Mount Everest having a ‘growth spurt’ – what’s giving rise to it?

Everest is having a ‘growth spurt’ as the shifting contours of the surrounding landscape cause the world’s tallest peak to spring upwards.

Climbers queue to reach the summit of Mount Everest. Picture: @nimsdai Project Possible / AFP

Mount Everest is undergoing a “growth spurt” as the shifting contours of the surrounding landscape cause the world’s tallest peak to spring upwards, a study has suggested.

At 8849m above sea level Everest is not only the world’s highest mountain but also surprisingly tall for its mountain range, towering over the rest of the Himalayas by about 250m. A new analysis, published in the journal Nature Geoscience, suggests that its extreme elevation is explained, in part, by a watercourse that flows about 60km away.

Over tens of thousands of years the Arun River has washed away billions of tonnes of rock and sediment, creating a large gorge. The researchers propose that this has led to what is known as “isostatic rebound” – where a section of the Earth’s outer crust loses mass and is then pushed upwards, due to the enormous pressure of the liquid mantle that lies beneath it.

The researchers calculate that Everest is now gaining about 2mma year due to this rebound ­effect, having increased in height by between 15 and 50m over the past 89,000 years.

Adam Smith, a PhD student at University College London and a co-author of the study, said: “Mount Everest is a remarkable mountain of myth and legend and it’s still growing. Our research shows that as the nearby river system cuts deeper, the loss of ­material is causing the mountain to spring further upwards.” The uplift also affects neighbouring peaks including Lhotse and Makalu, the world’s fourth and fifth highest mountains. Matthew Fox of UCL, also a co-author of the study, said: “Mount Everest and its neighbouring peaks are growing because the isostatic rebound is raising them up faster than erosion is wearing them down.

“We can see them growing by about 2mm a year using GPS instruments and now we have a better understanding of what’s driving it.”

According to the researchers, Everest is considered anomalously high for the Himalayas as the next three tallest peaks – K2, Kangchenjunga and Lhotse – are all, in terms of height, within about 120m of each other. Pressure from the collision of two tectonic plates – the Indian and the Eurasian – formed the Himalayas, with this process estimated to have begun 40 million to 50 million years ago.

These tectonic forces are still causing the mountain range to rise, but the new study has suggested this movement is being augmented by isostatic rebound for Everest, which stands on the border between China and Nepal, and other nearby peaks.

The Arun flows from Tibet into Nepal before merging with two other rivers to become the Koshi, which then meets the Ganges in northern India. Mountaineers often cross parts of it on their route to Everest base camp; it has cut a narrow but deep gorge through the Himalayas, dropping 7km in elevation over a 35km stretch.

“The upstream Arun River flows east at high altitude with a flat valley,” Dr Jin-Gen Dai of UCL, another co-author, said. “It then abruptly turns south as the Koshi River, dropping in elevation and becoming steeper.”

This unusual topography has probably contributed to Everest’s extreme height, he added.

THE TIMES