The Himalayan mountains formed at the boundary of two tectonic plates.
The surface of the Earth is composed of a series of large land masses that float on an underground layer of magma. These land masses, or tectonic plates, are constantly in motion and when the edges of the plates interact, the mass and momentum of the plates cause dramatic geological activity, such as earthquakes and volcanic eruptions, at the site of the interaction. The consequences of the interaction depends on the physical characteristics of the tectonic plates and the way in which the plates come together or move away from each other.
Convergence with Subduction
When tectonic plates move directly toward each other, it is known as convergence of the plates. Convergence usually results in subduction, a process in which the lighter or weaker tectonic plate slides under the other. When one plate is forced under the other, an enormous amount friction is generated which causes enough heat to eventually form a volcano. Along the Northwest coast of North America, a chain of volcanoes has been formed because of an oceanic plate sliding under the North American plate for many years. The plate that is forced underneath the other eventually comes into contact with underlying mantle and undergoes partial melting.
Convergence Collisions
When neither plate subducts, convergence can result in collision effects. The crust crumples and buckles, forming mountain ranges at the boundary of the two tectonic plates. The Indian and Asian plates began colliding 55 million years ago and formed the Himalayan mountains. These are the highest mountains on Earth and because the convergence of the two plates is ongoing, the Himalayas are getting progressively higher. The Himalayas are growing at a rate of 1/4 inch per year which, compared to other geological phenomenon, is a fast rate of growth.
Divergence
Tectonic plates moving away from each other is known as divergence. As the plates separate from each other, the result is either seafloor spreading or the formation of rift valleys. During seafloor spreading, magma wells through cracks at the point of divergence. The magma hardens and forms the newest rock of the sea floor. Seafloor spreading is also associated with ocean ridges. In areas of high-heat magma, the magma is propelled upward to form underwater mountain ranges divided by deep rifts down the middle. On land, divergence causes rift valleys, which are deep roughs bordered by two or more fault lines. One such trough is the Great Rift Valley in Africa which, millions of years from now, will cause eastern Africa to split from the main continent and form a new landmass.
Transform Motion
Two plates moving past each other experience transform motion. The rough edges of the two plates grind past each other in a halting, strike-slip motion as the edges catch on each other and then release when enough force builds up. The San Andreas Fault in California is one such boundary that results in a series of earthquakes as the two plates struggle past each other, but does not result in the formation of a mountain range or ocean.
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