A Tectonic Engine Room
Barren Island is the only confirmed active volcano in the entire Indian subcontinent. It is the emergent summit of a stratovolcano that rises 2,250 meters from the seafloor. The island itself is small, about 3 kilometers wide, with its highest point reaching 354 meters above sea level. The volcano's structure has a 2-kilometer-wide caldera, a large basin-shaped depression that formed during a major explosive eruption in the late Pleistocene epoch. This caldera is breached on its western side, allowing lava flows from historical eruptions to reach the sea.
The volcano's existence results from plate tectonics. It sits on the boundary where the Indian Plate is subducting, or sliding, under the Burma Plate. This subduction process generates magma deep beneath the Andaman Sea, which feeds the volcano. Barren Island is part of a volcanic arc that extends from Sumatra to Myanmar. The lava it produces is typically basalt and basaltic andesite, consistent with its subduction zone origins. Argon-argon dating of its oldest subaerial lava flows indicates they are approximately 1.6 million years old, while the volcano itself sits on oceanic crust that is about 106 million years old.
A History of Fire and Quiescence
The first recorded eruption of Barren Island occurred in 1787. Several other eruptions followed in 1789, 1795, 1803–04, and possibly 1852. After these events, the volcano entered a long period of dormancy, remaining quiet for over a century. This silence was broken in March 1991, when a new eruptive phase began that lasted for six months. Further eruptions occurred intermittently, including in 1994-95 and a significant phase from 2005 to 2010, which some geologists believe was linked to the massive 2004 Indian Ocean earthquake.
In January 2017, a team from the National Institute of Oceanography observed the volcano erupting again. This marked the beginning of its current, near-continuous state of activity. The eruptions are typically Strombolian in nature, with small, frequent bursts of activity. These episodes, lasting five to ten minutes at a time, eject ash clouds and send fountains of red lava into the air. These recent eruptions are rated as a 2 on the Volcanic Explosivity Index (VEI), indicating their relatively low intensity.