How to measure a mountain: Everest height called into question

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Story highlights

  • Since 1955, Everest's official height has been 8,848 meters
  • Studies show that there might have been some elevation changes over the years
  • In the past, Nepal has rejected height measurements calculated by foreign teams

(CNN)Did Mount Everest shrink after Nepal's massive 2015 earthquake? Has it lost a few meters of snow cover due to global warming? Is it getting taller due to shifting continental plates?

To clear up these frequently raised questions once and for all, the Nepalese government has kicked off the long and arduous mission of re-measuring the height of the world's tallest peak.
    In 1856, Everest's height was first calculated to be 8,840 meters (29,002 feet) above sea level by a team led by British surveyor Sir George Everest, the man whom the mountain was named after. Later, in 1955, the figure was adjusted by eight meters to 8,848 (29,028 feet), which has remained the official height to date.
    Climbers stand on a ridge over a valley leading north into the Khumbu region as they try to get a clear view of Mt. Everest, April 18, 2015.
    "Since multiple scientific studies show that there might have been some changes in the height of Everest, it became the Nepali government's responsibility to check and clarify the matter," Ganesh Prasad Bhatta, director general of Nepal's Survey Department, told CNN.
    Bhatta said his office had been planning to undertake the mission since 2012, but it never materialized. Strong doubts from the international scientific community that Everest's elevation changed after 2015's 7.8-magnitude earthquake gave the department a push to jump-start the project.
    The exercise, which is expected to cost the Nepali government around $1.5 million, is no ordinary feat for Bhatta's team.

    Expert team

    A small group of technicians has already started its work from a landmark in Nepal's Udayapur district roughly 1,500 meters above sea level.
    "The team will collect info from stations that'll be set up every two kilometers starting from Udayapur all the way to Everest's peak," Niraj Manandhar, head of Geodetic Survey branch in the department, told CNN. "Each and every data point will be recorded (to the closest) millimeter for accuracy."
    Mountaineers walk past the Hillary Step while pushing for the summit of Mount Everest as they climb the south face from Nepal, May 19, 2009.
    Nepal's surveyor general said the work so far has been preliminary, with the project officially starting in mid-July.
    Bhatta is hoping to have a team of about 50 people by August, and has reached out to "foreign scientists and experts who have already been involved in similar measurements of different mountains around the world," he said.
    Bhatta is also planning to get reputed geological groups like the International Association of Geodesy on board, and Sherpas will be trained to plant GPS receivers atop Everest.

    How is the altitude being measured?

    The height will be calculated using a combination of geodetic data received from three mechanisms: leveling instrument, gravity meter and GPS.
    GPS, or global positioning system, will play a crucial role, according to Bhatta. A signal receiver will be placed at every station, and the team will monitor signals sent between the receiver and satellites. They will then convert the time it takes the signals to arrive into a height measurement.
    The ancient trigonometric method of triangulation to measure a mountain's height (where the angles in a triangle formed by three survey control points) will not be used.
    "You'll have an answer within two years," Bhatta said.

    Various claims

    In 1999, an American team supported by the US National Geographic Society used GPS technology to calculate Everest's height as 8,850 meters. The figure was rejected by Nepal for not using government-approved measurement procedure.
    Then in 2005, a Chinese team measured the mountain and calculated a height of 8,844 meters. But since the research was not authorized by Nepal, the country did not recognize it as the official height either.
    Everest is officially in Nepal but sits at its border with Tibet.
    Bhatta said, "It is not mandatory for Nepal government to get the results ratified by the Chinese side."
    As a goodwill offer, his office is planning to ask the Chinese government to send its experts to be a part of the project.