The formation of mountains is called orogenesis in geology. This long process of mountain building is caused by the horizontal collision of tectonic plates. In other words, when two tectonic plates collide and push against one another, with one edge sliding and crashing beneath the other's; this is called subduction, which is the result of two tectonic plates convergence. There is crumpling of layers of rocks into folds as they rise up, gaining altitude. As a result, large masses of molten rocks and geological materials are uplifted in vertical tectonic movements, whose rate exceeds that of the exogenous process of destruction and removal (erosion) of rock or the process of buildup of sediments (accumulation), which lead to the leveling of the earth’s surface. Orogenesis, or orogeny, is characteristic of active regions of the earth.
When the term “orogeny” was introduced, it had been established that the crumpling of layers of rock into folds led directly to the formation of mountains. One hallmark of orogeny is the formation of orogenic belts, which are elongated areas of deformation that borders continental cratons. Young orogenic belts, in which subduction is still taking place, are characterized by frequent volcanic activity and earthquakes, such as relatively new mountain ranges from the Tertiary period, like the Himalayas, Andes or the Rocky Mountain Range. Older orogenic belts, on the other hand, are typically deeply eroded to expose displaced and deformed strata. These are often highly metamorphosed and intrusive igneous rocks, which are called basoliths (granite and quartz monzonite).
Orogenesis is a geological term introduced by the American geologist G. Gilbert in 1890 to designate mountain building and intense deformation by folding and faulting. Gilbert singled out orogenic movements of the earth’s crust and contrasted them to epeirogenic movements, that is, slow upward and downward movements. The concept of orogeny was further developed by the French geologist G.-E. Haug, who, in 1907, proposed that orogeny be distinguished only within geosynclinal regions. Subsequently, in 1919, the German geologist H. Stille hypothesized that the chief result of orogeny was not the formation of mountains but rather the formation of folds.
