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Scientist Claim They Know Why There Is A Gravity Hole In The Indian Ocean

Scientist claim they know why there is a gravity hole in the Indian Ocean after being perplexed by the intriguing phenomenon where Earth's gravitational pull is weaker, the mass is lower than normal, and the sea level dips by an astonishing 328 feet (100 meters).

William Willis
Jul 24, 202327307 Shares384610 Views
Scientist claim they know why there is a gravity hole in the Indian Oceanafter being perplexed by the intriguing phenomenon where Earth's gravitational pull is weaker, the mass is lower than normal, and the sea level dips by an astonishing 328 feet (100 meters). After extensive research, a team of scientists from the Indian Institute of Science in Bengaluru, India, now believes they have found a credible explanation for its formation: the involvement of magma plumes from deep within the Earth, similar to those that give rise to volcanoes.
Using cutting-edge supercomputers, the researchers simulated the process behind the area's creation, delving as far back as 140 million years. Their findings, recently published in the journal Geophysical Research Letters, revolve around an ancient ocean that no longer exists. This discovery sheds light on the enigmatic origins of the gravity hole and offers a plausible explanation rooted in the geological history of the region.

A Disappearing Ocean

While humans have grown accustomed to envisioning Earth as a flawless sphere, the reality is quite different.
The Earth is basically a lumpy potato. So technically it’s not a sphere, but what we call an ellipsoid, because as the planet rotates the middle part bulges outward.- Coauthor Attreyee Ghosh, a geophysicist and associate professor at the Centre for Earth Sciences of the Indian Institute of Science
Earth is far from being uniform in its density and properties, resulting in variations that significantly impact its surface and gravitational field, as explained by Ghosh. These density differences within the planet influence the geoid, which refers to the level water would take if poured over Earth's surface. The geoid is shaped by how the material inside the Earth's interior, with varying masses underneath, attracts the surface.
The enigmatic "gravity hole" in the Indian Ocean, officially known as the Indian Ocean geoid low, represents the lowest point in this geoid and serves as the most significant gravitational anomaly. It forms a circular depression that begins just off the southern tip of India and spans approximately 1.2 million square miles (3 million square kilometers). This peculiar anomaly was first encountered during a gravity survey conducted from a ship in 1948 by Dutch geophysicist Felix Andries Vening Meinesz and has since remained a puzzle to researchers.
"It is by far the biggest low in the geoid, and it hasn’t been explained properly," Ghosh said.
In their quest for answers, Ghosh and her team employed sophisticated computer models to rewind the geological clock by an astounding 140 million years. This journey into the past allowed them to gain insights into Earth's ancient configuration when continents and oceans were positioned differently, and the density structure exhibited significant variations.
The researchers conducted 19 simulations, tracing the evolution of tectonic plate movements and the behavior of magma, the molten rock residing within the Earth's mantle, a thick layer between the core and the crust. Remarkably, in six of these simulations, a geoid low akin to the one observed in the Indian Ocean materialized.
The critical factor that consistently emerged in all six models was the presence of magma plumes surrounding the geoid low, along with the specific structure of the mantle in the region. These elements are believed to be the key drivers behind the formation of the enigmatic "gravity hole," as explained by Ghosh. By experimenting with different parameters of magma density, the researchers discovered that the geoid low failed to materialize in simulations where plumes were absent.
The genesis of these plumes can be traced back to the ancient history of India's landmass. Approximately tens of millions of years ago, India occupied a vastly different position, with an ocean separating its plate from Asia.
As India drifted northward, the ocean vanished, and the Indian plate eventually collided with Asia. This collision led to the subduction of the oceanic plate within the mantle, potentially triggering the formation of the plumes, which brought low-density material closer to the Earth's surface.

Scientists unravel the mystery of Indian Ocean | Latest English News | WION

The Future Of The Geoid Low

Based on the team's calculations, the geoid low took shape approximately 20 million years ago. As for its future, it remains uncertain whether it will ever vanish or relocate to a different location.
“That all depends on how these mass anomalies in the Earth move around,” Ghosh said. “It could be that it persists for a very long time. But it could also be that the plate movements will act in such a way to make it disappear - a few hundreds of millions of years in the future.”
The research has garnered attention from experts in the field who find it intriguing and commendable for exploring significant hypotheses, potentially stimulating further investigations. Professor Huw Davies from Cardiff University in the UK, who was not part of the study, expressed interest in the findings and emphasized the importance of delving deeper into this subject.
Dr. Alessandro Forte, a geology professor at the University of Florida in Gainesville, also not associated with the research, praised the use of computer simulations to unravel the origins of the Indian Ocean geoid low. He noted that this study represents an improvement over previous ones, as it incorporates both the descent of cold material through the mantle and the involvement of hot rising mantle plumes.
Despite the overall positive feedback, Dr. Forte pointed out a couple of flaws in the study's execution, which may warrant further attention and refinement in future research efforts.
"The most outstanding problem with the modeling strategy adopted by the authors is that it completely fails to reproduce the powerful mantle dynamic plume that erupted 65 million years ago under the present-day location of Réunion Island," he said. "The eruption of lava flows that covered half of the Indian subcontinent at this time - producing the celebrated Deccan Traps, one of the largest volcanic features on Earth - have long been attributed to a powerful mantle plume that is completely absent from the model simulation."
Forte raised another concern, highlighting the disparity between the geoid (surface shape) predicted by the computer simulation and the real-world observations. The discrepancies are particularly noticeable in regions such as the Pacific Ocean, Africa, and Eurasia.
Although the authors acknowledged a moderate correlation of around 80% between the predicted and observed geoids, they didn't provide a more precise numerical measure of the match in the study. This mismatch indicates the possibility of deficiencies in the computer simulation. Ghosh pointed out that the simulations cannot account for every conceivable factor, suggesting that some important elements might be missing from the models.
That’s because we do not know with absolute precision what the Earth looked like in the past. The farther back in time you go, the less confidence there is in the models. We cannot take into account each and every possible scenario and we also have to accept the fact that there may be some discrepancies on how the plates moved over time. But we believe the overall reason for this low is quite clear.- Coauthor Attreyee Ghosh, a geophysicist and associate professor at the Centre for Earth Sciences of the Indian Institute of Science
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