Convergent Boundaries

    Professor Archit Rathi and his intern Mak Kapetanovic are here to tell you about convergent boundaries.  Plate Boundaries are the reason for most of the geological activities you see on our planet.
Out of the three types of plate boundaries, convergent boundaries are the only boundary that actually has two plates moving toward each other. A key feature of convergent boundaries is subduction. Subduction, in simple terms, is a geological process, in which two plates collide and one sinks beneath the other due to density differences. There are three types of convergent boundaries:

* Oceanic-Oceanic
* Continental-Oceanic
* Continental- Continental

The first boundary I stated was oceanic to oceanic. This means two lithospheric plates which are both oceanic will collide. An example of this occurring is in Indo-Australian zones Plate and the Pacific plate. Subduction zones are the cause for a lot of geological changes too. In a boundary such as this, the more aged plate will be subducted, as a result of a higher density. For example, when a plate is forced down, a trench is formed, as a plate reaches down into the asthenosphere (where the trench is), magma (molten rock inside of the earth) is produced. This magma will soon rise up to the surface and form a chain of volcanoes, which is commonly referred to as the volcanic island arc.

The second boundary I would like to list is the convergent boundary with continental to continental plates.  Again, this means two lithospheric plates which are both continental will collide. Though, in these boundaries, as a head on collision occurs, the crust is now pushed up or sideways. The reason for this is that because since both continental plates are less dense than the mantle, the plates cannot be subducted. It can cause, two continents to meet at a subduction zone. In your EarthComm textbooks it clearly states that the spreading ridge will be subducted causing another continent to be pulled over.  For example, around 50 million years ago the Indian plate and the Eurasian plate collided. This is called the suture zone. The Eurasian plate went over the Indian plate. This event is the reason for the Himalayas. To this day, the Indian pate is still under the Eurasian plate, and it is getting smaller. 


Intern Mak Kapentanovic

Oceanic to Oceanic convergent plate boundaries

Oceanic to oceanic plate boundaries occur between two oceanic lithospheric plates. It is very similar to other types of convergent plate boundaries due to the fact that it is still two plates moving together. In most situations this causes subduction. Since this subduction is located underneath the ocean, it causes deep sea trenches. It also causes deep volcanoes to form on the plate that is not being subducted underneath the other one. When these volcanoes erupt, as they tend to do, the lava cools and forms island arcs. One of the more common examples of this is Hawaii.

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