What is Seafloor Spreading?
Seafloor spreading is a continuous process that comes about at mid-ocean ridges through volcanic activities and gradually splits away from the ridges. This idea of seafloor spreading plays an important role in the development of plate tectonics which reforms geological thoughts during the last quarter of the 20th century.
In the early 1960s, American geophysics proposed the seafloor spreading hypothesis in which basaltic magma from the mantle rises to form a new ocean floor at mid-point ranges. On each side of the ridges, the seafloor moves from the ridges towards the deep-sea trenches where it is deflated and recycled back into the mantle. A test of the hypothesis of seafloor spreading was offered by the studies of Earth magnetism.
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Undersea Mountain Range (Mid Oceanic Ridges)
Undersea mountain ranges are the mountain ranges that are mostly or entirely underwater, and specifically under the surface of an ocean. If undersea mountain ranges emerge from current tectonic forces, they are often referred to as the mid-oceanic range. The largest and renowned undersea mountain range is the mid-oceanic range - the Mid Atlantic Range.
Plate Tectonics
The theory of plate tectonics states that the outer shell of the Earth is divided into the different plates that slide over the mantle, the rocky inner layer above the core. The plates behave like a hard and immovable shell when compared to the Earth's mantle. This stronger layer is known as the Lithosphere.
The Earth's lithosphere is made up of seven or eight major plates and many minor plates. The lithosphere, which is the rigid outermost shell of the planet ( the crust and upper mantle) is split up into tectonic plates. When these plates collide, their relative motion determines the type of plate boundary like convergent, divergent, or transform.
Volcanic activity, mountain - buildings, earthquakes, and ocean trenches formation occur along these plate boundaries ( or faults). The relative movement of plates typically ranges from 0 to 100 mm annually.
Types of Plate Boundaries
The three types of plate boundaries are convergent plate boundaries, divergent boundaries and transform plate boundaries.
Convergent Plate Boundaries - Convergent plate boundaries occur when two plates are pushing towards each other.
Convergent Plate Boundaries Example
The boundary between the Indian Plate and the Eurasian Plate at the Himalayas.
The borderline between the South American Plate and the Nazca Plate along the west coast of South America.
Divergent Plate Boundaries - Divergent boundaries occur when two plates move apart from each other.
Divergent Plate Boundaries Example
The boundary between Arabian Plate and the African Plate in the Red Sea.
The boundary between Antarctic plates and the Pacific.
Transform Plate Boundary - The transform plate boundary takes place when two plates slide past each other.
Transform Plate Boundaries Example
The boundary between Australian plate and Pacific plate crossing New Zealand.
In California, the borderline between the North American Plate and the Pacific Plate.
What is the Subduction Zone?
A subduction zone is a place where two tectonic plates sink back into the mantle and are recycled. Where two tectonic plates come across at a subduction zone, one deviates and slides beneath the other, bending down into the mantle. (The mantle is considered to be the hotter layer under the crust).
Both continental crust and oceanic crust are transported by tectonic plates, or they may be formed by only a single kind of crust. Oceanic crust is denser than continental crust. The oceanic crust at a subduction zone generally sinks into the mantle underneath the lighter continental crust. (As per the scientist, the oceanic crust may grow so old and dense that it collapses and immediately forms a subduction zone).
If the same kind of crust such as continent-continent collides, the plates may crash and collapse together like crashing cars without subducting. The giant Himalaya mountain chain was formed this way when India struck into Asia.
Earth is the only planet where subduction occurs and subduction zones are its important tectonic features. Subducting is the result behind plate tectonic, as without it plate tectonics cannot take place.
Did You Know?
One of the two major processes of plate tectonics is seafloor spreading, while the other being subduction.
The renowned examples of mid-ocean ridges are the Mid- Atlantic Ridge and the East Pacific Rise.
Seafloor spreading occurs at mid-ocean ridges and obtains basalt, the rock that forms the oceanic crust.
Subduction zones are often observed near earthquakes.
The biggest crash scene on Earth is the subduction zone.
The oceanic crust is denser than the continental crust so when subduction occurs the oceanic crust goes under the continental crust.
A subduction zone was found by scientists in 1960.
At times continent-continent crash together without subducting which would cause and make the mountains like the Himalayas.
FAQs on Seafloor Spreading
1. What is the simplest way to explain seafloor spreading?
Seafloor spreading is the process where new oceanic crust is formed at mid-ocean ridges and spreads outwards. Think of it like a giant conveyor belt at the bottom of the ocean. Magma from the Earth's mantle rises, cools to form new rock at the ridge, and then this new floor slowly moves away on either side, pushing the continents along with it.
2. Where does seafloor spreading primarily occur?
Seafloor spreading happens at mid-ocean ridges, which are underwater mountain ranges. A major example is the Mid-Atlantic Ridge, which runs down the centre of the Atlantic Ocean. This is where tectonic plates are pulling apart, allowing molten material to rise and create the new seafloor.
3. Who is credited with proposing the theory of seafloor spreading?
The theory of seafloor spreading was proposed by an American geophysicist named Harry Hess in the 1960s. His theory provided the mechanism that explained how continents could move, which was a key part of Alfred Wegener's earlier theory of continental drift.
4. What are the main pieces of evidence that support seafloor spreading?
The key evidence for seafloor spreading includes several important observations:
- Rock Age: The youngest rocks on the ocean floor are found at the mid-ocean ridges, and they get progressively older as you move away from the ridges.
- Magnetic Stripes: The ocean floor has alternating patterns of magnetic polarity, like stripes. These stripes are symmetrical on both sides of the ridges and record the reversals of Earth's magnetic field over millions of years.
- Sediment Thickness: The layer of sediment on the ocean floor is thinnest at the ridges and becomes thicker farther away, indicating that the crust near the ridges is newer.
5. If new seafloor is always being created, why doesn't the Earth get bigger?
The Earth maintains its size because the process is balanced. While new oceanic crust is created at mid-ocean ridges, older crust is simultaneously destroyed at deep-ocean trenches. In a process called subduction, the older, denser oceanic plate bends and slides beneath another plate, recycling back into the Earth's mantle.
6. What is the difference between seafloor spreading and continental drift?
Continental drift is the observation that continents have moved over time, a theory proposed by Alfred Wegener. However, Wegener couldn't explain how they moved. Seafloor spreading is the mechanism that explains this movement. It is the process of new crust formation at ridges that pushes the tectonic plates, and the continents on them, apart.
7. How does seafloor spreading relate to real-world events like earthquakes and volcanoes?
Seafloor spreading is a direct result of tectonic plate movement. The interaction at plate boundaries is what causes most of the world's geological activity. Volcanoes often form along mid-ocean ridges where magma rises. Earthquakes occur as the plates pull apart, grind past each other, or collide at subduction zones.
