GEOGRAPHY- CLASS-11: FUNDAMENTALS OF PHYSICAL GEOGRAPHY
CHAPTER-3
Interior of the Earth
1. Multiple Choice Questions
(i) Which one of the following earthquake waves is more destructive?
Answer: (c) Surface waves
Explanation: Surface waves travel along the Earth's surface and produce the strongest ground shaking. Therefore, they cause the maximum destruction during an earthquake.
(ii) Which one of the following is a direct source of information about the interior of the Earth?
Answer: (a) Earthquake waves
Explanation: Seismic (earthquake) waves travel through the Earth's interior and help scientists understand its internal structure.
(iii) Which type of volcanic eruptions have caused Deccan Trap formations?
Answer: (b) Flood
Explanation: The Deccan Traps were formed by repeated flood basalt eruptions, where large quantities of lava spread over vast areas.
(iv) Which one of the following describes the lithosphere?
Answer: (b) Crust and upper mantle
Explanation: The lithosphere consists of the Earth's crust and the rigid uppermost part of the mantle. It is divided into tectonic plates.
2. Answer the following questions in about 30 words.
(i) What are body waves?
Answer:
Body waves are seismic waves that travel through the Earth's interior. They are of two types: P-waves (Primary waves) and S-waves (Secondary waves).
(ii) Name the direct sources of information about the interior of the Earth.
Answer:
The direct sources of information about the Earth's interior are earthquake (seismic) waves, materials obtained from mining, and rocks brought to the surface by volcanic eruptions.
(iii) Why do earthquake waves develop a shadow zone?
Answer:
Earthquake waves develop a shadow zone because their speed and direction change when they pass through different layers of the Earth. S-waves cannot travel through the liquid outer core, while P-waves are strongly refracted.
(iv) Briefly explain the indirect sources of information of the interior of the Earth other than those of seismic activity.
Answer:
Indirect sources include the study of gravity, magnetic field, meteorites, and Earth's density. These help scientists estimate the composition and structure of the Earth's interior.
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:
Earthquake waves produce different effects on the rocks through which they travel. As seismic waves move through the Earth's interior, they change their speed and direction depending on the density and physical state of the rocks. P-waves travel through solids, liquids and gases by compressing and expanding the rock particles in the direction of wave movement. S-waves move only through solids and produce a shearing motion at right angles to the direction of travel. They cannot pass through the liquid outer core. When seismic waves pass from one layer to another, they are reflected and refracted because of differences in density. These changes help scientists determine the structure, thickness and composition of the Earth's interior. Thus, the behaviour of earthquake waves provides valuable information about the different layers of the Earth.
(ii) What do you understand by intrusive forms? Briefly describe various intrusive forms.
Answer:
Intrusive forms are igneous rock bodies formed when magma cools and solidifies beneath the Earth's surface. Since the magma does not reach the surface, it cools slowly and forms coarse-grained rocks. Different intrusive forms are produced depending on the way magma enters the surrounding rocks. A batholith is a very large mass of intrusive rock. A laccolith is a dome-shaped intrusion that pushes the overlying rock upward. A lopolith is a saucer-shaped intrusion that bends downward. A phacolith forms along the crests and troughs of folded rocks. A sill is a horizontal sheet of magma that forms between rock layers, while a dyke is a vertical or steeply inclined sheet cutting across existing rock layers. These intrusive landforms become visible after erosion removes the overlying rocks.