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Guyot, the Mountain Under the Sea

Radar scan of guyots on the sea floor

Radar scan of guyots on the sea floor

Ferdinand Magellan, had no idea about the nature of his most famous discovery. In 1521, he reached a large body of water with favorable winds and calm seas. He named it Mar Pacifico (translated, “peaceful seas”). Little did he know that the tranquil ocean had a violent secret underneath its surface.

Being the largest ocean in the world, the Pacific Ocean is the home to countless undersea volcanoes. In addition, the ironically named ocean is a graveyard for a type or dormant volcanoes—ones that once towered above the ocean’s surface before the peaceful seas reclaimed them.

Rising more than 3000 ft from the ocean’s floor and with an estimated 2000 of these volcanoes existing in the Pacific ocean alone, guyots are reminders of how treacherous and inhospitable this “peaceful ocean” was and still is.

Guyots are isolated underwater volcanic mountains. They are distinctive from other submarine mountains and underwater volcanoes (seamounts) because of their flat tops (some are measured up to six miles in diameter) as well as evidence that they were once above sea level. Many are crowned by remnants of drowned coral atolls and coral reefs, which can be dated back to the Cretaceous period (100 million to 65.5 million years ago).

In many respects, this name refers to an underwater mesa, which guyots look like.

Most of those found in the Pacific have summits that lie, 3000 to 6,600 feet below sea level. However, there are some that have summits at 660 feet below sea level. Like many underwater volcanoes, they have a slightly concave shape with slopes of 20-degree gradation.

Sometimes, guyots are labeled seamounts. However, this can be misleading. Seamounts are underwater volcanoes that have never reached the surface of the ocean. Another name associated with guyots is tablemount. In many respects, this name refers to an underwater mesa, which guyots look like.

Origin of Its Name

The name is derived from a Swiss-American geographer and geologist named Arnold Henry Guyot. He lived and died and the 19th century and was most likely unaware of the existence of these tablemounts that now bare his name.

In 1965, Harry Hammond Hess discovered these formations and christened them guyots. A former Navy commander in World War II, Hess used data collected from echo-sounding equipment on the ship he commanded. Upon reviewing these data, he discovered the distinctive shape of the guyots.

The choice of the name, as Hess explained, had little to do with the scientist. Instead, he came up with the name because the shape of the mountains reminded him of Guyot Hall, the flat top geography building on the campus of Princeton University. (Still, Guyot Hall was named after Arnold Henry Guyot).

How Were They Formed?

Hess speculated that guyots were once volcanic islands that were “beheaded" by wave action or rising oceans. Since then, many researchers have theorized that the flat top was created by wave erosion.

Evidence supports Hess. The existence of fossils, such as shallow water coral reef, gives indications to this belief.

Other factors exists as considerations. It is agreed among researchers that guyots were created from volcanic action and they rose from the sea floor. Also, according to a University of Texas in Dallas website, the movement of the ocean floor played a major part in its creation.

“Due to movement of the ocean floor away from oceanic ridges," the UT-Dallas site states, "the sea floor gradually sinks and the flattened guyots are submerged to become undersea flat-topped peaks.”


Like all volcanoes, guyots started as an extrusion of lava breaking through vents or weak spots on the ocean floor. However, the origin of these vents is most likely caused by a major building block of land itself: tectonic plate movements.

Guyot's Relevance to Science

In the Pacific, guyots “move” north along the ocean floor. The evidence of this can be found in the coral fossils usually found in guyots in the North Pacific. Often coral can thrive if the water is shallow, the water temperature is right, or they’re located near tropic zones.

And why are they moving? The answer is simple: they sit atop tectonic plates, just as every continent and island throughout world is, too.

Nobody is sure what killed off the corals that once thrived on them.

The discovery of guyots helped scientists affirms the validity of the tectonic plate movement theory. The fossils and other data from these underwater volcanoes have helped researchers understand the violent, but essential nature of tectonic plate movements. It helped them to understand how it forms lands, and then sink them.

While guyots help to explain these movements, it also creates a mystery of sorts. Nobody is sure what killed off the corals that once thrived on them. While the movement away from the tropic zone on the Pacific Plate is one belief, another hypothesis suggests that they were killed by unusually anoxic (oxygen-depleted) conditions that developed suddenly—a situation possibly related to intense seafloor volcanism in the Pacific during the Cretaceous.

Guyots may not be seen by the casual observer, or be sighted from the surface of the ocean. However, they are more frequent than one expects.

They were born from violence, then shaped by erosion, and, eventually, sunk and moved by plate tectonics. While the Pacific was called a peaceful sea by early European explorers, its reality as a very active and violent place is affirmed by the presents of these flat top submarine mountains.

originally posted at

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This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2018 Dean Traylor


jgshorebird on March 26, 2018:

Thanks Dean, I learned something.

Doris James MizBejabbers from Beautiful South on March 12, 2018:

Very interesting, Dean. Well researched and written article informing us of these sea volcanoes. We knew that they had to exist, but most of us had no idea what they were called.

Larry Conners from Northern Arizona on March 09, 2018:

Very interesting, thank you...Looking back at recent history there is the extraordinary description of the explosion of Krakatoa in 1883...Surely this is now a "seamount" beneath the waves in similarity to the Guyot mountains you have described...Well written and informative...again, thank you.