Subduction and plate movement

• ​Next up --- understanding the process of subduction

• ​sea-floor spreading makes new crust!

• ​subduction destroys old crust!

​A subduction zone is the biggest crash scene on Earth.

​

​It is when two tectonic plates collide.

​If the sea-floor is spreading at mid ocean ridges, and this is ultimately what pushes the continental crust around, then it only makes sense that continental crust will collide at some point.

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​Sometimes continental crust collides with other continental crust.

​

​Other times continental crust may collide with ocean crust.

​

​Sometimes ocean crust collides with ocean crust.

Where two tectonic plates meet at a subduction zone, one bends and slides underneath the other, curving down into the mantle. (The mantle is the hotter layer under the crust.) 

​

​Oceanic crust is denser than continental crust. At a subduction zone, the oceanic crust usually sinks into the mantle beneath lighter continental crust.

​

​Where the ocean crust is pulled beneath a deep ocean trench is formed. This is different than a mid ocean ridge.

​* As rock cools it

​becomes more

​dense. Dense rock

​sinks.

​

* ​Old ocean crust is

​more dense than

​young ocean crust.