The Everest we climbed together in those years

On May 25, 1960, the Chinese mountaineering team brought a five-star red flag to the summit of Mount Everest, creating the first human ascent of Mount Everest from the north slope; on May 4, 2022, 13 members of the Mount Everest scientific expedition team successfully climbed to the summit of Mount Everest. This is the first time that my country's Mount Everest scientific expedition has exceeded 8,000 meters in altitude, which is of epoch-making significance in the history of scientific exploration and research on the Qinghai-Tibet Plateau.

Over the past 62 years, we have climbed this peak again and again, hoping to understand its secrets - constantly updating the measurement of Mount Everest's height and successfully setting up the world's highest automatic weather station. The harsh environment and unexpected dangers make every climb a gamble.

In those years, how did we measure the height of Mount Everest to get the most accurate result? What difficulties did the scientific expedition team have to overcome when they broke through 8,000 meters?

Part 1

How to measure the height of Mount Everest?

We know that the elevation of a mountain is its altitude, that is, the height difference from sea level to the top of the mountain. A more precise or professional term is the normal height of the mountain.

Since the earth is a sphere, we cannot really measure the relative height difference from sea level to a mountain peak. Instead, we measure the distance from an equivalent plane - a quasi-geoid with the same gravity constant to the top of the mountain in the plumb line direction. The reason why we use a quasi-geoid is that it is difficult to find a surface with exactly the same gravity constant through measurement, so we can only use an approximate plane that has the significance of measuring engineering.

Schematic diagrams of the earth's various surfaces commonly used in surveying and mapping (Image source: self-made by the author)

Therefore, the method used to measure Mount Everest is the "surrounding observation" method. That's right, "surrounding observation" is more scientifically called triangulation, that is, observing the measured point from two locations at the same time. You only need to measure the distance between the observation points and the angles at which the two observation points observe the measured point to get the position of the measured point; if you need to know the three-dimensional spatial position of the measured point, you only need to add one observation point. By adding observation points and adjusting the observation results, you can achieve the result of improving the observation accuracy.

From 1966 to 1968, under the organization of the Chinese Academy of Sciences, the Chinese conducted a large-scale comprehensive scientific survey of Mount Everest and its surrounding areas. They formed two teams in 1966 and 1968. Not only did they establish a high-level and high-quality measurement control network in the Mount Everest area, but they also had more measurement stations closer to Mount Everest. They also carried out triangulation, leveling, astronomy, gravity, physical ranging, refraction tests and other measurement work, making full preparations for subsequent data correction and adjustment.

The level of this control network construction exceeded India's previous construction specifications. The final calculated altitude of Mount Everest was 8849.75m (without taking into account the thickness of snow on the peak), with a maximum difference of 3.01m.

In 1975, China once again measured Mount Everest. In addition to further strengthening and improving the control network, it was the first time that a 3.51m red metal measuring beacon was erected on the summit of Mount Everest with the assistance of mountaineers. The depth of snow on the summit was also measured. This was a pioneering effort and breakthrough in the history of measuring the height of Mount Everest.

A group photo of the surveying and mapping team when they reached the summit in 1975 (Photo source: National Bureau of Surveying and Mapping, edited by the author)

The final result of this measurement was 8848.13m (the snow depth at the peak center was about 0.92m), with a mean error of ±0.35m. This data result was used until 2005, when China accurately measured the rock surface elevation of the top of Mount Everest at 8844.43m.

At 11:08 Beijing time on May 22, 2005, a Chinese mountaineering survey team successfully reached the summit of Mount Everest, the world's highest peak. In addition to setting up a GPS control network, they also achieved joint measurement at the summit and at the observation station, and used radar detectors to measure the ice and snow layer.

2005 Mount Everest height measurement route and GPS joint measurement network (Image source: Reference 3)

The height of Mount Everest announced by China to the world this time is 8844.43m, which is quite different from the previous one because it is the net height without cap (excluding the thickness of the ice and snow layer on the top of the peak). When measuring the height of Mount Everest in 2005, the Chinese mountaineering survey team used radar detection technology to measure the thickness of the ice and snow covering the top of Mount Everest, which improved the accuracy and reliability of measuring the snow depth on the top of the peak.

Over time, the height of Mount Everest has been changing with the movement of geographical plates. In order to obtain more accurate data, the Mount Everest Altitude Measurement remeasured the height of Mount Everest in 2020.

Thanks to the high-precision control network we built in the Mount Everest area, China's 2005 surveying and mapping results are undoubtedly the most accurate among the several sets of data currently recognized by the world.

Part 2

How to overcome environmental risks?

The difficulty of climbing Mount Everest can probably be described by this poem by Du Fu.

The wind is strong and the mountains are high, the monkeys are howling sadly, the birds are flying back due to low oxygen and low pressure.

Endless ice and snow are falling, and endless tasks are coming.

Due to the influence of mountain effect and pass effect on wind pressure, the mountain is naturally "faster" and the surface coverage at different heights on the south slope of Mount Everest is different. After sunrise, obvious convection will form, and hot air will rise along the slope and begin to condense into clouds near the height of the peak. After it exceeds the peak, it will be blown to the east by the strong westerly wind, which is the beautiful "cloud flag" we see in the photo. The height of the "cloud flag" depends on the speed of the wind passing over the top of the mountain. The higher the speed, the lower the "cloud flag" will be pressed.

Flag cloud on Mount Everest (CC0)

We are familiar with the fact that plateau hypoxia is not a decrease in the proportion of oxygen. Hypoxia is only a superficial phenomenon. The root of the problem is the decrease in air pressure due to the increase in altitude. The low pressure at high altitudes not only greatly affects the mobility of people, but also causes incomplete combustion in vehicles such as cars due to low pressure. Conventional water tank refrigeration cannot achieve the desired effect, and is greatly restricted after 5,600 meters. In addition, the low temperature also limits the use of some types of batteries, bringing huge challenges to links such as material supply.

The problem is far more than that. The surface coverage landscape is simple but the micro-topography is complex. This description of Mao Dun brings an explosive difficulty index to the field work experience. Due to the extremely harsh environment of the work area, even after years of accumulation, the understanding of the environment is not high. Previously, due to the limitations of remote sensing measurement technology, the base map for mapping was the result of aerial telemetry and adjustment at a scale of 1:100,000. The scale is too small and many terrain details cannot be reflected. The endless snow and ice cover, the difference in the characteristics of the objects is small, but the possibility of change is high. It is difficult to remember visually and is more dependent on the positioning of the handheld device.

The most important thing is that the scientific expedition task is far from simple mountain climbing. Different personnel need to undertake corresponding scientific expedition tasks. Taking geology as an example, geological mapping needs to be carried out according to the designated routes, including the collection of various hand specimens. In the collection process, in addition to relying on the exposed bedrock conditions on the surface, geological boundaries must also be taken into account: the commonly used tracing method and crossing method are to trace and cross-cut along the geological boundaries to find the adjacent geological boundaries. Therefore, the exploration process must also be adjusted according to the results of the field discovery, which puts huge pressure on the coordination of the entire work schedule. All these require not only that field personnel need to have very good physical talents, but also outstanding work ability and on-the-spot experience.

The process of conquering the peak and asking about the height of Mount Everest is the history of human beings' understanding of the earth, nature, testing and exploring the level of science and technology. It is also the process of human beings challenging themselves and breaking through the limits of technology. Over the past few decades, "Climbing Mount Everest" has carried the heroic history of Chinese people's exploration of Mount Everest, and the constantly updated figures are full of the hardships and fearlessness of the first generation of Chinese climbers in their first expedition to Mount Everest.

References:

1. Zhu Liang. Determination of the height of Mount Everest[J]. Scientia Sinica Mathematica: Science in China, 1976, 19(1):74-84.

2. Chang Jiqing. Brief introduction to the previous height measurements of Mount Everest[J]. Bulletin of Surveying and Mapping, 2005(10):2-6.

3. Chen Junyong, Pang Shangyi, Zhang Ji, et al. Reflections on the results of my country's 35-year altitude measurement of Mount Everest [J]. Acta Geodaetica et Cartographica Sinica, 2001, 30(1):1-5.

4. ZHANG Chijun. Relative Problems and Thoughts on Qomolangma Elevation Determination. GEOMATICS AND INFORMATION SCIENCE OF WUHAN UNIVERS, 2003, 28(6): 675-678.

5. Chen Junyong, Pang Shangyi, Zhang Ji, et al. Snow surface elevation at the top of Mount Everest and global warming[J]. Advances in Earth Science, 2001, 16(1):12-14.

6. Chijun Zhang. Determination of the geoid and elevation of Mount Everest - and the role of vertical gravity gradient in it [J]. Chinese Journal, 1997, 42(23):2543-2545.

7. Guo Chunxi[1], Wang Bin[1], Cheng Chuanlu[1], et al. Elevation measurement of Mount Everest[J]. Journal of Earth Sciences and Environment, 2009(1).

Produced by: Science Popularization China

Author: Jing Bo

Producer: Computer Network Information Center, Chinese Academy of Sciences

The article only represents the author's views and does not represent the position of China Science Expo

This article was first published in China Science Expo (kepubolan)

Please indicate the source of the public account when reprinting

Please indicate the source of the reprint. Reprinting without authorization is prohibited.

For reprint authorization, cooperation, and submission matters, please contact [email protected]