UP PCS Mains-2024

Introduction

A volcano is a place where gases, ashes, and molten rock material lava escape to the ground. A volcano is called an active volcano if the materials mentioned are being released or have been released in the recent past.

The layer below the solid crust is the mantle. It has a higher density than that of the crust. The mantle contains a weaker zone called the asthenosphere. It is from this that the molten rock materials find their way to the surface. The material in the upper mantle portion is called magma. Once it starts moving towards the crust or it reaches the surface, it is referred to as lava.

Body

Classification of volcanoes:

• Based on frequency of Eruption:
  • Active volcanoes: They erupt frequently and are mostly located around the Ring of Fire.
    • For example, Mount Stromboli is an active volcano, and it produces so much of Gas clouds that it is called the Lighthouse of the Mediterranean.
  • Dormant Volcanoes: These are not extinct but have not erupted in recent history. The dormant volcanoes may erupt in the future.
    • For example, Mount Kilimanjaro, located in Tanzania also the highest mountain in Africa is known to be a dormant Volcano.
  • Extinct or inactive volcanoes have not erupted in distant geological pasts. In most cases, the crater of the Volcano is filled with water making it a lake.
    • For example, Deccan Traps, India.
• Based on the nature of the eruption and the form developed at the surface:
  • Shield Volcanoes: These volcanoes are the largest of all the volcanoes on the earth. These volcanoes are mostly made up of basalt, a type of lava that is very fluid when erupted. For this reason, these volcanoes are not steep. They become explosive if somehow water gets into the vent, and they are characterized by low explosivity. The upcoming lava moves in the form of a fountain and throws out the cone at the top of the vent and develops into a cinder cone.
    • The Hawaiian volcanoes are the most famous examples.
  • Composite Volcanoes: These volcanoes are characterized by eruptions of cooler and more viscous lava than basalt. These volcanoes often result in explosive eruptions. Along with lava, large quantities of pyroclastic material and ashes find their way to the ground. This material accumulates in the vicinity of the vent openings leading to formation of layers, and this makes the mounts appear as composite volcanoes.
  • Caldera: These are the most explosive of the earth’s volcanoes. They are usually so explosive that when they erupt, they tend to collapse on themselves rather than building any tall structure. The collapsed depressions are called calderas. Their explosiveness indicates that the magma chamber supplying the lava is not only huge but is also in close vicinity.
  • Flood Basalt Provinces: These volcanoes outpour highly fluid lava that flows for long distances. Some parts of the world are covered by thousands of square km of thick basalt lava flows. There can be a series of flows with some flows attaining a thickness of more than 50 m. Individual flows may extend for hundreds of km.
    • The Deccan Traps from India, presently covering most of the Maharashtra plateau, are a much larger flood basalt province.
  • Mid-Ocean Ridge Volcanoes: These volcanoes occur in oceanic areas. There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins. The central portion of this ridge experiences frequent eruptions.
• Areas that are prone to volcanic eruption:
  • Ring of Fire: It is a path along the Pacific Ocean characterized by active volcanoes and frequent earthquakes. The majority of Earth’s volcanoes and earthquakes take place along the Ring of Fire. It is also referred to as the Circum-Pacific Belt.
  • Mount Cotopaxi: It is an active stratovolcano in the Andes Mountains, located in Ecuador. It is because of the convergence of the Nazca Plate and South American Plate, where the Nazca Plate is subducting below the South American Plate.
  • Mount Merapi: It is Indonesia’s active volcano on Java Island, it is erupting because of the convergence of the Indian Australian Plate and the Pacific Plate. Other volcanoes such as Mount Semeru and Mount Bromo are also located in Indonesia.
  • Sakurajima: It is one of Japan’s most active volcanoes and eruptions of varying levels take place on a regular basis. It is because of the convergence of the Eurasian Plate and Pacific Plate.
  • Mount Etna: It is the highest Mediterranean island mountain and the most active stratovolcano in the world. The volcano sits on the edge of a convergent plate boundary between the Eurasian Plate and the African Plate.
  • Mount Nyiragongo: It is part of the Virunga volcanic chain and owes its existence to the activity of the African Great Rift. It sits above the point where the African plate is moving apart.

Conclusion

Thus, volcanoes are closely related to the regions of intense folding and faulting, they occur along coastal mountain ranges, on islands, and in the mid oceans. Interior parts of the continent are generally free from their activity, most of the active volcanoes are found in the Pacific region.