Here is a good paper by S. Self in the 2006 Philosophical Transactions of the Royal Society, dealing with the frequency & the nature & the size of the Effects (local and global) and Hazards caused by the very largest volcanic eruptions.
It is extremely readable, and avoids unnecessary geological jargon:
Volcanic eruptions_V.large_effects (good paper)_(S.Self_2006_PhilTransRoyalSoc__364__2073).pdf