On September 13 and September 20, 2025, India’s only active volcano Barren Island in the Union Territory of Andaman and Nicobar erupted. The volcano’s first recorded eruption was in 1787, and eruptions continued up to 1832. The volcano then stayed dormant for 159 years before erupting again in 1991, followed by more eruptions in 1994-95, 2005-07, 2008-April 2010, December 2010, 2013-2014, 2017, and 2022. Officials have described the latest eruptions as ‘minor’.
The eruption on September 20 was preceded by a magnitude 4.2 earthquake that struck the region two days earlier. Considering that this quake occurred along the seismically highly active boundary of the Indian Plate and the Burmese Plate, which are part of the much larger Java-Sumatra-Andaman subduction zone, why do the eruptions occur?
Down To Earth (DTE) took this question to Hetu Sheth, Professor of Igneous Petrology and Volcanology in the Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai. Sheth has studied the Barren Island volcano along with his younger colleague Prof. Alok Kumar of Banaras Hindu University. DTE asked Sheth about the connection between earthquakes and the Barren Island Volcano, as well as the link between it and a warming planet. Excerpts:
Rajat Ghai (RG): What is the geological makeup of the volcano on Barren Island?
Hetu Sheth (HS): Tectonic plates are moving all the time. They either move away, towards, or slide past each other. If two converging adjacent plates are continental, thus dominantly composed of low-density granite, they form a “collisional” mountain belt, such as the Himalayan Range formed by collision between the Indian and Tibetan continental plates some 50 million years ago. However, an oceanic plate composed of basalt is denser than a continental plate, so convergence between them leads to the oceanic plate diving (subducting) under the continental one. For example, the east-moving Pacific Plate is currently subducting beneath the west-moving South American continent, forming the Andes Mountain range with many active volcanoes. Similarly, in the Andaman region, the Indian Plate is currently moving from southwest to northeast and subducting beneath the Eurasian Plate, which is itself divided into numerous smaller plates, one of which is the Burmese Plate. Subduction leads to friction, which in turn causes earthquakes, whereas the subducting plate and the region into which it enters undergo melting due to high temperatures and the fluids carried down by the subducting plate. The melting produces new basaltic magma, which rises through the plate, and erupts at the surface of the Earth forming volcanoes such as Barren Island.
RG: Why have volcanoes not been recorded on the Indian mainland?
HS: Most volcanoes on Earth are located over plate boundaries. Indian mainland has many ancient volcanoes, such as the 65-million-year-old Deccan Plateau, but lacks modern volcanoes owing to the absence of plate boundaries and subduction anywhere nearby. Currently, subduction is only ongoing in the Andaman region. In fact, there are other volcanoes near Barren Island, all currently dormant. One of them is Narcondam (“Narak Kundam”), 140 km NNE of Barren Island and also within Indian territory, whereas the others are still below sea level but should become emergent above sea level in future.
RG: Did the 2004 Indian Ocean Tsunami have an impact on Barren Island and its volcano?
HS: The 26 December, 2004 megaearthquake of magnitude ~9.3, originating in northern Sumatra, produced great tectonic deformation of the plates and produced a disastrous tsunami. However, whereas there are claims (and some evidence) that large earthquakes trigger volcanic eruptions, this is difficult to demonstrate for Barren Island. I do not think that the December 2004 megaearthquake was responsible for subsequent eruptions of Barren Island, because the volcano has already been erupting regularly (every few years) from 1991. I argue in my 2014 technical research paper, titled What drives centuries-long polygenetic scoria cone activity at Barren Island volcano? (published in Journal of Volcanology and Geothermal Research, Elsevier), that Barren Island’s volcanic activity is not related to earthquakes in the region, but is due purely to magmatic processes in the Earth’s interior.
RG: Do you think eruptions in Barren Island will increase in the coming future because of a warming planet?
HS: Again, there are ideas that climate change and global warming could increase volcanic activity. For example, a melting ice cap decreases the load on the underlying crust, and this decompression may allow the magma already present in the crust to rise and erupt. However, much more research is currently required to assess such ideas. A direct connection between climate change and what goes on inside the depths of Earth is to be rigorously tested. On the contrary, the impact of large volcanic eruptions on climate and weather are well recognised and appreciated. Much research is ongoing on these themes, and geology and volcanology can be exciting careers for young Indians.