7th CBSE Notes on Our Changing Earth: Internal Movements

OUR CHANGING EARTH

05/10/2022

OUR CHANGING EARTH

Internal Movements

Date: 05/10/2022 Day : Wednesday

Que : Explain the Continental drift theory ?

Answer : 

1.  The splitting of the huge landmass into seven big continents is known as the theory of continental drift
2. In the year 1915, a German meteorologist and geophysicist Alfred Wagener introduced the theory of continental drift to describe and partially explain the present arrangement of continents and ocean basins.
3. He proposed that 200 million years ago there was a supercontinent called Pangaea 
4. The Pangaea was surrounded by large water body is called Panthalassa.
5. A long shallow inland sea called the Tethys Sea divided Pangaea into two massive blocks
6. Northern block is called Laurasia or Land of Angara
7. Southern part is called Gondwana
8. As year pass the Pangaea was broken into several pieces called plates due to internal pressure and temperature of the earth 
9. It took millions of years for the continents to reach the present shapes and positions on the globe.

Que : Explain lithospheric plate with plate tectonics?

Answer : 

1. All the continents and even the oceans are actually situated on massive rigid slab of solid base of rocks called Lithospheric ‘Plates’ or Tectonic plates
2. The word " Tecton" is derived from the Greek, means "Build"
3. There are seven major plates and several minor plates.
4. These plates actually ‘float’ on the mantle due to circular movement of molten magma
5. These plates constantly being pushed a few mm for each year and started drifting each other.
6. The region where the two plates meet and push each other, a lot of pressure is exerted by each of them on the other.
7.  One plate is pushed under the mantle while the other plate is pushed up to form a chain of mountains. 
8. This movement of plates is called ‘Plate Tectonics'. 
9. This process can also cause the sudden movement like earthquakes etc.

Que : What is an Earthquake ?

Answer : 

1. An earthquake is the sudden shaking and trembling of the earth. 
2. This shaking and trembling causes the movement of a series of shock waves on the earth’s surface 
3. That results in widespread destruction

Que : What is a Volcano ?

Answer : 

A vent or an opening in the earth’s crust that allows hot molten lava, ash and gases to escape from below the surface is called a volcano

Que : How are Endogenic forces classified ?

Answer : 

The Endogenic forces is the Geological forces that occur beneath the surface of the earth 

It is associated with the energy originated in the interior of the solid earth

The endogenic force can be classified in the following ways

Que : How are Volcanoes classified on the basis of the frequency of eruption ?

Answer : 

Based on the frequency of eruption or activity displayed, volcanoes can be categorized into three types as follows

Active Volcanoes	Dormant Volcanoes	Extinct Volcanoes
Active volcanoes are those that erupt regularly.	Dormant volcanoes are volcanoes that have not erupted for many years but have the potential to erupt again	Extinct volcanoes are those that have not erupted in thousands of years and show no signs of eruption in the future as well.
Mauna Loa, an active volcano located in the Pacific Ring of Fire in the Hawaii Islands, is the world’s largest volcano in terms of height as well as mass.	Mt. Vesuvius in Italy is an example of a dormant volcano It last erupted in 1944.	Mt. Kilimanjaro is an extinct volcano

Que : How does the Richter scale indicate the intensity of an earthquake ?

Answer : 

1. The recordings from a seismograph, when interpreted through the Richter scale, indicate the intensity of an earthquake. 
2. The Richter scale has a range of 0–9. 
3. The readings on the Richter scale start from 3.5 because people can hardly feel earthquakes that measure 2.0 or less on the Richter scale. 
4. An earthquake of over 5.0 can cause distinct tremors that can make things fall. 
5. A really strong earthquake measures at 6.0 or higher on the scale. 
6. However, an earthquake that measures 7.0 on the Richter scale is classified as a major earthquake. 

Que : What precaution to be taken to avoid much damage from earthquake? 

Answer : 

1. In highly seismic areas, the use of mud or timber is better than heavy construction material.
2. Keep roofs as light as possible.
3. It is better if the cupboards and shelves are fixed to the walls,
4. Avoid hanging wall clocks, photo-frames, geyser etc.
5. Leave your building and move to open areas if you are outside the home during earthquake.
6. Drop down onto your hands and knees before the earthquake knocks you down during earthquake.
7. Standing against the corner of a wall inside a building
8. Take shelter under a steady table and stay there till shaking stops
9. Keep away from high rise buildings, trees, signboards, electric poles.
10. If you are in a vehicle, remain inside it.
11. Spread awareness through drills, about the safety measures to be follow before and after earthquake.