Mount Everest has grown up to 164 ft taller because of the combined forces of erosion and upward pressure from beneath Earth’s crust, researchers have said.

Experts say a nearby river is cutting into the landscape around the mountain, eroding away a large amount of rocks and soil. This process is causes a section of Earth’s crust to float upwards because the intense pressure below is greater than the downward force of gravity.

Erosion from a river network about 46 miles from the mountain is carving away a substantial gorge, causing it to rise up by as much as two millimetres a year over the past 89,000 years.

Study co-author Adam Smith, a PhD student at UCL Earth Sciences in London, said: “Mount Everest is a remarkable mountain of myth and legend and it’s still growing.

“Our research shows that as the nearby river system cuts deeper, the loss of material is causing the mountain to spring further upwards.”

Lead author Dr Xu Han, from China University of Geosciences, said: “The changing height of Mount Everest really highlights the dynamic nature of the Earth’s surface.

“The interaction between the erosion of the Arun river and the upward pressure of the Earth’s mantle gives Mount Everest a boost, pushing it up higher than it would otherwise be.”

The tallest mountain on Earth, Mount Everest is 29,000 ft high and rises about 820 ft above the next tallest peak in the Himalayas.

However, it is considered to be an anomaly, as the next three tallest peaks – K2, Kangchenjunga and Lhotse – all differ only by about 390 ft from each other.

Today, the Arun river runs to the east of Mount Everest and merges downstream with the larger Kosi river system.

Over millennia, the Arun has carved out a substantial gorge along its banks, washing away billions of tonnes of earth and sediment.

Co-author Dr Jin-Gen Dai, of UCL Earth Sciences, said: “An interesting river system exists in the Everest region. The upstream Arun river flows east at high altitude with a flat valley.

“It then abruptly turns south as the Kosi river, dropping in elevation and becoming steeper. This unique topography, indicative of an unsteady state, likely relates to Everest’s extreme height.”

The uplift also affects neighbouring peaks including Lhotse and Makalu, the world’s fourth and fifth highest peaks respectively.

Co-author Dr Matthew Fox, of UCL Earth Sciences, said: “Mount Everest and its neighbouring peaks are growing because the isostatic rebound is raising them up faster than erosion is wearing them down.

“We can see them growing by about two millimetres a year using GPS instruments and now we have a better understanding of what’s driving it.”

The study, published in the Nature Geoscience journal, looked at the erosion rates of the Arun, the Kosi and other rivers in the region.

The researchers were able to determine that about 89,000 years ago the Arun river joined and merged with the Kosi river network, causing more water to be funnelled through the Kosi and increasing its erosive power.

With more of the land washed away it triggered an increased rate of uplift, pushing the mountains’ peaks higher.