When you win a spelling bee  or run the fastest marathon for your group, you've topped  all of the competition.

But that doesn't mean you stop there. You probably keep going and improving, trying to beat your own record.

And when it comes to the  tallest mountain in the world, Everest is doing the same. Throughout its history, it has  grown much more than its neighbors. Everest is taller than all other mountains, not just because it's in the Himalayas, but because of its own unique  and weird circumstances pushing it higher into the sky  than other Himalayan peaks.

And it's not done yet. [♪ INTRO] Tens of millions of years  ago, a tectonic plate south of Eurasia crashed into the  continent’s southern border. The land at this fault line crumpled  up like the hood of a car in a head-on crash, and rose more  than 3 kilometers into the air. Then around 50 million years  ago, it sustained another blow when the slab of land that’s now  India slammed into the same spot.

India could have acted like a giant shoe horn, sliding underneath the edge  of the Eurasian plate and shoving the land above it  even higher into the air, turning the Himalayan Mountains  into the tallest peaks in the world. But in the race to the top, one  mountain surged past the rest. One that has gained international  recognition as a giant among giants.

The tallest mountain in the world. Locals know it as Chomolungma or Sagarmatha. You might know it as Everest.

Even after Everest outgrew  its Himalayan neighbors, it never stopped rising. Today it  towers over them by about 250 meters, and it continues to grow at around  double the rate that experts expect. And we do expect Everest to be growing some, even though it might seem like there aren’t giant land masses smashing into it anymore.

Because in fact, India is still  pushing into the rest of Asia. That’s causing land to move in a bunch of complex ways along the fault line, including up. At the same time, ordinary weathering  is wearing down the Himalayas, just like it wears down all mountains.

That’s erosion at work. And even though this erosion  itself shaves mountains down, it also makes them taller! I know that sounds like the opposite  should happen.

But let me explain. The ground isn’t as sturdy  as it feels to you or me. It’s not even really staying in one place.

Earth’s crust, the part that we stand on and that Everest is made out of,  is floating on top of the mantle, a layer of rock that can flow slowly,  like a thick layer of caramel. So the crust can move! Meaning that ground level doesn’t necessarily  stay at ground level.

One of the things that move the crust along the caramel river mantle is weight. When the crust becomes heavier, it  sinks deeper down into the mantle. And when it gets lighter,  like when part of a giant mountain gets eroded away, it  lifts out of the mantle more.

It’s just like what happened in  the cinematic masterpiece, Titanic. Rose was floating on the door  slightly submerged in the water. But it was slightly submerged because Jack was holding onto the door, weighing it down.

Once Jack let go, Rose could float  higher and lived to tell the tale. The door is Mount Everest. The water is the mantle.

And Jack eroded away. Which is why it didn’t matter that there was enough room on the door for Jack. He was weighing it down and they both would be exposed to more cold water and freeze!

The point is: Everest will float higher or lower on the mantle depending how heavy it is. Exactly how much it sinks or rises depends on the specific geology of the  area, but it can be a lot! During the last Ice Age, when the  continents were covered in thick, heavy glaciers, parts of North  America sank down hundreds of meters!

In fact, Everest is still springing  back from the last ice age, which ended around 11,000 years ago. All this change takes time to unfold because the mantle is still solid rock,  so it doesn’t slosh around as easily as the water under a floating door. But little by little it  keeps pushing Everest higher.

And, okay, it’s only rising by  2 millimeters a year these days. But over the lifetime of a mountain,  even a little growth adds up! It helped make Everest the  tallest mountain in the world.

The problem is, even after you  account for the continental impacts, ice age, and erosion, all of these  effects still don’t explain why Everest is rising faster than all of the  other Himalayan mountains around it. For that, we need to go back  to Everest’s early years. But before I can tell you about that, an ad.

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Or just be sure to order the shirt  before April 18th if you want one. Soon after the peaks of the Himalayas reached the top of the world, they  became home to glaciers. And as seasons came and went,  the meltwater streaming off glaciers in the warmer months  carved channels into the rock.

And so, Everest’s rivers were born. Some rivers ran east or west.  Others meandered north or south. But by the time the earliest climbers  were making their way up Everest, they noticed that one river  wasn’t quite like the others.

The Arun River runs along  the base of Mount Everest. It starts off flowing east…  but then it abruptly cuts back and travels south before eventually  dumping into a bigger river. And rivers don’t usually form  in weird shapes like that.

Maybe the river predated  Everest, and the mountain somehow poked through the Arun River  to give it this bizarre path. But researchers think that’s far more peaceful than what actually happened. Coexistence with the river that was already there?

Not a chance. This river is more likely to be evidence of what scientists call river piracy. Like, the river itself was a  pirate …or the victim of piracy.

One river can steal another river’s water! It happens now and then when there’s a shift in the way water flows over land. Like after earthquakes or erosion.

And it can create weird paths when it combines waterways that flow in different directions. So in a 2024 study, scientists set out to confirm if something like this ever  happened to the Arun River. They used computer simulations to analyze a bunch of tributaries nearby and, sure enough, found that there was definitely  something odd about the Arun.

It didn’t just have a weird route. Its channel was steeper than other tributaries. And the river was also more powerful.

It eroded much more sediment than its neighbors. When the researchers put  all these pieces together, it started to look like the Arun River really was captured by another river  at some point in the past. Based on their models, they  estimated that this happened 89,000 years ago, merging  the flows from two rivers into one powerful river following  the bizarre path we see today.

And as all the water from those two rivers churned through a single channel, it would have deepened the gorge and carried off  a bunch of heavy sediment. Suddenly, land next to Mount Everest must have started getting lighter faster. Then, this land would have  started floating higher, like Rose on the door.

Now, a piece of land isn’t  quite like a door that can just bob up and down without  affecting the stuff around it, because one piece of land is  connected to all the land around it. So as one spot floats higher, it  tugs on the area surrounding it. In this case, the rising land around the Arun River gave Everest a pull upward.

Models suggest that the loss of so  much sediment over the last 89,000 years lightened Everest enough to  rise dozens of meters since then. But because of the way the  crust lays on top of the mantle, it wouldn’t have lifted all of the Himalayas. In this case, the crust’s flexibility is key.

Just because it’s made of rock doesn’t mean it’ll act like a granite countertop. For example, if you put a bowling ball under a slab of granite countertop, you’d create a slope that lifts all or most of the granite above where it was before. But if you put that same  bowling ball under a mattress, sure, the middle will lift up where the ball is.

But the edges of the mattress will be much closer to the ground than  in the countertop example. The Earth’s crust is flexible  enough that the rivers had more of a mattress effect  than a countertop effect, making Everest taller than its neighbors. That would make river piracy a huge  missing link in Everest’s story.

But it still doesn’t fully  explain why Everest grows so fast. So we have even more discoveries to make in the future as this mystery unfolds. It’s not a coincidence that Everest  is the tallest mountain we have.

It got its height from colliding landmasses, an ice age, pirate rivers, plain-old erosion, and maybe some other factors  that we still haven’t discovered! At the end of the day, Everest  has reached the peak of what a mountain can be on our planet.  But it’s not stopping there. So, climbers, good luck. [♪OUTRO]