The Andes is a young fold mountain range stretching from north to south in the west of South America. It is very high and steep running roughly parallel to the west coast. The Andes is formed by folding, a tectonic process taking place along the destructive plate boundary.
The Nazca Plate which is an oceanic plate in the west is dragged to move towards the South American Plate which is a continental plate in the east. The force driving the two plates to collide is resulted by converging subcrustal currents of magma in the asthenosphere below the earth crust. Such slow collision of the two plates takes place very slowly over millions of years in earth’s history.
Due to the heavier density of the oceanic crust, the Nazca Plate is subducted into the mantle at the plate boundary. An ocean trench is formed along this point of subduction. The Peru-Chile Trench is located in the northwest coast of South America. As continuous weathering and erosion by agents like wind, water and ice take place on the earth surface of the South American continent, all eroded materials are transported by these erosional agents and flow down to the ocean by rivers. These sand and mud are deposited at the ocean bed over the years and thicken to form layers and layers of sediments. Due to continuous deposition, sedimentation, compression and compaction, these materials are hardened into sedimentary rocks at the bottom of the ocean / trench / geosynclines.
Continuous convergence of subcrustal currents and plate collision move the two plates and shorten the plate boundary. Compression from both sides thus push the thick layers of sedimentary rocks up, resulting in folding. Folding and uplifting take place at the same time. These rocks are folded up above sea level, and subsequently form high fold mountains, as in this case, the Andes. Folding is always associated with vulcanicity. During the million years of folding and uplifting, the hard rocks may crack...