Earthquakes are dangerous collisions between plates (generally convergent and transform). Earthquakes generally happen at boundaries but can also happen with faults. If an earthquake is to occur more than just one thing can happen e.g. tsunamis can form from quakes in the ocean, craters/cracks in the Earth's surface can appear and buildings can collapse. When plates rub against each other like when oceanic crust rubs against continental crust the friction can cause earthquakes which can have catastrophic results.
Heat rises and so does magma this magma flowing out of the Earth (lava) is one of the things that make up the world. The magma makes steaming water and geysers appear on the surface. Volcanoes like earthquakes are just results from a larger picture.