The event made Mount Everest unusually high

With an altitude of 8,848.86 m above sea level, Mount Everest is the highest point on land. However, this mountain peak is higher than it should be, according to Adam Smith, a researcher at the Department of Earth Sciences at University College London. In the Himalayas, the elevation difference between most peaks is about 50 – 100 m. But Everest is 250 m higher than K2, the second highest mountain. “This could suggest that something interesting is going on,” Smith said.

GPS data shows that Everest is growing at a rate of about 2 mm per year, greater than the expected rate of increase for the Himalayas. To find the root cause, scientists, including Smith, studied whether strange rivers in the Himalayas caused the mountain to rise. New research published in the journal Nature Geoscience on September 30.

“The Arun River is strange because it flows in an L shape. Most rivers look like trees with a relatively straight trunk and branches (tributaries) flowing into the trunk. However, the Arun flows east-west in the upper reaches, then turns 90 degrees and flows south through the Himalayas. This suggests that the river may have recently changed shape and been captured by another river,” Smith explained.

In the new study, the team of experts used numerical modeling to simulate how the Kosi River network – which flows through China, Nepal, and India – evolved over time. They then compared the model with existing terrain to determine which simulation was the best match.

As a result, the Arun River (now a major tributary of the Kosi River), about 75 km from Everest, was “captured” by the Kosi about 89,000 years ago. This diversion of the river led to increased river erosion, creating the massive Arun Gorge. The formation of the canyon and river erosion removed large volumes of soil, making the surrounding area lighter and allowing Mount Everest to rise. According to models, the mountain has grown 15 – 50 m since the arrest event.

The research team is unclear what led to this arrest. Maybe this river eroded into the other river. Another possibility is that a glacial lake overflowed, causing a catastrophic flood that washed away the natural barrier between the Kosi and Arun rivers.

Everest is expected to continue growing until the river network has fully responded to the changes, Smith said. The next step in the research may be to take a closer look at the gorge and other places through which the Arun River flows. This will help the research team more accurately determine when the capture event occurred.