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The Padma earthquake changed the course of 2,500 years ago. Could it happen again?

The Padma earthquake changed the course of 2,500 years ago.  Could it happen again?
The Padma earthquake changed the course of 2,500 years ago.  Could it happen again?

 


Can a river abandon its current channel and make a new course due to seismic activities such as an earthquake?

This is a question that geologists around the world have pondered for decades, and they have finally reached a concrete conclusion, with a groundbreaking study published in the journal Nature Communications on June 17.

The study is titled “Cascading Risks of a Major Earthquake in the Bengal Basin and a Sudden Overturn of the Ganges River.”

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The study makes a strong case for the potential impact on Bangladesh, known for its large, dynamic river systems and related flood challenges, if it experiences similar earthquakes in the future due to the ongoing collision of the Indian, Eurasian and Burmese tectonic plates.

First, the study shows that a powerful earthquake, estimated at magnitude 7 or 8, that struck about 2,500 years ago may be responsible for the current course of the Ganges.

The Ganges originates in the Himalayas and flows for about 1,600 miles, eventually merging with other major rivers, including the Brahmaputra and Meghna. These rivers form a complex network of waterways that flow into the Bay of Bengal, covering the regions of Bangladesh and India.

The combination of a large river getting ready to collapse, and a large earthquake nearby, is clearly a rare event, as both are very rare. That's why it's important to find that this happened 2,500 years ago and can be documented.

Dr. Michael Stickler, a geophysicist at the Lamont-Doherty Earth Observatory

Together they form the second largest river system in the world in terms of drainage, surpassed only by the Amazon River.

Today, the Ganges River, known as the Padma in Bangladesh, lies about 50 kilometers south of Dhaka. However, using satellite images, the research team found evidence of its previous path about 100 kilometers from the city.

It is now a low-lying area about 1.5 km wide that extends intermittently parallel to the current riverbed for a distance of about 100 km. The old canal is filled with mud, often flooded, and is used to grow rice.

Geologists have long worried that a large earthquake could change the course of rivers in Bangladesh, said study co-author Dr. Michael Stickler, a geophysicist at the Lamont-Doherty Earth Observatory, part of the Columbia Climate School. This study provides evidence that this has already happened at least once in the past.

According to him, the Ganges-Padma is currently located near the western edge of the Indo-Burma subduction zone. This suggests that there is a possibility that the earthquake could raise the river channel, leading to another separation.

“The combination of a large river being ready to collapse, and a large earthquake nearby, is clearly a rare event, as both are very rare. For this reason, it is important to find that this happened 2,500 years ago and can be documented.” Dr Stickler told Business Standard.

Lead author Dr. Lise Chamberlain, an assistant professor at Wageningen University in the Netherlands, emphasized the fact that although the chance of recurring earthquakes associated with the movement of the river's path is low, if such an event occurred today, it would be an “extreme event” for Bangladesh.

Bangladesh is a low earthquake-prone country but is highly vulnerable to major earthquakes. The country's geotectonic configuration, which lies along two of the planet's active plate boundaries, indicates high potential for future damaging earthquakes and the possibility of rare but very large quakes that could cause damage far from their epicenters.

Dr. Syed Humayun Akhtar, Vice Chancellor of Bangladesh Open University

“Our study shows that in addition to damaging shaking of buildings and infrastructure, a large earthquake can lead to the risk of river flooding in Bangladesh,” she said.

Dr. Syed Humayun Akhtar, Vice Chancellor of Bangladesh Open University and another co-author of the study, emphasized that the findings of this study have profound implications.

He pointed out that the earthquake in 1787 caused the Brahmaputra River to change its course to become the Jamuna River. Likewise, the Meghna River, which previously flowed along the slopes of Lalmai, was shifted 20 to 40 kilometers westward by a major earthquake approximately 1,000 to 1,200 years ago.

According to him, Bangladesh is a low earthquake-prone country but highly vulnerable to major earthquakes. The country's geotectonic configuration, which lies along two of the planet's active plate boundaries, indicates high potential for future damaging earthquakes and the possibility of rare but very large quakes that could cause damage far from their epicenters.

Geological records show that large earthquakes have devastated the country and the surrounding region several times in the historical and prehistoric past, leaving imprints in the sediments, such as liquefaction, sedimentary eruptions from subsurface high-pressure geological horizons, changes in landform, and river subsidence.

For example, the earthquake on April 2, 1762, on the Arakan coast, led to the eruption of mud volcanoes at Sitakunda Hill about 300 kilometers north of the epicenter. The eruption brought out large masses of crystalline limestone from deep-rooted formations.

“The earthquake was so violent and devastating that it triggered a tsunami and disturbed the water bodies of the Giles and rivers in Dhaka, causing the loss of 500 people. Boats were also capsized and houses were swept away,” said Dr Akhtar, who is also a former professor of geology. At Dhaka University.

He also noted that the country's location adjacent to the very active Himalayan Front in the north and the Burma deformation front in the east, exposes it to strong tremors from a variety of seismic sources that can produce tremors of magnitude 8 or more.

Notably, Dr. Akhtar also co-authored another study in 2016 that found evidence of increased pressure in Bangladesh, where two tectonic plates lie beneath the world's largest river delta.

The threat is a subduction zone, where one part of the Earth's crust, or tectonic plates, slowly pushes under another.

The largest earthquakes on Earth, such as the 2004 Indian Ocean tsunami and the 2011 Tohoku earthquake in Japan, have occurred along these areas. However, all known subduction zones have been under the ocean, but this one lies entirely underground, greatly doubling the threat level.

“The effects of strong tremors from such an earthquake would directly affect much of the country, including densely populated Dhaka. Large earthquakes occur less frequently than serious floods, but they can affect much larger areas and have economic and social impacts.” And long-term political effects, Dr. Akhtar explained.

Hence, Dr. Stephen Goodbread, chair of the Department of Earth and Environmental Sciences at Vanderbilt University, and another co-author of the study, suggested that the study could help planners and policy makers in Bangladesh “make better, scientifically informed decisions about infrastructure design and placement.” In the future.”

Sources

1/ https://Google.com/

2/ https://www.tbsnews.net/features/panorama/earthquake-changed-padmas-course-2500-years-ago-can-it-happen-again-880126

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