Chapter: Formation of Mountain Ranges
Orogenesis – Orogeny
In this animated graphic I will show you schematically how mountain ranges are formed. The shown way of mountain range formation can be found for example in the Himalayas, where the Indian plate crashes against the Eurasian plate.
It can also be found in the Alps, where the African plate meets the Eurasian plate. In both examples the first named plate is subducted. This plate causes a swelling of the continental crust. Instead of 18.7 to 21.7 miles it will measure 37.3 to 43.5 miles. As this rock has a lower density it wants to rise. It's the same principle as if you where to push a cork or a PET bottle underneath water: the object will come back to the surface all by itself. The same thing is happening with the much too deep lying continental crust, the only difference being that it takes millions of years. So from the start on a continually rising mountain range develops. But as soon as there is an elevation erosion starts. That's why a mountain range can't grow to infinity and will one day vanish completely.
This was only one way of how mountains can form; they can also grow in different ways. Therefore I will explain you the formation of the Andes. If we look at the situation from a plate tectonic angle we will see that the Nazca plate is moving around 4 inches/year in the direction of South America. In this process the Nazca and part of the Antarctic plate are being subducted deep in to the earth's interior. As the subducted crust is oceanic, this process happens mostly voluntary. Nevertheless, constant earthquakes are caused. In addition volcanism has developped. As the continental crust measures about 43 miles underneath the Andes they are lifted up just like the Himalayas. Also the lava, which flows out when eruptions take place, elevates the surrounding areas even more.