Mount Etna has been spewing circular rings of smoke into the skies over Sicily. The rings, known as volcanic vortex rings, appeared this month after a small vent opened.
The phenomenon occurs when enough pressure builds up for magma inside the crater to push condensed gases through the vent. Experts say the activity does not mean that Mount Etna will erupt in a particularly spectacular way, but that it is a sign of active volcanoes around the world. The phenomenon was first recorded on Etna in 1724, followed by periodic sightings, most recently last year, and quite spectacularly in 2000.. Several volcanoes in the world have driven volcanic vortex Rings, from Mount Redoubt in Alaska to Mount Eyjafjallajallajkul in Iceland, to the Momotombo volcano in Nicaragua, one volcanologist says. The rings can remain in the air for between one and ten minutes, depending on weather conditions, experts say, but if there is turbulence, they fall apart more quickly.