Plate tectonic theory shows that the crust of ... denser rock melting and the magma being forced up to the surface. South America has a great example of a convergent plate boundary.

Over two hundred fifty million years ago, India, Africa, Australia, and South America were all one continent ... The continents are carried by the Earth's tectonic plates like people on an escalator.

Most geologic activity stems from the interplay where the plates meet or divide. The movement of the plates creates three types of tectonic ... in the Andes of South America.