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Home > Ocean > Oceanography > Sea Mounts

Geography of the Sea: Sea Mounts

Seamounts are submarine elevations, or underwater mountains. They are at least 700 meters in height and were created by volcanic activity. They are mountains, just like we see on land, but the tops of them don’t break the surface of the ocean. Many of the sea mounts throughout the world have their peaks far below the ocean surface, often over a mile down. For many years, people thought that the bottom of the sea was a flat plain. Imagine the surprise when surveyors discovered there were entire mountains under the sea! Some of the sea mounts were found to rise up over a mile from the ocean floor. There is a newly formed, recently discovered sea mount south of the big island of Hawaii where a new volcano is building up from the ocean floor. Named Loihi, the sea mount will one day become a new island, part of the Hawaiian Island chain, when it breaks the surface of the sea. Right now, the summit of Loihi is 3,178 feet below sea level. Scientists expect it will take approximately 10,000 to 40,000 years for Loihi to lose the title of “sea mount” and become an island.

map of mid-atlantic ridgeUnder sea mountains don’t always occur singly, in isolation. Entire mountain ranges have been discovered on the sea floor. Equipped with the latest in sonar equipment for taking soundings of the sea floor, oceanographers in the 1950s conducted the most thorough investigation of the ocean floor to date. The sonar maps they generated, which profiled the sea bed, showed incredibly high mountains, in long chains, some of them extending unbroken for thousands of miles. In the years since the first discovery of undersea mounts, the Mid-Atlantic Ridge has been measured and mapped to reveal an underwater mountain range that is over 46,000 miles long, winding from the Arctic Ocean, around Africa, Asia and Australia, to North America. Compare that to the longest mountain range on land – the Andes Mountains in South America are only 4,700 miles long. The Mid-Atlantic Ridge is almost 10 times longer than the Andes!

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