Water And Oceanography

Lurking under the Sea Guyots

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The great Portuguese explorer, Ferdinand Magellan, had no idea what he was sailing on. 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 sea had a violent secret underneath its surface.

Being the largest ocean in the world, the Pacific Ocean is the home to countless undersea volcanoes. And many of them are huge. Also, it is a place where volcanic islands can be easily swallowed up by the waves. These particular volcanoes are better known as guyots.

Rising more than 3000 ft from the ocean’s floor and estimated be 2000 in the Pacific, 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 6 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).  

Most of those found in the Pacific have summits that lie 3, 3000 to 6,600 feet below sea level. However, there are some that have summits at 660 feet below sea level. Like many underwater volcanos 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 tablemounts. In many respect 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.

Guyots were first discovered and named by Harry Hammond Hess in 1965. A former Navy commander in World War II, Hess used data collected from echo-sounding equipment on the ship he had commanded. Upon reviewing these data, he discovered the distinctive shape of the Guyot.

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. 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 (utdallas.edu, 2012).  

Other factors have been considered. It is agreed that guyots were created from volcanic action and it 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.

“Due to movement of the ocean flooraway 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.  

Guyots Importance to Science

In the Pacific, guyots travel along the ocean floor, moving north.  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.

The discovery of guyots helped scientists affirms the validity of the tectonic plate movement theory. The fossils and other data from these underwater volcanos have helped researchers understand the violent, but essential nature of tectonic plate movements. It has helped 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 really 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 (Encyclopaedia Britannica Online, 2012).

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, and 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. 

More about this author: Dean Traylor

From Around the Web

  • InfoBoxCallToAction ActionArrowhttp://en.wikipedia.org/wiki/Guyot
  • InfoBoxCallToAction ActionArrowhttp://www.utdallas.edu/~pujana/oceans/guyot.html
  • InfoBoxCallToAction ActionArrowhttp://www.britannica.com/EBchecked/topic/250080/guyot