Written by Prakriti Panwar, a grade 11 student

Mount Everest, the tallest mountain in the world, has grown by 85 cms since 1954, when it was last measured.

How did that happen?

So, the earlier measurement was done by the Survey of India – India’s mapping organization – and the height was said to be 8,848 meters (this height included the snow on top). This number is what’s been recognised and accepted since 1954 by most references around the world, except by China.

China never agreed to the number, and sent an expedition in 2005, which came up with a different height. And this method did not count the snow on top of the mountain.

Then, last year Nepal also sent its people to measure the mountain, followed by China this year (again). Now both the countries have claimed that the height is a little bit more than what India had measured.

So, has the mountain grown? Why did they re-measure?

A couple of reasons

• There have been some debates about the fact that the exact height of the mountain may have changed after the 2015 earthquake in Nepal.
• China had never accepted India’s figure
• The Everest is believed to be growing every year due to tectonic plate collision

Ok, so how exactly do you measure a mountain?

It’s basically Trigonometry – for those who don’t know what this is – it’s the study of the relationships between side lengths and angles of triangles.

And for measuring a mountain, we think of it as a gigantic triangle and apply the rules of trigonometry to measure it.

In a triangle there are three sides and three angles. So, if you know any of the three numbers, as long as one of those is the side, you can work out the size of the other sides. There are three sides and three angles in any triangle. If we know any three of these quantities, provided one of them is a side, all the others can be calculated. For measuring a mountain, these same principles are used – you find out one basic angle and distance (from what’s called the point of elevation) and the height can be calculated.

But, it’s a little bit more complicated than that.
Two main points to consider

• Base: What’s the base? Meaning, from which surface do you measure the height? The main issue is agreeing on what is the base of the mountain.
• Height: What should be seen as the real height – should it be the rock height, or snow cladding on top of it too should be counted?

Usually, the height is taken as that above, what’s called, the sea level. This is the average of the surface of Earth’s water bodies that are used as the base for measuring heights. In the case of Mount Everest even the sea level is a bit of an issue because of gravity (the sea level here is said to be higher).

Don’t we have better technology to help measure a mountain?

We do.

Nowadays we use, what’s called the Global Positioning System or GPS for this. Planes that are fitted with GPS fly over the mountains that get data on the height. That’s then fed into a computer to calculate the height.

But, here again, it’s the sea level that’s an issue – because the gravity can be different from place to place, so sea level (or what’s seen as the base) can differ.

So, what’s the official height now?

China and Nepal have declared the new height as 8,848.86m (29,032 ft).

Some facts about Mount Everest

• It’s 50-60 million years old
• It was formed out of the collision of the Indian and Eurasian tectonic plates
• It’s still growing – rises about half a metre every 100 years

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