A gravity hole is found in the Indian Ocean. What is it and What do scientists think about it? Digging deep into the mystery

A gravity hole has been found in the Indian Ocean. It is actually a spot where the gravitational pull of the Earth is weaker, and where its mass is actually lesser than normal. At this point, the sea level decreases by around 328 feet (100 meters).

For a very long time, geologists have been stressing over the issue. However, researchers from the Indian Institute of Bengaluru, have successfully found the explanation behind its formation. The proposed hypothesis states that plumes of magma emerging from the depths of the Earth may have led to the formation.

In order to arrive at this hypothesis, the team made use of supercomputers to stimulate the formation of the region, tracing its history as far as 140 million years ago. Published in the Geophysical Research Letters, the findings revolve around an ancient ocean that has disappeared.

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The ocean that no longer exists

Many believe that the shape of the Earth is actually that of a perfect sphere. However, this is not true.

A co-author of the study, associate professor at the Centre for Earth Sciences of the Indian Institute of Science, and a geophysicist, Attreyee Ghosh expresses that the Earth is actually 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,” she further expressed.

Earth's density and properties are not homogenous in nature. Therefore, it won't be wrong to say that some regions of the planet are clearly more dense than others. This difference in density impacts the surface of the Earth and its gravity. The geophysicist further explains that if one pours water on the Earth's surface, the level taken by the water is known as a geoid. This is controlled by the differences in density in the material underneath the Earth, as they attract the surface of the planet in differing ways based on the amount of mass underneath.

Officially known as the Indian Ocean geoid low, the gravity hole in the Indian Ocean is actually the lowest point in that geoid. Its most significant gravitational anomaly, which creates a circular depression, commences just off the southern tip of India and spreads across approximately 1.2 million square miles.

It was Felix Andries Vening Meinesz, a Dutch geophysicist, who discovered the anomaly in the year 1948. The discovery happened at the time of a gravity survey from a ship. 

Ghosh further expressed that it is the biggest low in the geoid so far. Moreover, it has not been explained completely till now.

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The geophysicist and her colleagues made use id computer models to go back 140 million years to view the complete scenario in the geological light and fetch a potential answer to the mystery. After the experiment, she says that some information is present about how the planet looked like back then. She further reveals that the oceans and continents were actually in different locations. The density structure was quite different too.

This information worked as a starting point. Up to the present day, the team conducted around 19 simulations and recreated the tectonic plates shift, the behavior of magma, and everything happening inside the mantle of the planet. In a total of six such simulations, a geoid low identical to the Indian Ocean geoid low was created.

What connected all these six simulations was the presence of magma plumes surrounding the geoid low. Along with the structure of the mantle in the area, the plumes of magma are thought to be agents behind the creation of the gravity hole, explains Ghosh. In areas where the plumes weren't found, the formation of a low did not take place.

It was the extinction of an ancient ocean that originated the plumes. This took place as the landmass of India drifted and collided with Asia millions of years ago. “India was in a very different place 140 million years ago, and there was an ocean between the Indian plate and Asia. India started moving north and as it did, the ocean disappeared and the gap with Asia closed, Ghosh explained. The formation of plumes could have been possible as the oceanic plate went inside the mantle, thereby bringing the low-density material closer to the surface of the Earth.

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