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What is the science behind volcanic eruptions?

GS Paper 1

Syllabus:  Important Geophysical phenomena such as earthquakes, tsunamis, Volcanic activity, cyclones, etc.


Source: Indian Express

Direction: This is a static portion. Just go through the article to understand volcanoes. Revise your notes too.

Context: Mauna Loa, the world’s largest active volcano erupted after 38 years spewing ash and debris.

Why do volcanoes erupt?

Chambers, which have the potential to cause volcanic eruptions, are found at a relatively shallow depth, between six to ten 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.

Why are some volcanic eruptions explosive and some not?

  • Runny magma makes for less explosive volcanic eruptions that typically are less dangerous. Since the magma is runny, gasses are able to escape, leading to a steady but relatively gentle flow of lava out of the mouth of the volcano. The eruption at Mauna Loa is of this kind. 
  • If magma is thick and sticky, it makes it harder for gasses to escape consistently. This leads to a build-up of pressure until a breaking point is reached. At this time, the gasses escape violently, all at once, causing an explosion. Lava blasts into the air, breaking apart into pieces called tephra. Mount Vesuvius, which obliterated the city of Pompeii, is an example of an explosive volcano.


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Qn. Elucidate the process of volcano formation and its types. Also, mention a few examples of the global occurrence of volcanic eruptions in recent times and their impact on the regional environment. (250Words)


Practice Question:

Consider the following statements:

    1. The Barren Island volcano is an active volcano located in the Indian territory.
    2. Barren Island lies about 140 km east of Great Nicobar.
    3. The last time the Barren Island volcano erupted was in 1991 and it has remained inactive since then.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 and 3

(c) 3 only

(d) 1 and 3

Solution: A

Barren Island is located in the Andaman Sea, about 140 km from Port Blair. Barren Island volcano is the only active volcano located in the Indian territory, Andaman Islands.