Detailed explanations in West Bengal Board Class 8 Geography Book Solutions Chapter 2 Unstable Earth offer valuable context and analysis.
WBBSE Class 8 Geography Chapter 2 Question Answer – Unstable Earth
Multiple Choice Questions & Answers : (1 mark for each question)
Question 1.
J. T. Wilson introduced the word ‘Plate’ in-
i) 1965
ii) 1906
iii) 1970
iv) 1955
Answer:
i) 1965
Question 2.
Machenziae and Parker gave information on plate movement in-
i) 1967
ii) 1990
iii) 1965
iv) 1960
Answer:
ii) 1965
Question 3.
The vivid explanation of the plate tectonic theory was given by-
i) W. J. Morgan
ii) J. T. Wilson
iii) Alfred Wegener
Answer:
i) W. J. Morgan.
Question 4.
Asthenosphere lies –
i) 500-600 km below the crust
ii) 300-400 Km below the crust
iii) 200-300 kmbelow the crust
iv) 100-200 Km below the crust.
Answer:
iv) 100-200 Km.
Question 5.
Krakatua volcano has become active after-
i) 200 years
ii) 400 ycars
iii) 500 years
iv) 300 years
Answer:
i) 200 years.
Question 6.
The percentage of active volcano in the earth-
i) 10%
ii) 15%
iii) 20%
iv) 30%
Answer:
ii) 15%
Question 7.
The percentage volcanocs of the world are located in the middle of the plate on hot spot About-
i) 2%
ii) 3%
iii) 5%
iv) 8%
Answer:
iii) 5%.
Question 8.
The focus of the earthquake is located at the depth of –
i) 50-100 Km
ii) 100-150 Km
iii) 150-300 Km
iv) 200-250 Km
Answer:
i) 50-100 Km.
Question 9.
San Francisco was almost completely destroyed in a devastating earthsuake in-
i) 1910
ii) 1912
iii) 1904
iv) 1906
Answer:
1906
Question 10.
Percentage of earthquakes on the earth occur in the Pacific belt
i) 60%
ii) 70%
iii) 20%
iv) 40%
Answer:
ii) 70%.
Question 11.
Every year the powerful volcanic activities in the continental area are more than-
i) 20
ii) 10
iii) 40
iv) 50
Answer:
iv) 50.
Question 12.
The eruption of mount Pole occured in-
i) 1906
ii) 1202
iii) 1908
iv) 1905
Answer:
i) 1906.
Question 13.
Enormous loss of life and property took place due to the eruption of Mount St Helen in-
i) 1975
ii) 1980
iii) 1991
iv) 1900
Answer:
ii) 1980.
Question 14.
At the time of eruption many people die for-
i) cancer
ii) asthma
iii) suffocation
Answer:
iii) suffocation.
State whether True or False : (1 mark for each question)
1. The earth crust is made up of 18 small plate.
2. The outer mantle is located 300-400 Km. deep under the earth crust.
a. The temperature of asthenosphere is 1500° C.
4. The fold mountains are called ‘Young’.
5. The tectonic plates moved on asthenosphere.
6. popa of Mayanmar is a active volcano.
7. Primary wave is the fastest seismic wave and reaches the earth’s surface before all other waves.
8. The interior of the earth is still very hot.
9. Example of old fold mountain is Rocky.
10. Volcanism and earthquake are examples of sudden earth novements.
Answer:
1. false
2. false
3. true
4. true
5 true.
6. false
7. true
8. true
9. false
10. true.
Fill in the blanks : (1 mark for each question)
1. The temperature of asthenosphere is _______.
2. ______ is the deepest trench of the earth.
3. The divergent plate margin is called _______ plate margin.
4. The mountains are formed more than ______ years ago.
5. When the magma flows on the earth crust it is called ______.
6. The mountains like Himalaya Alps are formed ______ lack years ago.
7. ______ of earth is active volcano.
8. _______ is an alternative source of energy.
9. The epicentre of earthquake is ______ km deep.
10. In year ______ earth quake occur in
11. In 1906 the magnitude of the earthquake was _______.
12. ______ city was destructed in earthquake.
13. Earthquake takes place in earth at _________.
14. _____people had lost their life in Tsunami.
15. Damage and destruction was caused in ______ countries of South-East Asia.
16. On 26th January 2001 in _______ of Gujarat almost one lakh people lost their lives for severe earthquake.
17. Sudden of ______ earth the houses are broken.
18. Most of the active _______surround Pacific ocean as a ring.
19. The ring of earthquake in India is generally _________.
20. The magnitude of earthquake is measured by _________.
21. From the epicentre of the earthquake two types of wave spread out along the _____
22. Almost each and every ______ is earthquake prone.
23. Most of the focus of the earth quake located at the depth of _______ km.
24. ________ of N.ars is the highest voleanoes of the solar system.
25. A type of dense viscous lava comes out from the volcanoes of Indonesia which is known as _____ in Hawaiean language.
Answer:
1. 1500° C
2. Mariana
3. constructive
4. 3 – 4 millions of years
5. lava
6. 40
7. 15% Neutron
8. Geothermal energy
9. 50-100
10. 1955 kolce of Japan
11. 8.5
12. Sunfrancisco
13. 20%
14. 36000
15. 111
16. Bhuj
17. temor
18. Volcanoes
19. Himalaya mountain region
20. Seismograph
21. earth crust
22. margin of the plate
23. 50-100
24. Olympus Mars.
25. Aa.
Match the column A with column B.
| Columu A | Column B |
| a. There are 6 major | i. at a rate of 10 cm/year |
| b. The earth’s crust is made of | ii. occur in Pacific Ring of Fire |
| c. Sometimes two plates move towards | iii. and 20 minor plates |
| d. Pacific Ocean plate is moving | iv. cannot be forecasted |
| e. The interior of the earth | v. due to an earthquake |
| f. 70 percent of all earthquake on the earth | vi. each other and collide |
| g. Unlike other natural disasters, an eartquake | vii. a few rigid and solid plates |
| h. Sometimes coastal land may be submerged | viii. is still very hot |
Answer:
a) There are 6 major and 20 minor plates.
b) The earth’s crust is made of a few rigid and solid plates.
c) Sometimes two plates move towards each other and collide.
d) Pacific Ocean plate is moving at a rate of 10 cm / year.
e) The interior of the earth is still very hot.
f) 70 percent of all earthquake on the earth occur in Pacific Ring of Fire.
g) Unlike other natural disasters an eartquake cannot be forecasted.
h) Sometimes coastal land may be submerged due to an earthquake.
Very Short Questions & Answers : (1 mark for each question)
Question 1.
Which scientist introduced the term ‘Plate’?
Answer:
In 1960 Canadian geophysicist – J. T. Wilson introduced the term ‘Plate’.
Question 2.
Who gave information on plate movement?
Ans:
In 1967 Mekensil and Parker gave information on Plate movement.
Question 3.
Who gave vivid explanation of the Plate tectonic theory?
Answer:
In 1967 W. J. Morgan and Le Pichon gave vivid explanation of the plate tectonic theory.
Question 4.
What is the deepest trench of the world? In which ocean does it lie?
Answer:
The deepest trench in the world is Mariana trench. It lies in Pacific ocean.
Question 5.
How is Alps mountain formed?
Four in one (viii)-24
Answer:
Alps mountain is formed when African and Eurasian plates converged to each other.
Question 6.
Name the main fold mountain of the world.
Answer:
Most of the fold mountains of the world have formed for convergence of the continental plates. These are Applachian Ural Aravalli etc
Question 7.
What is Volcanic mountain?
Answer:
The mountains those are formed by deposition of volcanic material is called volcanic mountain. Example-Fujiyama of Japan.
Question 8.
When did the volcanism start?
Answer:
Volcanism started millions of years ago?
Question 9.
In which countries volcanism have occured?
Answer:
Volcanism have occured in Japan Italy India Indonesia etc.
Question 10.
How is the ‘process affecting earth’s crust’ is classified?
Answer:
The process affecting earth’s crust is classified into the types – (i) Endogenetic process (ii) Exogenetic process.
Question 11.
What is lava?
Answer:
The melted viscous substance of the earth’s interior is called magma and when it comes out on the earth surface it is called lava.
Question 12.
Which is the highest volcano of the solar system?
Answer:
Olympus Mons of the Mars is the highest (27 Km) volcano of the solar system.
Question 13.
What percent volcano on the earth is active?
Answer:
15% volcanoes on the earth is active.
Question 14.
What is earthquake?
Answer:
When energy trapped in the blastic interior of the earth is suddenly released the earth crust experience temors which is called earthquake.
Question 15.
In which year devastating earthquake occured?
Ans:
Devastating earthquake occured in 2004 300000 lives were lost and enormous damage causc d over 11 countries in south east Asia.
Question 16.
What is Seismograph?
Answer:
A Seisomograph is the instrument measuring the magnitude of an earthquake.
Question 17.
In which year earthquake occured in Chili?
Answer:
In 1960 earthquake occured in Chili.
Question 18.
What was the level of the scale of the earthquake of Chili??
Answer:
The level of the level of the scale was 8.5.
Question 19.
At what percent the earthquakes occur in the Mid Continental Belt?
Answer:
20% earthquakes occur in the Mid Continental Belt.
Question 20.
Name the volcanoes of ‘Pacific Ring of Fire’?
Answer:
The volcanoes of Pacific Ring of Fire are Fujiyama (Japan) Pinatubo (Philippines), Krakatau (Indonesia) St. Helen (USA) Popocate peti (Maxico) Cotopaxi (Equador) ete.
Question 21.
What is the similarity between volcanism and earthquake?
Answer:
Volcanism and earthquake are both sudden manifestations of endogenetic forces.
Question 22.
What contribute to an area being more prone to disasters?
Answer:
Worldwide increase of population unplanned urbanization construction of heavy multistoried buildings roads dams and reserviors and illegitimate mining – all contribute to an area being more prone to disasters.
Question 23.
How can earthquake form natural harbour?
Answer:
Due to earthquake sometimes coastal land may be submerged due to an earthquake thereby forming an natural harbour.
Question 24.
Give an example where mud island emerged from under the water due to earthquake.
Answer:
A ‘mud island’ has emerged from under the water off the Karachi coast.
Long Questions & Answers : (3 marks for each question)
Question 1.
Write a short note on voleanism.
Answer:
From the time of the creation of the earth the volcanic erruption is occuring for millions of years. At the time of volcanic erruption the hot matter materials ash gases etc comes out from the openings of the earth. After frequent erraption lava is accumulated around the mouth of the volcano forming a cone shaped mountain. This type of mountain is called volcanic mountain as it is formed by deposition of the volcanic material. For example – Fujiyama of Japan Vesuvious of Italy Barren of India Krakatoa of Indonesia. In different geological time the temperature of earth’s atmosphere has been controlled by the process of volcanisation and finally has reached present favourable condition.
Question 2.
How volcanism takse place?
Answer:
The interior of the earth is still extremely hot. Naturallyb rocks are supposed to melt in 2000° C temperature at mantle. But for the extreme pressure of the upper layer the melting point is increased. Thus the rocks melts partly become slipping and flows like plastic. In some part of outer mantle the rocks melts completely. The density of the melted rock is lower. It is lighter than other partially melted rocks of the surrounding. The pressure and the melting point of magma decreases proportionally with the rising upward of magma. The liquid portion of magma turns into gas and water vapours under extreme pressure. Then the magma comes out to the earth’s surface through the opening of earth crust.
Question 3.
How is the earth quake formed?
Answer:
Almost all plate margin in the earth are highly earthquake prone and so all the volcanoes and the centres of earthquake are lie at same place. Besides natural causes like tectonic slides earthquake can also occurs from artificial or non natural causes like digging of underground pits mines and tannels construction of reservoirs and bomb explosion.
Question 4.
What is Contiuental Drift Theory?
Answer:
According to the continental Drift Theory of Alfred Wegener-about 300 million years ago all the present day landmasses were united as a supercontinunt called pangea. Later on it began to break apart and the pieces direted in different directions. Actually the continental crust was floating over oceanic crust. But the Continental Drift Theory could not fully explain the causes of earthquake or formation of oceans countries and mountains volcanism.
Question 5.
What is the divergent plate margła?
Answer:
When two oceanic plates move away from each other hot molton magma comes upward from the earth’s interior and new oceanic crust and mid oceanic ridges are formed from the hot molten magma after getting cooled and solidified. This is called divergent plate margin.
Question 6.
What is Mariana trench?
Answer:
For the moving towards of each other of continental and oceanic plate heavy oceanic plate get submerged under the continental plate. As the result deep oceanic trench is developed in this way. Mariana trench of the Pacific is the deepest trench of the world.
Question 7.
What is divastating plate margin?
Answer:
When the molten materials come out from the interior along the plate margins several volcanoes and volcanic islands are formed along the subduction plate margin. As the earth quake and earth movements are the regular phenomena in this areas of the crust. This type of plate margin is called divastating plate margin.
Question 8.
What is Seismic waves?
Answer:
Energy generated by an eartinquake spreads out in the form of waves from the focus and the epicenter to other parts of the earth just like the radial surge of waves after a stone is dropped on water. These waves are called Seismic waves.
Question 9.
Classify the Seismic waves?
Answer:
Seismic waves are of three types.
a) Primary wave : It is the fastest seismic wave (6 Km / sec) and reaches the earth’s surface before all other waves. This wave travels through solid liquid and gaseous media through a push and pull process.
b) Secondary wave : It reaches the earth’s surface immediately after the primary wave (3-5 Km . sec ). This wave can not travel through liquid and gaseous media. It travels only through solids.
c) Surface waves or level waves: Two types of this wave (3-4 Km / sec) spread out from the epicenter of the earthquake along the eart’s surface. These waves are responsible for most of the damages caused by eartquakes.