How to measure a mountain

The first recorded attempt to measure Everest using modern calculations came in 1856, when surveyors commissioned by the then Inspector General of India George Everest estimated its height at 29,002 feet. Without going into the sinuses and cosines of the boat, suffice it to say that using precise distance measurements and multiple readings of angles from different positions, it is possible to use trigonometry to determine the height of any characteristic. A key tool in this exercise is the theodolite, which helps measure angles. It’s a lot like a tool you’ve probably noticed using road construction engineers. As it turned out, the height determined by British Raj officials was quite close to what Indian officials would calculate in the 1950s using more modern tools: 29,028 feet or 8,848 meters. He is still the most cited figure for the height of Everest.

NOW, EXPERTS ARE AT HEIGHTS USING GPS

The key tool used by Chinese and Nepalese inspectors was a GPS receiver, which was transported to the top of Everest. The time factor required for signals to travel from the receiver to multiple satellites and the distance of these satellites from fixed objects provides a very accurate approximation of the location and height of the peak.

A member of a Chinese surveying team installs surveying equipment on the summit of Mount Everest (Photo Xinhua via AP)

A member of a Chinese surveying team installs surveying equipment on the summit of Mount Everest (Photo Xinhua via AP)

But while GPS and similar systems could have allowed large jumps in mounting height, measuring a mountain depends significantly on several moving parts.

OF SEA LEVELS AND SNOW

GPS can tell you where the peak is, but to find the height of a mountain it’s just as important to know where the bottom is. Because the mountains are measured as their height above sea level.

A global satellite navigation system receiver is seen attached to a tripod while measuring the height of Mount Everest (photo: AFP)

A global satellite navigation system receiver is seen attached to a tripod while measuring the height of Mount Everest (photo: AFP)

170 years ago, the Everest crew, led by mathematician Radhanath Sikdar, solved the sea level problem, actually working in their direction as far as the Bay of Bengal, using a network of line-of-sight stations until Everest itself was visible and could be measured using trigonometric formulas.

Another factor that proves controversial is whether to calculate the depth of snow on a mountain top as part of its height. Nepalese inspectors used a ground-breaking radar to effectively measure the height of the snow above the rocky ridge of Everest, but in the past it has been debated whether snow should be part of the calculation.

HOW TO MEASURE THE SEA LEVEL

To accurately determine sea level while interpreting GPS data, scientists now rely on two models that conceptualize the shape of the Earth: the ellipsoid, which presents the Earth’s surface as smooth and uniform and is used to measure geographic coordinates; and geoid: a model that takes into account gravity and how it affects sea level and how the rotating Earth swells at the equator and flattens at the poles. The geoid model is a close proxy for the average sea level. Calculations involving ellipsoidal and geoid heights eventually give the orthometric height or height above sea level.

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By the way, EVEREST is still growing


Everest, like the rest of the Himalayan range, grows by about half a centimeter each year due to tectonic plate collisions. The Indian plate that pushes into the Eurasian plate in the last 40 to 50 million years makes the tip grow, although almost negligible.

Source: Alex Copley, University of Cambridge

Source: Alex Copley, University of Cambridge

But earthquakes have the opposite effect – they can reduce the height of a peak. The magnitude 7.8 earthquake that struck Nepal in 2015 possibly reduced Everest’s snow cover. Scientists have discovered that other peaks near the epicenter have seen their heights shrink by about a meter after the earthquake. It is estimated that an earthquake in 1934 cut the mountain by about two meters. Nepal’s investigation department said the 2015 disaster was a key reason behind measuring Everest’s height again.

Source: National Geographic, NOAA, Slate, media reports

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