How to measure a mountain

If you summit Mount Everest, you’ve accomplished an incredible feat few living beings can claim: climbing the tallest mountain in the world! Right? Well, sure—if you’re measuring the distance from sea level to Everest’s peak. That’s not the only way to measure a mountain. Olivia: There's a lot of ways that mountains can be measured. The most common way is the height above sea level. Other ways you can measure it are from the base of the mountain to the peak, or its prominence, so how far above the surrounding area the peak is. And if you change the system of measurement, the world’s tallest mountains change with it. Olivia: Because there's different ways to measure the height of a mountain, if you change the way that you measure it, so from base to peak, the highest mountain in the world would actually be Mauna Kea. But if you measure from sea level, the highest is Mount Everest. There’s also an argument for Denali in Alaska being the world’s tallest mountain! Whichever measurement system you use, the “tallest mountain” may not stay that way forever. Some mountains are actually growing. Olivia: The height of a mountain can change over time. Two of the main factors to consider here are that the Earth is still moving. The tectonic plates are constantly shifting and moving. So they can continue to push on each other and crumple or slip underneath and push up so that the volume of the rock continues to rise. The other main factor at play is what's happening above the Earth's surface. So over time, erosion can also affect the height as wind and rain change the topography of the mountain above the ground. Mount Everest is one example of this phenomenon. It actually grows a few millimeters every year. Sure, a millimeter or two isn’t much compared to the 29,000-foot height of Everest. But these incremental changes add up. In the past 89,000 years, Everest has grown anywhere from 50 to 165 feet. You know, I was planning on climbing Everest. But I figured I’d let it finish growing first.