Eli5 Why doesn’t low gravity mean higher sea level?



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The Indian Ocean geoid low is an abnormality where the density of the earth is less than the surrounding regions. Since there’s less mass, there’s less local gravity than the areas surrounding it. Note the key word here: it’s *surrounded* by more dense areas. Those areas would have higher gravitational pull, and consequently have a slight siphoning effect. This pulls water away from the Indian Ocean geoid low and lowers the sea level there.

Gravity attracts matter, so matter goes where gravity is stronger (if the matter is able to move there, which liquid water in an ocean is). Just like iron filings will pile up on top of a strong magnet, water will pile up on top of an area with stronger gravity (and thus avoid areas with weaker gravitational pull).

Not an expert but I think it’s also important to understand that water isn’t really compressible, this causes the water to “pile up” in higher gravity areas, rather than form low spots, as your intuition might suggest.