Model Question and Answers for APSC | 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.

Ans: Fold mountains are created where two or more of Earth’s tectonic plates are pushed together. At these colliding, compressing boundaries, rocks and debris are warped and folded into rocky outcrops, hills, mountains, and entire mountain ranges. Fold mountains are created through a process called orogeny.

Fold mountains are the most common type of mountain in the world. The rugged, soaring heights of the Himalayas, Andes, and Alps are all active fold mountains.

Located along the margins of continents:

• Fold mountains are often associated with continental crust. They are created at convergent plate boundaries, sometimes called continental collision zones or compression zones.
• Convergent plate boundaries are sites of collisions, where tectonic plates crash into each Compression describes a  set of stresses directed at one point in a rock or rock formation.

• At a compression zone, tectonic activity forces crustal compression at the leading edge of the crust formation. For this reason, most fold mountains are found on the edge or former edge of continental plate boundaries. Rocks on the edge of the continental crust are often weaker and less stable than rocks found in the continental interior.
• This can make them more susceptible to folding and warping. Most fold mountains are composed primarily of sedimentary rock and metamorphic rock formed under high pressure and relatively low temperatures. Many fold mountains are also formed where an underlying layer of ductile minerals, such as salt, is present.

  

The association between the global distribution of Fold Mountains and the earthquakes and volcanoes:

• As two plates converge, the denser plate subducts under the lighter plate. This subducted plate enters the Mantle region of earth which causes the 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.
• Continental-continental convergence is associated with earthquakes as a huge amount of energy is released when the denser plate pushes the lighter plate creating a fault zone along the margin.

  

The Ring of Fire also referred to as the Circum-Pacific Belt, is one such path along the Pacific Ocean characterized by active volcanoes and frequent earthquakes. Its length is approximately 40,000 kilometres (24,900 miles). It traces boundaries between several tectonic plates—including the Pacific, Juan de Fuca, Cocos, Indian- Australian, Nazca, North American, and Philippine Plates.