Major Earthquake 2,500 Years Ago Redirected Ganga River, can occur again: Research Finds

A new study by US researchers sheds light on a powerful earthquake that rerouted the Ganges River a staggering 2,500 years ago. The findings, published in Nature Communications, raise concerns about the vulnerability of Bangladesh, a densely populated region situated along the river's current course.

Previously Unrecorded Earthquake Reshaped the Ganges

Led by geophysicists at Columbia Climate School, the study revealed a previously undocumented earthquake of magnitude 7 or 8 that dramatically altered the Ganges' path. This massive event rerouted the river's main channel in what is now Bangladesh, a region susceptible to large earthquakes even today.

Scientific Evidence Points to Seismic Event

Scientists have documented numerous instances of river course changes, known as avulsions. This study, however, provides unique evidence for an earthquake triggering such a shift in a massive river like the Ganges.

"The ability of earthquakes to cause avulsions in deltas, particularly for a river as immense as the Ganges, was not definitively confirmed before," explained lead author Liz Chamberlain, an assistant professor at Wageningen University in the Netherlands.

Satellite Imagery Reveals a Hidden Past

Chamberlain and her team utilized satellite imagery to identify a potential clue – a formation that could be the Ganges' former main channel. Located roughly 100 kilometers south of Dhaka, the Bangladeshi capital, this low-lying area stretches for approximately 1.5 kilometers in width and runs nearly parallel to the river's current course for about 100 kilometers. Presently, this area is filled with mud, prone to flooding, and primarily used for rice cultivation.

Unearthing Seismic Signatures

During their investigation, the researchers stumbled upon a freshly dug excavation site for a pond. Upon closer examination, they discovered sand volcanoes erupting at the surface. These geological markers, called seismites, measured 30 to 40 centimeters wide and pierced through 3 to 4 meters of mud.

The systematic orientation of these seismites offered a crucial clue. Their uniformity suggested a simultaneous formation, potentially triggered by a single event.

Chemical Analysis Confirms the Earthquake's Timing

Chemical analysis of sand grains and mud particles from the site provided further confirmation. The tests revealed that both the eruptions (seismite formation) and the subsequent abandonment and infilling of the river channel occurred around 2,500 years ago.

Moreover, researchers discovered a similar site approximately 85 kilometers downstream within the old channel, exhibiting mud infilling that dated back to the same period.

A Powerful Earthquake, a Lasting Impact

The combined evidence points to a large-scale, sudden avulsion event triggered by a powerful earthquake, estimated at magnitude 7 or 8 according to the study, funded by the US National Science Foundation.

This discovery raises concerns about the potential for future earthquakes in the region. A 2016 study led by Michael Steckler, a geophysicist at Lamont-Doherty Earth Observatory (part of Columbia Climate School), suggests that these areas are accumulating stress, potentially leading to earthquakes comparable to the one that struck 2,500 years ago.

Historical records reveal the devastating impact such events can have. The last major earthquake of this size occurred in 1762, triggering a deadly tsunami that traveled up the river all the way to Dhaka. Evidence also points to a similar event around 1140 CE.

"Large earthquakes have the potential to impact vast areas and leave long-lasting economic, social, and political repercussions," commented Syed Humayun Akhter, the vice-chancellor of Bangladesh Open University.