Here's a perfectly spherical moon seen in 2D. If it spins fast enough on its axis it will flatten at the poles and bulge at the equator. Notice how the bulge is not a localised deviation from a spherical shape. Rather, it has a very broad base - or more technically a long wavelength. According to the shrinkage hypothesis, we now cool the moon and the bulge will turn into a highly localised ridge. How does this work ?