Why Mount Everest Is the World’s Tallest Mountain

How ‘River Piracy’ Helped Give Mount Everest a Progress Spurt

By Michael Marshall & Nature journal

How did Mount Everest come to be the world’s tallest mountain, towering greater than 200 metres above the subsequent two highest peaks? Geologists counsel the mountain owes a part of its additional top to 2 historic rivers that flowed via the Himalayas and merged about 89,000 years in the past. The ensuing erosion eliminated a lot rock and soil that Everest has rebounded upwards by as a lot as 50 metres, they are saying.

The outer crust of Earth responds to the removing of mass by slowly rising, says co-author Matt Fox, a geologist at College Faculty London. “This has increased the elevation of Everest.”

Everest, also referred to as Chomolungma and Sagarmāthā, stands 8,849 metres above sea degree, within the Himalayan mountain chain, which additionally comprises the world’s third-highest peak, Kanchenjunga (8,586 metres) and isn’t removed from the second-highest, K2 (8,611 metres). The Himalayas have been pushed up by the ongoing collision of India with the remainder of Asia.

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Fox and his colleagues argue, in a research printed in Nature Geoscience as we speak, that a part of the reason for Everest’s excessive top lies within the close by Arun River.

Historical stream

The Arun rises north of the Himalayas however its course shortly turns south, reducing a gorge via the mountains earlier than becoming a member of the large Kosi River. “For 100 years, people have wondered why this river cuts through the tallest mountain ranges,” says Fox.

One chance is that the Arun was like that earlier than the Himalayas fashioned. Nevertheless, many geologists suspect the Himalayas have been there first. They suppose that the Arun as soon as had a special course, and that it eroded its manner via the mountains till it merged with a northerly river. This sort of occasion is named river seize or river piracy, says Fox.

“It could have been quite a dramatic event,” says Fox. “It might have happened during a time of flooding.”

Fox, working with colleagues together with Jin-Gen Dai, a geologist on the China College of Geosciences in Beijing, discovered that the Arun is a dramatic gorge with near-vertical sides in comparison with neighbouring rivers, suggesting it’s comparatively younger. They used fashions to simulate the doable seize occasion, and located that it could have elevated erosion alongside the river’s path, explaining the bizarre channel.

The arguments for seize are fairly robust, says geologist Peter van der Beek on the College of Potsdam in Germany. “They clearly show it’s different from the other rivers,” he says, “and you wouldn’t see that if it was a pre-existing river.” Earlier research have pointed to cases of river piracy elsewhere within the Himalayas, and to erosion alongside the Arun affecting close by mountains.

The group’s best-fit mannequin means that the Arun seize occasion occurred 89,000 years in the past. Since then, the Arun has quickly eroded its channel, carrying away huge quantities of sediment. Launched from this mass, the crust might bob slowly upwards. The group estimates that this ‘isostatic rebound’ has added between 15 and 50 metres to Everest’s elevation. Comparable mechanisms have been described earlier than, together with within the Himalayas.

Too simplistic?

Van der Beek is much less satisfied by these arguments. He says the timing of the river seize is unsure, as a result of the group used a easy mannequin of river behaviour.

And the estimates of the mountain rising by 15–50 metres rely upon the long-term charges of tectonic uplift and erosion, which aren’t effectively understood, he provides. That’s partly as a result of measurements of those charges return for only some a long time: not lengthy sufficient to incorporate dramatic seismic occasions. Van der Beek factors out that in 2015, a magnitude-7.8 earthquake in Nepal brought about many Himalayan mountains to subside by round 1 metre. Over lengthy timescales, a number of massive quakes can considerably have an effect on mountain top.

This text is reproduced with permission and was first printed on October 1, 2024.