NCERT Solutions for Class 11 Geography Chapter 10 - Interior of the Earth

Question 1:

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

  1. P-waves
  2. S-waves
  3. Surface waves
  4. None of the above

(a). P-waves

Question 2:

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

  1. Earthquake waves
  2. Volcanoes
  3. Gravitational force
  4. Earth magnetism

(c). Earth magnetism

Question 3:

Which type of volcanic eruptions have caused Deccan Trap formations?

  1. Shield
  2. Flood
  3. Composite
  4. Caldera

(c). Flood

Question 4:

Which one of the following describes the lithosphere?

  1. Upper and lower mantle
  2. Crust and upper mantle
  3. Crust and core
  4. Mantle and core

(b). Crust and upper mantle

Question 5:

What are body waves?


Body waves are generated due to release of energy at the focus. There are two types of body waves. These are called P and S waves.

Question 6:

Name the direct sources of information above the interior of the earth.


(a) Mining : Mining provides information about solid materials. Gold mines in South Africa are 3 to 4 km deep. Beyond this depth, the temperature is high and it is not possible to go deep.
(b) Bores and wells : The deepest Bores is at Kola Region in Arctic Zone (12 km deep).
(c) Volcanic eruptions : These provide lava for further study.

Question 7:

Why do earthquake waves develop shadow zone ?


It is true that earthquake waves are recorded all over the world. But earthquake waves are not recorded in specific zones. Such a zone is called shadow zone. In these zones, P and S waves are not recorded.

Question 8:

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


The indirect sources are :
(a) Temperature
(b) Pressure
(c) Density
(d) Meteorites
(e) Gravity.

Question 9:

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


Intrusive forms. The lava that is released during volcanic eruptions on cooling develops into igeneous rocks. The cooling may take place either on reaching the surface or also while lava is still in the crustal portion. Depending on the location of cooling of lava igneous rocks are classified as volcanic rocks (cooling at the surface) and plutonic rocks (cooling in the crust). The lava that cools within the crustal portions assumes different forms. These forms are called intrusive forms.
(1) Batholiths. A large body of magmatic material that cools in the deeper depth of crust develops in the form of large domes. They appear on surface only after the denudational processes remove the overlying materials. They cover large areas and at times assume depth that may be several kilometres. These are granitic bodies. Batholiths are cooled portion of magma chambers.
(2) Lacoliths. 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 located at deeper depths. It can be regarded as the localised source of lava that finds its way to surface. The Karnatak plateau is spotted with domal hills of granite rocks. Most of these, now exfoliated, are the examples of lacolith (or batholiths).
(3) Lapolith, Phacolith and sills. As and when the lava moves upwards portion of the same may tend to move in horizontal direction wherever it finds a weak plane. It may get rested in different forms. In case if develops into a saucer shape, concave to sky body, it is called lapolith. A wavy mass of intrusive rocks at times 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 (subsequently developed as batholiths). These are called the phacoliths.
1. Dykes; 2. Sill; 3. Lacolith; 4. ‘Cedar-tree’ Lacolith; 5. Lapolith; 6. Phacoliths; 7. Batholith.
The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of material. The thinner ones are called sheets while the thick horizontal deposits are called sills.
(4) Dykes. When the lava makes it way through cracks and through the fissures developed in the land it makes almost perpendicular to the ground. It gets cooled in the same positions to develop wall like structure. Such structures are called dykes. These are most commonly found intrusive forms in the western Maharashtra area. These are considered as the feeders for the eruptions that led to the development of Deccan traps.