### Reaching a New Height – December 9, 2020

In 2019, Nepalese mountaineers surveyed the mountain, making their own measurements for the first time, while a Chinese team did the same in 2020. As of this Monday, Nepal and China jointly announced the new height of Everest: 8848.86 meters (29,032 ft.), or 0.86 meters/2.82 feet higher. After the major 7.8 earthquake hit Nepal in 2015, scientists wondered if that had impacted Everest’s height, as other Himalayan peaks closer to the epicenter reduced in height by a meter. This new measurement reveals that the earthquake did not impact Everest’s height, but evidence from the 2017 climbing season shows that it did lead to the collapse of the iconic Hillary Step – the last challenge climbers encountered before reaching the summit. Climbing the Hillary Step had the danger of a 10,000-foot (3,000 m) drop on the right (when going up) and an 8,000-foot (2,400 m) drop on the left!

So, how were these measurements made? The heights of mountains are measured with the mean sea level as the base – so it’s less about working out the where the top is than where the bottom would be. Nepal used the Bay of Bengal as its sea level, but given that India had already surveyed a point closer to Everest from the bay, near the India-Nepal border, they were able to provide the Nepalese surveyors with the height from that point as well. Then, from there, Nepali surveyors created a network of line-of-sight stations stretching nearly 250 km (155 miles) to the point where Everest first becomes visible, thereby creating a chain of points they could measure and add together. The Chinese surveyors used the Yellow Sea in the eastern province of Shandong as their sea-level base.

Surveyors from both sides used trigonometry to calculate the height of the summit. The formulas they used calculate the height of a triangle by multiplying its base with its angles. But for all that ground work, someone still needs to be on top of the mountain!

“Once the surveyor’s beacon had been placed on the summit, surveyors at stations around the summit measured the distance from six points to the beacon, which meant at least six triangles could be calculated to determine the mountain’s height,” says Jiang Tao, associate researcher at the Chinese academy of surveying and mapping. Both sides also used high-precision GPS to receive elevation data from numerous receivers in their calculations.

For those interested in the history of Everest height measurements, check out: http://www.dos.gov.np/everest/downloads/Nitin_Joshi.pdf