Haritha

Chapter 10 South America

Introduction: The Continent of South America is situated to the south of North America. Once it was connected to North America through the ‘Isthmus of Panama’.

In 1914, South America becomes separated from North America by constructing the Panama Canal cut through the Isthmus of Panama. The continent was unknown to the Europeans for a long period. Therefore, when the continent was discovered by the Europeans, they called it as ‘New World’.

Read and Learn all WBBSE Notes For 8 Class Middle School Geography

South America forms a part of Latin America which includes the states of Central America south of the United States and the West Indies. Latin was the ancient language used by Romans in the past. Modern languages of Spanish, Portuguese, Italian, and French are derived from Latin.

People from southern Europe speaking these languages settled in this part of the Western Hemisphere. Therefore, this part of the Western Hemisphere is called, ‘Latin America’.

Location: South America is situated between 81°21′ West longitude in the west and 34°50′ West longitude in the east; and 12°28′ North latitude in the north and 56° S latitude in the south. Since nearly. 85% of the continent falls within the southern hemisphere, it is called a ‘Southern Continent’.

The continent is also called the ‘Continent of Western Hemisphere’ as it is entirely located to the west of 0° longitude. South America is a triangular-shaped continent that is wider in the north and gradually tapers to a point in the south. It stretches for 7562 km from north to south and for 5310 km from west to east as its widest part.

Boundary: The continent of South America is bounded on the east by the Atlantic Ocean, on the west by the Pacific Ocean, on the north by the Caribbean Sea and the Panama Canal and on the south by the narrow Drake Strait and Antarctic Ocean.

Tierra del Fuego, an igneous island, lies off the southeast coast of South America and is separated from the mainland by the Strait of Magellan. Cape Horn is the southernmost tip of the continent.

Area: South America occupies about 17.8 million square kilometres area. It is the fourth largest continent of the world according to its size and population. Its area is six times greater than India.

Population: The population of South America is about 385 million (385000000).

Geographical Importance: South America is a typical continent exhibiting all kinds of physical and economic features. These are as follows:

Island Continent: South America is bordered on all sides by ocean waters. So it is called an ‘Island Continent’.

Presence of various types of physiography: There are lofty young fold mountains of the Andes; the Great Central Plain covered by the Llanos, the Selves, the Gran Chaco and pampas; the double eastern highlands of Guiana and Brazil and the deeply indented coastline of the southern end.

A continent of contrasts: South America is a continent of contrasts. The hot wet equatorial forests of the Amazon Basin and the Atacama Desert of Peru-the driest of the world, the high barren plateau of Bolivia, the temperate grassland of Argentina and the Mediterranean coast of Chile-all differ widely in climate and vegetation.

Rich in native flora and fauna: The continent is rich in native flora and fauna which are peculiar to other continents. The hevea brazillensis which yields rubber is a native tree of South America. Native animals include the alpaca and vicuna which are prized for their wool and the llama.

Presence of dense forest: The entire northern part of the continent is covered by dense evergreen rain forests, called ‘Selvas’ through which light cannot reach inside. The Selva is also called the ‘Land of Twilight’.

Developed in agriculture: South America has always been mainly an agricultural continent, exporting agricultural products to Europe and North America.

Developed In Industry: Though agriculture is still the chief occupation manufacturing industries have also developed in Argentina, Brazil, Chile and Peru.

Abundance In Raw Materials: There are sufficient raw materials in South America which are needed for different industries, such as:

Minerals like:
(1) Iron ore,
(2) Copper ore,
(3) Bauxite;

Crops like:
(4) Coffee,
(5) Cocoa,
(6) Sugarcane,
(7) Rubber,
(8) Cotton etc.;

Animal-based raw materials like:
(9) Wool,
(10) Meat,

Leather and forest-based raw materials, like:
(11) Timber.

Potential In Power Resource: Though there is a scarcity of power resources there is high potentiality in the generation of hydel power by the turbulent rivers and thermal power.

Prospective continent: With its immense resources awaiting development, South America’s future holds great promise.

Chapter 10 South America Physical Features of South America Physiographically

South America may be divided into five divisions-

1. The Western Mountains,
2. The Northern Plateau,
3. The Eastern and The Central Highlands,
4. The Central Plains and
5. The Coastal Plains

The Western Mountains: The Andes Mountains, also known as the ‘Western Cordilleras’ is the most prominent feature of the continent. The Andes Mountains extend continuously parallel to the west coast for a distance of over 7250 kilometres.

It is the longest mountain in the world. It is broad in the north in Bolivia (about 640 kilometres) and gradually becomes narrow in the south. The mountains contain high peaks such as Mt. Aconcagua (7021 meters), (6277 m) and Cotopaxi Chimborajo (5896 m).

Chimborgo is the highest active volcano in the world. Cotopaxi is the second-highest active volcano in the world. Aconcagua is the highest peak of the Andes. There are many volcanic peaks in the mountain ranges. The high peaks are permanently covered with snow and ice.

The Andes is the world’s longest as well as the second loftiest young fold mountains. The Andes mountains is frequently affected by earthquakes.

The Andes mountains consist of two or three parallel ranges with basins of plateaus between them. Central cordillera runs through the middle of Colombia in a north-south direction.

The Occidental mountain range lies west of central California and the Oriental mountain range lies east of the central Cordillera. The southern part of the Oriental mountain range is known as the ‘Real mountain’ which stands along the border between Chile and Argentina.

Lake Titicaca located on the Andes along the border between Peru and Bolivia is the highest lake (3800 m) of the world and also the largest lake of America. The Uspallata pass lying to the southwest of Aconcagua is the only break in the continuous chain of the Andes.

The Northern Plateau Region: The region that extends from the Andes in the western part of the continent to the Atlantic coast in the east is called the Northern Plateau Region.

Due to the processes of erosion and denudation by rainfall, river and wind, the plateau has been reduced to a low height. This region covers Venezuela, Guyana, Surinam and Guiana and is also known as Guiana s 48 Highland. In Venezuela the plateau is highest where Merida is the highest mountain and the highest peak is Marta (5105 m).

The Central and Eastern Highlands: There is another highland in South America. In the east of the continent, it is known as ‘Brazilian Highland’ and in the central region of the continent as ‘Mato Grosso’,

Pacific Ocean Plains Ocean Eastern High Land Atlantic which, actually, links the Andes Mountain in the west and the Brazilian Highland in the east. Brazilian Highland slopes very steeply to the Atlantic coast in the east, while it descends gently to merge with the Central Plains in the west. The greater part of the plateau is occupied by the ‘Campos’ grassland.

The Central Plains Or Lowlands: The Central Lowlands or Plains lie between the Eastern Highlands and the Andes. They consist of four areas from north to south. These are as follows:

The Plains Of The Amazon Basin: This is the largest and northernmost part of the plain. This plain is located in the equatorial region. So a major portion of this plain is covered by dense evergreen rain forests called ‘Selvas’. The slope of this region is from west to east.

The Plains Of The Orinoco Basin: The Orinoco river basin in Venezuela and Colombia has formed a narrow plain extended in the southwest to northeast direction. ‘Llanos’, the tropical grassland covers this plain.

The Plains Of The La-Plata Basin: La-Plata, the most important estuary of the Parana -Paraguay and Uruguay river of the southern part of south America has formed another narrow plain extending from the north to the south through the countries of Bolivia, Paraguay, Uruguay and Argentina.

The Pampas Plain: An extensive temperate grassland called ‘Pampas’ lies to the south of the La-Plata in Argentina. In the north the grassland where some deciduous trees are found with scattered presence of scrubs it is known as ‘Granchaco’. The southern part of the Pampas is very dry and has formed the Patagonia, Desert.

The Coastal Plains: There is a very narrow coastal strip bordering the Pacific Ocean coast of Ecuador and Colombia as the Andes rise very steeply from the shore of the Pacific Ocean. The coastline of South America is almost smooth except in the southwest where it is broken. Many fiords have formed by glacial erosion through which the sea water enters the continent.

Many islands are also found in the ocean, such as the Galapagos islands lie off the coast of Ecuador, Juan Fernandez lies off the coast of Chile; Tierra del Fuego and Falkland island lie off the coast of Argentina and Trinidad Tobago, Barbados and Grenada islands lie off the coast of Venezuela.

Chapter 10 South America Drainage System Or Rivers Of South America

Many rivers are found in the continent of South America. Rising in the Equatorial regions most of the rivers of the content supply more water.

The plateau of Mato Grosso, located in the central part of South America, acts as a water divide between the northern and southern parts of the continent. Most of the rivers of the continent have organised either in the Mato Grosso or in the Andes and flow eastward to the Atlantic Ocean.

The characteristic features of the rivers or drainage system of South America are as follows:

1. Most of the rivers of South America are rain-fed and originate from the Equatorial region of the continent.
2. The rivers are perennial as they are fed by snow or equatorial convectional rain. Some of these rivers are suitable for the generation of hydel power.
3. Most of the rivers are long in length and large in volume.
4. Most of the rivers originated from the Mato Gross plateau or the Andes mountains.
5. There are some west-flowing rivers which originate from the Andes mountains are short in length.
6. Except for the Orinoco river, no other river has formed a delta near its mouth.

According to their direction of flow rivers of South America may be grouped into following categories :

1. East flowing rivers,
2. North flowing rivers,
3. South-flowing rivers and
4. West flowing rivers.

Important Rivers Of South America:

Types Of The Rivers	Name of the Rivers
East flowing Rivers.	The Amazon, Orinoco, Sao-Francisco
North flowing Rivers	Madeira, Purus, Tapajos, Xingu, Araguaia, The Magdalena.
South flowing Rivers	Paranaiba, Parana, Paraguay, Uruguay, Rio-de-la Plata, Salado, Colorado,Rio-Negro, Chico, Rio Branco.
West flowing Rivers	Short but turbulent rivers which originated in the Andes and flow into the Pacific Ocean.

 

East Flowing Rivers:

(1) The Amazon River System: The Amazon river, the chief river of South America is the World’s greatest and mightiest river. This is the longest river of South America and the Second longest river of the world (6447 km). In 1541, the great Spanish traveler ‘Orellana’ called this river as ‘Amazons’.

It owes its name to the race of female warriors called the ‘Amazons’ of Greek legend. The river basin is also called the ‘Amazonia’ i.e. ‘the land of the female warriors’. The river basin covers about 7:04 million square kilometres which is the world’s largest river basin.

The source of the river Amazon is considered as a lake which is located on the top of the Andes. Another opinion is that the river Amazon originated from Mt. Mishmi (5597 m) on the Andes in Peru and then flows northward.

Rising as the ‘Maranon’ in the central Peruvian Andes, it is joined by another two headstreams including the ‘Napo’ and the ‘Ucayali’. Then it escapes from the Andes through narrow gorges and flows eastward over the lowlands to meet the Atlantic off north-eastern Brazil.

The river is fed by more than one thousand tributaries flowing down from Peru, Bolivia, Ecuador, Colombia, Venezuela and Brazil. The seven tributaries namely Madeira, Jurua, Purus, Japura, Tocantins, Negro and Xingu are longer than 2000 kilometres.

The Madeira (3350 Km long) is the longest tributary that flows from Bolivia. On the other hand, the Negro (2253 km long) though shorter in length, is the largest tributary of the Amazon.

Rising in the equatorial regions of Colombia, it supplies more water to the Amazon than any of the other tributaries. It is estimated that 20% of all the water that runs off the Earth’s surface is carried by the Amazon.

The width of the river varies from 1.5 km to 14 km and near the mouth it is 80 km. So it is no wonder that the Amazon is called the ‘River Sea’. The large volume of freshwater discharged by the river makes the seawater less salty for more than 160 km from the shore.

The river Amazon is navigable up to 3200 km from its mouth. A large volume of water with great velocity is discharged through the wide mouth of the Amazon river to the Atlantic Ocean.

The mouth of the Amazon river is quite wide and water from the ocean enters the river during high tide. Ocean currents are also very strong in this region. Due to such conditions, no delta has been formed in the mouth of the Amazon river.

The Amazon river is called World’s largest river due to the following causes :

1. The Amazon river is the second longest river (6447 km) of the world (the Nile is the longest, 6671 km).
2. The Amazon basin is the largest river basin of the world (7050000 sq. km)…
3. This basin is located in the Equatorial climatic region. Heavy
4. As the location of the Andes in the way of northeast trade winds, moisture-laden air gets obstructed by the mountain, causing heavy precipitation.
5. The discharge of water per second is 209000 cubic metres.
6. There are about more than 1000 tributaries and innumerable distributaries of the Amazon. They are quite long.

(2) The Orinoco River System: The name ‘Orinoco’ is derived from the American word meaning ‘Place of Paddle’ i.e. navigable place.

This river is flowing in the northern part of South America. After rising from the southwestern Guiana Highlands of Venezuela, the Orinoco flows for some 2736 km to meet the Atlantic where it forms a delta.

After coming down from the highland the river has crossed the dense forests, grasslands, swamps one after another flows north-eastward along the edge of the highland in a giant arc and then finally has drained into the Atlantic Ocean.

Important tributaries of the Orinoco river, that have originated either in the Andes or in the Guiana Highlands are- Meta, Guaviare and Caroni. The Carrao, a tributary to the river Caroni, has formed the highest waterfall of the world- the ‘Angel’ waterfall. It is about 979 metres high (3212 feet).

Casiquiare, another tributary to the river Orinoco has joined river Negro-the tributary to the Amazon river.

(3) Sao-Francises: Sao-Francisco is another important river of South America. This river is about 3200 km long. It originates in South Central Minas Gerais state of Eastern Brazil, flows north, north-east and eastward and falls into the Atlantic Ocean.

It is the main river of eastern Brazil. The river, an entirely Brazilian river, is called the ‘River of National Unity’ by the Brazilians because of its importance in navigation and as a source of hydel power.

North-flowing rivers:

(1) Madeira: Maderia is a river of west Brazil and it is the most important tributary of the river Amazon. It is about 3350 km long and formed by the confluence of Bolivian rivers Mamore and Beni at the Brazilian border. Then it flows north-eastward and falls into the Amazon below Manaus.

(2) Purus: This navigable river is one of the important tributaries of the Amazon river. It is a river of north-west and central of south America. It is about 3402 km long and rises in the Andes mountains in southeast Peru. It flows north-eastward across the Amazonas state, Brazil and falls into the Amazon river above Manaus.

(3) Tapajos: This is a river of North Brazil. It is about 1307 km long and formed by that junction of the Juruena and Teles Pires rivers on the south end of the border between the Amazonas and Para states. It flows northeastward and falls into the Amazon river at Santarem. Important rubber plantations are found along its banks.

(4) Xingu: It is a river of central and northern Brazil. It is about 1993 km long and it rises in several headstreams in the northern part of the plateau of Mato Grosso. It flows northward through northeast of Mato Grosso state and central Para state and falls into the Amazon river near its mouth.

(5) Araguaia: This is a river of central Brazil. It is about 2113 km long and it rises in the south-central of the Mato Grosso state and flows northward and falls into the Tocantins river.

(6) The Magdalena: The Magdalena river which originates in the Andes mountain flows northward to drain into the Caribbean sea.

South Flowing Rivers:

(1) Paranaiba: Paranaiba is one of the headstreams of the Parana river. It is about 810 km long and rises in west central of Minas Gerais state. It flows westward and south-westward to unite with Rio Grande and form the Parana river.

(2) Parana: The Parana river is one of the chief rivers of South America (Parana is an Amerindian word meaning ‘father of the waters’). It is 4880 km long. The Parana flows mainly across high plateaus before it meets Paraguay. After this, the river flows through a broad floodplain before entering the Plata estuary.

(3) Paraguay: The southward-flowing Paraguay river (2566 km) is the main tributary of the Parana. It flows south through Paraguay before being joined by the Pilcomayo river at Asuncion. Unlike the Parana, Paraguay is a river of plains flowing across a wide stretch of marshes. The river meets the Parana at Corrientes.

(4) Uruguay: Uruguay (1662 km) is another important river. It is the Spanish from of the local Amerindian word meaning ‘the river of painted birds’. After originating from southeast Brazil, Uruguay flows in a curve and joins the Parana to form the Plata river estuary on the Atlantic coast between Uruguay and Argentina.

(5) Rio-de La-Plata: The Rio-de la Plata is a Spanish word which means ‘Silver River’. The name ‘Rio-de La-Plata’ is misleading because it is not a river at all. It is actually an estuary of Parana and Uruguay rivers between Uruguay and Argentina. It is one of the widest estuaries in the world. It is around 225 km across its mouth and is about 270 km long at its longest point.

(6) Salado: There are three south-flowing rivers in Argentina which are called Salado One of these rivers which rises in the Andes mountains and is flowing in the northern part of Argentina. It is more than 1782 km long and flows southeastwards and falls into the Parana river at Santa Fe.

The river which is flowing the western part is about 1377 km long. It flows along the south forming a boundary between Mendoza and San Luis Province turns south-eastward and emties into the Colorado river. The river of the eastern part in Buenos Aires Province is about 648 km long. It flows westward and falls into Samborombon Bay.

(7) Colorado: Originating in the Andes mountains the Colorado river flows into the Atlantic Ocean. This river is about 859 km long and flows along the Mid-Argentina.

(8) Rio-Neogro: This is the river of south-central Argentina. It is about 648 km long and flows eastward and then falls into the Atlantic Ocean.

(9) Chico: This is a river of South Argentina. It flows along the Province of Santacruz. This river is flowing southeastward and falls into the Atlantic Ocean at Santacruz.

(10) Rio-Negro Rio-Negro is a river of the north-western part of South America. It is about 2268 km. long, rises in East Colombia, where it is known as the Guai-nia flows eastward to Venezuela boundary, and then southward forming a section of the Colombia-Venezuela boundary, crosses into Brazil and continues south-eastward into Amazon river at Manaus, is joined also to the Orinoco river through the Casiquire river.

(11) Japura: This is a river of the northwest of South America. It is about 2835 km. long and rises in southwest Colombia, where it is known as the ‘Caqueta’ and flows southeastward across the Brazilian border and falls into the Amazon river.

(12) Rio-Branco/Parima: Rio Branco or Parima is a river of North Brazil. It is about 567 km. long and formed by the confluence of the Uraricoera. Tacutu; the river flows southward falls into the Rio Negro.

West Flowing Rivers: Besides the above rivers there are many streams that originate in the Andes but flow westward and fall into the Pacific Ocean. These rivers are short in length but turbulent. Therefore, these rivers are used in irrigation and the generation of hydel power.

Lakes of South America: There are a few big lakes in South America. These lakes are off two types i.e.

1. Freshwater lake and
2. Saline water lake.

Fresh Water Lakes: These are Lake Titicaca, Lake. Poopo, Lake Chiquita, etc. Lake Titicaca (8287 sq. km) located at a height of 3810 meters on the border of Bolivia and Peru is the highest navigable lake in the world. On this lake big ships ply from port to port. Lake Poopo is about 500 km. to the southeast of Lake Titicaca.

Saline Water Lake: Lake Maracaibo of northwest Venezuela is a saline water lake open to the sea. It is a shallow lake and the thick layers of sedimentary rocks under it are rich in oil deposits. In the eastern region, there are also a few small lakes in Brazil, most of them are saline water lakes.

Chapter 10 South America Climate Of South America

There are great variations in the climate of South America. This continent is called as a ‘Continent of diversified climate’ due to the following causes:

1. The continent is located on both sides of the Equator. The upper part of the continent is located in the northern hemisphere and the lower part is in the southern hemisphere. Hence, exactly opposite seasonal changes are found in the northern and southern hemispheres i.e. when summer exists in the north, winter prevails in the south.
2. Due to the Equatorial location either side of the equator has uniformly hot and humid conditions throughout the year. There is a little difference in temperature betwen summer and winter. There is no dry season.
3. The regions which are located away from the Equator to the north and south, there is greater contrast in temperature between summer and winter.
4. The Brazilian coast gets higher rainfall than the interior.
5. South of the Brazilian Plateau, the Pampas Lowlands are in the temperate zone, winters are cooler and summer are less hot. Rainfall is moderate with maximum summer.
6. Further south, the plateau of Patagonia, east of the Andes gets a low rainfall. This is a rain shadow region of the Andes. This is a temperate desert.
7. West of the Andes, the southern most region of Chile has marine or oceanic type of climate.
8. The Andes mountains region has climatic conditions varying according to height above sea-level.

Factors Affecting The Climate Of South America: There are great contrasts in the climate of South America and this is controlled by the following factors:

Latitudinal Extent: The important lines of latitude that cross the continent are the Equator (0°) in the north which passes through the Amazon estuary and the Tropic of Capricorn (232°S) which passes through the central part of the continent.

Thus the broad northern part of South America lies in the tropical zone and is hot throughout the year. While the narrow, southern part lies in the temperate zone has lower temperatures throughout the year.

Altitudinal Factor: The mountain ranges especially the Andes influence the climate in two ways. Firstly, because of its high altitude, places situated on the mountains are colder than those on the plains lying on the same latitude.

For example, Quito situated on the Equator at a higher altitude has an average temperature of about 14°C while Manaus in the Amazon lowlands, also on the Equator, has an average temperature of about 26°C. Secondly, the Andes lies close to the Pacific coast and extend from north to south.

In the north, it stands as a barrier to the trade winds which blow in from the Atlantic, and in the south, it prevents the rain-bearing westerlies from crossing over to the east. As a result, most of the Pacific coast is dry but its southern part gets rain throughout the year from the westerlies.

The steel plateau edges of the Brazilian highlands force the trade winds to rise and this results in heavy rain in the Brazilian coast throughout the year.

Prevailing Winds: The northeast and south-east trades blow toward the Equator in the tropical zone and cause rainfall in the eastern margin of the continent. The Westerlies Rainfall: Role of the Andes blowing from the Pacific Ocean cause rainfall to the southwestern coast and Tierra-del Fuego. Central Chile gets rainfall in winter from the westerlies but remains dry in summer when it comes under the influence of the southeast trades.

Shape Of The Continent: Because of its unique shape, wider in the north and tapered in the south, major portion of the continent lies in the torrid zone.

Distance From The Sea: The moderating influence of the sea is felt in the tapered and Southern part of the continent where it is narrow. In the coastal areas of the broad northern part of the continent is also enjoy a Maritime climate. But the upper part of the continent is wider. So the climate in the interior of the northern part remains unaffected by seas and oceans.

Ocean Currents: The cold Humboldt or Peruvian current flowing along the western coast of Chile and Peru has a cooling and drying influence. So the south west coast of South America remains cool and dry.

The warm Brazilian current flowing along the eastern coast of Brazil warms the winds blowing over the sea. As a result the sea winds pick up moisture and cause heavy rain throughout the year.

Seasonal Conditions Of The Important Elements Of Climate In Different Parts Of South America:

Temperature: In the month of June-July, it is summer in the northern part of the continent where the sun is overhead. So the average temperature becomes 21°C which gradually decreases towards the south where it goes below 5°C (i.e. winter). But in the Andes and in the extreme South at Tierra del Fuego temperatures drop below the freezing point.

In December-January, when the sun is overhead south of the Equator, southern Brazil and northern Argentina being near the Tropic of Capricorn are the hottest parts of the continent with an average temperature of 30°C.

Temperature decreases to about 18°C further south and the extreme south the summer temperature is about 10°C. However, because of high altitude, the temperature varies from 0°C to 16°C. in the Andes ranges.

Air Pressure And Winds: Low pressure prevails, all the year, over the Equatorial region in northern part of the continent. So, the Trade Winds are blowing from the northeast and south-east of the equator to this Equatorial Low-Pressure Belt. North-west westerly wind blows throughout the year over the southern part of the continent.

Rainfall: The saying ‘rain follows the sun’ is true for South America. The Amazon basin over which the sun shines more or less directly throughout the year gets very heavy convectional rain throughout the year.

In summer, most northeast and south-east trade winds blowing from the Atlantic Ocean, being obstructed by the Andes give heavy rainfall of 200 cm. or more which decreases gradually from the Atlantic coast in the east to the Andes Mountains in the west.

But the western side of the Andes becomes South America. The Seasons of Rain. dry as it is a ‘Rain Shadow’ area. So, it is found that the Atacama Desert is located in northern Chile bordering the Pacific Ocean coast.

Again the most northwest westerlies blowing from the Pacific Ocean give heavy rainfall to, the southern parts of the western coast as it is obstructed by the Andes mountains. Therefore, the Patagonia Desert is found in southern Argentina to the east of the Andes mountains where another Rain-shadow region has formed.

Climatic Regions Of South America: Based On The Variations In Temperature, Rainfall, Air pressure And Wind, South America May Be Divided Into The Following Climatic Regions.

1. The Equatorial Climate;
2. Tropical Savanna Climate;
3. Hot Tropical Climate;
4. Hot Tropical Desert Climate;
5. Medi-terranean Climate;
6. Temperate Desert Climate;
7. Warm Temperate Climate;
8. Cold Marine Climate and
9. Mountain Climate.

Climate Region Of South America:

Climatic Type/Region	Location	Climatic Characteristics
(1) The Equatorial Climate	Amazon and Orinoco basin near the Equator side by side in Brazil, Colombia, Venezuela, and southern Surinam.	(1)High Temperature (27’C) and humidity prevail throughout the year. Rainfall occurs about 200 cm/year.(2)Season change does not occur here (3)Convectional rain in the form of thunderstorms occurs more or less every day in the afternoon and there is no dry season at all.
(2) Tropical Savanna	Near the Orinoco river basin, and the Brazilian Highland, the grassland of Guinea.	(1)Summers are hot and Humid.(2)Winters are cool and dry.(3)Most of the rainfall occurs during summer.
(3) Hot Tropical Climate	Eastern Brazil	(1)Rainfall occurs In the summer.(2)Rainfall occurs due to moist trade winds from the east.(3)Summers are hot and humid.(4)Winters are cool and dry.
(4) Hot Tropical Desert	Atacama desert on the western part of the continent, Southern Peru, and northern Chile.	(1) The region is extremely hot and practically rainless. (2)Summers are very hot and winters are quite cold. (3)It is the world’s driest region.
(5) Mediterranean Climate	The southern part of the Atacama desert is located in Central Chile.	(1)Warm dry summers.(2)Mild wet winters. (3)Westerlies bring rain in winter. (4)The trades blowing over the land in summer fail to bring any moisture as well as rain.
(6)Temperate Desert	Desert regions of Patagonia in southern Argentina.	(1) Warm summer, (2) Cold winter,(3)Located in the rainshadow region of the Andes and receives only 13-15 cm. of rain annually. (4)It is called a temperate desert as it lies south of 40 latitudes.
(7)Warm Temperate (grass-land)Climate	South of the Tropical    region In north-eastern Argentina and Uruguay	(1) Moderate climate. (2) Summers are quite hot. (3) Rainfall decreases and so does the temperature.
(8) Cold Marine climate	South Chile and coastal regions of south-east Brazil.	(1) Cool climate.(2) Heavy rainfall throughout the year.(3) Moist wind blowing from the Atlantic ocean.
(9) Mountain Climate	Mountain Climate prevails in the western part of the continent in the Andes mountain region.	(1) As the temperature decreases with increasing altitude, at higher altitudes cold climate prevails.(2) The top of the Andes mountain year. (3) In the foothills warm climate prevails.

Chapter 10 South America Natural Vegetation of South America

As in other parts of the world, climate especially rainfall influences the natural vegetation of South America to a great extent. According to the variation in temperature and rainfall, natural vegetation of South America may be broadly divided into nine vegetation belts.

These are as follows:

Equatorial Rain Forest or Selva: The hot and humid climate has favored the growth of equatorial rain forests in the Amazon Basin and in the coastal regions of Guyana, Venezuela, Guiana, Surinam, etc. which receives heavy rain throughout the year. These forests are known as ‘Selvas’.

The Selvas of the Amazon Basin are the largest and densest expanse of equatorial forests in the world. The trees are hard evergreen and broad-leaved. The trees are 40/50 metres tall forming thick canopy through which sunlight cannot penetrate inside. So the ground is always damp and full of undergrowth.

Creepers are also common including the giant woody creepers called ‘lianas’ hanging from the branches. Thousands of species of trees are scattered all over the forest. As a result, it is difficult to obtain timber or forest products from the selvas. The trees are valuable hardwood varieties, such as Mahogany, Ablus, and Rubber. Brazil nut, Rosewood etc.

Tropical Grasslands or Savanna: This region lies north and south of the Equator. The Plateau of Brazil lying to the south of the Equator and a large part of the Orinoco river valley lying on the north are occupied by Tropical Grassland or Savannas.

Here rainfall is less and there is a distinct dry season that occurs only in summer and can support tall coarse grass and some trees many of which are acacias. These grasslands are locally called ‘Llanos’ in the Orinoco Basin and ‘Campos’ in the Brazillian Highlands.

Warm Temperate Forests or GranChaco: This type of vegetation region lies south of the Brazilian Highland, i.e. the Parana-Paraguay river basin (the lowlands of northern Argentina and Western Paraguay). This region is locally called the ‘Gran-chaco’, which means ‘Great hunting ground’.

This region has open forests of sub-tropical valuable hardwood deciduous trees and grasslands. The chief trees of this region are the ‘Quebracho’ tree meaning ‘axe breaker’ is an extremely hardwood variety and the ‘Parana pines’, a type of softwood in great demand for building purposes.

The Quebracho, which yields tannic acid which is of great use in the leather industry. The leaves of the ‘Yerba Mate’ bush are brewed to make a tea-like drink.

Temperate Grassland Or Pampas: An extremely temperate grassland locally called ‘Pampas’ is found in Uruguay and around Buenos Aires in the northeast of Argentina. This grassland with soft, short, and juicy grasses is an ideal pasture for rearing cattle and sheep.

Characteristics of the Temperate Grassland or Pampas:

1. The Pampas are vast grasslands.
2. The grasses of this region are shorter than Savanna grassland.
3. The grasses grow luxuriantly.
4. These grasslands provide the basis for the pastoral industry.
5. Parts of the grasslands have been cleared for cultivation.

Desert Vegetation: There are two types of deserts in South America-

1. The thin strip of hot desert in coastal Peru and northern Chile called the Atacama desert and
2. The temperate desert of Patagonia in southern Argentina. The desert of Patagonia in the southern0°Caribbean Seapart of South America is treeless with the scattered presence of the scrubs.

The Atacama desert is almost rainless, is practically 0° devoid of vegetation except for some cacti and prickly pear. Thorny bushes and scrub, however, grow in Patagonia.

Equatorial Rainforest or Selva Tropical Grasslands or Savanna Warm Temperate Forests or Granchaco Temperate Grasslands or Pampas Bushes Mountain Vegetation Mediterranean Vegetation Cool Temperate Forests Scanty Desert Vegetation.

Mediterranean Vegetation: In central Chile with its humid or wet winters and warm dry summers, warm evergreen trees and shrubs occur. The Mediterranean climate supports dwarf vegetation which has long roots, small and thick waxy leaves, and short stems so that water is not lost through transpiration during the summer drought.

Common trees are fig, walnut, chestnut, and acacia. Evergreen Laurel, cork oak. grow in wetter areas, while lavender and rosemary grow in drier areas. Fruits like Olives and grapes also grow well in this region.

Cool Temperate Forests: Mixed forests of temperate deciduous and coniferous trees occur in southern Chile where rain falls throughout the year. Valuable hardwood trees like oak, beech, ash, and elm grow everywhere.

Softwood coniferous trees like pine and fir grow where snowfall is common, Some of the important trees of these forests yield valuable timber.

Mountain Forests: Owing to variations in altitude, the Andes mountains have a variety of natural vegetation. So in the western part of the continent, different types of trees are found.

Evergreen tropical rainforests and grasslands are common at the foothills. A little higher, there is the deciduous forest and then mixed forest which with increasing altitudes passes into the coniferous forests and finally into the Alpine meadows. Above the meadows occurs perpetual snow.

Little or No Vegetation: Atacama desert in northern Chile is treeless and dotted with thorny shrubs and bushes.

Chapter 10 South America The Selvas Evergreen Forest:

The Selvas of the Amazon basin are the largest and densest expanse of evergreen equatorial rainforests in the world. The forest lies on both sides of the equator covering mainly the major portion of the Amazon basin.

It covers Brazil (60%), Peru (13%), Colombia (10%), and parts of Venezuela, Bolivia, Guyana, Surinam, and French Guiana. It covers an area of about 5.5 million square kilometers.

The hot and humid climate has favored the growth of the equatorial rainforest in the Amazon basin which receives heavy rain throughout the year. The annual average temperature varies from 25° 28°C and the annual average rainfall is about 250 300 cm. A few places rainfall exceeds 1000 cm.

Thus the trees are hard, evergreen, and broad-leaved. This region is, therefore, called as “The Equatorial Evergreen Rain Forest’. Though it is a region of bright sunshine the region abounds in dense, lush green and luxuriant vegetation throughout the year. As the trees have grown closely spaced trees form a common canopy or crown.

No wonder the sunrays are often fail to peep through the thick foliage of trees in these forests to reach the ground. It is the trees that have to view with one another to reach out to the sun, and hence they grow very tall (some trees are 40 – 45 meters). So, the region is known as the “Region of twilight”.

Over a small area hundreds of different species of trees grow side by side. Therefore, the trees do not occur in pure stands. These forests are known for valuable hardwoods like mahogany, ebony, rubber, rosewood, ironwood, green heart, ivory wood, Brazil nut, and balsa (a very light wood).

The trees are of different heights. The branches of the taller trees are so thickly intertwined that sunlight cannot pass through the roof or canopy of leaves and branches. Creepers climb up the trees weaving a maze as it were and there is a dense undergrowth. Thousands of species of trees are scattered all over the forest.

As a result, it is difficult to obtain timber or forest products from the Selvas. Apart from the oceans, these forests are our largest source of atmospheric oxygen. It supplies about 20% of the earth’s oxygen and is termed the “lungs of the world”.

These evergreen forests are known for beautiful birds and butterflies. They occur in all sizes and in bright colors of every hue. The region overflows with insects and worms too. There are numerous termites, mosquitoes, spiders, ticks, driver ants, and tsetse flies.

Among the tree animals, there are monkeys, known for their wits and acrobatics. Apes, the closest cousins of human beings, are also found here. Puma and Jaguar of the Amazon valley are tiger-like animals that dwell upon trees. They mostly hunt monkeys for their food. Sloths, flying foxes, (bats), tree lizards, tree frogs, and flying squirrels are the other tree dwellers.

The Anaconda is the longest python that dwells here. It girdles its prey suffocating it to death. The forest rivers are full of a wide variety of fishes along with crocodiles and turtles. In the rivers, there are also found alligators and carnivorous Piranha fish.

Ten percent of the world’s total leaving species is found here. 25 lakh insects and four lakh species of trees exist here.

This region is very thinly populated because the weather is unhealthy. The density of the population in the Amazon basin is about two (2) persons/square kilometer. Primitive economic activity still prevails in a large part of the Amazon basin.

There are some groups of people still living deep inside the jungle. Though there is an amazing variety of valuable trees in the Selvas, lumbering is not well developed.

This is mainly because-

1. Thousands of species of trees are scattered all over the forest. So the same type of trees is hardly found close together. As a result, it is difficult to obtain timber/lumber from the selvas.
2. Most of the trees are very hard and difficult to saw.
3. After sawing, it is difficult to bring down the tree since the upper boughs of other trees are interlaced, and lianas twine round them.
4. The trunk is too heavy to be dragged upto the river over the soft forest floor. In the presence of these difficulties, lumbering is not developed in the Selva region.

Chapter 10 South America The Pampas Region

The grassland of Pampas in Argentina represents one of the great wheatlands and battlefield of the world. This is the most prosperous region of Argentina. The word ‘Pampas’ is derived from the spanish word ‘Pampa’ which means ‘extensive open plain land’.

An extensive grassland surrounding Buenos Aires in a semi-circle or like a crescent moon, to the northeast of Argentina, is called the ‘Pampas’.

Location: The region lies in the La-Plata basin. This region occupies one-fourth of Argentina and most of Uruguay and it also includes a small part of southern Brazil. It extends from 30°S to 40°S latitudes and 54° west to 65° west longitude between the Andes and the Atlantic.

Boundary The Pampas region is bounded on the north by uninhabited Gran Chaco, on the south by the Patagonia desert, on the west by the foothills of the eastern slopes of the Andes, and on the east by the Atlantic.

Physiography: The Pampas is a flat lowland sloping gently towards the Atlantic. It is formed by the silts, sands, clay, and loess soils deposited by the river and wind. Silts are very much fertile and in some places more than 150 meters thick.

There are a few hills because of which the plain appears to be rolling. There are two hills -Sierra del Tandil and De la Ventana (1300 m) in the Province of Buenos Aires. These are actually, the extended parts of the Brazilian Highlands. The region is higher in the western margin (about 450 m.) and it is only 20 meters in the east.

Rivers: The important rivers of the region are Uruguay (1593 km) and the Parana (4880 km). They have joined with each other near the north of Argentina’s capital Buenos Airesas La-plata estuary to fall into the Atlantic Ocean. The tributary of the Parana in this region is the Salado.

Two other rivers are Colorado and Negro in the south. Following the slope, they all flow into the Atlantic. The Paraguay river is also a tributary of the Parana river.

Climate: The climate of this region is warm temperate type. Due to the close proximity with the ocean, the climate is comfortable here. The average summer temperature (In January) varies between 20°C to 26°C and in winter (In July) temperature varies between 8°C to 12°C. Annual rainfall varies between 50-100 cm. The rainfall increases from west to east.

Frost is common in winter. In summer, a strong cold wind called the ‘Pampero’ blows one the Pampas from the southwest. This is often welcomed since it not only towers the temperature but also causes rain that refreshes the pastures.

Natural Vegetation: The Pampas is a Typical temperate grassland supporting hardly any tree. The grass, though shorter than the Savanna grass, is softer and juicier. As the rainfall is more in the eastern part of the region the grasses are tall.

The original Pampa grass is now being replaced by other European grasses like Alfalfa. A few trees like Eucalyptus grow on the hills of the east-central part of this region. A few trees are also found mainly along the rivers. At present, most of the grassland has been destroyed for agricultural purposes.

Irrigation: Due to the insufficient river flows over the Pampas, irrigation is needed. So, wells are dug and wind pumps are used to tap underground water for irrigating the agricultural lands.

Agriculture: The western part of the Pampas is a semi-desert. This region called the dry Pampas is thus mostly barren, but the humid Pampas in the east is the chief source of the agricultural wealth of Argentina. It is one of the richest livestock cum crop-producing land of the world. Pampas region is famous for wheat cultivation.

1. Mild cool climate,
2. Rainfall,
3. Rolling plains,
4. Fertile soils favour the cultivation of wheat.

Here Wheat is the leading crop. 60% is exported to other countries. So the Pampas is known as the “Wheat basket of South America”. Maize, flax, cotton, linseed, barley, sugarcane, oats, and soybean are also cultivated. Fruits (apricots, apples, cherries, pears, and peaches) and vegetables are grown especially around the big cities.

Other fodder crops cultivated are rye and other oilseeds. Different types of agricultural products are grown here in abundance. So the Pampas region is called “The Granary of South America”.

Animal Rearing: The Pampas region is the grazing ground for Argentina’s famous cattle. Sheep are also reared here. Cattle are raised on the tall grasses in the east and sheep are raised in the west and southern parts of drier and cool climates. A rench where 20000 cattle and sheep are raised, is locally called ‘Estancia’ each of which covers 4000 acres of land.

They are raised for meat, hides, wool, milk, and milk products (Powdered milk, butter, cheese, cream etc.) which are expected in large quantities to the foreign countries Argentinas beef is prized throughout the world for its superior quality and flavor, Argentina is the largest exporter of beef in the world.

Beef extract, and ground bones are also produced here. Buenos Aires, La Plata is noted for animal products cordoba located on the foothills of the Andes is a famous dairy center. Dairy farming is also practiced around large cities meet the huge daily demands for dairy products in the local markets.

Merino sheep are reared in the drier south and southwest and the English breeds elsewhere. Thus large amounts of mutton and wool are exported to Europe.

Mineral resource: The Pampas region is not rich in mineral resources. Little copper ore and tungsten are available on the hills in the north. A little quantity of gold is also available on the bank of the river Salado.

Transportation: The lowlands of the pampas are well served by a network of roads and railway lines. There is also a transcontinental railway line from Buenos Aires to Valparaiso in chile passing through the Andes mountains. Export-import.

Industry: The pampas region is poor in mineral resources. As a result, no large-scale and metallurgical industries have been developed here. Industrial development has taken place based on agricultural and animal raw materials.

Important industrial activities are-

1. Dairy farming,
2. Meatpacking,
3. Leather,
4. Wool and other consumer goods, manufacturing.Important industrial centers are Buenos Aires, Laplata, Cordoba, and Rosario other industrial activities of these centers,
5. Engineering,
6. Chemical,
7. Cotton textile,
8. Food processing,
9. Oil refinery etc.

Population: Pampas Region is not well populated. The vast grasslands are usually used as pastures and farmlands. Gauchos, the cowboys who are engaged to look after the cattle, are actually pastoral nomads. But the cities are well-populated, Such as,

1. Buenas Aires,
2. Bahia Blanca,
3. La-Plata,
4. Rosario and
5. Cordoba.

Buenos Aires: This is the capital, principal city, and chief port of Argentina. This is a million city (12.05 million in 2001), and the second largest city of South America. It is situated at the estuary of La Plata and an important industrial as well as trading center of Argentina. This is known as the ‘Paris of South America’.

Bahia Blanca: It is situated on the Atlantic Coast and chief seaport of Argentina.

La-Plate: La Plata is a modern city cum industrial center.

Rosario: It is situated on the Parana, a natural link between the Gran Chaco and the Pampas. It is a rail and road hub and on important river port cum industrial center.

Cordobadairy center: Cordoba is also a fast-growing industrial cum tourist center and famous dairy center.

WBBSE Notes For 8 Class Middle School Geography

Chapter 4 Pressure Belts And Winds

The atmosphere or the sphere of the air envelope the layers of invisible gases that surrounds the earth. It is held to the earth by the force of gravity and rotates with it. It represents the gaseous realm of the earth. It is mobile/ elastic, both compressible and expansible. The atmosphere is a vital part of human existence on earth.

Air Pressure: The atmosphere is composed of air and other particles like water vapour and other materials. Though the air is very light, it has weight. It also exerts pressure on the earth’s surface. The weight of air on the unit area of the earth is called ‘air pressure or atmospheric pressure’.

Read and Learn all WBBSE Notes For 8 Class Middle School Geography

It was Toricelli, a disciple of Galileo, who first practically measured air pressure in 1643. The atmosphere exerts a pressure of more than kg/sq. cm (1-03 kg/cm or 6-68 kg/inch) at sea level or 760 mm/cm or 76 cm or 1013-25 millibars. Air exerts pressure equally on all sides, we are supported by an equal pressure of air on all sides of our body. So, we do not feel this pressure.

There are two types of air pressure—(1)High pressure and (2) Low pressure.

More air molecules present in a definite volume of air develop high pressure and fewer air molecules present in that airmass form low pressure. So, an air of high pressure is dense and that of the low pressure is thin. More than 1013-25 millibar pressure is called ‘High pressure’ and less than 986 millibar pressure is called ‘tow pressure’.

Variation in Air Pressure: Air pressure is not uniform over the surface of the earth but varies from place to place for the following conditions:

• Variation of Temperature,
• Altitude from the sea level,
• Rotation of the earth,
• Presence of water vapour,
• Depth of the atmosphere.

1. Variation of Temperature: Warm air is lighter and pressure is less. So, it goes up forming a low-pressure zone. We call this low pressure because the air is less dense, and exerts low pressure. On the other hand, cold air which is heavier and denser exerts more pressure and settles down on the ground forming a high-pressure zone.
2. Altitude from the sea level: Air is highly compressible. So, it is denser in the lower parts of the atmosphere and lighter with an increase of altitude. This air pressure will be higher over a lowland area and lower over a higher mountainous area.
3. Rotation of the earth: The rotation of the earth also causes variation in the air pressure. The air is thin around the sub-polar areas because of the rotation of the earth swings the bulk of the air towards the Equator.
4. Water vapour: Moist air is lighter than the air without it. Dry air is heavier than moist air because it contains more nitrogen and oxygen than humid air. This is why air pressure is low during the rainy season and in winter air pressure is high.
5. Depth: In the lower layer of the atmosphere is denser than at the higher level and therefore than pressure is high but as we go higher up the pressure of the air decreases because fewer air molecules are present in that airmass.

 

Chapter 4 Pressure Belts And Winds: Air Pressure Belts

 

There exists a definite pattern of alternate high and low-pressure belts over the earth’s surface. A ‘Pressure Belt, is a zone of uniform width, around the earth, extending in an East-West direction parallel to the lines of Latitude. On the earth’s surface, there are in all seven pressure belts. Four belts of high-pressure separate three low-pressure belts.

1. The Equatorial Low-Pressure Belt: The equatorial belt of low pressure extends from the Equator to 5°N and 5°S latitudes. This belt has been formed due to

• Vertical sun rays fall on this region throughout the year as such, air is warm and light all year round. The air expands and becomes lighter, rises upwards as convection currents and finally ascends to form this low-pressure belt,
• Presence of water vapour is more in this region. So water vapour further helps in lowering the air pressure there,
• Due to the rotation of the earth bulk of the air above this region swings towards the north and south, as such, air becomes, thin and formed low pressure.

Equatorial calm or Doldrums: The belt of equatorial low pressure is termed as ‘Doldrurns’-because there is no horizontal movement of air or wind. Air is continuous by ascending from this region. Thus, in the equatorial region, ‘Calm’ conditions prevail and the region is called Equatorial ‘calm or ‘Doldrums’ which means ‘to Stagnate’.

 

2. And 3. Sub-tropical High-Pressure Belts: Two sub-tropical high-pressure belts are formed near the tropics (Tropic of Cancer and Tropic- of Capricorn} and extend between 30° – 35° North and South latitudes.

The causes behind the formation of these two high-pressure belts are:

1. The warm and moist air over the Equator rises, cools and spreads towards the north pole and the south pole. On reaching latitudes 30° North and 30° South the air becomes cool, dense and heavy. Consequently, it descends to form these high-pressure belts. These are regions of calm with light winds and quiet, stable weather conditions,
2. Due to the rotation of the earth, cold air from the polar region swings towards this region.

Sub-tropical calm: Horse Latitude— in sub-tropical high-pressure belts, the air is calm. So, these high-pressure belts are known as the sub-tropical calms’, it is also frequently known as Horse latitudes’, it is explained that, in the colonial days of sailing ships carrying horses used to sail from Europe to the West Indies.

On the way, over these regions, because of the absence of horizontal wind, ships had to unload cargo. So, many horses were thrown into the Atlantic Ocean to make the ships lighter to conserve drinking water. Since then, the region between ^ ~~35° (25°—35°) parallels in both hemispheres are frequently called “Horse Latitudes’.

4. And 5. The Sub-Polar Low-Pressure Belts over the Arctic or Antarctic circle: Two subpolar low-pressure belts are located between 60°—65° North and South latitudes.

In these belts low pressure develops because—

1. The earth’s rotation swings the bulk of the air from these areas towards the Equator
2. Cold winds of the polar highs expand when they reach these two regions and
3. Warm and light westerlies blow above cold and heavy polar winds. So, in the sub-polar region, the density of air is less therefore, pressure is also low.

6. And 7. Polar High-Pressure Belts around North Pole and South Pole: Two high-pressure belts are found around the North Pole and South Pole because—

1. This is a region of permanently low temperature, as such, the pressure of the air is high,
2. Evaporation is less, so water vapour is almost absent and
3. The air that rises above the sub-polar regions swings and descends over these areas.

Pressure cells: Variations in the distribution of land and water cause variations in air temperature and pressure over land and water even in the same latitudes. For this, there is no continuous belt of pressure all over the world. The discontinuity of these bands of air temperature and pressure over the same latitudes forms isolated small cells of air pressure.

These concentric pressure centres or cell are known as ‘Pressure Cells’. in the northern hemisphere is greater variation due to the location of continents and oceans. Therefore, air pressure cells are seen more often over the northern hemisphere.

 

Shifting of Pressure Belts and Planetary Winds: The pressure belts of the world are formed mainly because of the heat of the sun. So, the pressure belts shift with the apparent annual movement of the sun. Owing to the revolution of the earth, there is an apparent movement of the sun from the northern hemisphere to the southern hemisphere with the movement of the sun, the pressure belts shift northward in the summer and southward in winter.

In June when the sub-solar point (vertical position of the sun) lies over the ‘Tropic of Cancer (231/2° North), it is summer in the Northern Hemisphere, as such, the pressure belts are shifted by 5° to 10° north of their normal positions. Similarly, in December, when the sun lies over the ‘Tropic of Capricorn (23%° South), it is summer in the Southern Hemisphere and the pressure belts shift by 5° to 10° south of their average positions.

With the shifting of the pressure belts, the wind belts also, shift their position which causes the change of their direction and velocity of flow. The swing of this whole wind system has a great impact on the climate of the region lying between 30° and 45° parallels of latitude in both hemispheres. These regions come under the ‘Trade winds’ which give rain to the eastern coasts of the southern part of Argentina, and Sudan but do not give any rain in the western margins (e.g. Mediterranean lands, southern chile) as they are off short there.

In winter, these regions come under the influence of the westerlies and receive sufficient rainfall. So, it is rightly said that rain follows the sun as the entire system of pressure belts and planetary winds follow the sun.

 

Chapter 4 Pressure Belts And Winds: Winds

 

The unequal distribution of heat on the earth’s surface causes the formation of high and low-pressure belts over the earth. Lighter air ascends to form the low-pressure belts while heavier air descends to form high-pressure belts.

Air current: The vertical movement of air over the earth’s surface is called ‘air current’.

What is wind: The horizontal movement of air from high-pressure to low-pressure areas along the earth’s surface is called ‘wind’.

 

Centrifugal force: The fictional force that acting, moves or tends to move away from a centre to an outward side is called ‘centrifugal force’.

Coriolis Force: It was named after the French mathematician Gaspard de Coriolis, who first described it inl835. A force resulting from the rotation of the earth deflects moving bodies to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This affects winds, ocean currents and humans.

Ferrel’s Law: The winds are deflected from their true gradient course due to the earth’s rotation. U.S. meteorologist William Ferrel following Coriolis force formulated a law in 1859 to deduce the direction of winds in the northern and southern hemispheres. It is known as Ferrel’s Law.

According to Ferrel’s law: If we stand with our faces in the direction in which the wind northern hemisphere southern hemisphere is blowing from high pressure to Westerlies are deflected to their right as South-West Westerlies. In the southern hemisphere, Trade winds are deflected in their left as South-East Trade Winds while westerlies become North-West Westerlies.

 

 

Buys Ballot’s Law: A Dutch meteorologist not only Christoph Buys Ballot postulated a law in 1857 which relates the wind direction to the position of air pressure areas. According to this law, “If an observer in the northern hemisphere stands with his backs to the wind atmospheric pressure will be lower on his left hand, in the southern hemisphere pressure is lower on his right. This is the result of Coriolis’s force on the earth.

Classification of winds: Winds can be classified into four major types:
1. Planetary winds,
2. Periodical winds,
3. Local winds and
4. Sudden or Irregular winds.

1. Planetary or Permanent Winds: In the surface of the earth, certain winds blow constantly in a particular direction from the high-pressure belt to the low-pressure belt throughout the year. These winds are called ‘Prevailing’ or permanent or Planetary or Constant winds. These winds are of three types—

• Trade winds,
• Westerlies, and
• Polar winds.

 

 

• An account of Trade Winds: The winds that blow regularly in a definite direction from the tropical high-pressure belts (30°—35° North and South latitudes) to the equatorial low-pressure belt in the both hemisphere are called ‘Trade Winds’. The name ‘trade’ is derived from the German word ‘trade’ which means ‘Track’. These winds blow in the same direction in a definite track, as such, these winds are called ‘Trade Winds’.

These winds were also helpful to the early traders who depended on the wind when sailing in the seas; hence, the name ‘Trade Winds’. In the northern hemisphere, their direction is north-easterly and in the southern hemisphere, south-easterly. As the trade winds come from the east in both the hemispheres, they are also called the ‘Easterlies’.

Origin of the Trade Winds: The Trade Winds are originated from a pressure gradient (difference in pressure) of the Sub-Tropical High-Pressure Belt to the Equatorial Belt of Low Pressure.

Types of Trade Winds: Trade Winds are of two types—

• Worth-East Traoe Wind
• South-East Trade Wind.

 

1. Worth-East Trade Wind: In the Northern Hemisphere, winds blowing towards the Equator, are deflected to the right and according to Ferrel’s Law become ‘Worth-East irade Winds.
2. South-East Trade Wind: Southern Hemisphere deflection of the wind is towards the left and the winds become ‘South-East Trade Winds’.

ITCZ or Inter-Tropical Convergence zone: A zone of low atmospheric pressure near and more or less parallel to the equator (5° North and 5° South), where the North-East, and SouthEast. Trade winds meet, being thus associated with the Doldsums is called ‘I.T.C.Z.’

The velocity of Trade Winds: In the Northern Hemisphere as the landmasses are the more, the velocity of the North-East Trade Wind is about 16 km/ hour. While in the Southern Hemisphere, water bodies are more, as such, the velocity of the South-East Trade Wind is a little more, about 22-23 km/hour.

Influence of Trade Winds: Since these Trade Winds blow from the cooler sub-tropical latitudes to the warmer tropics, they have a great capacity for holding moisture. On their way, while crossing the open oceans, they pick up moisture and give heavy rainfall to only the eastern parts of continents within the tropics.

While reaching the western part of the continents they get dry and give no rain. It is one of the reasons that the world’s great deserts like California, Sahara, Thar (India), Atacama (Peru and Chile in South America), Kalahari (In Africa) and the West Australian Desert have been formed.

2. Westerlies: The Winds that blow from the Sub-tropical High-Pressure belts towards the Subpolar Law Pressure belts in both hemispheres are called ‘Westerlies’. In the Northern Hemisphere, their direction is south-westerly and in the Southern Hemispheres, it is north-westerly. As they blow from the west in both the hemispheres, they are called the ‘Westerlies’.

Origin of the Westerlies: Due to the rotation of the earth low pressure develops over the Arctic and Antarctic Circles, while there is relatively high pressure over the Tropic of Cancer and Tropic of Capricorn. So, winds move from these high to the low-pressure belt as Westerlies.

Types of the Westerlies: The Westerlies are of two types—

1. South-West Westerly and
2. North-West Westerly.

Under the effect of Coriolis Force, westerlies are deflected. Following Ferrel’s Law, they become South-West Westerly in the Northern Hemisphere and North-West Westerly in the Southern Hemisphere.

Roaring Forties: In the southern hemisphere between 35° to 60° South latitudes westerlies are best developed due to the vast expanse of oceans and the absence of extensive landmasses. Westerlies of this zone are/therefore blow uninterruptedly with much greater force. It is called ‘Brave Westerlies’. When brave westerlies blow along 40° South depending on violent sounds made by these brave westerlies are called ‘Roaring Forties’.

Furious Fifties: When the brave westerlies blow along 50° South parallels of latitude then it is called ‘Furious Fifties’.

Screeching/Shrieking Sixties: When the brave westerlies blow along the 60° South parallels of latitude, then it is called ‘Screeching or Shrieking Sixties’.

Influence of Westerlies:

1. These winds are on-shore winds on the western coasts of continents and bring much precipitation. But the eastern parts remain comparatively dry.
   These winds are variable in strength and direction. Cyclones and anticyclones produce uncertain weather. The weather is changing due to clouds, fog, gales and snowfall.
2. The westerlies blow uninterruptedly with much greater force and regularly throughout the year. These are best developed in the southern hemisphere due to the large expanse of oceans, and the absence of extensive landmasses. Here these are termed as “brave westerlies” or “brave Westwinds”.The latitudes in which westerlies blow are called, “Roaring Forties, “Furious Fifties”, and “Shrieking Sixties”. These stormy violent winds are dangerous for shipping.
3. Westerlies bring winter rainfall in many parts of the Mediterranean region. It is to be noted that westerlies bring rainfall to the western coasts of the continent of temperate lands.

3. Polar Winds: Polar winds blow from Polar Highs of the Arctic and Antarctic to the sub-polar lows of the Arctic circle and Antarctic circle respectively. As these winds originate from the poles, they are known as ‘polar winds’.

The velocity of Polar Wind: Polar winds are very much weak, especially, in the northern hemisphere. In the southern hemisphere, it is relatively strong.

The latitudinal extent of Polar Winds: Blowing between 60° to 85° Parallels of latitudes.

Effects of Polar Winds:

1. Polar winds are very cold and dry as they blow from the poles and from the coldest parts to a warmer region.
2. They are extremely cold and are responsible for a bitterly cold climate.
3. They blow in high velocity and bring about cyclones, and blizzards.
   In the South Pole these stormy winds have greater velocity and intensity of force Sometimes, a situation of anticyclones prevails there.

 

Chapter 4 Pressure Belts And Winds: Periodic Winds

 

The winds which blow from time to time or in a certain period (season) of a year, are called. ‘Periodical winds’ viz.

1. Sea Breeze,
2. Land Breeze,
3. Monsoon-Land and sea breezes are a periodic type of winds and consist of a conventional system of winds.

These are caused by the differential heating of land and sea. These affect a narrow strip along the coast. These are also known as “monsoons on a smaller scale”.

1. Sea Breeze: During the daytime, the land gets rapidly heated up than the sea. The warm air rises to form a low pressure locally on land.
The sea being cooler develops a high pressure. So, a cool sea breeze blows from the sea to land. Thus, the winds complete a convection cycle.

Effects:

1. It brings cool and fresh air from the sea.
2.  Sea Breeze moderates the temperature of the coastal areas resulting in an equitable or maritime climate,
3. Its influence does not exceed 30 km from the coast.

2. Land Breeze: During the night the land becomes cooler than the sea. The cold and heavy air produces a local high pressure on land. The sea remains comparatively warmer with a low pressure. Therefore, a land breeze blows from land to sea. These are effective under calm, cloudless sky.

Effects:

1. The fishermen take advantage of the outgoing land breeze and sail out within the morning. They return with the incoming sea breeze in the evening.
2. The return current of warm air from the sea has a moderating effect on the temperature.

 

 

3. Monsoon Winds: The term ‘Monsoon’ is derived from an Arabic word meaning ‘season’. The winds that blow with the change of seasons is called ‘monsoon winds’. Thus monsoon winds are seasonal winds.

The term was first used for the monsoon winds blowing over the Arabian sea. In this wind system, there is a reversal of wind direction according to seasons. In summer, monsoons blow from sea to land and in winter monsoons blow from land to sea.

Origin: Monsoons are land and sea breezes on a large scale. These winds have a thermal origin. These are caused by the differentia! heating and cooling of land and water. The chain of events is from temperature through pressure and winds to rainfall.

In summer, the land gets more heated than the sea resulting in a low pressure on the land masses and a high pressure overseas. The winds blow from sea to land. Land breeze and sea breeze follow a daily rhythm over a small coastal areas.

Necessary conditions: The monsoons are developed under the following conditions.

1. The pressure of a large landmass (Continent).
2. The presence of a large ocean.
3. Long coastline.
4. Seasonal extremes of the temperature of land and water.

Areas: Monsoon winds mostly blow in tropical areas. The Himalayas separate these areas into two parts.

1. East Asian Monsoons blowing over China, Japan and Indo-China.
2. Indian Monsoons of India, Pakistan, Bangladesh and Myanmar.

Summer Monsoons: In summer the central, the central parts of landmasses like Asia get more heated than the seas and oceans around them. Therefore, low pressure develops over the land. As a result winds blow from the seas to land in summer. These winds are called the summer monsoons’. They bring heavy rain as they come from the seas.

Winter Monsoons: During winter, high pressure develops over the land masses and low pressure over the seas and oceans. Therefore, the winds start blowing from the landmasses towards the seas and oceans. These winds are called ‘winter monsoons’. These are dry winds for central part of Asia, particularly for most of India.

 

Periodical Local Winds:

Anabatic and Catabatic Wind: These are local slope winds. These winds are periodic winds which blow along the valley slopes. These are also diurnal in character. Mountain winds blow down the slopes at night while the valley winds ascend the slopes during the day.

Anabatic or Valley Wind: A local wind that blows upslope during the day in mountain areas is called ‘anabatic’ or ‘valley wind’. The air above the valley slopes is heated to a greater extent than air at the same height above the centre of the valley. Air thus rises up from the slopes and feeds an upper return current. As the winds rise, these are condensed and give heavy rain. These winds tend to moderate the temperature.

Catabatic or Mountain Wind: A cold downslope wind caused by the gravitational movement of cold dense air near the Earth’s surface is called ‘Catabatic’ ‘mountain wind’ ‘canyon wind’, or ‘gravity wind’.

During the night the winds at the mountain tops become cold and dense due to rapid radiation. This cold air, under, the influence of gravity, descends down the valley slopes. It is also known as ‘nir drainage’. Due to these, the front occurs in the lower parts of the valleys. Therefore, ‘citrus orchards’ in California and coffee ‘agendas’ in Brazil are grown on mountain or hill slopes.

 

Chapter 4 Pressure Belts And Winds: Local Winds

Due to local differences in heating and cooling on account of the configuration of land or distribution of land and water, certain winds are caused which are to be found even in the generalised wind belts of the world. These are called ‘Local Winds’. Most of the local winds are developed by local depression.

They affect only limited areas and blow for a short period. Some of the local winds are as follows:

1. Loo: Loo is a hot dry and dusty wind. It blows in the northwestern part of India. It desiccates and dries up surface moisture. It blows in the month of May and June over the northern plains, especially in U.P. in India.
2. Andhi: During summer months very dry sand storms are very frequent in the northwestern part (Rajasthan) of India. These dust storms are locally known as ‘Andlll’ because it overcasts the sky with dust and cloud.
3. Nor’wester’s (Kalbaishakhi): During the afternoon of summer months (Chaitra- BaishakK) life” thunderstorms along with rainfall mainly occur in West Bengal, it is known as ‘Kalbaishakhi’ 0ne Rainshadow region of India is the Deccan plateau or the northern part of the Meghalaya Plateau (Leeward side of the slope).
4. Chinook: Chinook winds are experienced on the leeward eastern slope of the Rockies and Prairies in the U.S.A. and Canada. It causes snow to melt and disappear very quickly for which Is known ns Snow-eater’, It thus makes pasture available. This raises the temperature of the area by 15C to 20C. In a couple of hours.
5. Fohn: Fohn Is a warm dry wind blowing across the Alps down the valley in Switzerland in spring.

Effects of Fohn:

1. It melts snow rapidly and hastens the growth of crops,
2. These winds make the winters mild.
3. These help animal grazing by removing snow from pastures.
4. The winds help in. the early ripening of grapes.

6. Bora: It is a cold and dry wind. It blows during winter along the Adriatic coast of northern Italy. It is a northern or north-easterly wind. It occurs when the atmosphere remains high over central Europe and low pressure over the Mediterranean. It pr generally cold and dry weather. But, sometimes, cause heavy cloud, rain and snow.

7. Mistral: A cold dry and usually strong northernly or north-westerly wind expo in South France, especially in the Rhone delta area is called ‘mistral’. It occurs when high pressure over France and low pressure over the Mediterranean (i.e. mainly in It is a forceful wind with a speed of 60 to 130 km./hour. It brings down temperature freezing point.

8. Simoom/Simoon: Simoon is a hot, dry and painful wind of summer in the Arabian and Saharan deserts. It carries many sand particles and thus reduces visibility and often resulting in localized dust storms or sandstorms.

9. Sirocco: A southernly wind that blov/s from North Africa across the Mediterranean sea to Sicily and south Italy, proceeding a depression moving eastward through the Mediterranean basin is called ‘Sirocco’, it is very dry and hot on the North African coast as a result of bavin blown off the desert, but after crossing the sea and picking up moisture it is often very hum! and enervating When it reaches Sicily and Italy.

10. Khamsin: A hot dry southernly wind that blov/s across Egypt and the South-East Mediterranean area from the Sahara is known as ‘Khamsin’ in Egypt. It proceeds depression moving eastwards through the Mediterranean Basin and occurs for a period of about 50 days between April and June, (the name Khamsin being the Arabic v/ord for fifty). Dust storms are frequent, but in areas where the wind has not crossed a stretch of ocean, the air may be quite humid.

11. Harmattan: Harmattan is a strong, hot, very dry and dusty wind blowing from a north-easterly or sometimes easterly direction over north-west Africa, from the Sahara to the north-west African coast, the southern limit averaging 5°N in January (mid-winter) and 12 N in July. Heavily dust-laden and parching in the interior, it helps to evaporate the high humidity of the Guinea coast, and thus seems a relatively cool and healthy wind in that area, hence its local name there ‘the Doctor.

12. Pampero: A type of cold wave or polar outbreak that occurs in parts of Argentina and Uruguay when very cold dry air is drawn in from the south or southwest behind an eastward moving depression. It commonly resembles a line squall with very dark clouds often augmented by dust blown up off fie- Pampas, and sometimes with rain, thunder and lightning.

 

Chapter 4 Pressure Belts And Winds: Variable Sudden Or Irregular Winds

 

Intense heating and cooling of land surface or water bodies, sometimes, develop severe low-pressure centre, depression or trough or centre of high pressure. On a place where the air pressure suddenly falls or rises within a short time. If causes strong winds to blow a great speed and changes or breaks in the wind system. Their direction, shape, extent and scope is uncertain.

These are known as ‘variable winds’ Their sudden movement and irregular nature cause them to he called ‘Sudden’ or irregular winds. Cyclones and anticyclones are examples of this type of wind.

Cyclones: When the stormy whirlwind comes is spirally moving in towards a low pressure centre, it is some of the characteristics of the cyclone,

1. Cyclone develops due to the formation of an intense low-pressure centre.
2. A cyclone has a low pressure at the centre and high pressure on the surrounding sides.
3. The wind movement in a cyclone is anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere.
4. It blows towards the centre of low pressure from all sides,
5. On reaching the centre of low pressure it moves upwards. short time.
6. In the structure of a cyclone, isobars from an oval or circular shape.
7. Rain falls at the centre of the cyclone.

 

Classification of Cyclones: Cyclones are divided into two types according to their formation and difference in their location.

1. Cyclones formed in the Tropical zone are called ‘Tropical Cyclones’ and
2. In the Temperate zone, the ‘Temperate Cyclones’.

Tropical Cyclone: Tropical cyclones are developed in the western margins of ocean and seas in the tropical region between 8° and 20* north and south latitudes.

The cyclones of the Tropics are thermal In origin and develop due to the local convection currents acquiring a whirling motion on account of the rotation of the earth. These develop at special seasons over the sea within the Tropics. The conditions most suited to their origin and development are

• Quiet air
• Highly saturated atmosphere and
• Great heat.

 

The following are some of the characteristics to the track of a tropical cyclone:

 

1. Between the Equator and 15° latitude, these storms turn towards the west with the trades.
2. Between 15° and 30° latitude the path is very uncertain. But these travel towards the north in the northern hemisphere and towards the south in the southern hemisphere.
3. As these cross 30° latitude they turn towards the east and their terrific energy declines.
4. tropical cyclones are usually small in size and they have a diameter of 100 to 500 km.
5. These strong winds exceeding 100 or 150 km/hour are common. Sometimes the velocity increases to 250 or 300 km/hour.
6. The centre of this cyclone has the lowest air pressure and it is called the ‘Eye of the cyclone’.
7. They are violent and very much destructive in nature. These cause heavy floods and huge destruction of life and property. Trees are uprooted, houses collapse, rail lines, roads and telecommunication lines are disrupted, the coastal parts are submerged.
8. Tropical cyclones are associated with dark cumulonimbus clouds and torrential rain accompanied by thunders and lightning.
   Parts of the East coast in India are badly affected by tropical cyclones in every year during late summer or autumn.

The chief areas of activity for tropical cyclones are the following:

1. West Indies and the coast of Florida. In that region, these are known as ‘Hurricanes’.
2. Philippine Islands, the coasts of China and Japan. These are known as ‘Typhoons’.
3. Bay of Bengal and the Arabian Sea, where these are known as ‘cyclones’.
4. Madagascar (Malagasy) and the coastal regions of East Africa.
5. North-east and North-western coasts of Australia.

Temperate cyclones: Temperate cyclones are common in the sub-polar low-pressure belt. They are found in the temperate region between 35 and 65 latitudes. These are most dominant over the North Atlantic Ocean and especially during the winter season. These cyclones are frontal in origin. They develop due to the meeting of warm tropical and cold polar airmass.

Characteristics Of Temperature Cyclones:

1. These Temperate cyclones are of frontal origin. There are six stages in the development of a temperate cyclone.
2. Temperate cyclones are much larger in size than of tropical cyclone and these have a diameter of 1000 to 2000 km.
   These are oval-shaped.
3. Wind velocity is comparatively moderate and in average it ranges between 30 and 50 km/hour.
4. These mostly originate in winter.
5. These are weaker than tropical cyclones.
6. Temperate cyclones are less destructive and less violent.
7. They bring rain and cloudy weather and last for a long period.

In India, temperate cyclones are experienced during January and February. They originate in the Mediterranean region and approach north-western part of India through Iraq, Iran and Pakistan. Punjab, Haryana, Uttar Pradesh and Uttarakhand receive rainfall and Jammu and Kashmir and Himachal Pradesh receive snowfall from these cyclones or depressions. The rainfall received in northwest India by temperate cyclones is very beneficial for the rabi crops.

Anticyclones: An anticyclone is just the reverse of a cyclone. It is a wind blowing spirally outward from a high pressure centre. The general characteristics of an anti-cyclone and its structures are as follows:

1. An anti-cyclone lies between two cyclones and it has no definite direction,
2. The isobars are far apart more especially towards the centre. Variations of temperatures are also noticed.
3. The winds are light and slow. They never grow violent and at the centre there is calm with variable winds. Anticyclones at Northern and Southern hemisphere.
4. Often cold and heat waves accompany the anti-cyclones.
5. Within an anti-cyclone there are local rains,
6. It is extensive and its velocity ranges from 30 to 45 km/ hour.
7. Winds in an anti-cyclone circulate in clockwise direction in the northern hemisphere. While it is anti-clockwise in the southern hemisphere.
8.  Anti-cyclonic conditions present calm and clear weather with sunny conditions.

 

 

Difference between Cyclones and Anti-cyclones:

Cyclones	Anti-cyclones
(1) Cyclone has low pressure at the centre.	(1) Anti-cyclone has high pressure at the centre.
(2) It blows toward; the centre of low pressure from all sides.	(2) It blows in all directions from the centre.
(3)In the northern hemisphere it moves anti-clockwise, and in the southern hemisphere, it clockwise.	(3)In the northern hemisphere it blows clockwise, and in the southern hemisphere, it is anti-clockwise.
(4) On reaching the centre of low pressure it moves upwards.	(4)It moves downwards.
(5) It is strong and lasts for a short time.	(5)It Is not very strong and generally continues for a long time.
(6) Bain falls at the centre of cyclones.	(6)It does not produce rain, rather, it brings fair weather.
(7) Winds arc warm and ascending.	(7)Winds arc cold and descending.
(8)l here present rough and cloudy weather accompanied by thunder, lightning and heavy rain or snow.	(8)Antl-cyclonic conditions present calm and dear weather with sunny conditions.

 

 

 

 

 

WBBSE Notes For 8 Class Middle School Geography

Chapter 2 Unstable Earth

1. Though the Earth apparently seems stable, it does not follow that it is fully stable. The earth’s crust has been undergoing changes for millions of years. The earth is unstable because it is regularly facing natural events like violent volcanic eruptions, earthquake tremors, shifting of plates, landslides, avalanches etc.
2. Though we cannot always feel this movement of the land on the surface of the earth, but the face of the earth is constantly shaped by these natural forces active above the surface of the earth and beneath it.

Read and Learn all WBBSE Notes For 8 Class Middle School Geography

• According to the ‘Continental Drift Theory’ of Alfred Wegner—about 300 million years ago, all the present-day continents of the world were united as an aggregated supercontinent called ‘Pangaea’, during the Carboniferous period.
• Later on, it began to break apart and the pieces drifted in two directions, e.g., (1) equatorward movement and (2) Westward movement. Actually, the continental crust (Sial) was floating over the oceanic crust (Sima). But this theory could not fully explain the causes of earthquakes or the formation of most of the continents, oceans, mountains and volcanism etc.
• In the 1960s, an elegant and exciting theory emerged that provided an elegant unifying explanation for all geological processes past and present. This theory is called ‘Plate Tectonics’ and it is a great scientific achievement of the decade of 1960s.

Definition of the plates and Plate-tectonics: The rigid lithospheric slabs or rigid and solid crustal layers are called ‘Plates’. The whole mechanism of the evolution, nature and motion of Plates and resultant reactions is called ‘Plate Tectonics’, in other words, the whole process of plate motions is referred to as ‘Plate Tectonics’.

It may be mentioned that the term ‘Plate’ was first used by Canadian geophysicist J. T. Wilson in 1965. Makenzie and Parker discussed in detail the mechanism of plate motion in 1967. W. J. Morgan and Le Pichon elaborated on the various aspects of Plate Tectonics in 1968. Now Continental Drift and displacement are considered a reality on the basis of Plate Tectonics.

The theory of Plate Tectonics comprises only four basic concepts:

1. The outer portion of the earth—its crust and uppermost segment of the mantle (i.e., lithosphere) is composed of large rigid units called Plates.
2. The plates move in response to the flow of the heat-softened ‘asthenosphere’ beneath them.
3. Most of the World’s large-scale geological activity, such as volcanic eruptions, and earthquakes, occurs at near plate boundaries.
4. The interiors of plates are relatively quiet geologically, with far fewer and milder earthquakes than occur at plate boundaries and little volcanic activity.

There are six large (major) and twenty small (minor) plates. The six major plates are the

1. Eurasian plate,
2. Indo-Australian plate,
3. American plate,
4. Pacific plate,
5. African Plate and
6. Antarctic plate.

Movements of the Plate and Geological History: The earth’s plates move relative to each other in several ways, and plate boundaries are categorized according to which type of movement they demonstrate. Here instead of a whole continent portion of the ocean is also attached to the plate. Here the North American continent plate moves westward away from Europe along with the western half of the Atlantic ocean.

There are three major types of boundaries:

1. Divergent or constructive plate boundary, where plates move apart,
2. Convergent or destructive plate boundary, where p|ates move together, and
3. Neutral or transform plate boundary, where plates move past one another in opposite directions.
4. Divergent or constructive plate boundary: When two plates diverge or follow different directions, the narrow space between the two is called a ‘rift’. The magma then fills this space. The such a plate boundary is called ‘divergent’ or ‘constructive plate boundary’.
5. Throughout the period of divergence, ocean basins continue to expand as molten rock erupts, creating new oceanic lithosphere that builds up to form the mid-ocean ridge. The process of plate growth at the mid-ocean ridge is known as ‘sea-floor spreading’. Japan and its adjacent islands along the western coast of the Pacific Ocean have been formed in this way.
6. Convergent or destructive plate boundary: When two plates converge or move towards the same point, they may either collide against each other or push the third plate with their combined force. The boundary of such plates is also called a ‘convergent or destructive ‘ plate boundary. The Himalayas were formed in this way from the sediments of the Tethys sea between the European and Indian plates.
7. Neutral or Transform plate boundary: Where two plates slide past or grind past one another along transform faults and thus crust is neither created nor destroyed, this is known as ‘Neutral or transform plate boundary’.Such is the case with San Francisco and Los Angeles, which are located within the San Andreas transform zone between the North American and Pacific plates.

 

Chapter 2 Unstable Earth Earth Volcanism

 

Volcanism: The process responsible for the upward movements of molten rock or magma through the Earth’s crust is called ‘volcanism’.
Volcano: The word ‘Volcano’ is derived from the greek term ‘Vulcan’ meaning the god of the underground.

A volcano is a vent or opening in the Earth’s crust through which magma and other materials erupt from the interior of the earth. Volcanoes usually consist of a conical hill or mountain formed from molten rock or lava, ashes and rock fragments ejected through the volcanic vent.

Parts of a Volcano:

1. Vent—The vent is the hole through which the volcanic materials come out.
2. Volcanic Pipe—Volcanic pipe is the narrow opening which connects the vent with the interior.
3. Crater—Crater is the funnel-shaped hollow at the core of the volcano.

Different types of volcanic eruptions: When solid, liquid and gaseous materials are thrown out of the interior of the earth, it is known as a ‘volcanic eruption’. There are two main modes of eruption-

• Central Eruption and
• Fissure Eruption:

1. Central Eruption: When lava erupts through a vent, violent explosion takes place. It results in the formation of the volcanic cone; such as Vesuvius and Fujiyama. A crater is formed at the summit. Most of the volcanoes are of cone and crater type. A chain of such volcanoes forms a volcanic mountain range.
2. Fissure Eruption: When there is a quiet upwelling of lava through fissures over a large area, it is known as a ‘fissure eruption’. It gives rise to extensive lava plains or plateaus. The Decan Trap of Peninsular India is an example of this type. It covers an area of 5 lahks sq. km with a thickness of lava sheets exceeding 1000 metres. Fissure eruption has taken place in Ireland and Iceland also.

Classifications of Volcanoes: Based on the frequency and nature of eruptions volcanoes are classified into three major types. These are as follows :

• Active volcanoes: The volcanoes that erupt frequently or are always emitting lava are called ‘active volcanoes’. Mouna Loa in Hawaiian islands is the largest active volcano of the world, other important active volcanoes are the ‘Vesuvius’ of Italy, ‘The Stromboli’ of Lipari island, ‘Etna’ of Sicily, ‘Erebus’ of Antarctica and ‘Barren’ island of India.

Active Volcanoes are of two types: (1) Incessant and (2) Intermittent volcanoes.

1. The volcano that erupts incessantly is known as an ‘incessant volcano’, e.g. Mt. Erebus of Antarctica,
2. The volcano that emits with intervals, is known as an ‘intermittent volcano’, e.g. Vesuvius of Italy.

2. Dormant Volcanoes: Dormant volcanoes are also called sleeping volcanoes’. These volcanoes have been active in the past and have stopped ejecting lave now, but can erupt again in any time, e.g. Mt Fujiyama of Japan.

3. Extinct Volcanoes: The volcanoes which have never erupted in human history are’ called ‘extinct’ or ‘dead volcanoes’, e.g. Mt. Kilimanjaro in Africa, Mt. Popa in Myanmar, Mt. Cotopaxi in Ecuador.

‘Aa’: A type of dense, viscous volcanic lava with a rough blocky structure is known as ‘Aa’, in the Hawaiian language.

‘Pa hoe hoe’: A type of highly fluid lava that spread out in sheets over vast areas from the volcanoes of the Hawaiian island is called ‘Pa hoe hoe’ in the Hawaiian language. The upper surface of this type of lava cools very quickly and looks like a twisted rope.

The constructive Effects of volcanoes:

1. volcanic eruptions increase the fertility of the soil.
2. The water of hot springs, Geysers is considered very useful for people.
3. The volcanoes result in the formation of precious stones, minerals, such as diamonds are due to volcanic eruptions.
4. The volcanoes provide us with crater lakes and depressions caused by the volcanoes.

Disadvantages of volcanoes:

• Volcanoes are highly destructive.
• They cause much loss of life and property.
• Many towns are buried under Lava.
• Crops are destroyed in large areas.
• Eruptions in the sea kill millions of fish.
• In the 1883 Krakatoa eruption 36000 persons were killed due to high tidal waves.
• Volcanic ash pollutes the atmosphere.
• Many poisonous gases kill animals in some areas.

Earthquake: Earthquakes are sudden, rapid and detectable vibrations, tremors or shaking caused in the earth’s crust by tectonic movements or volcanic eruptions.

 

Chapter 2 Unstable Earth: Causes Of EarthQuakes

 

Major causes of Earthquakes: Earthquakes occur frequently in unstable portions (subduction zones) of the earth’s crust. The two major endogenetic causes of earthquakes are volcanic eruptions and tectonic forces.

Minor causes of earth tremors include landslides or avalanches. Artificial or man—induced earthquakes or anthropogenic earthquakes are caused by human activities. So, there are two types of earthquakes, i.e. Natural earthquakes, and Artificial (anthropogenic) earthquakes.

Natural causes of Earthquakes:

1. The tectonic earthquakes are caused due to:

1. The dislocation of rock blocks during faulting activity,
2. Drifting of the continents and plates of the earth,
3. Mountain building movements (orogenic process) etc.

2. Volcanic earthquakes are caused due to:

1. Volcanic eruptions or explosions of the volcanoes and
2. Movements of molten rock (magma/lava) below, or within the crust.

3. Isostatic earthquakes are caused due to imbalance in the geological processes generally, the earthquakes of active zones of mountain building are included in this category.

4. Plutonic earthquakes occur at greater depths when heat is radiated from the earth’s interior the earth’s crust may contract giving rise to earthquakes.

5. Heavy rainfall in mountain regions often causes landslides that may cause earthquakes.
6. Avalanches in high mountain regions may also cause earthquakes.

Artificial or Anthropogenic (Man-induced) Earthquakes: Besides the natural causes of earthquakes, human activity also causes artificial earthquakes. These anthropogenic earthquakes are caused by the pumping of water and mineral oil reserves from underground aquifers and oil reserves respectively, deep underground mining, blasting of rocks by dynamites for constructional purposes (e.g. for the construction of roads, dams, reservoirs etc.), nuclear explosion, storage of huge volume of water in big reservoirs (Koyna earthquake in Maharashtra, India of 1967 due to Koyna reservoir) etc.

Focus or Centre of the Earthquake: The place of origin of an earthquake inside the earth is called the ‘centre’ or ‘focus of the earthquake’. Observations have shown that most of the centre or focus of the earthquakes lie within 16 kilometres from the surface of the earth.

It may be at a depth from 50 to 100 km and only a single earthquake occurs at still greater depths. The shock waves travel in all directions from the focus.

1. Epicentre: The point on the earth’s surface just vertically above the centre or focus of the earthquake which experiences the greatest intensity is called ‘Epicentre’. Being nearest, the intensity of vibration is maximum at the epicentre. So, an earthquake is the strongest and most destructive near the epicentre. Also, it is worth remembering that the effects of an earthquake are felt on a much wider area if its focus lies deep below the earth’s surface.

Speed of the earthquake waves: On the earth’s surface the speed of earthquake waves varies between 5 to 8 km per second, with the speed increasing inside the earth’s crust.

Seismic waves and their types: A shock wave generated by an earthquake is called a seismic wave’. Seismic waves are of three basic types: P-wave, S-wave and L-wave. The study of the waves is also important for understanding how earthquakes cause destruction to things in their path.

1. Primary wave or Push waves (P-wave): This is the fastest seismic wave (6 to 8 km/ Sec.) and reaches the earth’s surface before point of happening or focus by the displacement of surrounding particles. They are transmitted through solids, liquids and gases.
2. Secondary waves or Shake waves (S-wave): They travel through solids only under the crust. It reaches the earth’s surface immediately after the Primary (P) wave (3-5 km/Sec) The speed of secondary (S) waves is about 3/5 as fast as primary waves.
3. Surface waves/Long Waves(L- waves): They travel on earth’s surface. L (surface)-waves travel at around 3 km/sec. The waves cause vibrations inside the earth. These waves spread out from the epicentre of the earthquake. These waves are responsible for most of the damage caused by earthquakes.

Measurement of Earthquakes: Earthquakes are studied by a special subject known as ‘seismology’ or the science of earthquakes (from the greek word ‘seismic’ meaning earthquakes). That is why the instrument recording the shock waves is called the ‘Seismograph’.

This instrument helps in determining the source of the earthquake, the movements of the earthquake, waves etc. The function of a seismograph is to measure the intensity of the earthquake shocks. It can record and calculate the distance of vibrations thousands of kilometres away including the focus and the epicentre.

 

Seismogram: During an earthquake, the oscillation of the marker of a seismograph marks the paper to create a graph is called a ‘seismogram’.

Richter Scale: The intensity or severity of an earthquake is measured with reference to a scale called the ‘Richter Scale’. Prof.Charles F. Richter of California University created this scale, in 1935, which is named after him. This scale is placed on the seismograph.

It is a logarithmic scale and uses a system of rating. This scale ranges from 0 to 9, but in practice, there is no upper limit. Every increase or one number of magnitude means the motion is 10 times greater. Earthquakes of 7 and above intensity of the Richter scale are highly destructive.

Modified Mercalli Scale: The effect of an earthquake at a given spot is measured using an intensity scale—the Modified Mercalli Scale. The intensity varies with distance from the epicentre. It uses subjective analysis like the type of rock, earth, dwelling units etc. The scale has 12 divisions or degrees ranging from low to high intensity.

Earthquake Prone Regions of the World: Earthquakes are more common along fault lines running through the weakness zones of the earth. Earthquakes can also take place where there is a Hot Spot on a plate.

Convergent, divergent and transform (neutral) plate margins have earthquakes occurring along them. But earthquakes are frequent along the convergent plate margins because there is more intensity. Earthquakes occur in almost every part of the world, but they are frequent in the following well-defined belts.

1. The Circum-Pacific Belt: About 68% of all earthquakes are observed in the vast region of the Pacific Ocean as ‘the Pacific Ring of Fire’ or ‘Fiery Ring of the Pacific’ or ‘Fiery Girdle of the Pacific’. It is closely linked with the region of crustal dislocations and volcanic phenomena. Chile, California, Alaska, Japan, Phillippines, New Zealand and the Mid-ocean areas have many minors and major earthquakes in this belt.
2. The Mid-World Mountain Belt: About ZlS^qarthquakes of the world originate in this belt. It extends along the fold mountains of Europe and Asia. It runs through the Alps, the Caucasus and the Himalayas. This belt has folded mountains, large depressions and active volcanoes.
3. Other Areas: The remaining 11% of earthquakes of the world originate in other areas such as the Mid-Atlantic, Rift valley of East Africa, Central Siberia, Red Sea and the Dead Sea zone.

Earthquake Prone Regions of India: Our country India is an earthquake-prone land. About .two-third of this country is prone to earthquakes. On the basis of vulnerability to earthquakes, India can be divided into five seismic zones. The earthquakes in India are at present mainly confined to the Himalayan region and its foothills. They are also felt in the Ganges-Brahmaputra Valley.

But the earthquakes in the Koyna Dam region in 1968 and Latur in 1993 in the Deccan Tableland (Plateau) came as surprise because it was considered a earthquake-free region. Scientists believe that while in the former case reservoir caused cracks in the rocks, in the latter case the movement of the Indian Plate might have been the cause.

 

Effects of Earthquakes: The change brought by earthquakes on the surface of the earth:

1. The earthquakes sometimes cause landslides and give to rise to the formation of block mountains and rift valleys.
2. The earthquake block the flow of rivers and causes lake formation.
3. The earthquakes sometimes changed the courses of rivers due to landslides causing severe floods.
4. Depression-causing lakes are formed.
5. Many springs and waterfalls are formed.
6. They can cause vertical and lateral displacement of parts of the crust and raise or lowering of parts of the sea floor.

Destructive Effects:

1. There is loss of life and property due to violent earthquakes.
2. Fractures and cracks are formed, and railway lines are twisted.
3. The earthquake causes tsunamis or tidal waves which destroy houses, buildings and also the life of man and animals.
4. Dislocate electric wire and cause a fire.
5. The earthquakes cause landslides and disturb the isostatic equilibrium.
6. Many towns are destroyed. The communication system is disturbed due to the destruction of roads, bridges etc.

Constructive Effects: Earthquakes have some advantages also—

1. Sometimes earthquakes cause the emergence of the coast and bring fertile shores out of the water to give a chance to develop crop production.
2. The rift valleys are converted into lakes which become a source of water.
3. Sometimes earthquakes cause the formation of hot springs which are very useful to people.
4. Many minerals, gems and precious stones come out of the interior of the earth.
5. Bays are formed along the coast to provide new harbours.
6. Earthquakes provide knowledge about the interior of the earth.
7. Sometimes the earthquake waves help in the formation of fold mountains which are very good from a climatic point of view.
8. The earthquakes sometimes cause submergence in coastal lands and result in the formation of inlets, bays, and gulfs which make the site favourable for the development of fishing and shipping etc.

Tsunami: Tsunami is a Japanese word, that means waves of harbour’ (Tsu = harbour, nami – Wave) or, it also means ferocious oceanic quake’ (Tsu = ferocious, ‘na’ = oceanic; mi = quake). It is known as destructive sea waves.

When a severe earthquake takes place below the ocean bed, its tremors give rise to huge wall-like sea waves rushing to the coastal areas. These sea waves are often as high as 27 metres, and as long as 160 kilometres travelling at a jet speed of 800 km/hour. Quite common along the coast of Japan and certain regions of the Pacific Ocean, Tsunamis can be more destructive.

About 3 lakh lives were lost and enormous damage was caused over eleven countries in Southeast Asia, including India, by a tsunami resulting from an earthquake of 8-9 magnitude under the Indian Ocean on 26th December 2004.

Prevention of Earthquake: Forecast and Essential Planning—Man is unable to prevent earthquakes, all he can do is to take steps for safety. Though earthquakes can not be predicted, but some preventive measures and planning can save many lives.

Sometimes our own observations, like sudden changes in atmospheric conditions and abnormal behaviour of animals, can help us to forecast the arrival of an earthquake. The suitable earthquake-proof building structures need to be encouraged. Disaster management infrastructures are also needed.

Disaster Management:

1. Identifying the risk factors in a building.
2. Planning to fight hazards.
3. To keep essential materials to the case of an emergency handy.
4. To repair the weak and dilapidated parts of a house.
5. To take shelter under stout furniture during an earthquake.
6. Appraising the injuries and damages when the tremors stop.
7. Disaster management and executing the pre-planned steps.

What to do when an earthquake occurs:

1. Come out of the house or school building quickly and stay in the open field.
2. Quickly go under a table.
3. Close the door and windows and stay indoors.
4. Pack essentials before leaving the house.
5. Disconnect electricity.

WBBSE Notes For 8 Class Middle School Geography

Chapter 1 Interior Of Earth

1. The Earth our homeland is one of the members of the Solar system. The earth is a planet. Among all planets of the Solar system as well as the Universe, the earth is a unique planet because it contains life and it is possible for these main reasons—air (atmosphere), water (hydrosphere) and soil or rock (lithosphere).

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2. Some scientists believe that about 4600 million (460 crores) years ago, the earth was born as a gaseous ball. As the earth has been cooled for millions of years, most of its components slowly condensed to form liquids. When it passed through a molten stage light substances floated up from deep inside to lie upon its fiery surface. Then they cooled and hardened.

3. This hard outer layer of the earth is called the ‘earth’s crust’. |f a cup of hot milk is kept, a creamy layer is formed on the top when it cools down, but just below the creamy layer, the milk remains liquid and hot for a few minutes. So the interior of the earth is still in a liquid state which we can realise from the occasional eruptions of the volcanoes.

Information regarding the earth’s interior: Exploring the earth beneath our feet is a more difficult task. If we want to know what lies hidden in the centre of the earth we should able to dig up a borehole to the centre of the earth from the surface of the earth whose length is about 6400 kilometres (the radius of the earth is 6368 km).

Although man has not been able to sink boreholes more than 8 km into the earth’s crust. He is able to obtain information on the nature of the earth’s interior by studying molten materials (magma/ lava) emitted from volcanoes and by studying the behaviour of seismic waves (earthquake waves).

By using a seismograph, a graphic recording of earthquake waves, scientists are able to get some idea of the kinds of rocks which are found below the earth’s surface. We need its elementary knowledge in Geography because this understanding is essential to follow the nature of changes taking place on the earth’s surface.

Temperature and pressure inside the earth: The evidence of volcanic eruptions and hot springs indicates that high temperatures prevail in the interior of the earth. A progressive rise in temperature with increasing depth is recorded in mines and deep wells all over the world, the average rate of increase being 1°C for every 32 metres of descent.

At the same time, there is a tremendous increase in the pressure of overlying layers on the earth’s interior. Thus, even under extremely high temperatures towards the central part of the earth, the liquid nature of its core has acquired the properties of a solid and is probably in a plastic state.

Geothermal Energy: The energy that is derived from the internal heat of the earth is called ‘geothermal energy’. The temperature increases with depth at approximately 1°C for every 32 metres, some of this heat is transported to the surface by geysers, hot springs and volcanoes.

What is magma: Molten rock materials charged with gases and at a very high temperature lying beneath the earth’s surface is called ‘magma’.

What is Lava: Molten or particularly molten magma that is extruded from a volcano or volcanic fissure out onto the surface of the earth, where it cools and solidifies is called ‘Lava’.

Distinguish between Magma and Lava:

Magma	Lava
(1)Magma is hot, sticky molten material the interior earth.	(1) Lava is solidified form of magma on the surface of the earth.
(2)It contains solutions of water and gases.	(2)Gases and water disappear after evaporation.
(3)It comes out during volcanic eruptions.	(3)It cools down as it comes into contact with atmosphere.

 

Hot spring: A spring of hot water that flows out of the ground is called a hot spring’ Unlike a geyser, the water is not forced out under great pressure and flows continuously instead of intermittently. In many areas hot springs are associated with past or present volcanic activity. They are also found in non-volcanic areas. In India hot springs are found in Rajgir (Bihar), Bakreswar (West Bengal) etc.

The density of the Earth: The mass of a substance per unit volume is called ‘density. It is expressed in gm/cm3. It helps to give the idea of how closer or farther the molecules and atoms of a particular matter exist. The average density of the earth’s surface is only 2-6 to 3-3 gm/cm³. The average density of the core of the earth is about 11 gm/cm³. It increases up to 13 to 14 gm/cm³ at the centre of the earth. In respect of artificial satellites average density of the earth is 5-5 gm/cm³.

Seismic Waves: There is a change in the course and velocity of the waves on crossing the boundaries of different zones inside the earth. If the ground through which the waves travel is solid, they behave in one way. If it is liquid the waves behave in a different way.

 

Their velocities in both cases differ There are three types of waves known as ‘P’ or longitudinal or Primary waves, ‘S’ waves or transverse or secondary waves, and the long ‘L’ waves or surface waves which are recorded by a seismograph. The velocity of the first two types of waves increases with depth but only up to 2900 km.

Afterwards ‘S’ waves passing accorss the direction of their movement do not pass the ‘P’ waves travelling in the direction of their movement generally pass at a recorded velocity. The long ‘L’ waves do not pass and do not go deeper in the earth.

The ‘S’ waves cannot pass through a liquid and are transmitted only through a rigid or a solid body. The velocity of the ‘P’ waves passing through inner core again increases as compared to their passage through inner core again increases as compared to their passage through the outer core.

Layers of the Earth: At present, by observing the seismic waves and the lava coming out of a volcano, scientists have identified three concentric layers in the earth’s -interior from the surface of the earth to the core or centre of the earth. These layers are ‘the crust’ (lithosphere), ‘mantle’ and ‘core’ of the earth.

(1) Lithosphere: The word ‘l*’tho’jn Latin -means ‘rocks’ or stone. The word lithosphere thus means a ‘rocks sphere’. lt is rightly called the ‘rocky skin’ 0f the earth. Lithosphere is the outermost solid layer of the earth. It is found both on the continents and in oceans.

It forms a thin crust (the earth’s crust). The average thickness of the lithosphere is 60 km. It is spread over 29% of the earth’s surface. The thickness of the lithosphere is greater on the continents than on the ocean floor. The rocks of this crust are of lower density than those below the crust.

The crust of the earth: The outer part of the lithosphere immediately below the. newer sedimentaries on the surface is called ‘the crust of the earth’. The earth’s crust is now regarded as a series of plates which are gradually being pushed apart, away, from the zone where they formed. This layer is composed of light materials like silicon, aluminium, magnesium etc. The crust has two distinct parts.
These are—(1) sial and (2) Sima.

(1) Sial: This is the uppermost layer of the earth. This layer is called the ‘crust of the earth’. Silica and aluminium predominate in this layer and hence it is also called Sial (Silicon = Si and Aluminium = Al) Though it is composed of light rocks, its density is only 2-75g/cm³.

The principal rock of this layer is granite. In some places ‘Sial’ is 60 km thick. Continents have been formed by this layer and it is also called ‘continental crust’. This layer is absent in ocean floors.

(2) Sima: This layer is found below the layer of Sial,’ It has an average thickness of 6-8 km. and a density of 3 g/cm³. This layer is composed mainly by Magnes (a). So it is called Sima. This layer forms the ocean floors. So it is also called the ‘oceanic crust’.

Sima layer is about 5km thick and the principal rock of this layer is basalt. Though these two layer is in a solid state, the lighter ‘Sial’ is considered as ‘floating’ on the denser ‘Sima’ layer.

 

Distinguish between ‘Sial’ and ‘Sima’:

Sial	Sima
1.    The upper part of the earth’s crust.	1.    Sima layer lies below the Sial layer.
2.    It is composed of SiOica and aluminium.	2.    It is composed of Silica and Magnesium
3.    Continents are made of Sial.	3.    This layer forms the ocean floors.
4.    It is called ‘continental crust’.	4. It is called ‘Oceanic Crust’.
5.    It is lighter than Sima.	5.    It is heavier than Sial.
6.    Principal rock of this layer is granite.	6.    Principal rock of this layer is basalt.
7.    This layer is about 60 km thick in some Places.	7.    This layer is about 5 km. thick.
8.  Specific gravity is lower than Sima.	8. Specific gravity is higher than Sial.

 

Discontinuity Line: The line of limit or boundary between two layers within the Earth that possess very different physical properties is called discontinuity Line’. These boundaries were discovered by the study of the behaviour of seismic waves as they travelled through the heart.

Conrad Discontinuity: The line of limit or boundary on which the lighter granite made a lower portion of continental mass (Sial) joins the heavy basaltic ocean floor (Sima) is known as ‘Conrad Discontinuity’.

Mohorovicic/MohoDiscontinuity: Thelineoflimitorboundaryinbetweenthecrustofthe earth (lithosphere) and the Mantle (Mesosphere) is called the ‘Mohorovicic’ or ‘Moho Discontinuty’.

Repetti Discontinuity: The line of limit or boundary in between the ‘Crofesima’ and ‘Nifesima’ is called ‘Repetti Discontinuity’.

Gutenberg Discontinuity: The line of limit or boundary in between the Centrosp ere (core) and Mesosphere (Mantle) is known as the Gutenberg Discontinuity’.

Lehman Discontinuity: The line of limits or boundary in between the inner core and the outer core of the earth is called’Lehman Discontinuity’.

Significance of lithosphere to man: Lithosphere is useful for man in many ways

• Lithosphere provides land for human settlements.
• Soils of the lithosphere are indispensable for the growth of plants and crops.
• Many types of minerals and fuels are found in the lithosphere.
• Atmosphere is heated up by radiation from the lithosphere.
• Lithosphere is responsible for the exchange of water from oceans to atmosphere.

Chapter 1 Interior Of The Earth: Mantle

 

Asthenosphere: That portion of the interior of the Earth lying beneath the crust (lithosphere) and above the core (centrosphere) is called ‘Mantle’or ‘Mesosphere’. Its upper limit is the Mohorovicic discontinuity, which lies at an average depth of 35-40 km below the surface of the earth, and it descends as far as the Gutenberg discontinuity which lies about 2900 (2895) km. This layer is composed of nickel, iron, silicon, magnesium etc.

The specific gravity of this layer is about 4 to 5. Temperature of this layer is about 2000°C much less than the core but quite higher than lithosphere. The mantle is subdivided into two layers—(1) Outer Mantle or ‘Crofesima’ and (2) Inner Mantle or ‘Nifesima’.

The upper part of the mantle (40 to 700 km) is composed of chromium (CRO), (Ni) iron (fe), silicon (Si) and magnesium (Ma) and the lower part of the mantle is composed of nickel, iron (fe), silicon (Si) and magnesium (Ma). i.e. 700 to 2900 km (2895 km).

Volcanic eruptions originate in the upper part of this ‘Crofesima’ layer. This layer is also significant in the formation of fold mountain, earthquakes, continental drift etc. This part of the mantle is known as the ‘Asthenosphere’ (Asthenosphere is a Greek word, which means ‘weaker layer’).

Due to excessive heat and pressure, the rocks are here in a state of viscosity—just as molasses or melted asphalt. Comparatively lighter materials come upwards when heated geothermally, and allow the heavier ones to go downward. This is happened to be a sort of convectional current. From this part of the mantle molten rocks or magma find their way to the earth’s surface through cracks or faults.

 

Chapter 1 Interior Of The Earth: Centrosphere or Barysphere or Core of the Earth

 

The central portion of the Earth’s interior is called the ‘core ‘barysphere'(‘bary’ from greek word ‘baros’ meaning weight). The innermost layer which encircles the centre of the earth is also called the ‘core’ or the mental is the centrosphere.

This layer extends from the centre of the earth to about 3500 (3475) km. This is the hottest, heaviest and densest layer of the earth’s interior and is composed mainly of nicloel (Ni) and iron {fe) which gives its name ‘NIFE’ or ‘Nife’.

The density, of the core, is between 10 – 12 gm/cm³. So this dense layer is also called the ‘Barysphere’. The temperature of the core is estimated at 5000°C. Geologists have divided the core into two sub-layers— (1) Inner core and (2) Outer core.

1. Inner Core: The layer that lies surrounding the centre of the earth is called the ‘inner core’. It is nearly 5100 km to 6368 km deep. The tempereture of this layer is about 2700°C and at very high pressure. This layer remains in a solid state.
2. Outer Core: The layer which encircles the inner core is known as ‘the outer Core’. It is nearly 2895 (2900) km to 5100 km deep. The outer core does not transmit the ‘S’ waves of earthquakes, which suggests that it is liquid.

Temperature, pressure and specific gravity of the inner core are much higher than of the outer core. Outer core is in a molten state because of high temperature. But the inner core is solid probably due to the tremendous pressure of the overlying rocks.

WBBSE Notes For 8 Class Middle School Geography

Chapter 3 Rocks

What is rocks: In geography, the word ‘rock signifies any non-metallic natural substance found in the earth’s crust whether it is soft like clay or hard like a stone. A rock is simply an aggregate of various minerals, but in the scientific sense, the term ‘rock means, ‘the materials that make up the earth’s crust’. A rock has no definite chemical composition as minerals.

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Types of Rocks: Rocks can be classified into three types according to their mode of origin:

1. Igneous Rocks,e-8- Basalt, granite etc.,
2. Sedimentary Rocks, E.g: Sandstone, Mudstone, Limestone etc. and
3. Metamorphic Rocks,e-g: Gneiss, Marbles, slate etc.

1. Igneous Rocks: Igneous rocks are those rocks which have been formed by the cooling and solidification of Lava. The word “igneous” is derived from the Latin word “Ignis” meaning ‘fire’. In the beginning, when the Earth was born, it was just a glowing ball of gas.

 

Gradually, it cooled down and its molten volatile surface solidified. In this way, the igneous rocks formed at the first on the earth’s crust. Hence, it is called ‘Primary Rock’.it has no layer and that is why it is called ‘Unstratified Rock’.

Characteristics of Igneous Rocks:

1. Igneous rocks are formed by the cooling and solidification of hot molten lava and magma.
2. These rocks are compact, massive and crystalline.
3. These rocks are hard and resistant.
4. The rocks do not contain any fossil.
5. They contain several kinds of minerals, though they are not rich in mineral resources.
6. These rocks are sometimes transparent,
7. There is no layers in this rock.
8. Metallic minerals are common in this rock.

Types and Examples of Igneous Rocks: According to origin igneous rocks are of two types—

1. Extrusive igneous rocks
2. Intrusive igneous rocks.

1. Extrusive Igneous rocks: Igneous rock formed by the cooling and solidification of magma that has poured out onto the surface of the Earth is called Extrusive Rock,e.g. Basalt, Obsidian.

2. Intrusive Igneous rock: Igneous rock that has solidified below the Earth’s surface is called intrusive rock’ Granite is the most common intrusive rock. According to its depth intrusive igneous rocks are further subdivided into two types—(1) Plutonic and (2) Hypabyssal.

1. Plutonic: At a great depth in the earth’s interior it is known as ‘Plutonic roc’s e.g. granite, gabbro etc.’
2. Hypabyssal: At a shallow depth just beneath the earth’s surface, the rocks formed are called ‘Hypabyssal rock’.e.g. dolerite and porphyry.

Distinguish between Intrusive Igneous rock and Extrusive igneous rock:

Extrusive Igneous Rock	Intrusive Igneous Rock
(1)Extrusive igneous rock is the name given to magma erupting and solidifying after the escape of gases as lava on reaching the surface of the earth.	(1) The intrusive igneous rock is formed by solidification of magma at moderate or below depths beneath the earth’s surface.
(2)  This variety is also named as volcanic rock.	(2) The deep-seated intrusive rocks are known as ‘plutonic rocks’.
(3)    As lava cools down rapidly on the earth’s surface, its grains are very small.	(3)    As solidification of magma occurs at great depths below the earth’s surface, the cooling is obviously slow and as a result, very large size grains are formed in this rock.
(4)These rocks have a glossy appearance.	(4)These rocks are not glossy in appearance.
(5) These rocks are more compact and harder than intrusive rocks.	(5)These rocks are less compact and softer than extrusive rocks.
(6) These rocks are mainly two types: 1. Lava rock (eg. Basalt) and 2. Pyroclastic rock (e.g. Tuff).	(6)Intrusive rocks are of two types according to their depth, (1) Plutonic (at a great depth, eg. granite, and (2) Hypabyssal (at a shallow depth e.g. Dolerite).

 

Classification of Igneous Rocks Based on Chemical Compositions:

Name of the Rock	Content of Silica	Examples
Acidic Rock	More than 65%	Granite
Intermediate Rock	55% to 65%	Diorite, Andesite
Basic Rock	45% to 55%	Basalt, Dolerite
Ultra Basic Rock	Less than 45%	Peridotite

Chapter 3 Rocks: An Account Of Two Igneous Rocks

 

1. Granite: Granite is an intrusive igneous rock. It is composed of quartz, feldspar, mica and hornblende. It is highly crystalline and glossy. Granite is a brown or golden colour with black and white dots. It is one of the hardest and most durable rocks.

This type of plutonic rock cools and consolidates very slowly, so coarse grains are found in this rock. Granite is an acidic rock as it contains a high percentage (over 70%) of silica. It is very much resistant to erosion and it is very heavy. Granitic landforms are generally rounded and dome-shaped. The continental crust of the earth is mainly formed by this rock. It is used as a building material. Metalled roads are also constructed with it.

 

2. Basalt: Basalt is a fine-grained extrusive igneous rock. It is a dark-coloured crystalline rock formed by the solidification of lava. It is composed of feldspar, olivine, pyroxene and hornblende. This highly erosion-resistant, hard, heavy rock may be grey to black in colour.

This rock is highly permeable and many joints, cracks etc. are present in this rock. As magma (lava) cools and solidifies rapidly on the surface of the earth, basalt is fine-grained. The oceanic crust is mainly formed of this igneous rock. Flat-topped landforms are formed in regions composed of basalt rock. It is an important house-building material.

 

Economic Significance of Igneous Rocks:

1. Igneous rocks supply different types of minerals.
2. Granite is used for house-building and idol-making.
3. Pumic Stone is used as a sharpener.
4. Basalt and dolerite is quarried for road-making.
5. Gravestones, monuments, etc. are made from these hard rocks.

2. Sedimentary Rocks: A rock composed of sediments and generally having a layered (stratified) appearance is called ‘Sedimentary rock’.It has been named after the sediments forming it. The word ‘Sediment’has been derived from the Latin word ‘Sedene’which means to settle or settle down.

Formation of Sedimantary Rocks: Sedimentary Rocks have been formed by the deposition of sediments (gravel, sand, silt or clay) brought by wind, ice and river. These sediments are deposited in river beds, depressions, lakes and seas in the form of layers. After a long period, due to the pressure of the overlying layers, the sediments become hard compact rocks. Silica and calcite act as cementing agents.

These rocks are also called ‘stratified rocks as these occur in the form of layers or strata. Mudstone and sandstone are formed in this way. Coal and petroleum are formed by fossils of plants and animals.

According to origin and composition, Sedimentary rocks are classified into three types:

1. Mechanically formed
2. Organically formed and
3. Chemically formed rocks

1. Mechanically formed Sedimentary Rocks: These rocks have been formed by the deposition of sediments derived from other rocks.
Examples: Landstone, Mudstone, Shale etc.

2. Organically formed Sedimentary Rocks: These rocks are formed from the remains of plants and marine animals.
Example: Dolomite, Calcite, Gypsum, etc..,

3. Chemically formed Sedimentary Rocks: These rocks are mostly precipitated from a solution of certain salts.
Examples: Dolomite, calcite, gypsum etc.

Characteristics of Sedimentary Rocks:

1. The sedimentary rocks are formed by the sediments and remains of primary rocks.
2. These rocks are non-crystalline rocks.
3. These rocks contain particles of various sizes and shapes.
4. These rocks are formed in stratus of horizontal layers and are therefore known as ‘stratified rocks’.
5. These rocks cover nearly 70% of the total surface of the earth.
6. These rocks contain several kinds of fossils.
7. These rocks are easily weathered and eroded.
8. These rocks bear the marks of ripples, waves and mud.
9. These rocks are less hard than igneous and metamorphic rocks.
10. These rocks are porous and fragile These rocks are highly permeable and lighter than other rocks.
11. Porosity is a major character of this rock.
12. Organic matter, such as coal, mineral oil, natural gas, and limestone are found in this type of rock.

Types of Sedimentary Rocks: Based on the origin of sediments sedimentary rocks are mainly two types,

1. Clastic Rockand
2. Non-Clastic Rock.

1. Clastic Rock: ‘Clastic’is derived from the greek word ‘Klastos’which means ‘broken’. The rocks that are formed from fragments resulting from the breakdown of pre-existing Rocks is called clastic rocks,e.g. Sandstone, Mudstone etc.
2. Non-clastic Rock: The rocks that are formed from chemical or organic processes is called Nion-clastic rocks,e.g. Dolomite, Limestone, Rocksalt etc.

Fossils: Sometimes while sediments are being deposited plants, animals or any organism are also embedded in the layers of sedimentary rocks as they are solidified, cemented and converted into rocks. These rocks or their parts, impressions or remnants left in the sedimentary rocks, are called ‘fossils’.

An account of some Important Sedimentary Rocks:
Limestone: Limestone is the most important calcareous rock of sedimentary origin. It consists essentially (about 50%) of calcium carbonate. These are wholly or partly organic origin. They contain hard parts of various organisms, such as the shells of molluscs and the skeleton of corals. Limestone is soluble in water. Limestones are widely used in cement and chemical industries. It is also used as a building material.

 

Sandstone: Sandstone is a sedimentary rock. It is porous consisting of grains of sand, bound together by such substances as calcium carbonate or silica. Sandstones are of different colours. The stone which contains silica, keolin and calcium carbonates if whitish; but when it contains ferrous oxides, the stone looks in red or brownish colour. Sandstones are hard and useful as house-building materials.

Shale: Shale is a fine-grained sedimentary rock produced from clay. These rocks are usually finely stratified and thus they readily split into thin layers. These rocks are so soft that they easily disintegrate. These stones are used in making utensils and other household materials

Economic Significance of Sedimentary Rocks:

1. Many valuable minerals are found in these rocks.
2. Coal, petroleum, natural gas are the major sources of power.
3. Limestone and sandstone is used for building purposes.
4. Bricks from clay, cement from limestone and glass from sandstone is made.
5. Many types of chemicals (calcites, gypsum, salts, boron etc.) are also obtained from these rocks.
6. The fossils are useful to trace out the past history of the earth.

Distinguish between Igneous Rock and Sedimentary Rock:

Igneous Rock	Sedimentary Rock
(1)Igneous rocks are formed due to the cooling of magma or lava.	(1)Sedimentary rocks are formed by the deposition of sediments.
(2)These rocks are massive and found in bulks.	(2)These rocks occur in layers or strata.
(3) These are hard and resistant rocks.	(3)These are soft rocks.
(4) These rocks have different types of crystals.	(4)These rocks contain minute particles.
(5)These are also known as Primary rocks.	(5)These rocks are known as Secondary rocks.
(6)These rocks do not contain fossils.	(6)These rocks contain fossils of animals and plants
(7)These are impervious rocks.	(7) These are previous rocks.
(8)Joints are found in this rock.	(8)These rocks have no joints.
(9) These rocks are not easily eroded due to weathering and erosion.	(9) These rocks are easily eroded due to weathering and erosion.
(10)These rocks are formed in depressions, sea beds, lakes and river beds.	(10) These rocks are formed in depressions, sea beds, lakes and river beds.

 

Distinguish between Igneous Rock and Metamorphic Rock:

Igneous Rocks	Metamorphic rock
(1)Igneous rocks are formed due to the cooling of lava magma.	(1)Metamorphic rocks are changed due to heat, pressure and chemical action.
(2) These are crystalline rocks.	(2) These rocks are highly crystalline.
(3) These are hard, massive rocks	(3) These are hard resistant rocks.
(4)Igneous rocks are primary rocks	(4)Pre-existing igneous and sedimentary rocks are changed to metamorphic rocks.
(5) Granite and Basalt are formed as igneous rocks.	(5)Granite is changed into gneiss, and limestone is changed into marble.

 

3. Metamorphic Rocks: Rock formed when the pre-existing sedimentary or igneous rock is altered as a result of changes by immense heat of the earth’s interior or a tremendous pressure of the overlying rocks is called ‘metamorphic rock’ (Greek ‘means’ means ‘changed’, ‘morphe’, means ‘form’).

The mineral composition and the structure of the rock can be altered. Examples of metamorphic rocks include Granite changes into Gneiss, Limestone changes into Marble, Sandstone changes into Quartzite and Coal changes into Graphite.

Agents of Metamorphism: Three factors have a major effect on metamorphism.
They are—

1. Temperature,
2. Pressure and
3. Chemical processes.

On the basis of the agency involved there are two types of metamorphism.

1. Thermal Metamorphism: The process by which a rock undergoes change as a result of excessive heat and pressure of the intrusive mass of molten igneous rock is known as ‘Thermal Metamorphism’, such as limestone is changed into marble and sandstone into quartzite. It is also called ‘Contact Mctamorplusm’.

2. Dynamic Metamorphism: The modification of rocks by pressure during extensive earth movement is known as ‘Dynamic Metamorphism’. It is also known as ‘Regional metamorphism’ On account of the regional effect brought in metamorphism.

Characteristics of Metainorphsc:

• Metamorphic rocks are massive, completely crystalline and hard.
• These rocks can not be eroded easily.
• These rocks are very rich in minerals.
• During metamorphism minerals become oriented in a specific fashion. It facilitates mining operations.
• No fossil is found in metamorphic rock because excessive heat and tremendous pressure destroy the fossil.
• These rocks supply many house-building materials, example, Marble, Slate, Gneiss, etc.

An account of three common metamorphic rocks:

Marble: Marble is a coarse-grained crystalline metamorphic rock, derived from limestone. It appears in different colours, such as white, red, black, green and yellow. Dolomite, hornblende and talc are important constituent elements. Marble is used as a building material. Palaces are also constructed with it.

Slate: Slate is produced by metamorphic processes from shales. It is a fine-grained metamorphic rock produced by heat and pressure from fine clay. Its colour varies from grey to black. It has well-marked cleavages. It ready to split into thin, smooth plates, suitable for roofing purposes.

Gneiss: Gneiss is a metamorphic form of granite rock. This rock is found in banded structure. This banding is the most characteristic feature of a typical gneiss. This banding is due to the separation of light and dark materials in crude layers of previous rock. It is very much hard and massive. It is widely used as house-building material.

 

Economic Significance of Metamorphic Rocks:

1. Marble can be very well carved, into desired shapes. So, it is extensively used by architects.
2. Many house-building materials like marble, slate, etc. are obtained from these rocks.
3. Many minerals are found in these rocks. So,’ these rocks are very rich in minerals.
4. As rearrangements and redistribution of minerals take place in metamorphic processes, so valuable minerals are found conveniently in successive layers. It facilitates mining operation.
5. These attract a huge mining population.
6. Slates are used in making blackboards and can be used as a substance for writing.

The Rock Cycle: Rocks in the earth’s surface gradually change from one major type to another due to various processes acting on them. The change of one rock into another under different conditions is known as the ‘rock cycle’. Igneous rocks were formed first in the earth’s crust.

The agents of denudation disintegrated these original igneous rocks into sediments. These sediments were deposited in water bodies to form sedimentary rocks. Both igneous and sedimentary rocks were subjected to the processes of metamorphism to form metamorphic rocks.

 

 

Metamorphic rocks in turn were denuded to form sedimentary rocks. Both metamorphic and sedimentary rocks may get buried deep inside the earth due to tectonic movements. There they melt to form magma. Such magma may rise to the earth’s surface through volcanic activity and solidify to form igneous rock. Thus, the rock cycle goes on and the rocks continue to get transformed from one type to another.

Influence of rocks on landforms: Rocks influence the formation of different landforms, eg.,—

1. Regions having granite rocks have rounded landforms, like in the Telenana plateau.
2. Surfaces made of basalt rocks form hills with flat surfaces or tops.
3. Limestone and rocksalt areas having rivers flowing over them, have many underground caves.
4. Hard rock being difficult to erode, need more time to be eroded, so generally form highland, while soft rock is easy to erode so they get eroded soon to form plains or river valleys or lowlands.

Dee can Trap: Lava covered hill slopes of the Deccan (Maharastra Plateau) on weathering have formed terraces resembling a flight of stairs. They are popularly known as the ‘Deccan Trap’. Weathering, erosion and denudation have given the rise to such a typical ‘Trap Landscape’.

Karst Topography: Limestone consists” chiefly of calcium carbonate which is insoluble. The carbon dioxide, which rainwater absorbs from the air, turns the insoluble carbonate into soluble bicarbonate. It dissolves limestone and gives rise to caves, cavities and broken lands, stalactite and stalagmites develop in these caves by the accumulation of sediment derived from precipitation. Limestone landforms are popularly known as ‘Karst Topography’.

 

Characteristics of few Rocks:

Igneous Rock	Sedimentary Rock	Metamorphic Rock
(1)Hot molten materials from the earth’s interior cool and turn solid to form igneous rocks.	(1)    These rocks formed after the deposition of sediments and compared on the floor of water bodies to form sedimentary rocks.	(1) These rocks formed after the change of igneous and sedimentary rocks under the influence of pressure, temperature chemical action etc.
(2)These rocks are hard and not easily eroded.	(2)These rocks are softer than igneous and metamorphic rocks.	(2)These rocks are harder.
(3)These rocks are heavy.	(3)These rocks are lighter than igneous rocks.	(3) These rocks are heavier than the other two rocks.
(4) They have no bedding planes.	(4)They have distinct bedding planes which are clearly visible.	(4)Generally they do not have bedding planes.
(5) They have no fossils.	(5)Fossils are present.	(5)No fossils are found.
(6)Some igneous rocks have quartz crystals.	(6)No quartz crystals are present.	(6)Crystalline igneous rocks when metamorphosed become more crystalline with more crystals.

 

Rock-forming minerals: Most of the rocks found in the earth’s crust are composed of various minerals. About two thousand mineral species are known on the surface of the earth. Out of these, mainly twenty-four minerals constitute the rocks of the earth’s crust. Among them following ten important minerals are as follows :

1. Feldspar,
2. Quartz,
3. Mica
4. Clay minerals,
5. Augite,
6. Calcite and Dolomite,
7. Hornblende,
8. Olivine,
9. Chlorite
10. iron.

Brief Account of some important minerals:

1. Quartz: Quartz crystals are six-sided prisms and pyramids. These are very hard often whitish or milkfish, grey, pink or violet. They look like glass or crystal. Clear crystals are used in optical instruments. It is also used as a stone cutter, glass cutter and in ornaments.
2. Feldspar: Feldspar is less hard than quartz, although harder than glass. The colour is. white, light shades of grey and pink. It is the most common type of mineral making up 60% of the total weight of the earth’s crust. Pure feldspar is used in the making of porcelain and “ as mild abrasive.
3. Gypsum: Gypsum is a chemically formed sedimentary rock as wed as a mineral. It is
   a hydrated crystal of calcium sulphate. It is fairly soft, light and yellow-coloured. It is used in making fertilizers, cement and in construction industries.
4. Mica: Mica is a group of silicate minerals that have perfect cleavage, so they split easily into thin plates. It is a common mineral in igneous and metamorphic rocks and is responsible for the characteristic shiny appearance of many metamorphic rocks such as schists. The most common types are biotite, which is dark black in colour, and muscovite which is light white.

It is a very soft mineral only a trifle harder than the fingernail. Mica is a poor conductor of heat and electricity. it is used in preparing electrical goods, decorative glitters and paint. it is used as insulator in electrical equipment.

Distinguish between Rocks and Minerals

Rocks	Minerals
(1) Rock is an aggregate of minerals.	(1) Mineral contains only one ore and has an atomic structure.
(2) A rock is a natural solid material forming the earth’s crust.	(2) A mineral is a natural inorganic compound found in rocks.
(3) A rock does not have a definite chemical composition.	(3) It has a definite chemical composition.
(4) Rocks are mainly three types—lineouts, sedimentary and metamorphic.	(4) There are about 2000 types of minerals.

 

Why the Chhotonagpur Plateau is called “the Storehouse of Minerals in India: The Chhotonagpur Plateau region of India is called the ‘Storehouse of Minerals in India’. The variety of minerals extracted are— coal, iron,-ore, limestone, mica, copper, uranium, manganese, asbestos, graphite etc.., and are the most important. A besides large amount of minerals are found in this plateau, like uranium, limestone, mica, fire, clay, manganese etc.

In the Chhotonagpur plateau the following reserves of minerals are found—coal (40%), Copper (94%), iron-ore (42%), mica (56%), bauxite (30%), China clay (52%), fire clay (35%) of the reserves of India, besides these there are very large resumes of limestone, asbestos, graphite, lignite, uranium etc. in this plateau.

In this way such a large amount and variety of minerals are available in the Chhotonagpur plateau and the main occupation of the people of this region is related to minimal and mineral-based industries that it has gained the title “the Storehouse of Mineral in India”.

The influence of Minerals: Different types of rocks are found in nature. Most of the rocks found in the earth’s crust are composed of various minerals. So, there is a great influence of minerals in nature.

1. The different cheracteristics like—colour, hardness, lustre, cleavage, chemical reactions etc. are dependent on minerals.
2. The soil which is rich in iron and aluminium is hard and red at the top. The Laterite and Red soils with an excess of minerals like iron and aluminium are less fertile and perform poorly in agriculture.
3. Many mineral springs are useful for curing skin diseases.
4. Soil rich in gypsum is soft and light yellow in colour.
5. Abundance of solf calcite leads to the formation of Limestone which is easily eroded.
6. Soft, Porous and permeable sedimentary rocks are abundant in places where petroleum and natural gas are found.
7. The main occupations of the people may be related ot mining and mineral based
   industries.

Formation of soil from rocks: The uppermost thin layer of the looser materials of the earth’s crust that sustains living beings is called soil. It forms slowly over a long period by the mechanical and chemical weathering of bedrock. Weathering is the breaking up of rocks by the elements of weather like temperature, rainfall, winds, river, sea waves, glaciers etc.

The loose weathered materials or rock wastes lying above the bedrock and blow the ground surface is called regolith. It includes the parent material from which soil is formed. This debris then interacts naturally with water, air and organe matter (humus and living organisms), bacteria etc.) to form soil. Characteristic features of a soil usually depend oh the nature of the layer of rock underneath i.e., parent rock.

 

Example: Black soil, Red soil and Sandy soils are made mainly from Basalt, Granite and Sandstones respectively.

WBBSE Notes For 8 Class Middle School Geography