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Scientists have known about the existence of a “gravity hole” in the Indian Ocean for decades, but don’t know why it exists.
Officially known as the “Indian Ocean Geoid Low,” it is not a conventional physical hole, but rather a part of the ocean where gravity is lower than average.
This drop in gravity means that the water level is about 100 meters lower than the surrounding area – like a groove in a ‘bumpy potato’.
Now a team of researchers in India claims the gravity hole was formed by plumes of low-density magma rising from Earth’s mantle.
These plumes were generated by the remnants of a submerged tectonic plate called Tethys, which was lost when India became part of Asia 50 million years ago.
The gravity hole, also called a geoid, is not a physical hole, but a part of the ocean where gravity is lower than average. The Indian Ocean geoid layer (IOGL) is the deepest geoid on Earth
The Earth’s mantle is a layer of silicate rock between the crust and the outer core. Pictured are the layers of our planet
Mantle plumes — upwellings of abnormally hot rock in the Earth’s mantle — are generally caused by gravitational anomalies around the Earth.
The new study was conducted using computer simulations by two geophysicists from the Indian Institute of Science in the city of Bengaluru.
“Using these simulations, we were able to see that this geoid layer did not exist at some point and then took shape about 20 million years ago,” study author Attreyee Ghosh told MailOnline.
“Such studies would help us address many of Earth’s unresolved features in the future.”
Earth is often depicted as a perfectly round sphere in illustrations and physical spheres, but experts think it looks more like a “bumpy potato” in shape.
Our planet’s uneven surface is due to regions of non-uniform gravity due to the uneven distribution of matter in its interior.
The surface deformations are compounded by the movement of tectonic plates that have created mountains and valleys on the Earth’s surface.
Since the oceans cover about 70 percent of the Earth’s surface, these deformities also affect the shape of the oceans.
‘Geoid anomalies’ are generated by uneven mass distribution within the deep Earth. One such low-gravity point is located just south of the Indian Peninsula, called the Indian Ocean Geoid Low (IOGL), which extends much of the way south of the Indian subcontinent.
The ‘Indian Ocean Geoid Low’ was discovered in 1948 by Dutch geophysicist Felix Andries Vening Meinesz (pictured)
This is illustrated no more than by the Geoid Low in the Indian Ocean, which is found about 700 miles south of the Indian Peninsula.
It was discovered in 1948 by Dutch geophysicist Felix Andries Vening Meinesz during a gravity survey on ships, when he found that the sea level in the region was significantly lower than the global average, indicating a gravitational anomaly.
Although we’ve sent missions to explore the outer reaches of our solar system, the deepest boreholes on Earth only reach a few miles, so searching for answers within our planet is a bit of a challenge.
To address this, the experts used computer tracking software how Earth’s tectonic plates have moved around the hole over the past 140 million years.
Violent interactions between the tectonic plates may hold clues to why this gravitational anomaly exists today, they thought.
It’s common knowledge that the Earth’s lithosphere—the rocky, outer shell—is made up of about 15 tectonic plates that are constantly moving and rubbing against each other.
About 50 million years ago, the relatively small Indian plate began to collide with the much larger Eurasian plate, creating the Himalayas.
Before then, the Indian Plate was part of an ancient southern “supercontinent” today called Gondwana, but it began to drift northward.
When the Indian plate collided with the Eurasian plate, another plate between the two — Tethys — subducted and engulfed the mantle.
Map showing the arrangement of Earth’s tectonic plates today. Note the relatively small Indian plate, highlighted in red
The Indian Plate used to be part of an ancient southern “supercontinent” today called Gondwana. Pictured are the historical plates and their movement as Gondwana broke up (a process thought to have started about 120 million years ago)
Tethys was the site of a vast ocean, home to a diverse ecosystem of marine life, including fish, sharks, whales, and dolphins.
According to the researchers, plates of the Tethys plate sank into Earth’s lower mantle and lifted magma, creating the plumes.
“These plumes, along with the mantle structure near the geoid layer, are responsible for the formation of this negative geoid anomaly,” they say in their paper.
The team says the question of how the Geoid Low formed in the Indian Ocean is “controversial,” but they show the plumes were “integral” in their creation.
Their study has been published in the journal Geophysical Survey Letters.