Indian Ocean Geoid Low

The Indian Ocean Geoid Low (IOGL) is a gravity anomaly in the Indian Ocean. A circular geoid low situated just south of the Indian peninsula, it is the region with 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 remained largely a mystery until May 2023, when the weak local gravity was empirically explained using computer simulations and seismic data.

Location, characteristics, and formation
The gravity anomaly, or "gravity hole", is centered 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.



Based on plate tectonics acting over millions of years, the "gravity hole" is believed to have been caused by fragments from the sunken floor of the much older Tethys Ocean in the narrowing gap between India and Central Asia, as the sinking fragments were offset by mantle plumes of lower-density hot magma from the Earth's interior. Because of this lower density, the gravitational pull in the IOGL region is currently weaker than normal by about 50 mgal (0.005%), the largest gravity anomaly on Earth. The geoid low is believed to have formed around 20 million years ago.