The Everest higher than it should be: here's why

At 8,849 meters (29,032 ft) above sea level, Everest is the tallest peak in the world. However, it is higher than it should be. And that puzzles scientists.

A recent study suggests that a river "captured" another watercourse around 89,000 years ago. This event triggered massive erosion in the Himalayan region, altering the mass balances around Mount Everest.


The Arun River, located 75 km (47 miles) from Everest, played a key role in this geological transformation. By carving deep into the Earth's crust, it lightened the surrounding land, causing vertical growth.

River erosion consequently allowed Mount Everest to rise by 15 to 50 meters (49–164 feet) over the past 89,000 years. According to researchers' numerical models, this process continues at a rate of 2 mm (0.08 inches) per year.

This phenomenon doesn't affect only Everest. Neighboring mountains, like Lhotse and Makalu, are also experiencing similar growth linked to the same river network.

The capture of the Arun by the Kosi could have been triggered by erosion or by a flood linked to the rupture of a glacial lake. Researchers are not yet certain of the exact mechanism.

The next step will be to examine in more detail the gorge of the Arun River and to refine the dates of this geological event. Everest may still hold more surprises.

How can a river make Everest grow?

Mountains are not fixed. In fact, they are subject to tectonic forces and erosion, two opposing yet closely related processes. When a river like the Arun erodes the land around Everest, a phenomenon called "isostatic rebound" is triggered.

The principle is simple: imagine the Earth's crust as a boat floating on an ocean. When weight is removed, the boat rises. Similarly, if the Earth's crust loses mass due to river erosion, it becomes lighter.

This lightening allows the crust to rise under the influence of internal forces from the mantle. The more the Arun River carves out its gorge, the more it removes tons of rock and sediment. This reduced mass allows the underlying ground to "float" higher, leading to the gradual rise of the mountain.

This phenomenon may seem minimal, but over millennia, the accumulation of this isostatic push results in a measurable increase in the height of mountains like Everest, as well as its neighbors.