Why are the world's fold mountain systems located along the margins of continents? Bring out the association between the global distribution of fold mountains and the earthquakes and volcanoes.
World’s fold mountains are located on the margins of the continents because fold mountains are formed from the folding of crust and uprising of the sediments accumulated by rivers along the margins of the continents by the collision of two continental plates or a continental plate and an oceanic plate. An example of fold mountains formed by converging of two continental plates are Himalayas mountains and fold mountains formed by convergence of a continental plate and an oceanic plate are Andes mountains, Appalachians mountains etc.
As fold mountains form due to folding of crust , with the passage of long time the folding continues and crust becomes over folded and strata(layers) of rock develop. It is called Over-thrust fold. Now, further folding leads to fracture in rock called Nappe. Upper layer of rock slides over lower layer leading to release of tremendous amount of energy which causes Earthquakes.
As two plates converge, the denser plate subducts under the lighter plate. This subducted plate enters onto the Mantle region of earth which causes melting of rocks to form Magma. Due to high pressure underneath this magma comes out from the up-lying continental plate in the form of Lava, causing the formation of volcanoes at some distance from continental margins.