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.