The world’s highest mountain has grown taller. Mount Everest now has a new official height of 29,031.69 feet (8,848.86 metres) above sea level, according to a survey conducted by China and Nepal.
This is almost two feet taller than the previous official height. Until now, Nepal and China, the two countries covered by Mount Everest, couldn’t agree upon whether the height should include the mountain’s snow cap.
The last time China measured the Himalayan summit was in 2005, and it only included the rock height of the mountain. Meanwhile, Nepal was using a 1954 survey conducted by an Indian organisation to determine its official height of 29,028 feet above sea level.
Over the last two years, both China and Nepal have worked in tandem to measure the new height of the world’s tallest mountain. They used a combination of the techniques previously used to measure Mount Everest. Before GPS technology and satellites were used to measure the height of mountains, surveyors used a device termed a theodolite, which is a precision optical instrument. This instrument is mounted on a tripod to measure the angles between two designated points. Prior to 1999, surveyors would physically use this heavy equipment and systematically measure Mount Everest from sea level to its visible peak.
While Nepal used the Bay of Bengal as the sea base, working with figures given by India from a previous survey, China measured its sea-level base from the Yellow Sea. A team of four surveyors from Nepal spent nearly two years training to climb the summit, and built a network of stations stretching across 250 kilometres, till the peak was visible, to create a chain of points to measure and calculate.
To calculate the height of the summit, both countries used a trigonometric formula that calculates the height of a triangle by multiplying its base with its angles. Both teams used 12 lower peaks looking up at the Everest summit to make their calculations as precise as possible.
While the Nepalese team climbed the summit last year, China’s surveyors did so this May, becoming the only team to reach the top after Nepal suspended all climbing expeditions and China banned all foreign flights due to the coronavirus pandemic. While Nepal used global navigation satellite systems to get the exact elevation data for their calculations, China used BeiDou navigation satellite system, their version of GPS.
Mount Everest, which was formed by the collision of tectonic plates more than 50 million years ago, still grows by half a metre every century. The mountain was re-measured after some geologists suggested that a massive avalanche that took place in 2015 could have changed its height. The avalanche was caused by a 7.8 magnitude earthquake, which killed nearly 9,000 people in Nepal.
Some geologists believe this earthquake might have shrunk Mount Everest. This was after scientists revealed that other Himalayan peaks such as Langtang Himal, mostly to the north of Kathmandu and close to the epicentre, had fallen in height by about a metre post-earthquake.
However, many argue that Mount Everest, like other Himalayan peaks, may have actually risen over time due to shifts in tectonic plates it sits on. Experts believe that major earthquakes can reverse this process of growth.