Interior of the EarthClass 11 Fundamentals of Physical Geography NCERT Solutions
10 Solutions
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Solution 1 of 10
Q11
(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
Solution
Answer: (c) Surface waves
Explanation: According to the chapter, surface waves are generated when body waves interact with surface rocks. These waves move along the surface, cause the displacement of rocks, and are responsible for the collapse of structures, making them the most destructive type of earthquake waves.
Q21
(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
Solution
Answer: (b) Volcanoes
Explanation: The chapter classifies sources of information about the Earth's interior into direct and indirect sources. Volcanic eruptions are a direct source because the molten material (magma) from the interior is thrown onto the surface, where it becomes available for laboratory analysis. Earthquake waves, gravitational force, and earth magnetism are all listed as indirect sources.
Q31
(iii) Which type of volcanic eruptions have caused Deccan Trap formations?
(a)
Shield
(b)
Flood
(c)
Composite
(d)
Caldera
Solution
Answer: (b) Flood
Explanation: The text describes Flood Basalt Provinces as volcanoes that outpour highly fluid lava flowing over long distances. It explicitly states, "The Deccan Traps from India, presently covering most of the Maharashtra plateau, are a much larger flood basalt province."
Q41
(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
Solution
Answer: (b) crust and upper mantle
Explanation: The chapter defines the lithosphere in the section on 'The Mantle'. It states, "The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 km."
Q12
(i) What are body waves?
Solution
Body waves are earthquake waves that are generated due to the release of energy at the focus of an earthquake. They are named 'body waves' because they travel in all directions through the body of the Earth. There are two types of body waves: P-waves (primary waves) and S-waves (secondary waves).
Q22
(ii) Name the direct sources of information about the interior of the earth.
Solution
The direct sources of information about the interior of the Earth are:
- Surface Rocks: The most easily available solid earth material from the surface or from mining areas.
- Deep Drilling Projects: Projects like the "Deep Ocean Drilling Project" and the "Integrated Ocean Drilling Project" provide materials from deeper parts of the crust.
- Volcanic Eruptions: Molten material (magma) that is thrown onto the surface during an eruption provides direct samples for analysis.
Q32
(iii) Why do earthquake waves develop shadow zone?
Solution
Earthquake waves develop a 'shadow zone' because the waves are affected by the different layers of the Earth's interior, particularly the liquid outer core.
- S-waves cannot travel through liquid material. Therefore, the liquid outer core blocks S-waves entirely, creating a large shadow zone beyond 105° from the epicenter.
- P-waves can travel through liquid but are refracted (bent) when they pass from the solid mantle into the liquid outer core. This refraction creates a band-like shadow zone for P-waves between 105° and 145° from the epicenter, where no direct P-waves are recorded.
Q42
(iv) Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.
Solution
Other than seismic activity, the main indirect sources of information about the Earth's interior are:
- Temperature, Pressure, and Density: Analysis shows that temperature, pressure, and density all increase with depth. By studying the rate of this change, scientists can estimate the conditions and material properties within the Earth.
- Meteors: Meteors that reach the Earth are believed to be formed from similar materials as our planet. Their structure and composition provide valuable clues about the composition of the Earth's interior.
- Gravitation: The force of gravity is not uniform across the Earth's surface. Variations, known as gravity anomalies, give information about the uneven distribution of mass in the Earth's crust.
- Magnetic Field: Magnetic surveys provide information on the distribution of magnetic materials in the crustal portion, offering insights into the distribution of materials in this layer.
Q13
(i) What are the effects of propagation of earthquake waves on the rock mass through which they travel?
Solution
The propagation of earthquake waves causes vibrations and exerts different forces on the rock mass through which they travel. The effects vary depending on the type of wave:
-
P-waves (Primary waves): These waves vibrate parallel to the direction of wave propagation. This movement exerts pressure on the material, causing it to stretch and squeeze. This leads to changes in the density of the rock mass as the wave passes through.
-
S-waves (Secondary waves): These waves vibrate perpendicular to the direction of wave propagation in the vertical plane. This motion creates crests and troughs in the material, shaking the rock mass up and down.
-
Surface waves: These waves also vibrate perpendicular to the direction of propagation and are confined to the surface. They are considered the most damaging because they cause significant displacement of rocks. This leads to ground shaking, structural collapse, and other destructive effects on the landscape and human-made structures.
Q23
(ii) What do you understand by intrusive forms? Briefly describe various intrusive forms.
Solution
Intrusive forms are landforms created when lava released during a volcanic eruption cools and solidifies while still within the Earth's crust, rather than on the surface. These formations, also known as plutonic rocks, only become visible on the surface after the overlying rock has been removed by denudational processes like erosion.
Various intrusive forms include:
-
Batholiths: These are very large masses of granitic magmatic material that have cooled in the deeper parts of the crust, often forming the core of major mountain ranges. They appear as large domes on the surface after erosion.
-
Lacoliths: These are large, dome-shaped intrusive bodies with a flat base, connected to a magma source below by a pipe-like conduit.
-
Lapolith: When lava moves horizontally and settles in a saucer-shaped, concave form, it is called a lapolith.
-
Phacoliths: These are wavy masses of intrusive rocks found at the base of synclines or the top of anticlines in folded rock layers.
-
Sills and Sheets: These are near-horizontal bodies of intrusive igneous rock. The thicker deposits are called sills, while the thinner ones are called sheets.
-
Dykes: When lava makes its way through cracks and fissures and solidifies in a position that is almost perpendicular to the ground, it forms a wall-like structure called a dyke.