Indian Ocean Geoid Low (IOGL)

Published: 6th Jul, 2023

Context

Researchers at the Indian Institute of Science have revealed the secrets of the giant gravity hole that rests in the Indian Ocean.

What is the Indian Ocean Geoid Low (IOGL)?

There is an enigmatic “gravity hole” in the Indian Ocean.
It is not the kind of “hole” that would allow the entire ocean to be drained. However, there is a massive anomaly in the Earth’s crust that has a much weaker gravitational attraction than usual.
It is located about 600 miles below the surface of the Earth.
This “gravity hole” is actually the Indian Ocean Geoid Low (IOGL), which spans an area of more than two million square miles.
Type of structure: Humongous structures
Shape: The gravity hole is not actually a perfect sphere, as Earth's gravitational field is not uniform due to variations in density and mass distribution.

What forms it?

The distribution of mass within Earth is not homogeneous, with denser regions in some areas and less dense regions in others.
These variations in density and mass create differences in gravitational attraction, leading to the formation of the geoid.
The irregularity in the gravitational field causes anomalies, resulting in differences in the strength of gravity at different locations on the Earth's surface, which influences the Earth's shape.
The shape is also affected by the planet's rotation, gravitational forces, and internal structure.

How are they formed (Key-findings)?

The scientists looked inside Earth's surface, nearly 1,000 kilometers beneath the crust where once an ancient ocean plunged nearly and stirred up hot molten rock, nearly 30 million years ago.
The team then looked at how the tectonic plates moved along each other in the past 140 million years when the Indian plate had just begun separating from the larger Gondwanaland.
Every time for the gravity hole anomaly to form plumes of hot, low-density magma was required, and the first such plume appeared nearly 20 million years ago, and as the plumes intensified so did the gravity hole.
Low density anomalies: The researchers found that 'low density anomalies' or the presence of lighter materials in the upper to mid mantle below the IOGL, were responsible for the gravity low in this region.
Mantle plumes: Plumes are integral in generating the IOGL. Mantle plumes or the rising up of abnormally hot rock within the Earth’s mantle can result in low density anomalies.

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