Mount Everest’s surprising growth is linked to an ancient river merger, scientists say. Photo: Shutterstock Earth’s tallest mountain, Mount Everest, is 8.85km above sea level – and it is still growing. Mount Everest and the rest of the Himalayas have been growing taller since they first formed about 50 million years ago when the Indian subcontinent collided with Eurasia.
But Everest is growing more than expected from this alone. Scientists now think it is because of how two nearby river systems combined.
The Kosi river merged with the Arun river about 89,000 years ago. Researchers estimated that Everest has gained roughly 15 to 50 metres (40 to 164 feet) in height due to this change in the river system. That translates to an uplift rate of roughly 0.2 to 0.5mm per year.
The geological process at work, they said, is called isostatic rebound. It involves the rise of land masses on Earth’s crust when the weight of the surface diminishes (see graphic). The crust, Earth’s outermost layer, floats on the mantle layer, which is made of hot, semi-liquid rock.
In this case, the merger of the rivers caused erosion to happen more quickly. This process has carried off huge amounts of rock and soil, reducing the weight of the area near Everest.
“When a heavy load, such as ice or eroded rock, is removed from the Earth’s crust, the land beneath slowly rises in response, much like a boat rising in water when cargo is unloaded,” said geoscientist Dai Jingen of China University of Geosciences in Beijing. Dai is a leader of the study that was published last month in the journal Nature Geoscience.
Study co-author Adam Smith is a University College London doctoral student in Earth sciences. Smith said they used GPS measurements to study the rising of Everest and the rest of the Himalayas.
This uplift outpaces the continued surface erosion caused by factors such as wind, rain and river flow. As this erosion continues, Everest’s uplift rate from isostatic rebound may increase, Smith said.
“This research underscores our planet’s dynamic nature,” Dai said.
Is Everest the only mountain that is “growing”?
Other mountains near Everest are also growing because of isostatic rebound. This includes Lhotse, the world’s fourth highest mountain, and Makalu, the fifth highest. Lhotse is growing at a rate similar to Everest. Makalu, which is closer to the Arun, is growing at a faster rate.
In addition to the Himalayas, Scandinavia is another region where the land is rising. This is a response to the melting of thick ice sheets that covered the region during the last Ice Age. On average, it is increasing by 9mm every year.