River capture lifted Everest 15-50 metres, study finds

August 28, 2026 at 01:05 PM2 min

This digest was compiled by AI from multiple sources — links to the originals are below.

A river capture event around 89,000 years ago stripped rock from the Arun-Kosi gorge, triggering isostatic rebound that lifted Mount Everest 15 to 50 metres higher than plate tectonics alone can explain. The uplift accounts for the anomalous height of Everest, Lhotse and Makalu above the collision of the Indian and Eurasian plates. The finding resolves a long-standing puzzle in Himalayan geology.

Key Facts

The Arun River captured a large stretch of Tibetan Plateau headwaters, more than tripling its drainage area and feeding the Kosi system.
The best-fitting model dates the capture event to around 89,000 years ago, within a broader window of 50,000 to 100,000 years.
Isostatic rebound from the removal of eroded rock lifted Everest, Lhotse and Makalu by 15 to 50 metres.
The study was published in Nature Geoscience in 2024 by Xu Han of China University of Geosciences and co-authors Adam G. G. Smith and Matthew Fox of University College London.

River Piracy Mechanism

River piracy, or stream capture, occurs when one river erodes backward and diverts the headwaters of a neighbouring river into its own channel. The Kosi River's channel cut backward through the mountains and annexed the upper reaches of the Arun River, gaining a large new catchment. The capture more than tripled the Arun's drainage area and dramatically increased water volume flowing through the Kosi gorge. Modelling indicates the Kosi then eroded downward far faster, stripping away a huge mass of rock and sediment over tens of thousands of years.

Isostatic Rebound Uplift

Isostatic rebound works like a ship rising when cargo is unloaded: removing rock load lets the crust float higher on the mantle. The erosion in the Arun-Kosi gorge reduced the load on the crust beneath Everest, causing it to rise over a wide area. The uplift of 15 to 50 metres explains the anomalous height of Everest, Lhotse and Makalu above the level expected from plate collision alone. The study, titled 'Recent uplift of Chomolungma enhanced by river drainage piracy', was published in Nature Geoscience in 2024.