Have you ever seen a volcano up close and personal?  The rupture in the crust allows hot lava,ash, and gases to escape 
No only in pics or on tv but they are amazing
Volcanoes occur because the crust is broken into 17 major tectonic plates and they float on a hotter, softer layer  so there is movement.  
They are so massive and dangerous, really scary when you thing about it
I would actually love to be able to see the one in Hawaii, it's actually a hotspot also and it's postulated that the lava there is coming from the core-mantle boundary 3000km deep