Volcanoes

Volcanoes are said to be the Earth’s geologic architects. Volcanoes have created more than 80% of the Earth’s surface. The hot active volcano eruptions laid the foundation of the earth where life blooms and flourishes.

A volcano is like an Earth’s surface opening from where the gases, ashes, and molten rock material escapes and gushes onto the ground. From the asthenosphere (upper mantle located below the Earth’s crust), the molten rock material finds its way to come upon the Earth’s surface. The molten rock material in the asthenosphere is called “magma”. When this magma comes out on the Earth’s surface, it gets the name “lava”.

The materials that flow out during an active volcano burst are lava, pyroclastic debris, volcanic bombs, ash, Nitrogen, sulphur, small quantities of Chlorine, hydrogen, and argon gases.

Classification of Volcanoes

The classification of volcanoes is based on three different bases:

1. Volcanic activity.
2. Nature of Eruption.
3. The form developed at the surface.

Volcanoes can be of three different kinds based on their eruption activities:

1. Active volcanoes

An active volcano is an erupting volcano, or it may explode again sometime in the future. There are around 1,500 potentially active volcanoes in the world. Examples are Kīlauea in Hawaii, Mount Etna in Italy and Mount Stromboli also in Italy.  

2. Dormant volcanoes 

A dormant volcano has not erupted for a long time. However, it may burst out in the future.

Examples are Mount Kilimanjaro, Tanzania, Africa and Mount Fuji in Japan.

3. Extinct volcanoes 

Extinct volcanoes have never erupted in the long run of human history. Mount Thielsen in Oregon and Ben Nevis are some of the examples of extinct volcanoes.

Based on the eruption or the nature of the explosion and the form developed at the surface, volcanoes can be of different types:

1. Shield Volcanoes

The incoming lava moves in the form of a fountain. It then throws out the cone at the top of the vent and shapes like a cinder cone. These shield volcanoes are called cinder cone volcanoes.

The lava of shield volcanoes is fluid and made up of basalt. It is due to this reason that these shield volcanoes are not steep.

The shield volcanoes are low-explosive volcanoes, but they become volatile if water gets into the vent.

For example: Kilauea and Mauna Loa , Fernandina , Karthala, Erta Ale, Tolbachik, Masaya, and many others.

2. Composite Volcanoes

The composite volcano’s eruptions are cool and more vicious eruptions than basalt. The eruptions of composite volcanoes are often explosive, and with lava, large quantities of pyroclastic material and ashes make their way to the surface. They then accumulate in the vicinity of the composite volcano that leads to the formation of layers. 

Examples are: Mount Fuji in Japan, and Mount Cotopaxi in Ecuador.

3. Caldera

These volcanoes are the most explosive. They tend to collapse on themselves rather than build large figures. It is because of their high explosive action. Their eruption tells us that the magma chamber supplying the lava is big enough and close.

The collapsed depressions are called the calderas.

For example: Crater Lake, in Oregon.

4. Flood Basalt Province

The eruption of these volcanoes brings out highly fluid lava to long distances. The lava flow could be more than 50m thick, and the flow may go to hundreds of km.

Most of the Maharashtra Plateau is covered by Deccan Traps, and they are an example of a large flood basalt province.

5. Mid-Oceanic Ridge Volcanoes

The mid-oceanic ridge volcanoes are found in oceanic areas.

There is a whole system of mid-ocean ridges that is more than 70,000 km long that runs across almost all the ocean basins. The volcanic burst occurs mostly in the central part of this ridge system.

Role of tectonic plates in Volcanism

• To explain plate tectonics, the theory of plate tectonics holds that the Earth’s outer shell is separated into many plates that glide over the mantle, the rocky inner layer above the core
• In contrast to the Earth’s mantle, the plates operate as a hard and solid shell. The lithosphere is the name given to this tough outer layer
• The earth’s lithosphere is composed of seven or eight major plates and many minor plates 
• The lithosphere is a rigid outermost shell of earth and is broken up into tectonic plates
• When these plates meet, their relative motion determines the type of boundary like convergent, divergent, or transform.
• Volcanic activity, earthquakes, mountain-building, and oceanic trench formation occur along these plate boundaries
• For instance, Earthquakes often occur when tectonic plates converge at a convergent boundary, where tectonic plates diverge at a divergent barrier, and where tectonic plates grind past each other at a transform boundary

Conclusion

Conclusively, we have looked into what volcanoes are while looking at its classification. We can hence state that a volcano is a break or fissure in the Earth’s crust that allows lava, ash, rocks, and gases to erupt. An active volcano is a volcano that has recently erupted. The asthenosphere is a weaker zone in the mantle. The substance found in the asthenosphere is magma.