India's only active mud volcano, nestled on Baratang Island in the Andaman and Nicobar archipelago, has roared back to life after two decades of silence, captivating scientists and locals alike. When the volcano erupted on October 2, 2025, it was more than just a geological spectacle—it was a window into Earth's ancient past. Samples collected from the site have now been dated to the Oligocene epoch, a period that ended some 23 million years ago, according to the Geological Survey of India (GSI).
The GSI's Deputy Director General, Santanu Bhattacharjee, explained the significance of these findings during a recent assessment. "We visited the site on October 8-9 to assess the mud eruption reported on October 2. We had collected the mud sample and found that it belonged to the Oligocene age," Bhattacharjee told The Tribune. This epoch, stretching from around 33.9 to 23 million years ago, was marked by dramatic changes—global cooling, the spread of grasslands, and the emergence of mammals like the first elephants, cats, and dogs. It's a slice of prehistory rarely glimpsed so directly.
The samples weren't just any old mud. Lithoclasts—rock fragments ejected from the volcano's crater—were found to be composed of sandstone and shale from the Mithakari Group, a geological formation rooted firmly in the Oligocene period. According to Bhattacharjee, "The lithoclasts ejected from the crater were found to be composed of sandstone and shale of the Mithakari Group, belonging to this geological period." For geologists, this is a treasure trove, offering clues about the tectonic and environmental conditions of ancient India.
But the eruption itself was no small affair. The GSI's field team observed a dramatic transformation at the site. "A total of four clusters of mud volcanoes consisting of several small vents have been observed, spread over an area of about 500 sqm with a height of about 2 metre at the centre. This marks a significant increase in the area of the eruption site from the earlier record of 100 sqm and height of one metre. All clusters of vents were continuously emanating liquid mud and gases," Bhattacharjee reported. The expansion from 100 to 500 square meters, and from a one-meter to a two-meter central height, underscores the scale of this latest event.
Standing near the vent clusters, GSI scientists measured surface temperatures ranging from 29.3 to 30.07 degrees Celsius. The mud's pH hovered between 8.0 and 8.3, indicating a weakly alkaline environment. "An oily blackish sheen was also observed at a few vents as thin layers on the surface of the muddy material," Bhattacharjee noted—a detail that hints at the complex geochemistry brewing beneath the surface.
The origins of mud volcanoes have long fascinated geologists, and Baratang's recent eruption is no exception. Bhattacharjee outlined several possible causes: "This includes diapiric movement of over-pressured surface shale layers due to loading of terrigenous sediments, rapid subsidence or lateral tectonic compression, hydrocarbon generation in deep subsurface and expulsion of fluid from depth along deep-seated fracture/fault." In plain English, it's a cocktail of geological forces—shifting sediments, tectonic stress, and the slow churn of hydrocarbons deep below the crust.
While the eruption has provided scientists with invaluable data, it's also prompted safety concerns for residents and tourists. Baratang Island, with its lush forests and unique natural features, draws visitors from across India and beyond. But mud volcanoes are unpredictable, and the risk of sudden, violent eruptions can't be ignored. The GSI has urged the Andaman and Nicobar administration to take swift action. "We have asked them to reinforce fencing and hazard signage for sensitising the public regarding the unpredictability of violent mud eruptions, and maintain closure of all other approaches other than the viewpoint," Bhattacharjee said. The agency has recommended restricting public access, constructing a designated viewpoint at the end of the approach way, and keeping all other routes closed to ensure safety.
For local authorities, balancing scientific curiosity, public interest, and safety is a delicate act. The mud volcano has long been a point of pride and intrigue for the Andaman and Nicobar Islands, but the GSI's recommendations are clear: caution must come first. Reinforced fencing, hazard signs, and a single, safe viewpoint are now top priorities. The administration has been tasked with implementing these measures to safeguard both the curious and the unwary.
Beyond the immediate excitement and concern, the eruption has sparked renewed interest in India's geological heritage. The Oligocene epoch was a time of profound transformation. According to The Tribune, it saw the expansion of grasslands, a global drop in temperatures, and the rise of many modern animal groups. The Mithakari Group rocks ejected from Baratang's mud volcano are silent witnesses to this ancient world, preserved beneath layers of sediment and now brought to the surface by the restless Earth.
This isn't the first time Baratang's mud volcano has made headlines. Its last eruption occurred two decades ago, and the site has since been studied by geologists and visited by tourists alike. But the 2025 event stands out for its scale and the scientific insights it has yielded. The increase in the eruption's area and height, the continuous emission of mud and gases, and the discovery of Oligocene-aged material all make this a landmark event in Indian geology.
For scientists, the eruption is a rare opportunity to study the interplay of surface and subsurface processes in a dynamic environment. The presence of hydrocarbons, the alkaline nature of the mud, and the mix of sandstone and shale all point to a complex geological story—one that stretches back tens of millions of years. The GSI's ongoing analysis will undoubtedly shed further light on these processes, offering new understanding of how mud volcanoes form and evolve in the Indian subcontinent.
Meanwhile, for locals and visitors, Baratang's mud volcano remains a source of wonder—and, now more than ever, a reminder of nature's power and unpredictability. With new safety measures in place and scientists continuing their investigations, the island stands at the crossroads of curiosity and caution, its ancient secrets slowly bubbling to the surface.
As the mud continues to flow and the story unfolds, Baratang Island's volcano serves as a living link between past and present, a testament to the ever-changing face of our planet.
