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Volcanoes, volcanism, Distribution of Earthquakes and Volcanoes across the World

Volcanoes, volcanism, Distribution of Earthquakes and Volcanoes across the World

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  • GS 1 || Geography || Geomorphology || Volcanoes

What is a volcano?

  • A volcano is a vent or fissure in Earth’s crust through which lava, ash, rocks, and gases erupt. An active volcano is a volcano that has erupted in the recent past. The mantle contains a weaker zone known as the asthenosphere. Magma is the material present in the asthenosphere.

Causes of Volcanism- Difference in Temperature

Major types of volcanoes

  • Volcanoes are classified on the basis of nature of eruption and the form developed at the surface.
    • Shield Volcanoes:The Shield volcanoes are the largest of all the volcanoes on the earth, which are not steep. These volcanoes are mostly made up of basalt. They become explosive if in some way water gets into the vent, otherwise, they are characterized by low explosivity. Eg: Hawaiian shield volcanoes
    • Composite Volcanoes: Composite Volcanoes are characterized by outbreaks of cooler and more viscous lavas than basalt. They are constructed from numerous explosive eruptions. The major composite volcano chains are the Pacific Rim which is known as the “Rim of Fire”.
    • Caldera: Calderas are known as the most explosive volcanoes of Earth. They are generally explosive in nature. When they erupt, they are inclined to collapse on themselves rather than construct
    • any structure. The collapsed depressions are known as calderas.
    • Flood Basalt Provinces: Flood Basalt Province volcanoes discharge highly fluid lava that flows for long distances. Many parts of the world are covered by thick basalt lava flows.
    • Mid-Ocean Ridge Volcanoes: These volcanoes are found in oceanic areas. There exists a system of mid-ocean ridges stretching for over 70000 km all through the ocean basins. The central region of this ridge gets frequent eruptions.

Distribution of Earthquakes and Volcanoes across the World

  • Most known volcanic activity and earthquakes occur along converging plate margins and mid-oceanic ridges. Nearly 70 percent of earthquakes occur in the Circum-Pacific belt.
  • Another 20 percent of earthquakes take place in the Mediterranean-Himalayan belt including Asia Minor, the Himalayas, and parts of north-west China.
  • Since the 16th century, around 480 volcanoes have been reported to be active. Of these, nearly 400 are located in and around the Pacific Ocean, and 80 are in the mid-world belt across the Mediterranean Sea, Alpine-Himalayan belt, and in the Atlantic and Indian Oceans.
  • The belts of highest concentration are Aleutian-Kurile islands arc, Melanesia , and New Zealand-Tonga belt.
  • Only 10 percent to 20 percent of all volcanic activity is above the sea, and terrestrial volcanic mountains are small when compared to their submarine counterparts.

Volcanism in India

  • There are no volcanoes in the Himalayan region or the Indian peninsula. Barren Island (only active volcano in India) in the Andaman and Nicobar Islands became active in the 1990s. It is now considered an active volcano after it spewed lava and ash in 2017.
  • The other volcanic island in Indian territory is Narcondam, about 150 km north-east of Barren Island; it is probably extinct. Its crater wall has been destroyed.

Active and  Extinct volcanoes

References