WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes

Chapter 2 Topic C Earthquakes Analytical Type Questions

Question 1. What are the causes of earthquakes?
Answer:

Causes Of Earthquakes:-

The major causes of earthquakes are discussed below

1. Plate movements:

According to the Plate Tectonic Theory, when two plates move away or towards each other or slide past each other, an earthquake occurs along the boundary.

2. Contraction of the earth’s crust:

The increasing rate of contraction of the earth’s crust due to radiation causes earthquakes.

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3. Volcanism:

During volcanism, hot liquid magma and vapour come out due to the unloading of pressure which leads to earthquakes.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Earthquake due to plate movement

4. Landslides:

A landslide in the hilly regions due to heavy rainfall often triggers the occurrence of an earthquake.

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5. Avalanches:

Avalanches in mountainous regions cause severe earthquakes.

6. Faults:

Tectonic activities are responsible for the development of faults in rock layers. The variable stress and strain of the layers cause earthquakes.

Example- The Assam earthquake of 1950 was caused due to this.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Earthquake due to faults

7. Upheaval of fold mountains:

At the time of the upheaval of fold mountains due to the orogenic and epeirogenic forces, the surrounding areas experience earthquakes.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Earthquake due to upheaval of fold mountains

8. Fall of meteorites:

Falling of meteorites from the sky may cause earthquakes.

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9. Artificial causes:

  1. Pressure of dams
  2. Atomic explosions
  3. Unscientific mining, etc.

Question 2. Discuss the major earthquake belts of the world.
Answer:

Major Earthquake Belts Of The World:-

The earthquake belts may be classified into three groups on the basis of their plate boundaries

1. Pacific belt:

This belt sprawls over the Pacific Ring of Fire along both coasts of the Pacific Ocean. It extends from Cape Horn of South America to the Rocky Mountains of North America through the Andes of South America.

The remaining part extends over Alaska, the Kurile Islands, Japan, the Mariana Trench and south of the Philippines. In the south, it extends up to north-western New Zealand through Tonga.

This is the most earthquake-prone area and it experiences 70% earthquakes of the world.

2. Mid-World Mountain Belt or Mid- Continental Belt:

This belt runs through the Mediterranean Sea, Alps, Caucasus and Himalayas to the Pacific belt. It is the transitional belt of the Eurasian Plate and the Indian Plate.

Thus it is an important seismic zone and is called the Tethyan belt. About 20% of the earthquakes of the world occur in this belt.

3. Mid-Atlantic Belt:

This belt sprawls along the mid-oceanic ridge. The upwelling of magma along the oceanic plate boundary causes earthquakes. About 10% of the earthquakes on Earth occur along this belt.

Question 3. Discuss the impact of earthquakes.
Answer:

Impact Of Earthquakes

No one can feel the impact of a mild earthquake, but when it is severe, it results in a huge loss of life and property. It has several other impacts, like

Class 8 Geography WBBSE

Coastal upliftment:

The sea floor may be uplifted or subducted due to an earthquake. of faults, folds and Formation

Formation of faults, folds and Cracks:

Faults, folds or certain cracks on the earth’s crust may develop due to an earthquake.

Tsunami:

An earthquake just beneath the sea floor causes displacement, subduction and overriding of the plates. This deformation of the crust increases the vertical height of the water mass of the epicentre and the water rushes towards the coast.

Example-The earthquake in the Indian Ocean near Sumatra and Andaman islands caused a devastating tsunami on 26 December 2004.

Avalanches and landslides:

Often earth- quakes in hilly regions may cause landslides and avalanches. Example-The impact of the Chamoli earthquake in Garhwal Himalaya in Uttarakhand on 19 October 1991.

Change of river course:

An earthquake may change the direction of the flow of a river. The river Brahmaputra got diverted due to the Assam earthquake in 1887.

Apart from these, an earthquake is also a factor responsible for the formation of new lakes, and waterbodies, the destruction of settlements and the loss of lives and property.

Question 4. Write the differences between earthquakes and geo-tectonic movements.
Answer:

The differences between earthquakes and geo-tectonic movements are as follows-

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Differences between earthsquakes and geotectonic movements

Chapter 2 Topic C Earthquakes Short Analytical Type Questions

Question 1. What are the major seismic waves?
Answer:

Major Seismic Waves:-

Seismic waves can be classified into three groups

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Primary or P-wave:

The velocity of this wave is 6km/sec. This is the fastest travelling wave. This wave travels through solid, liquid and gas-all types of the medium through a push and pull process.

Secondary or S-wave:

The velocity of this wave is 3-5km/sec. This wave travels only through solid medium through up and down movements of particulate matter. Though it has less velocity than primary waves, it can cause severe damage.

Surface or L-wave:

A surface wave is formed at the epicentre of the earthquake from the combined effect of P and S-waves. This can also cause much damage and destruction.

Surface waves are of two types

  1. Love waves and
  2. Rayleigh waves.

2. What is a primary or P-wave?
Answer:

P-wave:-

The wave that touches the earth’s surface first, is known as the primary or P- wave.

Primary or P-wave Characteristics:

  1. It is much more powerful than any other seismic wave.
  2. It can pass through any medium-solid, liquid or gaseous under the crust.
  3. The length of this wave is short but it has the highest speed.
  4. The velocity of this wave is 6 km/sec. This wave passes through a push-and-pull process.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes p-wave

Question 3. What are secondary or S-waves?
Answer:

S-Waves:-

Besides P-waves, another important type of seismic wave are Secondary or S-waves.

Secondary or S-waves Characteristics:

  1. They are also known as transverse waves.
  2. The materials of the place through which the S-wave passes start to tremble and move in an up-and-down manner.
  3. S-waves cannot travel great distances. They are weaker than P-waves.
  4. They can pass through solid parts only. The velocity of these waves varies between 3-5 km/sec. Though their velocity is less than primary waves, they can still cause severe damage.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes S- wave

Question 4. What are surface or L waves?
Answer:

Surface Or L Waves:-

The waves that travel parallel to the earth’s surface from the focus of an earthquake are called surface or L waves. They are also. called side waves or lateral waves. Surface waves are of two types-Love waves and Rayleigh waves.

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Surface or L waves Characteristics:

  1. These waves can pass only through a solid medium.
  2. These waves are long. and are the last to reach the seismograph.
  3. Surface waves are formed at the epicentre of the earthquake from the combined effect of P and S-waves.
  4. These travel at a lower speed than the P and S-waves.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes L-wave

Question 5. Briefly write about Seismographs.
Answer:

Seismographs:-

A seismograph is an instrument measuring the magnitude of an earthquake. The various aspects of a Seismograph are discussed below

Seismographs Terminology:

The term ‘seismo’ is derived from the Greek word demos, meaning tremor and graph meaning ‘the graphical statement. A seismograph is an instrument that records graphical statements of earthquakes.

Seismographs Working mechanism:

Seismography works on some basic principles. A weight is suspended with a spring from a strong frame. A marker attached to the weight touches the roll of paper wrapped around a cylinder, under the weight.

The oscillation of the marker during an earthquake marks the paper and creates a graph. This is called a seismogram. Nowadays, tremors of earthquakes can be recorded in minute details with specialised computers.

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Seismographs Inventor:

John Milne, a British geologist who invented first modern seismograph in 1880.

Seismographs Utility:

From the records of this device, the location of focus and epicentre, the time, the duration and the intensity of an earthquake can be interpreted.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Sesimograph

Question 6. Write a short note on Richter Scale.
Answer:

Richter Scale:-

The various aspects of the Richter Scale are discussed below

Richter Scale Concept:

It is a scale devised to measure the magnitude of an earthquake as recorded by a Seismograph.

Richter Scale Inventor:

C.F. Richter, an American Seismologist, developed this scale in 1935.

Richter Scale Characteristics:

  1. This device has a scale ranging from 0-10.
  2. The intensity of the earthquake increases 10 times with the increase of each marking on this scale.
  3. The first five measures indicate low-intensity or micro-quakes. With each next unit, a rapid increase in the intensity of tremors is indicated.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Richer Scale

Question 7. Why are the Young Fold mountain regions geologically unstable?
Answer:

Young Fold Mountain Regions Geologically Unstable:-

The young fold mountain regions of the world are geologically very unstable due to

  1. The drifting of the active plates of the surrounding area
  2. Readjustment of the equilibrium of the whole region
  3. The continuous upheaval of the fold mountains
  4. The occurrence of landslides, earthquakes, avalanches, etc.

Question 8. Why are the regions of the fold mountains earthquake-prone?
Answer:

The Regions Of The Fold Mountains Earthquake-Prone:-

According to the Plate Tectonic Theory, when two continental plates collide with each other and the lighter plate overrides the heavier one along the suture line, tremendous pressure is created on the sediments lying in the intra-plate zone.

This causes the folding of the silt-deposited strata, which leads to the formation of fold mountains there.

Example- The Himalayas came into being due to the converging plate movements of the Eurasian and the Indian Plates. These tectonic activities, including collision, drifting and subduction of plates are responsible for earthquakes.

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This continuous process of development makes the fold mountain regions earthquake-prone.

Question 9. How is it possible to predict an earthquake?
Answer:

It Is possible to predict an earthquake:-

It is not easy to predict an earthquake. But scientists try to predict earthquakes by the nature of plate movements.

Spread of seismic waves:

Modern devices measure the variation of the seismic waves with the elasticity of the rocks.

The inclination of the Earth’s surface:

Studying the tilt of the earth’s surface around the epicentre of the earthquake before the occurrence of earthquakes.

The curvature of the rocks:

Studying the curvature of rocks measured with a tiltmeter.

Question 10. Briefly describe the phenomenon of Tsunami.
Answer:

Phenomenon Of Tsunami:-

Nomenclature:

The word ‘Tsunami’ is derived from two Japanese words- Tsu for ‘harbour’ and nami for ‘waves’- which means sea waves along the coastal harbour.

Tsunami Origin:

Volcanic eruptions just beneath the sea floor cause displacement, subduction and overriding of the oceanic plates, giving rise to earthquakes. These sudden movements of the earth’s crust increase the vertical height of the water mass of the epicentre and then water rushes towards the coast.

Tsunami Characteristics:

  1. These waves rush towards the coast at a height of 10 metre-20 metre.
  2. Their velocity is about 700km/h-800 km/h.
  3. The height of the waves at the coastal line becomes about 30 metres-40 metre.
  4. These waves can cause great devastation due to their force and long duration. Example-A massive tsunami occurred on December 26, 2004, because of the subduction of the Indian Plate below the Myanmar Plate.

 

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Origin of tsunami

Question 11. What are the do’s and don’ts at the time of an earthquake?
Answer: To protect ourselves during an earthquake, we should observe the following

Do’s at the time of an earthquake:

  1. The building should be evacuated at the time of tremors.
  2. The shelter should be taken under strong tables if we are unable to move out of the building.
  3. Torch, dry food and drinking water should be carried along.
  4. The shelter should be taken in a safe place at the time of tremors. We should stop driving and wait inside the car.

Don’ts at the time of an earthquake:

  1. Any electric wire should not be touched.
  2. The lift should not be used and we should not stand in the balcony.
  3. Pets or domestic animals should not be chained inside the house.

Question 12. The earth experiences tremors every moment-Explain.
Answer:

The earth experiences tremors every moment:-

The tectonic plates are dynamic in nature because they are floating on the asthenosphere. They move away or towards each other or slide past each other due to the action of internal convection currents.

As a result, the earth is always being shaken by these tectonic activities. But we can not sense all of these tremors because they may occur beneath the sea surface or in desolate areas. We can feel only the severe tremors.

Class 8 Geography Solution WBBSE

Chapter 2 Topic C Earthquakes Short Answer Type Questions

Question 1. Why is it dangerous to live in the cities of San Francisco and Los Angeles in California?
Answer:

It Is Dangerous To Live In The Cities Of San Francisco And Los Angeles In California

Both the cities, San Francisco and Los Angeles, are situated on the transform plate boundary in West America and along the San Andreas fault in California.

The whole area lies in an earthquake-prone region and is dangerous to human beings due to the sliding of the North American Plate past the Pacific Plate.

Question 2. What is the focus of an earthquake?
Answer:

Focus Of An Earthquake:-

The place in the interior of the earth where an earthquake originates is the focus of an earthquake. These are located at the depth of 50km-100km underneath the earth’s surface.

The seismic tremors generated from the focus spread out through different waves. It is to be noted that it is not only a point but is a wide area.

Question 3. Define the epicentre of an earthquake.
Answer:

Epicentre Of An Earthquake:-

The point on the earth’s surface vertically above the focus of an earthquake is known as its epicentre. This place is the nearest to the focus of the earthquake and gets damaged severely.

As the seismic waves reach here first, the intensity of the earthquake is the highest in this area and gradually decreases away from it.

Question 4. What are seismic waves?
Answer:

Seismic Waves:-

Different tectonic activities, due to an earthquake, cause tremors which spread out from the focus of the earthquake in the form of waves. These are called seismic waves.

These waves can be classified into three groups

  1. P-wave
  2. S-wave and
  3. L-wave.

Question 5. What do you mean by ‘Love wave’ and ‘Rayleigh wave’?
Answer:

The L or Surface wave is, of two types

  1. Love wave and
  2. Rayleigh wave.

The wave which spreads parallel to the earth’s surface is called the Love wave after the name of its inventor A.E.H. Love. On the other hand, Rayleigh’s wave passes through the earth’s surface and was named after its inventor physicist Lord Rayleigh.

Question 6. What do you mean by the antipode of the earthquake?
Answer:

Antipode Of The Earthquake:-

The place on the earth’s surface just opposite to the epicentre of the earthquake is called the antipode of the earthquake. The angular difference between those two points is 180°.

Question 7. What is isoseismic line?
Answer:

Isoseismic Line:-

Isoseismic line is an imaginary line which connects the points on the earth’s surface that experience equal tremors at the same time due to an earthquake.

Question 8. How does eruption of magma lead to the generation of earthquakes?
Answer:

Eruption Of Magma Lead To The Generation Of Earthquakes:-

When the hot and molten magma, including gases from the interior of the earth, comes out through the weak parts on the earth’s surface (joints, cracks or holes) due to the sudden release of pressure, it is called volcanism.

This sudden unloading of pressure disturbs the tectonic plates, giving rise to earthquakes.

WBBSE Class 8 Geography Chapter 2

Question 9. What should you do if an earthquake occurs all of sudden?
Answer: If an earthquake occurs suddenly, we should take the following measures

  1. We should come out from the buildings such as house or schools as soon as possible, find an open ground and stand there.
  2. If it is not possible to move out from the closed spaces, immediately we should hide under a strong table.
  3. If possible, we should pack essential items before leaving the house.
  4. During an earthquake, it is advisable to avoid the use of balcony or elevator of a multistoried building.

Multiple Choice Questions Choose The Correct Option

Question 1. One of the cities situated on the San Andreas fault is-

  1. Tokyo
  2. California
  3. Mexico City
  4. Washington

Answer: 2. California

Question 2. The San Andreas Fault is located along the western coast of-

  1. North America
  2. Asia
  3. South America
  4. Europe

Answer: 1. North America

Question 3. Most of the earthquake foci are located at depth of-

  1. 0km-2km
  2. 50km-100km
  3. 5km-10km
  4. 700km-1000km

Answer: 2. 50km-100km

WBBSE Class 8 Geography Chapter 2

Question 4. The only seismic wave that can travel through any medium is-

  1. Love wave
  2. Rayleigh wave
  3. P-wave
  4. S-wave

Answer: 3. P-wave

Question 5. The most intense earthquakes are noticed along the-

  1. Convergent boundary
  2. Divergent boundary
  3. Neutral boundary
  4. Indefinite boundary

Answer: 1. Convergent boundary

Question 6. A famous volcano in the Mid-World Mountain Belt is-

  1. Fujiyama
  2. Cotopaxi
  3. Vesuvius
  4. Krakatau

Answer: 3. Vesuvius

Question 7. Seismology in the study of-

  1. Earthquakes
  2. Plate movement
  3. Volcanism
  4. Rocks and minerals

Answer: 1. Earthquakes

Chapter 2 Topic C Earthquakes Fill in the blanks

Question 1. The place on the earth’s surface where the tremor reaches first is called _________.
Answer: Epicentre

Question 2. Actually, Love wave and Rayleigh wave are _________ waves.
Answer: Surface

WBBSE Class 8 Geography Chapter 2

Question 3. The seismic waves of an earthquake are detected by a _________.
Answer: Seismograph

Question 4. The intensity of the earthquake is measured by the _________ scale.
Answer: Richter

Question 5. The Richter scale measures the intensity of earthquakes on a range of _________.
Answer: 0-10

Question 6. Earthquakes are disastrous when they register intensity above on the _________ Richter scale.
Answer: 6

Question 7. The Pacific Ring of Fire experiences _________ % earthquakes of the world.
Answer: 70

Question 8. The most devastating earthquake was experienced by _________ island of Indonesia on December 26, 2004.
Answer: Sumatra

Chapter 2 Topic C Earthquakes Write True or False

Question 1. P-wave passes through solid matter only.
Answer: False

Question 2. An earthquake is felt mostly around its focus.
Answer: True

Question 3. The Himalayan mountain region in India is an earthquake-prone area.
Answer: True

Question 4. Earthquakes may occur along all and any of the plate boundaries.
Answer: True

Question 5. Tsunami is caused by a huge tremor beneath the sea floor.
Answer: True

Question 6. No earthquake occurs from a hotspot.
Answer: False

Question 7. The scientist Mercalli invented the Richter scale.
Answer: False

WBBSE Class 8 Geography Chapter 2

Chapter 2 Topic C Earthquakes Match The Columns

1.WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Match the following

Answer: 1. C, 2. D, 3. E, 4. B, 5. A

Chapter 2 Topic C Earthquakes Answer In One Or Two Words

Question 1. On which fault is the city of San Francisco situated?
Answer: San Andreas Fault.

Question 2. In which year was San Francisco devastated by a massive earthquake?
Answer: 1906.

Question 3. What are the types of earthquake waves?
Answer: P, S and L-waves.

Question 4. What is the average speed of a P-wave?
Answer: 6km/sec.

Question 5. Which one is the most devastating earthquake wave?
Answer: L-wave.

Question 6. Who invented the Richter Scale?
Charles Francis Richter.

Question 7. Which places in the world are most prone to earthquakes?
Answer: Young fold mountainous regions.

WBBSE Class 8 Geography Chapter 2

Question 8. What was the magnitude of the earthquake that occurred in Sumatra (Indonesia) on December 26, 2004?
Answer: 8.9 on the Richter scale.

Question 9. Name an earthquake event that was caused due to hydrostatic imbalance.
Answer: Koyna earthquake in Maharashtra.

Chapter 2 Topic C Earthquakes Conceptual Questions And Answers

Who am I?

Question 1. I was born due to the drifting of the American and the African Plates away from each other.’-Who am I?
Answer: Mid-Atlantic Ridge

Question 2. ‘I am the deepest trench in the Pacific Ocean.’-Who am I?
Answer: Mariana Trench

Question 3. I am a shallow geosyncline between Laurasia and Gondwanaland. Presently, the Mediterranean Sea is my modified form.’- Who am I?
Answer: Tethys sea

Question 4. I am a young fold mountain between the Eurasian Plate and the Indian Plate.’-Who am I?
Answer: The Himalayas

Question 5. I am the inclined earthquake-prone area along the plate boundary between two converging plates.’-Who am I?
Answer: Benioff zone

Chapter 2 Topic C Earthquakes Scrambled Words

1. LTEPA
2. MNAAARI
3. CANIOLS MV
4. SPOOTTH
5. RHTAEEKUAQ
6. RHRICTE

Answers:

1. PLATE
2. MARIANA
3. VOLCANISM
4. HOTSPOT
5. EARTHQUAKE
6. RICHTER

Chapter 2 Topic C Earthquakes Fill Up The Blanks In The Knowledge Hive

Tectonic activities and earthquakes are experienced frequently due to the instability of the crust along the convergent plate boundary. Make an information hub about the convergent plate boundary.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Fill in the blanks

Answers:

1. Two plates move towards each other along this boundary.
2. It experiences volcanism and earthquakes.
3. Along this boundary, new landforms like the Himalayas develop.
4. This boundary can be classified into three categories

  1. Continent-continent plate boundary
  2. Continent-oceanic plate boundary
  3. Oceanic-oceanic plate boundary

5. Along this boundary, the Benioff zone develops.
6. The meeting line of the two convergent plates is called the Suture Line.

WBBSE Class 8 Geography Chapter 8 Question Answer

Chapter 2 Topic C Earthquakes Crossword

 

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Crossword

CLUES

Down:

2. The Krakatau volcano is in this country.
3 The most famous volcano in Italy.

Across:

1. The deepest underwater sea trench.
4. Instrument for measuring earthquakes.
5. This plate boundary is formed when two plates move away from each other.

Answers:

Down: 2. INDONESIA, 3. VESUVIUS
Across: 1. MARIANA, 2. SEISMOGRAPH, 3. Divergent

Chapter 2 Topic C Earthquakes Advanced Questions And Answers

Question 1. Discuss the Continental Drift Theory as propounded by Alfred Wegener.
Answer:

Introduction:

German geophysicist and meteorologist, Alfred Wegener, propounded the Continental Drift Theory in 1912 but it could not come in light till 1922.

Before him, similar theories were also forwarded by Francis Bacon (1620), Antonio Snider-Pellegrini (1858), F.B. Taylor (1910) and several others.

WBBSE Class 8 Geography Chapter 8 Question Answer

Basic idea:

According to Wegener, all the land masses of the earth were united together until the Permian age. It was called Pangea and the remaining water bodies were called Panthalassa.

Later on, the Pangea was fragmented into two parts

  1. Laurasia on the northern side and
  2. The Gondwanaland on the southern side.

Gondwanaland included Africa, Antarctica, Australia, southern India and South America. According to him, the fragmentation of the Pangea created the present continents as they slowly drifted away.

Causes and direction of movement:

Wegener proposed

  1. Buoyancy
  2. Tidal force and

Differential gravitational force as the factors and force responsible for the movement of the fragmented lithospheric blocks. The continents drifted towards the equator due to the differential gravitational force and the westward movement took place due to tidal force.

Impact of Continental Drift:

The present-day continents and oceans were formed due to continental drift and it also caused the upheaval of fold mountains.

Evidence of Continental Drift:

The similarities between both the coasts on either sides of the Atlantic Ocean, regarding their shape, geology and topography, prove that they were united in ancient times and if they are to be reunited, they could be fixed point to point.

This is called Jig- Saw-Fit arrangement. Moreover, the places in the northern hemisphere which presently have a thick coal belt were probably the tropical climate regions previously. These evidence support the Continental Drift Theory.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Continental Drift Theory

Question 2. Identify the similarities and dissimilarities between Continental Drift Theory and Plate Tectonic Theory.
Answer:

Similarities And Dissimilarities Between Continental Drift Theory And Plate Tectonic Theory:-

There are many similarities and dissimilarities between the Continental Drift Theory of Alfred Wegener and the Plate Tectonic Theory of Wilson, Morgan, McKenzie, Parker and Pichon.

Similarities:

  1. Both of the theories go in favour of the continental movement.
  2. The two theories explain the formation of the young fold mountains.
  3. According to both the theories, horizontal forces are the triggering factors for the movement of landmasses.
  4. The Plate Tectonic Theory is established in the light of the Continental Drift Theory.

WBBSE Class 8 Geography Chapter 8 Question Answer

Dissimilarities:

  1. According to the Continental Drift Theory, SIAL is floating on the SIMA, whereas the Plate Tectonic Theory suggests the floating of SIAL and SIMA on the asthenosphere.
  2. The Continental Drift Theory does not explain the formation of mid-oceanic ridges, but the Plate Tectonic Theory has a proper scientific explanation for it.
  3. The formation and origin of fold mountains and volcanoes is explained better by the Plate Tectonic Theory than the Continental Drift Theory.
  4. The Continental Drift Theory suggests the westward and equatorward movements of the continents, while the other theory suggests for convergent, divergent and neutral movements of the plates.

Question 3. Write a short note on Mercalli Scale.
Answer:

Mercalli Scale:-

The intensity of an earthquake is also measured with the help of the Mercalli Scale. G. Mercalli, an Italian seismologist, devised this scale and it has been named after him as the Mercalli Scale.

There are 12 divisions on this scale, where- I= No destruction; II-III= Slight destruction; IV-V = Very little/insignificant destruction; VI-VII = Medium destruction; VIII- IX Major destruction; X-XII = Maximum destruction and severe damage.

Chapter 2 Topic C Earthquakes Formative

Participation

This segment will indicate how much the students have actively participated and taken the initiative during the class.

The present landmasses have been formed as a result of several geological activities initiated by internal forces. With reference to this information, answer the following:

Question 1. Which phenomena occur due to geological activities?
Answer: Mountain formation / Earthquakes / Volcanic eruptions/…

Question 2. What are the structural features of the Earth’s crust?
Answer: Hard and rough / divided into several segments / formed by the combination of the continental and oceanic plates/….

Question 3. Name some of the tectonic plates.
Answer: Eurasian Plate / Pacific Plate / American Plate/…

Question 4. What do you know about the plates which form the earth’s crust?
Answer: The plates are dynamic / these plates float on the asthenosphere / these plates move towards or away from each other and also move past each other in the opposite direction…

Question 2. What type of mountain do you see in the following picture? Along what type of plate boundary is it formed?
Answer: It is a type of fold mountain. It is formed along the convergent or destructive plate boundary.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Plate boundary

Chapter 2 Topic C Earthquakes Interpretation And Application

This segment will test whether the students have understood the topics, or whether they are just memorising them.

Question 1. Label the diagrams and fill up the chart correctly.
Answer:

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Lable the table , Fill the table

Question 2. Divide your class into five groups and make each group observe one of the five seismic zones in India. Point the big cities and famous places in each of these zones on the map.
Answer: There are five seismic zones in India. Locations of the major cities and famous places of India on these zones are

1. Very high earthquake-prone region: Srinagar, Guwahati, Kohima, Itanagar, Shillong, etc.

2. High earthquake-prone regions: Amritsar, Chandigarh, Patna, Haridwar, Siliguri, etc.

3. Moderate earthquake-prone region: Lucknow, Gandhinagar, Diu, Kolkata, Mumbai, etc.

WBBSE Class 8 Geography Chapter 8 Question Answer

4. Low earthquake-prone regions: Jodhpur, Jaipur, Ranchi, Chennai, Bhopal, etc.

5. Very low earthquake-prone region: Jhansi, Bangalore, Hyderabad, Gwalior, etc.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Major earthquake prone zones of India

Question 2. In which seismic zone is part of the country where you live situated? Has there ever been an earthquake there?
Answer: My name is Nikhil Samanta. I live in Krishnanagar, Nadia. This area belongs to India’s moderate earthquake-prone zone.
There have not been incidents of any earthquakes in our area in the recent past.

However, tremors of earthquakes occuring in other regions have been felt here. Example-tremors of the Sumatra earthquake in December 2004 and the Nepal earthquake in April, 2015 have been felt here in Nadia.

Question 3. Why was the city of San Francisco totally destroyed in the 1906 earthquake?
Answer: The city of San Francisco in the western USA is situated on the transform fault, i.e., San Andreas Fault in California. This fault forms a tectonic boundary between the Pacific Plate and the American Plate.

The Pacific Plate slides northwards along the margin of American Plate in this region. So the region is tectonically very unstable. Thus, the strong earthquake of 1906 almost devastated the city of San Francisco.

Chapter 2 Topic C Earthquakes Questioning And Experimentation

This segment will investigate the student’s understanding of the subject, questioning capacity, ability to explain and apply and urge for experimentation.

WBBSE Class 8 Geography Chapter 8 Question Answer

Question 1. What questions are raised in your mind by the images given below?
Answer:

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Different Types Of Plates Move

Why do the plates move?

  1. What happens when two plates move towards and clash against each other?
  2. Which plates in the earth’s crust are moving towards each other?
  3. What happens when two plates move away from each other?
  4. Which plates are moving away from each other?
  5. What happens when two plates move past each other in opposite directions?
  6. Why don’t all the plates move in the same direction?
  7. What would have happened if the plates would have been stationary?
  8. Why can’t we feel the movement of the plates?

Chapter 2 Topic C Earthquakes Aesthetics And Creativity

This segment will check the aesthetic sense and creativity of the students.

Question 1. Conduct a simple experiment to easily understand the process of volcanism.
Answer:

1. Materials required:

  1. A small and a large glass pot
  2. A small jug
  3. Some polythene
  4. Rubber band
  5. Pencils and
  6. Colours.

2. Process:

At first, the small pot is filled with hot water. Now some dark colour is poured in the water. After that the mouth of the small pot is sealed with the help of polythene and rubber bands.

Two or three holes are made on the polythene cover with the help of the tip of the pencil. Then this small pot is placed within the large pot. Cold water is poured in the large pot in such a way that the small pot gets submerged.

3. Observation:

Hot and coloured water rises and comes out of the holes of the polythene cover.

4. Explanation:

The water inside the small pot is lighter and greater in volume than the cold water in the large pot. Thus to bring an equilibrium in the pressure-temperature difference, the hot water rises and comes out from the holes of the polythene cover.

Magma from inside the earth comes out through the crater in a similar manner as a result of the pressure-temperature difference between the earth’s interior and exterior.

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Explaining of volcanism

Question 2. Make a model volcano that erupts lava.
Answer:

Method of making a model of the volcano:

1. Materials required:

  1. A piece of cardboard
  2. A tall thin container or bottle
  3. Paint
  4. Newspaper
  5. Plastic tapes, gums
  6. Sand or ash
  7. Coloured paper
  8. Vinegar, baking soda
  9. Red food colour and
  10. Soap water.

 

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Model of volcano

2. Process:

At first, the thin can is stuck to the middle of the cardboard with the help of tape. Now a cone is made by the pasting newspaper on all sides of the can. Then the outside of the volcano is covered with coloured paper.

After that sand or ash is spread on it with the help of gum. In this way the shape of the outer part of the volcano becomes ready. Now for volcanic eruption, some vinegar and soda water are poured into the can.

Some red colour is mixed into it. Now the model of a volcano is ready.

3. Observation:

Red lava is seen coming out from this volcano (model) just like an actual volcano.

4. Science behind eruption:

When we add vinegar to baking soda, a chemical reaction occurs. Carbonic acid is generated as a result of it. The mixture instantly separates into gas and liquid, producing carbon dioxide and water. The chemical reaction is as follows:

NaHCO3 + CH3 COOH→ Na+ H2 O + CO2 + CH3COO
(Baking soda) (Vinegar)

Question 3. In 2015, in the month of April, a devastating earthquake occurred in Nepal. It is believed that due to this quake, the height of the Himalayas has changed. Why did this happen? Explain the reason with the help of the subject matter of this chapter. Collect articles/pictures from newspapers/magazines of the Nepal earthquake.
Answer: Nepal is situated in the heart of the Himalayas. The Himalayan mountains are situated along the boundary of two convergent continental plates.

Approximately 65 million years ago, during the Tertiary period, the Indian Plate started to move towards the Eurasian Plate. The Eurasian Plate also started to move forward.

 

WBBSE Solutions For Class 8 Geography Chapter 2 Topic C Earthquakes Newspaper articles of the Nepal earthquakes

It has now been observed that the Indian Plate is going under the Eurasian Plate. Due to the movements of these two plates, the sediments in the Tethys Sea swelled up to form the Himalayas.

At this moment, the Indian Plate is moving in the direction of the north at a speed of 6 cm every year. The joining of the European and Indian Plates is still continuing.

The face-to-face movement of these plates led to the rise of the Himalayas and as long as the plate movements continue, the Himalayas will continue to rise.

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