Answer:
The broken areas of the crust provide an opening where magma can travel to the surface of Earth.
Explanation:
The locations of the vast majority of the volcanoes are along the plate boundaries, though the occasional one can be found in the interior of the plates (those are caused by hot spots). The reason why the volcanoes are mostly found along the plate boundaries is that it is there where the broken crust is found, so the magma can easily travel through them and reach the surface.
Because the crust is cracked, that means that there are gaps through it, so the very hot magma propelled by very high pressure is able to move through them and further widen them by melting the surrounding rock. As it does so, as the magma comes close to the surface, it pushes the crust up, creating a dome-like physical form on the surface. Eventually, it manages to break through the expanded crust, and from the top of it erupts, thus creating a volcano.
