Italy’s Mount Etna is erupting again, producing a series of beautiful vortex rings. Like a dolphin’s bubble ring or a vortex cannon, the volcano’s rings are formed when gases are rapidly expelled through a narrow opening. Such formations are extremely common but are generally not visible to the eye. In this case, steam has gotten entrained into the rings to make them visible. Vortex rings can maintain their structure over substantial distances. The photographer of these rings noted that they lasted as many as ten minutes before dissipating. (Photo credit: T. Pfeiffer; via NatGeo)