of feet straight up on both sides? What could possibly be strong enough to do that? I'll give you a hint: it's not a river.

Rivers are amazing, but they carve narrow, V shaped canyons over millions of years. Yosemite Valley isn't shaped like a V; it's shaped like a U, wide and flat on the bottom, with walls that go straight up. And there's really only one thing on Earth powerful enough to carve a U like that: ice.

A long, long time ago, Yosemite was covered by huge, slow moving rivers of ice called glaciers. Think of a glacier like a bulldozer, except instead of pushing dirt with a metal blade, it uses its own gigantic weight to grind away solid rock, one inch at a time, over thousands of years.

And here's the key part: not every glacier was the same size. There was one giant glacier filling the main valley; massive, thick, incredibly heavy. And feeding into it from smaller side canyons were skinnier, lighter glaciers. So the big giant glacier carved out Yosemite Valley, and those lighter glaciers, they couldn't dig as deep.

Water always runs downhill. So it runs into those little valleys, and then what does it do? It gets to Yosemite Valley and falls off the edge of the cliff. Scientists call the smaller canyon a hanging valley, because it's left hanging up in the air above the main valley floor. And Yosemite Valley is surrounded by them. That's why there isn't just one waterfall here; there's practically a whole neighborhood of them.

Meet the waterfall neighborhood

So let's meet the neighbors.

First up, the tall one: Yosemite Falls. This is the tallest waterfall in all of North America. And here's how tall that really is; picture two Empire State Buildings stacked right on top of each other. Yosemite Falls is almost exactly that tall. That's like a skyscraper who really, really loves water. Let's call it the tall one.

Next, I'm calling it the dancer: Bridalveil Fall. This one is light enough that on a windy day it actually sways sideways in the air instead of falling straight down. It's like dancing instead of falling. Every other waterfall in this valley just falls straight down, like it's got somewhere to be. Not Bridalveil; Bridalveil's got moves. Let's call it the dancer.

Next, the twins: Vernal and Nevada Falls. These two aren't one big waterfall; they're a staircase, a very dramatic staircase. Two separate falls, one right after the other, on the very same river. The twins.

Last one; this waterfall has been hiding in plain sight this whole time. It should be famous. It should have its own trophy right out front on a little pedestal. It should get an award every single year. But barely anyone's ever heard of it. Maybe it's humble. Maybe it just likes its alone time. Because this waterfall has a longer single drop than any other waterfall in this entire park; longer than the tall one, longer than the twins, longer than anything. It's called Ribbon Fall. I'm calling it the quiet champion, out here breaking records and telling absolutely nobody.

Remember, we said Yosemite Valley has a whole neighborhood of these hanging valleys. Today you've met a few of the neighbors. There are plenty more neighbors to discover here on your own Scout Mission. Four completely different waterfalls, four completely different stories. And every single one of them traces back to the same exact thing: ice that melted away thousands of years ago.

Guess that park sound

Okay scouts, it's time for a brain break. Let's play Guess That Park Sound. I'll play you a sound from this park, and you get to guess what's making it. Ready?

Now listen to this one. Okay, that's a waterfall, right? Do you think it's the same waterfall, or two completely different ones? Take your best guess. We'll come back to it right after the break.

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Guess that park sound: the reveal

Okay scouts, that was the exact same waterfall, just two completely different months. That roaring freight train sound, that's Yosemite Falls in springtime, when it's absolutely packed with melting snow. And that quiet little trickle, that's the very same waterfall just a few months later in late summer.

Which brings up a pretty interesting mystery: how can the exact same waterfall be a thundering monster in May and practically silent by September? Let's go find out.

Why waterfalls change with the seasons

Some of Yosemite's waterfalls, like Yosemite Falls, are fed by a fairly small patch of bare granite mountainside. Not many trees, not much shade. When spring hits, all that snow melts fast, and for a few wild weeks, the waterfall roars. But because that patch of mountain is small, it runs out of snow fast. By the end of summer, it's a trickle, or even completely dry.

Other waterfalls, like the twins, Vernal and Nevada, are fed by a much bigger, snowier area high in the mountains. More snow spread out over a bigger area means the water lasts a lot longer into the year.

And that little fact explains Horsetail Fall too. Remember, it only gets water from melting winter snow. That's exactly why it can only turn into fire in February; there's no snow melt left by summer, which means there's no waterfall at all.

Ice oddities

Now, since we're already talking about winter in Yosemite, let me ask you a question: what's the weirdest thing you've ever seen ice or snow do? I want to tell you about a few things that happen here that sound made up, but are completely true.

On full moon nights in spring, something secret happens when the waterfalls are roaring their loudest. Silver moonlight can bend through all that mist and create a rainbow, except it's made of moonlight instead of sunlight. It's called a moonbow, and yes, it's every bit as magical as it sounds. Imagine standing in the dark, feeling the spray, and watching a secret rainbow glow in the midnight sky.

In late winter, something called frazil ice forms, where mist from the waterfall freezes in midair before it even hits the water below, and tumbles into the creek as an icy, slushy soup. Yosemite practically invented the slushy; picture the world's biggest slushy machine running all night long, and nobody's even there to drink it.

And at the bottom of Yosemite Falls, all that freezing mist can pile up into a mountain of ice over 300 feet tall, made entirely of frozen waterfall spray. That's like the world's biggest snow cone. Let's call the flavor waterfall.

All these fun things are not magic, but they're pretty close.

Wildcard: true or false

Q1: Yosemite Valley was carved out by a giant, slow moving river of water.

False. It was carved by ice, a glacier. Rivers carve narrow, V shaped canyons; Yosemite is a wide U shape, and only a giant slab of ice grinding away for thousands of years is heavy enough to do that.

Q2: Horsetail Fall, the firefall, glows every single evening in February.

False. It needs three things to line up at once: water, a totally clear sky, and one exact angle of sunlight. Most February evenings, at least one of those is missing, and nothing happens at all.

Q3: In a very strong wind, a waterfall's water can actually blow upward instead of falling down.

True. When the wind is strong enough blowing straight up a cliff, it can catch a thin waterfall spray and push it back up into the air. So instead of falling, the water looks like it's floating or even flowing backward.

Scout Question

Yosemite Falls is a roaring monster in May, but practically vanishes into a quiet trickle by September. If you were planning a trip, would you rather see the park when the water is loud and roaring, or when it's low enough to explore the creek beds? Let's hear what some of you had to say.

Brindley, age 12

I'd rather plan a trip in September. I'd like to explore while hearing the quiet trickle of water. It makes me peaceful.

Kinsley, age 9

If I would plan a trip, it would be full May, because I like the waterfalls, the mist coming on me, and I like the whooshing sound of it.

Behind the mic

Scouts, I love hearing from you. Do you want to be on our podcast? Head to nationalparkscouts.com/contact and tell me. While you're there, check out our coloring pages, word searches, and bingo cards you can use on your park visit, and sign up for emails to find out which park we're visiting next.

What did you learn today that most adults don't know? I learned that every single waterfall in Yosemite Valley, even the one that turns to fire, all trace back to the exact same thing: ice from thousands of years ago that melted away and left some canyons hanging high above the valley floor.

Scout mission

Your mission

Every scout needs a mission. Here's yours.

If you're at home, look up a photo of Yosemite Falls in May and another photo of it in September. What's different? See if you can find a waterfall or stream near you that changes a lot between seasons too.

If you are visiting Yosemite, from Cook's Meadow or the bridge near Lower Yosemite Fall, find a spot where you can see the whole waterfall at once, top to bottom. Then walk closer toward the base. Notice how different it feels up close compared to far away, and see if you can spot the hanging valley it pours out of, way up at the very top.

Outro

You've officially met the whole waterfall neighborhood of Yosemite Valley. Some roaring, some small, and one that only shows off for 10 minutes a year. But we've barely scratched the surface of what this valley is hiding.

Next time, we're climbing the very cliff Horsetail Fall pours off of, solid granite, smooth enough for some of the best rock climbers on Earth to climb straight up. Scouts, your next adventure is waiting!