Vesuvius, like other many volcanoes is situated over magma chamber (in Italian: Camera Magmatica) that lais under most of the southern Italy, but its real extension is hard to detect deep within the Earth.
The magma in it is under great pressure, and, given enough time, that pressure can gradually fracture the rock around it creating a way for the magma to move upward. If it finds its way to the surface, then the result will be an eruption.
Our music comes to life under the Volcano, our music is the magma.