Scientists deepen understanding of Indian Ocean gravity hole

In its article, EcoNews features that one of the most fascinating geophysical phenomena on Earth, the Indian Ocean gravity hole, continues to intrigue scientists around the world. 

Located in the depths of the Indian Ocean, the "gravity hole," also known as the Indian Ocean geoid low, is an anomaly where gravity is weaker and sea levels dip more than 328 feet (100 meters) underwater. Discovered in 1948, this mysterious phenomenon puzzled scientists for years until modern computer models explained it through tectonic shifts and magma movement deep within the Earth's crust.

The origins of the gravity hole date back 140 million years, when it was part of the now-defunct Tethys Ocean, located between the supercontinents Laurasia and Gondwana. As the Indian plate moved northward and collided with the Eurasian plate, the Tethys crust was subducted into the Earth's mantle. This process displaced dense material known as the "African blob," allowing low-density magma plumes to rise, weakening gravity and creating the geoid low. In 2023, researchers used 19 computer simulations to confirm that magma plumes and mantle structure played a crucial role in forming this anomaly, with six simulations specifically replicating the geoid low.

The Earth’s surface doesn’t present the image of a perfectly smooth sphere, but rather resembles an “ellipsoid,” with a bulge at the equator. The planet is also marked by irregularities that influence its gravitational pull. As geophysicist Attreyee Ghosh, one of the lead researchers studying the gravity hole, puts it, “The Earth is basically a lumpy potato.”

These irregularities arise from planetary dynamics like tectonic movement, mantle convection, and ancient geological processes. The geoid represents how gravity is unevenly distributed across the Earth, illustrating how water would naturally settle under the influence of gravity alone.

The Indian Ocean geoid low stands out as being deeper than average over a vast area of 1.2 million square miles, making it the largest gravitational anomaly ever recorded. Its round depression at the southern tip of India highlights the connection between deep mantle activities and surface phenomena.

This study not only clarifies the mystery of the Indian Ocean gravity hole but also provides valuable insight into other gravitational anomalies around the world. These processes are likely at work in other low geoid regions, and geological maps will help deepen our understanding of the complex forces shaping Earth over millions of years.

Up to 20 million years ago, the Indian Ocean gravity hole existed, but there is currently no way to predict its future over the next hundred million years. It could continue to evolve as tectonic plate movements persist, but for now, it remains an incomplete chapter in Earth’s geological history, still influencing the planet's ongoing development. Science has yet to fully unravel this anomaly.

For example, the simulations don’t account for the mantle plume that powers volcanic activity at Réunion Island, which was responsible for the formation of the Deccan Traps 65 million years ago. This underscores the challenge of creating models for processes that have unfolded over millions of years, relying on incomplete information about Earth’s past.

Additionally, there is a known discrepancy between the modeled geoid and the actual geoid due to limitations in current data, particularly in areas like the Pacific and Africa. These discrepancies highlight the need for improved models and further data collection, especially through methods like seismic imaging.

The gravity hole in the Indian Ocean represents the result of deep geological processes, from evaporating oceans to rising magma plumes. While many such phenomena are no longer visible, there is still much to learn about this geophysical wonder. The research continues to deepen our understanding of Earth’s mysteries, revealing an ever-changing planet with countless secrets still hidden beneath the surface.

By Naila Huseynova