Short Notes - Geographical Phenomena

Category : UPSC


Geographical Phenomena


Plate Tectonics

  • The theory of plate tectonics states that lithosphere consists of several individual segments called plates.
  • Major Plates on Earth are.

(i) Antarctic plate

(ii) North American and South American

(iii) Pacific plate                      

(iv) Indian - Australian - New Zealand plate

(v)Africa/Eastern Atlantic Plate

(vi) Eurasian plate

  • Pacific plate is the largest plate while Juan de Fucaplate (off Western coast of North America) is the smallest. -\
  • The collision of the Indian plate against the Eurasian plate, leading to the formation of the Himalayas.



  • An earthquake is basically the vibration of Earth produced by rapid release of energy, along a fault.
  • Focus: Place of occurrence of anEarthquake inside the earth, where the energy is released. The ground ruptures at this spot, then seismic waves radiates outward in all direction.
  • Epicenter: The point on the earth's surface is located directly above the focus of an earthquake.
  • Seismic sensors called Seismographs, are located throughout the world can record the event.
  • Earthquake waves: Earthquakes generate pulses of energy called Seismic waves that can pass through the entire Earth. These are –
  1. Primary (P) Waves: These waves travel both through solid crust and mantle and liquid part of the Earth's core.
  2. Secondary (S) waves: Travels only through solid parts of the Earth.
  3. Long (L) Waves: It is confined mostly to the skin of the Earth's crust, thereby, causing most of the structural damage.
  4. The magnitude as the intensity of energy released by an earthquake is measured by Richter scale. It ranges between 0 and 9.

Seismic Zones of India-

India is divided into 5 seismic zones.

  • Zone 1 - Intensity V or below
  • Zone 2 - Intensity VI
  • Zone 3 - Intensity VII
  • Zone 4 - Intensity VIII
  • Zone 5 - Intensity IX and above


  • A volcano is an opening or rupture in planet's crust through which hot magma, volcanic ash and gases escape from the magma chamber below the surface.
  • Volcanic eruptions cause earthquakes when they erupt and sometimes earthquakes can cause volcanic eruptions.They mainly happen by the edges of tectonic plates.


Products of Volcanic eruption

  • Ash
  • Flying Rocks
  • Poisonous gases
  • Lava
  • Pyroclastic flows
  • Floods and Mudslides


Active Volcanoes

On the basis of frequency of eruption the volcanoes can be divided into-

Active volcano: It has the capacity to erupt at regular basis and its frequency is quite more.

Dormant volcano: Though it has the capacity to erupt but frequency of eruption is almost nil.

Inactive volcanos don't have the capacity to erupt.


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