Ever since Apollo 8 showed us a big blue marble rising above the lunar horizon, people have wanted to know all they could about Earth. Today, scientists know a lot more, but not every details makes it into the public ear. This means what we hear isn’t exactly what they’re trying to convey, but it’s close enough that everyone misunderstands each other perfectly.
Speaking of Mt. Everest—it’s not actually the tallest mountain on Earth. Mauna Loa (which translates to “Long Mountain“) is part of the island of Hawaii. It doesn’t look anywhere near as tall as Everest, but that’s only because it is mostly submerged, and all we can see are their summits.
From summit to base, Mauna Kea measures a little over 10.2 kilometers (6.3 mi), which makes it much taller than Everest. In addition, Mauna Loa brings more weight to the game and that makes all the difference. About half of the Island of Hawaii is part of Mauna Loa.
Volcanoes like Mauna Loa are called “shields” because they are wide and have a low profile like, well, a shield. They form when a volcano erupts lava at a very high rate. Molten rock pours out of Mauna Loa so quickly, it has little time to do anything other than pile up and cool. Mauna Loa has had frequent eruptions for up to a million years and is still very active.
You get a lot of volcano with a million years’ worth of output: 80,000 cubic kilometers (50,000 cubic mi) in fact. The Pacific Ocean is about 5 kilometers (3 mi) deep at the spot where Mauna Loa first started erupting. The big lava pile eventually pushed the mountain another 4.17 kilometers (2.59 mi) above sea level.
But there’s more. Mauna Loa’s massive weight has depressed the sea floor down another 8 kilometers (5 mi). Taking that into consideration, this volcano is over 17 kilometers (10.5 mi) high, making it by far the tallest mountain on Earth.