Intrusive and Extrusive volcanic landforms Upsc

Volcanic Landforms

The landform formed due to volcanic eruptions is divided into extrusive and intrusive landforms. This is based on the magma, that cools within the crust or above the crust. Intrusive landforms are formed under the surface of the earth when the magma cools and gets solidified.

Extrusive landforms are formed when the magma flows out of the earth called Lava. This Lava flows and gets solidified. The landforms from the lava are called Extrusive landforms.

Intrusive Forms

The lava that is released during volcanic eruptions on cooling develops into igneous rocks. The cooling may take place either on reaching the surface or while the lava is still in the crustal portion. 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.

Volcano Landforms

Batholiths

A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes. They appear on the surface only after the denudational processes remove the overlying materials. They cover large areas, and at times, assume depth that may be several km. These are granitic bodies. Batholiths are the cooled portion of magma chambers.

Lacoliths

These are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below. It resembles the surface volcanic domes of the composite volcano, only these are located at deeper depths. It can be regarded as the localized source of lava that finds its way to the surface.

The Karnataka plateau is spotted with domal hills of granite rocks. Most of these, now exfoliated, are examples of laccoliths or batholiths. Lapolith, Phacolith, and Sills. As and when the lava moves upwards, a portion of the same may tend to move in a horizontal direction wherever it finds a weak plane.

It may get rested in different forms. In case it develops into a saucer shape, concave to the sky body, it is called lapolith.

A wavy mass of intrusive rocks, at times, is found at the base of synclines or at the top of the anticline in the folded igneous country. Such wavy materials have a definite conduit to source beneath in the form of magma chambers (subsequently developed as batholiths).

These are called the phacoliths. The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of the material. The thinner ones are called sheets while the thick horizontal deposits are called sills.

Dykes

When the lava makes its way through cracks and the fissures developed in the land, it solidifies almost perpendicular to the ground. It gets cooled in the same position to develop a wall-like structure. Such structures are called dykes. These are the most commonly found intrusive forms in the western Maharashtra area. These are considered the feeders for the eruptions that led to the development of the Deccan traps.

Extrusive Volcanic Landforms

Extrusive volcanic landforms, also known as volcanic surface features, are the result of volcanic activity that occurs on or near the Earth’s surface. Unlike their intrusive counterparts, which form beneath the surface, extrusive landforms are created when magma erupts from a volcano and solidifies into various shapes and structures upon exposure to air or water.

Extrusive Volcanic Landforms

Key Features of Extrusive Volcanic Landforms:

Lava Flows

One of the most recognizable features of extrusive volcanic activity is lava flows. These molten rivers of magma travel down the slopes of a volcano, leaving behind a trail of solidified lava. The composition of the lava influences the texture and appearance of the flow, ranging from smooth pahoehoe to jagged ‘a’a flows.

Pyroclastic Deposits

Volcanic eruptions often eject a mixture of hot gases, ash, and volcanic rocks into the air. As these materials settle, they form pyroclastic deposits, creating diverse landforms such as ash cones, volcanic tuff rings, and ignimbrite plains.

Pyroclastic Deposits

Volcanic Cones

Extrusive volcanic cones are iconic landforms shaped by the accumulation of erupted materials around a vent. These cones can take various forms, including shield volcanoes with gentle slopes and stratovolcanoes with steeper, more conical profiles.

Volcanic Cones

Craters and Calderas

The explosive release of volcanic gases can result in the formation of craters and calderas. Craters are typically smaller depressions around the vent, while calderas are large, collapsed features formed by the emptying of a magma chamber during a major eruption.

Calderas in Fernandina Island in the Galápagos archipelago

Geological Significance:

Extrusive volcanic landforms offer a window into the dynamic processes occurring beneath the Earth’s surface. By studying these features, geologists can gain insights into the composition of magma, the nature of volcanic eruptions, and the interactions between Earth’s lithosphere and asthenosphere. Additionally, the deposits left behind by volcanic activity contribute to the formation of fertile soils, making volcanic regions agriculturally productive.

Notable Examples of Extrusive Volcanic Landforms:

  1. Mauna Loa, Hawaii:
    • As the largest shield volcano on Earth, Mauna Loa in Hawaii showcases the classic gentle slopes associated with shield volcanoes. Lava flows from Mauna Loa have extended into the ocean, creating new land and expanding the island of Hawaii over time.
  2. Mount St. Helens, USA:
    • The eruption of Mount St. Helens in 1980 resulted in the formation of a horseshoe-shaped crater and the deposition of pyroclastic flows. This event provided valuable data for understanding volcanic hazards and recovery processes.
  3. Eyjafjallajökull, Iceland:
    • The 2010 eruption of Eyjafjallajökull not only disrupted air travel but also left behind spectacular lava flows and ash deposits. The eruption highlighted the interconnectedness of geologic processes and global systems.

Conservation and Exploration:

While extrusive volcanic landforms offer invaluable insights into Earth’s geologic history, they also require careful conservation. Human activities in volcanic regions, including tourism and infrastructure development, must be managed sustainably to preserve these natural wonders. Responsible exploration allows us to marvel at the beauty of these landscapes without compromising their integrity.

Conclusion

In conclusion, the dynamic interplay between the Earth’s internal forces and its surface has given rise to two mesmerizing categories of volcanic landforms: intrusive and extrusive. Each of these geological wonders tells a unique story of the planet’s history, showcasing the relentless processes that have shaped our landscapes over millions of years.

Intrusive volcanic landforms, concealed beneath the Earth’s surface, whisper tales of molten magma pushing through cracks and fissures, creating awe-inspiring structures such as batholiths, dikes, and sills. These formations, often hidden from the naked eye, serve as geological time capsules, preserving a record of the Earth’s evolution and the complex movements within its crust.

On the other hand, extrusive volcanic landforms boldly announce their presence on the Earth’s surface, sculpted by the fiery dance of lava, ash, and gases. From the gentle slopes of shield volcanoes to the dramatic calderas formed by explosive eruptions, these features stand as testaments to the raw power of nature. They not only contribute to the creation of fertile soils but also provide researchers with invaluable insights into volcanic processes and hazards.

Both intrusive and extrusive volcanic landforms play integral roles in our understanding of Earth’s geology. They offer glimpses into the planet’s past, present, and future, guiding scientific exploration and contributing to our knowledge of geological processes. While intrusive landforms often remain hidden from view, their significance lies in the unseen forces that shape the Earth’s crust. Extrusive landforms, on the other hand, showcase the immediate and visually striking results of volcanic activity, leaving landscapes marked by lava flows, craters, and pyroclastic deposits.

As we marvel at the diversity and beauty of these volcanic formations, it’s crucial to recognize the importance of responsible exploration and conservation. Human activities, including tourism and development, should be approached with care to ensure the preservation of these geological wonders. By understanding and appreciating both intrusive and extrusive volcanic landforms, we deepen our connection to the Earth’s dynamic nature and gain a profound appreciation for the intricate processes that continue to shape our planet. The study of these volcanic features not only enriches our scientific knowledge but also fosters a sense of wonder and respect for the geological forces that define the ever-changing landscape of our world.

Reference

* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.
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