What causes continental crust to go under oceanic crust?

Question

What causes continental crust to go under oceanic crust?

Answer 1

It doesn't, the continental crust goes above the oceanic crust...

The reason is density, less dense things rise... although thicker, the continental crust is a lot less dense due to its composition, so it therefore rises above the denser oceanic crust.

Answer 2

Actually the continental crust does not go under the oceanic crust.

The materials that make up the oceanic crust are generally a lower density, and therefore would sink, they are known as Mafic types of rocks.

The continental crust has less of the heavy type of elements, therefore is less dense than the oceanic crust.  In regards to density, continental crust is less dense than oceanic crust.  These rocks are know as Felsic types.

In a density situation, less dense material will set on top of, or rise above more dense material.  Continental crust will therefore sit on top of oceanic crust.  

There is one situation where continental crust is forced back down close to the continetnal crust.  That would be in a zone of subduction.  As the oceanic plate moves downward, through friction the continental crust will be forced downward and be remelted to begin the process again.

Answer 3

Perhaps the same forces that allow the continents to be ABOVE the ocean plates. Some subduct and others rise.