Per researchers, there is a huge hole in the Indian Ocean. However, it is not the type which would drain all the ocean’s water. Instead, this is a term used by geologists to explain a particular place where the planet’s gravitational pull is less than the average.
This is because less mass under that spot makes the gravitational pull weaker than in any other place on Earth.
For years scientists have tried to understand the underlying cause behind such phenomenon and finally found out why there is a massive hole in the Indian Ocean.
Two geologists named Debanjan Pal and Attreye Ghosh from the Indian Institute of Science in Bengaluru city of India’s southern state of Karnataka, have put forward the explanation in their newly published study.
They say it was caused by plumes of molten rock coming from deep beneath Africa at the fringes of the sinking remains of an ancient ocean bed. In simpler words, its origins can be traced to an ancient ocean bed that got submerged due to tectonic plate movements.
They explained further that Earth is not a perfect sphere, and if it were the case, then gravity would have been the same at all points on its surface. However, our blue planet is flatter than a true sphere around the North and South Poles and bulges out near the equator.
Also, different places exert a different gravitational pull, which depends on the mass of the earth’s crust, mantle and core under them.
The earth’s most famous gravitational anomaly in the Indian Ocean is a significant dip in the geoid, also called the Indian Ocean Geoid Low. It spans over 3 million sq km and is centred around 1200 km southwest of India’s southern tip.
The dip cannot be seen at the surface. Due to low gravitational pull along with higher gravitational pull from neighbouring regions, the sea level over the hole is 106 m less than the global average, according to the new study.
Per the study’s author, this hole was first discovered in 1948, when Dutch geophysicist Felix Andries Vening Meinesz embarked on a ship-based gravity survey of the Indian Ocean.
Since then, many expeditions have been undertaken, and satellites were also employed to solve this mystery, but scientists could not understand it until now.
“What we’re seeing is that hot, low-density material coming from this LLSVP underneath Africa is sitting underneath the Indian Ocean and creating this geoid low,” Ghosh says, according to Scientific American magazine.
Pal says the African blob, which essentially causes the IOGL, is probably formed by “Tethyan slabs” deep in the mantle.
Experts believe these slabs are ancient remains of seabed from the Tethys Ocean, which was once between the supercontinents of Laurasia and Gondwana over 200 million years ago.
India and Africa were part of the Gondwana. However, India gradually moved in the northern direction into the Tethys Ocean, which led to the formation of the Indian Ocean around 120 million years ago.
“Plumes of molten rock arise when subducted slabs belonging to the old Tethys Ocean sink inside the mantle and reach the core-mantle boundary,” he said.
They also concluded that the nearby mantle played a vital role in forming this hole apart from the plumes.
References: wionews, newscientist, scientificamerican
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