New Delhi, Dec. 28: Scientists have discovered evidence to suggest that the rivers of Punjab flowed east into the Ganges until five million years ago when rising mountains diverted them westward into the Indus.

Geologists studying the chemical signatures of changes in the sediments carried by the Indus over the past 30 million years have found that the source of sediments changed five million years ago.

The Indus originates in Tibet and flows through India and Pakistan into the Arabian Sea. As rivers make their way to the sea, they carry fine grain sediments from the erosion of rocks upstream.

Geologists Peter Clift at the University of Aberdeen in Scotland and Jerzy Blusztajn at the Woods Hole Oceanographic Institution in the US studied sediments accumulated at the bottom of the Arabian Sea to determine how the erosional discharge of the Indus has changed over time.

Their studies have revealed that the source of the Indus sediments was dominated by erosion north of the Indus until five million years ago. After that, the river began to receive erosional products from Himalayan sources, the researchers said reporting their findings in the journal Nature.

They believe this change in the erosional pattern was caused by a re-routing of the Sutlej, Ravi, Chenab and Jhelum rivers from their original southeasterly flow into the Ganges and the Bay of Bengal to a westward flow into the Indus and the Arabian Sea.

This is “strong evidence for a major change in the geometry of the western Himalayan river system five million years ago, probably caused by a change in the mountains”, said Blusztajn.

The findings by Blusztajn and Clift appear to bolster independent claims by Indian scientists earlier this year that significant changes occurred in the Himalayas about five million years ago.

“Something dramatic happened in the Himalayas around that time,” said Sourendra Bhattacharya, a scientist at the Physical Research Laboratory in Ahmedabad who has been studying ancient climate.

Bhattacharya and his colleagues had analysed soil in the Shivalik mountains and detected telltale chemical signals of an abrupt intensification of the monsoon rainfall over India about six million years ago. They speculate that rising mountains could have led to the increase in rainfall.

“Given the margin of error in geological studies, five million and six million are relatively close. It’s possible the intensity of rainfall and the diversion of the rivers may be connected through the uplift of mountains by tectonic forces,” Bhattacharya said.

The Arabian Sea is one of the largest areas of sediment deposition in the oceans. Clift and Blusztajn used a number of sediment samples from scientific and industrial drilling sites in the Arabian Sea to reconstruct the changes in the sediments brought by the Indus.

They studied an element called neodymium in the sediments. Changes in the sediments would be reflected in changes in the chemical fingerprints of neodymium.

The studies showed differences between the Indus river sediments before five million years and after five million years.

Bhattacharya said the diversion of the four rivers to the Indus would also have caused changes in the sediment patterns in the Bay of Bengal. “This may be tested through a similar study in the Bay of Bengal,” he said.