In this way the rugged volcanic landscape of a mid-ocean ridge is created along the plate boundary. Seafloor spreading. Below the ocean floor, there are a few small deeper areas called ocean trenches. Features rising up from the ocean floor include seamounts, volcanic islands and the mid-oceanic ridges and rises. The oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium.
All the way down At depths below about 4, m 2. It is essentially flat because the rugged topography of the underlying basaltic crust is draped in sediment that can be up to five km three mi thick. A long crack in the oceanic crust forms at a mid ocean ridge. Molten material rises and erupts along the ridge. The youngest crust of the earth can be found near the seafloor spread in the centers or mid-ocean ridges.
But a new study shows that part of the eastern Mediterranean Sea may contain the oldest known oceanic crust. These tectonic plates rest upon the convecting mantle, which causes them to move.
These are driven by the heat produced by the natural decay of radioactive elements in the Earth. The crust here has been generated through igneous processes, which explains why the crust has much more incompatible elements than the mantle.
The crust is made up of the continents and the ocean floor. The crust is thickest under high mountains and thinnest beneath the ocean. The lithosphere is thinnest at mid-ocean ridges, where tectonic plates are tearing apart from each other. The theory of plate tectonics revolutionized the earth sciences by explaining how the movement of geologic plates causes mountain building, volcanoes, and earthquakes. Join our community of educators and receive the latest information on National Geographic's resources for you and your students.
Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Seafloor spreading is a geologic process in which tectonic plate s—large slabs of Earth's lithosphere —split apart from each other.
Seafloor spreading and other tectonic activity processes are the result of mantle convection. Convection current s carry heat from the lower mantle and core to the lithosphere. Seafloor spreading occurs at divergent plate boundaries.
The less-dense material rises, often forming a mountain or elevated area of the seafloor. Eventually, the crust cracks. Hot magma fueled by mantle convection bubbles up to fill these fracture s and spills onto the crust. This bubbled-up magma is cooled by frigid seawater to form igneous rock. Seafloor spreading occurs along mid-ocean ridge s—large mountain range s rising from the ocean floor.
The East Pacific Rise is a mid-ocean ridge that runs through the eastern Pacific Ocean and separates the Pacific plate from the North American plate, the Cocos plate, the Nazca plate, and the Antarctic plate. The Southeast Indian Ridge marks where the southern Indo-Australian plate forms a divergent boundary with the Antarctic plate. Seafloor spreading is not consistent at all mid-ocean ridges.
Slowly spreading ridges are the sites of tall, narrow underwater cliff s and mountains. Rapidly spreading ridges have a much more gentle slopes. The Mid-Atlantic Ridge, for instance, is a slow spreading center.
It spreads centimeters. The East Pacific Rise, on the other hand, is a fast spreading center. It spreads about centimeters inches every year. There is not an ocean trench at the East Pacific Rise, because the seafloor spreading is too rapid for one to develop! The newest, thinnest crust on Earth is located near the center of mid-ocean ridge—the actual site of seafloor spreading. The age, density, and thickness of oceanic crust increases with distance from the mid-ocean ridge.
Seafloor spreading was proposed by an American geophysicist, Harry H. Hess in By the use of the sonar, Hess was able to map the ocean floor and discovered the mid-Atlantic ridge mid-ocean ridge. He also found out that the temperature near to the mid-Atlantic ridge was warmer than the surface away from it. He believed that the high temperature was due to the magma that leaked out from the ridge. The mid-ocean ridge is the region where new oceanic crust is created. The oceanic crust is composed of rocks that move away from the ridge as new crust is being formed.
The formation of the new crust is due to the rising of the molten material magma from the mantle by convection current. When the molten magma reaches the oceanic crust, it cools and pushes away the existing rocks from the ridge equally in both directions. A younger oceanic crust is then formed, causing the spread of the ocean floor. The new rock is dense but not as dense as the old rock that moves away from the ridge. As the rock moves, further, it becomes colder and denser until it reaches an ocean trench or continues spreading.
It is believed that the successive movement of the rocks from the ridge progressively increases the ocean depth and have greater depths in the ocean trenches. Seafloor spreading leads to the renewal of the ocean floor in every million years, a period of time for building a mid-ocean ridge, moving away across the ocean and subduction into a trench. The highly dense oceanic crust that is formed after a progressive spreading is destined to two possible occurrences.
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