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. (UPSC 2014)

Fold mountains occur along continental margins because these are active plate boundaries where compression, subduction or collision folds thick sediments in geosynclinal belts into mountain chains.

Global association

• At convergent margins, oceanic–continental subduction creates ranges like the Andes and Rockies; continent–continent collision forms the Himalayas.
• These belts coincide with major seismic zones, especially the Circum-Pacific and Alpine-Himalayan belts, because plate movement and thrusting generate frequent earthquakes.
• Volcanoes are common where subduction occurs, as melting of the descending slab produces magma; hence volcanic mountain arcs such as the Andes and island arcs develop. In pure collision zones, volcanism is weak or absent.

Thus, fold mountains, earthquakes and volcanoes are concentrated along active plate margins, reflecting the same tectonic processes.