Barren Island volcano

Geography glossary

Also called: Barren Island · Topic: Interior of the Earth: Earthquakes, Volcanoes and the Layered Earth · NCERT: Class 7, Ch 1 "Geographical Diversity of India"; Class 11, Ch 2 "Structure and Physiography"

Meaning

Barren Island volcano is India's only confirmed active volcano. It stands on Barren Island in the Andaman Sea, about 140 km north-east of Port Blair (Andaman and Nicobar Islands). It formed because the Indian Plate subducts beneath the Burma microplate.

It matters because it is the only place in India where lava eruptions happen today. It also shows that India's island territory sits on an active subduction zone, the same zone that caused the 2004 tsunami.

Explanation

How it formed: subduction under the Andaman Sea

  • Plates are the large, rigid slabs that make up the earth's outer shell. Volcanoes mostly form where plates meet.
  • Subduction happens when one plate slides down under another plate into the mantle (the hot rock layer below the crust).
  • At Barren Island, the Indian Plate slides under the Burma microplate. The Burma microplate is a small plate under the Andaman Sea and Myanmar.
  • The sinking Indian Plate heats up and releases water.
  • The water lowers the melting point of the mantle rock above it, so that rock melts into magma (molten rock below the ground).

  • The magma rises and breaks through the sea floor. Over time it builds a volcano that rises above the sea as Barren Island.

  • Result: a volcanic arc, which is a curved line of volcanoes next to an ocean trench (a deep, narrow trough in the sea floor). Barren Island and Narcondam both sit on this arc.

  • Ring of Fire volcanoes around the Pacific form by the same process.

Type and shape

  • Stratovolcano: a steep cone built from many layers of lava, ash and rock pieces piled up over many eruptions.
  • Caldera: its crater is a large bowl-shaped hollow, and it is open to the sea on the west side.
  • Approximate position: 12.3° N, 93.9° E. It is marked in NCERT Class 7, Fig. 1.39.
  • Material erupted: lava, ash and gases.

Eruption history: why it counts as "active"

  • Active volcano: a volcano that has erupted in recorded history and still erupts.
  • Timeline:
  • 1787: an eruption was recorded.
  • After that came a long quiet period.
  • 1991: it erupted again.

  • Since 1991: it has erupted again and again.

  • The repeated eruptions since 1991 are what make it India's only confirmed active volcano.

Life on the island

  • No people live on the island.
  • It has a population of feral goats (goats that were once tame and now live in the wild).

Where it occurs

  • India: Barren Island, Andaman Sea, about 140 km north-east of Port Blair, Andaman and Nicobar Islands (about 12.3° N, 93.9° E).
  • Same volcanic arc:
  • Narcondam Island lies to the north (north-east) of Barren Island. It is a dormant volcano and is home to the endemic Narcondam hornbill (a bird found only on this island).

  • Baratang Island in Middle Andaman has India's best-known mud volcano.

  • Similar subduction volcanoes in the world: the Pacific Ring of Fire, a horseshoe-shaped belt around the Pacific. It includes the Andes, Alaska and the Aleutians, Japan, the Philippines, Indonesia and New Zealand.

Don't confuse with

  • Narcondam: it is on the same arc, to the north, but it is dormant. A dormant volcano has not erupted in recorded history but could erupt again. Barren Island is active.
  • Baratang mud volcano: it pushes out mud, water and methane because of gas and fluid pressure underground. It has no lava. Barren Island erupts real lava and ash.
  • Hotspot volcanoes (Hawaii, Réunion): these form far from plate edges, above a mantle plume (a rising column of very hot mantle rock). Barren Island forms at a plate edge, through subduction.
  • Deccan Traps: this is ancient flood basalt (huge sheets of lava) on the Indian mainland, linked to the Réunion hotspot. It is not an active volcano, and it was not formed by subduction.

Prelims Hooks

  • Barren Island = India's only confirmed active volcano. It is in the Andaman Sea, about 140 km north-east of Port Blair.
  • Cause: the Indian Plate subducts beneath the Burma microplate. It is a subduction (convergent) volcano, not a hotspot volcano.
  • Type: stratovolcano, with a caldera open to the sea on the west side.
  • Eruption years to remember: 1787 (recorded), then 1991 after a long quiet spell, with repeated activity since.
  • Andaman trio: Barren = active volcano; Narcondam = dormant (north of Barren, Narcondam hornbill); Baratang = mud volcano (mud, water, methane, no lava).
  • Trap: Barren Island is uninhabited by people, but it has feral goats.

Mains Points

  • Tectonic evidence (GS-I): Barren Island shows that the Andaman-Nicobar arc is an active subduction zone. The arc has an active volcano (Barren), a dormant one (Narcondam) and mud volcanoes (Baratang). Together they show how one plate boundary produces several kinds of volcanic features.
  • Disaster risk (GS-III): the volcano sits on the same subduction zone that caused the 2004 Sumatra-Andaman earthquake and tsunami. The islands therefore face eruptions, earthquakes and tsunamis together.
  • They need constant monitoring of volcanic activity.
  • They need an early warning system for the islands.

  • Tourism and settlements need careful planning, so that people and buildings stay out of high-risk zones.

  • Ecology and protection: the uninhabited island and the nearby Narcondam (with its endemic hornbill) are fragile island ecosystems. Monitoring and tourism rules must also protect their unique wildlife.

Related concepts

Read more

Sources

  1. 1Class 7, Ch 1 "Geographical Diversity of India"; Class 11, Ch 2 "Structure and Physiography" (primary)