Editing Guyot

{{Other uses}}
{{Short description|Flat-topped underwater mountain}}
[[File:Bear Seamount guyot.jpg|thumb|right|350px|The [[Bear Seamount]] (left), a guyot in the northern [[Atlantic Ocean]]]]

In [[marine geology]], a '''guyot''' ({{IPAc-en|ˈ|ɡ|iː|.|oʊ|,_|ɡ|iː|ˈ|oʊ}}),<ref>{{cite Merriam-Webster|guyot}}</ref><ref>{{cite Dictionary.com|guyot}}</ref> also called a '''tablemount''', is an isolated underwater volcanic mountain ([[seamount]]) with a flat top more than {{cvt|200|m|ft}} below the surface of the sea.<ref name="EBchecked"/> The diameters of these flat summits can exceed {{cvt|10|km|mi|sigfig=1}}.<ref name="EBchecked">{{cite encyclopedia |url=http://www.britannica.com/EBchecked/topic/250080/guyot |title=Guyot |encyclopedia=[[Encyclopædia Britannica]] |year=2010 |access-date=2010-01-14}}</ref> 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 [[table (landform)|tables]] (such as [[mesa]]s) 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]].<ref name="ShortHistory">{{cite book |last=Bryson |first=Bill |title=A Short History of Nearly Everything |location=New York |publisher= Broadway |year=2003 |page=178 |isbn=076790818X}}</ref> His data showed that some undersea mountains had flat tops. Hess called these undersea mountains "guyots", after the Department of Geosciences building at Princeton.<ref name="JeaPg">{{cite book |last=Bryson |first=Bill |date=2004 |title=A Short History of Nearly Everything |publisher= Broadway Books |isbn=076790818X}}</ref> 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]].<ref name="ShortHistory" />

==Formation==
Guyots show evidence of having once been above the surface, with gradual [[subsidence]] through stages from fringed [[reef]]ed mountain, [[coral]] [[atoll]], and finally a flat-topped submerged mountain.<ref name="EBchecked" /> Seamounts are made by extrusion of lavas piped upward in stages from sources within the Earth's mantle, usually [[Hotspot (geology)|hotspots]], to vents on the seafloor.  The volcanism invariably ceases after a time, and other processes dominate.  When an undersea volcano grows high enough to be near or breach the ocean surface, wave action or coral reef growth tend to create a flat-topped edifice.  However, all ocean crust and guyots form from hot magma or rock, which cools over time.  As the lithosphere that the future guyot rides on slowly cools, it becomes denser and sinks lower into Earth's mantle, through the process of [[isostasy]].  In addition, the erosive effects of waves and currents are found mostly near the surface: the tops of guyots generally lie below this higher-erosion zone.

This is the same process that gives rise to higher seafloor topography at oceanic ridges, such as the [[Mid-Atlantic Ridge]] in the Atlantic Ocean, and deeper ocean at [[abyssal plain]]s and [[oceanic trench]]es, such as the [[Mariana Trench]]. Thus, the island or shoal that will eventually become a guyot slowly [[Subsidence|subsides]] over millions of years.  In the right climatic regions, coral growth can sometimes keep pace with the subsidence, resulting in coral atoll formation, but eventually the corals dip too deep to grow and the island becomes a guyot.  The greater the amount of time that passes, the deeper the guyots become.<ref name="P7qOd">{{cite web|url=http://www.utdallas.edu/~pujana/oceans/guyot.html|title=Guyot|website=www.utdallas.edu|access-date=15 January 2019}}</ref>

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.<ref name="IvUIG">Seamounts are made by extrusion of lavas piped upward in stages from sources within the Earth's mantle to vents on the seafloor. 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 part of the Earth's mantle.</ref> There are thought to be up to an estimated 50,000 seamounts in the Pacific basin.<ref name="SeamountCount">{{cite journal | title=Pacific seamount volcanism in space and time | author=Hillier, J. K. | journal=Geophysical Journal International | year=2007 | volume=168 | issue=2 | pages=877–889 | doi=10.1111/j.1365-246X.2006.03250.x| bibcode=2007GeoJI.168..877H | doi-access=free| url=https://repository.lboro.ac.uk/articles/journal_contribution/Pacific_seamount_volcanism_in_space_and_time/9481115/1/files/17106296.pdf }}</ref> 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 {{convert|900|m|ft|abbr=on}} tall.<ref name="McGrawGuyot">{{Cite journal | url=http://www.accessscience.com/content/seamount-and-guyot/611100 | title=Seamount and guyot | journal=Access Science | access-date=2 February 2016| doi=10.1036/1097-8542.611100| url-access=subscription }}</ref>  One guyot in particular, the [[Great Meteor Seamount|Great Meteor Tablemount]] in the Northeast Atlantic Ocean, stands at more than {{convert|4000|m|ft|abbr=on}} high, with a diameter of {{convert|110|km|mi|abbr=on}}.<ref name="2aXWF">{{cite web|url=http://www.britannica.com/eb/topic-243463/Great-Meteor-Tablemount|title=Great Meteor Tablemount (volcanic mountain, Atlantic Ocean) – Britannica Online Encyclopedia<!-- Bot generated title -->|website=britannica.com|access-date=15 January 2019}}</ref>  However, there are many undersea mounts that can range from just less than {{convert|90|m|ft|abbr=on}} to around {{convert|900|m|ft|abbr=on}}.<ref name="McGrawGuyot" />  Very large oceanic volcanic constructions, hundreds of kilometres across, are called [[oceanic plateau]]s.<ref name="V63VR">{{cite web|url=http://www.answers.com/topic/seamount-and-guyot?cat=technology|title=Answers - The Most Trusted Place for Answering Life's Questions|website=Answers.com|access-date=15 January 2019}}</ref> Guyots have a mean area of {{convert|3,313|sqkm|sqmi|abbr=on}}, which is much larger than typical seamounts, which have a mean area of {{convert|790|sqkm|sqmi|abbr=on}}.<ref name="QsHHK">{{Cite journal | doi=10.1016/j.margeo.2014.01.011|title = Geomorphology of the oceans| journal=Marine Geology| volume=352| pages=4–24|year = 2014|last1 = Harris|first1 = P.T.| last2=Macmillan-Lawler| first2=M.| last3=Rupp| first3=J.| last4=Baker| first4=E.K.|bibcode = 2014MGeol.352....4H}}</ref>

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]].{{Citation needed|date=July 2022}} 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 [[seamount]]s.

==See also==
{{portal|Oceans}}
* [[Evolution of Hawaiian volcanoes]]
* [[Kodiak–Bowie Seamount chain]]
* [[New England Seamounts]]

==References==
{{reflist}}

==External links==
* [https://oceanservice.noaa.gov/facts/guyot.html NOAA: What is a guyot?]

{{physical oceanography|expanded=other}}

{{Authority control}}

[[Category:Guyots| ]]
[[Category:Physical oceanography]]
[[Category:Plate tectonics]]
[[Category:Seamounts]]