Mount Everest Is Still Growing — and a Hijacked River 47 Miles Away Is Pushing It Up

Every schoolroom map calls Mount Everest 8,849 metres — full stop, fixed forever. It isn't fixed. Nepal and China's own joint survey team confirmed in 2020 that the summit sits at 8,848.86 metres, itself 86cm taller than Nepal's previous official figure, precisely because the mountain keeps moving. And in September 2024, a team from China University of Geosciences and University College London published the clearest explanation yet for why Everest, along with its neighbours Lhotse and Makalu, keeps getting taller: a river robbery that happened 89,000 years ago is still paying out today.

The river that stole a river

About 47 miles from Everest, the Kosi River network intercepted and absorbed a tributary called the Arun River — a process geologists call 'river piracy' or 'river capture'. Suddenly carrying far more water, the merged river system began cutting down through the Himalayan bedrock in the valleys below Everest far faster than before, hauling away enormous volumes of rock and sediment.

Removing that much mass from the Earth's crust has a predictable effect, and it isn't subsidence — it's the opposite. Study co-author Dr Adam Smith (UCL) compared it to a cargo ship losing its load: 'The ship becomes lighter and so floats a little higher.' As the crust beneath the eroded valleys lightened, it rebounded upward — a process called isostatic rebound — and dragged the nearby peaks up with it, the same way pressing down on one side of a foam mattress lifts the other.

How much of Everest is a river's doing

The team modelled the erosion and rebound and concluded the effect has added somewhere between 15 and 50 metres to Everest's height over the past 89,000 years, and is still adding roughly 2mm a year — on top of the uplift already caused by the Indian tectonic plate ramming into Asia, the collision that built the entire Himalayan range in the first place and continues today. In other words, Everest has at least two separate engines pushing it skyward at once: a 55-million-year-old continental collision, and a comparatively recent case of one river swallowing another.

Our guides walk trekkers into that view most weeks of the trekking season, on both the classic route and the quieter Gokyo side that trades the crowds for a wider look at Everest, Lhotse and Makalu together — the very three peaks this study is about.

Source: Smithsonian Magazine, reporting on Dai et al., Nature Geoscience (2024); height confirmed by the Kathmandu Post.

Cover photo: Shashank Brahmavar via Pexels (Pexels License).