How are Volcanoes Formed?

Tap to Read ➤ Prabhakar Pillai

Tall mountains with steep sides, oceanic islands or just deep holes in the ground, volcanoes have continued to enchant people since ages together, in spite of their terrifying effects. Speaking about their formation, understand that lava and ash cool down to form conical landforms, and repeated deposition of lava and ash layers forms volcanic structures.

Did you know?

The Public Broadcasting Service (PBS) has identified "Kīlauea" in Hawaii as the most dangerous volcano in the world. It has had "61 eruptions" since 1893, which also makes it world's most active volcano.

Strange Myths regarding Volcanic Formations

~ The Greeks thought that when Hephaestus, their God of fire and metalworking, made weapons for the Gods in his workshop under the surface of the Earth, and his tasks of heating and striking the metals caused the Earth to erupt.

Your browser doesn't support HTML5 video. ~ The Hawaiians believed that volcanic eruptions resulted from the rage of their fire Goddess Pele, who punished them by breaking the Earth open by striking it hard with her stick.

Frightening, mysterious, unpredictable, and immensely destructive, volcanoes have been intriguing people since time immemorial. In the ancient times, people had all sorts of myths with regards to volcanoes and their formation.

Your browser doesn't support HTML5 video. Today, however, lot of scientific researches have taken place with regards to this natural phenomenon, and we have a substantial amount of information about how and why the volcanoes are formed.

What is a Volcano?

A volcano is a hollow vent in the Earth's surface, through which hot, molten rock, called magma, along with some gases and hot ash, oozes out from the Earth's interior.

~ Magma erupting from a volcano is called lava. It is stored in the interior of the Earth in a large reservoir known as magma chamber. ~ The formation of magma takes place in here, by continuous melting of solid rock, owing to which, the temperature of the magma chamber is immensely high.

When the spilled lava cools down and solidifies, it forms a cone-shaped mound around the vent of the volcano. This landform, referred to as a 'volcanic mountain', may take thousands of years to form.

Apart from colossal mountains, some volcanoes also occur on ground level in the form of huge 'craters' on the surface of the ground.

Some volcanoes are also found in the oceans. Most of the time they are away from our naked eyes, since they are hidden under the water.

~ However, sometimes due to repeated eruptions, tall mounds are formed that rise above the surface of the water, thus giving rise to 'oceanic islands'.

Volcanoes are classified as active, dormant. and extinct. An 'active volcano' is the one that erupts or causes seismic activity on a regular basis.

~ A 'dormant volcano' is the one that has not erupted for a very long time, but could erupt again in the future. ~ Finally, a volcano that has been dormant for more than 10,000 years is called an 'extinct volcano'.

Formation of Volcanoes

A volcano is formed when magma, present in the Earth's interior, manages to rise up to the surface via a vent or a fissure. Hot ash and gases also escape from the interior of the Earth, along with magma. While the gases get thrown into the air, the magma and ash cool down forming distinctive volcanic landforms.

The Earth is made up of five different layers viz., the solid inner core, the liquid outer core, the liquid inner mantle, the upper mantle, and the crust.

~ The upper mantle comprises two distinct layers. The lower layer is the asthenosphere, which is semi-fluid in form. ~ The upper layer is that of the uppermost mantle, a.k.a rigid mantle, which is a solid layer of rock, just below the Earth's crust.

~ The Earth's crust and the uppermost solid mantle together form the lithosphere. ~ The Earth's lithosphere is like a huge jigsaw puzzle, with pieces of different shapes and sizes fitting into each other perfectly. These pieces are known as 'tectonic plates'.

The lithosphere (and hence the tectonic plates) rests on the asthenosphere (the lower layer of the upper mantle), which is the center of most volcanic activity that takes place underneath the Earth. The asthenosphere is highly viscous, ductile, and semi-fluid.

~ The asthenosphere is not stationary, since it is semi-fluid. Hence, the tectonic plates that rest on it are always in motion, though it is too slow to be perceived by human senses.

~ The tectonic plates display three kinds of movements. They either move towards each other (convergent boundaries) or away from each other (divergent boundaries) or just slide past each other (transform boundaries) in a horizontal manner.

Tectonic Plates and Volcano Formation

~ The magma in the asthenosphere is under tremendous pressure. ~ Volcanoes are formed when the hot magma underneath the Earth's crust hits upon a weak spot in the crust's composition.

~ This allows the magma to 'erupt', thus venting the heavy pressure that is built up underneath the crust. ~ These weak spots are often found along the boundaries of tectonic plates.

How do Tectonic Plates move?

Ways Tectonic Plates move

Tectonic plates may move in three ways. While, the convergent and the divergent boundaries might lead to the formation of volcanoes, the transform boundaries are not related to volcanic formation.

When one tectonic plate rises above the other The plate with greater weight/momentum rises above, while the other plate is depressed/subdued.

~ This 'subduction' of the depressed plate into the asthenosphere, and the friction between the two plates causes an imbalance in pressure and temperature. ~ This causes the asthenospheric magma and gases to erupt with enhanced force.

When both tectonic plates rise together Volcanoes are not usually formed in this case. However, such a movement gives rise to the formation of mountain ranges.

When both tectonic plates diverge When two plates diverge or pull away from each other, the underlying magma emerges from the resultant crack or fault, forming a volcano.

~ Divergent boundaries are usually found in oceanic plates, and are primary sources of newly formed ocean floors. The emergent lava may go on to form islands.

Volcanic Hot Spots

~ Volcanic hot spot is a fixed spot that is situated beneath the tectonic plates, through which the magma oozes out to the Earth's surface. ~ Heat at the location of a hot spot is more in comparison to other areas of the magma chamber and so, the process of melting of rock and subsequent rising of the magma is comparatively quicker at this point.

~ A volcanic hot spot is fixed; it does not move. But, a volcano is constantly in motion, as it is formed over the tectonic plates. ~ The volcano that thus passes the location of the hot spot, gets cut off from its source of magma, and becomes extinct in the future.

~ A volcanic hot spot always gives rise to volcanoes as new tectonic plates keep on coming into contact with it. ~ This ever-continuing cycle of volcano formation and extinction, thus results in the formation of a chain of volcanic landforms.

A lot of volcanoes have become tourist destinations in their own right, attracting numerous tourists from across the globe. 'Volcano Tourism' is a new concept that is being promoted worldwide, owing to the ever-increasing fascination of tourists towards volcanic sites, especially those of active volcanoes.

The volcanic sites offer, apart from opportunities such as climbing and hiking, unparalleled scenic beauty.