Divergent plate boundaries are those tectonic borders where tectonic plates pull away from each other and form a new crust. ScienceStruck takes you through some interesting facts about these divergent boundary zones on this Earth.
Gakkel Ridge in the Arctic Ocean is the slowest spreading ridge in the world. It’s rate of movement is less than 1 centimeter per year.
The movement of continents and formation of water bodies on the Earth is not just history. It is a process that is going on, even now, while you are reading about it. Features like mountains and rift valleys continue to take shape at a very slow pace, thus going unnoticed by humans generally. The landforms that we see on the Earth are a result of many geological processes, one of them being the movement of tectonic plates.
What is a Tectonic Plate?
The Earth’s interior is primarily divided into: (i) the Inner Core, (ii) the Outer Core, and (iii) the Mantle. This mantle consists of: (i) Asthenosphere (lower layer) and (ii) Lithosphere (upper layer). Above the mantle lies the Earth’s crust. The crust includes both the Continental and Oceanic crust. Thus, the lithosphere is made of the crust and the upper rigid part of the mantle. This is the concept of a “plate” in the plate tectonic theory.
According to the Plate Tectonics theory, there are three basic types of plate boundaries:
1. Convergent: Where two plates move towards each other and get pushed one below the other
2. Divergent: Where the plates move apart
3. Transform: Where plates slide past each other
This ScienceStruck post is dedicated to describing the divergent plate boundary with a useful diagram.
Definition and Meaning of Divergent Plate Boundary
The zone where two tectonic plates move away from each other is called the divergent plate boundary.
Divergence or separation of two plates occurs due to convection currents in the Earth’s upper mantle or asthenosphere. The heat within the mantle makes the lithosphere (layer below the Earth’s crust) melt. The molten magma that is under pressure, forces the plates to move apart. A rift is thus created between the two plates. The upwelling magma comes to the ocean surface, cools down, and forms the new oceanic crust of basalt. Continuous formation of the new crust pushes aside the crust formed earlier. Thus, the sea floor expands horizontally. This is known as sea floor spreading.
Facts about the Divergent Plate Boundary
- It is also called a constructive boundary, as a new crust is formed at this plate boundary.
- Tectonic plates move slowly and steadily. The ridge spreads or widens by a few centimeters every year.
- The sea floor spreading results in the formation of parallel sea mounts or even bigger mountains on the ocean floor.
- This was proved based on the symmetry and magnetic reversal that was found between the rocks formed on both sides of the ridge.
- The closer the rocks to the mid-oceanic ridge, the younger they are. Thus, the rocks on the edges or ends of the ridge are older.
- The sea floor spreading has been going on for over 100 million years, thus making a water body grow into the present Atlantic Ocean.
- Alfred Wegener’s Theory of Continental Drift is based on the concept of sea floor spreading.
- Fissure zone: It is a volcanic vent that pours out lava through a long vent made across layers within the mantle.
- Fissure is also a type of volcano. Thingvellir Fissure in Iceland is an example thereof.
- Fissure vents are not always explosive like volcanoes.
- The Mid-Atlantic ridge also has volcanoes present, like the Krafla, in northern Iceland.
- Krafla is known for its rifting activity, and lava eruptions are also seen here. This also causes the surface to get lifted at times.
- The Hawaiian Island is an example of a rising mantle plume forming a volcanic hotspot. Mantle plumes or rising molten magma can cause formation of hotspots on the continental plate.
- Triple Junction is the name given to the area between the African and Arabian plate. The Red Sea and the Gulf of Aden meet at this point.
Examples of Divergent Boundaries on Continents
- Iceland ridge: Though it is an island through which the Mid-Atlantic Ridge passes, it is an example of continental divergent plate boundary. There are two streams of this ridge in the southern part of Iceland.
- East African Rift zone: It includes the rift valleys present on the east and west side of Lake Victoria; also the larger Great Rift Valley refers to this region. There are many rift valley lake formations in this area, like Koka, Awasa, Abaya, etc.
- Ethiopian rift: It is formed due to divergence of the Nubian and Somalian plates.
- African and Arabian Plates diverge to form the Red Sea.
- Baikal Rift in Russia lies below Lake Baikal. (Amur plate on the east is drifting away from Eurasian plate on the west.)
Examples of Divergent Boundaries in Oceans
Mid-Atlantic ridge: The North American plate and the Eurasian plates have diverged to form the Mid-Atlantic ridge.
As we can clearly see from the image above, the horizontal fractures or cracks define the ridge between the North American plate on one side, and the Eurasian plate on the other side. These parallel faults on both sides of the ridge work as a crucial evidence, proving the sea floor spreading theory.
- Many small islands are located on this ridge, Iceland being one of them.
- Although underwater, it is one of the longest mountain ranges in the world.
- It’s existence was inferred by Matthew Fontaine Maury in 1850.
- Later, in 1872, it was discovered by the HMS Challenger Expedition.
It spreads at the rate of around 2 cm/year.
East Pacific Rise is the mid-ocean ridge in the Pacific ocean. It is a divergent boundary between the Pacific plate on the west and mainly the North American plate in the east. However, it is also surrounded by the Nazca plate, the Cocos plate, and the Rivera plate from other sides.
This is one of the fastest moving ridges of all the mid-oceanic ridges, as it spreads at the rate of around 7 cm/year. Hydrothermal vents and black smokers are found in the East-Pacific Rise.
Pacific-Antarctic ridge lies in the Pacific and the Antarctic Ocean.
The Southeast Indian ridge, in the southern part of Indian Ocean, separates the Indo-Australian plate from the Antarctic plate. Southeast Indian ridge, Pacific-Antarctic ridge and the East Pacific Rise are a continuous stretch of mid-oceanic ridges.
Similarly, Southwest Indian ridge and the Central Indian ridge are perpendicular to each other.
Juan de Fuca Ridge is a divergent boundary with a volcanic mountain range. (Pacific plate on the west and the Juan de Fuca microplate on its east).
Gakkel Ridge is a divergent plate between the Eurasian and the North American Plate.
Chile Rise: Between the Nazca and the Antarctic plate lies the Chile rise, which is being subducted (or pushed under at a convergent boundary) on its eastern end.
The interaction between the Earth’s interior and its impact on the surface has always been an interesting arena for the scientists of both disciplines―oceanography and geology. Despite several theories and major evidences supporting them, the exact mechanisms of processes like convection and the reasons behind plate tectonics are not yet known.