Context:

A recent study suggests that an earthquake around 2,500 years ago may have caused the Ganga River to abruptly change its course in present-day Bangladesh.

More on the news:

• The study was published in Nature Communications.
• It examines an undocumented earthquake that possibly had a magnitude of 7-8 and its impact on the Ganga River.

Key Findings:

River Course Change (Avulsion):

• The earthquake possibly rerouted the main channel of the Ganga River in present-day Bangladesh.
• Rivers in major deltas, like the Ganga, often change course, but earthquakes can cause these changes almost instantaneously.
• Researchers were exploring an almost 2-km-wide “paleochannel” (a well-preserved mud and sand archive of the river’s ancient course) about 45 km to the south of the modern Ganga River.
• Satellite images revealed the former main channel of the Ganga about 100 km south of Dhaka, Bangladesh.
• During their fieldwork, the team also found two large sand dikes (seismites) a kilometer to the east of the paleochannel.
  These dikes are formed when earthquakes disturb the river bed and cause sediments to flow as if they were liquid (liquefaction process).
  These sand dikes held the first proof that earthquakes can move rivers.

Research Methodology:

• To find the time when these two events occurred researchers used a technique called optically stimulated luminescence (OSL) dating.
  This method relies on estimating how long a mineral grain (i.e. a mineral particle less than a few millimeters in size, like quartz grains in sand or mud) has been buried by measuring the amount of natural radiation stored in it.
  Chemical analyses of sand and mud indicate the earthquake occurred around 2,500 years ago.

Possible Earthquake Sources:

• A subduction zone to the south and east, where an oceanic plate is pushing under Bangladesh, Myanmar, and northeastern India.
• Giant faults at the foot of the Himalayas to the north, which are gradually rising because the Indian subcontinent is slowly colliding with the rest of Asia.
  The study’s findings call for urgent forecasting of major earthquakes that can cause the avulsion of rivers thus making decision-makers and the people at large aware of the risk is of paramount importance so they can prepare better for such events in the future.