Around 2,500 years ago, India’s Ganges River experienced a significant shift due to a distant yet massive earthquake. This shift occurred in the delta, about 200 kilometers from where the river empties into the Bay of Bengal. The evidence of this ancient change in the river’s path was due to flooding caused by the shift, similar changes have been observed in other rivers today, especially far upstream, and this potential shifting of rivers in modern times could pose a threat to the hundreds of millions of people living in modern cities built on river deltas worldwide.
As rivers naturally meander across the landscape, especially in flat deltas, their courses can change gradually over time due to sediments piling up and diverting the river. However, earthquakes can trigger abrupt channel-jumping that can occur in a matter of weeks or days. Thus, after a river channel shifts, evidence of the old channel typically remains, with depressions and remnants of the old river seen in the landscape. Scientists discovered features known as seismites in the Ganges Delta, remnants of ancient sand volcanoes that formed due to seismic waves pressurizing a layer of watery sand, bursting upward through overlying layers of muddy sediment.
The seismites found in the Ganges Delta were caused by an earthquake that likely occurred around 2,500 years ago, based on analysis of sand grains within the sediment. Sand blows, as seen in the seismites, are rare and difficult to explain without the force of an earthquake. The earthquake itself probably ranged between magnitude 7 and magnitude 8, according to the researchers. The finding of seismites and evidence of the ancient river shift sheds light on the history of the Ganges River and the potential risks associated with seismic activity in the region.
The study of ancient seismic events provides insight into the vulnerability of regions like the Ganges Delta to future earthquakes and river shifts caused by such events. The potential threat is significant, with up to 170 million people living in the delta region at risk from flooding in the event of another earthquake-induced river shift. This vulnerability is further compounded by rising sea levels due to climate change, making the region even more at risk for flooding. Understanding and preparing for these events, despite not having experienced them firsthand, is a critical challenge that requires proactive measures to mitigate the potential impact on communities and infrastructure.
The discovery of ancient seismites and evidence of the Ganges River’s past shifts highlights the interconnected risks posed by seismic activity, river dynamics, and climate change in delta regions worldwide. Proactive planning and adaptation strategies are essential to address the threat of future earthquakes and river shifts, especially in densely populated areas like the Ganges Delta. By studying the geological history of rivers and the impacts of seismic events, scientists can better understand and anticipate the potential risks to vulnerable communities and ecosystems in these dynamic landscapes. Addressing these challenges requires a multidisciplinary approach that integrates geological, environmental, and societal factors to enhance resilience and promote sustainable development in delta regions facing complex and interconnected threats from natural hazards.
