In a groundbreaking discovery, researchers have revealed that an earthquake approximately 2,500 years ago may have caused the Ganga River to abruptly change its course. This seismic event, which was previously undocumented, is believed to have been of a magnitude 7-8 and could have significantly altered the landscape of present-day Bangladesh.
The study, published in the journal Nature Communications, suggests that the earthquake was powerful enough to reroute the main channel of the Ganga, one of the most significant rivers in the world. The Ganga, which originates in the Himalayas, eventually merges with other major rivers, including the Brahmaputra and the Meghna, before flowing into the Bay of Bengal. This river system forms the world’s second-largest delta, surpassed only by the Amazon.
The researchers, led by Elizabeth L. Chamberlain from Wageningen University in the Netherlands, used satellite imagery to identify what they believe was the former main channel of the Ganga, located about 100 kilometers south of Dhaka, the capital of Bangladesh. This ancient riverbed, now filled with mud and primarily used for rice cultivation, spans about 1.5 kilometers in width and runs parallel to the current course of the river for approximately 100 kilometers.
During a field exploration in 2018, the research team discovered seismites geological formations created by seismic activity—in the area. Chemical analyses of these formations indicated that the region was struck by a massive earthquake around 2,500 years ago, which likely triggered a rapid and dramatic change in the river’s course.
Co-author Michael Steckler, a geophysicist at the Lamont-Doherty Earth Observatory of Columbia Climate School in the U.S., highlighted the unprecedented nature of the discovery. “I don’t think we have ever seen such a big one (earthquake) anywhere,” Steckler said. “It could have easily inundated anyone and anything in the wrong place at the wrong time.”
The study also points out two possible sources for the earthquake. One is the subduction zone located to the south and east, where a massive oceanic plate is pushing itself under Bangladesh, Myanmar, and northeastern India. The other possibility is the giant faults at the base of the Himalayas to the north, which are gradually rising due to the ongoing collision of the Indian subcontinent with the rest of Asia.
This research marks the first confirmed instance of an earthquake driving an avulsion a sudden change in a river’s course in a delta, particularly for a river as vast as the Ganga. The findings have profound implications for understanding the seismic vulnerabilities of the region, especially as a 2016 study led by Steckler indicated that the tectonic stress in these zones is still building up and could potentially result in a similar catastrophic event in the future.
If such an earthquake were to occur today, it could affect approximately 140 million people, according to the study’s estimates. This highlights the urgent need for further research and preparedness in the region, which remains highly susceptible to seismic shocks.
The discovery not only sheds light on the ancient history of one of the world’s most iconic rivers but also underscores the ongoing risks posed by tectonic activity in densely populated areas of South Asia.