Mount Vesuvius is a volcano in Rome. It is most famous for erupting and killing the whole of Pompeii.
Volcanoes are usually situated where two of the earths plates meet. It is normally caused by the plates pushing against each other and lifting up.
Only active volcanoes can erupt. Some old volcanoes are dormant meaning they cannot erupt anymore.
Volcanoes erupt when the convection for the earths mantel gets too much and the lava explodes out of the top.
Once lava has left the volcano it cools and turns into igneous rock. The rock has crystals and they are diffrent sizes depending on how long they took to cool.