Ncert class 11 geography chapter 3 || Volcanoes and volcanic landforms

What is a volcano? Types of volcanoes.

Places where the molten magma, gases, ashes, and lava erupt from the ground. It’s called a volcano.

Active volcanoes, Dormant volcanoes, and Extinct volcanoes are three types of volcanoes.

Active Volcano – The lava, gushes, and ashes are being released or released out recently, called it active volcano.

Dormant volcano – It erupted a long time ago and has the chance to erupt again, called a dormant volcano.

Extinct volcano – It erupted thousands of years ago and has no chance to erupt again. Called an extinct volcano.

·        The asthenosphere part of the mental is the main source of magma. When it moves toward the Crust and reaches the surface, referred to as lava.

·        The material that erupts from the volcanoes is lava, pyroclastic debris, Volcanic bombs, Ash, dust, and gases like nitrogen compounds, sulphur compounds, and a small amount of chlorine, hydrogen, and argon.

 

 

Also, have different types of volcanoes based on the nature of eruption and the form developed at the surface level.

Shield volcanoes

·        It exists in large amounts in all volcanoes.

·        It is very fluid. It erupted like a fountain. That’s why these volcanoes are not very steep.

·        Mostly made of basalt rock.

·        If anyhow water gets into the vent becomes explosive, otherwise it has low explosiveness.

·        Develop a cinder cone shape structure on the mouth of the Volcano.

·        Example - Hawaiian volcanoes.

                            

 

Composite volcanoes

·        These erupted volcanoes are cooler and more viscous lava than basalt.

·        It is often explosive when it erupts.

·        Large amounts of pyroclastic material and ashes are erupted with lava.

·        For its viscousness, it accumulates on the mouth of the volcano and appears like a mountain structure.

·        Example – Mount Fuji.

 

 

                   

Caldera volcanoes

·        It is characterized as the most explosive Volcanoes of the Earth.

·        These are so explosive that they collapse themselves when they erupt. So, these volcanoes are not making any tall structures. This collapse creates depression, which is called caldera.

·        It indicated that the supply of magma is huge and also close to the vicinity.

·        Example – Yellowstone caldera.

                                 

 

Flood basalt provinces

·        It is highly fluid.

·        It flows around 100 km. Some parts of the world are covered by thousands of square km.

·        It attains a thickness of around more than 50 m.

·        Example – Deccan traps in India.

 

                     

Mid Ocean ridge volcanoes

·        It is a volcanic structure under the Oceanic water. By divergence of the tectonic plate creates a new crust under the oceanic water.

·        Stretches more than 70,000 km.

·        Frequent earthquake is experienced centre of these ridge areas.

·        Example - Mid-Atlantic ridge.

 

      (If you go for Google search through these different types of volcanoes' names, you will see each volcano's images)                   

 

Volcanic landform

Lava erupted from the volcanoes and cooled down on the surface. It developed as an igneous rock. But sometimes lava does not reach the surface. It cooled down in the crustal portion.

 Based on where lava cools down, Igneous rock is divided into 2 types. 1) Volcanic rocks, if Lava cools down to the surface level; 2) Plutonic rocks, If Lava cools down in the crustal portion.

Cooling down of lava in the Crustal Portion creates different types of forms. Which is called an intrusive form. Some of are

Batholiths

·        A huge amount of magma cools down in the deeper depths of the crustal level. And create a large doom-like feature.

·        It spread in a large area and depth, also several km.

·        If the surface is uncovered by a denudational process, then it appears on the Surface level.

·        It is a granite rock.

·        Basically, it is magma Chambers which is cooled down.

 

Lacoliths

·        It is a large dome dome-shaped Body connected by a pipe from below.

·        It looks like a volcanic dome of a composite volcano.

·        It is assumed that it is a localized source of lava.

 

Lapolith

·        When lava moves upward, some portion of Lava tends to move in a horizontal direction where it finds weak areas.

·        It develops like a saucer shape.

Phacoliths

·        It is wavy like Structure.

·        Connected with Magma Chamber from below.

Sill or sheet

·        It is a horizontal body.

·        Thinner ones are called sheets and thick ones are called sill.

Dykes

·        When Lava moved toward the surface through cracks. The fissures are developing. After cooling down, it develops into wall-like features.

·        Almost perpendicular to the ground.