The Mysterious Giant Gravity Hole in Indian Ocean

There is a massive “hole” in the Indian Ocean, researchers say—but it is not the kind that could drain away all that water. Geologists have been perplexed by this phenomenon and have sought to uncover its true origins. This gravitational anomaly has long been acknowledged as one of the most remarkable on Earth, and a recent study by Bengaluru’s Indian Institute of Science may have finally shed light on its causes.

THE MODEL

The researchers employed 19 mantle convection computer models, spanning from the Mesozoic era to the present day, to investigate the connection between different geological periods. Mantle convection refers to the movement occurring within the Earth’s middle layer, known as the mantle, where hotter and lighter materials rise to the top while cooler and denser materials sink due to gravity.

The models replicate the movements of tectonic plates over the past 140 million years. Through these models, the scientists the existence of “low density anomalies” in the upper to mid-mantle beneath the Indian Ocean Gravity Low (IOGL) is responsible for the region’s reduced gravity.

HOW THESE LOW DENSITY ANOMALIES CAME INTO EXISTENCE?

Mantle plumes—unusually heated rocks rising from within the Earth’s mantle—often cause such anomalies. However, this was not the case beneath the IOGL. Instead, the researchers found that hot material originating from the African super plume, a large section of the mantle that transfers heat from the core to the crust, deflected eastwards, likely due to the rapid motion of the Indian plate. This material ultimately accumulated beneath the IOGL.

Attreyee Ghosh, one of the study’s authors, explained, “A geoid low or a negative geoid anomaly would be caused by a mass deficit within the deep mantle. Our study explains this low with hotter, lighter material stretching from a depth of 300 km up to 900 km in the northern Indian Ocean, most likely stemming from the African super plume.”

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