From the top: measuring Everest

  • Written by  Geographical
  • Published in Mountains
Has the devastating 2015 Nepal earthquake altered the height of the world’s most famous mountain? Has the devastating 2015 Nepal earthquake altered the height of the world’s most famous mountain? Daniel Prudek
01 Jul
Is the official height of Mount Everest accurate?

The famous Hillary Step, at the top of Mount Everest, is gone. Or it isn’t. Mixed reports from mountaineers who returned to the summit this year have painted a confusing picture as to whether the iconic rock named after Sir Edmund Hillary still exists.

Regardless, one aspect of the mountain which has almost definitely changed since Hillary and Norgay first reached the top is its height; thanks to India’s ongoing tectonic collision with the rest of Asia, the peak rises by around three to five millimetres every year. Therefore, the Survey of India, the country’s central engineering agency in charge of mapping and surveying, is celebrating its 250th anniversary this year by re-measuring the mountain. It’s the latest such attempt to determine the accuracy of the generally accepted height of 8,848m (29,029ft) and is especially significant given the shaking the entire Himalayas were given by the devastating 2015 Nepal earthquake, believed to have caused the range to drop.

However, even with the most modern GPS technology, getting an exact measurement can be immensely complicated, involving the subtraction of snow thickness and average sea level from the entire distance between the summit and the centre of the Earth. ‘Ideally, one would drive a tunnelling machine from Kolkata to the Nepal-China border, and allow it to flood with sea water exactly half way, to make an underground canal from the Indian Ocean to beneath Mount Everest,’ describes Roger Bilham, Professor Emeritus of Geological Studies at the University of Colorado Boulder. ‘Then one would drill an elevator shaft from the canal to the summit and measure the distance between the water level – averaging the tides – and the rock summit.’ Acknowledging the impossibility of such a feat, he admits that triangulation calculations – which have an accuracy range as wide as ±30cm – will have to suffice.

Therefore, is the Indian survey likely to yield a new height for the mountain? It’s unlikely, suggests Bilham, who points out that any potential change is well within the range of uncertainty of the current height. ‘The reduced error is all that is happening,’ he explains. ‘We obtain new numbers and reduce the uncertainties as we get more adept with technology.’

This was published in the July 2017 edition of Geographical magazine.

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