Mountains are tall, but how tall can they be? Is mountain Everest the tallest mountain that Earth can support? There is a big limiting factor here - The Earth's crust is solid enough to support a mountain, but it cannot support infinite weight. The problem is that the crust is actually divided into the tectonic plates which float on a magma sea. Adding too much weight will cause the crust to sink deeper into the magma and simply melt and become magma itself!