Mountains- A history (Part-2)- Tectonic plates


Now, before going any further with our mountains, let us first see the various types of interactions possible between our 2 types of tectonic plates- The Oceanic crust and the Continental crust: The 3 basic interactions are converging boundaries, diverging boundaries and transform boundaries.

  • Converging- It is defined as the two plates moving towards each other, colliding in the process. Now, there are 3 possibilities-
  1. Continental-continental collision- Here, two continental landmasses( eg.- The North American plate or the Eurasian plate or collision of Australia, South America and New Zealand (It formed the Great Australian Dividing range)) collide and the two plates fold over one another and lead to the formation of fold mountains. Try using a paper bringing it closer from the opposite ends. The raised structure represents the fold mountains. They have no volcanic activity (though earthquakes are possible). Examples are the Urals, the Atlas, The Rockies, the Alps, the Himalayas
  2. Oceanic- Oceanic Collision- In these types of collision, the heavier oceanic plate subducts under the lighter oceanic plate(forming trenches- eg. Mariana Trench). Due to subduction, it reaches the area of high pressure and temperature in the mantle and thus melts converting to magma. This magma later rises and when it finds an opening (like the one created by the diverging limbs) in the oceanic crust, it comes out. It, hence, forms oceanic volcanoes, ridges and later volcanic islands like those of Indonesia and the Phillipines.
  3. Continental Oceanic Collision- When a continental and an oceanic plate collide, it leads to the formation of either fold mountains(Rockies) or trenches(Philippines Trench) or both(Andes and the Peru- Chile Trench).
  • Diverging- When two plates or landmasses move away from each other ,in the opposite directions, it is known as diverging. Even here, there are 2 possibilities-
  1. Continental continental diversion- When two continental plates move away from each other, it leads to the formation of rift valleys and plateaus. Examples are- The east African rift valley (formed due to the drifting apart of Arabian peninsular plate from African plate- they were connected millions of years ago).
  2. Oceanic oceanic diversion- It occurs when two oceanic plates move away from each other, creating a ridge in its wake. The Atlantic ocean is divides by a ridge known as the Mid oceanic ridge (named so because it passes through the middle of Atlantic ocean). Here, the plate boundaries of Africa, Eurasia, North America , South America diverge from each other. The Pacific and the Indian ocean are the other two oceans that have ridges.
  • Transform – When one tectonic plate moves past another, it forms transform plate boundary. These plate movements most commonly produce earthquakes as during movements the plates experience friction and intermolecular force of attraction due to which one plate might find itself bounded to another plate. Then, when the plates move past one another it requires a lot of energy and produces heat and waves. Example- the boundary between Pacific plate and North American plate in Western California.

Now, that we know about tectonic plates, studying the formation of mountains becomes a lot easier. Stay tuned for the 3rd part where we will look into the formation of various mountains and the tectonic plates and movements involved . Till then, take care (a smiley emoji).