Scientists unveil huge 'gravity hole' in Indian Ocean; Here's how it formed

Researchers at Indian Institute of Science (IISc) Bangalore have identified cause of an over three million square kilometres-wide 'gravity hole' in Indian Ocean.

Located just south of Sri Lanka, it is at this location Earth's gravitational pull is weakest & sea level is over 100 metre lower than global aver.

researchers ted that in absence of tides and currents on oceans, all water would settle onto a smoothly undulating shape called a geoid, rising wherever re is high gravity, and sinking where gravity is low.

resulting unevenness in ocean surface, kwn as “geoid amalies”, are generated by uneven mass distribution within deep Earth. One such amaly is found just south of Sri Lanka, spanning a vast extent.

Kwn as Indian Ocean Geoid Low (IOGL), it is dominated by a significant gravity low where ocean surface plunges down to 106 metres.

“ existence of Indian Ocean geoid low is one of most outstanding problems in Earth Sciences. It is lowest geoid/gravity amaly on Earth and so far consensus existed regarding its source," said Attreyee Ghosh, an Assistant Professor at Indian Institute of Science, Bangalore.

In a study published in journal of Geophysical Research Letters, team from IISc, in collaboration with researchers from GFZ German Research Centre for Geosciences, analysed reasons behind missing mass that is causing geoid low.

Though several studies in past have tried to answer this, most of m attributing it to a remnant of an earlier plate that dived into Earth's mantle beneath ar plate millions of years ago, re h been convincing explanation of source until w.

new study employed numerical models of ‘mantle convection’ to explain mass deficit. Mantle convection is a of movement caused within Earth's mantle or middle layer, where hotter and lighter material rise to top, and cooler and denser material sink due to gravity.

This convective movement within mantle was driven by seismic tomography models that use seismic waves to obtain a 3-dimensional picture of Earth's interior. researchers found that 'low density amalies' or presence of lighter materials in upper to mid mantle below IOGL, were responsible for gravity low in this region.

Mantle plumes or rising up of abrmally hot rock within Earth’s mantle can result in low density amalies. However, kwn mantle plume exists beneath IOGL, ruling out this ory, researchers said.

However, y found that re was hot material rising from African large low-shear-velocity province (LLSVP) or African superplume, in neighbourhood of IOGL, that was getting deflected eastward and terminating beneath IOGL.

deflection is possibly due to fast motion of Indian plate, researchers said.

"A geoid low or a negative geoid amaly would be caused by a mass deficit within deep mantle. Our study explains this low with hotter, lighter material stretching from a depth of 300 km up to 900 km in rrn Indian Ocean, most likely stemming from African superplume," Ghosh ded.