class 9 ICSE Solutions

ICSE Solutions for Class 9 Geography – Landforms of the Earth

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Exercises

I. Short answer questions.

Question 1.
What is meant by a landform ?
Answer:
A landform is a natural feature on the surface of the earth with a particular shape.

Question 2.
Why are the fold mountains called so ?
Answer:
Fold mountains are called so because of the result of large- scale earth movements caused by stresses in the earth’s crust. Such stresses may be caused by weight of the overlying rocks, movements in the mantle, the expansion or contraction of some part of the earth, etc. These stresses subject the rocks to compressive forces, producing wrinkling or folding along the lines of weakness. This is shown in fig. the raising of folds makes the fold mountains.

Question 3.
Give two chief characteristics of the fold mountains.
Answer:

1. The fold mountain system has parallel ranges.
2. A fold mountain region is also a region of sudden forces such as of volcanoes and earthquakes.

Question 4.
Give one example of each :

(a) Young fold mountains;
(b) Old fold mountain. Why they are called so

Answer:

(a) These mountains are made of light sedimentary rocks of recent tertiary age and are the highest mountain system which are still increasing their heights due to gradual upthrust force. The Himalayas are called young fold mountains.
(b) The Alpine-Himalayan system and Circum Parific mountain belt are the ‘Old Fold Mountains’ which existed as geosynclines 50-60 million years ago.

Question 5.
Give example of residual mountains.
Answer:
Examples of Residual mountains are Nilgiri, Parasnath and Rajmahal Hills in India and the Catskill range in the USA.

Question 6.
How is a rift valley formed ? Give one example of a rift valley.
Answer:
A rift valley is formed by the submergence of a big landmass between two high block mountains, e.g. the Rhine river flows through a rift valley in its middle course.

Question 7.
Give a brief definition of a plateau.
Answer:
The Himalayas are an important form of folding being the highest mountain range in the world.

Question 8.
Give one example of each :

(a) Intermontane plateau
(b) Volcanic plateau and
(c) Piedmont plateau

Answer:

(a) The Tibetan plateau
(b) The Plateau of Peninsular India.
(c) The Patagonian plateau of South America.

Question 9.
Give two points of importance of landforms.
Answer:
Various landforms display the internal and external forces of the earth, different climatic effects and features, forests, snow lands giving birth to rivers, coasts and islands as fishing regions. All these together make the earth beautiful and ideal for living and various activities.

Question 10.
What are known as epeirogenic movements ?
Answer:
The movements such as uplift and submergence working in vertical direction are known as epeirogenic movements. ‘Epeiros’ in Greek means continent ‘genic’ means building. As this movement created continents coming out higher from the oceans.

Question 11.
Name two landforms created by epeirogenic movements.
Answer:

1. Block mountains.
2. Rift valleys and basins are produced by epeirogenic movements.

Question 12.
Why are the sudden forces described as ‘Constructive forces ?
Answer:
Earthquakes and volcanic activities are described as sudden forces. These forces are described as ‘Constructive Forces’ because they create relief features on the surface of the earth. As volcanic erruptions result in the formation of volcanic mountains, extensive plateaus and also plains.

Question 13.
What are called endogenic forces ?
Answer:
Endogenic forces are the internal diastrophic forces working inside the interior of the earth related to the tectonic forces.

Question 14.
Name four relief features on the surface of the earth.
Answer:
The four major landforms are mountains, plateaus, plains, valleys and basins.

Question 15.
What are known as exogenic forces ?
Answer:
Exogenic forces work on the surface of the earth through water, wind and ice, resulting in changing the shape of landforms slowly.

Question 16.
Name the two land forms produced by exogenic forces.
Answer:

1. Alluvial and erosional plains
2. Glacial landforms.

Question 17.
Give one chief characteristic of the fold mountains.
Answer:
The fold mountains are formed by the lateral compression of sedimentary rocks as seen by the different layers of various types of rocks one upon another.

Question 18.
Give one example of volcanic mountains.
Answer:
Volcanic mountains are formed by erupting magma from the inner core on the surface e.g. Mt. Krakatoa is an active volcano on the western side of Java.

Question 19.
How is a rift valley formed ? Give one example.
Answer:
A rift valley is formed by the submergence of a big landmass between two high block mountains, e.g. the Rhine river flows through a rift valley in its middle course.

Question 20.
Give a brief definition of a plateau.
Answer:
A plateau is a higher tableland between mountain and valley, lower than mountain and higher than valley.

Question 21.
Give one example of each

(a) Intermontane plateau
(b) Piedmont plateau
(c) Volcanic plateau.

Answer:

(a) The Tibetan plateau.
(b) The Patagonian plateau of South America.
(c) The Plateau of Peninsular India.

Question 22.
How are erosional plains formed ?
Answer:
Erosional plains are formed by the agents of erosion in millions of years, when the higher landforms are eroded into level plain areas, e.g. Lorraine plain in France.

Question 23.
Give two points of importance of landforms.
Answer:
Various landforms display the internal and external forces of the earth, different climatic effects and features, forests, snow lands giving birth to rivers, coasts and islands as fishing regions. All these together make the earth beautiful and ideal for living and various activities.

II. Distinguish between each of the following 

1. Fold Mountain and Block Mountain.
2. Intermontane plateau and Volcanic plateau.
3. Structural plain and Depositional plains.
4. Tectonic mountain and Volcanic mountain.

Answer:

1. Fold Mountain :

1. Fold mountains is built by the tectonic forces folding the sedimentary rocks.
2. These are formed of light sedimentary rocks e.g. the Himalayas

Block Mountain :

1. Block mountain is built after the submergence of a landmass leaving behind the big blocks on the both sides.
2. These are formed by solid rocks standing on the both sides of a rift valley. e.g. Vosges mountain in France.

2. Intermontane plateau : These are the highest and most extensive types on the globe surrounded by hills and mountains. The plateau of Tibet is the highest plateau as well as most extensive intermontane plateau. Other examples are Columbian Plateau, North Americal Cordillera, Bolivian, Peruvian and Mexican plateaus.
Volcanic Plateau : In places where fissure eruptions have taken place magma erupts quietly through narrow fissures several kilometres in length. This magma spreads on the surface and cools down as a sheet of lava covering the surface of the land. Eruptions at intervals lead to the piling up of lava sheets one over the other in a series of steps. The Deccan trap region of Peninsular India has several lava sheets having a maximum thickness of about 200 metres. This region forms a lava plateau. Other examples are South African plateau, Columbian Plateau and Ethiopian plateau.
3. Structural plain : It is formed by the uplift of landmass by Diastrophic forces creating an extensive lowland. The Missouri – Mississippi plain of U.S.A. is an example, which came out of ocean by uplift force.
Depositional plains : These plains are formed by the deposition of materials which have been brought by various agents of transportation, eg.

1. River Deposition : The most widespread of these are alluvial plains like the Northern Plains of India; the flood plains like the Mississippi Plains in the USA, deltaic plains in Egypt and India
2. Wind Deposition : Most of such plains are sandy deserts like the Sahara in Africa and the Thar desert in India. They have irregular and undulating surface made by existence of sand dunes and hallows.
3. Marine Deposition : These plains are found in coastal regions. Examples are the east coast of India, the estuarine banks in the Netherlands, coast of Germany and Denmark.

4. Tectonic mountain :

1. It is built by the tectonic force working on the crust of the earth.
2. It is the result of upthrust force of the tectonic movement.
3. It may be built by sedimentary or metamorphic rocks.

Volcanic mountain :

1. It is built by the volcanic eruption from the interior of the earth.
2. It is the result of upthrust force of magma coming up on the earth surface.
3. It may be built by crystalline igneous rocks of particular composition.

III. Give one technical term for each of the following 

Question 1.
Block mountains with flattened summits.
Answer:
Horst Mountains.

Question 2.
Plateaus surrounded by hills and mountains on all sides.
Answer:
Intermontane plateaus.

Question 3.
Plateaus formed by lava.
Answer:
Volconic plateaus.

Question 4.
An extensive area of lowland with a level or gently undulating surface.
Answer:
Plain.

Question 5.
The compressional forces that cause folding of rocks and formation of fold mountains.
Answer:
Diastrophic forces.

Question 6.
The vertical movements which are the result of faults and cracks in the surface of the earth.
Answer:
Epeirogenic forces.

Question 7.
The forces operating on the surface of the earth.
Answer:
Exogenic forces.

Question 8.
Plateaus surrounded by mountains on one side and plains on the other.
Answer:
Piedmont plateaus

P Q. Fill in the blanks with suitable words.

1. Volcanic activity is a sudden movement.
2. The upfolds of the rock strata are called anticlines.
3. The Mid-Atlantic Ridge rises 3 km above the floor of the Atlantic.
4. The Great Plain of the USA was formed by Diastrophic forces.
5. The Great Northern plains of India were formed by River Deposition.

IV. Long Answer Questions.

Question 1.
1. Describe the formation of mountains and their types.
Answer:
Mountains are classified into three main types depending on the forces that have formed them. Three main types of mountains are

1. Fold Mountains : Fold mountains are the result of large-scale earth movements caused by stresses in the earth’s crust. Such stresses may be caused by weight of the overlying rocks, movements in the mantle, the expansion or contraction of some part of the earth, etc. These stresses subject the rocks to compressive forces, producing wrinkling or folding along the lines of weakness. This is shown in fig. The raising of folds makes the fold mountains.
   
2. Residual Mountains : Mountains which are subjected to weathering and erosion for a longtime, are lowered down and called residual or relict mountains.
   Denudation and erosion by natural agents like winds, water, snow etc., cause the mountains to be lowered but some resistant areas may remain and form residual mountains.
   They may also be formed on plateaus that are dissected by rivers. For example the hills and valleys in the Deccan plateau.
   Some examples of Residual mountains are Nilgiri, Parasnath and Rajmahal Hills in India and the Catskill range in the USA.
   
3. Block Mountains : Horst or a block mountain is an uplifted land mass situated between two adjacent faults. The central block is upthrown or land on the outer-sides of the faults is downthrown so that the central mass appears like a highland. Its surface is like a plateau, but it has steep edges. The Vosges mountains to the west of the Rhine Rift Valley and the Black Forest mountain to the east of the Rhine Rift Valley are good examples of Horsts.
   

Question 2.
Describe the characteristics of four different types of plateaus.
Answer:
Intermontane plateaus are the highest plateaus between highest mountains, e.g. Tibetan plateau. Piedmont plateaus lie between mountains and plains with steep slopes towards plains due to the force of flowing water downwards, e.g. Appolochian plateau of U.S.A., Patagonia plateau of South America Volcanic plateaus are created by volcanic eruption and Lava flows, e.g. Deccan plateau of peninsular India Uplifted plateaus are caused by the endogenic forces resulting in the dome shaped plateaus e. g. Chhotanagpur plateau in India

Question 3.
Describe the characteristics of structural plains.
Answer:
Structural plains are created by uplifting of a large landmass due to Diastrophic movements, e.g. plainofU.S.A. Erosionalplains are formed by eroding highlands into plain areas, e.g. Lorraine plain in France. Srinagar Valley of Kashmir is the result of glacial erosion, Sahara desert plain is the result of wind erosion. Karst plains are created by erosion of limestone rocks by ground water, e.g. Karst plain of Yugoslavia. Depositional plains are caused by large scale deposition of debris and silt deposited by the running water or rivers, e.g. Northern plain of India.

Question 4.
Explain the chief characteristics of depositional plains and their types.
Answer:
Depositional plains These plains are formed by the deposition of materials which have been brought by various agents of transportation, eg.

1. River Deposition : The most widespread of these are alluvial plains like the Northern Plains of India; the flood plains like the Mississippi Plains in the USA, deltaic plains in Egypt and India
2. Wind Deposition : Most such plains are sandy deserts like the Sahara in Africa and the Thar desert in India. They have irregular and undulating surface made by existence of sand dimes and hallows.
3. Marine Deposition : These plains are found in coastal regions. Examples are the east coast of India, the estuarine banks in the Netherlands, coast of Germany and Denmark.

Question 5.
Give a brief account of importance of landforms on the surface of the earth.
Answer:
Landforms play an important role for human activities by providing different aspects of landscapes, climatic variety, natural gifts of snowclad ranges, glaciers and rivers etc., various vegetation zones imparting innumerable forest’ products, agriculture and other occupations related to different types of landforms, natural beauty and tourism all these making this earth fascinating living world.

Practice Questions (Solved)

Question 1.
Describe the direction in which the following mountain systems lie and also point out the continents where they are found.

(a) Alpine Himalayan System
(b) Rocky-Andean System

Answer:

(a) Alpine and Himalayan System both run from West to East direction in Europe and Asia continents respectively.
(b) Rocky-Andean System both run from North to South in the western margins of North America and South America continents.

Question 2.
Describe the different stages in the growth of mountains.
Answer:
There are three different stages in the growth of mountains.

1. The geosyncline stage : The deposition of sediments in the sea-bed to form large geosynclines.
2. The Orogenic stage : The tectonic forces working horizontally push and press there geosynclines to form various folds.
3. Epeirogenic stage : When the whole mass of geosynclines is raised and buckled up and form a distinct series of troughs (synclines) and arcs (auticlines) i.e. Mountains and Valleys.

Question 3.
What are the different types of Geosynclines ?
Answer:
There are three types of Geosynclines

1. Monogeosynclines : Long, narrow geosynclines along narrow water bodies take the shape of narrow mountains such as Appalachian mountains of North America.
2. Polygeosynclines : Geosynclines laid down in wide and long water basin take the shape of broad and long mountain ranges like Rockies in North America.
3. Mesogeosynclines : The geosynclines lying between Europe and Africa continents resulted in various mountain ranges e.g. Alps and Pyrenees in Europe, Atlas in Africa.

Question 4.
Write a note on the characteristics of folded mountains.
Answer:
Folded mountains are formed by the forces of compression and contortion resulting in a series of synclines and anticlines, later on undergoing various erosive forces. All the highest mountain systems are example of folded mountains made of sedimentary rocks.

Question 5.
What are Block mountains ? How are they formed ?
Answer:
Block mountains are formed on the both sides of a rift valley, which is formed by deep submergence of a large landmass leaving behind two raised platform type blocks known as Block mountains. These landforms are created by displacement of landmass along fault lines known as faulting.

Question 6.
How can mountains be classified according to their different size and arrangement ? Describe in detail two of the classes of such mountains.
Answer:
Simply the mountains can be divided into 4 groups

1. Folded mountains
2. Block mountains
3. Volcanic mountains
4. Relict mountains

Volcanic mountains : are formed by the eruption and deposition of magma from the interior core to the land surface. According to their construction these are Cinder or Ash cones, Lava cones and composite cones, e.g. Fujiyama in Japan.
Relict mountains : These are formed by the continuous erosion ofthe original materials and giving birth to the hills of rounded peaks made of high density rocks, which have undergone excessive pressure and denudation by natural agents. One of the best example is Vindhyanchal mountain.

Question 7.
What are Block mountains ? How are they formed ?
Answer:
Horst or a block mountain is an uplifted land mass situated between two adjacent faults. The central block is upthrown or land on the outer-sides of the faults is downthrown so that the central mass appears like a highland. Its surface is like a plateau, but it has steep edges. The Vosges mountains to the west of the Rhine Rift Valley and the Block Forest mountains to the east of the Rhine Rift Valley are good examples of Horsts.

Question 8.
How can mountains be classified according to their different size and arrangement ?
Answer:
Mountains can be classified according to their different size and arrangement as given below :

1. CordillersThese are large regions of mountains topography which are characterised by a large number of chains and ranges.
2. System It is formed of several associated ranges. These ranges should be similar in position, form and structure although treanches or basins may separate them.
3. ChainIt is a series of ridges in one line although separated by trough like valleys.
4. RangeIt is a linear arrangement consisting of a large number of peaks and ridges separated by valleys. The different mountains possess a unity of form and structure.
5. Group It is a circular or massive arrangement of peaks and ridges. Group formations often result from the erosion of laccolths.
6. Ridge It is the individual arch or block that results from folding and faulting. It may be of various types according as the slope is steep on one side or the other.
7. Peaks These are formed by the less regular beds resisting denudation. They may be dome-like or pyramidical or needle-shaped. Their shape depends upon the rock structure and joint planes of the region. The peaks and ridges may either be arranged parallel to one another or may be quite isolated of may be arranged like features round a dome or they may be cones formed due to volcanic extrusion.

Question 9.
What are plateaus ? How are they different from mountains ? Give suitable examples.
Answer:
Plateaus Plateaus or table lands are elevated uplands, extensive in size and descending steeply to the surrounding regions. On the other hand, a portion of land surface rising considerably above the surroundings either as a single eminence or in a range if chain is called a ihountains.
Examples of Plateaus :

1. Deccan Plateau of India.
2. Tibetan Plateau (called the roof of the world)

Question 10.
What is a Piedmont Plateau ? How is it different from a Continental plateau ? Give suitable examples to illustrate.
Answer:
Piedmont Plateaus The plateaus which lie at the foot of the mountains are called Piedmont plateaus. These are flanked on one side by the plains or seas. The chief examples are the Colorado plateau or North America and the Patagonia Plateau of South America. Continental Plateaus The extensive and massive tablelands which rise abruptly from the bordering lowlands or from the sea are called continental plateaus. On most of their margins, there is sea. They seldom have mountainous rims. The major portion of Africa, Arabia, Spain, Australia, Peninsular India, Greenland and Antarctica are continental plateaus.

Question 11.
Write short notes on the following :

(a) Coastal plains
(b) Karst plains
(c) Peneplain
(d) Cuestiform plains.

Answer:

(a) Coastal plains : The plains situated near a sea coast are called coastal plains. They are formed by the sea waves after sea bottoms have emerged. The newly emerged plain is generally broad and wide and comprise of loosely compacted layers of mud and sand. Many coastal plains increased in which towards the sea because the sea waves continue adding matter to it.
(b) Karst plains : These plains are formed by the action of underground water, dissolving the regions made of chalk or limestone are called Karst plains. They are often flat-bottomed. Due to wind erosion and differential weathering, the topography is etched and rounded or even polished in a curious manner. Some of the relief features are quite fantastic in shape, especially the pebbles and other fragments that litter the surface of these plains.
(c) Peneplains : Very low undulating plains are called peneplains. They are almost plains.
(d) Cuestiform plains : The plains marked by a concentric arrangement of ridges and lowlands are called Cuestiform plains. Paris and London are the typical examples of such plains. They are made by river action on hard and soft rocks. Consequently they become rolling like the downs of S.E. England.

Question 12.
Why and how are the plains the centres of all human activity ?
Answer:
The plains are the centres of great economic advancement. The alluvial plains have been the cradles of civilisation from the earliest time. They have the following advantages to man:

1. Railways, roads and waterways can be easily laid.
2. They are the granary of the world.
3. Due to fine climate, fertile soil and facilities for movement, the plains have become thickly populated and most of the big cities and towns are situated in the plains of the world except in areas which suffer from harsh climate and temperature.

Question 13.
Differentiate between Young fold mountains and Old fold mountains.
Answer:
Old fold mountains : The fold mountains which were formed about more than 250 million years ago are called old fold mountains. For example, the Urals in Russia, the Appalachians in North America and the Aravalli range in India are old fold mountains. These mountain ranges are of low altitude and have gentle slopes.
Young fold mountains : The most recent phase of mountain building took place about 25 million years ago. The world’s highest mountain ranges were formed during this period. These are known as young fold mountains. They have rugged relief features because they have been subjected to denudation for a comparatively short period only.

Question 14.
Give reasons for the following :

1. Old fold mountains have low altitude and gentle slopes.
2. Young fold mountains have rugged relief features.
3. Young fold mountains are liable to Earthquakes and Volcanic action.

Answer:

1. Old fold mountains have low altitude and gentle slopes because they have been subjected to denudations for million of years.
2. Young fold mountains have rugged relief features because they have been subjected to denudation for a comparatively short period only.
3. Young fold mountains are liable to Earthquakes and volcanic action because these mountain regions are areas of crustal instability.

Question 15.
State two evidences that the Earth movements have taken place in the past.
Answer:
The evidences that the Earth movements have taken place in the past are as follows :

1. The basins containing sedimentary rocks indicate that such basins must have been below sea level in the past. The coalfields of the Damodar valley occur in such basins of the geological past.
2. Oilfields occur in basins containing old sedimentary rocks. Such basins are now occurring on the land. This shows that the portion of the crust which was once depressed must have been uplifted later.
3. llie Himalayas provide another evidence of the recent effect of Earth movements.

Question 16.
What causes Orogenic movemeiits ?
Answer:
Orogenic movements are caused by compressional or tensional forces.

Question 17.
What are the effects of Epeirogenic movements ?
Answer:
Effects of epeirogenic movements :

1. They cause rising or sinking of the crust. They may cause the elevation of broad areas as extensive as those of a continent or lowering of the sea level.
2. These movements are responsible for the formation of plateaux.

ICSE Solutions for Class 9 Geography – Rocks

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Exercises

I. Short Answer Questions 

Question 1.
State two points of distinction between rocks and minerals.
Answer:
Rocks :

1. Rocks contain minerals.
2. Rocks are the aggregates of minerals and other rock material.

Minerals :

1. Minerals do not contain rocks.
2. Mineral are the compounds of pure elements with a definite chemical Composition.

Question 2.
Name any three elements of the earth’s crust.
Answer:
These are silicon, aluminium, iron, magnesium, calcium, potassium, sodium and nickel.

Question 3.
Name three types of rocks.
Answer:
Three types of rocks are sedimentary, igneous and metamorphic rocks.

Question 4.
Why are the igneous rocks also called the primary rocks?
Answer:
The igneous rocks were the first to be formed. They form the basis of formation of other types of rocks. Thus, they are called primary rocks.

Question 5.
Give one difference between Extrusive igneous and Intrusive igneous rocks.
Answer:

• Extrusive igneous rocks are formed by the cooling of molten magma on the earth’s surface.
• Intrusive igneous rocks are formed when the magma solidifies within the earth’s crust forming coarse texture.

Question 6.
Name any two chief characteristics of Igneous Rocks.
Answer:
Igneous rocks are formed by cooling of magma and these are crystalline rocks and full of mineral compounds.

Question 7.
What is the main characteristics of Basic Igneous Rocks?
Answer:
Basic igneous rocks have higher percentage of oxides of denser elements and dark in colour, e.g. Basalt, dolerite etc.

Question 8.
Name two important landforms made by Igneous Rocks.
Answer:
Conical mountains and extensive lava plateaus.

Question 9.
What are Sills ?
Answer:
The magma takes place in between the layers of rocks and hardens after cooling, which is called Sill.

Question 10.
Which rocks are associated with ores of metals ?
Answer:
Igneous rocks are associated with ores of metals due to their origin by cooling magma resulting in crystalline rocks rich in mineral content.

Question 11.
Which rocks are associated with fossil fuels ?
Answer:
Sedimentary rocks are associated with fossil fuels due to fossils trapped in between layers of these rocks.

Question 12.
Mention any two chief characteristics of Sedimentary Rocks.
Answer:

• Sedimentary rocks are formed from material derived from other rocks including plant and animal remains. These rocks thus contain fossils.
• Sedimentary rocks are generally not crystalline. They are soft and layered as they are formed by deposition of sediments.

Question 13.
Give two examples of Sedimentary Rocks.
Answer:

1. Sandstone
2. Limestone

Question 14.
Name the rocks which are most widespread on the earth.
Answer:
Sedimentary rocks are most widespread on the earth.

Question 15.
Name the three stages of lithification of Sedimentary rocks.
Answer:
Lithification is the process of turning loose rock material into hard rock through evaporation, compaction and cementation.

Question 16.
Name the types Sedimentary rocks based on agents of formation.
Answer:
There are five main types of rocks on the basis of agents of formation:

1. Riverine Rocks These are formed by the sediments deposited by running water or river.
2. Lacustrine Rocks These are formed by the deposition of silt etc on the bed of lakes.
3. Glacial Rocks These are formed by the debris carried on and deposited by glaciers.
4. Aeolean Rocks These are formed by the deposition sand accumulation by the wind.
5. Marine Rocks These are formed by the deposition of sediments at the ocean floor. These types are Calcarious and Carbonaceous sedimentary Rocks.

Question 17.
Which agents are responsible for deposition of sediments?
Answer:
There are three main agents of deposition i.e., water, wind and ice, which mainly act as agents of change on the surface of earth for deposition of sediments.

Question 18.
What are known as metamorphic rocks ? Give two examples.
Answer:
Metamorphic rocks are formed by complete change of texture of rocks through volcanism and diastrophism, e.g., limestone is converted to marble and shale is transformed to slate.

Question 19.
What is Mechanical Metamorphism ?
Answer:
This is a mechanical Transformation in which texture of rocks is changed by crushing and rubbing processes associated with heat and compression created by mechanical action.

Question 20.
What is meant by Rock Cycle ?
Answer:
The earth is said to be 4700 million years old and the rocks came into existence 3400 years ago. Since then these rocks have undergone various changes by which multiple transformation took place within the rocks. This continuous process of transformation of old rocks into new rocks is known as rock cycle for figure See Page no. of this book.

Question 21.
What processes are involved in the formation of Igneous Rocks ?
Answer:
Igneous rocks are associated with volcanic activity, cooling of magma and mechanical weathering etc.

II. Explain these terms associated with rocks.

Question 1.
Extrusive Igneous Rocks.
Answer:
These rocks are formed by consolidation of erupted magma on the surface of earth.

Question 2.
Laccoliths and Batholiths.
Answer:
Laccoliths is formed by the intrusion of magma in the erupting channel just below the crust. Batholiths are deep seated dome shaped formation of magma intrusion, generally forming the base of mountain ranges, e.g., Ranchi Batholiths.

Question 3.
Fossil fuels.
Answer:
These are the fuels accumulated between two impermeable layers of the sedimentary rocks, e.g. peat, coal and petroleum etc.

Question 4.
Lithification of Rocks.
Answer:
It is the process of turning the loose material into hard rock, which helps in the formation of the sedimentary rocks found in different layers one upon another.

Question 5.
Metamorphism.
Answer:
It is the process of transformation of sedimentary and igneous rocks into metamorphic rocks through extreme temperature and compression by volcanism and diatrophism by physical and Chemical changes.

III. Distinguish between each of the following

P Q. Lava and Magma.
Answer:
Lava : Lava is the black molten material erupted in a volcano.
Magma : Magma is the compound of lava, stones, ash, debris etc. erupting out in a volcano.

Question 1.
Plutonic and Volcanic rocks.
Answer:
Plutonic rocks :

1. These are intrusive igneous rocks.
2. These cool down very slowly due to heat in the interior

Volcanic rocks :

1. These are extrusive igneous rocks.
2. These cool down abruptly due to less temperature on the surface region.

Question 2.
Thermal and Dynamic Metamorphism.
Answer:
Thermal Metamorphism :

1. It takes place due to extreme temperature which transforms the shape and texture of rocks.
2. The heat may be due to hot magma or friction of rocks.

Dynamic Metamorphism :

1. It takes place due to excessive compression created by tectonic forces within the earth.
2. It takes place through physical or chemical changes by deep pressure.

Question 3.
Sills and Dykes.
Answer:
Sills : The collection of magma between layers of rocks is called sill.
Dykes : The fillings of magma in the cracks or fissures of rocks are called dykes.

Question 4.
Calcarious and Carbonacious rocks.
Answer:
Calcarious rocks : The sedimentary rocks formed by the deposition of shells, skeletons of sea organism as corals, clams and oysters etc. are called calcarious rocks due to excess of calcium.
Carbonacious rocks : The sedimentary rocks formed by the deposition of large scale vegetation and animals etc. are called carbonacious rocks due to the excess of carbon.

Question 5.
Acid Igneous Rocks and Basic Igneous Rocks.
Answer:
Acid Igneous rocks : These are lighter rocks with silica content 65 to 85 percent with density less than 2 g/Cm³, e.g. Granite.
Basic igneous rocks : These are denser rocks with silica content 40 to 60 percent with average density between 2.8 g/Cm³ and 3.0 g/Cm³ e.g. Basalt.

IV. State the types of rocks for the formation of which the following processes are involved.

Question 1.
Solidification of magma on the surface of the earth.
Answer:
Extrusive igneous rocks

Question 2.
Formation of large crystals, coarse texture and slow cooling and compaction.
Answer:
Intrusive igneous rocks.

Question 3.
Accumulation takes place over long periods of time in seas, lakes and streams.
Answer:
Sedimentary rocks.

Question 4.
Decomposition of organic matter at different stages and over different periods of time.
Answer:
Carbonaceous Sedimentary rocks.

V. Long Answer Questions

Question 1.
Distinguish between rocks and minerals.
Answer:
The rocks contain minerals in the form of ores, but minerals do not contain rocks. Sedimentary rocks contain fossil fuels like coal and petroleum etc, igneous rocks are rich in minerals like copper, gold, iron etc, metamorphic rocks contain valuable building stones like marble and garnet, feldspar etc. Rocks have no definite chemical composition, while minerals have particular chemical composition.

Question 2.
Describe how are igneous rocks formed ? State their chief characteristics.
Answer:
Igneous rocks are formed by melting and cooling of magma originated from volcanic eruptions. These may be formed by diastrophism and volcanism. These rocks are strong, crystalline and dark in colour. These may be extrusive and intrusive on the surface and beneath the crust respectively.

Question 3.
How are igneous rocks classified on the basis of their chemical composition?
Answer:
On the basis of chemical composition igneous rocks may be classified into two groups i.e. Acid igneous rocks and Basic igneous rocks. Acid rocks have silica content 65-85 percent e.g. granite which is made up of large crystals of quartz, feldspar and mica. Basic rocks contain high percentage oxides of denser material, silica content is between 40-60 percent with a density of 2.8 g/cm³ and 3.0 g/cm³. Acid rocks are lighter than Basic rocks.

Question 4.
Classify the igneous rocks on the basis of their place of origin.
Answer:
On the basis of origin igneous rocks are divided into two groups i.e. Extrusive and Instrusive igneous rocks. Extrusive igneous rocks are found on the surface of the earth by cooling down of erupted magma. Intrusive igneous rocks are formed beneath the earth’s crust after solidification of magma.

Question 5.
How are sedimentary rocks formed ?
Answer:
Continuous deposition of sediments of silt, soil, debris etc. by water, wind and ice along lower landforms and solidification into different layers result in the formation of light sedimentary rocks.

Question 6.
Explain the formation of sedimentary rocks on the basis of agents of formation.
Answer:
There are five main types of rocks on the basis of agents of formation:

1. Riverine Rocks These are formed by the sediments deposited by running water or river.
2. Lacustrine Rocks These are formed by the deposition of silt etc on the bed of lakes.
3. Glacial Rocks These are formed by the debris carried oh and deposited by glaciers.
4. Aeolean Rocks These are formed by the deposition sand accumulation by the wind.
5. Marine Rocks These are formed by the deposition of sediments at the ocean floor. These types are Calcarious and Carbonaceous sedimentary Rocks.

Question 7.
How are sedimentary rocks classified on the basis of their formation ?
Answer:
There are three types of this type of rocks :

1. Mechanically formed rocks : Denudation of rocks by agents of change results in layers of sedimentary rocks by mechanism.
2. Chemically formed rocks : These are formed by evaporation of calcarious water and accumulated along lake and lagoon beds, e.g. gypsum and rock salt.
3. Organically formed rocks : These are formed by deposition of dead plants and animals e.g. limestone rock (or Calcareous rock) lignite, bituminous and anthracite coal are carbonaceous rocks formed by compression of vegetation under the layers of sedimentary rocks. In the same way petroleum in between the sedimentary rocks is the result of zurasic age dinosaurs e.g. shale rock, containing oil.

Question 8.
What is metamorphism ? What are its causes ?
Answer:
Metamorphism is a process of transformation of sedimentary and igneous rocks into the metamorphic rocks through physical and chemical reactions. Main causes are great temperature and pressure beneath the earth’s crust, which changes the original texture and form of the rocks into dense, crystalline and fine grained rocks.

Question 9.
What are the chief characteristics of metamorphic rocks?
Answer:
Metamorphic rocks are composed of fine particles and dense, smooth material. These are very precious rocks, particularly for building stones like marble, garnet, slate quartzite etc.

Question 10.
What is Rock Cycle. How does it keep the earth young?
Answer:
The earth is said to be 4700 million years old and the rocks came into existence 3400 years ago. Since then these rocks have undergone various changes by which multiple transformation took place within the rocks. This continuous process of transformation of old rocks into new rocks is known as rock cycle.

To keep the earth young, rock melts again resulting in formation of igneous rock. This disintegrated material again form sedimentary rock, it takes hundreds are thousands years.

Question 11.
Give a detailed account of lithiflcation of sedimentary rocks.
Answer:
Lithification means solidification. The loose material carried on by water, wind and ice is deposited slowly in different layers one upon another. Gradually the deposited sediments become solid and hard due to pressure and temperature. Evaporation results in the loss of water within the sediments and these are compacted and cemented. Compaction takes place by increasing weight and pressure of over lying sediments e.g. sand is converted to sandstone. Cementation takes place by bonding of compacted sediments by natural elements like calcium compounds, silica and iron with a property to bind the loose materials to solid state.

Practice Questions (Solved)

Question 1.
(a) What is meant by a rock ?
Or
What is meant by a ‘rock’ ? Name the main types of rocks.

(b) Differentiate between Rock and Mineral
(c) How are sedimentary and igneous rocks formed ?
(d) In what type of rocks do you find fossils and why ?
(e) How are rocks important to us ?

Answer:
(a) Rock : A rock can be defined as “an aggregate of minerals that forms a more or less definite unit of the earth’s crust”. A rock does not possess a definite composition like that of a chemical compounds, but is usually a mixture of various minerals.
The bulk of rocks is made up of silica or quartz and feldspar. Feldspar are composed of silica, aluminium, potassium and sodium or calcium. Some rocks are composed of grains cemented together, while several other are crystalline, compact or even glass-like.
All material (whether hard like stone or sand) of which the crust of the earth is composed are called rocks e.g, stone, clay, lava, sand, chalk, salt, coal marble etc.. On the basis of their mode of formation, rocks are divided into three types :

• Igneous rocks
• Sedimentary rocks
• Metamorphic rocks.

(b)
Rock :

1. A rock is a natural solid organic or inorganic material forming the crust of the earth.
2. A rock is an aggregate of minerals.
3. The physical properties of rocks vary.

Mineral :

1. The mineral is an organic element or compound which occurs naturally.
2. A mineral has an atomic structure.
3. It has fixed definite physical properties.

(c) Formation of Sedimentary rocks : Sedimentary rocks are formed by the process of consolidation of sediments deposited commonly in water bodies like seas or lakes. The sediments are derived by the rivers, glaciers, winds and waves. The sediments consist of loose particles of gravel, sand, silt and clay in various proportions. These loose particles get consolidated or compacted into hard rocks by the presence of cementing substances like lime or the pressure of overlying deposits.
Formation of igneous rocks : The rocks which are formed by the process of solidification of molten rock material (magma), are called igneous rocks.
The processes involved in the formation of igneous rocks are cooling and solidification.
Two types of igneous rocks are

• Intrusive igneous rocks
• Extrusive igneous rocks.

Formation of extrusive rocks : These rocks are also known as volcanic rocks, because they are formed by the solidification of lava on the earth’s surface. As on the outer surface of the earths’ crust the rate of cooling and solidification is more rapid than in the interior, the different minerals composing the magma have less time to become crystalline. The crystals formed are small. Basalt is a good example of this type of rock. Extrusive rocks are much more fine-grained as compared to intrusive granite. The hot magma free of gases is converted into lava on reaching the surface. It takes the form of lava flows, lava sheet and lava plateau. The north-western part of Peninsular India, known as the Deccan Trap, covers a great area of basaltic regur soil formed by the weathering of these rocks. Basaltic lava rocks cover a wide area in Columbia, the Snake Plateau of U.S.A. The other name of extrusive rock is Volcanic
Rock The properties of extrusive rocks :

1. These rocks are formed by the solidification of lava on the earth’s surface.
2. These rocks are very fine-grained.
3. They are usually dark coloured.

The other name given to intrusive rock is Plutonic rock.
Formation of intrusive rocks : When the molten material of the interior part of the earth’s crust finds its way through clefts or spaces that it has made by pushing the surrounding rocks apart, and does not reach the surface. This is known as the Intrusive Rocks. Dolerite and granite are the best examples of intrusive rocks.
Properties of intrusive rocks :

1. They have large crystals.
2. They are very compact.
3. They are glassy in appearance.

(d) Fossils are found in sedimentary rocks. Organic remains of plants and animals or their skeletal impressions are called fossils. Fossils help us in fixing the relative ages of rocks.
(e) The dead sea abounds in chemically formed sedimentary rock because the evaporation of water from it is rapid.

Question 2.
(a) Name different types of sedimentary rocks.
(b) What physical agents are involved in the sedimentary rocks ?
(c) How are chemically-formed sedimentary rocks produced?
(d) How are chemically-formed sedimentary rocks formed? Give examples.
(e) Sedimentary rocks are also called stratified rocks. Why?
OR
Why sedimentary rocks are called stratified rocks ?
Answer:

(a) There are three types of sedimentary rocks on the basis of the nature of sediments, their origin, composition and mode of formation. These are mechanically-formed sedimentary rocks, organically formed sedimentary rocks and chemically- formed sedimentary rocks.
(b) Rain water, wind, ice or the running water are the agents involved in the formation of sedimentary rocks. These agents break and carry on loose material and deposit it in various low lying areas to convert into the solid sedimentary rocks.
(c) Chemically-formed sedimentary rocks are produced through evaporation of water from solutions containing minerals. In this ways a rock like ‘gypsum’ is produced. Other examples are nitrates and potash etc.
(d) Chemically formed sedimentary rocks are formed through chemical action of water. Some mineral like limestones and salts are dissolved into the water and after the evaporation of water form a particular type of rock which is formed by the chemical sedimentation of limestones into gypsum and salt into various types of nitrates.
(e) During the formation of sedimentary rocks, the sediments are deposited in waterbodies and get sorted out according to their size. The sediments accumulate in different layers or strata arranged one above the other. Each layer or stratum has particles of given size. In sedimentary rocks each layer or stratum has particles of a given size. Therefore, sedimentary rocks are also called stratified rocks.

Question 3.

(a) What is meant by the term ‘metamorphism’ ?
(b) Distinguish between Thermal metamorphism and Dynamic metamorphism.
(c) Distinguish between Regional and Contact metamorphism.
(d) What are metamorphic rocks ?
(e) Give some examples of metamorphic rocks formed from sedimentary and igneous rocks.

Answer:
(a) The term metamorphism means change of form. It may be physical or chemical or both.
(b) Thermal metamorphism : When the transformation of the original rock takes place principally because of the influence of high temperature, the rock is said to be caused through Thermal metamorphism. For example, graphite (from coal) and slate (from clay). The heat may result from the intrusion of hot magma or from the friction of moving rock layers. It may also occur due to chemical changes.
Dynamic metamorphism : When the transformation of the original rock takes place mainly because of the influence of pressure at a great depth within the earth’s crust, it is known as Dynamic Metamorphism.
(c) Regional metamorphism When metamorphism of bed rocks takes place over a very large area, it is called Regional metamorphism. It is usually caused by the movement of the earth’s crust. Contact metamorphism when it takes place over a small area, it is called Local Metamorphism or Contact Metamorphism. It commonly occurs when hot magma comes in contact with other rocks.
(d) Metamorphic rocks are those rocks which were formerly igneous or sedimentary rocks, but owing to extreme heat and pressure in the interior of the earth it has been changed or altered to such an extent that they are quite different from what they once were slate, which is in reality clay, and marble’ which is in reality lime stone. Other examples of metamorphic rocks are quartzite from sand stone, graphite from coal, gneiss from granite and Mica from Schist.
(e)
(a) Sedimentary Rocks :

1. Limestone
2. Clay and Shale
3. Sandstone
4. Coal

Metamorphic Rocks :

1. Marble
2.  Slate
3. Quartzite
4. Graphite

(b)
Igneous Rocks :

1. Granite
2. Basalt

Mctamorphic Rocks :

1. Gneiss
2. Schist

Question 4.
Classify the following rocks into sedimentary, igneous and metamorphic

Answer:

(a) Shale — Sedimentary rock
(b) Gneiss — Metamorphic rock
(c) Quartzite — Metamorphic rock
(d) Slate — Metamorphic rock
(e) Marble — Metamorphic rock
(f) Coal — Sedimentary rock
(g) Clay — Sedimentary rock
(h) Schist — Metamorphic rock
(i) Granite — Igneous rock
(j) Graphite — Metamorphic rock
(k) Dolomite — Sedimentary rock
(l) Peat — Sedimentary rock
(m) Basalt — Igneous rock
(n) Rock salt — Sedimentary rock
(o) Lime-stone — Sedimentary rock
(p) Gypsum — Sedimentary rock
(q) Loess — Sedimentary rock

Question 5.
Give one word for the following

(a) The outer layer of the earth.
(b) The lower part of ocean floor, comprising mainly of silica.
(c) Rocks formed by the cooling and solidification of molten rock from beneath the earth crust.
(d) Stratified rock formed organically but from vegetative matter-swamps and forests.
(e) The upper part of lithosphere, which is rich in silica and aluminium.
(f) The core of the earth occupied by rock in iron and nickel.
(g) Igneous rocks, which contain a high percentage of silica.
(h) Igneous rocks, which contain a low percentage of silica.
(i) A sedimentary rock, which is composed of microscopically fine, soft and smooth particles.
(j) The best example of chemically-formed sedimentary rock, which has been formed by the evaporation of water from solution containing minerals.

Answer:

(a) Crust
(b) SIMA
(c) Igneous rocks
(d) Carbonaceous rocks
(e) SIAL
(f) Nife
(g) Acidic igneous rocks
(h) Basic igneous rocks
(i) Clay
(j) Gypsum

Q. 6. Fill in the blanks

1. The interior layer is the core, which is made up mainly of iron and nickel, and is called Nife.
   
2. Organically formed sedimentary rocks are formed by the deposition of shells and skeletons of organism.
3. Breccia rock is formed, when the angular and coarse grains of some durable minerals are cemented together.
4. Aeolian is the best example of the wind deposited stratified rock.
5. Basic igneous rock contain a low percentage of silica and a high percentage of basic oxides.
6. Extrusive rocks are also known as volcanic rocks.
7. Basaltic lava rocks cover wide area in Peninsular India and Columbia, the Snake Plateau of the U.S.A.

Question 7.
Give one example of an area of :

1. Igneous rocks
2. Metamorphic rocks,
3. Sedimentary rocks in India

Answer:

1. Deccan Plateau
2. Narmada Basin
3. Himalayan Region

Question 8.
What is the basis for the classification of rocks ?
Answer:
The basis for the classification of rocks are their mineral composition, colour and texture.

Question 9.
Why are Sedimentary rocks called the Secondary rocks?
Answer:
Sedimentary rocks are called Secondary rocks or derived – rocks because they are derived by the denudation of other rocks.

Question 10.
How are sedimentary rocks classified ?
Answer:
Sedimentary rocks are classified into the following types according to the nature of sediments, their origin, composition and the mode of formation.

1. Inorganic rocks or Mechanically-formed Sedimentary Rocks :- These type of rocks are formed by the deposition of land derived material. When the river began to flow, they eroded the rocks and washed away to the sea. Clay, shale, sandstone were formed in this way. These rocks are called inorganic rocks.
2. Organically formed Sedimentary Rocks :- These rocks are formed by the deposition of plants and sea organisms. Millions of years ago, there grew huge forest in marshy places. In course of ages they were buried underground and the internal heat changed them into coal. Moreover, there are millions and millions of sea-organisms whose skeleton are made of Calcium carbonate derived from sea water. After their death skeleton sink to the bottom of the seas and are formed into lime true and chalk and coal.
3. Chemically-formed Sedimentary Rocks :- There rocks are formed by the evaporation of water from solution containing mineral. Various kinds of salts precipitate from waters of shallow desert lakes, where evaporation of the water is rapid. Gypsum is the best example of this kind of rocks. Several nitrates and potash are also chemically formed sedimentary rocks.

Question 11.
State the properties of metamorphic rocks.
Answer:
Properties of metamorphic rocks :

1. These rocks are harder and more resistant than the original rocks.
2. These rocks have their minerals arranged in a series of bands.

Question 12.
Give one term for the following statements :

1. Formed when mud layers compacted under great pressure composing 80% of this rock.
2. It has a definite chemical composition with its own chemical and physical properties.
3. Igneous rocks of deep seated origin.
4. Sheet like body of igneous rock.
5. Rounded or sub-rounded fragments, usually water-born cobbles, pebble and gravel, cemented together by a matrix of calcium carbonate, silica, etc.
6. Formed by evaporation in saline lakes.
7. Fine grained metamorphic rock, generally produced by the low grade metamorphism of shale.
8. Type of metamorphism in which changes are caused due to high pressure.

Answer:

1. Shale
2. Mineral
3. Plutonic rocks
4. Sill
5. Conglomerate
6. Rock salt
7. Slate
8. Dynamic metamorphism.

Question 13.
Why are the Igneous Rocks called Primary Rocks ?
Answer:
It is believed that the earth was in a molten state in the beginning Igneous rocks were the first rocks to be formed due to cooling and solidification of molten matter. Hence these are called Primary Rocks.

Question 14.
Why fossils are preserved in Sedimentary and not in Igneous rocks ?
Answer:
Fossils are remains of vegetation and animals buried under the sediments. The sedimentary rocks are stratified rocks and are found in layers. These fossils are preserved in between these layers. But in Igneous rocks, the fossils are destroyed due to high temperature of lava.

Question 15.
How is Plutonic rock formed ? Give an example of an Plutonic rock.
Answer:
Plutonic rocks are the igneous rocks which are formed as some depth in the earth’s crust, when a molten material gets solidified under pressure. Granite is very good example of a Plutonic rock.

Question 16.
Give reasons for the following :

1. Extrusive rocks generally have small crystals.
2. Silicates are the most common rock forming minerals.
3. Rocks are of great economic significance.
4. Man’s habitat is the biosphere and not the lithosphere in the true sense.

Answer:

1. Extrusive rocks generally have small crystals because in the formation of these rocks, the solidification of magma takes place at a slower rate.
2. Silicates are the most common rock forming minerals because they are most common minerals in the Earth’s crust.
3. Rocks are of great economic significance Some of the main benefits of rocks are as follows :
   • After disintergration, they turn into valuable soils.
   • They are the store-houses of a large number of minerals.
   • They are the source of precious metals like gold, silver, platinum etc.
   • They are source of fuel-minerals.
   • They provide different types of stones.
4. The composite zone inhabited by most living creatures is called biosphere. It includes a part of the atmosphere, the hydrosphere and a part of the lithosphere. All three layers are essential for life to exist.
   As lithosphere is only a small part of the biosphere, therefore, man’s habitat is the biosphere and not the lithosphere in the true sense.

Question 17.
Distinguish between Intrusive and Extrusive Rocks :
Answer:
Intrusive Rocks :

1. Intrustive rocks are formed beneath the surface of the Earth.
2. These rocks have large size crystals due to slow cooling.
3. These are also known as plutonic rocks.
4. Granite is an example of these rocks.

Extrusive Rocks :

1. Extrusive rocks are formed on the surface of the Earth.
2. Crystals are not formed due to rapid cooling of lava.
3. These are also known as volcanic rocks.
4. Basalt is an example of these rocks.

ICSE Solutions for Class 9 Geography – Earthquakes

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Exercises

I. Fill in the blanks below

1. Most earthquakes occur on account of the strain in the earth’s crust.
2. P (primary or push waves) are the first earthquake waves to be recorded on a seismograph of an earthquake.
3. The last of the earthquake waves to arrive on the surface of the earth are L (surface or long) waves.
4. The giant sea waves caused by earthquakes in the oceans are called Tsunamis.
5. About 70 per cent of the earthquakes occur in the Circum- Pacific-Mountain Belt.

II. Short Answer Questions

Question 1.
What is called an earthquake ?
Answer:
An earthquake is defined as a tremor below the surface of the earth which causes shaking of the earth.

Question 2.
State two natural causes of an earthquake.
Answer:
Natural causes are the movement of tectonic plates and volcanic activities.

Question 3.
Name one man-made cause of an earthquake.
Answer:
Construction of large scale dams, thrust of rivers along fault lines, dumping of chemical wastes also cause earthquakes due to imbalance in isostatic balance of the earth’s landforms, e.g. Koyna dam caused an earthquake in Maharashtra.

Question 4.
What are known as seismic focus and epiceptre with respect to an earthquake ?
Answer:
The point of origin of earthquake waves is called seismic focus and the centre vertically above the seismic focus nearest to the earth’s crust is called epicentre.

Question 5.
What is known as Richter scale ? State its uses.
Answer:
Ritcher scale is used to measure the intensity of earthquake through a scale, which is motivated by a needle attached to this instrument The zigzag wavelength of the earthquake comes on the screen and calculated from 1 to 9 scale measured in centimetres.

Question 6.
How are earthquakes useful ?
Answer:
Earthquakes cause energy release to put the earth in good shape; several landforms are uplifted to build large plains e.g. Sagami Bay uplifted 200 m, Landslides cause the formation of lakes in Himalayan region.

Question 7.
Give any two destructive effects of earthquakes ?
Answer:
Destructive effects are collapse of structures, submergence of coastal parts e.g. Dwarka submergence, these change the course of rivers, danger to human life and motivation of tsunami waves causing drastic calamities.

Question 8.
What is tsunami ? How is it caused ?
Answer:
Tsunami is a large furious destructive sea waves caused by the force of an earthquake along the moving tectonic plates, volcanic activity landslides and meteorite impact.

Question 9.
How do Japanese predict earthquakes ?
Answer:
Japanese use the methods of measuring changes in sea level and variations in Earth’s magnetic field to predict earthquakes.

Question 10.
Name the two belts where most of the earthquakes occur.
Answer:
Two belts are the Circum-Pacific Mountain belt and the midworld mountain belt of high fold mountains like the Alps, Himalayas etc.

III. Match the following

Answer:

IV. Long Answer Questions

Question 1.
Describe how earthquakes are caused on the surface of the earth.
Answer:
When the earth’s crust is unable to accommodate itself to the strain due to isostatic imbalance, so sudden release of energy results in violent shock or an earthquake. The earthquakes are caused by severe tectonic movement of plates, volcanic eruption forces and isostatic imbalance often taking place due to diastrophism creating ups and downs in landform construction.

Question 2.
Explain the three types of earthquake waves. What is the difference between seismic focus and epicentre ?
Answer:
Three types of earthquake waves are :

1. P-primary waves,
2. S-Secondary (or Shear waves) and
3. L-Long waves (or Surface waves).
   

Seismic focus.is located in the interior of earth’s crust from where the earthquake waves originate and the epicentre is the nearest point vertically below the region of earthquake effect.

P Q. What is the Tsunami ? How ist it produced ? What are its effects ?
Answer:
Tsunami is very destructive sea wave rising high upto several metres and jump furiously along the coastal areas like the hood of a snake. The name ‘tsunami’ is from the Japanese words : ‘Tsu’ and ‘nami’ meaning ‘harbour’ and ‘wave’ respectively. So tsunamis are harbour waves.
It is produced mainly by undersea earthquake along the gaps of tectonic plates, volcanic thrusts, great landslides and meteorite impact.
They can cause a lot of destruction on the shore. They are sometimes mistakenly called “tidal waves,” but tsunamis have nothing to do with the tides.

Question 3.
Compare and contrast the constructive effects and the – destructive effects of an earthquake.
Answer:
Constructive effects :

1. Earthquakes help the earth release its stored up energy. The majority of the earthquake occur around. The plate margins. This energy release helps to keep the earth in good shape.
2. On account of both vertical and lateral displacement of the earth’s crust, earth-quakes may raise or lower parts of earth especially near the seashore. Sagami Bay of Japan was uplifted 200 m in 1923.
3. Landslides triggered by earthquakes cause formation of lakes as has happened at many places in the Himalayan region.

Destructive effects :

1. Human beings have settlements in active earthquake zones. Most often the houses and other structures collapse causing great loss of property.
2. The forces of uplift and subsidence also cause submergence of coastal parts. For example: Dwarka in Gujarat which now lies submerged under the sea.
3. Earthquakes have changed the course of rivers in the past. They have thus rendered many areas unsuitable for irrigation and agriculture. They cause danger to human life.

Question 4.
Is it possible to predict an earthquake ? Give reasons to support your answer.
Answer:
No till now it is not possible to predict an earthquake. Earthquake prediction in the past was left to astrologers and mystics. Today it is a respectable scientific pursuit. The Russians were the first to discover P and S seismic waves in 1960s on the basis of which predictions were made. These waves still are the only means available to seismologists to predict earthquakes.
The theory of Plate Tectonics offers another means of prediction on scientific lines. Japanese use the methods of measuring changes in sea level and variations in Earth’s magnetic field to predict earthquakes. However, no method is still foolproof as has been proved by recent earthquakes in Japan, India and the USA.

Question 5.
How are earthquakes distributed over the globe ?
Answer:
The earthquakes are common along the weak tectonic belts affected by continuous tremors due to the movement of plates one upon another. Main belts are Circum-Pacific Mountain belt and Mid-World Mountain belt of fold mountains which are still in the process of upthrust forces increasing their height.

Question 6.
How is the intensity of earthquakes measured ? What instruments are used ?
Answer:
Ritcher scale and Mercalli scale are used to measure the intensity of earthquakes. Ritcher scale measures through a graphical scale in zigzag graph from 1 to 9 and Mercalli scale observes it from 1 to 12 points scale.

Practice Questions (Solved)

Question 1.
(a) What is an Earthquake ?
(b) How it is caused ?
(c) Describe the world’s distribution of earthquakes.
(d) What are the advantages and disadvantages of Earth quakes.
OR
What are the effects of Earthquakes ?
(e) Name the major earthquakes of India from 1991 to 1997.
Answer:
(a) The sudden mild or violent shaking of a part of the earth is called an earthquake. An earthquake is generally accompanied by a rumbling and tremors.
(b) Causes The chief known causes of earthquakes are believed to be as follows :

1. When a dormant volcano erupts into activity or an active volcano discharges matter with greater violence the surrounding areas feel tremors or earthquakes.
2. When the interior of the earth cools and contracts the outer crust in some places cracks and faults are caused. This movement causes earthquake.
3. Some time water percolates so deep down into the earth that it turns into steam on account of the internal heat. This steam expands and tries to force its way out. This pressure causes an earthquake.

(c) The earthquakes are distributed along two major belts namely circum Pacific earthquake belt (Ring of fire) and the Mid¬World, Mountain Earthquake belt along the great fold mountain zone.
(d) Earthquakes brings about changes on the surface of the earth which are very harmful to man.

Destructive Effects :

1. Many towns are destroyed and there is considerable loss of life and property.
2. They cause floods by uplifting of land in the’ course of river.
3. Some places are submerged under the sea.
4. Big cracks and fissures are formed on the surface of the river and they interrupt communications.
5. Some times rivers disappear or change their courses or get flooded. Railway lines are twisted.
6. They cause great tidal waves, which may bring havoc to the coastal areas.

Constructive Effects :

1. Precious metals and minerals come up to the surface for the use of man.
2. New lands for habitation above the surface of the sea are formed.
3. Some times new springs and water falls are formed which help in irrigation.
4. Violent earthquakes have led to the formation of hills and mountains.
5. Bays and gulfs are formed along the coastal land to provide new ports and harbours.

(e) Major earthquakes of India from 1991 to 1997

1. Latur -1991
2. Uttarkashi – 1993

Question 2.
Name the important Earthquake-belts of the world.
OR
Indicate two major belts of Earthquakes.
Answer:

1. Circum – Pacific Earthquake Belt :- i.e. round the Pacific Ocean. This belt goes along with the coast of America and East coast of Asia.
2. Mid World Mountain Earthquake Belt :- This belt runs through the middle of Asia from East and goes beyond the Mediterranean sea as far as the West Indies. This belt, however, is not so active as Pacific Belt.

Question 3.
Name the instrument used to record Earthquakes.
Answer:
The instrument used to record Earthquakes’ is called Seismograph.

Question 4.
Name some Earthquakes which caused great damage.
Answer:
Some Earthquakes which caused serious damage to property and life are :

1. Lisbon Earthquake of 1755
2. South Carolina Earthquake of August 1886
3. The Japan Earthquake of Oct. 28, 1891
4. Kanga (Himachal pradesh) Earthquake of April 1905
5. Tokyo (Japan) Sep. 1923
6. Quetta 1935
7. Bihar 1934
8. California Earthquake of April, 1966
9. Turkey Sep. 1975
10. Iran 1968
11. Peru 1970
12. Tangshan (China) Earthquake of July, 1976
13. Broach Earthquake of 1970 affected part of Gujrat.
14. Earthquake of 1988, had its epicentre near Darbhanga and affected parts of North Bihar, Nepal and Bangladesh.
15. The Bhuj earthquake of 2001 devastated many cities of Gujarat.

Question 5.
Earthquakes occur in the Mid-Atlantic belt.
Answer:
Earthquakes occur in the Mid-Atlantic belt because here the sea floor spreading is the main cause for earthquakes.

Question 6.
How do earthquakes affect landscape ?
Answer:
Earthquakes cause rise and fall of landmasses, create fault scarps, offset streams and other land features and cause landslides. Earthquakes waves also destroy houses and man-made structures, buckle and twist the railway lines electric and telegraph lines etc.

Question 7.
What was the cause of Koyna earthquake in India ?
Answer:
Koyna Dam is located in Maharashtra on the Deccan plateau. This part was considered a stable block free from earthquakes. But Koyna earthquake in 1986 was a big surprise. In the reservoir of the dam water gathered was more than its capacity. It disturbed the local isostatic balance. It caused an earthquake and caused cracks in the rocks. It may be called a man-made earthquake.

Question 8.
Describe the main type of Earthquake Waves.
Answer:
Earthquake Waves :- Earthquake waves travels in all directions from the Focus. There are three types of earthquake waves :

1. Longitudinal Waves : These are known as Primary Waves ‘P’
2. Transverse Waves : These are known as Secondary Waves ‘S’.
3. Surface Waves : These are called Long Waves or ‘L’ Waves.

Question 9.
Name the causes of earthquakes.
Answer:

1. Volcanic eruptions
2. Faulting
3. Elasticity of rocks
4. Local causes
5. Epeiro, Genetic events.

Question 10.
Why are earthquakes related to volcanoes ?
Answer:
There is a close relationship between an earthquake and a volcano. Earthquakes and volcanoes occur in small belts, i.e. Mid world belt and Circum pacific belt. Their distribution shows a similar pattern. Volcanic eruption lead to earthquakes. Volcanic eruptions are the local cause of earthquakes.