NCERT Class 11 Geography Chapter 3 Interior of The Earth

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NCERT Class 11 Geography Chapter 3 Interior of The Earth

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Interior of The Earth

Chapter: 3

GEOGRAPY [ PART – I ]

SHORT ANSWER TYPE QUESTIONS

Q.1. Name the three layers of the earth.

Ans. The three layers of the earth are:

(i) The crust.

(ii) The mantle. and

(iii) The core.

Q.2. What are the two main materials of the earth’s core?

Ans. 1. Nickel.

2. Iron.

Q.3. What is a seismograph?

Ans. Seismograph is a delicate instrument which records the earthquake waves.

Q.4. Name two types of body waves.

Ans. The two types of body waves are P waves and S waves.

Q.5. What is the asthenosphere?

Ans. The upper mantle extending from the crust to the depth of about 650 km is the asthenosphere. It occupies the upper 300 to 400 km.

Q.6. What is the temperature of the core of the earth?

Ans. The temperature of the core of the earth is about 2000°C.

Q.7. What are the three types of earthquake waves?

Ans. Three types of waves are:

1. P or Primary waves.

2. S or Secondary waves.

3. Lor long waves.

Q. 8. What are various sources of heat in the earth?

Ans. 1. Radioactivity.

2. The heat of aggradation.

3. The temperature of materials of which the earth is made.

Q.9. What is the total depth of the earth’s crust?

Ans. 6400 km from the surface of the earth.

Q.10. What is the radius of the earth core?

Ans. The average radius of the earth’s core is 3470 km.

Q.11. Name the two types into which the forces changing the face of the earth have been categorised.

Ans. 1. Endogenic Forces.

2. Exogenic Forces.

Q.12. Which of the earthquake waves travels fastest?

Ans. P waves.

Q.13. Name the waves that follows the circumference of the earth.

Ans. L waves.

Q.14. By which metals is core made of?

Ans. Core is made up of nickel and iron.

Q.15. What are body waves?

Ans. 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. Therefore, it has been named as body waves. These are of two types: P-waves and S- waves.

Q.16. How do you measure magnitude of an earthquake?

Ans. We measure magnitude of an earthquakes using Richter Scale.

SHORT ANSWER TYPE QUESTIONS

Q.1. Define Focus and Epicentre.

Ans. Focus: It is a point inside the earth surface from where an earthquake starts. It is always hidden inside the earth. Focus of an earthquake may be found at the depth of 100-200 km.

Epicentre: It is a point on the earth surface which records the seismic waves for the first time. Maximum destruction from an earthquake is caused on the epicentre. Epicenter is located just perpendicular to the focus.

Q.2. Name the direct sources of information about the interior of the earth.

Ans. The direct sources of information about the interior of the earth are:

1. Earth material or rock availed from mining areas and deep drilling projects.

2. Materials availed from the volcanic eruptions.

Q.3. Describe the two types of surface waves.

Ans. Surface waves are those earthquake waves which move freely along the upper crust of the earth. These produce disastrous effects of earthquakes.

These are of two types:

(i) Rayleigh waves or R-waves: These are named after English Physicist, Lord Rayleigh. These are similar to water waves travelling across the surface of a still pond when a pebble is tossed into water.

(ii) Love waves or L-waves: The second type of surface waves is the love waves. These move at right angle to the direction of wave motion.

Q.4. Write short notes on:

(i) Focus.

Ans. Focus: The place of origin of an earthquake inside the earth is called the focus.

(ii) Epicentre.

Ans. Epicentre: The point on the earth’s surface vertically above the focus is called epicentre.

(iii) Fissure.

Ans. Fissure: When lava rises through cracks it is called fissure erruption.

(iv) Ring of fire.

Ans. Ring of fire: The circum pacific belt of vaccums is called Ring of Fire.

(v) Tsunami.

Ans. Tsunami: Seismic waves caused in ocean are called in tsunamis in Japan.

Q.5. Why do earthquake waves develop shadow zone?

Ans. The earthquake waves develop shadow zones because the P and S waves follow a curved path in the interior of the earth which proves that the density increases inside the earth. P and S waves are recorded along the surface near the focus of the earthquake. Beyond the depth of 2900 km ‘S’ wave disappear and P waves travel with reduced velocity. On reaching the core ‘S’ waves disappear and P waves are refracted as a result there is no wave for a distance. This area is known as shadow zone. Normally it is found between 105° to 145°.

Q.6. What are the three types of earthquake waves?

Ans. The three types of earthquake waves are:

(i) ‘P’ or longitudinal waves or primary waves: These waves travel in the direction of their movement. They can travel through solid as well as liquid matter.

(ii) ‘S’ or transverse or secondary waves: These waves travel at right angle to the direction of their oscillation. They can travel in solid media only.

(iii) ‘L’ or Long Waves: These are surface waves. These do not go deep into the earth.

Q.7. What are body waves?

Ans. Body waves are earthquake waves. Body waves are generated due to the release of energy at the focus. They radiate and move in all directions from the point of hypocentre or the ‘focus’ and travel through the body of the earth. Hence the name body waves.

Q.8. What are the three types of volcanoes?

Ans. On the basis of mode and frequency of eruption volcanoes are classified into three types:

(i) Active volcanoes: The volcanoes that erupt frequently and are always emitting lava are called active volcanoes. Mauna Loa in Hawaii Islands is the largest active volcano in the world.

(ii) Dormant volcanoes: Dormant volcanoes are also called sleeping volcanoes. These volcanoes have been active in the past, stopped ejecting lava now but can erupt any time. The visuvius of Italy is such a dormant volcano.

(iii) Extinct volcanoes: The volcanoes which have never erupted in human history are called extinct or dead volcanoes. Kilmanjaro in Africa is the example of such volcanoes.

Q.9. Briefly explain the indirect sources of information of the interior of the earth other than the seismic activity.

Ans. The indirect sources of information of the interior are:

1. Density: The density of the sedimentary rocks is 2.7 and beneath the sedimentary rocks the density of igneous rocks is 3.5. This means that the density inside the earth is much higher. It is estimated that the core of the earth has the density of 11 to 12.

2. Temperature: There is a gradual increase in the temperature as depth increases. The rate of increase is 12°C per km at a depth of 100km. It is 2°C/km at a depth of 300 km and 1°C per km, below it.

3. Pressure: Like density and temperature, pressure also increases with the increase in depth inside the earth. It is due to overlying layers or depressions of the heavier material. It is estimated that the pressure at the centre of the earth is about 3500 kilobars.

The other indirect sources include gravitational magnetic field and the seismic activity. The gravitational force is greater near the poles and lesser at the equator.

The gravity values also differ according to the mass of the material. Uneven distribution of the mass of material within the earth influences this value.

Q.10. Describe the Earth’s mantle.

Ans. Beneath the crust in lithosphere is the mantle. It has a thickness of about 2900 km. It behaves like an elastic solid. It has two major parts:

1. The upper mantle (upto 650 km, this is called asthenosphere).

2. The lower mantle (upto 2900 km). It is elastic as well as plastic in nature.

Q.11. Describe the distribution pattern of volcanoes in the world.

Ans. Distribution of volcanoes: There are about 500 active or dormant volcanoes. Most of the volcanoes are found in coastal areas or areas affected by earthquakes. These are found in three well defined belts.

(i) Circum Pacific Belt: This belt surrounds the pacific ocean. It is also known as ‘Pacific Ring of Fire’ well known volcanoes are Karakatoa (Java) Fijiyama (Japan) Cotopaxi (Bolivia).

(ii) Mid World Mountain Belt: This belt is extended east west direction along the Alpine Himalayan region. Well known volcanoes of the world are strombli, Etna.

(iii) The African Rift Valley: This bet passes through the Red sea upto rift valley of Africa. Most important volcanoes are Kilmanjaro and Mt. Kenya.

Q.12. Describe the different parts of volcanoes.

Ans. (i) Volcanic vent: Extrusion of lava takes place from an opening called Volcanic vent.

(ii) Crater: A saucer shaped depression is created around the vent and is known as crater.

(iii) Culdera: Due to explosion a stups did crater is formed and called caldera.

Q.13. Distinguish between Gutenburg discontinuity and Mohorovicic discontinuity.

Ans. 

Gutenburg Discontinuity	Mohorovicic Discontinuity
1. The boundary between the mantle and core at the depth of 2900 km is called Gutenburg’s discontinuity.	1. The boundary between the crust and the mantle is called Mohorovicic discontinuity.
2. It was observed by the seismologists, Beno Gutenburg in 1926.	2. It was observed by Yugoslav seismologist Mohorovicic in 1909.

Q.14. Distinguish between body waves and surface waves.

Ans.

Body Waves	Surface Waves
1. P and S waves are called body waves.	1. L waves are called surface waves.
2. These travel through the solid body of the earth.	2. These move along the free upper crust of the earth.
3. These do not pass through liquid medium.	3. These can pass through liquid medium and move at right angle to the surface of the earth.

Q.15. Distinguish between Longitudinal waves and Transverse waves.

Ans. 

Longitudinal Waves	Transverse Waves
1. In these waves, particular move to and fro in the direction of the waves.	1. In these waves, particles move at right angles to the direction of the wave motion.
2. These are known as Primary waves or P waves or sound waves.	2. These are known as Secondary waves or S- waves.
3. These waves can travel through liquid, solid and gaseous media.	3. These waves travel only in solid media.

Q.16. Distinguish between crust and core of the earth.

Ans.

Crust of the earth	Core of the earth
1. This is the outermost layer of the earth.	1. This is the innermost layer of the earth.
2. It has an average density of 2.73.	2. It has an average density of 17.2.
3. It covers about 0.5% by part of the earth.	3. It covers about 83% by part of the earth.
4. It is made up of Silica and Aluminium.	4. It is made up of Nickle and Ferrum.

Q.17. Name the direct sources of information about the interior of the earth.

Ans. Some of the direct sources are:

Mining: It is a process by which commercially variable valuable mineral resources are extracted from Earth’s surface which includes precious stones, rocks and solid fuels.

Drilling: Scientists world over are working on two major projects such as “Deep Ocean Drilling Projects” and “Integrated Ocean Drilling Project”. The deepest drill at Kola, in Arctic Ocean, has so far reached a depth of 12 km.

Volcanic Eruptions: When molten material is thrown onto the surfaced earth during volcanic eruption it becomes available for analysis.

Q.18. Write short notes on:

(i) Earthquake Shadow Zone.

Ans. Some specific areas where earthquake waves are not reported are known as earthquake shadow zones. A zone between 105° and 145° from the epicentre of the earthquake is identified as the shadow zone for both P and S waves. The shadow zone of S-waves is much larger than the shadow zone of P-waves and it is little over 40 percent of the earth’s surface.

(ii) Mohorovicie Discontinuity

Ans. The abrupt changes in the velocity of siesmic ways suggest that the crust is distinguished from the mantle. The surface of sudden increase in wave velocity which sprates and crust above from the mantle below is called Mohorovicie discontinuity or M. discontinuity. The ‘P’ waves near the surface travel at about six km/s and increase to 7 km per second to the base of the crust. This is named after the yugoslav sies mologist Mohorovicie who first recognised the discontinuity in 1909.

LONG ANSWER TYPE QUESTIONS

Q.1. Describe the land forms of Volcanic Topography.

Ans. Following are the land forms of Volcanic Topography:

(i) Crater: A crater is a funnel shaped hollow formed at the centre of volcano. It is formed by an explosion. A crater filled with water is known as a crater lake such as Lonar lake in Maharashtra.

(ii) Caldera: Calderas are very large volcanic depression. Colderas are formed by explosion and collepse. The top of the cone is blown off and a broad depression or crater is formed. Coldera of Japan is called ‘A Volcano of hundred villages’.

(iii) Ash cones: Ash or cinder cones are made of loose ash and dust. They have concave slopes.

(iv) Shield cones: These are formed by basic lava which is poor in silica. It cools down quickly and travels a long distance. There are flat low cones with a small angle of slopes such as Mauna Loa in Hawaii Islands.

(v) Lava domes: These are formed by acid lava which is rich in silica. It cools down slowly around the crater. Then are steep convex sided high domes such as Puy de dome in France.

Q.2. How do the waves of different types tell us about the changes in the nature of different layers of the earth’s interior?

Ans. The most important indirect source to know the interior of the earth is the data collected through earthquake waves.

There are three types of earthquake waves:

(i) ‘P’ waves or primary waves or longitudinal waves. These waves can travel through solid as well as liquid media.

(ii) The ‘S’ or secondary or transverse waves can travel in solid media only. These waves are slow in motion.

(iii) ‘L’ waves or surface waves move along the boundaries between solid, liquid and gaseous. media. They do not go deep into the earth. They have a very low velocity.

The velocity of the waves increase if they travel through denser media. The velocity of first two types of waves increases with depth but only upto 2900 kilometres. Afterwards ‘S’ waves do not pass and ‘P’ waves pass at a reduced velocity. The velocity of ‘P’ waves passing through inner

core again increases as compared to their passage through the outer core. Based on this finding the scientists have estimated that the iron and nickel of the core of the earth may be in liquid state.

Q.3. What do you understand by intrusive forms? Briefly describe various intrusive forms.

Ans. The lava that is released during volcanic eruptions on cooling develops into igneous rocks. The cooling may take place on their reaching the surface or also while the lava is still in the crustal portion. The lava that cools within the crustal portion assumes different forms called intrusive forms. They are as follows:

(i) Batholiths: A large body of volcanic material that cools at the deeper depth of crust develops in the form of large domes. They appear on the surface only after denudation process removes the overlying material. These are the cooled portions of the magma chambers.

(ii) Localiths: These are the 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. Karnataka plateau is spotted with dome-shaped hills of granite rocks.

(iii) Lapoliths: When lava moves upwards, portions of the same may tend to move in horizontal direction whenever it finds a weak plane. It may get rested different forms. If it develops into a saucer-shape, concave to the sky body, it is called lapoliths.

(iv) Phacoliths: The wavy mass of intrusive rocks found at the base of synclines or at the top of anticline in folded igneous regions are called the phacoliths.

(v) Sill or sheet: Near horizontal bodies of the intrusive igneous rocks are called sill or sheet.

(vi) Dykes: When the lava cools in fissures developed in the land, such structure are called dykes.

Q.4. Explain different types of earthquakes.

Ans. The various types of earthquakes are:

(i) Tectonic earthquake: The most common ones are the tectonic earthquakes. These are generated due to sliding of rocks along a fault plane.

(ii) Volcanic earthquake: A special class of tectonic earthquake is sometimes recognised as volcanic earthquake. However, these are confined to areas of active volcanoes.

(iii) Collapse earthquake: In the areas of intense mining activity, sometimes the roofs of underground mines collapse causing minor tremors. These are called collapse earthquakes.

(iv) Explosion earthquake: Ground shaking may also occur due to the explosion of chemical or nuclear devices. Such tremors are called explosion earthquakes.

(v) Reservoir Induced earthquake: The earthquakes that occur in the areas of large reservoirs are referred to as reservoir induced earthquakes. Sometimes earthquakes also occur in mines due. to mining processes. Sometimes earthquakes also occur below the oceans on surface of the ocean causing tsunamis.

Q.5. What are the effects of propagation of earthquake waves on the rock mass through which they travel?

Ans. The earthquake waves affect the rock mass through which they travel. Propagation of earthquake waves is not similar. P waves exert pressure on the material in the direction of the propagation. Consequently, it creates density differences in the material. Other waves vibrate perpendicular to the direction of the propagation. The direction of vibration of S wave is perpendicular to the wave direction in the vertical plane. They create troughs and crests in the material through which they pass. The surface waves or L-waves are the most dangerous waves and vibrate in perpendicular direction to the surface in horizontal plane. This causes displacements of the rock mass and collapse of structures.

Q.6. Explain the interior structure of the earth.

Ans. The interior structure of the earth can be classified into three parts:

(i) Crust.

(ii) Mantle.

(iii) Core.

(i) Crust: It is the outermost solid part of the earth. It is brittle in nature. The thickness of the crust varies under the oceanic and continental areas. Oceanic crust is thinner as compared to the continental crust. The mean thickness of oceanic crust is 5 km whereas that of the continental is around 30 km. The continental crust is thicker in the areas of major mountain systems. It is as much as 70 km thick in the Himalayan region. It is made up of heavier rocks. It is having density of 3 g/cm3. This type of rock found in the oceanic crust is basalt. The mean density of material in oceanic crust is 2.7 g/cm3.

(ii) Mantle: The portion of the interior beyond the crust is called the mantle. The mantle extends from Moho’s discontinuity to a depth of 2,900 km. The upper portion of the mantle is called asthenosphere. The word astheno means weak. It is considered to be extending upto 400 km. It is the main source of magma that finds its way to the surface during volcanic eruptions. It has a density higher than the crust’s (3.4 g/ cm3). The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 km. The lower mantle extends beyond the asthenosphere. It is in solid state.

(iii) Core: The earthquake wave velocities helped in understanding the existence of the core of the earth. The core- mantle boundary is located at the depth of 2,900 km. The outer core is in liquid state while the inner core is in solid state. The density of material at the mantle core boundary is around 5 g/cm3 and at the centre of the earth at 6,300 km, the density value is around 13g/cm3. The core is made up of very heavy material mostly constituted by nickel and iron. It is sometimes also called the nife layer.