Clues to ancient Kosi superflood say it could happen again today Premium

Geologists from Edinburgh and Glasgow universities, led by Prof. Rajiv Sinha from IIT Kanpur, studied sedimentary cores from Karnali, Ganga, and Kosi rivers to reconstruct floods in Miocene era. The team found evidence of an extreme monsoon event and hyperconcentrated flows 11,000 years ago in the Kosi river, which can cause floods, clogging, and avulsion. Climate change could increase the odds of such events, making integrated disaster management strategies essential.

At Rajiv Sinha’s laboratory in IIT Kanpur lie soil, sand, and rocks drilled out from across thousands of metres under the Karnali, Ganga, and Kosi rivers. Each sample, called a “sedimentary core” is held in a container 7.6 cm wide; together, they create snapshots of the rivers’ ancient history.

Every centimetre of these cores reveals the size and kind of sediment that the rivers were carrying at a point in time. The cores thus show how the composition of these sediments changed over time.

These cores have proved crucial to Prof. Sinha and a team of geologists from the Universities of Edinburgh and Glasgow, who are reconstructing river floods in the Gangetic plain between 23 and 5 million years ago, in the Miocene era.

Based on these studies, the researchers have reported that climate-change-related and seismic events ravaging the planet today could create super-floods that could be catastrophic for people in the Gangetic plain, in a paper published in the journal Communications Earth and Environment on August 23.

The findings signal that we need to urgently update India’s disaster management strategy to account for what Prof. Sinha calls “cascading hazards”: natural disasters that are triggered by other disasters.

The study began with a peculiar observation.

As rivers flow from their origins in the mountains to the plains, they carry rocks, gravel, and sand. The heavier particles – rocks and gravel – settle down earlier in the river’s trajectory whereas the lighter particles settle later. The part of the river’s path where there is a gradual transition from heavier to lighter particles on the riverbed is called the gravel-sand transition.