The Indian Ocean Geoid Low (IOGL) is a gravity anomaly in the Indian Ocean. A circular region in the Earth’s geoid, situated just south of the Indian peninsula, it is the Earth’s largest gravity anomaly.It forms a depression in the sea level covering an area of about 3 million km² (1.2 million sq mi), almost the size of India itself. Discovered in 1948 by Dutch geophysicist Felix Andries Vening Meinesz as a result of a ship’s gravity survey, it remains largely a mystery. In May 2023, the weak local gravity was attempted to be explained through a hypothesis that used computer simulations and seismic data.

The gravity anomaly, or “gravity hole”, is centred southwest of Sri Lanka and Kanyakumari, the southernmost tip of mainland India, and east of the Horn of Africa. Due to weaker local gravity, the sea level in the IOGL would be up to 106 m (348 ft) lower than the global mean sea level (reference ellipsoid), if not for minor effects such as tides and currents in the Indian Ocean.

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