On the other side of the plain is usually an oceanic trench, where the seafloor dramatically plummets. The plains are almost entirely flat, with very little variation in their elevation. Depth variation is usually only as much as 10 to centimeters per kilometer of horizontal distance. This means that the slope is not only minimal, but dependent on the expanse of the plain itself.
Abyssal plains can range as far as thousands of kilometers, forming huge plateaus beneath the sea. The seafloor spreads when the lower oceanic crust melts, due to activity within the Earth's mantle. When the plates spread, it allows magma to rise from underneath, where it begins to cool and form a new oceanic crust. This crust will continue to spread as the process repeats over time. Abyssal plains exist as a sort of blanket, smoothing the rough crust over time on oceanic ridges and sea beds.
Sediments, silt and natural debris builds up on the ocean floor. These sediments can be anything from clay and volcanic ash; to sand, gravel or silt, as well as organic matter like plant matter, parts of decaying organisms, or microscopic organic matter. Unnatural particles play a part as well, as pollutants such as chemical precipitates or debris from nearby continental coastlines can add to the natural silt.
As these sediments build up, they create flat or slightly sloped plains which rise from the bottom as they cover over the natural ocean floor. The average thickness of these plains is roughly 1 kilometer. Because they are made of such small particles and tiny debris, this shows how abyssal plains take a significant amount of time to build up.
Abyssal plains are found on the ocean floor, usually off the coast of major continental coastlines. However, there are significantly more abyssal plains in the Atlantic Ocean than in any other. Some can be found within the Indian Ocean , but very few exist in areas within the Pacific Ocean.
The rest of the Oceanic crust is made up of valleys, rifts, hills trenches and underwater mountain ranges. The largest Abyssal plain on Earth is called the Sohm plain. This is a preview of subscription content, log in to check access. Becker, J. Marine Geodesy , 32 , — CrossRef Google Scholar. Harris, P.
Geomorphology of the oceans. Marine Geology , , 4— Heezen, B. World ocean floor panorama. In full color, painted by H. Google Scholar. IHO, A seamount is an underwater mountain formed by volcanic activity. Seamounts — undersea mountains formed by volcanic activity — were once thought to be little more than hazards to submarine navigation. What are Seamounts? Seamounts are underwater mountains that rise hundreds or thousands of feet from the seafloor.
They are generally extinct volcanoes that, while active, created piles of lava that sometimes break the ocean surface. Typically, they are cone shaped, but often have other prominent features such as craters and linear ridges and some, called guyots, have large, flat summits. Seamounts have a big effect on the deep-sea environment. They accelerate ocean currents, generate waves, increase upwelling, and amplify tides.
These changes improve the food and nutrient supply for filter feeders while removing waste and reducing sediment build-up. Marine mammals, sharks, tuna, and cephalopods all gather over seamounts to feed, as well as some species of seabirds when the seamounts are shallow. The volcanic rocks on the slopes of seamounts contain large populations of suspension feeders, especially corals.
Before the eruption, Axial Seamount had last spilled lava over the seafloor in —an eruption that scientists discovered completely by accident. Seamounts are volcanic in origin, and if during their geological life, they never reach the surface, they retain their conical shape, some having craters on top and others without. But seamounts that erupt and grow to reach the surface have their conical tops flattened as a result of both erosion and coral reef growth.
A guyot, or seamount, is an undersea mountain. Seamounts are formed by volcanic activity and can be taller than 10, feet. They can be isolated or part of large mountain chains. The New England Seamount contains more than 30 peaks that stretch miles from the coast of New England. How are Guyots Formed? Volcanic activity forms a guyot under the ocean. Vents in the seafloor over an area of volcanic activity may produce lava periodically to grow a guyot or other seamount formation.
The largest three guyots are all in the North Pacific: the Kuko Guyot estimated 24, km2 , Suiko Guyot estimated 20, km2 and the Pallada Guyot estimated 13, km2. These data indicate that guyots originate as volcanic islands at the shallow crests of mid-oceanic ridges and rises.
During and immediately after their formation, the islands are truncated by wave erosion. Guyots of the western Pacific Ocean are capped by drowned coral atolls and coral reefs. Seafloor spreading occurs at divergent plate boundaries. The less-dense material rises, often forming a mountain or elevated area of the seafloor.
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