How does gravity smooth a planet?

Question

Over time, gravity (on a macro scale) and erosion (on a micro scale) will work together to smooth out a planet. How does the gravity work? Is it like erosion on a massive scale (ie pulling down the outside of a mountain) or does it un-deform the planet like unsqueezing a water ballon (ie by pulling the inside of a mountain and forcing the sea bed up to make room)? I have included some crude sketches to illustrate what I mean.

Super Erosion:

Un-deforming:

Answer 1

For things the size of planets, gravity smooths them out through erosion and, to make things really smooth, wave action, underwater sedimentation, and tides.

For very dense objects like white dwarf and neutron stars and black holes, gravity is so overwhelmingly powerful that it smooths them out directly, without having to rely on erosion or anything else.