Scientists have known about the existence of a ‘gravity hole’ in the Indian Ocean for decades but were long puzzled as to why it exists.
Officially known as the ‘Indian Ocean Geode Low’, this is not a conventional physical hole, but rather a region of the ocean where gravity is lower than average.
This dip in gravity means that the water level is about 340 feet lower than the surrounding area – like a notch in a ‘bumpy potato’.
Now, a team of researchers in India claims that the gravity crater was formed by a low-density magma plume rising from the Earth’s mantle.
These plumes were generated by the remains of a submerged tectonic plate called the Tethys, lost when India became part of Asia 50 million years ago.
Also known as a geoid, a gravity hole is not a physical hole, but a region of the ocean where the gravity is lower than average. The Indian Ocean Geode Low (IOGL) is the deepest geode on Earth
Earth’s mantle is a layer of silicate rock between the crust and the outer core. Image is the layer of our planet
Mantle plumes – upwellings of abnormally hot rock within the Earth’s mantle – are generally thought to be caused by gravitational anomalies around the Earth.
The new research was conducted using computer simulations by two geophysicists at the Indian Institute of Science in Bangalore.
Study author Atrei Ghosh told MailOnline, ‘Using these simulations we can see that this geoid lot was non-existent at one point and then took shape around 20 million years ago.
‘This kind of research will help us in the future to solve many of the still unresolved features of our Earth.’
Earth is often depicted as a perfectly round sphere in diagrams and physical globes, but experts believe it is more like a ‘bumpy potato’ in shape.
Non-uniform gravity fields result from the uneven distribution of matter within the uneven surface of our planet.
Adding to the surface deformation is the movement of tectonic plates that have created mountains and valleys on the Earth’s surface.
Since oceans cover about 70 percent of the planet’s surface, these deformations also affect the size of the oceans.
The ‘geode anomaly’ is generated by uneven mass distribution within the deep Earth. The low gravity point is found just south of the Indian Peninsula, called the Indian Ocean Geode Low (IOGL), which extends south of the Indian subcontinent.
The ‘Indian Ocean Geode Low’ was discovered in 1948 by Dutch geophysicist Felix Andries Venning Mainz (pictured).
About 700 miles south of the Indian peninsula is found which is not depicted by the Indian Ocean Geode Low.
It was discovered in 1948 by the Dutch geophysicist Felix Andries Venning Mainz during a ship-based gravity survey, 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 probe the outer reaches of our solar system, Earth’s deepest boreholes only go down a few miles, so finding answers within our planet is a bit of a challenge.
To combat this, experts used computer software to track how Earth’s tectonic plates may have shifted around the crater over the past 140 million years.
Violent interactions between tectonic plates may hold clues as to why these gravitational anomalies exist today, they thought.
It is well known that the Earth’s lithosphere – its rocky, outermost shell – is made up of about 15 tectonic plates that are constantly crossing and crushing each other.
About 50 million years ago, the relatively small Indian plate began to collide with the much larger Eurasian plate, creating the Himalayas.
Earlier, the Indian plate was part of an ancient southern ‘supercontinent’ known today as Gondwana, but it began drifting northwards.
When the Indian plate collided with the Eurasian plate, another plate between the two – the Tethys – subducted and became encased in the mantle.
The map shows the arrangement of the Earth’s tectonic plates today. Note the relatively small Indian plate marked in red
The Indian plate was part of an ancient southern ‘supercontinent’ known today as Gondwana. There are images of the historical plates and their movement as Gondwana broke up (a process thought to have started about 120 million years ago).
Tethys was a vast ocean location, home to a diverse ecosystem of marine life, including fish, sharks, whales, and dolphins.
According to the researchers, slabs of the Tethys plate sink into the Earth’s lower mantle and churn up magma, creating plumes.
‘These plumes, along with mantle structures around the geoid low, are responsible for creating this negative geoid anomaly,’ they say in their paper.
The team says the question of how the Indian Ocean geode low came about is ‘debatable’, but they show that plumes were ‘integral’ in its creation.
Their research is published in the journal Geophysical Research Letters.
The Earth is moving beneath our feet: tectonic plates move through the mantle and create earthquakes as they scrape against each other.
Tectonic plates are composed of the upper part of the Earth’s crust and mantle.
Below is the asthenosphere: the warm, viscous conveyor belt of rock on which tectonic plates ride.
Earth has fifteen tectonic plates (pictured) that together shape the landscape we see around us.
Earthquakes typically occur at tectonic plate boundaries, where one plate sinks beneath another, pushing another up, or where plate edges scrape against each other.
Earthquakes rarely occur between plates, but can occur when ancient faults or rifts deep below the Earth’s surface are reactivated.
These regions are relatively weak compared to the surrounding plates, and can easily slip and cause earthquakes.