[Rockhounds] There is a ‘gravity hole’ in the Indian Ocean, and scientists now think they know why

[Kreigh Tomaszewski]

There is a “gravity hole” in the Indian Ocean — a spot where Earth’s
gravitational pull is weaker, its mass is lower than normal, and the sea
level dips by over 328 feet (100 meters).

This anomaly has puzzled geologists for a long time, but now researchers
from the Indian Institute of Science in Bengaluru, India, have found what
they believe is a credible explanation for its formation: plumes of magma
coming from deep inside the planet, much like those that lead to the
creation of volcanoes.

To come to this hypothesis, the team used supercomputers to simulate how
the area could have formed, going as far back as 140 million years. The
findings, detailed in a study
<https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL102694>
published
recently in the journal Geophysical Research Letters, center around an
ancient ocean that no longer exists.
https://www.cnn.com/2023/07/24/world/gravity-hole-geoid-low-indian-ocean-scn/index.html

The origin of the Earth's lowest geoid, the Indian Ocean geoid low (IOGL)
has been controversial. The geoid predicted from present-day tomography
models has shown that mid to upper mantle hot anomalies are integral in
generating the IOGL. Here we assimilate plate reconstruction in global
mantle convection models starting from 140 Ma and show that sinking Tethyan
slabs perturbed the African Large Low Shear Velocity province and generated
plumes beneath the Indian Ocean, which led to the formation of this
negative geoid anomaly. We also show that this low can be reproduced by
surrounding mantle density anomalies, without having them present directly
beneath the geoid low. We tune the density and viscosity of thermochemical
piles at core-mantle boundary, Clapeyron slope and density jump at 660 km
discontinuity, and the strength of slabs, to control the rise of plumes,
which in turn determine the shape and amplitude of the geoid low.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL102694