Eli5 Geoid low Indian Ocean

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Can someone explain how there can be a low spot in an ocean? I understand there is lower gravity there, but I just don’t understand how water could have a low spot. It is visible from space? I don’t get it.

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The gravity is weaker at the spot because Earth is not a uniform sphere and part of the Earth’s interior is less dense under the spot. The gravity is therefore relatively stronger in the regions surrounding the spot. Water is slightly pulled towards the areas with stronger gravity away from the area with weaker gravity because that is how mass moves in gravitational fields. The effect is incredibly small compared to the size of the whole Earth, it is not visible from space.

The Earth is less dense there, so their less gravity pulling down on the water there, and more gravity pulling away. You would not be able to notice this from space even with highly sensitive equipment.

Hudson Bay in Canada is in a similar situation.