WBBSE Notes For Class 7 Geography Chapter 4 Landforms

Chapter 4 Landforms Notes

Why are not all places on the earth’s surface similar?

The surface of the earth which is made of various types of rocks is neither stable nor permanent in its form. Somewhere it is higher, or in others, it is flat and even slopes.

Being subject to pressure, movement, forces of tension and compression and fracture, the form of the earth’s surface continuously changes.

There are two types of forces working on the earth’s surface-

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1. Endogenetic forces and
2. Exogenetic forces.

1. Endogenetic forces have their origin deep down in the earth’s interior and work from below. They can be said to be two types-

Slow forces which bring about subsidence and elevation, cause folds and faults in the crust of the earth and is known as mountain-building activity. These activities are carried on slowly and are called Diastrophism.

The sudden forces include within their scope the earthquake and volcanic eruptions.

2. Exogenetic forces are connected with the atmosphere and consequently are external to the earth. Rain, snow and sun on one hand and running water (river), wind and moving ice on the other, are always busy levelling down the irregularities of the earth’s crust.

Out of the continuous action and reaction of these two types of forces- one trying to raise from within the interior and the other trying to level down the raised surfaces-are born the various form seen on the earth’s crust.

These are called landforms and they exercise a very powerful influence on the life and activities of man on this planet on which we live.

The term ‘landform’ is applied by physiographers to each of the multitudinous features that taken together make up the surface of the earth. Any feature of the earth’s surface that possesses. a particular shape and form are called a ‘landform’.

It describes the shape, size and Mountai structure of the land.

“major landforms “

In fact, a landform is a natural phenomenon of a land area.on the earth’s surface. There are many forms of land on the surface of the erotic earth. Continents, oceans, mountains, plateaus, valleys; deltas etc.

These are some the examples of landforms. Height, slope, and relief are the chief elements giving diversity to landforms.

Landforms Must Have The Following Characteristics

1. It must have a distinctive surface feature quite different from others.
2. Its rock structure and general formation must be quite prominent.
3. It must be so conspicuous that it may be included in any description of physiography.

 

Landforms can be divided into three orders. First-order landforms are continents and oceans. Mountains, 1000 m Plateaus and Plains are among the second-order landforms. The third-order landforms include mountain Sea sections, hills, valleys, deltas etc.

There are three major landforms on the earth basis of height, slope, structure, ruggedness and irregularities.

“various landforms “

These are-

• Mountains and hills,
• plateaus and
• plains.

 

Mountains And Hills

A mountain is a very high, rocky, steep-sided, uneven rugged landmass with a narrow peak or summit.

Characteristics Of Mountains And Hills :

1. Mountains are the highest lands on earth.
2. Mountains occupy extensive areas.
3. These are rocky and rugged landforms.
4. They are irregular and uneven.
5. In general, mountains rise to comparatively high altitudes, usually more than 1000 metres.
6. Most of the mountains are characterised by deep valleys, gorges and long steep slopes.
7. The lower part or foot of a mountain is called it’s base.

“landforms of the world “

Tops of the mountains have conical peaks. The sharp or narrow pointed top of a mountain is called it summit or peak. A single more or less isolated summit is called a ‘Peak’.

A Mountain Have Several Forms Viz.

1. Mountain ridge,
2. mountain range,
3. mountain chain,
4. mountain system,
5. mountain group and
6. cordillera.

 

1. 1.  Mountain ridge: A mountain ridge is a system of long, narrow and high hills.
   2.  Mountain range: A mountain range is a system of mountains and hills having several ridges, peaks/summits and valleys.
   3.  Mountain chain: A mountain chain consists of parallel long and narrow mountains of different periods.
   4.  Mountain system: A mountain system consists of ‘different mountain ranges of the same period.
   5.  Mountain group: A mountain group consists of several unsystematic patterns of different mountain systems.
   6.  Cordillera: Cordillera is a community of mountains having different ridges, mountain chains and mountain systems. The mountains region of the western part of North America is the best example of the cordillera.

 

Chapter 4 Landforms Mountain Knot

Many mountain ranges spread out in different directions converging or meeting in a highland which is called a Mountain knot. Example-The Pamir plateau of Asia.

Hills: Hills are natural lower highlands of the earth’s surface, not so high as mountains (Considerably ranging between 300 m to 1000 m) and stretching over a less extensive area with less steeply inclined sides. eg. Rajmahal Hills of Jharkhand, Ayodhya, Susunia, Biharinath etc. of West Bengal are examples of hills.

Types Of Mountains: There are different types of mountains, Based on their mode of formation four main types of mountains can be distinguished-

1. Folded mountains,
2. Block Compression mountains,
3. Volcano or mountain of accumulation and
4. Relict or residual mountain.image

 

Folded Mountain

Folded mountains are formed due to the folding of crustal rocks by the compressive force generated by endogenetic forces coming from within the earth.

Characteristics Of Folded Mountains :

1. Folded mountains are the youngest mountains on the earth’s surface,
2. These have been formed due to the folding of sedimentary rocks by compressive forces.
3. The fossils are found in the rocks of the folded mountains. It means that the sedimentary rocks of folded mountains were deposited in shallow seas.
4. Folded mountains extend for greater lengths but their widths are smaller than their lengths.
5. Folded mountains are generally found in an arc shape having one side concave shape and the other side convex slope.
6. Folded mountains are found along the margins of the continents facing oceans.

Folded Mountains are of two types-

1. Young Fold Mountains:

have been formed during the most recent mountain-building periods. The Himalayas, the Alps, the Rockies and the Andes are prominent examples.

Old fold mountains have formed during earlier mountain-building periods, like the Urals, the Appalachians etc. The Aravallis are considered to be the oldest folded mountain.

2. Block Mountains:

An upland mass created by the uplift of land through earth movements between faults or by the sinking of the land outside the faults is called a block mountain.

Characteristics :

1. Block mountains are formed due to forces of tension.
2. A block between two parallel faults is raised, or the land on either side is dropped below. The upstanding landmass is known as Block mountain or a Horst. The other lower side of the fault seems to be a valley which is called Rift valley or Graben.
3. These mountains have broad flat tops and steep slopes.
4. These mountains may be called Fault mountains.

Examples are Black Forest mountain in Germany, Vosges mountain in France, and Vindhyas and Satpuras in India.

 

Volcano Or Mountain Of Accumulation

When magma or lava gushing out from the interior of the earth spread and solidifies, a mountain is formed by the accumulation of lava: This type of mountain is called a volcano/a volcanic mountain or mountains of accumulation.

Mt. Fuji in Japan, Barren of Andaman island in India, Vesuvius in Italy, and Krakatau in Indonesia are some examples.

“landforms of the earth project “

Volcano Characteristics :

1. Volcanic mountains are formed by the deposition of volcanic materials like lava, ash etc.
2. If the lava is basic a flat top is formed; if the lava is acidic a steep-sided top is formed.
3. These build up a volcanic cone after a long period.
4. The vendor crater is found in this type of mountain.

 

Residual Or Relict Mountain

When an original highland (mountain/plateau) is eroded for a long time, its soft rocks are removed and the hard rocks stand out as mountains. These are called Residual or Relict mountains.

Nilgiris of Southern and Aravalli of North-Western India are examples of this type.

Relict Mountain Characteristics :

1. These mountains are formed by denudation by rivers glaciers wind etc.
2. Softer rocks are eroded quickly and height is reduced.
3. A few hard rocks are left standing these are the remaining parts of once-high mountains or plateaus. The mountain top is rounded and no sharp peaks are visible.
4. The mountain slope is not steep but gentle.
5. Their height is not very high.

 

Chapter 4 Landforms Plateau

A plateau is an extensive upland that has an almost flat undulating topped surface with steep sides.

Plateau Characteristics :

1. Plateaus are extensively flat undulating upland areas with altitudes of above 300 meters from their base level. They have steep sides and deep edges.
2. They often look like tables standing above the surroundings and for this, they are, sometimes called Tablelands.
3. The plateaus are of different heights.
4. Plateaus are the most ancient landmass on the earth’s surface.
5. The top of a plateau may be undulating or flat.

Formation Of Plateaus:

Plateaus are formed in the following ways-

1. Sometimes, a vast stretch of land on the earth’s surface rises to a higher level owing to the earth’s movements and forms a pair genic or Continental plateau.
2.  Vast stretches of South Africa, Antarctica, Greenland and Western Australia are occupied by the Continental plateau. At the time of the fold mountain formation, the Intermontane plateau is formed.
3. Sometimes lava, thrown out by volcanoes piles up and forms a plateau which is called Lava Plateau. The Deccan Trap is an example of Lava plateau.
4. Sometimes, Plateaus are formed when the mountains are worn away by the forces of nature like rivers, moving ice, wind etc. Chhotonagpur plateau is an example of this type of plateau. These are called Dissected plateaus.

 

Intermontane Plateaus :

The plateaus which have mountain rims around their surroundings are known as Intermontane plateaus. The upliftment of fold mountains often builds up the intermontane plateaus in between their ranges.

The Tibetan Plateau in between the Himalayas and the Kunlun is an example of this plateau which is the largest and most extensive plateau in the world.

The Pamir in Asia is the highest plateau (4873 m.) in the world and that is why it is called the ‘Roof of the world’. The Ladakh Plateau (3500 m) of Kashmir is the highest plateau in India.

Lava Plateau: The Plateaus which are formed by volcanic lava, are called lava plateaus. These plateaus are formed as a result of the lava flow in volcanic regions.

The plateau of Maharashtra, situated in the northwest of the Deccan Plateau in India is an example of this type of plateau.

Dissected Plateaus:

Sometimes, the softer parts of a plateau or highland are worn away by water, glacier, and wind but the harder parts remain as before. The plateau is then divided into a number of uplands and valleys.

It is called a dissected plateau. The Chhotonagpur plateau of Jharkhand in India presents a classic example of the dissected plateau.

 

Chapter 4 Landforms Plains

An extensive area of flat or near leveled or gently undulating land, usually lowland is called a plain. Plains are formed by the internal earth movements and the external agents of nature, such as the sun, rain, running water, and the glacier.

The plains are formed in the following ways:

1. Tectonic (Natural, Uplifted, and Depressed) plains are formed by the earth’s movements and earthquakes.
2. Depositional plains are formed by the deposition of alluvium, lava, sand, etc.
3. Erosional plains are formed by the agents of erosion and denudation.

 

 

The plains which are formed by the deposition of alluvium are called alluvial plains. The Indo-Ganga-Brahmaputra plain of North India is an example of an alluvial plain.

Lava which is extruded by fissure eruption accumulates over vast, flat low-lying stretches from a plain. It is known as a Lava plain. This plan is found on the margin of the Lava plateaus of the Deccan in India.

A plain may be formed by the deposition of fine sand and silts blown by the wind. This is called Loess plain. The largest loess plain of the world is found in the Hwang Ho basin of Northern China.

 

Chapter 4 Landforms Effects Of Landforms On Our Lives

Landforms exert a significant influence on the life and activity of man. Different types of landform influence differently and for this, we see different types of modes of life on the different parts of the earth. Mountain, plateaus, and plains exert their influence differently.

Influence Of Mountain On Human Lives And Activities :

The Following Are The Influence Of Mountain On the Life And Activity Of Man :

1. The rugged topography, a thin layer of soil, and rocky surface of the mountainous land are not suitable for agriculture.
2. Steep slopes and rocky lands hinder the construction of good roads. The forests of the mountain provide timber, fuel, and many other forest
3. products. Terraced farming is practiced on mountain slopes and some special types of crops and fruit such as tea, orange, apples, etc. are grown on the mountain valley.
4. Mountain act as a climatic barrier. High and extensive mountain ridges control the climate.
5. The old and relict mountains are rich in minerals.
6. Mountains are the source of many rivers. The waterfalls of the mountain offer good sites for the development of hydroelectricity.
7. Many boundaries are formed by high mountains. These serve as natural barriers between countries. They provide natural boundaries and security.
8. Underdeveloped communication systems, difficult means of earning a livelihood, etc. cause mountain areas to have scarce settlements.
9. Beautiful natural scenes of mountains have always attracted tourists to mountains. Entertainment is provided in these areas.

Influence Of Plateaus On Life And Activity Of Man :

The plateaus influence human activities in various ways :

1. The plateaus are famous for minerals. Many plateaus are rich in many minerals as such they are called ‘storehouses of minerals.
2. Plateaus are rocky and rugged, so they hinder agriculture. But the rich black soil of the lava plateau in the Deccan provides an example of rich agriculture.
3. Some plateaus provide mining facilities and the metallurgical industry.
4. Plateaus are not completely smooth as plains. The rugged and dry surface of the plateaus hinders transport and communication.
5. The rugged surface of the plateaus does not favor navigation. However, the swift-flowing rivers are favorable for hydroelectric power generation.

Compared to mountain regions transport and communication network is developed in plateau areas and earning of a livelihood is easier. Thus human settlements are moderate in density.

Influence Of Plains On Life And Activity Of Man :

Plains are smooth for human habitation and easy living. The plains exert tremendous influence on human lives and activities. They may be enumerated in the following ways:

1. Plains are open fields with open-air environments.
2. Fertile plains are the best areas for agricultural development.
3. The plains provide the best facilities for transport and communication.
4. Plains in many ways offer facilities for human settlement and encourage economic activities.
5. The agricultural products of the plain provide raw materials for many agro-based industries. These industries support a high density of the population.
6. The fertile alluvial plains are the birthplace of ancient civilization, culture, and learning.