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Nepal & China Remeasured Mount Everest. How Tall Is It Now?

LULU GARCIA-NAVARRO, HOST:

You may think you know the answer to this question - how tall is Mount Everest? Well, the answer may be changing. The world's tallest mountain stands on the border of China and Nepal. And there was an earthquake there five years ago, which may have altered its height. So those two countries have remeasured the mountain. NPR's Lauren Frayer has more.

LAUREN FRAYER, BYLINE: Last year, Roxanne Vogel summited Everest and stood at 29,029 feet.

ROXANNE VOGEL: That's the closest to heaven that I will ever get, and it's kind of life-changing when you're up there.

FRAYER: She trained for years with that one number in mind.

VOGEL: But the number itself - 29,029 - it just becomes something that you fixate on.

FRAYER: But it may turn out that Vogel did not stand at 29,029 feet. The mountain's height is changing with the movement of plates in the Earth's crust. Scientists are honing better technology to measure it. So over the past two years, China and Nepal remeasured Everest and are due to release their findings any day now. The task of measuring what, in English, we call Everest but in Nepal they call Sagarmatha, in Tibet, Chomolungma - dates back to the 19th century.

(SOUNDBITE OF ARCHIVED RECORDING)

UNIDENTIFIED NARRATOR: To George Everest, following his survey of 1841...

FRAYER: British colonial surveyors used theodolites, optical instruments that measure angles and heights from afar. B. Nagarajan was one of George Everest's successors at the Survey of India office.

B NAGARAJAN: Very heavy machines they've carried forward to make this measurement.

FRAYER: Nowadays, all you have to do is climb to the summit with a GPS receiver - easier said than done, says Dinesh Manandhar, a GPS expert from Nepal.

DINESH MANANDHAR: It's a very harsh environment there - very, very windy.

FRAYER: Surveyors have about a half an hour to connect to multiple satellites and use ground-penetrating radar to measure ice and snow. But all of that data from the top of the mountain, it's only half the story because you need a reference point, sea level, Manandhar says.

MANANDHAR: And that's the biggest problem. It's land everywhere. The nearest sea level is in India.

FRAYER: So they measure sea level in India, China and hundreds of other places to get the average. And then they have to take into account the Earth's rotation and gravity to estimate what sea level would be if there were a sea at Everest's base. Compare that to GPS readings from the top of the mountain, and they get the height - except the Himalayas are moving.

SRIDEVI JADE: The Himalayas are on plate boundary between Indian and Eurasian plate.

FRAYER: Sridevi Jade is an engineer who's calculated that the movement of those two plates is pushing Everest skyward by about a foot every 300 years. Once in a while, earthquakes come along and erase that, though. A 1934 quake took about 2 feet off the mountain, Jade says. One of the reasons China and Nepal have remeasured is that they want to know what a 2015 quake in Nepal might have done to Everest's height.

It's also a matter of national pride. Most previous measurements were done by foreigners. And Manandhar, the GPS expert from Nepal, says...

MANANDHAR: Why don't we measure our own mountain?

FRAYER: Climbers like Roxanne Vogel hope to find out that they actually climbed higher than they thought. But she says she keeps in mind whenever she's climbing any mountain...

VOGEL: It's a living thing, and it's constantly changing.

FRAYER: And that's what scientists say matters to them - what Everest's changing height tells us about the planet overall.

Lauren Frayer, NPR News.

GARCIA-NAVARRO: And for more about Everest, check out NPR's science podcast Short Wave. They just released an episode all about this. Transcript provided by NPR, Copyright NPR.


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