Science behind Volcanic Eruptions

Context

Recently the world’s largest active volcano named Mauna Loa erupted after 38 years, covering the night sky of Hawaii’s Big Island in an incandescent red hue.

Probable Question

Explain the science behind volcanic eruptions and why some of them are explosive and some are less. (150 words, 10 marks)

About the Volcanoes Eruption

• Earth's surface gets hotter the deeper one goes under the surface, towards its core. 
• There is a term called geothermal gradient which is the amount that the Earth’s temperature increases with depth.
• Geothermal gradient indicates heat flowing from the Earth’s warm interior to its surface. 
• This heat starts melting the rocks, at a certain depth which creates what geologists call ‘magma’.
• Magma is lighter than solid rock and hence it rises, collecting in magma chambers. 
• These magma chambers have the potential to cause volcanic eruptions and are found at a relatively shallow depth, between 6-10 km under the surface. 
• As magma builds up in these chambers, it forces its way up through cracks and fissures in Earth’s crust. This is what we call a volcanic eruption. 
• The magma that surfaces on the Earth’s crust is referred to as lava, this lava is explosive sometimes.
• Volcanic Explosivity Index (VEI): It is a scale, ranging from 1-8, and is used to measure the explosivity of a volcano. A higher VEI indicates more explosivity. 

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Explosive and Implosive Volcanic Eruptions

The intensity and explosiveness with which a volcano will erupt depend on the composition of the magma.

Less Explosive Volcanic Eruption

• It generally happened when the magma is runny.
• The runny magma allows the gasses to escape easily and thus leading to a steady, relatively gentle flow of lava, out of the mouth of the volcanoes.
• It is less dangerous, as the slow pace of lava flow gave people enough time to move out of its way.
• Geologists are also able to predict the flow of the lava depending on the incline and exact consistency it has.

Also Read: Mineral and Energy Resources of India- NCERT Notes UPSC

Explosive Volcanic Eruption

It is caused due to thick and sticky magma. 

• The thick and sticky magma makes it harder for gasses to escape on a consistent basis. 
• This leads to a build-up of pressure until a breaking point is reached and the gasses escape violently causing an eruption. 
• Lava blasts into the air, breaking apart into pieces called tephra. 
• Severity: These can be extremely dangerous, ranging from the size of tiny particles to massive boulders.
• Clouds of Tephra: The thick clouds of tephra race down the side of the volcano, they destroy everything in their path. 
• Blankets of Ash: Ash erupted into the sky and falls back to Earth like powdery snow. If thick enough, blankets of ash can suffocate plants, animals, and humans. 
• Mudflows: If the hot volcanic materials mix with nearby sources of water, they can create mudflows that have been known to bury entire communities alive. 
• Example: Mount Vesuvius, which obliterated the city of Pompeii, is an example of an explosive volcano.

Some famous volcanoes

• Active volcanoes: Any volcano that has erupted within the Holocene period (in the last 11,650 years) is considered to be “active” by scientists. Mauna Loa is the world’s largest active volcano.
• Dormant volcanoes: They are those active volcanoes that are not in the process of erupting currently, but have the potential to do so in the future. Mauna Loa was a dormant volcano for the last 38 years. 
• Extinct volcanoes: These are ones that scientists predict will never face any further volcanic activity. Ben Nevis, the tallest mountain in the UK, is an extinct volcano.

Volcanoes in India

The only active volcanoes in India are in Andaman and Nicobar Island, which too erupted 150 years ago. Following is the list of volcanoes in India:

• Baratang Island: It is in the Andaman Islands and is active since 2003.
• Barren Island: It is also in the Andaman Islands, and it is active since 2017.
• Narcondam: It is also in the Andaman Islands and is a semi-dormant volcano.
• Deccan Plateau: It is in Central India.

News Source: The Indian Express

https://indianexpress.com/article/explained/explained-sci-tech/mauna-loa-volcano-science-behind-volcanic-eruptions-8296584/

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