The creation of mountains

The origin of mountains (orogenesis) occurs after tectonic movements make rock layers fold and overlap. All the Earth’s surface, the lithosphere, is divided into rigid areas called continental plates and oceanic plates. These lithospheric plates continuously move and whenever they bump into each other, they form mountain chains.
How were the Andes created?
The Andes Cordillera started to form 250 – 200 million years ago after the crash between an oceanic plate (Nazca plate) and a continental plate (South-American plate). During the crash, the oceanic plate submerged under the continental plate. The movement and friction between the rock layers provoked earthquakes and a partial melting of the rocks. The melted rocks, less dense than the surrounding ones, move towards the higher part, as an air bubble would do when submerged into the water. In this way volcanoes are created, and melted rocks (magma) reach the Earth’s surface.  The Andes include numerous volcanoes that have formed two parallel mountain chains. The most internal and oldest chain is close to the ocean. The two chains are called Western Cordillera and Eastern Cordillera.
How was the Himalayas formed?
All big Asian chains, starting from Turkish mountains, to Iran, Afghanistan, Nepal, China, Sumatra and Java result from the crash between continental plates. In particular, the Himalayan chain formed after the crash between the Indian plate and the Euro-Asian plate that 30 million years ago were still separated by an ocean called Thetis. The plate collision, that started 45 million years ago, led to the disappearance of the ocean and the compression of rocks, which corrugated, folded and were lifted towards the top. The collision between the plates has not finished yet and Himalayan mountains are still lifting at a speed of 5 centimetres every year.
The Dead Sea, the Caspian Sea and the Lake of Aral are the remains of the Thetis Ocean, that disappear after the approach and crashing of the plates.
How were the Alps formed?
The Alps were formed after a crash between the Euro-Asian continental plate and the African continental plate, which were also separated by the Thetis ocean. In particular, 100 million years ago, the African plate changed its movement direction and went northwards with a speed of few centimetres a year. It compressed the rocks of the Thetis ocean crust against the Euro-Asian plate. The African plate moved like a huge bulldozer, scratching and piling up all the material that encountered during its journey. When the two continents crashed, part of the rocks that formed the ocean floor were trapped by the rocks that formed the continents and pushed to the top to form the Alps.
Subsequent and more complex movements occurred into different directions and led to the creation of the Apennines.

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