[puppypower (OP)]

The earth has a bulge at the equator, making the earth wider then tall. If we turned the earth on its side, so the equator was at the top, the equator's bulge would look like a large hill on the map. The question is since water seeks its own level, why doesn't it flow downhill to the poles and pool there?

[chiralSPO]

The bulge is due to the rotation of the Earth. Just like a beaker of water that is stirred very quickly forms a vortex that appears to defy gravity.

Q: Why doesn't the water flow "down" to fill the hole in the middle of the beaker?
A: Because it is more favorable for it to be at the edge of a rotating environment than at the center, even if it means going up.

[chris]

Thanks Chiral; good example

[evan_au]

The earth has a bulge at the equator, making the earth wider then tall.

The Earth's oceans are in an equilibrium where the tug of gravitation towards the center of the Earth exactly matches the tug of centrifugal force pulling it out towards the equator. This results in a shape which is like a squashed soccer ball (Equatorial radius: 6,378 km, Polar radius: 6,357 km). This shape is called the Geoid, and is used by GPS to estimate your height above sea level (rather than your distance from the center of the Earth).

This equilibrium adjusts the ocean height by kilometres. The tidal tugs of the Sun and Moon modify this by a few meters on a daily basis.

If we turned the earth on its side, so the equator was at the top, the equator's bulge would look like a large hill on the map.

If we changed the axis of Earth's rotation by 90°, then the ocean bulge would be in the wrong place, and would slosh to find a new equilibrium. The more viscous mantle would take longer to adjust to the new equilibrium, resulting in large areas of land being submerged, and ocean floor being exposed.

But changing the Earth's axis by 90° would take a catastrophic event like a collision with another planet, so a few oceans sloshing around would be the least of our worries.

[puppypower (OP)]

Another possible answer is connected to some research that was done by NASA. It turns out the earth is denser north-to-south compared to east-to-west. So it is like having 1 kg of iron N-S and 1 kg of feathers E-W. Both have the same mass, but the bag of feathers will bulge more.

As shown below, this NASA data shows the poles have higher gravity than the equator.

[chiralSPO]

I think that the variation in surface gravity is a product of the distortion, not the other way around...

[puppypower (OP)]

I think that the variation in surface gravity is a product of the distortion, not the other way around...

The earth is wider at the equator. In terms of gravity, wider at the equator should mean there should be more material at the equator is we assume uniform density. Therefore the equator should have the highest gravity, at the equator, not the lowest. The most likely explanation is there is less mass over distance at the equator; lower density. Experiments were able to directly show that the earth is denser north to south, using seismic waves from earthquakes.

What is interesting about this, at least to me, is when we talk of General Relativity and gravity and the curvature of space, it turns out the earth's curvature is like a sine wave north to south, instead of a simple circle. This observation may be a way to unify gravity with the EM force, using traditional assumptions, since a simple curvature, is modified by causes stemming from physical chemistry; magnetic field and the alignment of chemical phases by the field. It is proof of concept.

[Bored chemist]

The earth has a bulge at the equator, making the earth wider then tall.

Do you know why?
It's because the Earth's spin throws stuff out to the sides. It does the same with the water.