Scientists solve mystery of Indian Ocean's “Gravity Hole”

Scientists have finally uncovered the mystery behind a massive “gravity hole” lurking beneath the Indian Ocean — a longstanding geological enigma that has puzzled researchers for decades, according to a report published by The Earth yesterday.

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It said: Earth carries an invisible ocean “water level” called the geoid. If only gravity and rotation shaped the oceans, the surface would match that geoid everywhere. However, south of India, the geoid sinks sharply.

At the centre of this sunken feature, the geoid lies about 330 feet (100 meters) below the global average, a dramatic signal known as the Indian Ocean Geoid Low (IOGL).

This low water level region raises a clear question: what underground forces could cut such a deep “gravity hole” while leaving a normal-looking seafloor?

The feature sits in the ocean basin without obvious scars. That points to changes inside the planet rather than in the crust. The puzzle centres on how mass moved and settled in the mantle over long periods.

According to the study's lead author Debanjan Pal, an Indian Institute of Science (IISc) doctoral student, the IOGL was discovered in 1948 during a ship-based gravity survey by Dutch geophysicist Felix Andries Vening Meinesz.

However, the cause of this phenomenon wasn't known until this study was completed.

The authors of the new study built computer simulations of mantle flow that span roughly the last 140 million years.

They fed in reconstructions of plate motions, let old oceanic slabs sink, let hotter, lighter upwellings rise, and calculated how those shifts in mass tugged on gravity.

They aimed to match the size and outline of the Indian Ocean Geoid Low using a realistic reconstruction of Earth's history rather than a single snapshot.