How volcanoes form: their types and India's only active volcano
Magma and lava, active, dormant and extinct volcanoes, the "Ring of Fire", history's great eruptions and Barren Island, India's only active volcano.
Rohit Tandon · 21 October 2026 · 4 min read
When molten rock, gases and ash burst out from inside the Earth, it is called a volcanic eruption. Volcanoes are frightening, but they have also played a big part in creating new land, fertile soil and even Earth's atmosphere. Here is how volcanoes form, what types there are, and which volcano in India is still active today.
The difference between magma and lava
Inside the Earth, below the crust, the great heat melts rock in some places. This molten rock underground is called magma. Magma is lighter than the solid rock around it, so it rises through cracks. When it comes out at the surface, it is called lava. Lava can be anywhere from 700 to 1,200 °C.
Where do volcanoes form?
Earth's outer shell is broken into several large "plates", which keep shifting very slowly. Most volcanoes form at the edges of these plates — where one plate sinks beneath another, or where two plates pull apart. Around the edges of the Pacific Ocean there is such a long belt of volcanoes that it is called the "Ring of Fire"; about 75% of the world's volcanoes lie in it. Some volcanoes also form at "hotspots" in the middle of plates, such as the Hawaiian Islands of the USA.
Types of volcanoes
| Basis | Type | Meaning / example |
|---|---|---|
| Activity | Active | Has erupted recently or is likely to — such as Etna in Italy and Barren Island in India |
| Activity | Dormant | Quiet for a long time but could erupt again — such as Narcondam in India |
| Activity | Extinct | Not expected to erupt again |
| Shape | Shield | Built from runny lava, broad and gently sloping — such as Mauna Loa in Hawaii |
| Shape | Composite (strato) | A tall cone built from layers of lava and ash — such as Mount Fuji in Japan |
India's only active volcano
India's only active volcano is Barren Island, in the Andaman and Nicobar Islands, about 135 kilometres north-east of Port Blair. "Barren" means bare — no people live on the island. It has erupted several times since 1991. Nearby Narcondam Island is a dormant volcano. Millions of years ago India too saw gigantic eruptions — lava that flowed about 66 million years ago formed the "Deccan Traps" in and around Maharashtra, where fertile black soil good for cotton is found today.
Did you know? The sound of the 1883 eruption of Krakatoa in Indonesia was heard about 4,800 kilometres away — it is considered one of the loudest sounds in recorded history. In 1815 the eruption of Tambora, also in Indonesia, spread so much ash into the sky that the next year, 1816, became known in Europe and America as "the year without a summer".
Some great eruptions in history
- Vesuvius (79 CE): buried the city of Pompeii in Italy under ash; excavations found the whole city almost as it was.
- Tambora (1815): among the most powerful eruptions ever recorded.
- Krakatoa (1883): the eruption and the tsunami it caused killed thousands of people — read The biggest tsunamis in history.
- Mount St Helens (1980): in the USA; a whole side of the mountain was blown away.
Volcanoes have benefits too
Soil formed from volcanic ash is very fertile. Countries such as Iceland get electricity and hot water for homes from the Earth's heat, called "geothermal energy". Islands such as Hawaii and Iceland were themselves built by volcanoes. The word "volcano" comes from "Vulcan", the Roman god of fire. The tallest volcano in the solar system is Olympus Mons on Mars — read The planets of the solar system.
Key points
- Molten rock underground is called magma, and lava once it comes out.
- Most volcanoes form at the edges of tectonic plates.
- About 75% of the world's volcanoes are in the "Ring of Fire".
- India's only active volcano is Barren Island in the Andamans.
- The Deccan Traps were formed by ancient volcanic lava.
Frequently asked questions
Which is India's only active volcano?
Barren Island in the Andaman and Nicobar Islands.
What is the difference between magma and lava?
Molten rock inside the Earth is magma; the same rock is called lava once it reaches the surface.
More articles: Geography · Geography questions.
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