Isostasy

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Isostasy means a state of balance or equipoise in which equal mass underlies equal areas on the earth’s surface. It explains how large landforms remain in gravitational equilibrium even though they ri…

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The term isostasy is derived from the German word Isostasios, meaning equipoise or state of balance. The name fits the idea that the earth’s surface features remain balanced.

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The term isostasy was first used by the American geologist Dutton in 1889. He used it to explain gravitational equilibrium between continents, oceans, mountains, plateaus, and plains on a rotating ear…

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Higher landforms are lighter because they must extend deeper into the earth to stay balanced. Low-lying areas are denser. This relationship helps explain why continents, mountains, and ocean basins re…

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The level of compensation is the depth below the earth’s surface below which density does not vary. Above this level, landforms of different sizes and densities remain in balance.

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Pierre Bouguer observed that the plumb-line deflection near Chimborazo was much less than expected. This was an early clue that mountains were not pulling as strongly as their mass suggested.

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It showed that mountain mass did not produce the expected gravitational pull. This suggested that some hidden balance existed beneath the surface, which later became the basis of the doctrine of isost…

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Sir George Everest’s survey of the Indo-Gangetic plain south of the Himalayas revealed plumb-line discrepancies. The astronomically measured latitude and the triangulation-measured latitude did not ma…