Earthquake 2500 years ago abruptly changed Ganga river’s course

Sub: Geo

Sec: Geomorphology

Context:

In 2018, geochronologist Elizabeth Chamberlain and her team from Wageningen University studied the movement of river channels in the Ganga delta, focusing on a 2-km-wide “paleochannel” 45 km south of the modern Ganga, now a rice cultivation area.
Geological measures revealed the Ganga avulsed about 2,500 years ago, leaving behind the paleochannel.

Discovery of Sand Dikes:

The team found two large sand dikes east of the paleochannel, indicating liquefaction due to an ancient earthquake.
These dikes provided evidence that earthquakes can move rivers, confirmed by an earthquake of magnitude 7 to 8 causing the Ganga’s course shift over two millennia ago.
The study emphasizes the need for forecasting major earthquakes to prevent river avulsion.

How Earthquakes Move Rivers?

The earthquake likely originated from the Indo-Burma mountain ranges or the hills of Shillong, with a significant impact irrespective of the exact location.
The composition of sand dikes showed conclusive evidence of a major ancient earthquake.
Using optically stimulated luminescence (OSL) dating, Dr. Chamberlain’s team determined the avulsion and the earthquake occurred around 2,500 years ago.
OSL dating method relies on estimating how long a mineral grain (i.e. a mineral particle less than a few millimetres in size, like quartz grains in sand or mud) has been buried by measuring the amount of natural radiation stored in it.
Samples from the paleochannel and sand dikes indicated the same time frame, supporting the hypothesis that the earthquake caused the avulsion.

Future Hazards and Research

Large earthquakes potentially triggering river avulsions can lead to devastating floods, especially in densely populated regions like the Ganges-Meghna-Brahmaputra delta.
Human activities and climate change increase the risk of avulsion, with rapid subsidence and extreme weather events contributing factors.

Source: DTE