In the midst of the Indian Ocean, there exists a mysterious gravity hole that has intrigued scientists since its discovery in 1948.
Although we often envision Earth as a perfect, smoothly rotating sphere, the reality is far more complex. The planet’s surface is uneven, with flattened poles, bulging equator, and a diverse topography of peaks and valleys scattered across its expanse.
These variations in the landscape lead to fluctuations in gravitational forces at different locations, forming what is known as a geoid—an imaginary sea level surface that undulates across Earth. While most of these gravitational variations have been explained, the origin of this vast 3 million square kilometer depression remains a puzzle.
The gravity in this region is exceptionally weak compared to its surroundings, causing the sea level to be 106 meters lower than the global average.
Geophysicist Debanjan Pal and doctoral student Attreyee Ghosh from the Indian Institute of Science in Bangalore delved into the mystery in a paper published in Geophysical Research Letters. They pointed out that previous studies focused solely on the present-day anomaly, failing to address how this geoid low came into existence.
To unravel the mystery, the researchers took a different approach. Instead of solely examining the geological processes within the gravity hole or geoid low, they explored the surrounding area. Utilizing 19 computer models with varying parameters, they simulated the movements of Earth’s tectonic plates around this low over the last 140 million years.
The outputs of the models were then compared to observations of the current geoid low, and the ones that matched shared a common feature: low-density plasma plumes rising from beneath the low.
In the distant past, India and Australia were once part of the southern supercontinent, Gondwana, which began breaking apart around 100 million years ago. As the Indian tectonic plate migrated northward towards the European plate, it traversed over the ancient seabed of the Tethys Sea, which eventually sank into Earth’s mantle, forming the Indian Ocean in its wake.
This melting process generates plumes of low-density magma that exert a downward pull on the surface. The effect is intensified by the presence of other large masses, like the Tibetan plateau, which contributes to a gravity high, amplifying the overall effect.
The research team proclaimed, “By incorporating a realistic plate motion history, we have successfully replicated a reasonable correlation with the observed seismic velocity anomalies in the Indian Ocean region. Our findings eloquently demonstrate that, apart from plume-derived hot material gathering in the upper mantle of the northern Indian Ocean, the presence of hot anomalies below 1,000 km (e.g., African LLSVP) also contributes to this geoid low.”
While these findings align with Ghosh’s previous modeling work published in 2017, there are skeptics, and concrete evidence will be necessary to confirm this theory. Scientists will need to provide supporting data, likely collected from earthquake observations in and around the geoid low, to validate their predictions.
