There’s a huge gravity hole in the middle of the Indian Ocean that has stumped scientists for decades.
The million-square-mile anomaly isn’t a physical hole, but an area of the ocean where Earth’s gravity is lower than average.
Scientists studying the “hole” have long thought there must be something underneath it that is causing the strange effect.
But, a recent study says that researchers were better off looking at the hole from the outside, rather than under it, to find out how it was formed.
They believe that plumes from molten rocks rising up out of the remains of an old ocean bed may be responsible.
A million-square-mile gravity hole that is lowering the oceans
Gravity varies very slightly over the surface of the globe.
Most variations are easily explainable. For example, a dense continent may have a higher mass, and thus incline slightly more towards gravity, than if it were a thin crust zone.
But scientists have struggled to explain the gravity hole in the Indian Ocean, known as the Indian Ocean geoid low.
The difference in gravity is not huge. Bernhard Steinberger of the German Research Centre of Geosciences (GFZ) told Insider that you wouldn’t notice the difference if standing in the center of the anomaly.
But it is significant enough that ocean levels over the 1. 1-million-square-mile patch are about 300 feet lower than in the surrounding oceans.
” I think that what most people assume is that something of low density must be underneath, causing this,” stated Steinberger.
“But in that paper, they have actually a different theory,” he said.
To understand the anomaly, scientists had to look around the hole
To understand what’s causing the hole, geophysicist Attreyee Ghosh and doctoral student Debanjan Pal at the Indian Institute of Science in Bangalore asked a computer to simulate what may have happened.
They plotted 19 different scenarios looking at how tectonic plates may have moved around the hole over the past 140 million years.
Their study, published in Geophysical Research Letters in May, found that only a few scenarios could account for the gravity hole, and in none of these models was the low gravity caused by what was directly underneath it.
Instead, they found the hole was likely caused by plumes of low-density magma.
“It’s something you could have thought of before, you just wouldn’t think of it because you tend to think there must be something underneath,” said Steinberger, who was not involved in the study.
“You’ve got a cutout that looks like it was made by a negative,” said Steinberger.
It goes back 120 million years ago
The most likely explanation for the gravity hole goes back to the separation of Gondwana, the supercontinent at the origin of Africa, Australia, and India, about 120 million years ago, according to the study.
As India separated from Africa and went to smash into the European plate, the ocean that used to be there, called Tethys, was split apart and squished between the continental plates.
Whilst some tiny pieces of this plate remain in the Mediterranean Sea, the majority of it is slowly re-melting back into Earth’s deep interior near Eastern Africa. As the dense mantle melts away, it creates plumes of low-density magma, contributing to the low gravity area.
At a similar time, nearby masses, such as the Tibetan plateau create a gravitational high that amplifies the effect. Steinberger explained.
Looking forward, surveys of the oceans will have to confirm that these plumes exist in real life, not just on computers, Himangshu Paul at the National Geophysical Research Institute in India, told New Scientist.
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