In 1856, Mount Everest was first measured by the Great Trigonometrical Survey of India, which calculated its height to be 29,002 feet. Over the last 150 years, however, other surveys and measurements by climbers have done their own calculations. The problem is: none of those measurements quite match up.
Now, the nation of Nepal is sending its own team up the mountain to conduct several different survey methods on the world’s tallest mountain in the hopes of arriving at a definitive height—and to see if a major 2015 earthquake took the mountain down a peg or two.
Jonathan Carey at Atlas Obscura reports that after the 7.8 magnitude earthquake hit the Himalayas in April 2015, it reshaped some parts of the mountain range. Satellites showed that areas of ground around Kathmandu were lifted, while the height of the mountains in the Langtang region of the Himalayas dropped over 3 feet. The data also showed that Everest had dropped about an inch.
That’s one reason Nepal began putting together its mega-survey in 2017. The other reason the tiny mountain nation is spending upwards of $2.5 million on the project is to put to rest long standing debates about the mountain's height. Carey reports that, in the 1950s—a century after the original survey, an Indian team measured Everest at 29,029 feet, which still considered its official height. That number was confirmed by Chinese surveyors in the 1970s. Americans bearing newfangled GPS gear measured it at 29,035 feet in 1999 and another Chinese survey in 2005 found that without ice and snow on top, the mountain was only 29,017 feet.
Nepal disagreed with the 2005 Chinese finding and planned to send up its own team in 2011, but, The Kathmandu Post reports, lack of funding and political instability put the plans on pause.
The latest attempt to measure the mountain is now a source of national pride. “Nepal has never measured Everest on its own although the world's highest peak lies in its territory,” Ganesh Prasad Bhatta, Nepalese head of government surveying, told AFP in 2017 when the project was first announced. “So we want to prove to our people that Nepal is capable of measuring Everest.”
Now, after two years of preparations and training, chief surveyor Khim Lal Gautam and his team are preparing to take their equipment to the summit during the current Everest climbing season, which is usually a brief window of calm weather in May.
In total, 81 people have worked on the survey, which will measure the mountain in four ways: using precise leveling, trigonometric leveling, gravity surveys, and a Global Navigation Satellite System survey technology gifted to Nepal by New Zealand.
“The combination of these surveys will provide us with a centimeter level accuracy,” Susheel Dangol, chief survey officer of the Everest Height Measurement, tells the Kathmandu Post. “The observation is not difficult. But climbing Everest will be challenging for the surveyors.”
Luckily, chief surveyor Gautam knows the ropes, literally: he summited Everest in 2011. “It will not be easy to work in that terrain, but we are confident our mission will be successful,” he tells AFP.
That success will depend on the cooperation of the notoriously fickle weather on the world’s highest peak. Only about 30 percent of people who attempt to climb the mountain make it to the summit, meaning there’s a good chance that the survey could be called off.
If the Nepalese team does make it to the summit and has the time and energy to conduct their surveys, they hope to issue a report on their findings in January 2020, which will perhaps establish a rock solid height for the world’s highest mountain—until the next earthquake or tectonic shift changes the peak once more.