Mount Everest, the tallest mountain on Earth at 5.5 miles (8.85 km) above sea level, is still rising. The Himalayas, including Everest, are undergoing a continuous uplift that began approximately 50 million years ago due to the collision of the Indian subcontinent with Eurasia. However, recent findings suggest that Everest’s growth exceeds expectations based solely on this tectonic activity, a phenomenon linked to the significant merging of adjacent river systems.
Research indicates that Everest’s height has increased by about 49-164 feet (15-50 meters) from changes in the regional river dynamics, particularly following the merger of the Kosi and Arun rivers around 89,000 years ago. This corresponds to an uplift rate of approximately 0.01-0.02 inches (0.2-0.5 millimeters) annually.
The scientific concept at play is known as isostatic rebound, wherein land masses rise on Earth’s crust when surface weight is reduced. The Earth’s outer layer floats over a mantle of hot, semi-liquid rock. In this instance, the Kosi river has overtaken the Arun, leading to significant erosion that has diminished the weight in the Everest region.
“Isostatic rebound is similar to how a floating object shifts its position as weight is removed,” explained geoscientist Jin-Gen Dai from China University of Geosciences in Beijing, a study co-author. “As heavy loads like ice or eroded material are taken away, the Earth’s crust gradually rises, comparable to a boat lifting in water when cargo is offloaded.”
The primary gorge of the merged river system is located around 28 miles (45 km) east of Everest. Researchers modeled the river system’s evolution and found that isostatic rebound contributes roughly 10% to the mountain’s annual uplift.
This geological process is also observable in other regions. “A classic example is Scandinavia, where the land continues to rise in response to the melting of the thick ice sheets from the last Ice Age,” Dai noted, highlighting how this phenomenon affects coastlines and landscapes long after the ice has vanished.
According to Adam Smith, a University College London Earth sciences doctoral student and co-author of the study, GPS data confirm the ongoing elevation of Everest and the Himalayas. The rate of uplift surpasses the erosion caused by elements like wind, rain, and rivers, and may even increase as erosion continues, Smith indicated.
Nearby peaks, such as Lhotse, the fourth highest, and Makalu, the fifth, are also experiencing uplift due to the same processes. Lhotse’s uplift rate is akin to that of Everest, while Makalu, closer to the Arun, has a slightly higher rate.
“This research highlights the Earth’s dynamic nature. Even a seemingly permanent feature like Mount Everest is influenced by ongoing geological processes, illustrating that our planet is in constant flux, often in ways we do not notice in our daily lives,” Dai stated. The Earth’s solid outer layer consists of large plates that shift gradually over time due to plate tectonics, explaining the Himalayas’ rise from the collision of these plates.
