Editing Mount Everest (section)

==Surveys==
===19th century===
[[File:MountEverestRelief.png|thumb|upright=1.5|Mount Everest [[Cartographic relief depiction|relief map]]]]
[[File:Tibetan Plateau and Mount Everest.png|thumb|Profiles of the full elevation of Mount Everest]]

In 1802, the British began the [[Great Trigonometrical Survey]] of India to fix the locations, heights, and names of the world's highest mountains. Starting in southern India, the survey teams moved northward using giant [[theodolite]]s, each weighing {{convert|500|kg|lb|abbr=on}} and requiring 12 men to carry, to measure heights as accurately as possible. They reached the Himalayan foothills by the 1830s, but [[Kingdom of Nepal|Nepal]] was unwilling to allow the British to enter the country due to suspicions of their intentions. Several requests by the surveyors to enter Nepal were denied.<ref name=everest_bwp70>{{cite book |title= Everest – The Best Writing and Pictures from Seventy Years of Human Endeavour |editor=Peter Gillman| year=1993 |publisher=Little, Brown and Company|isbn=978-0-316-90489-6 |pages=10–13}}</ref>

The British were forced to continue their observations from [[Terai]], a region south of Nepal which is parallel to the Himalayas. Conditions in Terai were difficult because of torrential rains and [[malaria]]. Three survey officers died from malaria while two others had to retire because of failing health.<ref name=everest_bwp70/>

Nonetheless, in 1847, the British continued the survey and began detailed observations of the Himalayan peaks from observation stations up to {{convert|240|km|mi|abbr=on}} distant. Weather restricted work to the last three months of the year. In November 1847, [[Andrew Scott Waugh]], the British [[Surveyor General of India]], made several observations from the Sawajpore station at the east end of the Himalayas. [[Kangchenjunga]] was then [[List of past presumed highest mountains|considered the highest peak in the world]], and with interest, he noted a peak beyond it, about {{convert|230|km|mi|abbr=on}} away. John Armstrong, one of Waugh's subordinates, also saw the peak from a site farther west and called it peak "b". Waugh would later write that the observations indicated that peak "b" was higher than Kangchenjunga, but closer observations were required for verification. The following year, Waugh sent a survey official back to Terai to make closer observations of peak "b", but clouds thwarted his attempts.<ref name=everest_bwp70/>

In 1849, Waugh dispatched James Nicolson to the area, who made two observations from Jirol, {{convert|190|km|mi|abbr=on}} away. Nicolson then took the largest [[theodolite]] and headed east, obtaining over 30 observations from five different locations, with the closest being {{convert|174|km|mi|abbr=on}} from the peak.<ref name=everest_bwp70/>

Nicolson retreated to [[Patna]] on the [[Ganges]] to perform the necessary calculations based on his observations. His raw data gave an average height of {{convert|9200|m|ft|abbr=on}} for peak "b", but this did not consider [[light refraction]], which distorts heights. However, the number clearly indicated that peak "b" was higher than Kangchenjunga. Nicolson contracted malaria and was forced to return home without finishing his calculations. Michael Hennessy, one of Waugh's assistants, had begun designating peaks based on [[Roman numerals]], with Kangchenjunga named Peak&nbsp;IX. Peak "b" now became known as Peak&nbsp;XV.<ref name=everest_bwp70/>

In 1852, stationed at the survey headquarters in [[Dehradun]], [[Radhanath Sikdar]], an Indian mathematician and surveyor from [[Bengal]] was the first to identify Everest as the world's highest peak, using [[trigonometry|trigonometric]] calculations based on Nicolson's measurements.<ref name=BBC_mwde>{{cite news|title=The man who "discovered" Everest|url=http://news.bbc.co.uk/2/hi/south_asia/3193576.stm|work=BBC News|date=20 October 2003|access-date=11 April 2008|first=Soutik|last=Biswas|archive-date=15 April 2008|archive-url=https://web.archive.org/web/20080415093207/http://news.bbc.co.uk/2/hi/south_asia/3193576.stm|url-status=live}}</ref> An official announcement that Peak&nbsp;XV was the highest was delayed for several years as the calculations were repeatedly verified. Waugh began work on Nicolson's data in 1854, and along with his staff spent almost two years working on the numbers, having to deal with the problems of light refraction, barometric pressure, and temperature over the vast distances of the observations. Finally, in March 1856 he announced his findings in a letter to his deputy in [[Kolkata|Calcutta]]. Kangchenjunga was declared to be {{convert|28156|ft|m|abbr=on|order=flip}}, while Peak&nbsp;XV was given the height of {{convert|29002|ft|m|abbr=on|order=flip}}. Waugh concluded that Peak&nbsp;XV was "most probably the highest in the world".<ref name=everest_bwp70/> Peak&nbsp;XV (measured in feet) was calculated to be exactly {{convert|29000|ft|m|abbr=on|sigfig=5|}} high, but was publicly declared to be {{convert|29002|ft|m|abbr=on|sigfig=5|}} in order to avoid the impression that an exact height of 29000&nbsp;ft was nothing more than a rounded estimate.<ref name=tas1982>{{cite journal|title=Letters to the Editor|journal=The American Statistician|volume=36|number=1|date=February 1982|pages=64–67|jstor=2684102|doi=10.1080/00031305.1982.10482782|last1=Stegman|first1=Charles E|last2=Bellhouse|first2=David|last3=Ehrenberg|first3=A.S. C|last4=Mantel|first4=Nathan|last5=Proschan|first5=Frank|last6=Gianola|first6=Daniel|last7=Searle|first7=S.R|last8=Speed|first8=F.M|last9=Milliken|first9=G.A}}</ref> Waugh is sometimes playfully credited with being "the first person to put two feet on top of Mount Everest".<ref>{{cite book|title=The Pendulum Paradigm: Variations on a Theme and the Measure of Heaven and Earth|page=267| author=Beech, Martin|year=2014| publisher=Universal-Publishers}}</ref>

===20th century===
[[File:CH-NP 79-80 Bdy Map50.jpg|thumb|Published by the Survey of [[Nepal]], this is Map 50 of the 57 map set at 1:50,000 scale "attached to the main text on the First Joint Inspection Survey, 1979–80, [[Nepal]]-China border." At the top centre, a boundary line, identified as separating "China" and "Nepal", passes through the summit contour. The boundary here and for much of the [[China–Nepal border]] follows the main Himalayan watershed divide.]]
<!--[[File:CH-NP 79-80 Bdy Map50.jpg|thumb|Published by the Survey of Nepal, this is Map 50 of the 57 map set at 1:50,000 scale "attached to the main text on the First Joint Inspection Survey, 1979–80, Nepal-China border." At the top centre, a boundary line, identified as separating "China" and "Nepal", passes through the summit contour. The boundary here and for much of the China-Nepal border follows the main Himalayan watershed divide.]]-->
[[File:ISS004E8852 everest.jpg|thumb|right|[[Kangshung Face|Kangshung Face (the east face)]] as seen from orbit]]

In 1856, Andrew Waugh announced Everest (then known as Peak XV) as {{convert|29002|ft|m|abbr=on|order=flip}} high, after several years of calculations based on observations made by the [[Great Trigonometrical Survey]].<ref>{{Cite book|last=Krakauer|first=Jon|title=Into Thin Air: A Personal Account of the Mount Everest Disaster|publisher=Anchor Books|year=1997|isbn=978-0-385-49478-6|edition=First|location=New York|pages=15–16|oclc=36130642}}</ref> 
From 1952 to 1954, the [[Survey of India]], using [[triangulation]] methods, determined that the height of Everest was {{convert|8847.73|m|ft|0|abbr=on}}.<ref name="everest-height-1952-1954">{{cite web |url=https://archive.org/details/Everest_201304 |title=Technical Paper No. 8, The Height of Mount Everest a New Determination (1952–1954) |last=Gulatee |first=Bihari Lal |publication-date=10 May 1955 |publisher=[[Indian Agricultural Research Institute]] |location=New Delhi, India |access-date=2 June 2023}}</ref> In 1975 it was subsequently reaffirmed by a Chinese measurement of {{convert|8848.13|m|ft|2|abbr=on}}.<ref name=ABC_au/> In both cases the snow cap, not the rock head, was measured.
The {{convert|8848|m|ft|0|abbr=on}} height given was officially recognised by Nepal and China.<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/world/south_asia/8608913.stm |title=Nepal and China agree on Mount Everest's height |work=BBC News |date=8 April 2010 |access-date=22 August 2010 |archive-date=3 March 2012 |archive-url=https://web.archive.org/web/20120303133522/http://news.bbc.co.uk/1/hi/world/south_asia/8608913.stm |url-status=live }}</ref> Nepal planned a new survey in 2019 to determine if the [[April 2015 Nepal earthquake]] affected the height of the mountain.<ref>{{cite news |last1=Daley |first1=Jason |title=Nepalese Expedition Seeks to Find Out if an Earthquake Shrunk Mount Everest Read |url=https://www.smithsonianmag.com/smart-news/nepalese-expedtion-wants-find-out-if-earthquake-shrunk-mount-everest-180971963/ |work=Smithsonian.com |publisher=Smithsonian Magazine |date=15 April 2019 |access-date=28 August 2019 |archive-date=31 May 2023 |archive-url=https://web.archive.org/web/20230531075731/https://www.smithsonianmag.com/smart-news/nepalese-expedtion-wants-find-out-if-earthquake-shrunk-mount-everest-180971963/ |url-status=live }}</ref>

In May 1999, an American Everest expedition directed by [[Bradford Washburn]] anchored a [[Global Positioning System|GPS]] unit into the highest bedrock. A rock head elevation of {{convert|8850|m|ft|0|abbr=on}}, and a snow/ice elevation {{convert|1|m|ft|0|abbr=on}} higher, were obtained via this device.<ref name="alpres">{{cite web|url=http://www.alpineresearch.ch/alpine/en/presse1.html|archive-url=https://web.archive.org/web/20070103165811/http://www.alpineresearch.ch/alpine/en/presse1.html|archive-date=3 January 2007|title=Elevation of Mount Everest newly defined|publisher=Swiss Foundation for Alpine Research|date=12 November 1999|access-date=1 April 2007}}</ref> Although as of 2001, it has not been officially recognised by Nepal,<ref>{{cite web|url=http://www.nepalgov.gov.np/countryprofile.php|title=Country Profile|publisher=Government of Nepal|year=2001|access-date=1 April 2007|archive-url = https://web.archive.org/web/20070314011131/http://www.nepalgov.gov.np/countryprofile.php |archive-date = 14 March 2007}}</ref> this figure is widely quoted. [[Geoid]] uncertainty casts doubt upon the accuracy claimed by both the 1999 and 2005 (see [[#21st-century surveys|§ 21st-century surveys]]) surveys.<ref>{{Cite web|last=US Department of Commerce|first=NOAA|title=GEOID18 Technical Details {{!}} GEOID18 {{!}} National Geodetic Survey|url=https://geodesy.noaa.gov/GEOID/GEOID18/geoid18_tech_details.shtml|access-date=9 March 2021|website=geodesy.noaa.gov}}</ref>

In 1955, a detailed [[Photogrammetry|photogrammetric]] map (at a scale of 1:50,000) of the [[Khumbu]] region, including the south side of Mount Everest, was made by [[Erwin Schneider]] as part of the 1955 International Himalayan Expedition, which also attempted [[Lhotse]].

In the late 1980s, an even more detailed [[topography|topographic]] map of the Everest area was made under the direction of Bradford Washburn, using extensive [[aerial photography]].<ref name="washburn_map"/>

===21st century===
On 9 October 2005, after several months of measurement and calculation, the [[Chinese Academy of Sciences]] and State Bureau of Surveying and Mapping announced the height of Everest as {{convert|8844.43|m|ft|2|abbr=on}} with accuracy of ±{{convert|0.21|m|in|1|abbr=on}}, claiming it was the most accurate and precise measurement to date.<ref name="Junyong Yanping Janli Chunxi 2010 pp. 122–131">{{cite journal | last1=Junyong | first1=Chen | last2=Yanping | first2=Zhang | last3=Janli | first3=Yuan | last4=Chunxi | first4=Guo | last5=Peng | first5=Zhang | title=Height Determination of Qomolangma Feng (MT. Everest) in 2005 | journal=Survey Review | publisher=Informa UK Limited | volume=42 | issue=316 | year=2010 | issn=0039-6265 | doi=10.1179/003962610x12572516251565 | pages=122–131| bibcode=2010SurRv..42..122J | s2cid=129376174}}</ref> This height is based on the highest point of rock and not the snow and ice covering it. The Chinese team measured a snow-ice depth of {{convert|3.5|m|ft|0|abbr=on}},<ref name=ABC_au>{{cite web|url=http://www.abc.net.au/science/news/enviro/EnviroRepublish_1478658.htm|title=Everest not as tall as thought|publisher=Australian Broadcasting Corporation|website=News in Science|date=5 October 2005|access-date=1 April 2007|archive-date=11 May 2011|archive-url=https://web.archive.org/web/20110511184616/http://www.abc.net.au/science/news/enviro/EnviroRepublish_1478658.htm|url-status=live}}</ref> which is in agreement with a net elevation of {{convert|8848|m|ft|0|abbr=on}}. An argument arose between China and Nepal as to whether the official height should be the rock height (8,844 m, China) or the snow height (8,848 m, Nepal). In 2010, both sides agreed that the height of Everest is 8,848 m, and Nepal recognises China's claim that the rock height of Everest is 8,844 m.<ref>{{cite news|url=http://news.bbc.co.uk/2/hi/south_asia/8608913.stm|title=Official height for Everest set|date=8 April 2010|work=BBC|access-date=16 August 2016|archive-date=31 May 2023|archive-url=https://web.archive.org/web/20230531063403/http://news.bbc.co.uk/2/hi/south_asia/8608913.stm|url-status=live}}</ref> On 8 December 2020, it was jointly announced by the two countries that the new official height is {{convert|8848.86|m}}.<ref>{{cite news|title=Mount Everest, the world's highest mountain, officially just got a little bit higher|url=https://www.cbsnews.com/news/mount-everest-height-agreed-china-nepal-worlds-highest-mountain-even-taller/?ftag=CNM-00-10aab7e&linkId=106576647|publisher=CBS|date=8 December 2020|access-date=8 December 2020}}</ref><ref name="dec 2020 height">{{cite news|publisher=BBC|title=Mt Everest grows by nearly a metre to new height|url=https://www.bbc.com/news/world-asia-55218443|date=8 December 2020|author=Navin Singh Khadka|access-date=8 December 2020|archive-date=25 December 2021|archive-url=https://web.archive.org/web/20211225034126/https://www.bbc.com/news/world-asia-55218443|url-status=live}}</ref>

It is thought that the [[plate tectonics]] of the [[Main Himalayan Thrust]] and related faults, which form the [[convergent boundary]] between the [[Eurasian Plate]] and [[Indian Plate]], are adding to the height and moving the summit northeastwards. Two accounts suggest the rates of change are {{convert|4|mm|in|abbr=on}} per year vertically and {{convert|3|to|6|mm|in|2|abbr=on}} per year horizontally,<ref name="alpres"/><ref>{{cite web|url=http://www.nationalgeographic.com/features/99/everest/roof_content.html|title=Roof of the World|publisher=[[National Geographic Society]]|year=1999|access-date=1 April 2007|url-status=dead|archive-url=https://web.archive.org/web/20070712170109/http://www.nationalgeographic.com/features/99/everest/roof_content.html|archive-date=12 July 2007}}</ref> but another account mentions more lateral movement ({{convert|27|mm|in|abbr=on|disp=or}}),<ref>{{cite web|url=http://www.mos.org/Everest/exhibit/platetectonics.htm|archive-url=https://web.archive.org/web/20061108172757/http://www.mos.org/Everest/exhibit/platetectonics.htm|archive-date=8 November 2006|title=Everest: Plate Tectonics|publisher=Museum of Science|year=1998}}</ref> and even shrinkage has been suggested.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/world/asia-pacific/4204539.stm|title=China fears Everest is shrinking|work=BBC News|date=25 January 2005|access-date=1 April 2007|first=Louisa|last=Lim|archive-date=3 October 2021|archive-url=https://web.archive.org/web/20211003102716/http://news.bbc.co.uk/1/hi/world/asia-pacific/4204539.stm|url-status=live}}</ref>

=== Comparisons ===
{{Main list|List of highest mountains on Earth}}

The summit of Everest is the point at which Earth's surface reaches the greatest distance [[above sea level]]. Several other mountains are sometimes claimed to be the "tallest mountains on Earth". [[Mauna Kea]] in Hawaii is tallest when measured from its base;{{NoteTag|name=base|The "base" of a mountain is a problematic notion in general with no universally accepted definition. However, for a peak rising out of relatively flat terrain, such as Mauna Kea or Denali, an "approximate" height above "base" can be calculated. Everest is more complicated since it only rises above relatively flat terrain on its north (Tibetan Plateau) side. Hence the concept of "base" has even less meaning for Everest than for Mauna Kea or Denali, and the range of numbers for "height above base" is wider. In general, comparisons based on "height above base" are somewhat suspect.}} it rises over {{convert|10200|m|ft|1|abbr=on}} from its base on the mid-ocean floor, but only attains {{convert|4205|m|ft|0|abbr=on}} above sea level.

By the same measure of base to summit, [[Denali]], in [[Alaska]], federally designated as Mount McKinley, is taller than Everest as well.{{NoteTag|name=base}} Despite its height above sea level of only {{convert|6190|m|ft|0|abbr=on}}, Denali sits atop a sloping plain with elevations from {{convert|300|to|900|m|ft|abbr=on}}, yielding a height above base in the range of {{convert|5300|to|5900|m|ft|abbr=on}}; a commonly quoted figure is {{convert|5600|m|ft|-2|abbr=on}}.<ref>{{cite web |url = https://www.pbs.org/wgbh/nova/denali/expedition/mission.html |title = Surviving Denali, The Mission |publisher = [[PBS|Public Broadcasting Service]] |website = PBS.org |year = 2000 |access-date = 7 June 2007 |archive-date = 20 November 2010 |archive-url = https://web.archive.org/web/20101120103239/http://www.pbs.org/wgbh/nova/denali/expedition/mission.html |url-status = live }}</ref><ref>{{cite news |url = http://www.upi.com/blog/2013/09/12/Mount-McKinley-83-feet-shorter-than-thought-new-data-show/4061379016741/ |title = Mount McKinley 83 feet shorter than thought, new data show |work = [[United Press International]] |access-date = 18 March 2014 |archive-date = 26 March 2022 |archive-url = https://web.archive.org/web/20220326072757/https://www.upi.com/blog/2013/09/12/Mount-McKinley-83-feet-shorter-than-thought-new-data-show/4061379016741/ |url-status = live }}</ref> By comparison, reasonable base elevations for Everest range from {{convert|4200|m|ft|-2|abbr=on}} on the south side to {{convert|5200|m|ft|-2|abbr=on}} on the [[Tibetan Plateau]], yielding a height above base in the range of {{convert|3650|to|4650|m|ft|abbr=on}}.<ref name="washburn_map">''Mount Everest'' (1:50,000 scale map), prepared under the direction of [[Bradford Washburn]] for the Boston Museum of Science, the Swiss Foundation for Alpine Research, and the [[National Geographic Society]], 1991, {{ISBN|3-85515-105-9}}.</ref>

The summit of [[Chimborazo]] in [[Ecuador]] is {{convert|2168|m|ft|0|abbr=on}} farther from Earth's centre ({{convert|6384.4|km|mi|1|abbr=on|disp=or}}) than that of Everest ({{convert|6382.3|km|mi|1|abbr=on|disp=comma}}), because the Earth bulges at the equator.<ref name="Robert Krulwich">{{cite web |url = https://www.npr.org/templates/story/story.php?storyId=9428163 |title = The 'Highest' Spot on Earth? |date = 7 April 2007 |website = NPR.org |publisher = [[National Public Radio]] |first = Robert |last = Krulwich |access-date = 4 April 2018 |archive-date = 30 January 2013 |archive-url = https://web.archive.org/web/20130130164111/http://www.npr.org/templates/story/story.php?storyId=9428163 |url-status = live }}</ref> This is despite Chimborazo having a peak of {{convert|6268|m|ft|1|abbr=on}} above sea level versus Mount Everest's {{convert|8848|m|ft|1|abbr=on}}.

===Context and maps===
{{wide image|File:Everest-3D-Map-Type-EN.jpg|800px|3D rendering of Mount Everest and surrounding terrain}}

Many of the highest mountains in the world are near Mount Everest, for example [[Lhotse]], {{convert|8516|m|ft|abbr=on}}; [[Nuptse]], {{convert|7855|m|ft|abbr=on}}, [[Changtse]], {{convert|7580|m|ft|abbr=on}} and [[Khumbutse]], {{convert|6636|m|ft|abbr=on}}.  On the southwest side, a major feature in the lower areas is the [[Khumbu Glacier|Khumbu icefall and glacier]], an obstacle to climbers on those routes but also to the base camps.
<!-- The image map below was added on 7 September 2007—see talk page under the title "Replacing - Enhancing Picture". -->
{{Himalaya annotated imagemap|width=600|caption=Southern and northern climbing routes as seen from the [[International Space Station]] (The names on the photo are links to corresponding pages.)}}