Earth's crust is divided into two categories, oceanic crust and continental crust. The oceanic crust is the one that is found in the oceanic plates, thus it is predominantly covered with water, while the continental crust is the crust that forms the continents, thus it is predominantly above the water. The oceanic crust is located slightly lower, they have higher density, but have lesser thickness. The continental crust is located slightly higher than the oceanic crust. This crust is significantly thicker, but it has lesser density, which is why it ''floats'' above. These two types of crust are constantly in interaction with each other, and when there is a collision between the two, the oceanic crust subducts below the continental crust. This results in the oceanic crust to move downwards to the mantle and get molten, thus destroyed, while the continental crust experiences uplift near the plate boundary. Other consequences are the emergence of volcanic island arcs and volcanic continental arcs, as well as intense earthquake activity.
