Views of Airy and Pratt on the Hypothesis of Isostasy

Introduction
The hypothesis of isostasy, developed in the 19th century, explains the equilibrium of the Earth's crust in response to vertical movements caused by the redistribution of mass. Two prominent geophysicists, Sir George Biddell Airy and John Henry Pratt, proposed different views on the concept of isostasy.

Airy's View on Isostasy
Airy, a British mathematician and astronomer, developed the initial concept of isostasy in 1855. He suggested that the Earth's crust is composed of lighter materials floating on a denser underlying layer. According to Airy, the crustal blocks are isostatically balanced, meaning they adjust their elevations to maintain equilibrium with the underlying materials.

Key Points:
- Airy proposed that the Earth's crust behaves like a floating iceberg or a ship in water, with the crustal blocks adjusting vertically to maintain equilibrium.
- He suggested that the compensation mechanism involves the flexure of the lithosphere, which allows the crustal blocks to float on the denser asthenosphere beneath.
- Airy's hypothesis of isostasy explained the observation that mountain ranges have deep roots below the surface, as the crustal material is compensated by deeper sinking of denser material.

Pratt's View on Isostasy
Pratt, another British mathematician and geophysicist, presented an alternative view on isostasy in 1855. He proposed that the compensation mechanism does not involve flexure but rather variations in the density of the crustal blocks. According to Pratt, the crustal blocks are isostatically balanced by differences in their masses, with denser blocks sinking deeper into the mantle.

Key Points:
- Pratt argued that the crustal blocks do not flex but adjust their depths based on their density variations.
- He suggested that regions with higher densities, such as mountain ranges, would have deeper roots, while regions with lower densities, such as basins, would have shallower roots.
- Pratt's hypothesis of isostasy explained the observation that mountain ranges have varying crustal thickness, with thicker crust beneath the mountains and thinner crust beneath basins.

Comparison and Conclusion
While both Airy and Pratt proposed explanations for the concept of isostasy, their views differ in terms of the compensation mechanism. Airy's hypothesis involves flexure of the lithosphere, while Pratt's hypothesis involves variations in density. However, both views acknowledge the concept of isostatic equilibrium, where the Earth's crust adjusts vertically to maintain balance in response to mass redistribution.

In conclusion, Airy and Pratt played significant roles in developing the hypothesis of isostasy and provided alternative explanations for the vertical movements of the Earth's crust. Their views continue to influence the study of isostasy and have contributed to our understanding of the dynamic processes occurring within the Earth's lithosphere.