The geological process of mountain building fits under the general term "orogenesis." This refers to the deformation of the Earth's crust at meeting points of the tectonic plates, which can move upward, downward, inward and outward.
Orogenesis occurs in three different ways: through volcanism, through folding and through fault block formation. Volcanoes form in areas where the crust is stretched thinnest, allowing magma to push through and build material on the surface. Folding occurs when tectonic plates push up or run over one another, crumpling the crust upward. With fault blocks, sections of the tectonic plates are broken up by faults; weaker areas sink, forming grabens, while the remaining horst sections become mountains.