A volcano, by definition, is any conical or dome shaped structure which is formed as a result of magma escaping to the surface of the Earth through a vent. Volcanoes, ranging from flat shield shaped to tall and steep ones, have played a key role in forming and modifying the planet upon which we live. More than 80 per cent of the Earth’s surface is of volcanic origin which supplied the ingredients vital to evolve and sustain life. Countless volcanic eruptions have created mountains, plateaus, and plains, which subsequent erosion and weathering have sculpted into majestic landscapes and formed fertile soils.
There are more than 500 active volcanoes (those that have erupted at least once within recorded history) in the world – although many more are hidden under the seas. Most active volcanoes are strung like beads along or near the margins of the continents and more than half encircle the Pacific Ocean as a ‘Ring of Fire’. Volcanoes tend to cluster where folding and fracturing of rocks provide channels for the escape of magma indicating that volcanism and seismic activity are often closely related, responding to the same dynamic Earth forces.
Volcanism in India
There are two major volcanic provinces in peninsular India and one active volcanic island (Barren Island) in the Andaman Sea. They are the older (100 million yrs) Rajmahal-Sylhet Volcanic Province in eastern India and the relatively younger (60 million yrs) and largest Deccan Volcanic Province (area 500,000 sq km) in central India. These two provinces had experienced two phases of a long period volcanism (100-60 million years ago) when the Indian plate was moving to the north after it broke and was separated from Antarctica some 180 million years ago.
The uninhabited Barren island volcano, 135 km from Port Blair, is the only active volcano in India with an area of 10 sq km. After lying dormant for about two centuries, it had erupted thrice in the recent years, in April 1991, December 1994 and May 2005. The other volcanic island in this sea is the ‘extinct’ volcano of Narcondum Island, north of the Barren Island.
These two volcanic islands, one extinct, lie on the volcanic arc that extends from central Burma (Myanmar) in the north to the Sumatra-Java in southeast. There are, however, a few volcanic seamounts, namely the Alcock Seamount about 60 km east of Barren and the Sewell Seamount about 200 km east of Car-Nicobar islands, which are yet to emerge above the sea level. Mainland India is thus almost free from volcanic hazards.