How Tall Is Mount Everest REALLY?

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Okay lauren fire. Today we are talking about mount everest. Which is the highest mountain on earth when you measure from sea level and today we're focusing on how that measurement is made weird we start. How about some old timey newsreel resort evidenced bothering his survey of eighteen hundred and forty one estimated his height pinton nine thousand feet back in the nineteenth century. When george everest brit was the surveyor general of india the used trigonometry to measure the height of the mountain like what we learned in middle school points angles and triangles totally. Yeah and incidentally the mountain got its english name from sir george everest but it was actually an indian mathematician. Radin seek dr. Who did most of the work and actually figured out that. This mountain is the highest point on earth. That sounds right for colonialism. Totally yeah okay. So how accurate was this trigonometry. Approach will i put that question to be nagaraj on. He's a geoscientist. One of george everest's successors at the survey of india office which still exists about is now staffed by indians. In fact i was sitting in the same chair. Our team location. Where you're sitting. Because i didn't want to change the room. So he says the trigonometry that his predecessors use throughout the nineteenth and twentieth centuries was surprisingly accurate. I mean the standard height. Everyone now uses for everest that twenty nine thousand twenty nine feet. It dates back to nineteen fifty five. Wow that's pretty impressive. Okay so how did they actually calculate that measurement for mountain like. Walk me through it. It was not easy. They measured it from eight different points throughout langdon distance and everything and computer and took the mean. It was a very difficult matter very heavy machines. Heavy machines called theod delights instruments used to measure angles between visit points on the horizon and vertical planes like a cross between a telescope and compass. You might have seen municipal surveyors using them sort of on a tripod. Oh ya know. I've seen those folks reflective vests and their little tripods them. Yes yeah okay. So but for measuring mountains. They are these big heavy versions. I don't know how many hundreds of kilograms they carried forward to make this measurement it has slowed colored most of the time we didn't know work so the foot that was put on. Who's very difficult nowadays. Nothing much what the chinese are doing. Our a nepalese are doing their hypic instrumentation with the chinese and the nepalese are doing now involves satellites so instead of measuring everest from afar on the horizon with these theod delight contraptions these send a team up to the top of the mountain with a hand held. Gps receiver hey. That sounds like a little easier to me. Maybe but maybe not. Here is d nash mandar. He's gps expert from nepal. Who teaches now at the university of tokyo. It's a very harsh environment. There that very windy and you have all these battery or power problems and like the people who climbed everest. They come steadier probably more than half an hour. I think that's limit for them because they already exhausted. So they've got thirty minutes to connect to multiple satellites because they are solar flares and interference. at altitude. You can't rely on just one reading and they have to measure the thickness of ice and snow underfoot because you wanna reading from the actual rocky mountain right and not the ice and so for that you need a ground penetrating radar so another piece of equipment to haul up the mountain. Yes oh fumbling. With all of that on top of everest. You've got wind. you've got your oxygen depleting. The clock is ticking and that is still the easy. Part monitor. Says because all of that data from the top of everest. It's only half the story. Yeah so you need to know from his point. And that's the biggest problem then need a reference somewhere but we don't have a seat difference in nepal because nepalis a landlocked country. It's land everywhere. The nearest sea level is in india. Sitting knew how high this mountain is you. I need to know how low sea levels and you need a reference point sea level which it turns out varies depending on where you are. Yeah i mean sea levels tricky right. It's not necessarily constant and climate change is really messing with sea level these days. Yeah and has monitor says there isn't even a cenex to so here's how they do it. They measure sea level in india at the bay of bengal at china's yellow sea at many other points hundreds of them to calculate the mean sea level. And then they figure out where sea level would be. if there were a ac- right next to everest o- okay and then you measure from there up to the peak. Oh no no. No you have to account for the shape of the earth bishop of the art okay. It's a live swyto very much. Swyto right the earth is elipsoid. Soil like a oval-shaped watermelon because of the earth rotation makes it kind of bulge slightly at the equator. Plus you have to account for how gravity effect sea level in different places around the world and mountains themselves affect gravity so the earth at sea level this invisible line along the earth's surface. It's actually like kind of lumpy. So you're telling me that we are standing on a lumpy elipsoid. That's exactly what i'm telling you. So sea level is actually not level at all and the next step. You got map. Those lumps essentially variations in the earth's gravitational force. And then you get the gop lead a. I'm sorry a joy d- yeah so the geo is the shape of the earth at sea level taking into account gravity and the planet's rotation. And now you follow that joy to appoint directly under everest. And that's what you use as a reference point for the mountains height okay so after all that sea levels gravity you finally get a reference point you take that you compare it to your. Gps measurement from the top of the mountain and you get everest height. Well not so fast. Because there's also these pesky plate tectonics oh my lord. This is harder than actually climbing everest. I'll say i'll say right now. Yeah yeah so. The mountains peak is variable to like and i'm not just talking ice and snow like the rock is actually moving. Sri daddy jaw is an engineer and expert on himalayan plate. Tectonics i have been field kinney. My philosophist been between behaviors and then ever asked is on the edge of two plates. The eurasian plate and the indian plate and j has measured how the indian plate is slipping underneath the eurasian plate and how that is pushing everest skyward measurements for last you. One point four million yearning threes in high. Like a few hundred years. We can only do bring Comes johnny has concluded that everest is gaining roughly a centimeter every ten years. So that's about a foot every three hundred years other scientists say that's far too conservative that the growth could be three times even four times that much but i mean however fast everest is rising. Things can happen very quickly to change that like earthquakes hung or at least they have in the past. So professor john day studied a nineteen thirty four quake that calculated took about sixty centimeters off the mountains height. So that's at least six hundred years of growth a raced in an instant and there's been another quake since in two thousand fifteen and we're not sure how that affected the height because there haven't been any definitive measurements since then so i'm guessing you're about to tell me it's time to remeasure mount everest. It is indeed so last year nepal sent up a team of scientists to do just that and this year with the climbing. Season cancelled for kelvin. China did the same and both countries have been analyzing their findings and their due to release the measurements pretty much any day. Now this is very exciting yes especially because most of the surveys of everest has been done by foreigners british colonial rulers. There was an american survey was an italian one and professor monitor. The gps expert from nepal says yes. He's motivated by science and the search for truth and all of this but you know also in part by the previous. Why don't we measure our own mountain and so nepal dead and we are waiting for those findings now. It may turn out to be taller shorter. Whatever the point though is that it's changing and that's what scientists say matters to them. Here's garage on the former survey of india guy again. I feel the joint will here. Shedding the knowledge will use the society beget understanding. What is there a big deal if you come and see okay. I'm announcing mall. Dividends did this much healthy that who cares you know because she missed the learning that teaching how people understand how do people perceive almost put in what model you used. Then be be happy if he's happy about what this tells us about. The earth overall the technology. They're fine tuning on. Everest has all these practical applications from agriculture to defense and scientists say if their research gets more eyeballs because it involves the tallest mountain in the world. Hey that's a great

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