A massive earthquake may have instantly changed the course of Ganga 2,500 years ago — and it could happen again

Imagine finding prime real estate along the banks of the most sacred river in your culture. Everything is perfect — rocky spots in the stream provide a daily catch of fish, the sun’s rays dance brilliantly on your hut all day, there’s abundant water for your crops, and you occasionally glimpse the elusive river dolphin, a creature of legend in your village. It’s the perfect place to raise your family.
But one night, you wake up to a thunderous rumbling followed by the torrential sound of rushing water. Stepping outside, you realise you've become the victim of what seems to be a celestial joke. The beautiful river that promised to nourish your family has vanished, leaving a dry valley in its place. This story might have been fiction, but a similar, very real fate might have affected the Ganga river in the ancient past.
Researchers have recently unveiled evidence of a previously unknown and extraordinarily powerful earthquake that struck near Dhaka, the capital of Bangladesh, approximately 2,500 years ago. This seismic event, estimated to have reached a magnitude of 7.5 or 8, was so forceful that it dramatically altered the course of the Ganga river, one of the largest rivers in the world.
The Ganga River, flowing approximately 1,600 miles from the Himalayas to the Bay of Bengal, is a vital waterway that merges with other major rivers like the Brahmaputra and the Meghna to form the largest river delta on Earth. This delta, known for its complex network of waterways, can naturally change course, but the violent rerouting caused by the ancient earthquake stands out as a unique geological event.
Typically, rivers can change course over years or decades due to sediment buildup, but an earthquake-driven avulsion of this magnitude and speed is unprecedented. As geophysicist Michael Steckler puts it, "I don't think we have ever seen such a big one anywhere."
The earthquake's immense power was buried in the landscape until recently discovered by a team of scientists who studied the geological clues in the region. Their research indicates that the quake caused a phenomenon known as avulsion, which rapidly rerouted the Ganga River. Satellite imagery initially revealed the clues, showing what appeared to be an old river channel running parallel to the Ganga about 62 miles south of Dhaka. Upon closer examination, the team found bands of sand cutting through the muddy ground. These bands, identified as seismites, are vertical layers of sand formed when an earthquake shakes watery soils.
Chemical analyses confirmed that these seismites formed during a single seismic event, leading the researchers to deduce the occurrence of a massive earthquake 2,500 years ago. Two possible mechanisms could have triggered this earthquake: the seismically active zone around the Shillong Massif mountains in northeastern India or the subduction of the Indian Ocean crust beneath Bangladesh, Myanmar, and northeastern India.
The study not only sheds light on an ancient earthquake but also raises concerns about future seismic activity in the region. A 2016 study led by Steckler indicated that both the Shillong Massif and the Indo-Burman subduction zone could potentially trigger similar magnitude earthquakes again. Such an event could have catastrophic effects, impacting around 140 million people in the densely populated regions of Bangladesh, India, and Myanmar.
The findings of this research have been published in Nature Communications and can be accessed here.