The Ganges River is not only a significant source of water for India but also holds major importance in terms of heritage, history, and religious activities. The river has played a significant role in shaping India's history as it traverses through multiple regions. A recent study has discovered that the Ganges underwent a sudden and drastic change in its course. This change was attributed to a massive earthquake that occurred approximately 2,500 years ago. While similar alterations have been observed in other rivers, they have mostly occurred further upstream. However, in the case of the Ganges, this ancient shift took place within the river delta, approximately 200 kilometers from its point of discharge into the Bay of Bengal.
The study says that earthquakes present severe hazards for people and economies and can be primary drivers of landscape change yet their impact to river-channel networks remains poorly known. The findings raise concerns about the potential impact of similar river course shifts on modern cities situated within river deltas worldwide. The threat of flooding from such shifts poses a significant risk to the hundreds of millions of people residing in these urban areas. “The recurrence of comparable earthquake-triggered ground liquefaction and a channel avulsion would be catastrophic for any of the heavily populated, large river basins and deltas along the Himalayan arc (e.g., Indus, Ganges, Brahmaputra, Ayeyarwady),” says the study. “The compounding effects of climate change and human impacts heighten and extend the vulnerability of many lowlands worldwide to such cascading hazards.”
Changes in a river's course can take a long time, sometimes spanning years to centuries, according to geophysicist Elizabeth Chamberlain from Wageningen University & Research in the Netherlands who was part of the team. However, the impact of an earthquake can cause a river to change its path in just weeks or days. When a river changes its course, the old channel can gradually fill with sediment. Nonetheless, traces of the old channel typically persist, as Chamberlain explains. She and her team spotted a crescent-shaped depression about 45 kilometers from the current Ganges by analysing satellite images of the Ganges Delta. This depression, measuring almost 2 kilometers wide and stretching for dozens of kilometers, was likely a main channel of the Ganges in the past.
Researchers have documented numerous changes in river courses, known as avulsions, some of which have occurred in response to earthquakes. However, Michael Steckler, a co-author of the study and a geophysicist at the Lamont-Doherty Earth Observatory, stated that they had never observed such a significant avulsion before. He mentioned that it could have easily overwhelmed anything or anyone in the wrong place at the wrong time.