Volcanic Landforms

In geography class 11: Volcanic landforms, the story is all about the variety of landforms of volcanoes. 

Volcanic eruptions are one of the most powerful forces on the planet, capable of drastically altering the surrounding area. A volcano is a landform formed by the eruption of lava from the Earth’s crust. Molten lava pushes the earth upwards when volcanoes erupt, until it exits the volcano’s vent. Continuous eruption creates layers of lava and raises or widens the volcano. 

Volcanic landforms are broadly classified into two landforms, they are:

1. Extrusive Landforms – Extrusive landforms are composed of material that has been thrown to the surface during volcanic activity. Lava flows, pyroclastic debris, volcanic bombs, ash, dust, and gases such as nitrogen compounds, sulphur compounds, and trace quantities of chlorine, hydrogen, and argon are among the items thrown forth.
2. Intrusive  Rocks – 

We’ll talk in detail about intrusive landforms and the different types of intrusive landforms. 

Intrusive landforms or Rocks

When the magma inside the crust cools down, this is how intrusive landforms or Rocks are formed.  In other words, these landforms or rocks originate under the Earth’s surface when hot lava cools and solidifies in the cracks and fissures of rocks that exist beneath the Earth’s crust. These are also known as igneous rocks.

What happens is when the volcano explodes, the cooling process takes place. The cooling takes place either on reaching the surface or inside the crust. The cooling of magma or lava forms the igneous rocks. If lava cools at the surface, then the igneous rocks formed are volcanic rocks or exterior landforms. If lava cools in the crust, then they are plutonic rocks or intrusive landforms or rocks. 

Intrusive landforms can be of many types: 

• Batholiths 

Batholiths are the granitic bodies of cooled portions of the magma chambers of the volcanoes. Batholiths are vast, and the depth is in kilometers.

When a large body of magmatic material cools down in the depth of the crusts, it takes the shape of large domes. It appears on the surface only after the denudation processes. These processes help in separating the overlying materials.

• Lacoliths 

Lacoliths are far-reaching dome-shaped intrusive volcanic landforms with a base level connected by a pipe-like conduit from below. The laccoliths resemble the surface volcanic domes of the composite volcanoes. The only difference is that they are located at deeper depths in comparison. 

The Domal Hills of Karnataka Plateaus are an example of laccoliths or batholiths intrusive landforms. These hills are made of granite rocks which are now exfoliated.

• Lapolith 

When the lava tries to go in an upward direction, and a part of it tries to move in a horizontal direction where there is a weak plane, it cools down and solidifies in the same form. 

If it develops into a saucer shape that is concave to the sky body, it is a lapolith. 

• Phacolith 

It cools down into a definite conduit in the form of magma chambers. These wavy materials then become phacoliths, which subsequently develop into batholiths.

• Sills or Sheets 

The horizontal bodies of the plutonic igneous rocks are called the sills or sheets. 

The thinner deposits are the sheets, and the thicker ones are called the sills. Together, they are sills or sheets. 

• Dykes 

When the lava finds its way through cracks, it solidifies in an almost perpendicular direction to the ground leading to the formation of dykes. When it cools and solidifies as a wall-like structure, then dykes are formed. Found in the Maharashtrian area, dykes are the most common type of intrusive landforms. 

Rocks are divided into three types: igneous, sedimentary, and metamorphic. Magma in the Earth’s mantle forms igneous rocks. They usually do not contain fossils, do not react with acids, do not have obvious layers, can be made of different minerals, sometimes have holes or bubbles, and may appear glassy. Volcanologists search for these igneous rocks to learn more about where they came from and whether they were formed during a volcanic eruption.

Geologists use the visual appearance of the rock as an initial clue to its composition, but then use specialised techniques to confirm their theories. Scientists at The University of Auckland, for example, use an electron microprobe to precisely measure the amounts of silica, iron, magnesium, and a variety of other chemicals found in rock samples. This information aids in the classification of the rock and may provide direct clues about the volcano and the eruption that formed it.

Studies say that dykes were the reason behind the formation and development of the mighty Deccan Traps. 

Types of Volcanic Rocks:

Magma in the Earth’s mantle forms igneous rocks. They normally do not contain fossils, do not react with acids, do not have visible strata, may be formed of diverse minerals, can include holes or bubbles, and may seem glassy. Volcanologists search for these igneous rocks to understand more about where they came from and if they were generated during a volcanic eruption.

When talking about volcanic rocks, it is significant to mention about:

1. Basalt

The majority of the Earth’s crust is made up of basalt rock. It’s a big, black, gritty rock. Basalt is related with large rock columns that may be found all over the world. High temperatures (about 1,200ºC) are required for the formation of basalt magma. It is hot and liquid when it erupts from the volcano. It has a low silica content (less than 50%) and a high magnesium and iron content, which gives the rock a black appearance.

2. Andesite

Because andesites contain less iron and more silica (50–60 percent), they are lighter in colour than basalt. Because of their chemical makeup, certain scoria rocks are classified as andesite. Magma containing andesite has a temperature range of 800–1,000ºC and creates steep-sided cone volcanoes (stratovolcanoes).

3. Rhyolite

Rhyolite is light-colored or white, which indicates that the rock is high in silica (more than 70%) and low in iron and magnesium. Rhyolitic magmas are connected with low temperatures (750–850ºC) and are often thick, preventing gases from escaping. Some rhyolitic rocks are relatively light, such as pumice, which may still have traces of trapped gas bubbles when the rock crystallised.

Conclusion

Conclusively, we looked into the different volcanic landforms or rocks. They are primarily divided into intrusive and extrusive rocks. We also looked into different volcanic rocks.