Volcanoes: Exploring Volcanoes and Their Impact on Earth

Volcanoes and volcanic landforms are captivating geological features that result from the Earth’s internal processes. Volcanic eruptions, driven by the release of molten rock, ash, and gases, shape the landscape, create new landforms, and, at times, pose significant natural hazards. The study of volcanoes and their associated landforams offers valuable insights into Earth’s dynamic nature and its potential for both destruction and creation.

• What defines a Volcano?: A volcano is a geological feature from which molten rock material, gases, ash, and other debris escape to the Earth’s surface. 
  • Earth’s Structure and Volcanoes: The Earth’s structure plays a pivotal role in the formation and activity of volcanoes. 
  • Mantle and Asthenosphere: Beneath the solid crust lies the mantle, denser than the crust. 
    • Within the mantle is a weaker, semi-fluid region called the asthenosphere. 
  • Magma Source: This is the source from which molten rock materials or Magma arise. 
  • Eruption Process: When magma moves towards or breaks through the Earth’s crust, it’s termed Lava.

Volcanic Landforms: Eruptions and Formative Materials

• The volcanic eruptions eject various materials, including:
  • Lava flows: Liquid magma that spills over the volcano’s rim.
  • Pyroclastic debris: Fragmented material produced by a volcanic blast.
  • Volcanic bombs: Large chunks of lava thrown out in an explosive eruption.
  • Ash and dust: Fine particles of volcanic rock and glass.
  • Gases: These can include nitrogen and sulphur compounds, and smaller quantities of chlorine, hydrogen, and argon.
  • The movement and ejection of these materials contribute to the diverse volcanic landforms found on the Earth’s surface.

What are the different types of Volcanoes and their characteristics?

Volcanoes are categorized based on the type of eruption they exhibit and the surface features they develop.

• Shield Volcanoes: These are among the Earth’s largest volcanoes, with famous examples like the Hawaiian volcanoes.
  • They are composed mainly of basalt, a fluid type of lava, making these volcanoes not very steep.
  • They generally have low-explosivity unless water enters the vent.
  • Lava, of these volcanoes,  emerges like a fountain, forming a cinder cone at the vent’s top.                                 

• Composite Volcanoes : They erupt cooler and more viscous lavas than basalt, leading to explosive eruptions that include large amounts of pyroclastic material and ashes. 
  • Accumulation of these materials near the vent forms layered structures, giving these volcanoes their “composite” name
  • Caldera: They are among the most explosive volcanoes. 
  • They tend to collapse post-eruption, forming depressions known as calderas.
  • The high explosiveness suggests large magma chambers close to the surface.       

• Flood Basalt Provinces: Such volcanoes emit highly fluid lava that can flow over vast distances. 
  • Some regions have extensive areas covered with thick basalt lava flows, with individual flows sometimes exceeding 50 m in thickness.
  • The Deccan Traps in India, covering much of Maharashtra, are a prominent example of a vast flood basalt province.
• Mid-Ocean Ridge Volcanoes
  • These volcanoes are observed in oceanic regions.
  • Central part of a vast system of mid-ocean ridges, spanning over 70,000 km across ocean basins, witnesses regular volcanic eruptions.

What are the Intrusive forms of Volcanic Landforms?

Intrusive Forms of Volcanic Landforms: 

• Lava to Igneous Rocks: The lava that is released during volcanic eruptions on cooling develops into igneous rocks.
• Cooling Locations: The cooling may take place either on reaching the surface or also while the lava is still in the crustal portion, contributing to the formation of various volcanic landforms.
• Volcanic and Plutonic Rocks: Depending on the location of the cooling of the lava, igneous rocks are classified as volcanic rocks (cooling at the surface) and plutonic rocks (cooling in the crust). 
  • The lava that cools within the crustal portions assumes different forms. 
• These forms are called intrusive forms.                                       
  • Batholiths: Magmatic material cools deep within the crust to form large domes known as batholiths, i.e. these are the cooled remnants of magma chambers.
    • Batholiths, often several kilometers deep, are granitic bodies that only appear on the surface after removal of overlying layers through denudational processes. 
  • Laccoliths: Laccoliths are underground formations resembling dome shapes, characterized by a flat underside and connected through a conduit, similar  to surface volcanic domes but positioned at greater depths. 
    • They act as localized origins of lava that can reach the surface. 
    • In the Karnataka plateau, numerous granite dome-shaped hills serve as examples of laccoliths or batholiths, showcasing the diverse nature of volcanic landforms.
  • Lapolith, Phacolith and Sills: 
    • Lava moving horizontally in weak planes can form saucer-shaped bodies called lapoliths. 
    • Wavy masses of intrusive rocks at the base of synclines or top of anticlines, connected to magma chambers, are termed phacoliths. 
    • Horizontal intrusive igneous rocks are classified as sills (thicker deposits) or sheets (thinner layers).
  • Dykes: Lava, on its way through cracks and the fissures of the land, when solidified almost perpendicular to the ground like a wall, is called Dyke. 
    • Found in abundance in western Maharashtra area, these are considered the eruptions that led to the development of the Deccan traps. 
    • The volcanic landforms resulting from these processes contribute to the diverse geological features of the region.