Mount Everest is the tallest mountain in the world – and it could be getting that much taller thanks to a Himalayan river.
According to a new study, because the Arun river is eroding rock and soil at its base, Mount Everest is being pushed upwards.
University College London researchers found that loss of landmass in the Arun river basin 75 kilometres away from the mountain is causing Everest's peak to rise by 2mm a year.
That's made it 15-50m taller today than it would otherwise be, the study said.
“It’s a bit like throwing a load of cargo off a ship,” study co-author Adam Smith told the BBC.
“The ship becomes lighter and so floats a little higher. Similarly, when the crust becomes lighter… it can float a little higher.”
Smith said the pressure from the collision of the Indian and Eurasian plates around 40-50 million years ago – which formed the Himalayas and the plate tectonics – remains the major reason for their continued rise.
The research found that as the river flows through the Himalayas it’s been carving away material from the Earth’s crust. The next layer under the crust, the mantle, is reduced and causes the now thinned crust to flex and float upward.
This causes an upward pushing force which means Everest and its neighbouring summits, Lhotse and Makalu, also move upward, the study said.
“Mount Everest and its neighbouring peaks are growing because the isostatic rebound is raising them up faster than erosion is wearing them down,” fellow co-author of the study Matthew Fox told the BBC.
“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.”
Some geologists not involved in the study told the BBC the theory was plausible but there was much in the research that was still uncertain.
Professor Hugh Sinclair with the School of Geosciences at University of Edinburgh told the BBC the underlying process identified by the UCL team was perfectly reasonable.
But, he added, the exact amounts and timescales of river incision and the consequent surface uplift of surrounding peaks had large uncertainties.
“Firstly, predicting river incision of such large catchments in response to drainage capture (one river capturing another river or lake) is challenging,” he said.
Secondly, said Sinclair, the distance over which mountains uplift from a point of intensive localised erosion is extremely hard to predict.
“However, even accounting for these reservations, the possibility that some of Everest’s exceptional elevation is linked to the river, represents an exciting insight.”
The research has been published in Nature Geoscience.
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