Intrusive and Extrusive Volcanic Landforms: Types and Formation

There are diverse geological features created by volcanic activity, these are collectively known as volcanic landforms. They include volcanoes, lava flows, ash deposits, volcanic cones, and calderas. These features result from the eruption of magma onto the Earth’s surface or its intrusion beneath the surface. Volcanic landforms can vary widely in size, shape, and composition, and they play a significant role in shaping the Earth’s surface and influencing local ecosystems.

Common Types of Volcanic Landforms 

Common Types of Volcanic Landforms are mentioned below:

A. Intrusive Landforms

• Depending on the location of the cooling of the lava, igneous rocks are classified below,
• Volcanic Rocks: These rocks cool at the surface.
• Plutonic Rocks: These rocks cool within the crust.
• Intrusive Forms: The lava that cools within the crustal portions assumes different forms.                                 
• Batholiths: Magmatic material cools deep within the crust to form large domes known as batholiths (granite bodies).
  • They are the cooled remnants of magma chambers.
• Lacoliths: Lacoliths are underground formations resembling dome shapes.
  • Characterised by a flat underside and connected through a conduit, 
  • Similar to surface volcanic domes but positioned at greater depths; Found in the Karnataka plateau. 
• Lapoliths: Lava moving horizontally in weak planes can form saucer-shaped bodies called. 
• Phacolith: Wavy masses of intrusive rocks at the base of synclines or top of anticlines, connected to magma chambers.
• Sills and Sheets: Horizontal intrusive igneous rocks are classified as sills (thicker deposits) or sheets (thinner layers).
• Dykes: Lava solidified almost perpendicular to the ground like a wall; found in abundance in the western Maharashtra area.

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B. Extrusive Landforms

• Extrusive Landforms: Landforms which are determined by the nature and composition of lava and other ejected materials which reach the surface of the earth.
• Volcanic Cones: Volcanic cones are mound-shaped landforms that build up around a volcanic vent or crater as a result of the accumulation of lava, ash, and volcanic debris during eruptions.
  • These are most typical of extrusive volcanic landforms.

• Lava Plateau: A lava plateau, also known as a volcanic plateau or basalt plateau, is a type of large, nearly flat or gently sloping landform that is primarily created by the accumulation of lava flows over a wide area.
  • These landforms are typically the result of effusive volcanic eruptions, where low-viscosity basaltic lava erupts from long fissures or cracks in the Earth’s crust, allowing the lava to spread out over a broad region.
  • Example:  Deccan Lava Plateau, Snake  Basin USA  
• Craters and Caldera: Volcanic craters are bowl-shaped depressions at the summit of a volcano, created by a combination of volcanic activity and geological processes.
  • When this crater is filled with water, it becomes a crater lake, such as Crater Lake in Oregon, USA. 
  • Generally, geographers believe that a caldera is an enlarged crater which is formed due to violent and explosive volcanic eruptions.
  • Some geographers have also pointed out that a caldera is formed due to the subsidence of the crater.
  • The exact answer to the formation of the caldera is still not known.
  • Example: Lake Toba in Sumatra and Lake Aira in Japan.

Conclusion

• Intrusive volcanic landforms form when magma cools and solidifies beneath the Earth’s surface, creating features like plutons, dikes, and sills. 
• Extrusive volcanic landforms form when magma erupts onto the Earth’s surface and cools quickly, creating features like lava flows, volcanic cones, and ash deposits. 
• So, intrusives are formed underground, while extrusives are formed above ground.

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