Diastrophism or tectonism is the group of mechanisms by which large-scale portions of the Earth's crust are deformed by natural processes. Such diastrophic processes lead to the formation of continents and ocean basins, mountain systems and rift valleys, and other related features by the chief mechanisms associated with the plate tectonic movements of the lithospheric plates of the planet. The study of diastrophism, or of tectonic processes, is the central unifying principle in much of modern-day geology and geophysics.

Five main kinds of diastrophic processes occur:

• 1.
  Orogeny, in which narrow mountain belts are formed
• 2.
  Epeirogeny, which is broad regional uplift or down warping of the crust
• 3.
  Isostasy, which is broad down warping or uplift related to loading and unloading of the crust
• 4.
  Eustasy, which is worldwide ...