Tuesday, 13 January 2015

Geography - Our Changing Earth

                          Our Changing Earth
What is Lithospheric plates ?
  • The lithosphere broken in to a number of plates knows as the lithosperic plates.
  • The earth's crust consists of several large and some small rigid, irregularly-shaped plates (slabs) which carry continents and the ocean floors.
  • These plates move around very slowly just a few millimeters 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 movements are divided on the basis of the forces which cause them.
What is Endogenic forces ?
The forces which act in the interior of the earth are called as endogenic forces.

What is Exogenic forces?
The forces that work on the surface of the earth are called as exogenic forces.

Endogenic forces sometimes produce sudden movements and at the other times produce slow movements. Sudden movements like earthquakes and volcanoes cause mass destruction over the surface of the earth.

What is Volcano ?


A volcano is a vent in the earth's crust through which molten material erupts suddenly.    

What is Earthqukes ?
When the lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all round the earth, these vibrations are called earthquakes.

What is focus?
The place inside the crust where the movement starts is called the focus.

What is Epicentre?
The place on the surface above the focus is called the epicentre.
Vibration travels outward from the epicentre as waves.
Greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the Centre. 

How many types of Earthquake waves?
  1. P waves or longitudinal waves 
  2. S waves or transverse waves
  3. L waves or surface waves

  • An earthquake is measured by a device called seismograph.
  • The magnitude of the Earthquake is measured on the Richter scale.
  • An earthquake of magnitude 2.0 or less can be felt a little.
  • An earthquake of magnitude 5.0 can cause damage from things falling.
  • An earthquake of magnitude 6.0 or more is considered very strong.
  • And earthquake of magnitude 7.0 or more is classified as a major earthquake . 
Source - NCERT

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