A Different Gravity in the Indian Ocean

The oceans are more mysterious, and yet more fascinating than you think!

- DOJA K

While the vast water bodies that surround us throw up a rare life-form here and there, with a bulk of their depths yet to be mapped by humans, there are a host of naturally-occurring anomalies that make the world's oceans all the more intriguing. And there's one such spot right off peninsular India's southernmost tip!

Gravity is the force that attracts objects toward the center of a planet or any other celestial body. However, did you know that gravitational pull varies across different parts of the Earth? The planet's standard gravity is 9.81 m/s², but in India, it fluctuates between 9.77 m/s² and 9.83 m/s². The highest and lowest gravitational pulls are found near the Himalayas and the Indian Ocean, over an area known as the Indian Ocean Geoid Low (IOGL).

The Indian Ocean is the third-largest ocean, covering about 70,560,000 sq km or roughly 20% of Earth's water surface. The Indian Ocean Geoid Low is located southwest of India, and this region has the lowest gravity on Earth, with values significantly below the global average. It has resulted in a sea level that is 106 meters lower than average. This area, often referred to as the Indian Ocean Gravity Hole (IOGH), or simply "gravity hole", is an anomaly that has puzzled scientists for decades.

The IOGL was first identified in 1948 by Dutch geophysicist Felix Andries Vening Meinesz during a gravity survey conducted from a ship. The anomaly remained largely unexplained until May 2023. The Indian Ocean Geoid Low is a circular region in Earth's geoid, located just south of the Indian Peninsula, covering an area of about 3 million sq km. A geoid is a hypothetical solid figure, whose surface corresponds to mean sea level and its imagined extension under (or over) land areas.

Why is gravity so low in this region?