Indian Ocean ‘gravity hole’ finally explained?

With the exception of a few “fanatic” people who limit themselves to denying one of the most basic scientific evidences, the Earth is round. Aristotle showed this more than 2,300 years ago. No more going back. However, the shape of the Earth is still a subject of scientific debate. Because there are nuances. In fact, the Earth is not a perfect sphere. It is slightly flattened at the shaft, due to its rotation.

Distribution of masses, geodes, and landform

But the complexity goes further if we consider the gravitational field. If we walk on what is called a reference ellipsoid, which is used to model the shape of the Earth, we realize that the gravitational field is slightly different. The reason: the uneven distribution of the masses that make up the Earth. Thus, scientists have identified another (theoretical) surface that explains these differences in gravitational field and mass distribution: this is the geoid. The geoid thus represents what is called the gravitational isopotential, that is, at any point on this theoretical surface the value of g is constant and the direction of the gravitational field is perpendicular to it. In a way, the shape of the geoid is closest to the shape of the Earth. Zoomed out and seen at a high degree of resolution, the shape of the Earth would be rather “potatooid,” with bumps and hollows attesting to the uneven distribution of masses at depth. However, it must be borne in mind that the differences in geodes do not exceed +/- 100 metres. Therefore, the approximation of the ellipsoid is more than satisfactory!

Basin in the Indian Ocean

But back to the potatoes. Because there is indeed an area that has intrigued scientists for a long time. In fact, one of the most striking anomalies in the geode’s shape is that of the Indian Ocean. This is a negative anomaly, which forms a “bottom” in the geode. So it would be related to a mass imbalance somewhere below the Earth’s surface. But what exactly is it?

Rising hot material after turbulence at the level of the African Supermassive Pillar

A new study published in the journal Geophysical Research Lettersproposes a new hypothesis. To understand, you have to dive more than 1,000 kilometers below the Earth’s crust, into the core of the mantle. This is where the culprit is thought to be: a piece of ancient crust from the ancient Tethys ocean fell beneath Africa in a subduction zone 30 million years ago. This piece of crust, cold and dense, would have disturbed a super mantle plume (LLSVP for Large low cutting speed county) those roots in the primary interface beneath the African continent. This upheaval would have spewed hot material within many mantle plumes beneath the Indian Ocean. However, whoever says a large mass of hot and not very dense matter says negative gravitational anomalies! These results come from numerical modeling that took into account geodynamic and tectonic evolution over the past 140 million years.

However, the hypothesis has yet to gain consensus within the scientific community, with some researchers highlighting the fact that there is no clear seismic evidence of mantle plumes under the Indian Ocean.