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Mount Everest (also known as Chomolungma or Sagarmāthā) is famously the highest mountain in the Himalayas and indeed on Earth. But why?

At 8,849 meters above sea level, Everest is around 250m taller than the other great peaks of the Himalayas. It is also growing by about 2mm each year—roughly twice as fast as it has been growing on average over the long term.

In a paper published in Nature Geoscience, a team of Chinese and English scientists say Everest's anomalous height and growth have been influenced by the Arun River, which flows through the Himalayas. They argue that the river's course changed around 90,000 years ago, eroding away rock that was weighing Everest down—and the mountain has bounced up in response, by somewhere between 15 and 50m.

The authors make a case for the river's contribution, but they acknowledge the "fundamental cause" of the peak's size is the tectonic processes that create mountains. To understand what's going on, we need to understand the forces that made the Himalayas in the first place, and the movements that let them grow so high.

The Tibetan blob

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