Geomorphology for Kerala PSC: PLATE BOUNDARIES

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Kerala PSC

Geomorphology for Kerala PSC: PLATE BOUNDARIES

Plate boundaries are generally of three types namely:

1. Constructive Margins or Divergent Plate Boundary

2. Destructive Margin or Convergent Plate Boundary

3. Conservative Margin or Parallel Boundary or Transform Fault Boundary

CONSTRUCTIVE PLATE MARGIN OR DIVERGENT PLATE BOUNDARY

If a plate boundary is said to be Divergent Plate Boundary if two plates move away from each other. As a result of this movement, the molten lava from the asthenosphere comes out from the crack develops between them. The to the surface continuously and after solidification forms a new crust. Hence, such plate boundaries are called constructive plate margins.  The divergence brings in two results

(i)          The formation of a new crust

(ii)        Formation of submarine mountains or ridges

The Mid Oceanic ridges are formed as a result of the divergence of oceanic plates. Magma comes out through the gap formed due to the divergence of plates and solidifies to form mountains. These types of mountains are known as Mid Oceanic ridges. The Mid-Atlantic ridge, the East-Pacific ridge and the Chagos- Laccadives ridge in the Indian ocean and other oceanic ridges have come into being in this manner. The rifts in the ocean floor may sometimes extend into the adjoining continents and split the continent into two. For example, the rift, which broke Arabia away from Africa and grafted it on to Asia, changed the appearance of both continents and opened up new seas-the Red sea and the Gulf of Aden.

DESTRUCTIVE PLATE MARGIN OR CONVERGENT PLATE BOUNDARY

When two plate move towards each other it is known as Convergent Plate Margin. When two plates collide with each other, the denser one is subducted below the lighter one. The region, where the subduction takes place is called Benioff zone or Subduction Zone. This plate margin is also known as consuming plate margin. The subducting plate is lost in the mantle. It is also called convergent plate margin as two plates converge here.The convergent plates interact with each other in three different ways.

(i) Oceanic- Continental Convergent Plate

When one oceanic plate and continental plate collide each other, denser oceanic plate gets subducted below the lighter continental plate as it is denser. In this process, a trench is formed.  Volcanoes are formed in the Benioff zone due to rise of magma. It comes out breaking the weak part of the crust. For example, the Western side of the American plate, where the Pacific plate is subducted below the American plate. It is the zone of active volcanoes.

(ii) Oceanic- Oceanic Convergent Plate

When both the converging plates are oceanic, the relatively denser plate gets subducted and, in the process, oceanic trenches and volcanic islands are formed. The convergence of the Pacific and the Philippines plates explains the formation of island, festoons and chain of volcanoes in that region. e.g. Philippines and Indonesian islands.

(iii) Continent- Continent Convergent Plate

When both the plates are continental, because of equal density fold mountains are formed. These regions are geographically unstable. e.g. the Himalayas.

CONSERVATIVE MARGIN OR PARALLEL BOUNDARY

Parallel plates do not create new crust or destroy the old as they slide past each other along a common boundary. They push each other and produce transform faults. Fault Zones are created along the Shear margin. Eg.: For example, the St Andreas fault in California. It marks the meeting place of two parallel plates, one carrying North America and the other carrying the Pacific Ocean. Highly seismic earthquakes are found along these boundaries. 

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