Tag: tectonic plates

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

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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).

Mountains- A history(Part-1)

Photo by Sam Kolder on Pexels.com

We have all seen mountains or hope to see them, after all they are a very famous holiday destination. All of us certainly have a wonderful mountain destination in our bucket list- be it the Himalayas, The Rockies, The Alps, Mt. Fuji or the Swiss Alps. But have you ever wondered how these mountains came into being? How is it that a flat piece of earth rose so high, almost touching the sky? Well, if you have, then here is the answer. And if you haven’t, even then a little extra knowledge never hurts anybody, right?

So, the mountains were formed millions and even billions of year ago (the oldest one-the Barberton Greenstone Belt in South Africa, is 3.6 billion year old) when the continents were being formed. The most widely accepted theory, currently, believes that the earth’s mantle(the astenosphere layer- a semi-solid) has convection current flowing through them(a result of differential heating- the lighter material rises whereas the denser material sinks ). This current belt in the astenosphere moves with it the lithosphere(continental crust, oceanic crust and the top-most part of mantle(upper mantle)). These movements in the lithosphere are the movements of continents and oceans that lead to earthquakes , volcanoes, tsunamis and the formation of volcanic islands, plateaus (all these for some other day) and fold mountains as well as volcanic mountains.

These convection currents move with them large pieces of land, ocean or both and these large pieces are termed as tectonic plates. There are currently 7 major and some minor tectonic plates. The major tectonic plates are-

  1. Indo-Australian plate
  2. North American plate
  3. South American plate
  4. Pacific plate
  5. Antarctic plate
  6. Eurasian plate
  7. African plate

The minor plates are-

  1. Fillipino plate
  2. Nazca plate
  3. Scotia plate
  4. Caribbean plate
  5. Indian plate
  6. Arabian plate
  7. Cocos plate
  8. Juan-de-fuca plate

Let us first see the types of mountains. There are 4 types of mountains-

  1. Fold mountains- These mountains are formed when one tectonic plate folds over the other, due to collision of two plate boundaries. The plates need not be continental as is in the case of the Alps , the Atlas and the Himalayas. An oceanic and a continental plate boundary collision can also form a fold mountain. The examples of such fold mountains are the Rockies and the Andes
  2. Block mountains- These mountains are formed due to the diverging plate boundaries. When two boundaries diverge, it creates a crack on the surface between them known as a rift. Later, the surrounding raised plate undergoes erosion and takes the shape of a mountain. Examples are The East African Rift Valley, The Rhine Valley, The Vindhyas and Satpuras .
  3. Volcanic mountains- Mountains formed due to fissures in the earth’s surface, that lead to release of magma. The examples are Mt. Fuji, Mt. Mayon. Also, they are known as mountains of accumulation.
  4. Residual mountains- Mountains that are either formed due to the erosion of existing mountains (denudation) or plateaus(dissection) by agents such as rivers, winds, glaciers. Examples are Mt. Manodnock (The Appalachians) , Highlands of Scotland, Scandinavia and Deccan Plateau.

The movement of the tectonic plates creates one of the above or even a combination of the above kind of mountains. Stay tuned for the next part to know how are many of the world mountains created and where are they located? Is there something common about their location? What is the reason for exceptions?