ancient-quake-altered-ganga-s-course

An earthquake around 2,500 years ago could have drastically altered the course of the Ganga River, according to a new study published in the journal Nature Communications.

 

Researchers suggest that this "undocumented" quake, potentially measuring 7-8 in magnitude, redirected the river’s main channel in what is now Bangladesh, a region particularly vulnerable to significant seismic activity.

 

Michael Steckler, a co-author of the study and a geophysicist at Lamont-Doherty Earth Observatory, Columbia Climate School, US, remarked, "I don't think we have ever seen such a big one (earthquake) anywhere. It could have easily inundated anyone and anything in the wrong place at the wrong time."

 

Originating in the Himalayas, the Ganga eventually merges with other major rivers, including the Brahmaputra and the Meghna, before flowing into the Bay of Bengal. Together, these rivers form the world's second-largest river system, second only to the Amazon.

 

River-course changes, known as 'avulsions,' are common in river deltas and have been documented globally, often occurring in response to earthquakes.

 

Rivers typically take years or even decades to change course, but an earthquake can cause an avulsion almost instantaneously, explained Steckler.

 

This study marks the "first confirmed instance" of an earthquake driving avulsion in river deltas, particularly for a massive river like the Ganga, stated lead author Elizabeth L. Chamberlain, an assistant professor at Wageningen University in the Netherlands.

 

By analysing satellite images, the research team identified what they believe was the former main channel of the river, located approximately 100 kilometers south of Dhaka, Bangladesh’s capital.

 

This area, about 1.5 kilometers wide and extending intermittently for around 100 kilometers almost parallel to the current river course, is low-lying and filled with mud. It frequently floods and is primarily used for rice cultivation.

 

In 2018, researchers exploring this area discovered features indicative of seismic activity, known as seismites. Multiple seismites formed simultaneously, and chemical analyses of the sand and mud suggested that an earthquake of approximately 7-8 magnitude struck the area around 2,500 years ago.

 

The researchers propose two possible sources for the quake. One potential source is a subduction zone to the south and east, where an oceanic crust plate is pushing under Bangladesh, Myanmar, and northeastern India.

 

Another possibility is the giant faults at the foot of the Himalayas to the north, which are rising due to the slow collision of the Indian subcontinent with the rest of Asia.

 

A 2016 study led by Steckler indicated that these zones are accumulating stress and could produce earthquakes similar to the one from 2,500 years ago. If a similar quake occurred today, it could affect approximately 140 million people, the study estimated.