thumb|right|350px|The [[Bear Seamount (left), a guyot in the northern Atlantic Ocean]]

In marine geology, a guyot (), also called a tablemount, is an isolated underwater volcanic mountain (seamount) with a flat top more than below the surface of the sea. Guyots are most commonly found in the Pacific Ocean, but they have been identified in all the oceans except the Arctic Ocean. They are analogous to tables (such as mesas) on land.

History

Guyots were first recognized in 1945 by Harry Hammond Hess, who collected data using echo-sounding equipment on a ship he commanded during World War II. His data showed that some undersea mountains had flat tops. Hess called these undersea mountains "guyots", after the Department of Geosciences building at Princeton. Hess postulated they were once volcanic islands that were beheaded by wave action, yet they are now deep under sea level. This idea was used to help bolster the theory of plate tectonics.

Seamounts provide data on movements of tectonic plates on which they ride, and on the rheology of the underlying lithosphere. The trend of a seamount chain traces the direction of motion of the lithospheric plate over a more or less fixed heat source in the underlying asthenosphere, the part of the Earth's mantle beneath the lithosphere. There are thought to be up to an estimated 50,000 seamounts in the Pacific basin. The Hawaiian–Emperor seamount chain is an excellent example of an entire volcanic chain undergoing this process, from active volcanism, to coral reef growth, to atoll formation, to subsidence of the islands and becoming guyots.

Characteristics

The steepness gradient of most guyots is about 20 degrees. To technically be considered a guyot or tablemount, they must stand at least tall. One guyot in particular, the Great Meteor Tablemount in the Northeast Atlantic Ocean, stands at more than high, with a diameter of . However, there are many undersea mounts that can range from just less than to around . Guyots have a mean area of , which is much larger than typical seamounts, which have a mean area of .

There are 283 known guyots in the world's oceans, with the North Pacific having 119, the South Pacific 77, the South Atlantic 43, the Indian Ocean 28, the North Atlantic eight, the Southern Ocean six, and the Mediterranean Sea two; there are none known in the Arctic Ocean, though one is found along the Fram Strait off northeastern Greenland. Guyots are also associated with specific lifeforms and varying amounts of organic matter. Local increases in chlorophyll a, enhanced carbon incorporation rates and changes in phytoplankton species composition are associated with guyots and other seamounts.

See also

  • Evolution of Hawaiian volcanoes
  • Kodiak–Bowie Seamount chain
  • New England Seamounts

References

  • NOAA: What is a guyot?