Mount Everest is currently 15-50 meters taller than it would otherwise be due to the erosion of rock and soil at its base by a river, according to a new study. Researchers from University College London (UCL) found that land loss in the Arun river basin, located 75 km (47 miles) away, is causing the world’s highest peak to rise by up to 2mm annually.
Study co-author Adam Smith explained the phenomenon by comparing it to a ship losing weight: “It’s like removing cargo from a ship, causing it to float higher. Similarly, when the Earth’s crust becomes lighter, it floats higher.” While the primary reason for the Himalayas’ rise remains the collision of the Indian and Eurasian tectonic plates 40-50 million years ago, the researchers say that the Arun river network also plays a role in lifting the peaks.
As the Arun river carves through the Himalayas, it erodes material from the Earth’s crust, reducing pressure on the mantle (the layer beneath the crust) and leading the crust to flex and float upward. This process, known as isostatic rebound, is pushing Everest and nearby peaks, such as Lhotse and Makalu, to move upward, the research published in *Nature Geoscience* states.
“Mount Everest and its neighboring peaks are growing because the isostatic rebound is lifting them faster than erosion is wearing them down,” said Dr. Matthew Fox, another study co-author. “We can observe this growth at a rate of about two millimeters a year using GPS instruments, and now we have a clearer understanding of the contributing factors.”
Although the theory has been met with some skepticism by geologists not involved in the study, they acknowledge that it is plausible. Everest, which straddles the border between China and Nepal, sees the Arun river flow from Tibet into Nepal, where it merges with other rivers to become the Kosi, eventually joining the Ganges in northern India. Given the steep terrain and the river’s force, the Arun can carve through large amounts of rock and soil.
The UCL researchers believe the Arun river gained its significant erosional capacity around 89,000 years ago, when it “captured” another river or water system in Tibet—a recent event in geological timescales. Dr. Xu Han of China University of Geosciences, who led the study during a research visit to UCL, noted, “The changing height of Mount Everest highlights the dynamic nature of Earth’s surface. The interaction between Arun’s erosion and the mantle’s upward pressure gives Everest a boost, making it taller than it would otherwise be.”
Professor Hugh Sinclair from the University of Edinburgh’s School of Geosciences, who was not part of the study, said the theory was reasonable but noted large uncertainties in the predicted rates of river incision and the consequent surface uplift. He explained that predicting the impact of river erosion on such large catchments and understanding how mountain peaks far from the erosion site respond to it is complex.
Despite these uncertainties, the UCL study provides valuable insight into the factors contributing to Everest’s exceptional height, suggesting that the Arun river’s powerful erosion is partially responsible for pushing the world’s highest peak upward.
