October 3, 2024
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How ‘river piracy’ contributed to Everest’s growth
Massive uplift caused by a phenomenon called ‘river piracy’ suggests a model that partially explains Everest’s staggering height
Everest is unusually high compared to other mountains in the Himalayas.
Daniel Prudek/Alamy Stock Photo
How did Mount Everest become the world’s tallest mountain, towering more than 200 meters above the next two highest peaks? Geologists suggest that part of the mountain’s extra height is due to two ancient rivers that flowed through the Himalayas and came together about 89,000 years ago. The resulting erosion removed so much rock and soil that Everest bounced upwards by up to 50 meters.
Co-author Matt Fox, a geologist at University College London, said the Earth’s outer shell slowly rises as mass is removed. “This increased the elevation of Everest.”
Everest, also known as Chomolungma and Sagarmus, is located at an altitude of 8,849 meters in the Himalayas, which also includes Kanchenjunga (8,586 meters), the third highest mountain in the world, and not far from the second highest mountain. K2 (8,611 meters). The Himalayas are being pushed up by India’s ongoing conflict with other Asian countries.
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Fox and his colleagues argued in a study published in 2006 that: natural earth science Today, part of the explanation for Everest’s extreme height lies in the nearby Arun River.
ancient stream
The Arun River rises north of the Himalayas, but its course soon turns south, carving a valley through the mountains before joining the mighty Kosi River. “For 100 years, people have wondered why this river cuts through the highest mountain ranges,” Fox said.
One possibility is that Arun was like that before the Himalayas were formed. However, many geologists doubt that the Himalayas were there first. They believe that the Arun River once had a separate channel and eroded through the mountains until it joined the river to the north. Fox said this type of event is known as river grabbing or river piracy.
“That could have been quite a dramatic event,” Fox said. “It may have happened during a flood.”
Working with colleagues including geologist Jing Geng Dai of the China University of Geosciences in Beijing, Fox found that the Arun River is a dramatic gorge with near-vertical sides compared to neighboring rivers and is relatively young. I found that this suggests that. They used a model to simulate possible trapping events and found that erosion along the river’s path increased, which could explain the unusual channel.
Peter van der Beek, a geologist at the University of Potsdam in Germany, says the arguments in favor of capture are pretty strong. “You can clearly see that it’s different from other rivers. If it was an existing river, you wouldn’t know it,” he says. Previous studies have pointed to river piracy occurring elsewhere in the Himalayas, and erosion along the Arun River affecting nearby mountains.
The team’s best model suggests that the Arun capture event occurred 89,000 years ago. Since then, the Arun River has rapidly eroded its channel, carrying away vast amounts of sediment. Once freed from this mass, the crust can slowly spring upwards. The researchers estimate that this “isostatic repulsion” increased Everest’s elevation by 15 to 50 meters. Similar mechanisms have been previously reported, including in the Himalayas.
Too simple?
Van der Beek is less convinced by these arguments. He said the timing of the river capture was uncertain because the research team used a simple model of river behavior.
And estimates that the mountain will rise 15 to 50 meters depend on the long-term rate of uplift and erosion of the Earth’s crust, which is not well understood, he added. Part of the reason is that these incidence measurements go back only a few decades, not long enough to include dramatic seismic events. Van der Beek pointed out that the magnitude 7.8 earthquake in Nepal in 2015 caused much of the Himalayas to sink by about one meter. Multiple large earthquakes over long timescales can have a large impact on mountain height.
This article is reprinted with permission. first published October 1, 2024.
