Here's why:
* Composition: Oceanic crust is primarily composed of basalt, a dark, dense volcanic rock. Continental crust is mostly made of granite, which is lighter and less dense.
* Age: Oceanic crust is constantly being created at mid-ocean ridges and is therefore younger than continental crust. Older oceanic crust is denser due to cooling and the weight of sediments accumulated on its surface.
This density difference means that when the two plates collide, the denser oceanic crust is forced to bend and slide beneath the lighter continental crust, creating a subduction zone.
