In the June 2024 paper in Nature Communications, scientists reported that an earthquake of magnitude 7 to 8 caused the Ganga River to dramatically shift its course approximately 2,500 years ago.
Earthquakes
- About: Earthquake refers to the sudden shaking of the earth’s crust. It is highly destructive of all the natural disasters. They occur when there is a rupture in the Earth’s surface, typically along a fault line, leading to seismic waves that propagate through the ground.
- Causes of Earthquakes:
- Tectonic Activities: Earthquakes result from a series of earth movements brought about by a sudden release of energy during the tectonic activities in the earth’s crust.
- Other causes: It could also be triggered by volcanic eruption, rock falls, landslides, subsidence, particularly in the mining areas, impounding of dams and reservoirs, etc.
- Measuring Earthquakes:
- Seismographs: It is an instrument to detect and record seismic waves produced by earthquakes.
- The time, location and intensity of an earthquake from the information recorded by a seismometer.
- This record also provides information about the rocks the seismic waves travelled through.
- Seismographs: It is an instrument to detect and record seismic waves produced by earthquakes.
Liquefaction:
- Liquefaction occurs when loosely packed, water-logged sediments near the ground surface lose their strength due to strong ground shaking during an earthquake.
- The soil behaves like a liquid, leading to major damage. This phenomenon has been responsible for substantial damage in historical earthquakes worldwide
- For instance, during the Bhuj Earthquake of 2001, strong shaking caused liquefaction in fine silts and sands below the water table in the Rann of Kachchh. Mineral grains settled and expelled their interstitial water to the surface.
- Scaling Earthquake Events: The earthquake events are scaled either according to the magnitude or intensity of the shock.
- Richter Scale: The magnitude scale is known as the Richter scale. The magnitude relates to the energy released during the quake. The magnitude is expressed in absolute numbers, 0-10.
- Mercalli Scale: The intensity scale is named after Mercalli, an Italian seismologist. The intensity scale takes into account the visible damage caused by the event. The range of intensity scale is from 1-12.
- Scaling Earthquake Events: The earthquake events are scaled either according to the magnitude or intensity of the shock.
Key Findings from the Research
- Discovery of Sand Dikes: During fieldwork, scientists found two large sand dikes a kilometre east of an ancient river channel.
- These dikes, formed by liquefaction during an earthquake, showed that sediments flowed like liquid due to seismic activity.
- Evidence of Earthquake
- Presence of Dikes: The team suspected these dikes indicated a major earthquake event, which was later confirmed.
- The dikes provided the first evidence that earthquakes can change the course of rivers.
- Presence of Dikes: The team suspected these dikes indicated a major earthquake event, which was later confirmed.
- Study Results
- Shift of Ganga River: The magnitude of the earthquake caused the Ganga River to shift its course over 2,500 years ago.
- Presence of Paleochannel: This shift created a well-preserved paleochannel (Ancient riverbed) in the area, which is now used for rice cultivation.
- Timing Correlation: The timing of the sand dikes’ formation matched the river’s avulsion, supporting the link between the earthquake and the river’s shift.
- Optically Stimulated Luminescence (OSL) Dating for Timing Analysis:
- About: Optically Stimulated Luminescence (OSL) dating is a method used to determine the burial age of sedimentary deposits. It was used to determine the timing of both the earthquake and the river avulsion.
- Mechanism of OSL Dating: OSL dating estimates how long mineral grains have been buried by measuring the natural radiation stored in them.
- To estimate the amount of energy stored, the researchers shine blue light on the grains, causing the trapped electrons to escape the crystal structure and return to the atoms.
- When they do so, they emit a photon of light.
- A photomultiplier tube captures the photons and estimates their number, leading to a measure of the trapped energy.
- Unresolved Questions
- The exact origin of the earthquake remains unknown.
- Researchers suggest it could have originated in the Indo-Burma mountain ranges or the Shillong hills, where the Indian and Eurasian tectonic plates meet.
- The exact origin of the earthquake remains unknown.
Future Hazards and Preparedness
- Increased Risk from Earthquakes
- The discovery that large earthquakes can trigger major river avulsions reveals their potentially greater impact than previously understood.
- River avulsions have caused some of history’s deadliest floods, with severe cascading effects on heavily populated areas like the Ganges-Meghna-Brahmaputra delta.
- Exacerbating Factors
- Human activities and climate change increase the risk of river avulsions.
- Factors include rapid subsidence near riverbanks due to widespread embankments and rising sea levels coupled with extreme weather events.
Way Forward
- Need for Future Research
- Future research should investigate the frequency of quake-driven avulsions and develop forecasting methods for such major earthquakes.
- Decision-makers and residents in the delta region must prepare for the risks associated with these avulsions.
- Implications for Future Preparedness: The research highlights the need for better earthquake forecasting to prepare for potential river shifts.
- Experts stress the importance of increasing public awareness and preparedness for such seismic events.
- Regional Cooperation
- Effective preparedness requires collaboration between India, Bangladesh, and Myanmar in research, monitoring, and support.
Overview of the Ganga River
- About : The Ganga is India’s longest river, flowing over 2,510 km through mountains, valleys, and plains. It is considered the most sacred river in Hinduism.
- Basin and Coverage
- The Ganga basin spans 1,086,000 sq. km across India, Tibet, Nepal, and Bangladesh.
- In India, it drains 861,452 sq. km, about 26% of the country’s land area.
- Source and Course
- Originates in the Gangotri Glacier in the Himalayas, initially called Bhagirathi.
- Becomes the Ganga at Devprayag upon joining the Alaknanda.
- Tributaries
- Principal right-bank tributaries: Yamuna, Son.
- Left-bank tributaries: Ramganga, Ghagra, Gandak, Kosi, Mahananda.
- Important sub-tributaries: Chambal, Betwa.
- Delta and Discharge
- Joins the Brahmaputra in Bangladesh, flowing as the Padma.
- Widens into the Ganges Delta in the Sundarbans before emptying into the Bay of Bengal.
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