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Plate Tectonics

Basic Science Behind Plate Tectonics

 Dr. Abhinandan Bhardwaj PhD


What are Plates?

Earth's hard outer layers are divided into large blocks called plates.  These consists of Earth's crust and upper part of Mantle. To learn about Interior of Earth click here

The Earth's crust and firm upper layer of mantle from the lithosphere is about 60 miles (100km) thick. This is not one continuous structure but its divided into dozen huge curved pieces called lithospheric plates like parts of a giant jigsaw ( See Picture Below). The plates drift around the world, changing the shapes of their oceanic crusts, and carrying their continents with them.

The Main Plates of Earth: The main plates are Eurasian Plate, Indian -Australian Plate, Pacific plate, Antarctic Plate, African plate, Arabian plate, Philippine Sea Plate, South American Plate, Caribbean Plate etc.

How do Plates form and move:

According to the new "plate-tectonics" theory, scientists believe that the Earth's surface is broken into a number of shifting  plates, which average about 60 miles in thickness. According to plate tectonics the lithospheric plates, move and change shape, driven by the incredible heat, pressure and movements in the mantle. Molten rocks well up from the mantle and cool, joining onto some edges of oceanic crust and enlarging their plates . These are called  constructive plate boundaries. meanwhile as plate slide about, other plate edges are pushed down and melt back into mantle,  these are called destructive plate boundaries.

How Plates Float?

Earth's Plates floats ( As shown in the picture below) on a partly molten layer within the mantle. Currents in the partly molten rocks slowly move the plates around. Where the plates are moved apart, liquid rock called magma rises and plugs the gaps. when magma hardens it forms new crustal rock.


Constructive Pate boundaries:

The most active regions for making new areas of oceanic plates are called constructive plate boundaries. In the Atlantic ocean this happens at the chain of undersea peaks that runs along the middle of the ocean, the mid Atlantic Ridges the melted rocks from below cool and add to the plates, forcing them to go sideways. This process is pushing the Americas away from Europe and Africa making Atlantic ocean wider at the rate of about 2 inches per year.

Volcanoes and Plate Movements

 Most of the world's active volcanoes are located along or near the boundaries between shifting plates and are called "plate-boundary" volcanoes. However, some active volcanoes are not associated with plate boundaries, and many of these so-called "intra-plate" volcanoes form roughly linear chains in the interior of some oceanic plates. The Hawaiian Islands provide perhaps the best example of an "intra-plate" volcanic chain, developed by the northwest-moving Pacific Plate passing over an inferred "hot spot" that initiates the magma-generation and volcano-formation process. The peripheral areas of the Pacific Ocean Basin, containing the boundaries of several plates are dotted by many active volcanoes that form the so-called "Ring of Fire". The "Ring" provides excellent examples of "plate-boundary" volcanoes, including Mount St. Helens.


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