Biggest Mountain: Mauna Loa
Only about 13,448 ft/4100m of Mauna Loa are above sea level, so it may not seem like a very tall mountain. But, when you start measuring Mauna Loa from its true base on the bottom of the ocean, in the Hawaiian Trough, the total height exceeds that of Everest by over 3/4 of a mile. Mauna Loa is Hawaiian for "Long Mountain", probably because of its long, gently sloping shape. If you want to get really technical, Mauna Kea, a neighbor of Mauna Loa on the same island of Hawaii, is actually the tallest mountain in the world. Mauna Kea is about 350 ft/107m taller than Mauna Loa, but its mass doesn't compare to that of Mauna Loa. Mauna Loa takes up a lot of space because its mass is 9,700 cubic miles/40,000 cu km of mountain.
Mountain Born of Fire
What makes Mauna Loa such a big mountain is the way it was formed. As part of the Hawaiian islands, Mauna Loa is a volcano, just like many others found on the island chain. The volcanoes in the Hawaiian islands are different from the cone-shaped, explosive, "fire breathing" dynamos that most of us think of when volcanoes come to mind. Mauna Loa is one of many shield volcanoesthat make up the Hawaiian Islands. These are volcanoes that, compared to their more violent companions, erupt slowly and quietly. What really distinguishes a shield volcano is its shape - they are usually much wider than they are tall. Shield volcanoes are created when red hot lava oozes out from cracks, or fissures in the earth's crust.
In the case of the Hawaiian islands, the fissures were in the ocean floor. The lava cools as it comes in contact with the ocean water. The newly deposited lava raises the level of the ocean floor just in the area around the fissure. Over time, and many oozing eruptions, a gently sloping sea mount forms. A sea mount is, quite simply, a mountain on the floor of the ocean, only the top doesn't reach above the surface. Over a million years, or more, lava slowly builds up the sea mount until the top reaches above the surface of the sea. When this happens, it finally earns the title of island. What causes volcanoes in the middle of the Pacific Ocean? Find out more about hot spots ->
Photo courtesy of J. Griggs, USGS (1991)
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