Mount Everest, the world's most iconic and tallest peak, may be even higher than previously believed. A new study by researchers from University College London (UCL) has found that the mountain is 15 to 50 meters taller than it otherwise would be, thanks to the influence of a nearby eroding river. And the most fascinating part? Everest is still growing!
How a River is Pushing Everest Higher
The study, published in Nature Geoscience, reveals that a river system about 75 kilometers away from Mount Everest is carving out a deep gorge, removing massive amounts of rock and soil. This erosion is causing a process known as isostatic rebound, where the Earth's crust “springs” upward due to the loss of weight on its surface. As a result, Mount Everest is rising at a rate of around 2 millimeters per year. Over the past 89,000 years, this steady upward push has added between 15 and 50 meters to the mountain's height.
Currently standing at 8,849 meters (29,032 feet), Mount Everest—known as Chomolungma in Tibetan and Sagarmāthā in Nepali—is not only the tallest mountain on Earth but also towers over other Himalayan peaks by about 250 meters. This elevation difference makes Everest an anomaly compared to neighboring giants like K2, Kangchenjunga, and Lhotse, which have height differences of only around 120 meters between them.
The Science Behind Everest’s Growth
Everest’s extra height can be explained by the process of isostatic rebound. When erosion strips away landmass, the reduced weight on the Earth's crust allows it to rise. This happens because the pressure from the liquid mantle below is greater than the force of gravity pressing down on the crust. While this process typically occurs at just a few millimeters per year, over long periods, it can have a significant impact on a region's topography.
According to researchers, this uplift began about 89,000 years ago when the Arun River joined the nearby Kosi River system. As these rivers merged and intensified their erosion, large amounts of rock and soil were swept away, reducing the weight on the Earth's crust and allowing Mount Everest and surrounding peaks to rise higher.
The Role of the Arun and Kosi Rivers
Today, the Arun River runs east of Mount Everest and eventually merges with the Kosi River downstream. Over millennia, the Arun has carved a deep gorge, removing billions of tons of sediment. This ongoing erosion contributes directly to the upward push beneath Mount Everest, keeping the mountain growing taller.
Dr. Jin-Gen Dai from the China University of Geosciences, a co-author of the study, explained that the river system in this region is quite unique. The Arun River initially flows eastward at high altitudes along a relatively flat valley before making a sharp turn southward, where it becomes part of the Kosi River and plunges in elevation. This dramatic shift in topography helps explain why Mount Everest’s height is so extreme compared to other peaks in the Himalayas.
Neighboring Peaks Are Growing Too
The uplift isn’t exclusive to Mount Everest—it also affects nearby peaks like Lhotse and Makalu, the fourth and fifth tallest mountains in the world, respectively. These peaks are experiencing similar growth due to the same isostatic rebound effect. Makalu, being the closest to the Arun River, is seeing an even higher rate of elevation increase than Everest.
According to Dr. Matthew Fox from UCL’s Earth Sciences department, “Mount Everest and its neighboring peaks are growing because the isostatic rebound is lifting them faster than erosion can wear them down. Using GPS instruments, we can track this growth at a rate of about 2 millimeters per year, and now we have a clearer understanding of the forces driving it.”
Drainage Piracy: The Key to Everest’s Growth
The study also sheds light on a process called drainage piracy, which occurred about 89,000 years ago when the Arun River merged with the Kosi River network. This increased the volume of water flowing through the Kosi system, boosting its erosive power and removing more sediment from the landscape. As more land was stripped away, the isostatic uplift accelerated, pushing the peaks higher.
Lead author Dr. Xu Han from the China University of Geosciences, who conducted this research during a visit to UCL, emphasized the dynamic nature of the Earth's surface: “The changing height of Mount Everest highlights the continuous interaction between erosion and the upward pressure of the Earth’s mantle. It’s this interaction that has given Everest its extra boost, pushing it to heights it otherwise wouldn’t have reached.”
Everest’s Rise Continues
This groundbreaking study offers new insights into the forces that are continuously reshaping Mount Everest and its surrounding peaks. As erosion from nearby rivers continues and the isostatic rebound effect persists, Everest may keep growing taller for millennia to come. As our understanding of these geological processes deepens, we can expect to learn even more about how Earth's most famous mountain continues to defy the limits of height.