There's a gravity hole in the Indian Ocean and scientists found the cause

Originally published at: There's a gravity hole in the Indian Ocean and scientists found the cause | Boing Boing


So does this mean there is technically a very shallow “dip” into that part of the ocean? How much of different are we talking? Does the surrounding ocean want to flow into the dip?

ETA - I see I misunderstood that there is LESS gravity there than more. Neat.


Any octopus?


And all this time, I was thinking it was an oblate spheroid.


Here’s a photo


Dang, I had “Earth devoured by a primordial black hole” on my 2023 bingo card.

Coincidentally, if you ever wondered what a 5 Earth mass black hole would look like? Here it is, courtesy of Scholtz and Unwin 2019.


Yes, 100 meters lower. The mantle below this spot is less dense, so it pulls on nearby ocean water less and has less ocean there. Sounds like the difference in density has been known for a bit, and the new part here is a proposed mechanism for the difference to form.


gravity is actually less there so the water has (already) been pulled out to the areas on the sides to compensate, making the water “flat” from the perspective of gravity if not visually, or geometrically


'But now they know the likely source of this strange phenomenon: plumes of molten lava spewing from beneath Africa ’

The proposed cause is down to a slab of Mantle that previously underlay the Tethys Ocean. This ocean was destroyed during collision of India with Asia which led to the initial formation of the Himalayan ranges. During this time, the uppermost part of the Mantle under the ocean which formed part of the oceanic plate was subducted deeper into the Mantle.

This is cooler, denser Mantle than the surrounding material so it continues to sink towards the Core-Mantle boundary (what happens to subducted plates is still something of a mystery). As it sinks, the Mantle slab disturbs the overlying Mantle, allowing hotter, less dense Mantle to take its place, some of which rises up as plumes under the Indian Ocean. The lower density of the rising Mantle means it has less gravitational attraction than regular Mantle, so it appears on the surface as a negative gravity anomaly.


The important question is: have any Instagram influencers gone to the site to see if they “lose weight with this one simple trick?”


So why is the water level lower - if less gravity, I’d expect the level to be higher. (IANAPhysicist as is probably bleedin’ obvious!)


You’re imagining that less gravity means the water isn’t pulled down as much, right? But water doesn’t compress much, and it’s not stuck in a column…if there is more gravity somewhere else, the water will flow away to there instead, leaving a lower point behind.

Edit: I guess a couple people already said better than me. :cup_with_straw::cup_with_straw::cup_with_straw:


Gravity, eh? How does that work? :wink:


I want someone to attempt to explain this phenomenon to a flat earther.



how the flat earth generates gravity is a mystery to all

i thought of an analogy. gravity is sometimes depicted as a well, or a hill, where stronger is deeper, weaker is higher. so this spot would be like a little hill rising up from a plane. if that were a real hill, and the whole area was covered by a lake, the water would be flat ( once it had settled ) - even though there’s still a hill under the surface

even though gravity isn’t physical geometry, it does bend space so effectively it’s the same thing as far as the water is concerned


You summed it up nicely! I shared @anothernewbbaccount 's wonder at this.

I’m thinking a swimmer/observer wouldn’t “feel” the water’s slope, even if it was present visually.

I find gravity anomalies all the time: folks think I’m uncoordinated or intoxicated. Maybe I should wear instruments to prove local aberrations.


That’s still a mind bender? If I could try to go further, since there isn’t an actual hill under the water, ie the bottom surface is normalized, the water appears to reverse-mimic/mirror the lack of hill. It forms a geographic depression while flat re gravity?


I must say that I am utterly disappointed that in a handful of decades we have gone from the Blue Marble:


to this lumpy play-doh nightmare of a spud…


Which is a more specific kind of ellipsoid, one which is wider around its minor axis. And even if it weren’t, listen to Asimov: “[W]hen people thought the earth was flat, they were wrong. When people thought the earth was spherical, they were wrong. But if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together.”

The earth is far closer to an oblate spheroid than it is to the least lumpy potato there has ever been. A perfectly unblemished, perfectly spherical potato has enough surface roughness that if you scaled it to Earth-sized, the entire planet would be covered in multi-mile-high mountains and valleys. The actual imperfections of a real potato would be orders of magnitude larger, like if there were a thousand-mile-across cavern just under the surface of France, or if Everest were 800 miles tall and 400 miles wide, and these were both considered unremarkable facts.

@blackeye Love the thought of someone traveling around with a bag of Cavendish balances to leave anywhere that happen to stumble or trip.


Oh sure, it’s a “low density area”. Looks like the Foundation’s found a way of explaining away SCP-3000 to the normal world.