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Isostasy

ICSE · Class 11 · Geography

Quick revision notes for Isostasy — ICSE Class 11 Geography. Key concepts, formulas, and definitions for last-minute revision.

43 questions36 flashcards5 concepts

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Key Topics to Revise

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1. Meaning and Basic Idea of Isostasy

  • The term isostasy is derived from the German word Isostasios, meaning in equipoise or state of balance.
  • The term isostasy was first used by Dutton in 1889.
  • Isostasy explains the gravitational equilibrium between continents, oceans, mountains, plateaus, and plains on a rotating earth.
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2. Early Observations and Evidence

  • Pierre Bouguer sowed the seeds of the doctrine in 1735 during the Andes Expedition.
  • Bouguer found that plumb-line deflection near Chimborazo was much less than expected.
  • This showed that mountains were not pulling the plumb line as strongly as their mass suggested.
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3. Airy's Concept of Isostasy

  • Sir George Airy was the Astronomer Royal who proposed his views in 1855.
  • Airy explained isostasy using the Law of Floatation.
  • He held that continents are made of lighter sial floating on denser sima.
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4. Pratt's Concept of Isostasy

  • Archdeacon Pratt proposed his views in 1855 after studying the gravitational pull of the Himalayas.
  • Pratt theorised lighter rocks below the Himalayas and denser rocks below the Indo-Gangetic plain and the southern peninsula.
  • He concluded that mountains, plateaus, plains, and oceans have densities in ascending order.

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Full Notes

Key Concepts

Isostasy means equipoise or a stateThe term was first used byPierre Bouguer noticed during the AndesSir George Everest's 1854 surveyThis is the level below

Frequently Asked Questions

What are the important topics in Isostasy for ICSE Class 11 Geography?
Key topics in Isostasy include Isostasy: Complete Concept Overview, Isostasy: Concept Overview and Key Components, Isostasy – Complete Concept Overview. These are the concepts ICSE Class 11 examiners draw on most — study them first, then practise related questions.
How to score full marks in Isostasy — ICSE Class 11 Geography?
Understand the core concepts first, then work through the 43 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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