Volcano: A Natural Hazard
Let’s start from the very basic question:
What exactly is a volcano?
A volcano is like a natural vent or chimney through which molten rock (magma), gases, and ash from the Earth’s interior escape to the surface.
When this magma comes out through the vent, it is called lava, and over time, the accumulation of this lava around the vent forms a cone-shaped mountain, which we commonly recognize as a volcano.
🔥 Classification of Volcanoes
Volcanoes are broadly classified based on their activity:
| Type | Description |
| Active Volcano | Erupting currently, or has erupted in recent times (showing signs like gas release or tremors). |
| Dormant Volcano | Not erupted for a long time but may erupt again in the future. |
| Extinct Volcano | Has not erupted for over 10,000 years, and no possibility of future eruption. |
The explosiveness of an eruption depends on:
- How easily magma can flow, and
- The amount of gas trapped in the magma.
→ More gas = more pressure = more explosive eruption.
⚙️ Causes of Volcanic Eruption
Volcanoes are geologically linked to the movement of tectonic plates.
The Earth’s crust isn’t one solid piece — it’s broken into plates floating on molten rock.
Volcanic eruptions mainly occur where these plates meet or move.
1. Divergent Boundaries
When plates move away from each other, magma rises to fill the gap.
Example: Mid-Atlantic Ridge.
2. Convergent Boundaries
When plates collide, one plate slides below the other (subduction).
The subducted plate melts due to high temperature and pressure, forming magma which rises to the surface.
Hot Spots
Sometimes volcanoes form away from plate boundaries — over what’s called a “Hot Spot.”
A hot spot is a fixed zone deep within the Earth’s mantle where a plume of hot magma rises toward the surface.
As tectonic plates move over this hot spot, new volcanoes form.
Example: Hawaiian Islands in the Pacific Ocean.
In India, Barren Island is a result of such hotspot activity.
🇮🇳 Volcano Risk in India
India is not a volcanically active country, but we do have a few identified volcanoes — most of them extinct, except one active.
The only active volcano in India is:
🏝️ Barren Island Volcano, Andaman & Nicobar Islands
- Dormant for nearly 150 years, it erupted again in 1991.
- Another eruption occurred in 2017, spewing ash and gases.
- The island is uninhabited, and the northern part is completely barren — hence the name.
This volcano lies along the Alpine–Himalayan Belt, which extends from the Mediterranean region through Asia up to the Andaman Sea — the same belt that causes earthquakes in northern India.
Recent Update
- In September 2025, Barren Island erupted twice within a week — on the 13th and 20th — with the latter eruption triggered by a nearby magnitude 4.2 earthquake
📋 List of Important Volcanoes in India
| Sr. No. | Volcano Name | Type | Location / State |
| 1. | Barren Island | Active | Andaman Islands |
| 2. | Narcondam | Extinct | Andaman Islands |
| 3. | Baratang | Extinct | Andaman Islands |
| 4. | Deccan Traps | Extinct | Maharashtra |
| 5. | Dhinodhar Hills | Extinct | Gujarat |
| 6. | Dhosi Hill | Extinct | Haryana |
🪨 Special Mention: Deccan Traps
- “Traps” means steps in Swedish, referring to the step-like layered structure formed by solidified lava flows.
- Formed by massive volcanic eruptions around 65 million years ago, which covered large parts of western and central India.
- These eruptions released gases that contributed to the extinction of dinosaurs.
- Today, this region has black cotton soil (Regur) — formed from basaltic lava.
