Class 9 Social Science Geography Chapter 1 Change of the Earth’s Surface The answer to each chapter is provided in the list so that you can easily browse throughout different chapters Assam Board Class 9 Social Science Geography Chapter 1 Change of the Earth’s Surface and select needs one.
Class 9 Social Science Geography Chapter 1 Change of the Earth’s Surface
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Change of the Earth’s Surface
Textual questions and answers Exercise:
Q.1: Give an outline of the distribution of continents and oceans of the world.
Ans: The distribution of continents and oceans of the world is as below:
A large portion of the earth surface formed by land slightly above sea-level is called the continents. The continents plains, plateaus, hills and mountains, river valleys, deserts and coastal plains are found to occur.
A large portion of the earth’s surface by the oceans and seas including rivers, lakes etc. is known as the oceans. In the oceans also submerged plateaus, plains, ridges, trenches, coral are there. Hydrosphere and landmass cover 71% and 29% of the earths’s surface.
Q.2: Explain why there has been change over the earth’s surface.
Ans: The Earth’s surface is constantly changing. These changes mostly occur in very minute ways which over time accumulates to create the earth’s physical features we observe around us today.
Some of these changes take thousands of years. When you look around and you might see a mountain, river, plateau, valleys, or rock boulders. These all didn’t just appear suddenly rather most of them had a building process like building a house.
In a continuous process the surface of the earth has been changing and will change in future also. The quantity of cropland, hilly area and vegetative area have been decreasing at large extent in the earth due to the speedy increase of population. Over population is equivalent to problem. As a result of these, the volume of rain decreases significantly. Many drought hit areas are created considerably. And green cover also decreased.
The clean air is polluted worldwide by the extensive industrialisation. Many mega project are established ignoring the environmental concern. Global warming has been increased. Unlimited volume of water is deposited in the river by melting huge amount of ice of polar and Himalayan region. These excess water creates undesired flood in the surrounding areas. If such random meltdown is going on, then this flood creates havoc in the world. The surface will be changed and new landform will be seen tremendously.
As a result of these, the possibility of scarcity of water is brightened by decreasing the water store in polar and Himalayan region. So, many new desert areas may be created in the earth surface. The water of river, sea, lake etc. may dry up also.
Q.3: What is meant by exogenic factor? Mention some exogenic factors.
Ans: The two geomorphic processes endogenous (internal) and exogenous (external) can be defined as the forces which lead to the changing of the earth’s movements and shape the surface of the earth.
The external process that act upon the earth’s surface and make changes in it is called exogenic factor. The exogenic factors basically operate externally upon the earth’s surface.
Some exogenic factors are: sun, atmosphere, wind, rain, river, glacier and sea waves etc.
Q.4: Why are earthquakes and volcanic eruption called endogenic factors?
Ans: Actually earthquakes and volcanic eruptions are endogenic since there origin is from below the crust of the earth. Exogenic processes have their origin on the surface of the earth, for instance, weathering and erosion takes place on the surface of the earth.
Q.5: What do you mean by a river basin? Draw a diagram of a river basin.
Ans: Generally, reivers along with their tributaries from basins of their own. Thus basin is an areas wherefrom a river along with its tributaries carry water downward.
The water sources of rivers many be rainfall snow deposit over the mountains or springs coming out from the earth’s interior.
Q.6: What is a tributary? Name two major tributaries of the Brahmaputra.
Ans: The smaller branches of water that flow into the main river are called tributaries.
Two major tributaries of the river Brahmaputra are: Dhansiri and Varalu.
Q.7: Give an outline of river erosion.
Ans: Rivers are dynamic structures. They change their inflow patterns continuously and naturally. These differences affect river bank soil stabilization as the river bank absorbs the energy. River bank corrosion is a part of this changing nature. When banks of a river wear down by watercourse, it’s called river bank corrosion.
Substantially river banks are made of stratified layers with cohesive and cohesion accoutrements.
The river banks have three zones:
Bank zone and
The Toe zone is positioned between the ordinary water position and low water position which makes it vulnerable to erosion.
However, vulnerability is increased, If non-cohesive accoutrements are at the toe zone.
But at the time of lowering water position, cohesive banks are most susceptible to corrosion because of their low water permeability.
Q.8: What do you mean by lateral erosion a river?
Ans: The erosional capacity of a river changes after it enters a plain from the steep mountainous slope. In the mountainous region, the river channel is narrow and deep with high velocity of flow. With the decline of slope towards the plain, the velocity decreases and the sediments transported from the highland begin to be deposited. As a result, in the plains, channel depth declines. Then the river starts widening it channel through lateral. cutting just to maintain its normal flow. By eroding the banks the river widens its channel to carry the water down. Such kind of river erosion is known as bank or lateral erosion.
Q.9: What is ox-bow lake? Draw a diagram to show how it is formed.
Ans: The term “oxbow” refers to the U-shaped river meander or curled, twisting route. An oxbow lake develops when a meander is severed from the rest of the river.
(1) Sediments are removed off the riverbank, creating a bend, and then deposited on inside banks as a result of slower moving waters, which causes rivers to meander.
(2) The two outside banks of one or two meanders may gradually erode toward one another as river meanders become more pronounced and curved. The neck of land between the meanders gets narrower as the banks between them keep eroding.
(3) The river eventually carves a new, straighter path after the neck of the meander is entirely eroded.
e.g. ox-bow lakes are found in large numbers in the respective valleys of almost all the significant rivers like the Barak and the Brahmaputra in Assam.
Q.10: What is floodplain? Write how is formed.
Ans: A floodplain or flood plain is an area of land adjacent to a stream or river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge. The soils usually consist of levees, silts, and sands deposited during floods.
Floodplains develop in two common ways: erosion and deposition (also known as aggradation). When rivers start to meander, curving from side to side, the water erodes the banks of the river and creates a wide flat area around the sides.
Q.11: Write how and where sandbars are formed in a river channel.
Ans: The materials carried down by the rivers are deposited on the banks and the river mouths to form a variety of features.
Sandbars are formed by the mud and sands carried down by the river in the middle of the river beds and sometimes near the banks. These are generally temporary in nature. The water currents bring about changes in their shape and size. Some of them are wiped away by currents. In winter, large number of sandbars of different sizes are seen in the Brahmaputra river bed.
On the other hand, the sandbars formed of the sediments on the river bed are significant from various points of view, Sandbars are formed both on the sides and the middle of the river bed. Generally sandbars are temporary and of various sizes and shapes. The speedy flow of the river during summer affects the size and shape of the sandbars. Sometimes bank erosion completely wipes them out. The sandbars become visible when river water subsides during winter. A large number of sandbars are there on the bed of the Brahmaputra. The great river island Majuli is a kind of sandbar of the river Brahmaputra.
Q.12: How are the deltas formed?
Ans: The formation of a delta does not happen overnight. It is a very slow process because it requires the water to change and form the landscape.
Rivers flow from higher elevations down to their lowest elevation where they meet a larger body of water, like the ocean. When they reach this low elevation, the water begins to slow down.
During its journey downward, the river has picked up sediment and nutrients from higher elevations and has been carrying them downward. For the most part, the river will have been moving too fast for the sediment and nutrients to deposit along the river.
Rivers often create deltas through the spread of sediment like sand, mud, silt, and gravel. At the beginning, the sediment is small and does not have much effect on the area. However, over time, the sediment settles, and is continually covered by more settling sediment.
Q.13: Write why the wind action is strong in the deserts.
Ans: Because in deserts there are low amount trees in desert which prevents soil erosion and prevents strong winds in direction.
The desert regions have less amount of vegetation and other geographical components. This emptiness of the desert regions also help into the fast travelling of the air currents without any problems of the surface obstructions.
Q.14: What is meant by deflation?
Ans: In the desert sands and dusts are easily transported from one part to the other. This type of flowing away of sands and dust is called deflation. Deflation often creates dust storm in the desert.
Q.15: How are the sand dunes formed?
Ans: The formation of a dune begins with the transportation of sand grains by the wind. When these grains of sand are deposited in a certain area, they can form a small mound or hill.
As more and more sand is added to this mound, a dune begins to form. This process is called “saltation.”
The shape and size of dunes are determined by several factors, including the amount and size of sand grains available, the speed, direction, and frequency of the wind, and the presence of vegetation.
Q.16: What is inselberg?
Ans: The low erosional hills generally seen in the deserts are called inselberg The German term inselberg means isolated Island mountain.
Q.17: Define glacier and state how it differs from a river.
Ans: The extremely cold areas of the earth’s surface are under ice cover. Such areas include the polar and the high mountainous parts. Huge amount of ice in layers are there in these areas. These deposits of ice come down very slowly over the surface slope. Such moving ice down the slope is called glacier.
- The moving heap of snow and ice is called glacier.
- E.g.: gangothri glacier, yamunothri glacier
- flowing water is called river.
- E.g.: kaveri river, ganga river.
Q.18: What is moraine? Draw a diagram to show different types of moraine.
Ans: The materials carried down by a glacier other than ice are called moraine.
Moraines are four types: (i) lateral moraine, (ii) ground moraine, (iii) medial moraine, (iv) terminal or end moraine.
The moraines thus carried along the valley sides are called lateral moraine. On the other hand, moraines are also carried over the valley floor. These are called ground moraine. Again in certain places, two different glaciers may meet. Then the lateral moraines of the two glaciers may merge and flow along the middle of the large glacier. Such moraines are called medial moraine.
The glaciers coming down from the mountains gradually confront relatively warm climate and at certain level the glacial ice starts melting. The heavy materials get deposited on the spot where the glacial ice melts. The moraines deposited in the terminus of the glacier are called terminal or end moraine.
Q.19: Write how a glacial horn a formed.
Ans: A glacial horn is a feature created by glaciers and what exactly this term. It is also known as a pyramidal peak.
An arete is the edge that forms in the land from cirque erosion, or when two cirque glaciers form up against each other, creating that sharp edge. When more than two aretes meet, this is a horn.
The glacial channels are long with U-shaped cross profile. Due to the friction caused by the transported materials, the glacial channels become deep and steep sided. Several glaciers may flow down from some mountain. In such situation, the erosional activities on all sides of the mountain make its peak sharp and conical. Such peaks are called glacial horn. In the Alps and the Himalayas many such erosional horns are there.
Q.20: What is a coast?
Ans: The land margins of the oceans are called coast.
Q.21: What is a beach? State its importance.
Ans: A beach is a narrow, gently sloping strip of land that lies along the edge of an ocean, lake, or river. Materials such as sand, pebbles, rocks, and seashell fragments cover beaches. Most beach materials are the products of weathering and erosion. Over many years, water and wind wear away at the land.
Beaches provide protection to residents living near the ocean by acting as a buffer against the high winds and waves of powerful storms or rough seas.
Q.22: Write how sea-waves bring about change in the coasts.
Ans: Several exogenic processes operate in the coastal areas. Rainfall, wind and sea-waves are important among them. Out of these three again, the sea-waves constantly operate in the coastal areas and bring about re- markable change in the concerned areas. However, wave action is not similar everywhere.
Factors like geological structure, depth of the nearby sea, presence of rivers, wind action, coastal vegetal cover, etc. determine the nature and strength of wave action. The intensity of wave action is also determined by the earthquakes that occasionally occur in the ocean floor.
In the coastal areas, sea-waves remain constantly in action. Continuous waves action in the coast give rise to certain special features. If the coast is composed of hard works like granite and basalt, then the coast becomes steep due to wave action. Such steep coast is called sea-cliff.
On the other hand, a very convenient features is found to develop in the sea-shore where wave action causes systematic deposites of sands. This type of depositional feature is known as beach.
Sometimes, the earth movement in the sea floor produces devastating waves called Tsunami. This kind of suddenly created strong waves cause extensive change in the coastal landscape.
Anyway, the geographical scenario of the coastal areas is primarily the product of the wave action. It is mainly the wave actions that have created certain specific features in the sea coast.
Q.23: Think and write about the probable changes of the earth’ s surface in future.
Ans: The Earth’s surface has been constantly changing since its formation over 4.5 billion years ago. These changes have been driven by various natural processes, such as plate tectonics, erosion, and climate change. As we look into the future, it is essential to consider the probable changes that the Earth’s surface may undergo and how these changes might impact life on our planet. One of the most significant factors influencing the Earth’s surface is plate tectonics. The movement of tectonic plates causes the continents to drift, leading to the formation of new landmasses and the disappearance of others. In the future, it is expected that the continents will continue to move, eventually merging to form a new supercontinent.
This process, known as the supercontinent cycle, has occurred multiple times in Earth’s history, with the most recent supercontinent, Pangaea, breaking apart around 200 million years ago. The formation of a new supercontinent could lead to significant changes in global climate, ocean circulation, and biodiversity. Another critical factor shaping the Earth’s surface is climate change. As global temperatures continue to rise due to human activities, the polar ice caps are melting at an alarming rate.
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