There is a ‘gravitational hole’ in the Indian Ocean and scientists think they know why

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

This anomaly has long puzzled geologists, but now researchers at the Indian Institute of Science in Bengaluru, India, have discovered what they believe is a reliable explanation for its formation: plumes of magma coming from the depths of the planet, very similar to those that give rise to volcanoes.

To arrive at this hypothesis, the team used supercomputers to simulate how the region formed, 140 million years ago. the findings, detailed in the study Recently published in the journal Geophysical Research Letters, it focuses on an ancient ocean that no longer exists.

surroundings disappeared

Humans used to think of the Earth as a perfect sphere, but this is far from the case.

“Earth is basically a lumpy potato,” explains Atreye Ghosh, study co-author, geophysicist and associate professor at the Indian Institute of Science Center for Geosciences. “Technically, it’s not a sphere, but what we call an ellipsoid, because as the planet rotates, the central part bulges outward.”

Ghosh added that our planet is heterogeneous in its density and characteristics, as some areas are denser than others, which affects the Earth’s surface and gravity. He explained, “If you pour water on the surface of the Earth, the level that the water reaches is called a geode, and it’s controlled by these differences in density in the matter inside the planet, that they pull on the surface in very different ways depending on the mass underneath.”

“It’s by far the largest depression in the geode, and it’s been underexplained,” Ghosh said.

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

From that starting point, the team has run 19 simulations so far, recreating the shifting of tectonic plates and the behavior of magma, or molten rock, within the mantle, the thick layer of Earth’s interior that lies between the core and crust. Low geoids similar to those in the Indian Ocean formed in six of the scenarios.

Ghosh explained that the distinguishing factor in all six models is the presence of magma plumes around the lower geodes, which together with nearby mantle structure are thought to be responsible for the formation of the “gravitational hole”. Simulations were performed using different magma density parameters, and in those without plumes, depressions did not form.

According to Ghosh, the pillars arose from the disappearance of an ancient ocean when The Indian landmass has shifted And it ended up colliding with Asia tens of millions of years ago.

“140 million years ago, India was in a very different place and there was an ocean between Indian and Asian dishes. India started moving north, and as it happened, the ocean disappeared and The gap with Asia has closedHe explained that the descent of the oceanic plate towards the inner part of the mantle can stimulate the formation of plumes, bringing the low-density material closer to the Earth’s surface.

The future of low geodes

According to the team’s calculations, the lower geode formed about 20 million years ago. It’s hard to tell if it will disappear or move on.

“It all depends on how these mass deformations move on the ground,” Ghosh explains. “It can go on for a long time. But it can also act as plate motions in a way that makes them disappear, a few hundred million years into the future.”

Huw Davies, a professor in the School of Earth and Environmental Sciences at Cardiff University, UK, said the research is “definitely interesting, and identifies interesting hypotheses, which should encourage more work on this topic.” Davis was not involved in the study.

Dr. Alessandro Forte, a professor of geology at the University of Florida in Gainesville, who was also not involved in the study, believes there are good reasons to run computer simulations to determine the origin of the low-lying geoid in the Indian Ocean, and that this study is an improvement over its predecessors. Previous research only simulated descents of cold material through the mantle, rather than including plumes rising from the warm mantle.

However, Forte notes that he found two flaws in the study’s implementation.

“The most notable problem with the modeling strategy adopted by the authors is that it does not reproduce at all Strong dynamic mantle columnthat erupted 65 million years ago under the current location of Reunion Island. The eruption of pyroclastic flows that covered half of the Indian subcontinent at that time – producing traps Deccanone of the largest volcanic features on Earth – has long been attributed to a robust mantle plume completely absent from model simulations.”

Another problem, Forte added, is the difference between the geodes, or surface shape, predicted by the computer simulation and the actual problem: “These differences are particularly noticeable in the Pacific Ocean, Africa, and Eurasia.” The authors state that there is a moderate association, about 80%, between predicted and observed geographic items, but do not provide a more accurate measure of how numerically they match. [en el estudio]. This mismatch indicates that there may be some deficiencies in the computer simulation.”

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

“This is because we don’t know with absolute accuracy what the Earth looks like. The further back in time we go, the less confident we are in the models. We can’t take into account every possible scenario and we also have to accept the fact that there may be some inconsistencies in how the plates move over time,” he said. “But we think the general reason for this low level is very clear.”