The Mystery of The Gravity Hole Beneath the Indian Ocean

Indian scientists unearthed the secrets of the enormous gravity hole in Indian ocean

The Indian Ocean is home to one of the most mysterious and fascinating phenomena on Earth: a giant gravity hole that covers more than two million square miles of the ocean floor. This area, known as the Indian Ocean geoid low (IOGL), has the lowest relative gravity on the planet, and also the lowest sea level, which is about 100 meters below the global average.

But what causes this gravity hole, and how did it form? For decades, scientists have been puzzled by this question, and have proposed various theories involving tectonic plates, mantle plumes, and ancient oceans. Now, two researchers from the Centre for Earth Sciences, Indian Institute of Science, Bangalore have come up with a new explanation that may shed some light on this enigma.

A journey back in time

To unravel the mystery of the IOGL, Debanjan Pal and Attreyee Ghosh used computer simulations to reconstruct the history of the Earth's tectonic plates and mantle dynamics over the past 140 million years. They focused on the region below Africa, where they suspected that some clues might lie.

They found that about 30 million years ago, a large slab of an ancient ocean called the Tethys Sea sank into the mantle beneath Africa, creating a slab graveyard at a depth of more than 1,000 kilometers. This slab graveyard disturbed the hot molten rock in the mantle, causing it to rise up in plumes that reached the base of the Indian Ocean.

These plumes, according to Pal and Ghosh, are responsible for creating the IOGL by thinning and heating up the crust and lithosphere (the rigid outer layer of the Earth) in that area. This reduced their density and mass, and consequently their gravitational attraction. The result is a huge dent in the geoid, which is a hypothetical surface that represents the shape of the Earth based on its gravity field.

A plausible hypothesis

Pal and Ghosh's hypothesis is consistent with previous observations and measurements of the IOGL, such as its shape, size, location, and depth. It also explains why there is a correlation between the IOGL and some volcanic features in the Indian Ocean, such as the Réunion hotspot and the Chagos-Laccadive Ridge, which are likely related to mantle plumes.

However, their hypothesis is not without challenges and limitations. For one thing, it relies on computer models that may not fully capture the complexity and variability of nature. For another thing, it does not account for other possible factors that may have contributed to the IOGL, such as plate motions, surface erosion, or climate change.

Therefore, more data and evidence are needed to test and validate Pal and Ghosh's hypothesis, and to explore other alternative explanations. One way to do that is to deploy more seismometers on the seafloor of the IOGL area, which can provide more information about its structure and composition. Another way is to collect more samples of rocks and sediments from the ocean floor, which can reveal more about its history and evolution.

A fascinating discovery

The IOGL is not just a curiosity for scientists. It also has implications for various fields of study and applications, such as geodesy (the science of measuring and representing the Earth), geophysics (the science of studying the physical properties of the Earth), oceanography (the science of studying the oceans), navigation (the art and science of determining one's position and course), and climate change (the long-term changes in the Earth's climate).

For example, knowing more about the IOGL can help us improve our models of sea level changes over time, which can affect coastal communities and ecosystems. It can also help us understand more about how tectonic plates interact with each other and with the mantle, which can affect earthquakes and volcanoes. And it can help us appreciate more about how our planet works as a dynamic system that constantly changes over millions of years.

The IOGL is a remarkable feature of our planet that deserves more attention and exploration. Thanks to Pal and Ghosh's work, we may have taken a step closer to solving its mystery.

Source: 

(1) Giant ‘Gravity Hole’ in the Ocean May Be the Ghost of an Ancient Sea. https://www.scientificamerican.com/article/giant-gravity-hole-in-the-ocean-may-be-the-ghost-of-an-ancient-sea1/.

(2) Indian Ocean hides a giant 'gravity hole': Here's how it formed. https://www.msn.com/en-in/news/techandscience/indian-ocean-hides-a-giant-gravity-hole-heres-how-it-formed/ar-AA1dpyPH.

(3) What is the mysterious gravity hole in the Indian Ocean?. https://www.firstpost.com/explainers/what-is-the-mysterious-gravity-hole-in-the-indian-ocean-12823662.html.

(4) Did you know there’s a giant ‘gravity hole’ in Indian Ocean? IISc scientists may have found out why. https://www.msn.com/en-in/news/other/did-you-know-there-s-a-giant-gravity-hole-in-indian-ocean-iisc-scientists-may-have-found-out-why/ar-AA1dpQGe.

(5) There's a Giant Gravity Hole In The Indian Ocean, And We May Finally .... https://www.sciencealert.com/theres-a-giant-gravity-hole-in-the-indian-ocean-and-we-may-finally-know-why.

(6) Scientists investigate mysterious 'gravity hole' in Indian Ocean. https://www.bbc.co.uk/newsround/66085069.