WELCOME TO OUR SOCIAL SCIENCE PRESENTATION�Part- Two
��GEOGRAPHY �OUR ENVIRONMENT�CLASS – VII, CHAPTER – 03�OUR CHANGING EARTH
Prepared by:-
Kapil Rawani
TGT ( Social Science)
Mobile no:- 8280283168
Email id:- warrior.kapil@gmail.com
JNV Durgapur, Burdwan
West Bengal, PATNA REGION
OUR CHANGING EARTH
Good morning dear students,
I am again with you. In our previous class we were discussing about the topic OUR CHANGING EARTH, where we have discussed some points like, exogenic and endogenic forces, Earthquake, Volcanic eruption and some more points about the internal forces of the earth.
In our todays session we are going to discuss about the forces and happenings which are responsible for changing the earth externally
MAJOR LAND FORMS
The landscape is being continuously worn away by two processes – weathering and erosion. Weathering is the breaking up of the rocks on the earth’s surface. Erosion is the wearing away of the landscape by different agents like water, wind and ice. The eroded material is carried away or transported by water, wind, etc. and eventually deposited. This process of erosion and deposition create different landforms on the surface of the earth.
WORK OF A RIVER
The running water in the river erodes the landscape. When the river tumbles at steep angle over very hard rocks or down a steep valley side it forms a waterfall
WORK OF A RIVER
As the river enters the plain it twists and turns forming large bends known as meanders. Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer. In due course of time the meander loop cuts off from the river and forms a cut-off lake, also called an ox-bow lake. At times the river overflows its banks. This leads to the flooding of the neighbouring areas. As it floods, it deposits layers of fine soil and other material called sediments along its banks. This leads to the formation of a flat fertile floodplain. The raised banks are called levees.
WORK OF A RIVER
As the river approaches the sea, the speed of the flowing water decreases and the river begins to break up into a number of streams called distributaries. The river becomes so slow that it begins to deposit its load. Each distributary forms its own mouth. The collection of sediments from all the mouths forms a delta.
WORK OF SEA WAVES
The erosion and deposition of the sea waves gives rise to coastal landforms. Sea waves continuously strike at the rocks. Cracks develop. Over time they become larger and wider. Thus, hollow like caves are formed on the rocks. They are called sea caves. As these cavities become bigger and bigger only the roof of the caves remain, thus forming sea arches. Further, erosion breaks the roof and only walls are left. These wall like features are called stacks. The steep rocky coast rising almost vertically above sea water is called sea cliff. The sea waves deposit sediments along the shores forming beaches.
Sea arch
Sea cave
Stack
WORK OF ICE
Glaciers
Glaciers are “rivers” of ice which too erode the landscape by bulldozing soil and stones to expose the solid rock below.
Glaciers carve out deep hollows.
As the ice melts they get filled up with water and become beautiful lakes in the mountains. The material carried by the glacier such as rocks big and small, sand and silt gets deposited. These deposits form glacial moraines.
WORK OF WIND
An active agent of erosion and deposition in the deserts is wind. In deserts you can see rocks in the shape of a mushroom, commonly called mushroom rocks. Winds erode the lower section of the rock more than the upper part. Therefore, such rocks have narrower base and wider top. When the wind blows, it lifts and transports sand from one place to another. When it stops blowing the sand falls and gets deposited in low hill – like structures. These are called sand dunes When the grains of sand are very fine and light, the wind can carry it over very long distances. When such sand is deposited in large areas, it is called loess. Large deposits of loess is found in China.
Sand dunes
RECAPITULATION
HOME WORK
1. What is erosion?
2. How are flood plains formed?
3. What are sand dunes?
4. How are beaches formed?
5. What are ox bow lakes?
Give reasons.
(i) Some rocks have a shape of a mushroom.
(ii) Flood plains are very fertile.
(iii) Sea caves are turned into stacks.
(iv) Buildings collapse due to earthquakes.
THANKING YOU
Prepared by:-
Kapil Rawani
TGT ( Social Science)
Mobile no:- 8280283168
Email id:- warrior.kapil@gmail.com
JNV Durgapur, Burdwan
West Bengal, PATNA REGION