Scientists have known about the existence of a “gravity hole” in the Indian Ocean for decades, but have long been puzzled as to why it exists.
Officially known as the ‘Indian Ocean Low Geoid’, it is not a conventional physical hole, but rather a region of the ocean where gravity is lower than average.
This drop in gravity means the water level is around 340 feet lower than the surrounding area, like a groove in a ‘bumpy potato.’
Now, a team of researchers in India claims that the gravity hole was formed by columns of low-density magma that rose from the Earth’s mantle.
These plumes were generated by the remnants of a collapsed tectonic plate called Tethys, which was lost when India became part of Asia 50 million years ago.
Also known as a geoid, the gravity hole is not a physical hole, but rather a region of the ocean where gravity is below average. The Indian Ocean Low Geoid (IOGL) is the deepest geoid on Earth
The Earth’s mantle is a layer of silicate rock between the crust and the outer core. The image shows the layers of our planet.
Mantle plumes, outcroppings of abnormally hot rock within the Earth’s mantle, are generally believed to be caused by gravitational anomalies around Earth.
The new study was carried out using computer simulations by two geophysicists at the Indian Institute of Science in the city of Bangalore.
“Using these simulations, we were able to see that this low geoid did not exist at some point and then took shape around 20 million years ago,” study author Attreyee Ghosh told MailOnline.
“These kinds of studies would help us address many of the still unresolved features of Earth in the future.”
Earth is often depicted as a perfectly round sphere in illustrations and physical globes, but experts believe it looks more like a “bumpy potato” in terms of its shape.
The uneven surface of our planet is due to areas of non-uniform gravity resulting from the uneven distribution of matter within it.
Added to surface deformations is 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 planet’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 lies just to the south of the Indian peninsula, called the Indian Ocean Geoid Low (IOGL), which spans a large expanse south of the Indian subcontinent.
The ‘Lower Indian Ocean Geoid’ was discovered in 1948 by Dutch geophysicist Felix Andries Vening Meinesz (pictured)
This is not illustrated other than by the Low Indian Ocean Geoid, which can be found about 700 miles south of the Indian peninsula.
It was discovered in 1948 by the Dutch geophysicist Felix Andries Vening Meinesz during a gravity survey from a ship, when he found that the sea level in the region was significantly lower than the world average, indicating a gravitational anomaly.
While we’ve sent missions to probe the farthest reaches of our solar system, Earth’s deepest shafts shrink to just a few miles, making searching for answers within our planet is challenging.
To address this, the experts used computer software to track how Earth’s tectonic plates may have moved around the hole in the last 140 million years.
Violent interactions between tectonic plates may provide clues as to why this gravitational anomaly exists today, they thought.
It is well known that the Earth’s lithosphere, its rocky outermost layer, is made up of around 15 tectonic plates that are constantly moving and crushing each other.
Around 50 million years ago, the relatively small Indian plate began to collide with the much larger Eurasian plate, forming the Himalayas.
Prior to this, the Indian plate was part of an ancient southern “supercontinent” now referred to as Gondwana, but had begun to drift north.
When the Indian plate collided with the Eurasian plate, another plate between the two, the Tethys, subsided and plunged into the mantle.
The map shows the arrangement of Earth’s tectonic plates today. Note the relatively small Indian plate, marked in red
The Indian plate used to be part of an ancient southern “supercontinent” now referred to as Gondwana. Pictured are the historical plates and their movement as Gondwana broke up (a process believed to have started around 120 million years ago)
Tethys was the location of a vast ocean, home to a diverse ecosystem of marine life, including fish, sharks, whales, and dolphins.
According to the researchers, slabs of the Tethys plate dug into Earth’s lower mantle and stirred up the magma, generating the plumes.
‘These columns, together with the mantle structure in the vicinity of the low geoid, are responsible for the formation of this negative geoid anomaly,’ they say in their paper.
The team says the question of how the low Indian Ocean geoid arose has been “controversial”, but they show that the plumes were “integral” in their creation.
Their study has been published in the journal Geophysical Investigation Letters.
The Earth moves under our feet: tectonic plates move through the mantle and produce earthquakes by rubbing against each other
Plate tectonics are made up of the Earth’s crust and the upper part of the mantle.
Below is the asthenosphere: the conveyor belt of warm, viscous rock on which tectonic plates move.
Earth has fifteen tectonic plates (pictured) that together have shaped the landscape we see around us today.
Earthquakes typically occur at tectonic plate boundaries, where one plate dips under another, pushes another up, or where plate edges scrape against each other.
Earthquakes rarely occur in the middle of plates, but they can occur when old faults or rifts deep below the surface are reactivated.
These areas are relatively weak compared to the surrounding plate and can easily slip and cause an earthquake.