Tambora, the cause of “the year without a summer” left a caldera 5 miles in diameter. The Campi Flegrei caldera is 7.5 miles in diameter. Try cubing those diameters to determine how much more “nuclear winter” CF could have caused. I would do it myself, but never was a math wizz.
Sunken Civ: I looked at some of the articles on CF that you provided the link for. On one of them I found the link below which is an interesting one on the language possibilities of Neanderthals.
http://www.abc.net.au/science/news/stories/s1323798.htm
Thanks glee'.
Tambora's crater is 3.7 miles across; although some sources put the amount of crud expelled at 50 cubic miles, the current consensus estimate is about 36 cubic miles.In 2004, scientists discovered the remains of a village, and two adults buried under approximately 3 meters (nearly 10 feet) of ash in a gully on Tambora’s flank -- remnants of the former Kingdom of Tambora preserved by the 1815 eruption that destroyed it. *Wow, they must have been thirsty when they found 'em.
Volcanic eruptions are locally devastating, but any worldwide effects are mild. The Campi Flegrei eruption 39,000 years ago has been linked to the so-called extinction of the Neandertal (see the keyword links for a couple of topics), the fact is, volcanic eruptions and their effects are typically exaggerated and/or misstated.
The wikipage-ia has the figure of 48 cubic miles expelled in that CF eruption -- which compares well with Tambora -- followed by a period of 25,000 years of undersea activity which over that time produced a volcano 9.3 miles in diameter (that's not the crater, apparently, but the whole cone etc).
After a couple of thousand years of apparent quiesence, the current, even slower, and geologically different activity started going on, continuing about 7500 years, with Monte Nuovo forming in the 16th century. Overall the caldera is a lake, but there are a bunch of big muddy sloppy gassy vents where the activity is going on today.