Could a mountain as high as Mars’s Olympus Mons be possible on Earth?

What governs the maximum height of mountains on Earth? Could a mountain as high as Olympus Mons on Mars (21.9 kilometres, more than double the height of Everest) be possible on our planet?

Hillary Shaw
Newport, Shropshire, UK

Any mountain on a near-spherical object causes an excess load on the surface, as gravity is trying to pull it down to ground level. Rock isn’t quite solid, either. Given enough time, heat and stress, it will flow like very stiff molasses.

So, on Earth, Mars or elsewhere, a mountain can only get so high before the crust below ceases to support…