The tallest mountain in the world might surprise you.

As the first light of dawn illuminated Pokhara, I gestured toward the massive shadow looming over the city's myriad twinkling lights and inquired about the mountain’s name. "That’s not a mountain; it’s a hill," replied Rabina, my guide from Nepal, regarding the 8,500-foot Odane Hill. "Really?" I questioned. To be considered a mountain, says Rakesh Shahi, owner of Mystik Mountains Adventures in Kathmandu, the peak needs to maintain year-round snow cover, typically occurring above 18,000 feet. I had to concede; the massive profile of Annapurna South, with its snow-covered summit nearly reaching 24,000 feet, made Odane seem small. Yet, even Annapurna is outclassed by Everest, which holds the title of the world's tallest mountain. Or does it? The answer hinges on how you look at it.

What’s the method for measuring mountains?

When measuring from sea level, Everest reigns supreme at 29,032 feet and is still growing. The collision of the Indian and Eurasian tectonic plates that form the Himalayas is ongoing, explains Lynn Moorman, a professor of Earth and Environmental Sciences at Mount Royal University in Calgary, slowly pushing up the continental land. "They [tectonic plates] shift at a rate comparable to how fast your fingernails grow." However, as Everest gains height, it is also being eroded by natural elements, earthquakes, and avalanches.

Using an alternative measurement method, the U.S. could claim the title of the world's tallest mountain. Mauna Kea, a dormant volcano in Hawai’i, stands at 13,796 feet above sea level. Yet, when factoring in the additional 19,700 feet that the volcano extends below sea level, Mauna Kea's total height reaches an impressive 33,500 feet, making it far taller than Everest.

Alternatively, with a different method of measurement, South America could claim the title of the tallest mountain in the world. When measuring from the center of the Earth, Chimborazo, situated near the equator at 20,564 feet in Ecuador, takes the crown. This is due to the Earth being more elliptical than spherical. Picture gently squeezing a soft ball at its poles; it bulges outward at the equator. As Lynn Moorman explains, "The distance from one point on the equator to its opposite is longer than from pole to pole." Thus, in this perspective, Chimborazo is farther from the Earth's center and taller than Everest.

What methods were used to measure Everest?

Naturally, the tools for measurement have evolved over the years, impacting the official heights recorded. In the 19th century, the Survey of India employed trigonometrical calculations to determine Peak (XV), later named after Sir George Everest, at 29,002 feet. However, a survey in 1954 revised this figure, adding 26 feet. The latest measurements from Nepal in 2019 and China in 2020 further increased the height by four feet, bringing the current official total to approximately 29,032 feet.

Interestingly, the Appalachian Mountains, which formed between 300 and 500 million years ago, may have once rivaled or exceeded Everest in height. Stretching 2,000 miles from Canada to Alabama, this range has had far more time for natural forces to erode its peaks. Who knows? In another 100 million years, Everest might just be a modest hill.