PLUS researcher uncovers how earthquakes redefine river courses

An earthquake around 2500 years ago dramatically altered the course of the Ganges River in India, an international team of scientists revealed. This seismic event redirected the main channel of the Ganges into what is now Bangladesh, causing a significant "river avulsion" and reshaping the ancient landscape. If a similar earthquake struck today, it would be catastrophic for the densely populated region.

Published in Nature Communications, the study offers new insights into predicting natural hazards and their impacts. "Earthquakes are among the best-studied geohazards," explains geologist and co-author of the study Christoph von Hagke, of the Paris Lodron University of Salzburg (PLUS). While it’s well known that river disruptions, like dam collapses, can be disastrous, it was largely unknown that earthquakes could induce river avulsions, especially in delta estuaries. "This applies even to a river as significant as the Ganges", von Hagke notes.

A modern-day earthquake of this magnitude in Bangladesh, one of the world's most densely populated areas, could trigger flooding, destabilise sand deposits, and cause severe ground shaking, affecting millions living in the Ganges floodplain.

Digging deep

The research team reconstructed the ancient earthquake and river avulsion by analysing sediment layers. The sustained shaking forced pressurised sand into overlying clay, forming vertical sand dikes or "seismites." These indicators, found globally, helped pinpoint the earthquake's magnitude and epicentre.

We discovered extensive sand dikes, 30-40 centimetres wide, breaking through 3-4 meters of clay, located over 180 kilometres from the nearest probable seismic zones, suggesting a prehistoric earthquake of magnitude 7-8", says von Hagke.

The research, involving multiple scientific disciplines, underscores the importance of understanding past geological events to improve predictions of future natural disasters. 

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