Structure of the answer:

• Meaning of volcano
  
  
• Mechanism and causes for its formation
  
  
• Distribution of volcano (with the help of data)
  
  
• Conclusion
  
  

Volcanos or vulcanism comprises of all phenomena connected with movement of heated material from interior/mantle towards the earth surface. The volcano may be “active volcano” like Mount Etna or “dormant volcano” like Mount Vesuvius or Extinct volcano that have no indication of future eruption.

Volcanos are mainly associated with the weaker zones of the earth and is a result of several interconnected processes, such as:

• Gradual increase of temperature with depth e.2-3 degree centigrade with every 100 meters.
  
  
• Reduction in pressure on magma due to splitting of the plates.
  
  
• Origin of gases and vapours due to heating of water (when it reaches underground surfaces of earth).
  
  
• Ascent of magma under forces of gases and vapours.
  
  
• “Theory of Plate tectonics” further lays down that volcanism is closely associated with plate boundaries. For ex.- When plate boundaries move in opposite direction like mid oceanic ridges causes splitting of plates and pressure releases. Similarly, destructive/ convergent plate boundaries are associated with explosive volcano.
  
  

Distribution of volcanos around the world: Generally, 80% of the volcanoes are located on the converging plate boundaries and 15% are located on constructive plate boundaries. On this basis there are three major belts of volcano---

• Circum-pacific belt: along the east and west coast of Pacific Ocean. This area is also called Pacific Ring of Fire because of many earthquake and volcanic eruptions. It starts from Mount Erebus of Antarctica-Andes-Rockies-Alaska-Japan to Indonesia. Ex- Mount Cotopaxi
  
  
• Mid Continental belt: where volcano mainly arises from convergence of continental plates and are explosives. Ex- Mount Kilimanjaro
  
  
• Mid Atlantic belt: where volcanic activities due to splitting of plates. Ex- Helena Mountains (Iceland)
  
  

Thus, on basis of above analysis it can be said that volcanic areas mainly arises from disturbance in earthly crust and have a profound impact on environment.