A major earthquake 2,500 years ago rerouted the Ganges River in what is now densely populated Bangladesh, according to a new study published in Nature Communications. This previously undocumented seismic event dramatically altered the river’s course, showcasing the profound impact of earthquakes on river dynamics.
GANGES RIVER ; HISTORICAL CONTEXT
The Ganges River, originating in the Himalayas, spans approximately 1,600 miles, merging with the Brahmaputra and Meghna rivers to form a complex network of waterways. These rivers empty into the Bay of Bengal, creating the world’s second-largest river system by discharge, after the Amazon. The river’s path is traditionally influenced by sediment deposition, which naturally leads to periodic shifts in its course.
GANGES RIVER ; GEOLOGICAL FINDINGS
Michael Steckler, a geophysicist at Lamont-Doherty Earth Observatory, remarked on the rarity of such an extensive avulsion caused by an earthquake. Unlike typical river course changes driven by sediment buildup, earthquake-related avulsions can occur almost instantaneously. This discovery highlights the unique geological event that dramatically altered the Ganges’ flow.
GANGES RIVER ; DISCOVERY IN SATELLITE IMAGERY
Using satellite imagery, the researchers identified what they believe to be the former main channel of the river, located about 100 kilometers south of Dhaka. This area, filled with mud and frequently flooded, has been used primarily for rice cultivation. The distinct features of the landscape suggested a sudden shift, likely triggered by seismic activity.
In 2018, Liz Chamberlain and her team found an excavation for a pond that revealed vertical dikes of light-collared sand piercing through horizontal mud layers. These features, known as seismites, are caused by earthquakes, where shaking forces sand layers upward, creating sand volcanoes. The seismites in this area were about 30 to 40 centimetres wide and extended through 3 to 4 meters of mud, indicating a powerful seismic event.
GANGES RIVER ; CHRONOLOGICAL EVIDENCE
Chemical analyses of sand grains and mud particles confirmed that the seismites and the channel’s abandonment occurred approximately 2,500 years ago. Similar seismite features were found 85 kilometres downstream, further supporting the theory of a massive earthquake triggering the avulsion.
POSSIBLE SEISMIC SOURCES
The earthquake likely originated from one of two sources. One possibility is a subduction zone to the south and east, where oceanic crust is being pushed under Bangladesh, Myanmar, and north-eastern India. Alternatively, the quake could have originated from the splay faults at the Himalayas‘ base, where the Indian subcontinent is colliding with Asia. Steckler’s 2016 study indicates that these zones are accumulating stress, potentially causing future earthquakes of similar magnitude.
Previous studies document a significant earthquake in 1762, which generated a tsunami that reached Dhaka. Another notable quake occurred around 1140 CE. These historical events underline the region’s seismic vulnerability.
IMPLICATIONS FOR MODERN BANGLADESH
The 2016 study estimates that a modern earthquake of this magnitude could impact 140 million people, highlighting the substantial risk to Bangladesh’s population. “Large earthquakes impact large areas and can have long-lasting economic, social, and political effects,” said Syed Humayun Akhter, vice-chancellor of Bangladesh Open University.
The Ganges is not alone in facing such risks. Other rivers in tectonically active deltas include China’s Yellow River, Myanmar’s Irrawaddy, and several rivers along the U.S. West Coast, such as the Klamath, San Joaquin, and Santa Clara. Additionally, the Jordan River spans borders across Syria, Jordan, the Palestinian West Bank, and Israel, all of which are susceptible to similar seismic influences.
This study not only reveals the dramatic impact of a 2,500-year-old earthquake on the Ganges River but also underscores the broader seismic risks in delta regions worldwide. As Bangladesh continues to develop, understanding these geological hazards is crucial for mitigating future risks and protecting vulnerable populations.
