Mystery Earth's Largest Gravitational Hole Bottom Indian Ocean
The Mystery of Earth's Largest Gravitational Hole at the Bottom of the Indian Ocean (Photo: Times of India)
- The gravitational hole at the bottom of the Indian Ocean is the largest on Earth, and this has been a mystery that has baffled scientists since the hole was discovered in 1948.
Now a team of researchers from the Indian Institute of Science (IIS) think they have found the answer. According to them, the hole in the Indian Ocean was caused by fragments from a sunken ocean or the bottom of another much older ocean.
In this mysterious part of the Indian Ocean, the gravitational pull is much weaker than anywhere else on Earth. This gravitational hole, is the largest (and deepest) gravitational anomaly in the world, and is officially known as the Indian Ocean Geoid Low (IOGL). The Geoid is a theoretical model of worldwide sea level, whose irregularities are related to variations in Earth's gravity.
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There is nothing mysterious about variations in gravity associated with differences in the density of subsurface and underwater rock layers. What remains unexplained is the size and amplitude of the anomaly in the Indian Ocean.
More air than water
This gravitational hole is centered around 1,200 km southwest of Kanyakumari (Cape Comorin), the southernmost tip of the Indian subcontinent. This circular depression in the ocean has an area of about 3 million square km, which is almost the size of India itself.
Due to lower local gravity, sea level in IOGL is up to 106 meters lower than the global average. This adds a huge volume of air where there should be water. Calculations of the back of the envelope show that as a result of this anomaly, about 100 cubic km of water was displaced.
This anomaly was discovered by Felix Andries Vening Meinesz, a Dutch geophysicist who invented a tool for measuring gravity in the sea. the tool was named Golden Calf because of its color. Sailors in submarines carrying such instruments must remain motionless in their berths during measurements.
A pioneer of submarine gravimetry, Vening Meinesz spent much of his career exploring the oceans in submarines and research vessels. He discovered several anomalies in the Earth's gravitational field that he attributed to plate tectonics, none of which were larger or stronger than those in the Indian Ocean.
This prominent Dutchman is actually thinking in the right direction. However, at that time, there was no computing to strengthen the findings to determine the cause more closely. The true cause of IOGL was still unknown until May 2024, when the journal Geophysical Research Letters published research conducted by IIS researchers.
Starting from a period of 140 million years ago, the IIS team ran various simulations via supercomputers to explore how tectonic and volcanic forces shaped the world we know today.
The various models that produce gravity holes very similar to the IOGL all have one thing in common: a plume of low-density magma rises to displace higher-density material, thereby weakening the area's gravity.
How holes are formed
Here's a possible scenario: about 120 million years ago, the Indian plate separated from the Gondwana supercontinent, and collided with the Eurasian plate. The collision would eventually give rise to the Himalayas. But before it got there, the Indian Plate passed over the Tethys Plate, closing the ancient ocean of that name.
As fragments of a plate called the Tethyan plate are pushed deeper into the Earth's mantle, they displace some of the material trapped in the 'African blob', a continent-sized bubble of magma about 1,000 km beneath East Africa. About 20 million years ago, this relatively light substance rose to the surface in the form of lumps.
"Together with the mantle structure near the lower layer of the Geoid, the plume is responsible for the gravity anomaly over the southern tip of India," the IIS team wrote.
Although researchers can estimate the low age of the Geoid, it is difficult to predict when or if the Geoid will shift or disappear.