On Tuesday, China and Nepal announced the results of a year-long joint survey of the tallest mountain in the world. According to their measurements, Mount Everest is 29,031.7 feet tall, about two feet taller than the most widely accepted height.
The result comes one year after China’s top leader Xi Jinping announced that China and Nepal would jointly measure the mountain, which sits on the border of Nepal and Tibet. Everest’s height is slowly increasing because of the shifting of Earth’s tectonic plates, and may have shrunk after a magnitude 7.8 earthquake in 2015. The new measurement is important not only because it seeks to clear up discrepancies in other, older measurements of the peak, but also because Nepal was able to prove its ability to survey the mountain with its own resources.
“The project was a matter of national pride for Nepal and a prestigious undertaking for the Nepali government. I feel very proud that we were able to complete it successfully,” says Susheel Dangol, Deputy Director General at Nepal’s Department of Survey, to CNN’s Sugam Pokharel and Rhea Mogul. “Nepal and China jointly processed the surveyed data and came up with the result.”
Measuring a mountain is a years-long undertaking. Nepalese surveyors trekked up the south side of the mountain in 2019, and took their measurements at the peak at 3:00 a.m. local time to avoid crowds of climbers, Freddie Wilkinson reports for National Geographic. The Chinese team scaled the north side of the mountain this spring, when the paths were clear because of the Covid-19 pandemic.
Surveyors used a combination of satellite measurements, taken with GPS and the Chinese counterpart Beidou, and triangulation, taken with laser theodolites, which use angles to measure the height difference between two points. At the summit, chief survey officer of the project Khimlal Gautam used ground-penetrating radar to measure how much snow was packed between their feet and the mountain’s actual rocky peak. It was the first time that a surveyor had gathered data from the mountain’s peak, Bhadra Sharma and Emily Schmall report for the New York Times.
Nepal had planned to survey the peak since 2017, when the country rebuffed India’s request to measure the mountain.
The previous most commonly used measurement of Mount Everest, 29,029, comes from a survey conducted by India in 1955, although several different measures have been put forward in the last few decades. In 2005, a Chinese survey estimated the peak at 29,017 feet tall, while a survey sponsored by the National Geographic Society in 1999 concluded that the peak is 29,035 feet tall, Colin Dwyer reports for NPR.
The first triangulation measurements of the mountain come from the middle of the 19th century, when mathematician Radhanath Sickdhar concluded that Everest is the world’s highest peak, per National Geographic. Sickdhar worked under the British-India Survey Office’s surveyor general Sir George Everest, who retired to Britain. His successor in the role of surveyor general, Andrew Waugh, recommended that the Royal Geographic Society name the mountain Everest in 1865.
Rejecting that colonial-era name, Nepal and China used the mountain’s local names, Sagarmatha in Nepal and Chomolungma in Tibet, during the new height announcement, per the New York Times.
This probably won’t be the last time that scientists will want to reevaluate the mountain’s altitude. The mountain may rise as much as a quarter of an inch each year, Jason Daley reported for Smithsonian in 2017, due to the Earth’s geological activity. The Indian tectonic plate is sliding underneath the Eurasian plate, causing sediments at the edge of each plate to push each other further skyward, Maya Wei-Haas writes for National Geographic.
But for now, the measurement will likely become the new, most-used descriptor of Everest’s height.
“It will be difficult to improve on the new number,” says University of Colorado geologist Roger Bilham to the Washington Post’s Joanna Slater and Ankit Adhikari. The Nepal surveyor team’s measurements are “remarkable for their density.”