Rajasthan Board RBSE Class 11 Physical Geography Chapter 7 Earthquakes and Volcanoes
RBSE Class 11 Physical Geography Chapter 7 Text Book Questions
RBSE Class 11 Physical Geography Chapter 7 Multiple Choice Questions
Question 1.
In which category can Etna volcano of Italy be placed?
(a) Active
(b) Extinct
(c) Dead
(d) Dormant
Answer:
(a) Active
Question 2.
In which of the following categories can we keep Vesuvius volcano of Italy?
(a) Active
(b) Extinct
(c) Dead
(d) Dormant
Answer:
(d) Dormant
Question 3.
Mount Popa volcano of Myanmar is which of the following types?
(a) Active
(b) Extinct
(c) Dead
(d) Dormant
Answer:
(b) Extinct
Question 4.
Those volcanoes which emit from one vent can be kept under which category of earthquakes?
(a) Rift eruption
(b) Central eruption
(c) Dead
(d) Dormant
Answer:
(b) Central eruption
Question 5.
In India, “The Deccan Plateau” is formed by which type of volcanic eruption?
(a) Fissure eruption
(b) Central eruption
(c) Dead
(d) Dormant
Answer:
(a) Fissure eruption
RBSE Class 11 Physical Geography Chapter 7 Very Short Answer Type Questions
Question 1.
Write the definition of earthquake.
Answer:
Earthquake refers to a sudden violent shaking of the ground, typically causing great destruction, as a result of movements within the earth’s crust or volcanic action. This shaking of the earth’s surface is known as earthquake.
Question 2.
Write the names of substances which are erupted from volcano.
Answer:
Vulcanicity erupts various types of gases, small and big rocks and their fragments magma and lava in liquid form.
Question 3.
What are Secondary Waves?
Answer:
S waves are also known as secondary waves. These waves reach the earth’s surface after the primary waves. Due to this reason, they are called secondary waves.
Question 4.
Write the names of two active volcanoes.
Answer:
Two active volcanoes are Etna and Stromboli respectively.
Question 5.
Write the names of two extinct volcanoes.
Answer:
Two extinct volcanoes are Mount Popa of Myanmar and Koh – E – Sultan of Iran respectively.
RBSE Class 11 Physical Geography Chapter 7 Short Answer Type Questions
Question 1.
Explain the Elastic Rebound Theory.
Answer:
Professor F. S. Reid had propounded the Elastic Rebound Theory to explain seismic faults. According to this theory, rocks are elastic as rubber and they expand if stretched. The nature of these rocks is just like rubber. They stretch up to a certain extent. After that, they break down and the broken land parts re – stretch themselves and gain their place.
The tendency of breaking up of rocks in this manner and re – gaining of position by the broken parts has been termed as Elastic Rebound Theory by Prof. Reid. The incidence of earthquake arises due to this process of expansion and re – contraction.
Question 2.
How do earthquakes originate by vulcanicity? Explain.
Answer:
Vulcanicity is a major reason of occurrence of earthquakes. Vulcanicity and earthquakes are considered to be an integral counterpart of each other. Along with volcanic eruption, when active gases and vapor push themselves to come out from the lower part of the surface, a violent vibration takes place on the surface spontaneously and dreadful earthquake is experienced.
In the same way, at places where the surface is weak, active gases break the crust violently and come out on the surface in explosive form along with the eruption of volcano. Along with this type of violent eruption, shaking takes place in the crust. This activity becomes responsible for earthquakes just like the earthquakes which occurred during the eruption of Etna, Vesuvius and Krakatoa volcanoes.
Question 3.
How do earthquakes occur due to water load? Explain.
Answer:
When immense volume of water gets deposited on the surface part, the rocks which are situated under the bottom of the water deposit get transformed due to excessive load and pressure. When this change takes place in a rapid manner, earthquake is experienced. Here, water deposit refers to man – made reservoirs and dams built on the crust. Large dams are built on rivers under various multipurpose projects and river – valley projects.
In this manner, when excess water is deposited in the form of large reservoirs, load and pressure suddenly increases upon the crust due to which the crust starts rearranging itself and it results into occurrence of earthquakes. For example, the earthquake which occurred in Koyna of Maharashtra is considered to be a result of construction of Koyna Dam.
Question 4.
Explain the types of volcanoes.
Answer:
Significant difference is found in the process and frequency of volcanic eruption. Some volcanoes erupt in a violent manner in the form of a rapid explosion, while others erupt in a silent manner. Some of them calm down quickly, while others take time. Some volcanoes remain calm for some time and become active again.
Regarding the above mentioned diversities as the base, volcanoes are mainly categorized on two bases.
- On the basis of period of eruption
- On the basis of nature of eruption
Classification of Volcanoes has been shown in the following table:
Question 5.
Give examples of active volcanoes.
Answer:
Those volcanoes, which continuously erupt lava, gases and various types of substances, are known as active volcanoes. Number of such volcanoes in the world is around 500. Etna and Stromboli of Italy are the major ones among such volcanoes. Pinatubo of Philippine is also an active volcano.
RBSE Class 11 Physical Geography Chapter 7 Essay Type Questions
Question 1.
State the reasons for the origin of earthquake and describe the types of seismic waves.
Answer:
Earthquake is a natural disaster. Various reasons are responsible for it. Following are these reasons:
- Faulting.
- Vulcanicity
- Water load
- Contraction of the crust
- Iso – static Adjustments
- Elastic Rebound Theory
- Plate tectonics
- Human activity
i. e., nuclear explosion, deep mining, etc.
Description of Seismic Waves:
Seismograph is used to record seismic waves. Following is a description of these seismic waves –
1. P – Waves:
These are also known as primary waves. Starting from the seismic focus, these waves are the first to reach the surface. Average speed of these waves varies from 8 to 10 km. per second. When these waves pass through rocks, vibration takes place in rock particles in the direction of the movement of the waves. Primary waves pass through all the three mediums- solid, liquid and gaseous. These waves travel like sound waves.
2. S – Waves:
These waves are known as secondary waves. These waves reach the surface , after the primary waves. Speed of these waves is 5 km. per second. When these waves pass through the rocks, vibration in rocks takes place at a right angle to the direction of the waves. Nature of these waves is similar to that of to tidal waves or light waves. These slanting waves become extinct as they reach the oceanic regions.
3. L – Waves:
These waves are also known as surface waves. These waves travel for the longest distance. As these waves spread all around on the surface from the epicenter, they are known as long waves. Speed of these waves is 3 km. per second. These waves cause maximum destruction in earthquake region. These waves are the last to reach the surface. These waves become extinct in greater depth. These waves pass through water also. On the seismograph, these waves are denoted by the symbol ‘L’.
This categorization of seismic waves has been depicted through the following diagrams:
Question 2.
Classify earthquakes and describe their distribution in the world.
Answer:
Earthquakes which originate on earth surface vary on the basis of their nature and reasons of origin. On this basis, earthquakes have been classified into the following types:
Distribution of Earthquakes in the World:
Across the world, most earthquakes take place in regions of newly – folded mountains, volcanic regions and in coastal regions. These are such regions where there is disarrangement in ground balance or the surface is weak. Distribution of earthquakes in the world is found in the form of the following belts:
1. Circum – Pacific Belt:
This is the most extended earthquake region of the world which experiences almost two – third (around 63 per cent) earthquakes of the world. This belt is spread in the form of a circle around the Pacific Ocean in the islands and continents.
Four major conditions of earthquake, viz. region of conjunction of ocean and land, newly folded mountainous region, destructive plate of volcanic region and border deviation region exist in this belt. Western coastal regions of North and South America, regions from Kamchatka peninsula of Asia up to islands of Eastern Asia, i.e., Kuril, Japan, Taiwan and Philippines are included in this belt.
2. Mid – Continental Belt:
This is also known as the Mediterranean belt. Earthquakes originate here due to rupture of geological faults and balancing activity. Almost 21 per cent earthquakes of the world occur in this region. Region of Portugal up to the Himalayas, Tibet and south – eastern island groups are included in this belt. Earthquake region of India also comes under this belt. Italy, China, Asia Minor, Hindukush, Himalayas, Alps, Myanmar are the major regions of this belt.
3. Mid – Atlantic Ridge Belt:
This belt is situated beside the Mid-Atlantic Ridge, which extends from western islands group of the Atlantic Ocean up to Bouvet Island in the south. Its branch extends from Nile Valley up to Great Rift Valley in Africa. Earthquakes occur here mainly due to the formation of convergent faulting, plate deviation and vulcanicity. Most of the earthquakes occur on the equator.
The distribution of earthquakes in the world has been depicted with the help of the following map:
Question 3.
Mention the causes for occurrence of volcanic eruptions and classify them.
Answer:
Causes of volcanoes:
Various factors are responsible for occurrence of volcanic eruptions. Following are the major factors among them:
- Unbalance (a word used about a person slightly crazy).
- Evolution of gases.
- Increase in temperature of the crust.
- Decrease in pressure.
- Plate tectonics.
Classification of Volcanoes:
Volcanoes have been mainly classified on two bases:
- On the basis of period of eruption.
- On the basis of nature of eruption.
1. Types of volcanoes on the basis of their period of eruption:
On the basis of their period of eruption, volcanoes have been further classified into the following types:
(a) Active or Waking Volcano:
Those volcanoes which continuously erupt are known as active volcanoes.
For example: Etna and Stromboli.
(b) Dormant Volcanoes:
Those volcanoes which remain inactive for some time and erupt again are known as dormant volcanoes.
For example: Mount Vesuvius.
(c) Extinct or Dead Volcanoes:
Those volcanoes which have not erupted since a long time and in which water, etc. has filled in crater are known as extinct volcanoes.
For example: Mount Popa, Koh-i-Sultan, etc.
2. Types of volcanoes on the basis of their nature of eruption:
- Volcanoes with central eruption
- Volcanoes with fissure eruption
Volcanoes with central eruption:
Those volcanoes which erupt from a single bore and a single vent are known as volcanoes with central eruption. Such volcanoes have been further classified into the following parts:
- Hawaiian types of volcanoes.
- Stromboli – an types of volcanoes.
- Volcanian types of volcanoes.
- Pelean types of volcanoes.
1. Hawaiian Type of Volcanoes:
Explosive activity is less in this type of volcano and it erupts in a silent manner. The main reason for this is thinness of lava and lack of fierceness in gases. Examples of this type of volcanic eruptions are seen mainly in Hawaiian Islands, therefore they are known as Hawaiian type of volcanoes.
2. Strombian Type of Volcanoes:
In this type of eruption, lava comes out in a relatively fierce manner, it is thick and sometimes the eruption is explosive. This type of eruption occurs in Stromboli volcano. On its name, volcanoes with this type of eruptions are known as strombolian type of volcanoes.
3. Volcanian Type of Volcanoes:
In this type of volcano, volcanic substances erupt with terrific explosion and excessive fierceness and after the explosion, gases mixed with ash and dust emerge up to a great height in the form of massive black clouds and they are visible shaped like a cauliflower. Naming of this type of volcanoes has been done on the basis of Volcanian volcano of Lipari Group of Islands.
4. Pelean Type of Volcanoes:
In this volcano, eruption is most fierce and violent and this is the most destructive type of volcano. Volcanoes which erupt just like the explosive eruption taking place in Pelee volcano situated in Martinique Islands in the western island group are known as Pelean type of volcanoes.
Volcanoes with Fissure Eruption:
In such volcano, lava erupts from fissure in a silent manner without any explosion. Lava is usually thin and as a result of this, lava plateau is formed. Colombian Plateau and Deccan Plateau of India are lava plateaus formed by fissure eruption.
RBSE Class 11 Physical Geography Chapter 7 Other Important Questions
RBSE Class 11 Physical Geography Chapter 7 Multiple Choice Questions
Question 1.
Cause of earthquake which struck Koyna in Maharashtra was-
(a) Faulting
(b) Water load
(c) Contraction of the crust
(d) Plate tectonics
Answer:
(b) Water load
Question 2.
Who propounded the Elastic Rebound Theory?
(a) Prof. F. S. Reid
(b) Morgan
(c) Jeffries
(d) Wegener
Answer:
(a) Prof. F. S. Reid
Question 3.
Which instrument is used to record seismic waves? .
(a) Climograph
(b) Hythergraph
(c) Ergograph
(d) Seismograph
Answer:
(d) Seismograph
Question 4.
What are primary waves?
(a) P waves
(b) S waves
(c) L waves
(d) Gama Waves
Answer:
(a) P waves
Question 5.
Which waves cause the most destruction?
(a) P waves
(b) S waves
(c) L waves
(d) Alfa Waves
Answer:
(c) L waves
Question 6.
Tsunami is a word from which language?
(a) French
(b) Arabian
(c) Hindi
(d) Japanese
Answer:
(d) Japanese
Question 7.
Which belt experiences the most earthquakes?
(a) Mid – Continental Belt
(b) Mid – Atlantic Belt
(c) Circum – Pacific Belt
(d) None of these
Answer:
(c) Circum – Pacific Belt
Question 8.
Which type of volcano is Vesuvius volcano?
(a) Active
(b) Dormant
(c) Extinct
(d) Pelean Type
Answer:
(b) Dormant
Matching Type Questions
Match Column A with Column B in the following:
Question A.
| Column A (Cause of earthquake) | Column B (Associated region) |
| (i) Faulting | (a) Krakotoa |
| (ii) Vulcanicity | (b) Human reasons |
| (iii) Water load | (c) Rift valleys |
| (iv) Isostasy | (d) Koyna |
| (v) Nuclear explosion | (e) Himalayan region |
Answers:
- (c)
- (a)
- (d)
- (e)
- (b)
Question B.
| Column A (Earthquake region) | Column B (Earthquake type) |
| (i) Earthquake in Krakotoa | (a) Isostatic Earthquake |
| (ii) Earthquake in California | (b) Volcanic earthquake |
| (iii) Earthquake in Hindukush | (c) Oceanic earthquake |
| (iv) Destruction of Fukushima | (d) Tectonic earthquake |
Answer:
- (b)
- (d)
- (a)
- (c)
RBSE Class 11 Physical Geography Chapter 7 Very Short Answer Type Questions
Question 1.
What are endogenetic forces?
Answer:
Forces which originate under the earth’s surface are known as endogenetic forces.
Question 2.
What are exogenetic forces?
Answer:
Forces which originate on or above the earth’s surface are known as exogenetic forces.
Question 3.
What is the definition of earthquake according to Monk house?
Answer:
According to Monk house, “The transmission of elastic shock waves towards the outside in all the directions due to the activity of contraction and adjustment in the structure of the earth’s crust is known as earthquake.”
Question 4.
What is meant by Fault?
Answer:
Fault refers to the imbalance of the rocks due to cracks and fissures which occur in rocks caused due to stress and compression in the earth’s crust.
Question 5.
What is meant by ocean deposits?
Answer:
Sediments which are deposited at the bottom of the sea are known as ocean deposits. These deposits can be biotic, abiotic, land, oceanic or cosmic.
Question 6.
What is Seismic Focus?
Answer:
Seismic Focus refers to that place in the earth’s crust where the earthquake originates.
Question 7.
What is Epicenter?
Answer:
Epicenter is that central point on the surface of earth on the right angle to the seismic focus, where seismic waves are firstly experienced.
Question 8.
What are Seismic Waves?
Answer:
When concussion occurs on the seismic focus, shaking takes place in the rocks. The waves produced due to this are known as Seismic Waves.
Question 10.
What is the speed of Primary Waves?
Answer:
Primary Waves travel at the speed of 8 to 10 km. per second.
Question 11.
What are land waves?
Answer:
L waves travel the longest distance on the surface and therefore they are known as long and land waves.
Question 12.
What is meant by artificial earthquakes?
Answer:
Earthquakes which originate due to human activities, are known as artificial earthquakes. These have local effect.
Question 13.
Into how many types have natural earthquakes been classified?
Answer:
Natural earthquakes have been classified on the basis of their origin into volcanic earthquakes, tectonic earthquakes, isostastic earthquakes and plutonic earthquakes.
Question 14.
What is meant by tectonic earthquakes?
Answer:
Tectonic earthquakes are such earthquakes which originated due to tectonic movements, i.e. stress and compression in the crust.
Question 15.
What is the meaning of plutonic earthquakes?
Answer:
Such earthquakes which evolve at a greater depth from the land are known as plutonic earthquakes.
Question 16.
What is meant by Tsunami?
Answer:
When an earthquake originates in an oceanic region, such inter – oceanic earthquakes give rise to great destructive oceanic waves. These waves are known as Tsunami.
Question 17.
Where do most earthquakes occur in the world?
Answer:
Most earthquakes in the world occur in Circum – Pacific Oceanic belt. This belt experiences almost 63 per cent of the world’s earthquakes.
Question 18.
Why do earthquakes originate in the Atlantic Ridge belt?
Answer:
Formation of convergent faults, deviation of plates and vulcanicity are the major reasons for evolution of earthquakes in the Atlantic Ridge belt.
Question 19.
Which instrument is used to record the intensity of earthquakes?
Answer:
Intensity of earthquakes is measured on the Richter scale. It contains numbers from 0 to 9.
Question 20.
What is meant by volcano eruption?
Answer:
Volcano is a sudden activity resulting from geological forces in which gases, rocky substances and hot liquid magma erupt from the ridge or rift of the land.
Question 21.
Write the definition of volcano as given by Uldin and Morgan.
Answer:
According to Uldin and Morgan, “Volcano is that process under which all the activities which take place under and outside the earth’s surface are included.”
Question 22.
On which bases has the classification of volcanoes been done?
Answer:
Volcanoes have been classified on the basis of their period of eruption and their nature of eruption.
Question 23.
Into how many types have volcanoes been classified on the basis of period of eruption?
Answer:
On the basis of period of eruption, volcanoes have been classified into three types-active volcanoes, dormant volcanoes and extinct volcanoes.
Question 24.
Into how many categories have volcanoes with central eruption been classified?
Answer:
Volcanoes with central eruption have been classified into Hawaiian type of volcanoes, Stromboli type of volcanoes, Vulcanic type of volcanoes and Pelean type of volcanoes.
Question 25.
Which factors are responsible for vulcanicity?
Answer:
Mainly, factors such as isostatic equilibrium, emergence of gases, increase in temperature inside the crust, decline in pressure and activity of plate tectonics are responsible for vulcanicity.
Question 26.
What is meant by active volcanoes?
Answer:
Volcanoes which erupt very frequently are known as active volcanoes.
Question 27.
What is meant by dormant volcanoes?
Answer:
Such volcanoes which erupt again after remaining in active for some time are known as dormant volcanoes.
Question 28.
Which belts of volcanoes are found to be present? .
Answer:
Circum – Pacific Oceanic belt, Mid – Continental belt, Mid – Atlantic Ridge belt and Eastern African Ridge, etc. are the major belts included in the distribution of volcanoes in the world.
RBSE Class 11 Physical Geography Chapter 7 Short Answer Type Questions (SA-I)
Question 1.
What is meant by earthquake? Explain.
Answer:
Endogenetic forces remain active in the internal part of the earth. Earthquakes evolve in the form of a sudden change due to these endogenetic forces. Normally, shaking of the earth’s surface is known as earthquake. This process of evolution of earthquake mainly takes place due to temporary imbalance in Isostatic equilibrium of a particular region. This process gives rise to destructive waves and it is a natural disaster.
Question 2.
How is Isostays helpful in causing earthquakes? Explain.
Answer:
Balance is maintained within various land forms of the earth such as mountains, plateaus, plains and oceanic deeps. When ever load increases in oceanic regions due to debris deposited by the process of erosion, a condition of momentary imbalance arises in the isostatic equilibrium. Earthquakes evolve due to this momentary imbalance. Earthquakes usually occur due to this reason in the Himalayan region.
Question 3.
Write down the characteristics of land waves.
Answer:
- Land Waves (L – Waves) are those which travel with the slowest speed.
- These waves cause the most destruction in the earthquake region.
- These waves travel for the longest distance.
- These waves spread only on land from the epicenter towards all around.
- Speed of these waves is 3 km per second.
Question 4.
Give a brief introduction of Mid-Continental Belt in context to earthquakes.
Answer:
Mid – Continental belt is also known as Mediterranean Sea belt. Around 21 per cent earthquakes are experienced in this belt. Earthquakes evolve in this belt due to the process of faulting and loss of isostatic equilibrium. India also comes in this belt. Regions up to Italy, China, Asia Minor, Hindukush, Himalayas and Alps are included in this belt.
Question 5.
What is the difference between active and extinct volcanoes?
Answer:
Following is the difference between active and extinct volcanoes:
| Active Volcanoes | Extinct Volcanoes |
| 1. These volcanoes erupt quite frequently. | 1. These volcanoes exhibit no eruption for a long time period. |
| 2. These volcanoes are found in regions which are active in tectonics. | 2. These volcanoes are usually centered in regions which are inactive in tectonics at present time. |
| 3. Main vent of such volcanoes remains clear and active. | 3. Mostly water, etc. gets filled up in vents of such volcanoes or they become blocked. |
Question 6.
What is the difference between Hawaiian Type and Stromboli Type volcanoes?
Answer:
Following differences are present in Hawaiian Type and Stromboli Type volcanoes:
| Hawaiian Type Volcanoes | Stromboli Type Volcanoes |
| 1. Explosive activity is less in these types of volcanoes. | 1. Eruption is violent in these types of volcanoes. |
| 2. Lava which erupts from these volcanoes is thin. | 2. Lava which erupts from these volcanoes is thick. |
| 3. These volcanoes are usually present in Hawaii Islands. | 3. These volcanoes are present in Stromboli Island. |
| 4. Lava spreads up to greater distance in these volcanoes. | 4. As the lava erupting from these volcanoes is thick, it spreads less. |
Question 7.
Clarify the difference between Vulcanian volcanoes and Pelean volcanoes.
Answer:
Following differences are present between Vulcanian volcanoes and Pelean volcanoes:
| Vulcanian Volcanoes | Pelean Volcanoes |
| 1. In these types of volcanoes, volcanic substances erupt along with violent explosion. | 1. Most violent explosion takes place in these types of volcanoes. |
| 2. Substances and gases erupting from these types of volcanoes go up to lesser height as compared to Pelean volcanoes. | 2. Substances and gases erupting from these types of volcanoes reach the most height. |
| 3. These volcanoes have been named on the basis of Vulcan volcano. | 3. These volcanoes have been named on the basis of Pelee volcanoes. |
Question 8.
Which regions have been included in the minor belt of volcanoes?
Answer:
Volcanoes situated in Hawaiian Islands of Pacific Ocean, and in Mauritius, Comoro, Reunion, etc. islands situated in the Indian Ocean. All these volcanic regions are present in regions apart from Circum – Pacific Oceanic belt, Mid Continental belt, Mid-Atlantic Ridge belt, East African belt, etc.
RBSE Class 11 Physical Geography Chapter 7 Short Answer Type Questions (SA-II)
Question 1.
Describe the contribution of plate tectonics and human reasons in the origination of earthquakes.
Or
Human activities and plate tectonics are responsible for the originatation of earthquakes. Explain.
Answer:
Effect of Plate Tectonics:
Plate tectonics extend a significant contribution in the origination of earthquakes because various plates are found under the earth’s surface. In these plates, deviation and convergence take place around the edges of the plates and they shift towards the left and right. The turbulence which occurs due to the changes in the earth’s crust assists in the originate of earthquakes.
Human Contribution:
Impact of human activities also plays a significant role in the origination of earthquakes. Various such activities are done by humans, which assist in emergence of conditions of earthquake. Human activities such as nuclear explosions, explosions done to blow off the rocks in mining areas, deep drilling and dams with massive volume of water built by humans increase the possibility of originatation of earthquakes. Heightening of the edges of mines or their falling down during the process of mining also give rise to origination of earthquake.
Question 2.
Classify earthquakes on the basis of their condition.
Answer:
Assuming their condition to be the basis, earthquakes have been mainly classified into two types:
- Terrestrial earthquakes
- Oceanic earthquakes.
1. Terrestrial Earthquakes:
Earthquakes experienced on land are known as terrestrial earthquakes. Earthquakes evolving in Mid – Continental belt usually are of this category.
2. Oceanic Earthquakes:
Earthquakes which evolve in the oceans are known as oceanic earthquakes. Oceanic waves are formed in the oceans from these types of inter-oceanic earthquakes. These oceanic waves are known as Tsunami. These types of oceanic waves usually prove to be extremely destructive in coastal regions. The tsunami which evolved due to a violent earthquake which had hit the region near Honshu Island in Japan had destroyed the entire Fukushima city.
Question 3.
What is the difference between central eruption volcanoes and fissure eruption volcanoes?
Answer:
Following are the differences between central eruption and fissure eruption volcanoes:
| Central Eruption Volcanoes | Fissure Eruption Volcanoes |
| 1. In these volcanoes, eruption occurs from a single pipe and vent. | 1. In these volcanoes, eruption occurs from multiple vents (ridges). |
| 2. These volcanoes erupt with high explosive force. | 2. These volcanoes erupt silently without explosion. |
| 3. Such volcanoes are present in larger number in the world. | 3. These volcanoes are usually less in number. |
| 4. Cones are usually more developed in these volcanoes. | 4. Cones are less developed in these types of volcanoes. |
Question 4.
What are the advantages of earthquakes?
Answer:
Earthquake is a natural disaster which usually has harm full and effects, but sometimes its positive impacts are also witnessed. Following is a brief description of these advantageous effects:
- Highlands evolve due to earthquakes which has a positive impact on the climate of that region.
- When coastal land gets depressed, the sea ports become wider and deeper. Due to this, an ideal condition evolves in context to big ships.
- The land submerged under the sea comes up, which results into formation of fertile plains. These plains are very useful for agricultural works.
- Earthquakes help us to understand the internal structure of the earth.
- Groundwater level changes due to the process of earthquakes. Sometimes, due to water level coming up, potable water supply gets facilitated.
- At times, due to earthquakes, resources of saline water are replaced by resources of fresh water.
Question 5.
Explain the reasons of vulcanicity.
Answer:
On regional basis, various factors are responsible for the origination of vulcanicity in the world. Following are the major factors visible in the world:
1. Isostatic Disequilibrium:
In isostatic regions, structural changes take place due to isostatic disequilibrium. This gives rise to vulcanicity.
2. Formation of Gases:
Isostatic water enters in the internal part of the earth through ridges and transforms into vapor which work as propulsive force in eruption.
3. Increase in Temperature of the Earth’s Crust:
Heat evolved by continuous fission o£ radioactive substances inside the earth’s crust causes the rocks to weaken and increase in volume. After this, lava erupts out of the weakened cracks.
4. Decline in Pressure:
Due to the pressure of upper layers, the rocks inside the earth’s crust remain in solid condition and they melt on decrease in pressure which encourages vulcanicity.
5. Plate Tectonic:
Vulcanicity also takes place due to the movements of various tectonic plates. Vulcanicity further intensifies if the plates move in opposite direction of one another.
Question 6.
What are the types of volcanoes on the basis of their period of eruption? Explain.
Answer:
Volcanoes in the world have been classified into the following main types on the basis of their period of eruption:
1. Active or Awake Volcanoes:
These types of volcanoes erupt frequently. Etna and Stromboli volcanoes of Italy are active volcanoes.
2. Dormant Volcanoes:
These volcanoes erupt again after remaining dormant for some time. Vesuvius of Italy is the same type of volcano, which has erupted in the years 1631, 1812, 1906 and 1943.
3. Extinct Volcanoes:
Those volcanoes which have not erupted since a long time period and in which water, etc. has filled up are known as extinct volcanoes. Mount Popa in Myanmar and Koh-E-Sultan in Iran are extinct or dead volcanoes.
Question 7.
Describe the substances which are secreted from volcano.
Answer:
During vulcanicity, various types of substances are erupted from inside the earth’s surface. Hot liquid substances, rock segments, lapilli, various gases, etc. are the major ones among them. All these substances can be mainly classified into the following parts:
1. Gases and Water Vapour:
Along with the eruption of volcano, water vapour, and gases such as carbon dioxide, sulpher dioxide, carbon monoxide, hydrogen chloride, ammonium chloride and other gases are evolved.
2. Solid Material:
Large – sized rock segments along with minute ash and dust are evolved from the volcano.
3. Liquid Material:
The entire molten rock material inside the earth’s surface is known as magma and when it comes out from the volcano on the earth’s surface, it is known as lava.
Question 8.
Explain the impact of vulcanicity.
Describe the advantageous and harmful impacts of volcanoes.
Answer:
Vulcanicity taking place on the earth’s surface is a natural disaster. Sometimes, along with its destructive impacts, creative impacts are also visible. A brief description of both these impacts of vulcanicity is given below:
1. Creative Impact:
After spreading out, the lava which evolves from volcano gives rise to fertile soil. Black soil present in Indian sub – continent is an example of creative impact of vulcanicity . Vulcanicity plays an important role in evolution of belts rich in various types of minerals.
2. Destructive Impact:
Lava and other substances and gases which flow along with volcanic eruption harm human life and environment and also destroy the cultural scenario. Many lives are lost due to volcanic eruption. Immense loss is caused due to submergence of coastal areas. Crores of sea animals and creatures die due to vulcanicity.
RBSE Class 11 Physical Geography Chapter 7 Essay Type Questions
Question 1.
Explain the causes for origination of earthquakes.
Answer:
Temporary imbalance in isostatic equilibrium of a particular place is the major cause of formation of earthquake. Following are the factors which create imbalance in the isostatic equilibrium due to which formation of earthquakes takes place:
1. Faulting:
Due to stress and compression of the isostatic forces, cracks and fissures form in the rocks and faults appear. Earthquakes originate during these activities and earthquakes occur due to this reason on the edges of newly folded mountains and ridge valleys.
2. Vulcanism:
Vulcanism is the major cause for formation of earthquake. At the time of volcanic eruption, when rapid and violent gases exert pressure to come out on the earth’s surface, sudden and violent turbulence takes place on the land. Destructive earthquakes occurred at the time of eruption of Etna, Krakatoa, Vesuvius, etc. volcanoes.
3. Water Load:
According to some scholars, due to the construction of massive dams, water gets deposited in the surface part in excessive amount, which leads to transformation in the rocks which are situated below the water deposit. Koyna Dam is regarded as one major cause of Koyna earthquake which occurred in Maharashtra in December 1967.
4. Contraction of the Earth:
Some scholars have regarded contraction of the earth to be the cause for formation of earthquakes. According to them, temperature of the earth is on a continuous decline due to radioactive activity. Due to this, the earth’s surface contracts due to cooling down. When this activity takes place in a rapid and violent manner, earthquakes are caused.
5. Isostatic Adjustments:
Normally, balance is present between various land forms of the earth such as mountains, plateaus, plains and oceanic bottom. Whenever load becomes more in oceanic regions due to debris deposited by erosion process, temporary imbalance is created in this isostatic equilibrium. In Himalayan mountainous regions, earthquakes usually occur due to this cause.
6. Elastic Rebound Theory:
According to Prof. F. S. Reid, rocks stretch up till some extent just like rubber. After this, they break down and the broken rock parts re – gain their place by re – stretching themselves, due to which, earthquakes are formed.
7. Plate Tectonic:
On their edges, plates diverge, converge or shift towards the right or left which create turbulence during these activities, which gives rise to earthquakes.
8. Other Reasons:
Apart from the above mentioned reasons, expansion of gases, breaking down of cliffs in oceanic regions, falling down of ceilings of caves, etc. result into earthquakes with small impact. Apart from this, man – made reasons, such as – nuclear explosion, explosion in mining regions, deep drilling, etc. also result in earthquakes which have local impact.
Question 2.
Give a detailed description of the types of earthquakes.
Answer:
Types of Earthquakes:
Various types of earthquakes continue to impact various parts of the earth. On the basis of nature and causes, earthquakes are classified into the following types:
1. Artificial Earthquake:
These occur due to human activities. These earthquakes have regional impact and their intensity is quite less.
For example:
earthquakes which occur due to drilling of mines, nuclear explosion, underground nuclear test, etc.
2. Natural Earthquake:
These are active earthquakes which occur due to natural factors. These are of the following types:
(a) Volcanic Earthquakes:
Those earthquakes, which occur due to vulcanicity or eruption, are known as volcanic earthquakes.
For Example:
earthquakes formed during the eruption of Vesuvius, Etna, Krokotoa, etc.
(b) Tectonic Earthquakes:
These are structural earthquakes, which are formed due to tectonic movements of the crust, such as- stress, compression, etc. These earthquakes do not form in extreme depths.
For Example:
California earthquake.
(c) Isostatic Earthquake:
These earthquakes occur due to imbalance in the isostatic equilibrium of the earth’s surface. These type of earthquakes are mostly experienced in newly folded mountainous regions such as the Himalayas, etc.
For example:
Hindukush and Nepal earthquake of 2015.
(d) Plutonic Earthquake:
Earthquakes which are formed at significant depths inside- the earth are known as plutonic or underground earthquakes. Very little information is available regarding the origin and intensity of such earthquakes.
3. Earthquakes on the basis of condition:
On this basis, earthquakes can be classified into two types:
(a) Terrestrial Earthquake:
Earthquakes which formed on land are known as terrestrial earthquakes. Earthquakes which occur in the Mid – Continental belt are mostly of this type.
(b) Marine Earthquake:
Earthquakes which formed in the oceans are known as marine earthquakes. These types of earthquakes give rise to high and destructive oceanic waves which are known as Tsunami in Japanese language. Due to Tsunami which emerged due to the violent earthquake that occurred near Honshu Island of Japan in the year 2011, the entire Fukushima city was destroyed.