Indian Ocean Has a ‘Gravity Hole’, Scientists Think Why

(CNN) — There is a “gravitational hole” in the Indian Ocean, where Earth’s gravity is so weak that its mass is less than normal and sea level drops by more than 100 meters.

The anomaly has long puzzled geologists, but now researchers at the Indian Institute of Science in Bengaluru, India, have discovered what they believe is a plausible explanation for its formation: columns of magma from deep within the planet, very similar to those that form volcanoes.

To reach this hypothesis, the team used supercomputers to simulate how the region might have evolved 140 million years ago. inventions, In detail in a study A recent publication in the journal Geophysical Research Letters focuses on an ancient ocean that no longer exists.

A missing sea

Humans think of the Earth as a perfect sphere, but that is far from the truth.

“Earth is basically a lump of potato,” explains study co-author Adreyi Ghosh, a geophysicist and associate professor at the Indian Institute of Science’s Center for Earth Sciences. “So technically it’s not a sphere, but we call it an ellipse because the center moves out as the planet rotates.”

Our planet is not uniform in its density and its properties, as some regions are denser than others, which affects the Earth’s surface and its gravity, Ghosh added. “If you pour water on the surface of the Earth, the level the water reaches is called the geoid, and it’s controlled by these density differences in the material inside the planet because they’re pulled to the surface in different ways depending on the mass underneath,” he explained.

“This is the largest dip in the geoid ever, and it has not been adequately explained,” Ghosh said.

To find a possible answer, Ghosh and his colleagues used computer models to get a picture of global geology going back 140 million years. “We have some information and some certainty about what the Earth looked like back then,” he explains. “The continents and oceans were in different places, and the density structure was also very different.”

From that starting point, the team has run 19 simulations to date, recreating the shift of tectonic plates and the behavior of magma, or molten rock, which is the thickest layer of Earth’s interior between the core and the crust. A lower geography like the Indian Ocean was formed in six scenarios.

A differentiating factor in all six models is the presence of magma plumes around the lower geoid, which is believed to cause a “gravity hole” to form along with the nearby mantle system, Ghosh explained. Simulations were carried out with different parameters of magma density, and in those without columns, depressions did not develop.

According to Ghosh, the columns originated from the disappearance of an ancient sea Indian landscape changed and ended up colliding with Asia several million years ago.

“140 million years ago, India was in a very different place, with an ocean between the Indian and Asian plates. India started moving northward, and just like that, the ocean disappeared. The gap with Asia was closed“, he explained. The descent of the oceanic plate towards the interior of the mantle would have triggered the formation of the columns, bringing the less dense material closer to the Earth’s surface.

The future of the low geoid

According to the team’s calculations, the lower geoid formed about 20 million years ago. It is difficult to know whether it will disappear or move on.

“These mass anomalies depend on how the Earth moves,” Ghosh explains. “It could be long-lived. But plate motions could be acting to make it disappear a few hundred million years into the future.”

Huw Davies, a professor at Cardiff University’s School of Earth and Environmental Sciences, UK, said the research was “certainly interesting, and outlines some interesting hypotheses that will encourage further work on this topic.” Davis was not involved in the study.

Professor of Geography at the University of Florida in Gainesville, Dr. Alessandro Forte, who was not involved in the study, believes there are good reasons to run computer simulations to trace the origin of the Indian Ocean geoid, and that the study is an improvement over previous ones. Previous research only simulated the descent of cooler material through the mantle, rather than including the rising plumes of the warm mantle.

However, Forte noted that he found two flaws in the process of the study.

“The most important problem with the modeling strategy adopted by the authors is that it is not reproducible. A powerful dynamic mantle columnerupted below the current location of Reunion Island 65 million years ago,” he said. Traps DeccanOne of the largest volcanic features on Earth – attributed to a powerful mantle plume that has long been completely absent from model simulations.”

Another problem, Forte added, is the difference between the geoid, or surface shape, predicted by computer simulations and the actual one: “These differences are particularly noticeable in the Pacific Ocean, Africa and Eurasia.” The authors note that there is a modest correlation of about 80% between the predicted and observed geoids, but do not provide a precise measure of how well they match numerically. [en el estudio]. This discrepancy suggests that there may be some flaw in the computer simulation.”

Ghosh says that not all possible factors can be accounted for in simulations.

“That’s because we don’t know exactly what the Earth looked like. The further back in time we go, the less confidence we have in the models. We can’t account for every possible scenario, and we have to accept the fact that there may be some inconsistencies in how the plates have moved over time,” he said. “But we think the general reason for this low level is pretty clear.”