According to a new study that was published in Nature Geoscience, a network of rivers around 75 kilometers from Mount Everest is ruthlessly chiseling away at a deep valley, removing landmass at an incredible rate. As a result of this ongoing erosion, Mount Everest is rising—not by small amounts, but by up to two millimeters year. This process has pushed the mountain upward by ranging from 15 to 50 meters over 89,000 years.
However, why is Everest so noticeably taller? Under our soles, an unseen yet potent force known as isostatic rebound holds a significant piece of the story. The Earth’s crust reacts by stretching higher as erosion from neighboring rivers removes enormous volumes of rock and debris. Imagine a boat rising while the cargo is being unloaded. Here, the crust begins to “float” on the denser, molten mantle underneath after losing mass. Over eons, the uplift reshapes landscapes, despite being a slow process that only occurs a few millimeters per year.
According to the research team, Mount Everest’s height has increased by 15 to 50 meters over the past 89,000 years due to this gradual but enduring occurrence. When the Arun river, which presently flows east of Everest, joined the wider Kosi river network, this tectonic boost began. Unthinkable amounts of earth were taken away by the river as it widened its gorge, causing the famous mountain to rise vertically.
One of the study’s co-authors, Adam Smith, a PhD student at UCL Earth Sciences, said, “Mount Everest, a peak steeped in myth and folklore, is still expanding. According to our research, Everest is able to rise because the rivers’ erosion reduces the pressure on the Earth’s crust.
Currently working nonstop, the Arun river flows east of Everest before joining the Kosi river downstream. With each drop of water it carries, the river has carved out a vast chasm and washed billions of tons of silt away over innumerable millennia.
Another co-author, Dr. Jin-Gen Dai of the China University of Geosciences, said, “This area has extraordinary topography. Before plunging southward and sharply steepening as it joins the Kosi, the Arun meanders eastward across a high-altitude, level valley. The mountain’s great height, shaped by a dynamic system in flux, is hinted at by this sudden change of elevation and landscape.
It’s not just Everest, either. This increasing trend is also being experienced by nearby summits like Makalu, the fifth-highest mountain in the world, and Lhotse, the fourth-highest mountain in the world. They are all raised similarly by the isostatic rebound, although Makalu, which is next to the Arun River, is raised a little more than the others.
A co-author of the paper, Dr. Matthew Fox of UCL Earth Sciences, clarified: “A delicate balance is being created by the constant erosion combined with isostatic rebound. The growth of Everest and the surrounding summits is outpacing their ability to be worn down by erosion. We can estimate this growth—roughly two millimeters annually—by looking at GPS data, and we now have a better understanding of the underlying mechanisms driving this rise.
Investigating the complex dance between rivers and mountains, the researchers discovered that the Arun river joined the Kosi network approximately 89,000 years ago, a phenomenon known as drainage piracy. The Kosi’s capacity to remove soil was accelerated by this merging, which sent more water—and hence more erosive power—into it. The uplift increased, pushing the peaks higher and higher as the landscape was gradually devastated.
“The changing height of Mount Everest gives an important indicator of how dynamic Earth’s surface truly is,” said lead author Dr. Xu Han of the China University of Geosciences, who finished the work during a research visit to UCL. Everest is propelled considerably higher than we may anticipate by the combination of the mantle’s upward pressure and the Arun River’s unrelenting erosion.
