Geologists Reveal a Surprising Reason Why Mount Everest Grows Taller Each Year

Mount Everest, the tallest mountain in the world, has been growing ever higher for roughly 50 million years. The peak, also called Chomolungma in Tibetan or Sagarmatha in Nepali, is part of the Himalayan range that has been uplifting as the tectonic plate under the Indian subcontinent collides with the rest of Asia.

“Although mountains may appear to stand still from the perspective of a human lifetime, they are in fact constantly in motion,” Jin-Gen Dai, a geoscientist at the China University of Geosciences in Beijing, tells the New York Times’ Robin George Andrews. And some of that constant motion is surprising to scientists.

It turns out, Everest is getting taller faster than expected—faster even than many of its Himalayan peers. Now, in a new study published Monday in the journal Nature Geoscience, Dai and other researchers suggest they have figured out why.

The counterintuitive cause appears to be erosion due to a merger of rivers located about 47 miles away from Everest. Rivers in steep mountains like the Himalayas remove vast amounts of rock from the range. While it might seem that this process would work against the mountain’s height, it actually has the opposite effect on the Earth’s crust.

“It’s a bit like throwing a load of cargo off a ship,” study co-author Adam Smith, a geoscientist at University College London, tells the BBC News’ Navin Singh Khadka. “The ship becomes lighter and so floats a little higher. Similarly, when the crust becomes lighter… it can float a little higher,” on top of the planet’s mantle.

The effect, which scientists call isostatic rebound, appears to be so great for Mount Everest because of an ancient case of fluvial “theft.” Using computer models, the researchers found that the nearby Arun River was captured by the flow of another river network, the Kosi, about 89,000 years ago. The high erosion of the combined rivers supercharged Everest’s growth, adding around two millimeters of additional height each year, for a cumulative total of 50 to 165 extra feet.

The Himalayas aren’t the only place on Earth where this adjustment of the crust is radically reshaping the land surface. When continental ice sheets melt at the end of ice ages, the Earth’s crust has to compensate for the loss of mass in a process similar to what’s happening at Mount Everest. Imagine sitting on a large couch cushion—in this analogy, your weight is like the ice sheet, and the cushion is the Earth’s crust. As you sit, the cushion sinks underneath you while rising on either side. When you stand up, or when the ice melts, the cushion rebounds where you were sitting but falls in the surrounding areas.

This means that global sea level doesn’t rise evenly on coastlines all around the world, like water filling a bathtub. Instead, sea-level rise at any given location depends in part on where glacial ice has melted. For example, New York City faces higher rates of sea-level rise than many other coastal locales because it’s still sinking as the Earth’s crust adjusts to the melting of a vast ice sheet that covered parts of North America about 24,000 years ago, according to NASA.

Sea level rise is so much more than melting ice

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Back in the Himalayas, the new study is just the start to understanding how the solid earth in the region is responding to ongoing changes like erosion.

“There are other river captures known to have occurred in the Himalaya,” says Elizabeth Dingle, a geomorphologist at Durham University in England who was not involved in the research, to the Guardian’s Nicola Davis. “It would be interesting to know whether similar effects are preserved elsewhere, or in other tectonically active mountain ranges more broadly.” The team also found that other peaks near Everest—including Lhotse and Makalu, the fourth and fifth tallest peaks on Earth, respectively—are also rising due to the same process.

But Everest’s height gives it a unique place in people’s minds all around the world, Dai says to Reuters’ Will Dunham.

“Physically, it represents Earth’s highest point, giving it immense significance simply by virtue of its stature,” he tells the publication. “Culturally, Everest is sacred to local Sherpa and Tibetan communities. Globally, it symbolizes the ultimate challenge, embodying human endurance and our drive to surpass perceived limits.”

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Rudy Molinek is Smithsonian magazine's 2024 AAAS Mass Media Fellow.