NCERT Solutions for Class 11 Geography (Fundamental of physical geography) Chapter 3 Interior of the Earth

NCERT
SOLUTIONS
CLASS - 11th

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Class : 11th

Subject : Geography

Chapter : 3

Chapter Name : Interior of the Earth

Q1 Multiple choice questions.

(i) Which one of the following earthquake waves is more destructive?

(a) P-waves (c) Surface waves

(b) S-waves (d) None of the above

(ii) Which one of the following is a direct source of information about the interior of the earth?

(a) Earthquake waves (c) Gravitational force

(b) Volcanoes (d) Earth magnetism

(iii) Which type of volcanic eruptions have caused Deccan Trap formations?

(a) Shield (c) Composite

(b) Flood (d) Caldera

(iv) Which one of the following describes the lithosphere:

(a) upper and lower mantle (c) crust and core

(b) crust and upper mantle (d) mantle and core

(i) (a) P-waves

(ii) (a) Earthquake waves

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(iii) (b) Flood

(iv) (b) Crust and upper mantle

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Q2 Answer the following questions in about 30 words.

(i) What are body waves?

(ii) Name the direct sources of information about the interior of the earth.

(iii) Why do earthquake waves develop shadow zone?

(iv) Briefly explain the indirect sources of information of the interior of the earth other than those
of seismic activity.

(i) There are two types of earthquake waves- Body waves and surface waves. Body waves are
generated due to the release of energy at the focus and move in all directions travelling through
the body of the earth.

(ii) The direct sources of information about the interior of the earth are-

→ Mining- It is the process of extraction of valuable minerals or other geological materials from
the Earth. The most direct source of information available is surface rock or the rock we get from
mining.

→ Drilling- Mining beyond a certain depth is not possible as it get hot. Therefore, scientist
resolve to drilling. Scientists world over are working on two major projects such as “Deep Ocean
Drilling Project” and “Integrated Ocean Drilling Project. With the analysis of materials collected
at different depths provides large volume of information.

→ Volcanic eruption- when the molten material i.e. Magma is thrown onto the surface of the
earth at the time of volcanic eruption. It provides direct information about the interior of the
Earth.

(iii) The shadow zone exists because the waves are refracted as they pass through the
boundary between the mantle and the core and are diverted from their original paths. P and S

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 3 Social Science Geography

waves follow a curved path inside the earth due to increasing capacity The shadow zone of
S-wave is much larger than that of P-waves.

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(iv) The indirect sources of information of the interior of the earth are-

→Temperature, Density and Pressure- The rate in the change of temperature, pressure and
density are known. With increasing distance from the surface towards the interior in deeper
depths these 3 factors also increases. Knowing the change in the temperature, pressure and
density the scientists have estimated the total thickness of the earth.

→Meteors- . The material and the structure observed in the meteors are similar to that of the
earth. They are solid bodies developed out of materials the same as, or similar to, our planet.
Hence, this becomes yet another source of information about the interior of the earth.

→Gravitation Force- the gravitational force is not the same at different latitudes on the surface.
It is greater near the poles and less at the equator. This is because the distance from the centre
of the earth to the equator is least. Similarly, the Gravitational force differs with the mass of
material. Such a difference is called gravity anomaly. Gravity anomalies give us information
about the distribution of mass of the material in the crust of the earth.

→Magnetic Field- Magnetic Survey helps provide information about the distribution of magnetic
materials in the crusal portion, and thus, provide information about the distribution of material in
this part.

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Q3 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?

(ii) What do you understand by intrusive forms? Briefly describe various intrusive forms.

(i) Since different types of earthquake waves travel in different manner. As they propagate, they
cause vibration in the body of the rocks through which they pass. P-waves vibrate parallel to the
direction of the wave. This exerts pressure on the material in the direction of the propagation.

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This leads to density difference in the material which subsequently results into stretching and
squeezing of material. Other waves that vibrate perpendicular to the wave direction in the
vertical plane create toughs and crests in the material through which they pass.

(ii) The lava released during volcanic eruptions on cooling develops into igneous rocks the lava
that cools within the crustal portions assumes different forms. These forms are called intrusive
forms.

Various intrusive forms are as follows-

→ Batholiths- A large body of magmatic material that cools in the deeper depth of the crust
develops in the form of large domes. They appear on the surface only after the denudational
processes remove the overlying materials.

→ Laccoliths- These are large dome-shaped intrusive bodies with a level base and connected
by a pipe-like conduit from below. It resembles the surface volcanic domes of composite
volcano, only these are located at deeper depths

→ Lapolith- As and when the lava moves upwards, a portion of the same may tend to move in a
horizontal direction wherever it finds a weak plane. It may get rested in different forms. In case it
develops into a saucer shape, concave to the sky body, it is called lapolith.

→ Phacoliths- A wavy mass of intrusive rocks is found at the base of synclines or at the top of
anticline in folded igneous country. Such wavy materials have a definite conduit to source
beneath in the form of magma chambers.

→ Sills- The near horizontal bodies of intrusive igneous rocks are called sill or sheet, depending
on the thickness of the material. The thinner ones are called sheet while the thick horizontal
deposits are called sills.

→ Dykes- When the lava makes its way through cracks and fissures developed in the land, it
solidifies almost perpendicular to the ground. It gets cooled in the same position to develop a
wall-like structure. Such structures are called dykes

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