There are three main types of mountains. block mountains formed by sections of the earth's crust that have been tilted or lifted up by the movement of two close fault lines, large cracks in the earth's surface. These are usually smaller than other types of mountains and are often separated by valleys. Volcanic mountains are formed by magma that is pushed out of the earth through a crack or weak place in the earth's crust. Fold mountains are formed when rock is "squeezed" together. When plates collide, the rock along the edges crumples, creating a huge zig-zag pattern in layers of the earth's crust. Upwarped mountains are formed when magma pushes up the earth's crust without breaking the surface. This creates a rounded mountain that gently slopes toward the surrounding land.