Deep under the Indian Ocean lies a gravity mystery unlike anywhere else on Earth

For over seventy years, the Indian Ocean Geoid Low (IOGL) has intrigued scientists as one of Earth’s most unusual gravitational anomalies. Located beneath the Indian Ocean, this mysterious dip represents the lowest point in the planet’s gravity field. Unlike a physical depression in the ocean floor, it is a distortion in the geoid, a model of Earth’s shape influenced by gravity and rotation. Studying the IOGL helps researchers understand the distribution of mass inside Earth, the dynamics of tectonic plates, and the planet’s geological history. Its discovery has provided crucial insights into Earth’s complex interior and gravity patterns.The Indian Ocean Geoid Low (IOGL) is not a trench or hole in the seabed but a massive depression in Earth’s geoid, spanning roughly 3.1 million square kilometres and plunging 106 metres below the average sea level of surrounding regions. This gravitational “low” indicates slightly weaker gravity in the area, causing a marginal dip in the local sea level. First discovered in the late 1940s by Dutch geophysicist Felix Andries Vening Meinesz using precise submarine gravimetric measurements, the IOGL has intrigued scientists for decades. It offers a rare window into Earth’s interior, shedding light on mantle dynamics, plate tectonics, and mass distribution beneath the crust.According to a recent study published in Geophysical Research Letters, the IOGL may have formed due to tectonic interactions over the last 30 million years. Researchers suggest that a fragment of the Tethys Ocean’s oceanic crust sank beneath the African continent. This subducted slab interfered with a superplume, a rising mass of hot mantle material beneath Africa, causing mantle flows to shift and disrupting the geoid above the Indian Ocean.Using advanced numerical simulations spanning 140 million years of tectonic evolution, scientists recreated how mantle plumes and subducted slabs interacted to produce the gravitational dip we observe today. These models provide the most comprehensive explanation yet for the formation of the IOGL.The IOGL highlights that Earth is far from a perfect sphere. Geophysically, our planet resembles “a potato with dents”, where gravity varies depending on the distribution of mass beneath the surface. The geoid, which represents Earth’s true gravitational surface, shows that some regions have stronger gravitational pull, while others, like the IOGL, are weaker. These variations influence sea level, ocean currents, and even satellite trajectories, making them critical for both scientific research and navigation.Understanding the IOGL is not only a matter of scientific curiosity. It has practical implications for geophysics, oceanography, and Earth system modelling. The gravitational anomaly helps scientists understand how mass moves in Earth’s mantle, how tectonic plates interact, and how deep mantle plumes influence surface phenomena. While some experts, such as Dr Alessandro Forte, have raised questions about the accuracy of current models, the anomaly remains a unique natural laboratory for studying the dynamic processes of our planet.Professor Attreyee Ghosh, lead author of the study, suggests that the IOGL could persist for hundreds of millions of years. However, ongoing plate movements and mantle dynamics may gradually alter or even erase the anomaly in the distant future. Regardless, it continues to offer a rare glimpse into the complex interactions inside Earth and highlights the importance of gravitational studies in understanding our planet.The IOGL is more than a scientific curiosity, it is a reminder that Earth is dynamic and ever-changing beneath the surface. By studying such anomalies, scientists can improve predictions about volcanic activity, tectonic shifts, and oceanic behaviour, ultimately contributing to a better understanding of natural hazards and global geological processes. For the public, it underscores that Earth is not a perfect sphere, but a planet with uneven gravity shaped by its tumultuous geological past.Also read | Scientists stunned by discovery of three never-before-seen snailfish in the Pacific Ocean