Mountains are landforms that rise well above the surrounding land, with steep slopes, often forming a peak over 600m distinguishing them from hills that are lower and roll on for many miles without any significant altitude gain (see Types and Formation of Mountains). There are 5 classes of mountains: fold mountains, block mountains, dome mountains, volcanic mountains and plateau mountains. The different types are distinguished by how they form.
Fold Mountains: Fold Mountains are formed when two tectonic plates on the earth’s crust move together. When the movement is between the boundary of a continental plate and an oceanic plate the sedimentary rock accumulated at the edge of the continents are forced upwards. This process can go on for long periods of time like 200 million years in the case of old fold mountains (like the Appalacians), while younger fold mountains (like the Rockies and Himalayans) are only 10 to 25 million years old (see Internet Geography, Fold Mountains).
Block Mountains: Block or fault-block mountains are formed by cracks, or faults, in the earth’s surface. The land between two parallel faults will either rise into a horst mountain, or fall into a rift valley. They are distinguished by sheer rock faces with the other side gently sloping like the Sierra Nevada mountains (see Fault-Block Mountains).
Dome Mountains: The dome mountain is formed by underground volcanic activity when magma forces its way up to sedimentary rock, but the magma does not quite break through to the surface. Instead the magma becomes the hard core of the rounded ‘dome’ shaped mountain (see Utah Geological Survey).
Volcanic Mountains: The volcanic mountain is formed by volcanic activity that reaches the surface bringing magma up as lava, ash and rocks that come to form the surface of the new volcanic peak. Further eruptions of the volcano will continue to build the mountain peak (see Wikipedia Volcanic Mountains) when the lava is composed of much basalt the lava is very fluid, flows further when molten and form very shallow, gently sloped mountain sides.
Plateau Mountains: Plateau mountains are mountains that are formed by erosion leaving a hard rock exposed with softer rock eroded away. Often the plateau mountain is found near a folded mountain as erosion from rivers and streams cuts into the plateau and creates mountain peaks from the formerly flat land (see Types and Formation of Mountains). At other times the mountain remains a relatively flat piece of land with softer surrounding land eroded away (see Wikipedia, Plateau).
Video clips demonstrating some of these mountain formation processes can be found at the BBC website, illustrating the processes with some spectacular real world mountains in all their dramatic beauty.