Indian Ocean "Gravity hole" - a visual explanation

[DaveC426913]

TL;DR Summary

A lot of people on Face thimnig that lower local gravity should equal higher sea levels

https://www.livescience.com/planet-...ield-created-by-the-death-of-an-ancient-ocean

This article has popped up on FB. A lot of people can't get their head around the idea that a localized low gravity area would cause a drop in sea level. Many, many seem to think the sea level would rise in a low gravity area (I guess they think water would ballooon up, like air).

I got fed up with trying to explain how gravity can certainly act laterally (such as standing near a mountain - or near Cavendish's steel balls ), and how we can only treat the Earth as a point source of gravity when it is nominally spherical and far away.

So I drew a diagram. I hope this puts an end to gravity hole doubters.

 

[Hornbein]

Yep, surface gravity should be everywhere the same on a liquid planet. Known to Isaac Newton. He even calculated the shape of the Earth though without the relativistic factor.

If surface gravity is less somewhere then water will flow away until it equalizes.

But doesn't the Moon attract water even though it decreases surface gravity? I'm too lazy to figure it out but suspect it has to do with the center of mass of the earth-moon system being not that far beneath the surface of the earth. So the moon actually increases surface gravity? Dunno.

 

[Orodruin]

If surface gravity is less somewhere then water will flow away until it equalizes.

This is incorrect. In absence of other effects, water will flow until its surface represents a level surface of the gravitational potential. In that case, a fluid parcel at the surface will have no force component tangent to the surface. There is no requirement that the field strength should be the same on the surface.

 

[AlexB23]

TL;DR Summary: A lot of people on Face thimnig that lower local gravity should equal higher sea levels

https://www.livescience.com/planet-...ield-created-by-the-death-of-an-ancient-ocean

This article has popped up on FB. A lot of people can't get their head around the idea that a localized low gravity area would cause a drop in sea level. Many, many seem to think the sea level would rise in a low gravity area (I guess they think water would ballooon up, like air).

I got fed up with trying to explain how gravity can certainly act laterally (such as standing near a mountain - or near Cavendish's steel balls ), and how we can only treat the Earth as a point source of gravity when it is nominally spherical and far away.

So I drew a diagram. I hope this puts an end to gravity hole doubters.

View attachment 354124

Thus makes sense, the water is attracted by gravity, so higher gravity would pull the water away from lower gravity areas. Would this have a compounding effect, as when there is more water in a higher gravity region, then there would be more mass of water as well to attract even more water, or is that impact negligible?