Divergent plate boundaries
The Earth's crust is made up of 6 major plates; they are the Pacific plate, American plate, Eurasian plate, African plate, Indo-Australian Plate and Antarctic plate along with some minor plates. These plates float on the molten magma of plastic asthenosphere. These plates form plate boundaries which are of three types
- Convergent plate boundaries: in which the lithospheric plates move towards each other.
- Divergent plate boundaries: in which the lithospheric plates move away from each other.
- Transform plate boundaries: in which the lithospheric plates slide past one another.
Divergent Plate Boundaries
Divergent plate boundaries can be defined as the locations where the lithospheric plates move away from each other. Divergent plate boundaries occur above the rising convection currents in the asthenosphere. These rising currents push up the bottom of the lithospheric plate, and the magma flows laterally below it. This lateral flow of the current drags the lithospheric plates in the direction of flow of current. At the point of the crest of upliftment the lithospheric plate is stretched, which breaks it and pulls the above plates apart, creating a divergent plate boundary.
Facts associated with divergent plate boundaries
According to the continental drift theory, all the different continents were part of one giant supercontinent which was known as Pangea. Due to the plate tectonics and rising Convection currents in the asthenosphere, the supercontinent Pangea broke apart and the different continents emerged and they began their slow migration towards their present locations. The divergent plate boundaries are the places where the lithospheric crust is being extended, thinned and broken due to extension stress. At the divergent plate boundaries, new lithospheric plates are created while the old lithospheric plates get destroyed somewhere else at the convergent plate boundaries.
The divergent plate boundaries and the continents initially produce rifts, which ultimately becomes rift valleys. Most of the active divergent plate boundaries occur between the oceanic tectonic plates. The divergent plate boundaries are also associated with volcanic Islands which occur when the lithospheric plates move apart from each other and produce gaps from which the molten lava comes out. At the divergent boundaries, new crust is created as the Magma is pushed up from the mental to the surface. The divergent plate boundaries are also associated with earthquakes which strike along the rift.
Divergent plate boundaries - Oceanic
When the divergent plate boundaries occur below the oceanic lithosphere, the rising convection currents from the magma lifts the lithospheric plate and produces a mid-oceanic ridge. The lithospheric plate is stretched due to the extensional forces and produce a deep fissure. When this fissure opens, the pressure on the heated magma is reduced. New magma flows through this fissure, which comes out and solidifies. This process is repeated in a cyclic manner.
Divergent plate boundaries examples include the mid-Atlantic Ridge. The area around the ridge is higher compared to the surrounding sea floor, due to the uplift of the oceanic plate by the convection currents below it. In these areas, the divergent plate boundaries are associated with submarine mountain ranges such as the mid-Atlantic ridge, volcanic activities in the form of fissure eruptions, seafloor spreading and shallow earthquakes.
Divergent plate boundaries location
Divergent plate boundaries are associated with seafloor spreading whose evidence has been found with younger oceanic crust near the ridges. The oceanic crust becomes progressively older away from the spreading centre. There is a gradual formation of new Oceanic crust close to the ridges and gradual spreading of these oceanic plates over time. The seafloor spreading over the past 200 million years has enlarged the size of Atlantic Ocean which has grown from a tiny inlet of water between Europe, Africa, and the Americas into the vast ocean of present times.
Divergent boundaries - Continental
The divergent boundaries below the thick Continental plate are not vigorous enough to form a clean single break through the continental plate. When the two Continental plates are pulled apart, faults develop on both sides of the rift. The central block of the plate slides downwards and earthquakes occur due to this movement. In the early part of the rift forming process, streams and rivers flow through this sinking rift valley which can form a long linear lake. If the rift grows deeper, its level can fall below the sea level and the ocean water can enter inside it. This can lead to the formation of a narrow sea inside the rift. If this rifting process continues, new ocean basin could be formed in that place.
This type of divergent plate boundaries includes the East African Rift Valley, which is in the early stage of development. The continental plate of that area has not been completely rifted as the East African Rift Valley is presently above the sea level. The example of the completely developed rift valley is the Red Sea, where the plates have been fully separated and the central Rift Valley has dropped below the sea level.