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Syllabus

Isostasy — Syllabus

ICSE · Class 11 · Geography

What Isostasy covers in ICSE Class 11 Geography: 4 topics, for the 2026-27 session. Part of the ICSE Class 11 Geography syllabus.

43 questions36 flashcards3 formulas & key relations5 concepts

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4 Topics · ICSE Class 11 Geography · 2026-27

Topics in Isostasy

1

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.
2

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.

Key Concepts

Central concept: Isostasy

Meaning of the termBasic ideaDuttonPierre BouguerSir George EverestPlumb-line deflectionKaliana and KalianpurHimalayan gravitational anomaly

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Frequently Asked Questions

What are the important topics in Isostasy for ICSE Class 11 Geography?
Key topics in Isostasy include Meaning and Basic Idea of Isostasy, Early Observations and Evidence, Airy's Concept of Isostasy, Pratt's Concept of Isostasy. Study these first, then practise questions on each for Class 11 exams.
How should I revise Isostasy for Class 11 exams?
Learn the core ideas first, then work through the 43 practice questions on Isostasy. Revise 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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