SEBA Board Solution Class 9 Geography Chapter 1 Change of The Earth’s Surface
SEBA Board Solution Class 9 Geography Chapter 1 Change of The Earth’s Surface full exercise Solution by Computer Sir. Here in this page we have provided SEBA – The Board Of Secondary Education, Assam Class 9 Geography Chapter 1 all Question Answer Solution.
SEBA Board Solution Class 9 Geography Chapter 1: Overview
Board |
SEBA / Assam State Board |
Class |
9 |
Subject |
Geography |
Chapter Number |
1 |
Chapter Name |
Change of The Earth’s Surface |
Topic |
Solution |
1.) Give an outline of the distribution of continents and oceans of the world.
Ans.
The earth’s surface consists of both landmass or continents and hydrosphere or oceans.The continents consist29%of the total earth’s surface The landmass is distributed in different forms like mountains, plains, river valleys, plateaus, deserts and coastal plains. The oceans cover 71% of the earth’s surface. These are distributed in different forms like rivers, ponds, lakes, waterfalls, oceans etc.Many plateaus, trenches, ridges are also found on the ocean floor.
2.) Explain why there has been change over the earth’s surface.
Ans.
There are various features on the earth’s surface like continents, plains, plateaus, hills, rivervalleys, deserts etc.All these features are result of some type of processes like weathering, erosion, deposition, landslide, sea-waves etc which are taking place continuously. Moreover, there arebiotic elements like animals and vegetations also. These factors change the physical and chemical ingredients of the earth and bring about the changes on the surface of the earth forming and modifying the face of the earth. These are exogenic forces of the earth. The endogenic forces like volcanoes, earthquakes also change the surface of the earth.
3.) What is meant by exoganic factor? Mention some exogenic factors.
Ans.
There are two types of forces that cause changes on the surface and shape of the earth.They are called exogenic and endogenic forces. The exogenic forces cause changes on the outside. The exogenic forces are sunlight, rainfallwind, river, glacier, sea-waves.
4.) Why are earthquakes and volcanic eruption called endogenic factors.
Ans.
Earthquakes and volcanic eruptions take place inside the surface of the earth and bring about changes in the shape of the earth and also inside the depth of the ocean. These forces cause unevenness on the surface of the earth and make the ocean-beds irregular in. Thus, these are called as endogenic forces.
5.) What do you mean by a river basin? Draw a diagram of a river basin.
Ans.
River Basin-A River in its course makes various types of features like estuary, river-basin, delta, meander etc. A river basin is that area of land in which a river flows through a river system, it is an area which is drained by the river and its tributaries. The water flows through all the tributaries and gets into the main river and then finally flows into the ocean and seas. River basins are created by all rivers through erosion, transportation and deposition work.
DIAGRAM OF A RIVER BASIN:
6.) What is a tributary? Name two major tributaries of the Brahmaputra.
Ans.
Tributary – The smaller streams of river which flow into the main river and increase the volume of the water of the main river is called as the Tributary. The two major tributaries of the Brahmaputra are the Dhanasiri, Jiabharali
7.) Give an outline of river erosion.
Ans.
The river acts as an erosional agent, its sources of river water like rainfall, snow etc also act as erosional agent. The rain water when flows it starts eroding the top soil of the earth’s surface.The snow when melts and moves starts eroding the surface of the earth in its course. Theerosion work of the river also depends on thesurface of the river basin, the hardness of the rock under the water and amount of the water flowing in the river.
8.) What do you mean by latersal erosion of a river?
Ans.
The river works as an erosional agent. This erosion starts from the upper course and continues till it reaches its mouth. The river slows down as it reaches to the lower course, the slope of the plain reduces and the sediments that were carried by the river gets deposited. The width of the riverincreases as it cuts the sides of its bank to flow. This erosional work of the river by cutting its banks and widening of its channel creates ‘U’ shaped or ‘V ‘shaped valleys. This kind of erosion activity of the river is known as bank or lateral erosion.
9) What is ox-bow lake? Draw diagram to show how it is formed.
Ans.
Ox-bow lake- The Ox- Bow Lake or the Horse-Shoe Lake is result of the erosional activity of the river in its middle course. As the river flows in its middle course, it starts flowing in zigzag mannermaking a meander like formation. When this meander becomes very extensive, the river makes a ‘S’ like shape. The river is unable to carry large amount of water due to its meander like movement especially during summer. It starts to flow in a straight manner and leaves behind a curved feature in its course. This curved feature becomes a lake in a shape of a horse -shoe or an ox-bow. Thus, in this manner an Ox-Bow Lake is formed. Ex- Rivers like Brahmaputra and the Barak of Assam have created many ox-bow lakes.
FORMATION OF OX-BOW LAKE
10.) What is floodplain? Write how it is formed.
Ans.
The river does depositional work in its middle and lower course. All the sediments that the river brings along with itself from the upper course starts getting deposited inthe banks of the river in its middle and lower course. This continuous deposition of the sediments creates alluvial plains on both side of the banks.Theseplains are called as Flood Plains. During floods, sands, silt and mud are carried by the river and are spread into the river banks. These floodplains are very fertile and suitable for the cultivation of crops. Rivers like Brahmaputra, Ganga, Indus, Nile, Amazon make extensive floodplains.
11.) Write how and where sandbars are formed in a river channel.
Ans.
Sandbars are formed due to depositional work of the river in its middle and lower course. The sediments like sand, silt and gravel are deposited by the river and forms the sandbars. Sandbars are formed in the middle of the river and also on both the sides of the river beds. The sand bars are long and narrow in size and are temporary formation. The speed of the river affects the shape and size of the sandbars. The erosion of the river banks moves the sandbars. They are mostly visible during the winter when the river has less water and speed is also slow and its capacity to carry sediments is also less. Many sandbars are found in the Brahmaputra River.
12.) How are the deltas formed?
Ans.
The river when reaches its lower course its speed goes down and the capacity to carry the sediments also reduces.As the river reaches its mouth, it starts depositing the load of sediments in the shallow sea into which it flows ultimately.The deposits by the river build a conical shaped feature known as Delta. The Delta looks like the Greek letter Δ. Many rivers like the Ganga, the Brahmaputra, the Nile, the Mississippi etc form delta in their mouths. The Sunderban Delta formed by the river Ganga and the Brahmaputra is the world’s largest delta.
13.) Write why the wind action is strong in the deserts.
Ans.
In the desert areas wind has three activities, erosion, transportation and deposition.The wind blows very strongly in the deserts. The natural vegetation is very little in the deserts so the wind can act easily on them without muchobstruction, sand and dust gets easily transported from one place to another. Deserts have dry weather which is why the sandy soil is always dry. This helps the erosional activity of the wind.
14.) What is meant by deflation?
Ans.
The sand, silt, dust particles are blown by the wind from one place to another in the deserts. The blown away items are again deposited in another place. This continuous processof blowing away of sand and dust is called Deflation. Deflation causes desert storms. Deflation also causes depressed areasfrom where sand and dust are blown. This depression areas create temporary lakes which are deep in size.
15.) How are the sand dunes formed?
Ans.
The sand, dust and silt which get transported from one place to another in the deserts due to deflation gets deposited in some places. When the blowing wind gets obstructed by bushes, rocksetcits speed gets slow and the sand and silt start getting deposited on a particular place.This is a continuous process and slowly the land gets heightened gradually and hill like structures are formed. These hills of sand and silt are called Sand Dunes. The size and shape of the sand dunes get affected by the path, flowand strength of the wind blowingand nature of the place.The sand dunes are locally known as Barchans.
16.) What is inselberg?
Ans.
Inselberg- The term is derived from German language meaning isolated island mountain. This feature is found in deserts. An Inselberg is formed due to the abrasion of the steep and high hills. When continuous erosion of low-lying area takes place,a steep-sided hill of solid hard rocklike granite rises upward. These are called INSELBERG. These are steep and dome -shaped cap made of hard rocks. Inselbergs are very common features of white desert of Egypt.
17.) Define glacier and state how it differs from a river.
Ans.
The areas like polar regions and high mountains are mostly under huge layers of ice. These deposits of ice move very slowly on the land surface as sheets of ice. This moving ice coming down from the mountain valleys like rivers and are known as GLACIERS. The glaciers also work as erosional, depositional and transportationagent.
Difference between River and Glacier:
GLACIER | RIVER |
Glacier is sheet of ice. | River is a stream of water. |
The Glacier moves in the mountain valleys. | The river starts from mountains, travels through plains and reaches the sea. |
Glaciers are found only in high mountains and polar regions. | Rivers are found in all parts of the world. |
18.) What is moraine? Draw a diagram to show different types of moraine.
Ans.
Moraines- Glaciers also work as erosional and depositional and transportation agent. Glaciers carry lot of sediments along with ice. These sediments get deposited and transported by the glacier along -with ice. These deposits take the shape of long range of hills of rock piles, clay etc. Moraines are four types: a. Lateral Morain, b. Ground moraine, c. Medial moraine, d. Terminal moraine.
DIAGRAM OF MORAINE:
19.) Write how a glacial horn is formed.
Ans.
Glacial Horn- The glaciers flow from different mountains at the same time. The erosion of the mountain peaks and its sides of the mountains take place in large amount due to the continuous movements of the glaciers. The peaks get sharper and more conical in shape. These conical shaped peaks are called as Glacial Horns. The Glacial Horns are found in the Alps and the Himalayas.
20.) What is a coast?
Ans.
The area of land beside the oceans are called the Coast. The winding line along the coast which is present acts as a contact between the ocean and the land is called the coast line.
21.) What is a beach? State its importance.
Ans.
The plain which develops beside the sea shore which experiences continuous waves. The continuous flow of waves deposits large quantity of sands. This deposit slopes towards the sea and is known as the Beach. These beaches consist of fine sand particles and small pebbles. The long beaches attract huge number of tourists which is beneficial for the development of economy of the country
22.) Write how sea-waves bring about change in the coasts.
Ans.
Sea waves are exogenic force which work as erosional, transportation and depositional agent. The sea waves work continuously and cause different changes in the coastal areas. Different features which are created by the sea -waves are Sea-Cliffs, Beaches etc.
Sea -Cliffs – When the coast is made of hard rocks like granite and basalt, the coast line becomes very hard due to the continuous sea waves flowing on these hard rocks. The solid coast becomes steep and moves up vertically as a result of erosional work of the waves and are called as Sea-Cliffs.
Beaches – The plain which develops beside the sea shore which experiences continuous waves. The continuous flow of waves deposits large quantity of sands. This deposit slopes towards the sea and is known as the Beach. These beaches consist of fine sand particles and small pebbles.
Apart from these features, the sea waves also cause destruction like Tsunami which is caused by the earthquake in the sea floor. The waves caused by the Tsunami are of huge heights and cause tremendous sound. These waves break down the coastline and cause devastation on the coastlines.
23.)
24.) The humans have been exploiting the earth and her resources for several years. Initially when the need was simple the relation with the earth and nature was in balance. As humans developed, they started to live a settled life and their requirements also increased. The balance started to break. Activities like deforestation for making settlements, agriculture, mining of minerals startedin extensive way. These activities started to disturb the balance of ecology. The technology and its advancements and usage by the humans have further deteriorated the situation. Exploration of ocean life, climate engineering etc activities which are carried out by humans without much consideration about the consequences are causing significant changes to the planet. The global warming, melting of ice sheets, changes in climate, burning of forests due to excessive heat, scarce rainfall are the causes that can lead to the extinction of human race and the planet earth may gradually go into evolution resulting in restoration of the original natural environment which is not disturbed by human intervention.
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