CHANGE OF THE EARTH'S SURFACE
*Exogenic factors of change of the earth's surface
*Works of river
*Works of wind
*Works of glacier
*Sea- wave action
➤The surface of the earth is composed of continents (landmass)and oceans (hydrosphere).In the earth surface hydrosphere cover 71% and landmass cover 29%. Hydrosphere includes oceans and other water sources and continents includes plains, plateaus, hills, mountains,river valleys, deserts and coastal plains etc.
Q. What are exogenic forces ?
Ans: The exogenic forces operate from outside visibly. The exogenic forces include sunshine, wind, rainfall, river, glacier and sea-waves.
Q. What Endogenic forces?
Ans: The endogenic factors work in the earth's interior invisibly.It include mainly earthquake and volcanic eruption.These factors are generally responsible for making the land surface and the ocean bottoms irregular.
Q. What is river basin?
Ans: River basin is an area from where a river alongwith its tributaries carry water downward.
Q.What are the main Works of river?
Ans:River works in following ways:
a) Erosion
b) transportation
c) deposition.
a)Erosion: when a river flows down from highland, it naturally erodes the surface of the basin. Generally ,when the atmospheric moisture comes down to the earth in the form of rain,erosion begins over it.
b) Transportational works: Transportation is another work of a river. Generally, the salts present in the soil come into contact with river water and these are transported to the sea or ocean in dissolved state.
c) Deposititional Works: The rivers carries sediments and deposite it in the channels, banks and mouths.The materials that carried down by the rivers are deposited on the banks and the river mouths to form a variety of features.Among them sand bar, floodplain, natural levee and delta are important.
Q.How a river carries sediments?
Ans: A river carries sediments in the following ways:
a) Some are carried in dissolved state
b) some others in suspended state
c) other in rolling state over the channels.
Q. What is a river channel?
Ans: A river channel is the elongated path through which the river flows from source to mouth.
Q. What is hydraulic action?
Ans: The channel materials exposed to water flow come under the direct action of water. Such water action is known as hydraulic action.
Q. What is lateral erosion?
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 transperned from the highland begin to be deposited . As a consequence, the channel depth declines in the plains. Then the river starts widening its channel through lateral cutting just to maintain its normal flow. Then the river widens its channel to carry the water down by eroding.Such kind of river erosion is known as bank or lateral erosion.
1) Hydrosphere covers ____ percent of the earth's surface.
Ans: 71 percent.
2) Landmass or lithosphere covers ____ percent of the earth's surface.
Ans: 29 percent.
3) Write about features of earth's surface.
Ans: The earth's surface is covered with Hydrosphere and lithosphere. In the lithosphere or in the continents , plains , hills and mountains, river valleys ,deserts and coastal plains are found. Similarity, in the oceans submerged plateaus, plains , ridges , trenches, corel reefs are found.
4) Give two examples of exogenic factors.
Ans: sunshine, wind , rainfall, insolation, river , glacier, sea - waves.
5. Give two examples of endogenic factors.
Ans: earthquake and volcanic eruption.
6. Give a reason for what earthquake and volcanic eruptions occur?
Ans: Due to plate tectonic.
Q. Write two sources of exogenic factors?
Ans: sun and the earth's atmosphere.
Q. During which age, most parts of the earth's surface was remained under ice cover?
Ans: Ice age.
Q. Write two sources of rivers?
Ans: Rainfall, snow deposits over the mountains or springs coming out from the earth's interior.
Q. On what factors the erosive power of a river depends?
Ans : a) the structure of the basin surface,
b) hardness of the underlying rocks,
c) amount of water flow.
Q. What is meandering course?
Ans: The river course becomes zigzag when it flows over the gentle slopes slops of the plains.The lateral erosion makes the river course further zigzag.Such a zigzag course is called meandering course.
Q. What is horse - shoe lake?
Ans: In certain parts of the plain, the river channel may be highly meandering. Such a course fails to carry huge amount of water during summer. Then the river straightens its course leaving aside the most winding course. The cut-off part then takes the form of a lake or beel . Shaped like a horse-shoe, this type of lake is called horse-shoe lake.
Q. How a river carries sediments?
Ans: A river carries sediments in three different ways-
(a) some are carried in disolved state,
(b) some others in suspended state and
(c) other in rolling state over the channels.
Q. What is bed load?
Ans: Generally, the salts present in the soil come into contact with river water and these are transported to the sea or ocean in dissolved state. On the other hand, tiny particles of sand, mud and silt are transported by water current in suspended state and deposited on the river bed and banks. These are also transported to the oceans. Moreover, relatively big particles are transported down by current in rolling state. These materials are also called bed load. When the water gradually becomes weak over the plain the rolling loads get deposited over the river bed.
Q. Write some depositional features of a river.
Ans: sand bar, floodplain, natural levee, delta.
Q. What is floodplain?
Ans: As a result of long continued sediment deposition, alluvial plains are formed on both the banks. Such plains are called floodplain.
Q. Give an example of sandbar of the river Brahmaputra.
Ans: Majuli.
Q. What is natural levee?
Ans: The materials which deposited may take the shape of a long embankment . As it formed naturally it is called natural levee.
Q.
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