Those on the Italian island of Sicily were treated to an unusual sight in the skies this weekend, as the ancient Mount Etna, which is the largest active volcano in Europe, sent cloudy rings floating to the heavens. The “volcanic vortex rings,” as they are known by scientists, are formed by magma bubbling beneath the volcano’s surface, which then bursts and sends hot gas hurtling through a cylindrical vent at high speed. The gas forms into a ring shape as it shoots up the narrow shaft, and it takes on a white, cloud-like hue because it’s made of 80 percent water vapor. “The rings look pretty much like the ‘smoke rings’ produced by an able smoker,” Boris Behncke, a volcanologist at the Italian National Institute of Geophysics and Volcanology’s Etna observatory, told The Washington Post on Monday. He added that the smoke-blowing phenomenon isn’t rare or unique to Etna—the storied mountain is just “the most prolific volcano on this planet in terms of vapor rings.”