Isostasy in geography UPSC

The term Isostasy was first used by American geologist Dutton. The literal meaning of the Isostasy is the "stage of balance". It is the mechanical stability between the earth's crust( upstanding parts such as plains, plateaus, mountains, etc,  and low-lying parts such as the ocean floor ) and mantle on the rotating earth. It maintains an equilibrium state between buoyancy force and gravitational force. Buoyancy force pulls the crust up Ward and gravitational force pushes the crust downward.

There are mainly two views on Isostasy:

• Airy's Views
• Pratt's Views

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Airy's Views: 

Airy views on isostasy

Airy was the first to give a detailed explanation about Isostasy. As per Airy:

• Continents are made of lighter material Sial and there are floating on denser material made of Sima.
• Continents have the same density hence to keep balance, the height of mountains is a proposition to depth root underneath.
• He used the boat and iceberg concept of floating, a large part of the boat and iceberg remains in the water to keep its balance. 
• In the same concept of boats, Himalayan is floating on Sima and a large part of Himalayan roots deep down in Sima (denser rock) to keep it afloat.
• The individual peak & valleys of mountains need not be separately balanced, as the crustal rocks have enough strength to maintain minor relief.

Criticism of Airy's Views:

• The density of mountains, plains, and plateaus need not be the same.
• The very long root of Himalayan is not possible due to intense heat & pressure in Sima.

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Pratt Views

Pratt's views on isostasy

As per Pratt:

• The density of mountains, plains, and plateaus is different.
• The density of mountains should have lower than the density of plateaus
• There is an inverse relationship between height and density.
• His idea is the uniform depth with varying thickness

For Explanation, please watch the below videos:

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