Since its violent eruption on November 11, Sicilian volcano Mount Etna has been spurting ash regularly, the most recent of which are taking the form of smoke rings.
Although it is difficult to assess their size due to the lack of a nearby landmark in the sky, the diamtere of the rings is estimated to be between 50m and 100m.
Volcanologist and tour guide Tom Pfeiffer took this image and offers other photos on his Volcano Discovery site. He believes the rings were created by a relatively recent crater, that has seen its ducts transformed by the latest big eruption.
It’s a relatively rare, but not exceptional, phenomenon: Mount Etna is actually accustomed to this, as can be seen by the video below, taken in 2009.