Mount Everest is nearly 1,000 feet (304 meters) taller than its surrounding Himalayan peaks, causing scientists to wonder exactly why the giant mountain stretched its neck out so much more than its neighbors. Now, a team thinks they have an answer: The mountain isn’t piling on more stones; rather, the land around it is eroding, pushing the mountain upwards.
As a result, Mount Everest—also known as Chomolungma or Sagarmāthā—is growing by up to .08 inches (2mm) per year, according to a study published earlier this week in Nature Geoscience. Furthermore, over the past 89,000 years the 29,032-foot (8,849m) peak sprouted between 50 feet (15m) and 164 feet (50m).
The three tallest peaks besides Everest—K2, Kangchenjunga, and Lhotse—are all around the same height, about 1,000 feet (305m) shorter than the world’s tallest mountain.
“Mount Everest is a remarkable mountain of myth and legend and it’s still growing,” said Adam Smith, a researcher at University College London and co-author of the study, in a university release. “Our research shows that as the nearby river system cuts deeper, the loss of material is causing the mountain to spring further upwards.”
How does this happen? Well, to the east of the mountain is the Arun River, which downstream merges with the Kosi River system. Over tens of thousands of years, the Arun River has eroded its banks, washing sediment downriver.
“The upstream Arun river flows east at high altitude with a flat valley. It then abruptly turns south as the Kosi River, dropping in elevation and becoming steeper,” said study co-author Jin-Gen Dai, an earth scientist at the China University of Geosciences, in the same release. “This unique topography, indicative of an unsteady state, likely relates to Everest’s extreme height.”
GPS measurements suggested that the mountain has undergone a higher rate of uplift in recent years than the long-term trend of the mountain’s growth. The team developed a numerical model to track the mountain’s growth and concluded that around 89,000 years ago—ancient history to us, but extremely recent in Earth’s evolution—the Arun River merged with the Kosi River network. When that happened, the latter network took on more water, increasing the amount of erosion that occurred on the riverbanks and accelerating the mountains’ uplift.
“Mount Everest and its neighboring peaks are growing because the isostatic rebound is raising them up faster than erosion is wearing them down,” said Matthew Fox, an earth scientist at UCL and co-author of the paper, in the same release. “We can see them growing by about two millimetres a year using GPS instruments and now we have a better understanding of what’s driving it.”
But the pattern isn’t limited to Everest. According to the researchers, the uplift is also occurring in Lhoste and Makalu, the fourth and fifth-highest peaks in the world. While the uplift rates in the three peaks are similar, Malaku’s is likely slightly higher because it is closest to the Arun River.
The research is a reminder of how interconnected the planet’s surface is—even the flow of water through Earth’s rivers can change the shapes of its most familiar mountaintops.
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