Seafloor spreading

Seafloor dispersing is a geologic procedure in which tectonic plates—large slabs that Earth"s lithosphere—split apart from every other.

You are watching: What happens to old oceanic crust as new molten material rises from the mantle


Seafloor dispersing is a geologic process in which tectonic plates—large slabs that Earth"s lithosphere—split personally from each other.
Seafloor spreading and also other tectonic activityprocesses room the an outcome of mantle convection. Mantle convection is the slow, churning activity of Earth’s mantle. Convection currents lug heat indigenous the reduced mantle and core to the lithosphere. Convection currents likewise “recycle” lithospheric materials earlier to the mantle.
Seafloor spreading occurs in ~ divergent plate boundaries. Together tectonic plates gradually move away from every other, heat from the mantle’s convection currents renders the crust an ext plastic and also less dense. The less-dense product rises, often forming a hill or elevated area the the seafloor.
Eventually, the crust cracks. Hot magma fueled by mantle convection bubbles approximately fill these fractures and also spills onto the crust. This bubbled-up magma is cooled by frigid seawater to form igneous rock. This absent (basalt) becomes a new part the Earth’s crust.
Seafloor dispersing occurs along mid-ocean ridges—large mountain ranges climbing from the ocean floor. The Mid-Atlantic Ridge, because that instance, off the north American plate from the Eurasian plate, and also the south American plate native the afri plate. The eastern Pacific rise is a mid-ocean ridge the runs with the eastern Pacific Ocean and separates the Pacific plate indigenous the north American plate, the Cocos plate, the Nazca plate, and the Antarctic plate. The south east Indian Ridge marks whereby the southern Indo-Australian plate forms a divergent boundary v the Antarctic plate.
Seafloor dispersing is not consistent at all mid-ocean ridges. Gradually spreading ridges are the website of tall, small underwater cliffs and mountains. Swiftly spreading ridges have actually a much more gentle slopes.
The Mid-Atlantic Ridge, because that instance, is a slow spreading center. It spreads 2-5 centimeters (.8-2 inches) every year and forms an ocean trench about the size of the grand Canyon. The east Pacific Rise, top top the other hand, is a fast spreading center. That spreads around 6-16 centimeters (3-6 inches) every year. There is no an ocean trench in ~ the east Pacific Rise, since the seafloor spreading is too rapid for one to develop!
The newest, thinnest tardy on earth is located near the facility of mid-ocean ridge—the actual website of seafloor spreading. The age, density, and thickness of oceanic crust boosts with street from the mid-ocean ridge.
The magnetism the mid-ocean ridges assisted scientists very first identify the procedure of seafloor dispersing in the at an early stage 20th century. Basalt, the once-molten rock that makes up most brand-new oceanic crust, is a relatively magnetic substance, and scientists started using magnetometers to measure up the magnetism the the ocean floor in the 1950s. What they discovered was that the magnetism the the ocean floor roughly mid-ocean ridges was separated into matching “stripes” top top either side of the ridge. The specific magnetism the basalt rock is established by the Earth’s magnetic ar when the magma is cooling.
Scientists determined that the same procedure formed the perfectly symmetrical stripes on both side of a mid-ocean ridge. The continual procedure of seafloor dispersing separated the stripes in an orderly pattern.
Oceanic crust progressively moves away from mid-ocean ridges and also sites of seafloor spreading. Together it moves, it i do not care cooler, more dense, and much more thick. Eventually, larger oceanic tardy encounters a tectonic boundary through continental crust.
In part cases, oceanic tardy encounters an active plate margin. An energetic plate margin is one actual bowl boundary, wherein oceanic crust and continental tardy crash right into each other. Energetic plate spare are regularly the site of earthquakes and volcanoes. Oceanic crust developed by seafloor dispersing in the east Pacific Rise, because that instance, might become part of the Ring the Fire, the horseshoe-shaped pattern of volcanoes and also earthquake zones roughly the Pacific ocean basin.
In other cases, oceanic late encounters a passive plate margin. Passive margins room not bowl boundaries, but areas where a single tectonic key transitions from oceanic lithosphere to continent lithosphere. Passive margins space not web page of faults or subduction zones. Thick layers that sediment overlay the transitional tardy of a passive margin. The oceanic crust of the Mid-Atlantic Ridge, because that instance, will certainly either become part of the passive margin on the north American plate (on the east shore of north America) or the Eurasian plate (on the west coast of Europe).
New geographic features can be developed through seafloor spreading. The Red Sea, because that example, was developed as the afri plate and the Arabian plate tore away from every other. Today, only the Sinai Peninsula connects the Middle east (Asia) through North Africa. Eventually, geologists predict, seafloor dispersing will totally separate the two continents—and join the Red and Mediterranean Seas.
Mid-ocean ridges and also seafloor spreading can additionally influence sea levels. As oceanic crust moves far from the shallow mid-ocean ridges, that cools and also sinks as it becomes more dense. This increases the volume that the s basin and also decreases the sea level. For instance, a mid-ocean ridge device in Panthalassa—an old ocean that surrounding the supercontinent Pangaea—contributed come shallower seas and greater sea levels in the Paleozoic era. Panthalassa was an early form of the Pacific Ocean, which today experiences less seafloor spreading and also has a much less considerable mid-ocean ridge system. This helps explain why sea levels have fallen significantly over the past 80 million years.
Seafloor spreading disproves one early component of the concept of continental drift. Supporters of continental drift initially theorized the the continents relocated (drifted) with unmoving oceans. Seafloor spreading proves that the s itself is a website of tectonic activity.
Seafloor spreading is just one part of plate tectonics. Subduction is another. Subduction happens where tectonic plates crash into each other instead of spreading apart. At subduction zones, the sheet of the denser plate subducts, or slides, beneath the less-dense one. The denser lithospheric material then melts back into the Earth"s mantle.
Seafloor spreading creates brand-new crust. Subduction destroys old crust. The two forces about balance each other, therefore the shape and also diameter the the earth remain constant.

Earth"s newest late is created at website of seafloor spreading—red sites on this map.

Map courtesy NOAA


Seafloor spreading and also rift valleys are common features at “triple junctions.” Triple junctions space the intersection of three divergent key boundaries. The triple junction is the main point where three cracks (boundaries) break-up off at about 120° angle from every other.
In the Afar Triple Junction, the African, Somali, and Arabian bowl are dividing from every other. The great Rift Valley and also Red Sea (a major site the seafloor spreading) are the an outcome of bowl tectonics in the Afar Triple Junction.

area where 2 or more tectonic bowl are relocating away from each other. Likewise called one extensional boundary.


the sudden shaking that Earth"s crust caused by the relax of energy along error lines or from volcanic activity.


mid-ocean ridge whereby seafloor dispersing is occuring at more than 100 millimeter (4 inches) a year.


scientific instrument offered to measure the presence, strength, and also direction of Earth"s magnetic field.


slow activity of Earth"s hard mantle resulted in by convection currents transferring warmth from the internal of the planet to the surface.

lithospheric an ar where oceanic tardy transitions to continental crust there is no faults or subduction zones.


base level because that measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.


movement of tectonic plates bring about geologic task such as volcanic eruptions and also earthquakes.


massive slab of hard rock consisted of of Earth"s lithosphere (crust and upper mantle). Likewise called lithospheric plate.

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an opening in the Earth"s crust, with which lava, ash, and gases erupt, and additionally the cone constructed by eruptions.


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