The height of Mt Everest has changed with advances in survey technology. The Great Trigonometric Survey Of India in 1856 declared Mt Everest as the highest mountain in the world at exactly 29,000ft. But since surveyors thought no one would believe such a round figure, they added 2ft to it so it sounded more precise.
There are also many different ways to calculate the elevation of Mt Everest: from mean sea level, from the lowest depth of the ocean, or even the distance from the centre of the Earth which would mean that some Andean peaks would actually be ‘taller’ because the planet is not perfectly round but has a slight bulge along its equator.
Then there is the question of whether the true elevation is the bedrock at the summit, or should the 4m thick icing on the top of Everest also be added to the height? The height is also not static – the peak is undergoing tectonic uplift of about 1cm a year, and the ice cover on the summit varies in thickness because of precipitation, wind and (of late) global warming.
More recently, geologists and scientists have also come up with different figures for the impact of the 2015 earthquake– most agree that Mt Everest may have shrunk by about 3cm, and been displaced southwards by a metre or more.
“The height of Everest is constantly changing due to tectonic activity, of which the 2015 Gorkha Earthquake is only the most recent contribution,” explains Christopher Pearson of the University of Otago in New Zealand who worked with Nepal surveyors on the measurement in 2018. “Since the present measurements are fairly old, we needed to update it.”
The New Zealand government assisted Nepal’s Survey Department to install GPS equipment on the summit and train technicians in processing the GPS data, geodesy, levelling and gravity measurements.
Says Navin Manandhar, formerly with the Geodetic Branch of the Survey Department who helped develop the methodology for re-measurement: “This body of work is a matter of pride for Nepal, but is also a huge undertaking and with the whole world keenly waiting for the result, it has not been easy.”
Indeed, Survey Department officials are tight-lipped about the final height, and will not even give a hint about whether Mt Everest is taller or shorter. The reason for the sensitivity is that the governments of China and Nepal have signed an MoU to cooperate in the re-measurement and agreed during President Xi Jinping’s state visit to Kathmandu last October to announce the result jointly.
Even if the new height of Mt Everest is found to be lower than it is now, there is no danger of its demotion from being the highest mountain in the world. The second highest peak, Mr K2 in Pakistan is only 8,611m.
Nepal’s own survey team led by Khim Lal Gautam climbed the mountain on 22 May 2019, and installed GPS equipment and ground-penetrating radar at the summit. The team risked its life, with Gautam losing a toe to frostbite in the process.