CNN reports that “There is a ‘gravity hole’ in the Indian Ocean — a spot where Earth’s gravitational pull is weaker, its mass is lower than normal, and the sea level dips by over 328 feet (100 meters).”
This anomaly has puzzled geologists for a long time, but now researchers from the Indian Institute of Science in Bengaluru, India, have found what they believe is a credible explanation for its formation: plumes of magma coming from deep inside the planet, much like those that lead to the creation of volcanoes. To come to this hypothesis, the team used supercomputers to simulate how the area could have formed, going as far back as 140 million years. The findings, detailed in a study published recently in the journal Geophysical Research Letters, center around an ancient ocean that no longer exists.
Humans are used to thinking about Earth as a perfect sphere, but that’s far from the truth. “The Earth is basically a lumpy potato,” said study coauthor Attreyee Ghosh, a geophysicist and associate professor at the Centre for Earth Sciences of the Indian Institute of Science. “So technically it’s not a sphere, but what we call an ellipsoid, because as the planet rotates the middle part bulges outward.” Our planet is not homogeneous in its density and its properties, with some areas being more dense than others — that affects Earth’s surface and its gravity, Ghosh added. “If you pour water on the surface of the Earth, the level that the water takes is called a geoid — and that is controlled by these density differences in the material inside the planet, because they attract the surface in very different ways depending on how much mass there is underneath,” she said. The “gravity hole” in the Indian Ocean — officially called the Indian Ocean geoid low — is the lowest point in that geoid and its biggest gravitational anomaly, forming a circular depression that starts just off India’s southern tip and covers about 1.2 million square miles (3 million square kilometers).