Will Mount Everest always be the world's tallest mountain?

Mount Everest is the world's tallest mountain as measured from sea level. But will it hold that title forever?

To answer this question, first we must understand how mountains form and how Mount Everest and the rest of the Himalayas got so tall. One way tall mountains form is when two tectonic plates collide. As one begins to subduct — or move under — the other, crust gets mushed around, upheaved, and turned into mountains.

According to Rob Butler, a geologist at the University of Aberdeen in Scotland, the heights of the mountains that form during these collisions depend on many factors. These characteristics include the thickness of the crust, which is determined by the intensity and length of the tectonic collision, and the crust's temperature, which is determined by its age.

"Think of the crust not as a solid, but as a viscous liquid, like maple syrup," Butler told Live Science. Like cold maple syrup, cold crust is more viscous and, therefore, firmer. So thicker, colder crust can form taller mountains than thinner, warmer crust can.

Other than the thickness and temperature of the crust, the most important factor in determining the height and growth of mountains is erosion.

Related: What's the oldest mountain range in the world? (How about the youngest?)

"It's because erosion is so effective that [the Himalayas] are one of the fastest rising systems of rocks on the planet," Butler said. This is because of a principle called isostasy. Much like a container ship floating in the ocean, the less material that's stacked on Earth's crust, the higher it floats above the mantle, the planet's middle layer.

So the more material that is transported away from a mountain — whether via a river, a glacier or heavy rains and landslides — the more the mountains around it can rise. In fact, a 2024 study found that the rapid erosion of a river network more than 45 miles (72 kilometers) from Mount Everest helped the peak grow between 49 and 164 feet (15 and 50 meters) in the past 89,000 years.

Although erosion is one factor in mountains' growth, it is also part of what causes them to shrink, explained Matthew Fox, co-author of the study and a geologist at University College London. "[Whether mountains grow or shrink] depends on this balance between the rates of erosion and the rates of uplift," Fox told Live Science. If the rate of uplift is higher, the mountain will grow. If the rate of erosion is higher, the mountain will shrink.

Some scientists have suggested that Nanga Parbat, one of Everest's Himalayan neighbors and the ninth-tallest mountain on Earth, is growing fast enough to one day overtake Everest in height. However, Butler and Fox doubt this will happen. Although Nanga Parbat is growing faster than Everest due to rapid erosion, it is also eroding faster due to the intensity of monsoons in that area. In contrast, Everest is growing and eroding more slowly, leaving it at a fairly constant 2,000 feet (610 m) taller than Nanga Parbat.

However, Butler doesn't discount the possibility that another Himalayan mountain may take the throne someday. Weather factors could change over time, he said, causing shifts in the peaks' growth rates. "[Tectonic collision in the Himalayas] is going to continue for another 10 million years," Butler said. "There's plenty of time to juggle these variables around a bit."

Nonetheless, Butler thinks it's unlikely there will ever be a peak significantly taller than Everest. The Himalayas sit in the sweet spot; they formed due to a very intense and long collision event with cold crust and high erosion rates due to monsoons. They were also penned in by surrounding mountain ranges, leaving little room for the crust to escape during the collision.

"If you squash things, they've got to go up or sideways," Butler told Live Science. "And when sideways is taken, they've got nowhere to go but up."

It's very rare for all of these factors to line up, Butler said, and it might not have happened before the Himalayas. Moreover, on Earth, gravity is too powerful to allow a mountain to get much taller than Everest's current height.

"If we're talking a few meters, or even a few hundred meters, there's every possibility that another mountain could overtake Everest," Butler told Live Science. "But in terms of doing something significant, like peaks that are 10 kilometers [6 miles] high, I would think probably not."