<\/span><\/h2>\n\n\n\nThe term isostasy<\/em> comes from the Greek word isostasios<\/em>, meaning equal standing<\/strong>.<\/p>\n\n\n\nIt was proposed by Clarence Dutton in 1889<\/strong> to explain the state of balance between landforms and the Earth\u2019s interior<\/strong>.<\/p>\n\n\n\nIn simple terms, isostasy explains how landforms remain mechanically stable despite differences in height, mass, and erosion<\/strong>.<\/p>\n\n\n\nWhat this really means is:<\/p>\n\n\n\n
\n- The Earth\u2019s crust is not rigid<\/li>\n\n\n\n
- It adjusts itself vertically to maintain gravitational balance<\/li>\n\n\n\n
- This adjustment helps explain mountains, plateaus, uplift, and subsidence<\/li>\n<\/ul>\n\n\n\n
Isostasy also helps address gravitational anomalies<\/strong> observed across the Earth\u2019s surface.<\/p>\n\n\n\n<\/span>Why Is Isostasy Important for UPSC?<\/span><\/h2>\n\n\n\nFrom an exam perspective, isostasy:<\/p>\n\n\n\n
\n- Explains mountain building and crustal stability<\/strong><\/li>\n\n\n\n
- Links geomorphology with plate tectonics<\/strong><\/li>\n\n\n\n
- Helps answer questions on uplift, subsidence, and rebound<\/strong><\/li>\n\n\n\n
- Is repeatedly asked in Geography Optional (Paper I)<\/strong><\/li>\n<\/ul>\n\n\n\n
UPSC expects clarity on:<\/p>\n\n\n\n
\n- Pratt\u2019s theory<\/li>\n\n\n\n
- Airy\u2019s theory<\/li>\n\n\n\n
- Plate tectonics interpretation of isostasy<\/li>\n<\/ul>\n\n\n\n
<\/span>Pratt\u2019s Theory of Isostasy (Compensation Theory)<\/span><\/h2>\n\n\n\nPratt\u2019s theory is also called the law of compensation<\/strong>.<\/p>\n\n\n\n<\/span>Core Idea<\/span><\/h3>\n\n\n\n\n- Equal masses underlie equal areas<\/strong><\/li>\n\n\n\n
- Landforms have equal thickness but varying densities<\/strong><\/li>\n\n\n\n
- Compensation occurs up to a fixed depth called the depth of compensation<\/strong><\/li>\n<\/ul>\n\n\n\n
In Pratt\u2019s model:<\/p>\n\n\n\n
\n- Higher landforms have lower density<\/strong><\/li>\n\n\n\n
- Lower landforms have higher density<\/strong><\/li>\n\n\n\n
- Density variation exists only up to a certain depth<\/li>\n\n\n\n
- Beyond this depth, material has uniform density<\/li>\n<\/ul>\n\n\n\n
This theory explains why areas with similar crustal thickness can have different elevations.<\/p>\n\n\n\n
<\/span>Modern Modification<\/span><\/h3>\n\n\n\nLater, Hayford and Bowie<\/strong> refined Pratt\u2019s idea by introducing the concept of a plane of compensation<\/strong> at around 100 km depth<\/strong>, which aligns closely with the thickness of lithospheric plates.<\/p>\n\n\n\nPratt\u2019s model fits best with mid-oceanic ridges<\/strong>, where density variation plays a major role.<\/p>\n\n\n\n<\/span>Airy\u2019s Theory of Isostasy (Flotation or Root Theory)<\/span><\/h2>\n\n\n\nAiry\u2019s theory is based on the principle of flotation<\/strong>.<\/p>\n\n\n\n
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