Mount Everest, straddling the border between Nepal and China, is the undisputed holder of the title of world’s tallest (above-ground) mountain, but its exact height is still unknown.
In 1957, Indian surveyors determined its height to be 8,848m, but recent measurements from the US and China vary be several meters.
Now, scientists from Nepal are going to take an accurate measurement.
The project will take two years, and will require the placement of reference points on the mountain, and then take GPS measurements from three separate high-altitude camps to calculate a precise height.
"Estimating the height of mountains is more difficult and complicated than it sounds," Dr Paul Tregoning, a geophysicist from the Australian National University, told Australian Geographic. "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."
However, there are some hidden challenges. "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 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 measured only the height of the rock underneath the snow cap, arriving at a figure of 8844.43m.
This new survey hopes to find a final, definitive height for the world’s tallest peak.
