Earthquake triggered volcano eruption on Andaman's island on September 20: Expert

India's only active volcano located on the uninhabited Barren Island in Andaman Sea erupted on Sept 20, presenting a visual extravaganza rare for south Asia. The episode was in fact the result of an earthquake of magnitude 4.2 that hit the region two days before the event.

Though the eruption was minor with no immediate risk to human settlements in Indonesian archipelago, the episode - fourth since 1991 - can't be overlooked as the island lies over a fault that moved, causing the Dec 2004 tsunami.

The fault's coordinates fall on the same latitude as the Barren Island volcano and in the vicinity of the longitude of the quake that made the magma chamber apt for "pre-mature magmatic eruption", said O P Mishra , director, National Centre for Seismology.

Such episodic volcanic eruption witnessed in 1991, '04 & '05: Official

O P Mishra said it was "earthquake shaking intensity" in magma chamber of Barren volcano that erupted this month. Barren Island is roughly circular with a diameter of approximately 3.2km where the volcano rises nearly 2km above the sea floor. Its average height is 300m above mean sea level.

"Andaman-Nicobar Island is located in the subduction complex consisting of the down going Indian plate intruding to the mantle of the overriding Sunda Plate where continuous earthquakes of moderate to strong strengths used to occur besides the micro seismicity in the area," said Mishra.

There are two magma related lava volcanoes located along active West Andaman Fault. Though Barren Volcano has been active for years, the eruption is intermittent and sporadic as and when magma chamber at the depths of 18-20km are activated. Lava and magmatic eruptions occur from time to time due to disturbance of the magma chamber by seismic energy generated from strong to moderate earthquakes that upwelled lavas to the surface through volcanic vents. "This type of episodic volcanic eruption was witnessed in 1991, 2004, 2005, and now in 2025," said Mishra.

He said the lava and magma persists and remains in the moving state and is pushed upward once the 'earthquake shaking' tries to bring the hot materials to the surface through cracks and fractures widened by the continuous seismically active cycle. The other volcano in the region, Narcondam, is, however, dormant at present.