AMAZING FOOTAGE: VOLCANO BLOWS OUT SMOKE RING
(FEDERALJACK) A rare phenomenon, where a visible vortex ring of steam and gas is expelled from a volcanic vent. Under special conditions, gas and steam expelled from a vent can form gas rings. It probably requires a particular geolometric configuration of a circular vent exit, as well as expulsion of gas in individual puffs with just the right velocity.
This phenomenon is quite rare, but has been witnessed at several volcanoes, including Stromboli and Etna. At Etna, a spectacular period lasting several months was observed in 2000, when one of its vents created hundreds of smoke rings each day, in rapid succession.