Mt Everest height to be clarified

By AAP and Beau Gamble 20 July 2011
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The precise height of the world’s tallest peak, Mt Everest, is unknown and now scientists have set out to confirm it.

MOUNT EVEREST, WHICH STRADDLES the border between Nepal and China, is generally thought to stand at 8848m – a height determined by Indian surveyors in 1957. But more recent measurements by teams from the US and China vary several metres.

Now, scientists from Nepal are planning to take the most accurate measurement to date.

Gopal Giri, a spokesman from the Nepalese land reform and management ministry, says that during border talks between Nepal and China, Chinese delegates revealed they often use their measurement of 8844m when referring to the height of Mt Everest.

“We have begun the measurement to clear this confusion. Now we have the technology and the resources, we can measure ourselves,” Giri says. “This will be the first time the Nepal government has taken the mountain’s height.”

The project will take two years, he says. Nepalese scientists plan to set up reference points on Mt Everest, before using global-positioning system (GPS) satellites to calculate a precise height.

Disputed height

Ever since it was first measured in 1856 as part of the Great Trigonometric Survey of British India, Everest’s exact height has been in dispute.

“Estimating the height of mountains is more difficult and complicated than it sounds,” says Dr Paul Tregoning, a geophysicist from the Australian National University. “To get an updated GPS height of the top of Mt Everest, it’s conceptually very simple: you go up to the top, turn on a GPS and it will calculate a height accurate to about 1m. But in practice, someone’s got to climb the mountain carrying the equipment.”

To obtain a precise measurement involves overcoming a number of technical challenges, he says. “The first problem is that the height must be a measurement with respect to something. It must be relative to sea level, for example, or to what is called a ‘reference ellipsoid’ – a mathematical surface.

The height that is provided by a handheld GPS, on the other hand, says Paul, is the height above this mathematical surface and is not related to sea level. Such surfaces are used by geographers as a more accurate basis for calculating elevation.

“It also becomes a requirement to define exactly what is meant by the ‘top’ [of the mountain],” Paul says. In 1999, a US team defined Mt Everest’s tallest point as the top of its snow cap, and they reported a height of 8850m – a figure currently accepted by the US National Geographic Society.

However, a survey by the Chinese Academy of Sciences and the State Bureau of Surveying and Mapping excluded the snow cap and measured only the height of the rock underneath. They arrived at a figure of 8844.43m.

Constantly growing

Mt Everest is growing taller by about 4mm per year, scientists suggest, due to uplift caused by the Indian tectonic plate pushing northward into Asia. Paul says the slow uplift rate will affect current calculations of its height, but only if the height is required to be known with millimetre accuracy.

Since Tensing Norgay and Edmund Hillary first conquered Everest’s summit in 1953, more than 3000 climbers have followed suit. At least 219 have died trying to do so.