What was the cause of the eruption of Vesuvius in 79 AD?

the Truth is a 6 mile chamber of magma underneath the volcano had pressure built and blew the top extrusive igneous rock of and not only produced a nuee ardente cloud (a fast moving cloud filled with magma and ash) but also a pyroclastic flow. that is what destroyed pompeii

Actually it was a sequence of previous earthquakes that occurred 17 years before.