Volcano Fireworks by Nature

Yes although many fireworks companies claim to have the biggest “volcanoes” or firework fountains. Nobody can beat the unpronounceable glacier of Eyjafjallajoekull in Iceland with its mountainous plumes of smoke and unending spewage.

Of course, we all prefer smokeless fountains but you have to take duration into consideration. Also, any volcano large enough to bring planes to a standstill would probably not pass BS safety tests and would certainly not be considered CAT 3.