Seafloor spreading

Seafloor spreading is a geologic procedure in i beg your pardon tectonic plates—large slabs the Earth"s lithosphere—split personally from every other.

You are watching: Part of molten rock at mid ocean ridges

Seafloor dispersing is a geologic process in i m sorry tectonic plates—large slabs of Earth"s lithosphere—split apart from each other.
Seafloor spreading and also other tectonic activityprocesses room the result of mantle convection. Mantle convection is the slow, churning activity of Earth’s mantle. Convection currents lug heat indigenous the lower mantle and core come the lithosphere. Convection currents additionally “recycle” lithospheric materials ago to the mantle.
Seafloor spreading occurs at divergent key boundaries. Together tectonic plates gradually move away from each other, warmth from the mantle’s convection currents makes the crust an ext plastic and less dense. The less-dense material rises, often creating a hill or elevated area that the seafloor.
Eventually, the tardy cracks. Hot magma fueled by mantle convection bubbles as much as fill this fractures and spills ~ above the crust. This bubbled-up magma is cooled by frigid seawater to kind igneous rock. This rock (basalt) becomes a brand-new part that Earth’s crust.
Seafloor dispersing occurs along mid-ocean ridges—large mountain ranges increasing from the ocean floor. The Mid-Atlantic Ridge, for instance, the end the phibìc American plate native the Eurasian plate, and also the southern American plate native the afri plate. The east Pacific rise is a mid-ocean ridge that runs with the east Pacific Ocean and also separates the Pacific plate from the phibìc American plate, the Cocos plate, the Nazca plate, and also the Antarctic plate. The south-east Indian Ridge marks where the southern Indo-Australian plate forms a divergent boundary through the Antarctic plate.
Seafloor dispersing is not regular at every mid-ocean ridges. Slowly spreading ridges are the website of tall, small underwater cliffs and mountains. Rapidly spreading ridges have a much an ext gentle slopes.
The Mid-Atlantic Ridge, for instance, is a sluggish spreading center. It diffusion 2-5 centimeters (.8-2 inches) every year and forms an ocean trench about the size of the grand Canyon. The eastern Pacific Rise, on the other hand, is a rapid spreading center. That spreads about 6-16 centimeters (3-6 inches) every year. Over there is not an ocean trench at the east Pacific Rise, since the seafloor dispersing is too quick for one come develop!
The newest, thinnest late on planet is located near the center of mid-ocean ridge—the actual site of seafloor spreading. The age, density, and thickness the oceanic crust boosts with distance from the mid-ocean ridge.
The magnetism that mid-ocean ridges aided scientists very first identify the procedure of seafloor dispersing in the early 20th century. Basalt, the once-molten rock that provides up most new oceanic crust, is a relatively magnetic substance, and also scientists began using magnetometers to measure the magnetism that the s floor in the 1950s. What they found was the the magnetism the the ocean floor approximately mid-ocean ridges was divided into equivalent “stripes” ~ above either next of the ridge. The particular magnetism the basalt rock is determined by the Earth’s magnetic ar when the magma is cooling.
Scientists determined that the same process formed the perfect symmetrical stripes top top both side of a mid-ocean ridge. The continual process of seafloor spreading separated the stripes in an orderly pattern.
Oceanic crust slowly moves away from mid-ocean ridges and sites of seafloor spreading. Together it moves, it i do not care cooler, an ext dense, and an ext thick. Eventually, enlarge oceanic crust encounters a tectonic boundary v continental crust.
In part cases, oceanic tardy encounters an active plate margin. An active plate margin is an actual bowl boundary, wherein oceanic crust and continental late crash right into each other. Energetic plate spare are often the website of earthquakes and volcanoes. Oceanic crust produced by seafloor spreading in the eastern Pacific Rise, for instance, might become part of the Ring that Fire, the horseshoe-shaped sample of volcanoes and also earthquake zones around the Pacific s basin.
In various other cases, oceanic late encounters a passive key margin. Passive margins space not key boundaries, but locations where a solitary tectonic bowl transitions from oceanic lithosphere to continent lithosphere. Passive margins are not sites of faults or subduction zones. Thick layers the sediment overlay the transitional tardy of a passive margin. The oceanic tardy of the Mid-Atlantic Ridge, because that instance, will certainly either become part of the passive margin on the north American key (on the east coast of phibìc America) or the Eurasian plate (on the west coast of Europe).
New geographic features can be created through seafloor spreading. The Red Sea, for example, was developed as the african plate and also the Arabian key tore far from every other. Today, only the Sinai Peninsula connect the Middle eastern (Asia) through North Africa. Eventually, geologists predict, seafloor spreading will completely separate the two continents—and join the Red and also Mediterranean Seas.
Mid-ocean ridges and seafloor spreading can additionally influence sea levels. As oceanic late moves far from the shallow mid-ocean ridges, the cools and also sinks together it becomes an ext dense. This boosts the volume of the ocean basin and also decreases the sea level. Because that instance, a mid-ocean ridge system in Panthalassa—an ancient ocean that surrounding the supercontinent Pangaea—contributed come shallower seas and higher sea level in the Paleozoic era. Panthalassa to be an early type of the Pacific Ocean, which this particular day experiences less seafloor spreading and also has a much less extensive mid-ocean ridge system. This helps explain why sea levels have fallen substantially over the previous 80 million years.
Seafloor spreading disproves an early part of the theory of continental drift. Pendant of continental drift originally theorized the the continents moved (drifted) v unmoving oceans. Seafloor spreading proves that the s itself is a website of tectonic activity.
Seafloor spreading is just one component of bowl tectonics. Subduction is another. Subduction happens whereby tectonic key crash right into each other instead of dispersing apart. In ~ subduction zones, the sheet of the denser plate subducts, or slides, beneath the less-dense one. The denser lithospheric material then melts earlier into the Earth"s mantle.
Seafloor spreading creates new crust. Subduction destroys old crust. The 2 forces roughly balance each other, therefore the shape and diameter the the planet remain constant.

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

Map courtesy NOAA

Seafloor spreading and also rift valleys are usual features at “triple junctions.” Triple junctions room the intersection of 3 divergent bowl boundaries. The triple junction is the central point where 3 cracks (boundaries) split off at about 120° angles from each other.
In the Afar Triple Junction, the African, Somali, and Arabian bowl are dividing from each other. The an excellent Rift Valley and also Red Sea (a significant site the seafloor spreading) room the an outcome of plate tectonics in the Afar Triple Junction.

area where 2 or an ext tectonic bowl are moving away from every other. Likewise called an extensional boundary.

the suddenly shaking of Earth"s crust led to by the release of energy along error lines or from volcano activity.

mid-ocean ridge where seafloor spreading is occuring at an ext than 100 millimeters (4 inches) a year.

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

slow motion of Earth"s solid mantle brought about by convection currents transferring heat from the inner of the planet to the surface.

lithospheric an ar where oceanic tardy transitions to continental crust without faults or subduction zones.

base level for measuring elevations. Sea level is identified by dimensions taken end a 19-year cycle.

movement the tectonic plates leading to geologic task such as volcanic eruptions and 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, through which lava, ash, and gases erupt, and additionally the cone built by eruptions.


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