Scientists explain Mount Everest’s anomalous growth in new study

Mount Everest is Earth’s tallest mountain, still growing due to isostatic rebound from a river system merger.

Mount Everest is the earth’s tallest mountain - towering 8.85 km above sea level - and is actually still growing.

While it and the rest of the Himalayas are continuing an inexorable uplift that dates back to their birth roughly 50 million years ago when the Indian subcontinent collided with Eurasia, Everest is growing more than expected from this alone. Scientists now think they know the reason why, and it has to do with the monumental merger of two nearby river systems.

Everest has gained roughly 15-50 m in height due to this change in the regional river system, with the Kosi river merging with the Arun river approximately 89,000 years ago, the researchers estimated. That translates to an uplift rate of roughly 0.01-0.02 inches (0.2-0.5 millimeters) per year.

The geological process at work, they said, is called isostatic rebound. It involves the rise of land masses on the earth’s crust when the weight of the surface diminishes. The crust, the earth’s outermost layer, essentially floats atop a mantle layer made of hot, semi-liquid rock.

In this case, the merger of the rivers – more like a hostile takeover, with the Kosi subjugating the Arun as the rivers changed course over time – resulted in accelerated erosion that has carried off huge amounts of rock and soil, reducing the weight of the region near Everest.

“Isostatic rebound can be likened to a floating object adjusting its position when weight is removed,” said geoscientist Jin-Gen Dai of China University of Geosciences in Beijing, one of the leaders of the study published on Monday in the journal Nature Geoscience.

“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,” Dai added.