Class 7 Geography Chapter 3 Notes
Class 7 Geography Chapter 3 Notes notes pdf provide you with a basic understanding of our Changing Earth. Inside Our Earth. Class 7th Geography Ch 3 Our Changing Earth notes, we discuss Lithospheric plates, Volcano, Earthquakes, Earthquake Preparedness, Work of a River, Work of Sea Waves, Work of Sea Ice, and Work of Wind. Students can also download class 7 geography chapter 3 notes pdf for offline study.
Our Changing Earth Notes Class 7
Our Changing Earth Notes Class 7 pdf is a very interesting chapter in class 7 geography notes. If you searching for Our Changing Earth Class 7 Notes Geography Chapter 3 we provide that in this post.
The earth’s crust consists of several large and some small, rigid, irregularly-
shaped plates (slabs) which carry continents and the ocean floor. The lithosphere is broken into a number of plates known as the Lithospheric plates.
- These plates move around very slowly – just a few millimetres each year. This is because of the movement of the molten magma inside the earth. The molten magma inside the earth moves in a circular manner
- The movement of these plates causes changes on the surface of the earth.
- The earth’s movements are divided into two types on the basis of the forces which cause them.
- Endogenic forces- The forces which act in the interior of the earth are called Endogenic forces.
- Exogenic forces- The forces that work on the surface of the earth are called Exogenic forces
+ genic (origin)
= Endogenic Exogenic
Endogenic forces sometimes produce sudden movements like earthquakes and volcanoes causing mass destruction over the surface of the earth.
A volcano is a vent (opening) in the earth’s crust through which molten material erupts suddenly
when the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all around the earth. These vibrations are called earthquakes.
- Focus– The place in the crust where the movement starts is called the focus of an earthquake.
- Epicentre- The place on the surface above the focus is called the epicentre. The greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.
- Vibrations travel outwards from the epicentre as waves.
There are three types of earthquake waves:
- P waves or longitudinal waves
- S waves or transverse waves
- L waves or surface waves
Although earthquakes cannot be predicted, Some common earthquake prediction methods
adopted locally by people include studying animal behaviour; fish in the ponds get agitated, and snakes come to the surface.
Where to take shelter during an earthquake —
Safe Spot – Under a kitchen counter, table or against an inside corner or wall.
Stay Away from – Fireplaces, areas around chimneys, and windows that shatter including mirrors and picture frames.
Be Prepared – Spread awareness amongst your friends and family members and face any disaster confidently.
Major Land Form
The landscape is continuously worn away by two processes –
- Weathering– Weathering is the breaking up of the rocks on the earth’s surface.
- Erosion– 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 creates different landforms on the surface of the earth.
Work of a River
The work of a river is described in the following steps
- The running water in the river erodes the landscape.
- Waterfall– When the river tumbles at a steep angle over very hard rocks or down a steep valley side it forms a waterfall
- Meanders– As the river enters the plain it twists and turns to form large bends known as meanders.
- Ox-Bow lake– 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.
- Floodplain- 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.
- Levees- The raised banks are called levees.
- Distributaries– When the river reaches the sea, the speed of the flowing water decreases and the river begins to break up into a number of streams called distributaries.
- Delta- 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 give rise to coastal landforms.
- Sea Caves- Seawaves continuously strike at the rocks. Cracks develop. Over time they become larger and wider. Thus, hollow caves are formed on the rocks. They are called sea caves.
- Sea Arches- As these cavities become bigger and bigger only the roof of the caves remains, thus forming sea arches.
- Stacks- Further, erosion breaks the roof and only walls are left. These wall-like features are called stacks.
- Sea Cliff- The steep rocky coast rising almost vertically above sea water is called a sea cliff.
- Beaches- The sea waves deposit sediments along the shores forming beaches.
Work of Ice
Glaciers are “rivers of ice” which erode the landscape by bulldozing soil and stones to expose the solid rock below.
- Lakes- Glaciers carve out deep hollows there. As the ice melts they get filled up with water and become beautiful lakes in the mountains.
- Glacial Moraines- The material carried by the glacier such as rocks big and small, sand and silt get deposited. These deposits form glacial moraines.
Work of Wind
In the deserts, the wind is An active agent of erosion and deposition.
- Mushroom Rocks- 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 a narrower base and wider top.
- Sand Dunes- 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.
- Loess- When the grains of sand are very fine and light, the wind can carry them over very long distances. When such sand is deposited in large areas, it is called loess. Large deposits of loess are found in China.
Key Points for Class 7th Geography Chapter 3 Notes
seismograph- An earthquake is measured with a machine called a seismograph.
Endogenic forces: The forces that act in the interior of the earth are called endogenic forces.
Exogenic forces: The forces that act on the surface of the earth are called as exogenic forces.
Earthquake: The vibrations caused by the movement of the lithospheric plates are called earthquakes.
Focus: The place in the crust where the movement starts is called the focus.
Epicentre: The place on the surface above the focus is called the epicentre.
Weathering: The breaking up of the rocks on the earth’s surface is known as weathering.
Erosion: The wearing away of the landscape by different agents like water, wind and ice is called erosion.
Waterfall: A place where a river or stream falls from a high place for example over a cliff or rock is known as a waterfall.
Meander: Large bends formed by the twisting and turning of a river while entering a plain area known as meanders.
Floodplains: Floodplains are areas where fine soil and other material get deposited during floods. These are very fertile.
Levees: The raised banks of a river are known as levees.
Distributary: 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.
Delta: It is a triangular area of land where a river has split into many smaller rivers before entering the sea.
Sea caves: Sea caves are hollow-like caves formed on the rocks.
Sea arches: When the cavities become very big, only the roof of the caves remains known as sea arches.
Stacks: Further erosion breaks the roof and only wall-like features remain. These features are called stacks.
Seacliff: The steep rocky coast rising almost vertically above seawater is called a sea cliff.
Beaches: The sea waves deposit sediments along the shores to form beaches.
Mushroom rocks: In deserts, rocks in the shape of a mushroom are very common. These are called mushroom rocks.
Sand dunes: In deserts, when the winds stop blowing, the sand falls and gets deposited in low hill-like structures known as sand dunes.
Loess: When very fine and light grains of sand get deposited in large areas, it is called loess.
Richter scale- The magnitude of the earthquake is measured on the Richter scale. An earthquake of 2.0 or less can be felt only a little. An earthquake over 5.0 can cause damage from things falling. A 6.0 or higher magnitude is considered very strong and a 7.0 is classified as a major earthquake.
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