Burning Tires
In Missouri, you're allowed to burn up to 5 tires per year. Not enough to simulate a volcanic eruption, but it sure does put out some black smoke!
Helped some friends take down a barn there, turned the old silo into a giant furnace and burned up all the junk wood. Then started shoveling asphalt shingles into it as well. Now we just so happened to be about 100 yards from I-70, so thick billowing black smoke was going across the interstate. I'm not sure if the semi trucks were blaring their air horns in appreciation of the show, or worried about the danger of driving through a cloud of blinding black smoke...