Unlock a deeper understanding of our planet’s hidden depths with our expertly crafted resource featuring New NCERT class 11 Geography Chapter-3: Interior of the Earth Solutions. Designed to help you navigate complex geological questions with ease, this guide provides structured, step-by-step answers to all textbook exercises.
1. Multiple Choice Questions
(i) Which one of the following earthquake waves is more destructive?
- (a) P-waves
- (b) S-waves
- (c) Surface waves
- (d) None of the above
Answer: (c) Surface waves
- Explanation: Surface waves (L-waves) are the last to report on a seismograph. They move along the Earth’s surface, causing rolling ground displacement and severe shaking, which leads to structural collapse and maximum destruction.
(ii) Which one of the following is a direct source of information about the interior of the earth?
- (a) Earthquake waves
- (b) Volcanoes
- (c) Gravitational force
- (d) Earth magnetism
Answer: (b) Volcanoes
- Explanation: Volcanic eruptions eject physical molten material (magma/lava) directly from the asthenosphere onto the Earth’s surface, providing actual rock samples for laboratory analysis. Earthquake waves, gravity anomalies, and magnetic surveys are indirect sources.
(iii) Which type of volcanic eruptions have caused Deccan Trap formations?
- (a) Shield
- (b) Flood
- (c) Composite
- (d) Caldera
Answer: (b) Flood
- Explanation: The Deccan Traps in India were formed by flood basalt eruptions, where highly fluid lava poured out over large distances, creating successive thick basaltic layers over hundreds of square kilometers.
(iv) Which one of the following describes the lithosphere:
- (a) upper and lower mantle
- (b) crust and upper mantle
- (c) crust and core
- (d) mantle and core
Answer: (b) crust and upper mantle
- Explanation: The lithosphere is the rigid outer layer of the Earth that comprises the entire crust and the solid, uppermost portion of the mantle, ranging in thickness from 10 km to 200 km.
2. Answer the following questions in about 30 words.
(i) What are body waves?
Answer: Body waves are seismic waves generated by the sudden release of energy at an earthquake’s focus. They travel through the Earth’s interior body in all directions and comprise Primary (P) and Secondary (S) waves.
(ii) Name the direct sources of information about the interior of the earth.
Answer: Direct sources include surface or mining rocks (such as deep gold mines in South Africa), materials collected from deep ocean drilling projects (like the 12 km Kola drill), and molten magma from volcanic eruptions.
(iii) Why do earthquake waves develop shadow zone?
Answer: Shadow zones occur because seismic waves refract or get absorbed when crossing internal density boundaries. P-waves bend due to density variations at the core-mantle boundary, while S-waves cannot pass through the liquid outer core.
(iv) Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.
Answer: Indirect sources include depth gradients of temperature, pressure, and density; chemical analysis of meteors; gravity anomalies reflecting mass distribution; and magnetic surveys revealing magnetic mineral concentrations in the Earth’s crust.
3. Answer the following questions in about 150 words.
(i) What are the effects of propagation of earthquake waves on the rock mass through which they travel?
Answer:
Seismic waves vibrate and stress rock masses as they travel through Earth’s interior and surface. Different wave types propagate through materials in distinct mechanical ways:
- P-Waves (Primary Waves): Vibrate parallel to wave propagation. They compress and stretch rock material along their path. This creates density fluctuations inside rock strata.
- S-Waves (Secondary Waves): Vibrate perpendicular to wave propagation in a vertical plane. They shear the rock mass. This movement creates crests and troughs within rock bodies.
- Surface Waves: Vibrate along outer rock layers, causing complex surface rolling. Surface waves are the most damaging. They cause severe physical displacement of surface rocks, ground shaking, and structural collapses.
- P-Waves ──► Parallel Vibration ──► Stretching & Squeezing (Compression)
- S-Waves ──► Perpendicular Vibration ──► Crests & Troughs (Shearing)
- Surface ──► Complex Rolling ──► Rock Displacement & Destruction
(ii) What do you understand by intrusive forms? Briefly describe various intrusive forms.
Answer:
Intrusive forms are igneous rock bodies created when magma cools and solidifies inside Earth’s crust rather than reaching the surface. Magma takes various structural shapes within crustal rocks:
| Intrusive Form | Key Characteristics & Structure |
| Batholiths | Massive granitic, dome-shaped bodies cooling at deep crustal depths. They represent fossilized magma chambers. |
| Laccoliths | Large dome-shaped bodies with flat bases, fed by pipe-like conduits beneath. |
| Lopolith & Phacolith | Lopoliths form saucer-shaped bodies concave to the sky. Phacoliths form wavy masses along folded rock anticlines and synclines. |
| Sills & Sheets | Near-horizontal tabular igneous layers. Thicker bodies are called sills; thinner deposits are sheets. |
| Dykes | Vertical, wall-like structures formed when magma solidifies inside crustal cracks and fissures. Dykes fed the Deccan Trap eruptions. |