Scientists believe they have finally solved the mystery surrounding the Earth’s lowest “gravity hole”.
The long-pondered mysterious depression spot in the Indian Ocean that experiences less gravity than the rest of the planet is likely due to large plumes of magma under the Earth’s crust, scientists have revealed.
There are low-density gravity holes located all over the planet, but the one in the Indian Ocean - named the Indian Ocean Geoid Low (IOGL) - is the most profound, spanning 1.2 million square miles off India’s southern coast and causing a 328-foot dip in the sea level.
To carry out the study, researchers used supercomputers to simulate the seismic formation of the Earth. They ran a total of 19 simulations, examining how tectonic plates moved over 140 million years. Six of the scenarios led to a geoid low, resembling the one in the Indian Ocean.
Scientists have suggested that the gravity hole may have formed as a result of the existence of magma plumes and mantle structures near the geoid low.
According to the study, the Earth’s surface is not a perfect sphere, but a rough shape - meaning there are places all over the world with lower or higher gravitational pulls. They said that while magma plumes do not cause lower gravity, they can affect the areas by causing a depression in the surface.
From the supercomputer data, the research team - led by scientist Attreyee Ghosh - estimated that the IOGL was formed around 20 million years ago as a result of the drifting and eventual collision of India’s subcontinent with Asia 40 million years ago.
Areas with more gravity include the Philippines, while other gravity holes include areas under Cuba and the Bahamas, but unlike these other gravitational anomalies, the IOGL has so far gone unexplained until now since its discovery in 1948.
Smaller shifts can normally be explained by either thickening or thinning of the Earth’s crust but this does not apply to the IOGL.
Through this study, researchers managed to provide an explanation for the gravitational pull differences. Ms Ghosh said: “The Earth is basically a lumpy potato. So technically it’s not a sphere, but what we call an ellipsoid, because as the planet rotates the middle part bulges outward.”
“Our planet is not homogeneous in its density and its properties, with some areas being more dense than others — that affects Earth’s surface and its gravity. If you pour water on the surface of the Earth, the level that the water takes is called a geoid — and that is controlled by these density differences in the material inside the planet, because they attract the surface in very different ways depending on how much mass there is underneath.
“India was in a very different place 140 million years ago, and there was an ocean between the Indian plate and Asia. India started moving north and as it did, the ocean disappeared and the gap with Asia closed.
“As the oceanic plate went down inside the mantle, it could have spurred the formation of the plumes, bringing low-density material closer to Earth’s surface.”
