Forgive me, but I am a bit confused. You say the event is based on history or rather historical events. Unless I have missed something, it seems your sample "events" are rather vague. You give "frightened the Pompeiians as a consequence of "sound of explosion", but for "black cloud of smoke" you answer, "darkened the sky". Surely a consequence to a "black cloud of smoke", but not exactly an historical event. Perhaps you can elaborate. Also, at the risk of offending you (not my intention at all, I think you've got a good premise here), I would have to say that "rain of hot ash" is in fact, a consequence not an event.
Hoping to work together,
NJDAFF