Mountains can be formed in a variety of ways

Both the land and the sea, which are the outer skin of the earth, ride on huge plates. These plates sometimes collide with one another and when they do, mountains are formed. In fact, years and years and years ago, Mt. Everest was not a mountain at all and was situated under the ocean. That is why seashells can be found on Mt. Everest.

When two plates butt up against each other, putting pressure on one another, the land is eventually lifted and folds over on itself. The formation of continents and mountains creates the varied surfaces on the earth. One plate can push on top of the other plate, which can cause the plate to slide downward and it begins to melt.

The melted rock blasts upward along weak spots and crack, which creates volcanoes. When plates stretch so far that they crack and slide, this forms fault-block mountains. Underwater mountains are created when plates spread away from each other and melted rock pushes up through the space that is left in between.

When the plates bump into each other, there is tremendous energy involved. As a result of the crash, the plates crumble and the crumbled plates create mountain ranges.

Mountains are also formed via erosion. Rivers carve deep grooves into high plateaus, which forms mountains in between the river valleys.

The Sierra Nevada mountain range in California is an example of mountains being formed along fault lines. When blocks of the earth are lifted and tilted over, two plates will grind together. The uplifted portion of the earth will form a mountain and the lower parts are filled in with material that has eroded.

Magma, which is located under the surface of the earth, can be pushed upward and form a mountain. However, the magma does not crack through the surface. The bulge that results will cool and harden into hard rock, much like granite. The layers of soft rock situated above the magma will erode and the result is a large dome-shaped mountain. If the magma does manage to break the surface, you have got yourself a volcano.

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Eventually, all mountains will crumble after millions of years of existence. The high, jagged peaks will turn into hills that are low and rounded. The mountains eventually wear away to the extent that they become sand on the beach or soil on the plains or ocean sediment.

Mountains disintegrate due to the elements, including wind, rain and ice. Water gets into the cracks that are present in rocks, which makes the cracks wider and bigger as the rocks expands with both cold and heat. Water takes its toll on the minerals in the rocks, washing them out of the rock, which prompts the rocks to crack even more and split off. Some of the rocks are large enough to be considered boulders and they can tumble down the mountain side.

The different types of mountains include dog tooth mountains, which means that masses of nearly vertical layers have become eroded. This rock is very hard and is a remnant of erosion. The jagged peaks protrude straight upward.

A castellated mountain is an example of a mountain that is made up of horizontal laying layers. These mountains look like ancient castles featuring vertical towers.

Some mountains are the result of horizontal layers of rocks that were thrust upward at a 50- to 60-degree angle. The outcome is a peak with a smooth, sweeping face on one side and a sharp steep face on the other side. This edge of this side will expose the uplifted layers.

A saw tooth mountain is made nearly completely of vertical rock layers and these layers resemble the blade of a saw.

Matterhorn mountains are created when glaciers polish four different sides of a summit, resulting in a square-topped summit.

Synclinal (depression) mountains are formed in dipping troughs whereas anticlinal (dome) mountains are compressed and do not always crack.

Sometimes a mountain defies classification. The study of the formation of mountains is a fascinating introduction to science education and geology. When this occurs, the mountain is referred to as a complex mountain. The mountain features both down folds and up folds that are very complicated in structure.

References:
A Teachers’ Guide: Learning about Mountains  
How Mountains Form Animation